Peter Stannard BSc, DipEd
Ken Williamson BSc (Hons), DipEd
Consultants David Greig Brighton Secondary School Margaret Shepherd Freeman Catholic College Technical art Brent Hagen Chris Dent Cartoons Chris Dent
ScienceWorld for NSW
First published 2009
Visit our website at www.macmillan.com.au
Acknowledgments The authors would like to thank Chuck Forzatti of Siena College for advice and suggestions, and those students from St. John’s College who helped with photographs.
Associated companies and representatives throughout the world.
The authors and publisher are grateful to the following for permission to reproduce copyright material:
Copyright © Anteater Publications and K. L. Books 2009
AAP Image, 17 (right), /AFP Photo/Leslie E. Kossoff, 101, /Wildlight, 268 (left); Anglo-Australian Observatory, 168, 169 (all), 170, 172 (top); ANT Photo Library, 260, 263 (bottom), 266, /Silvestris Fotoservice, 141 (top right); Anteater Publications, 2, 4, 10, 11 (bottom right), 11 (bottom left), 11 (top), 12, 17 left), 21, 22, 27, 30, 32 (all), 32, 36, 57, 60, 73 (bottom right), 73 (left), 73 (top right), 77, 82 (all), 83, 84, 92, 95, 96, 97, 98 (left), 107 (right), 108, 110 (all), 115, 117, 128, 139, 141 (bottom right), 141 (left), 153, 182, 185, 199, 200, 201, 207, 210, 211, 215 (left & right), 216 (all), 234, 235 (left & top), 239 (top), 253 (left & top), 255 (top & bottom right), 258, 263 (top), 267; Auscape International Photo Library, 79 (top right), /Clive Bromhall, 94, /Lindsay Cupper, 93 (bottom right), /Jean Paul Ferrero, 93 (top right), /Pavel German, 253 (bottom right), /Brett Gregory, 98 (right), /David Hancock, 26, /Dennis Harding, 52 (right), /C. Andrew Henley, 93 (left), /Steven David Miller, 268 (right), /Reg Morrison, 259, /Tom and Therisa Stack, 157; Australian Scenics, 252; BHP Science Awards, 43; Dr J. A. Campbell, University of Canterbury, Christchurch, 143, 144; Coo-ee Historical Photo Library, 154; Corbis/Digital Art, 198, /Eye Ubiquitous/Paul Seheult, 189, /Eye Ubiquitous/Paul Thompson, 179, /Lester Lefkowitz, 118; Rob Cruse, 8; CSIRO, 44; Digital Vision, 150; Fairfax photos/Jessica Hromas, 272 (top), /Dallas Kilponen, 271, /John Reid, 114, /Penny Stephens, 186; Getty Images, 52 (left), /David Robert Austen, 126, /Gabriel M. Coven, 127, /Hulton Archive/Stringer, 76 (top), /NASA JSC, 168 (top), /Oppurtunity-NASA, 158 (top left), /Graeme Robertson, 225, /Paul Souders, 67, /Time Life Pictures/Mansell 76 (bottom); Stockphoto/Björn Kindler, 125; Marine Themes, 254; Josh Mylne, 28; NASA, 151; National Oceanic and Atmospheric Administration/Department of Commerce, 107 (left); Newsphotos, 232 (right); Photodisc, 89, 172 (bottom), 226; Photolibrary, 19, 29, 61, 79 (bottom right), 91 (right), 142, 219, 255 (left), 272 (bottom), /J Hester and P Scowem, 171, /Phototake Science/Roland Birke, 78, /Science Photo Library, 69, 85, 90 (left), 102, 109, 212, 256, 261, /Science Photo Library/Canada-France-Hawaii Telescope/ J-C Cuillandre, 172 (middle right), /Science Photo Library/Kim Gordon, 172 (left), /Science Photo Library/Eric Grave, 79 (left), /Science Photo Library/David A Hardy, 159 (top right), /Science Photo Library/Peter Menzel, 228, /Science Photo Library/MSSSO/ANU, 165 (right), /Science Photo Library/Nasa, 158 (bottom left), 158 (bottom right), 158 (top right), 159 (bottom right), 159 (left), 161, 164, 165 (left), 167, /Science Photo Library/New York Public Library/Humanities & Social Sciences Library, 184, /Science Photo Library/Novosti, 168 (bottom), /Science Photo Library/Philippe Plailly, 180, /Science Photo Library/Chris Priest, 11 (middle), /Science Photo Library/Detlev Van Ravenswaay, 166 (all), 177, /Science Photo Library/Rosenfeld Images, 233, Science Photo Library/ Sheila Terry, 149, /Science Photo Library/Univ. of Birmingham High TC Consortium/IMI/David Parker, 239 (bottom), /Science Source/D. Phillips, 90 (right), /Richard Woldendorp, 14; Photos. com, 91 (left), 176, 255 (middle), 269; Plastic Logic, 251; Rubberball, 232 (left); Peter Stannard, 51; Professor Mike Tyler, 45; XTAL Enterprises /Duncan Waddell, 215 (left inset).
MACMILLAN EDUCATION AUSTRALIA PTY LTD
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Williamson, Ken ScienceWorld 8 for NSW / Ken Williamson, Peter Stannard. 9781420229127 (pbk.) Williamson, Ken ScienceWorld. Includes index. For secondary school age. Science—Textbooks. Science—Study and teaching (Secondary)
Other Authors/ Contributors: Stannard, Peter. Dewey Number: 500 Publisher: Peter Saffin Project editor: Hannah Koelmeyer Technical illustrators: Guy Holt, Brent Hagen and Chris Dent Cartoonist: Chris Dent Cover and text designer: Dimitrios Frangoulis Photo research: Lesya Bryndzia Typeset in Sabon, Univers and Helvetica Condensed by Dimitrios Frangoulis Cover image: Getty Images/Don Farrall Title page image: Photodisc Printed in Malaysia
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Contents Planning and safety check
1
Mixingandseparating
v
2
1.1 What’s a mixture? 1.2 Solutions 1.3 Separating mixtures Review PFA: Forensic science
4 5 11 23 25
2 Scienceatwork
26
2.1 What is science? 2.2 Experimenting 2.3 Solving problems Review PFA: Experimenting
3 Whatarethingsmadeof? 3.1 Properties of matter 3.2 Solid–liquid–gas 3.3 Using the particle theory Review PFA: From idea to theory
28 32 40 48 50
51 53 61 70 74 76
4 Buildingblocksoflife
77
4.1 Cells 4.2 Growth and reproduction 4.3 Reproduction and survival Review PFA: Stem cell research
79 89 93 99 101
5 Energyinourlives 5.1 What is energy? 5.2 Forms of energy 5.3 Energy comes—energy goes Review PFA: Nuclear power station inquiry
6 Investigatingheat 6.1 6.2
Heat and temperature Heat transfer
102 104 107 116 123 125
126 128 134
6.3 Heat in everyday life Review PFA: How a theory was rejected
7 Exploringspace 7.1 Observing the night sky 7.2 Exploring the solar system 7.3 Stars and galaxies Review PFA: Colonising Mars
143 147 149
150 152 157 169 175 177
8 Buildingblocksofmatter 178 8.1 Atoms and molecules 8.2 Elements and compounds 8.3 Chemical reactions Review PFA: Inside the atom
9 Foodforlife 9.1 The need for food 9.2 Digesting food 9.3 Using food Review PFA: GM foods podcast
10 Electricity
180 182 191 196 198
199 201 209 215 223 225
226
10.1 Electric charges 10.2 Electric currents 10.3 Electric circuits Review PFA: Conducting plastics
228 235 242 249 251
11 Livingsystems
252
11.1 Survival 11.2 Physical factors Review PFA: Murray River crisis
254 262 273 275
Answers to Reviews
276
Glossary
285
Index
289
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ScienceWorld8
Planning and Safety Check The best part of science is doing investigations and experiments. Flick through the book and find: in Chapter 1 where you separate mixtures by filtering and distillation ● in Chapter 2 where you learn how to design experiments ● in Chapter 4 where you learn how to use a microscope ● on which pages you do investigations with electric circuits. ●
p 140 Which type of material keeps you warmest in winter? 6 You will of course need to discuss your design with your teacher before you start. There are risks involved in doing investigations and experiments, but you can reduce the risks to yourself and others if you follow simple safety procedures. Make sure you can answer these questions: What are the safety rules for the laboratory?
●
What safety procedures are necessary when you see these symbols?
To get the most out of the investigations, you must be well prepared, and you must consider safety issues. This is why most investigations in this book have a Planning and Safety Check at the beginning. The first one is on page 6. Before you start an investigation you should follow these steps.
●
1 Read the investigation carefully and study the diagrams. Make sure you know the aim of the investigation, that is why you are doing it.
●
When should you use safety glasses?
●
What should you do if you get a chemical in your eyes or on your skin?
2 Make sure you know exactly what you will be doing. You will be working in a group most of the time so you will need to sort out who will be doing what. 3 You need to know which materials you will be using. You will also need to know how to use the equipment. 4 You usually need to prepare a data table in which to record your results. Sometimes the textbook shows you how to do this and sometimes you have to design it yourselves. 5 Experiments are open-ended investigations where you have to design your own tests to answer a question or solve a problem. Have a quick look at these: p 18
How can you make creek water pure enough to drink?
p 30
How much weight will a paper bridge support?
●
a b c What special precautions are necessary when you use a Bunsen burner?
Here’s all the equipment we need.
Why don’t you do the experiment? I’ll time it.
new cartoon front iv
Yeah, and I can record the data.
ScienceWorld 7 and 8 for NSW, Stage 4 Syllabus Checklist Prescribed focus areas Students learn about: 4.1
the history of science
4.2
the nature and practice of science
4.3
the applications and uses of science
4.4
the implications of science for society and the environment
4.5
current issues, research and developments in science
ScienceWorld 7 for NSW Chapter number
ScienceWorld 8 for NSW Chapter number
6, 11
6, 10
2, 5, 7, 8, 10
2, 3, 7, 8
9
4 4, 5, 9, 11
1, 3, 4
1
Domains 4.6.1
the law of conservation of energy
4.6.2
forces
5 5, 9
4.6.3
electrical energy
4.6.4
sound energy
4
4.6.5
light energy
4
4.6.6
heat energy
4.6.7
frictional force
4.6.8
electrostatic force
4.6.9
magnetic force
4.6.10 gravitational force
10
6 5 5
10
5, 6 5, 9
4.7.1
the particle theory of matter
4.7.2
properties of solids, liquids and gases
3, 6 3
4.7.3
change of state
3
4.7.4
elements
8
4.7.5
mixtures
1
4.7.6
compounds and reactions
8
4.8.1
cell theory
4.8.2
classification
4.8.3
unicellular organisms
4.8.4
multicellular organisms
4.8.5
humans
4.9.1
Newtonian model of the solar system
4.9.2
components of the universe
4.9.3
the structure of Earth
11
4.9.4
the atmosphere
3
4.9.5
the hydrosphere
8
4.9.6
the lithosphere
11
4.10
ecosystems
10
11
4.11
natural resources
4.12
technology
4, 6, 9
5
4 7 7, 10
4
4, 7, 10
4, 9 9
8
7 7
5
Skills 4.13.1 identifying data sources 4.13.2 planning first-hand experiences 4.13.3 choosing equipment or resources
1, 2, 7 2, 6, 10, 11
2, 3, 6, 9
1, 6
1, 6, 8, 9, 10
4.14
performing first-hand investigations
1, 2, 3, 4, 7, 10
1, 2, 3, 4, 8, 9
4.15
gathering first-hand information
2, 7, 11
5, 8, 9, 11
4.16
gathering information from secondary sources
8, 9, 10
6, 7, 11
4.17
processing information
2
2, 3, 5, 6, 7, 8, 9, 11
4.18
presenting information
2, 5, 7, 10
2, 3, 4, 5, 7, 8, 10, 11
4.19
thinking critically
3, 5, 6, 8, 9, 10, 11
1, 2, 3, 7, 9, 10, 11
4.20
problem-solving
2, 5, 9
1, 6, 10
4.21
the use of creativity and imagination
4.22
working individually or in teams
5
6, 10
6, 9
1, 2, 9, 10, 11
For more details see the Course Construction Guide in the ScienceWorld 8 for NSW Teacher Resource Book.
2 1 Mixingand Chapter separating Title
Planning page Getting started 1.1 What’s a mixture? page 4 Investigate 1 Soluble or insoluble? Activity page 8
1.2 Solutions page 5
Skillbuilder page 9 Concentrations Investigate 2 Filtering and decanting Investigate 3 Evaporating and distilling Experiment Water purification
1.3 Separating mixtures page 11
Investigate 4 Paper chromatography
Animation Froth flotation
Assessment task 1 Separating a mixture
TRB
Main ideas Chapter 1 crossword
Review and Lab review Chapter 1 test Learning focus: Possible career paths in science
Prescribed focus area Forensic Science
TRB
Chapter1 Mixingandseparating r you wil In this chapte
t…
l learn abou
LearningFocus ●
possible career paths in science (pages 19 and 25)
KnowledgeandUnderstanding ●
mixtures
Skills ● ● ● ● ●
choosing equipment or resources (Investigate 2 and 3) performing first-hand investigations (Investigate 1–3) thinking critically—inferring and predicting (Activity page 8 and Investigate 2–3) problem-solving using creativity and imagination (Getting Started page 3 and Experiment page 18) working in teams (Experiment page 18)
Work in a small group to solve one or more of these problems. ● Your four-wheel drive has broken down in the middle of the Simpson Desert and you have no water to drink. You find a damp patch of sand near the base of a cliff. How can you get drinkable water from this damp sand? ●Your uncle has given you a large bottle of 5c, 10c, 20c and 50c coins. Can you design a device to separate the coins? ● Your science teacher is very angry with the class. Someone has poured sand, salt and iron filings into one jar! Until they are all back in separate containers, no one can go to lunch. How can you separate this mixture?
3
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ScienceWorld8forNSW
1.1 What's a mixture? Different substances have different properties. For a start, they can be solids, liquids or gases. But there are many other properties which allow you to tell one substance from another. For example, you can detect sugar by its sweet taste. You can detect kerosene by its smell. Glass is transparent (you can see through it). Diamond is extremely hard. Beetroot is a purple-red colour. A piece of lead is very heavy. And so on. The materials around you can be grouped into pure substances and mixtures. Pure substances contain only one substance. They always have the same properties, no matter where they come from. Examples are sugar, gold, pure water and helium gas. However, most materials around you are mixtures—several different substances mixed together. Examples are air, soft drink, concrete and lipstick. The amounts of each part of the mixture (called their proportions) can vary widely. This changes the properties of the mixture. For example, concrete is a mixture of cement, sand, gravel and water. Mixing these four substances in different proportions will change the properties of the concrete. Fig 3
The parts of mixtures can be solids, liquids or gases. For example, soft drink is a mixture of water and carbon dioxide gas, plus sweetener, flavouring and colouring. Examples black coffee air soft drink smoke wine brass
liquid in liquid solid with solid
Main parts of mixture coffee powder in water nitrogen and oxygen carbon dioxide in water tiny bits of soot, dust, etc in air alcohol in water copper and zinc
Check! 1
Which of the following are mixtures, and which are pure substances? a air e orange juice b petrol f sugar c polluted water g helium gas d gold h concrete
2
Copy and complete these sentences.
Lipstick is a complex mixture.
Lipstick normally contains: • castor oil • beeswax • carnauba (to stop it melting) • esters (to make it slippery) • anti-oxidant (to stop it going off) • aloe (to stop lips becoming dry) • mineral oil (to make lips glossy) • red dye No. 21 • perfume
Type of mixture solid in liquid gas with gas gas in liquid solid in gas
The features by which a material can be identified are called ______. Materials that always have the same properties are called ______ substances. Materials that are made up of different substances are called ______. The properties of a mixture can ______. 3
Explain why concrete is a mixture and not a pure substance.
4
In your notebook, match up the following types of mixtures with the examples. smoke a mixture of gases b mixture of solids air c mixture of gas in liquid soil d mixture of solids in liquid muddy water e mixture of solids and gases lemonade
Chapter1 Mixingandseparating
1.2 Solutions When you stir sugar in a glass of water, it disappears into the water. We say it dissolves in the water. The sugar and water have mixed to form a solution. Solutions are very important to you. The food you eat is digested and dissolved in water. It is then carried around your body in the blood plasma, which is a solution consisting of about 90% water. The wastes produced by your body are also carried away in this solution. A solution is a special mixture that looks and behaves like a single substance. It consists of a liquid and the dissolved substance which is spread evenly throughout it. Consider what happens when instant coffee dissolves in hot water. The substance that dissolves (the coffee) is called the solute. The substance that does the dissolving (the water) is called the solvent. So the solute dissolves in the solvent, forming a solution.
solute (coffee)
Two liquids can also form a solution. For example, wine is a solution of alcohol (solute) in water (solvent). Fuel for two-stroke motor mowers and outboard engines is a solution of oil in petrol. A particular substance may not dissolve in every solvent. For example, salt is soluble in water, but insoluble in alcohol. Water is an excellent solvent, but to dissolve some things you have to use other solvents. Some commonly used solvents are shown in the table below.
Solute nail polish biro stains grease marks on clothes oil-based paint tar on car paintwork
solvent (water)
Solvent (dissolves the solute) nail polish remover methylated spirits eucalyptus oil turpentine kerosene
solution
When substances don’t dissolve A substance that dissolves is said to be soluble. A substance that will not dissolve is insoluble. Some insoluble substances sink in water (settle out), and others float on top. If you shake up an insoluble solid (such as chalk dust) with water it may seem to dissolve at first. However, if you look closely you will see that the liquid is cloudy and the chalk settles when you let it stand for a while. Such a mixture is not a solution, but a suspension. Muddy water is another example of a suspension, because the mud settles to the bottom when you let it stand.
solution
In a solution, the solid does not settle on standing.
suspension
In a suspension, the solid settles on standing.
5
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ScienceWorld8forNSW
Investigate
1 SOLUBLE OR INSOLUBLE? Aim To test whether various substances are soluble in water and in alcohol.
PART A
I s i t s oluble i n wate r? Method
Materials • • • • • •
1 Usethespatulatopickupasmallamountof salt—aboutthesizeofagrainofrice.Placethis saltinatesttube.Usethemarkingpentolabel the tube ‘salt’.
spatula Wear safety glasses.
SALT
testtubes(atleast6) rubberstopperstoittesttubes testtuberack spatula markingpen alcohol or methylated spirits Flammable (inadroppingbottle) • samplesof: salt sugar coffee flour Toxic iodine (solid) jelly crystals grass(groundup)
test tube rack
Planning and Safety Check Beforeyoustart,checkthatyouknowthe safetyrulesforyourlaboratory. Readthroughbothpartsoftheinvestigation, thenprepareadatatableliketheonebelow. Substance
Soluble Soluble Observations in water? in alcohol?
salt sugar coffee flour • Whydoyouhavetobecarefulwhenusing iodine?Howdoyoudisposeofleftover iodine?
Warning: Do not touch iodine with your fingers. It is poisonous. Your teacher will tell you how to dispose of any leftover iodine. Do not wash it down the sink.
2 One-thirdillthetesttube withwater.Shakethe tubeusingthefollowing method.Holdthe tubeirmlybetween yourthumband indexinger.Then tapthebottomofthe tubesharplywiththe indexingerofyourotherhand. (Youmayneedtopractisethis.) Record whether the substanceissoluble,slightly soluble(abitdissolves)orinsoluble. Record any other observations as well. For example,ifasolutionwasformed,whatcolour wasit?Wasasuspensionformed? 3 RepeatSteps1and2foreachoftheother samples.
Chapter1 Mixingandseparating
Discussion
PART B
I s i t so lub le i n alco hol?
1 Howcanyoutellwhetherasubstancehas dissolved or not?
RepeatPartA,usingalcoholormethylatedspirits insteadofwater.
2 Whichsubstancedissolvedmosteasilyin water? 3 Comparethesolubilitiesofthesubstancesin water and in alcohol. a Which substances were soluble in water but not in alcohol? b Which substances were soluble in alcohol but not in water? c Which substances did not dissolve in either water or alcohol? 4 Supposeyouhaveabirostainonyourschool uniform.Howcouldyouremoveit?
dropping bottle
Solubility A cup of coffee is like any liquid solution. It comes in many different strengths. If you like your coffee stronger, add more coffee powder. If you like it weaker, add less coffee. We use the terms dilute (dye-LOOT) and concentrated (CON-cen-TRAY-ted) to help us compare solutions. A dilute solution contains only a small amount of solute in a given volume of solvent. A concentrated solution contains a large amount of solute in the same amount of solvent. You may have used the terms weak cordial or strong coffee—but the correct scientific terms are dilute cordial and concentrated coffee. The colour of a solution gives you some idea of its concentration. The darker the colour,
dilute
concentrated
the higher the concentration. Or, a more dilute solution will be lighter in colour. These statements are generalisations. There is a limit to the amount of solute that will dissolve in a solution. When a solution will dissolve no more solute, it is said to be saturated. Until it reaches this point, it is unsaturated. If you add more solute to an unsaturated solution, it will dissolve. The amount of solute needed to saturate a solution depends on the temperature. For example, at room temperature (around 20°C) you can dissolve about 2 kilograms of sugar in a litre of water, but when the water is boiling (100°C) you can dissolve almost 5 kilograms. Most solids are more soluble in warm water than in cold water. We say that their solubility increases as the temperature increases. This is another generalisation.
7
8
ScienceWorld8 Colloids The Yarra River in Melbourne is well known for its brown colour. This is because the clay in the water is so fine that it will not settle to the bottom, as it would normally do in a suspension. Instead the clay particles are spread evenly throughout the water, forming what is called a colloid (COL-OID). A colloid has properties that are in between a solution and a suspension. The particles in a colloid may be tiny bits of solid, liquid droplets or gas bubbles. The colloid may also be a solid, a liquid or a gas. The following table lists the common types of colloids. A liquid-in-liquid colloid is called an emulsion (ee-MULL-shun). A common example is ordinary homogenised milk, where tiny globules of milk fat are spread throughout water. It is processed by forcing the milk through small holes to break up the larger fat globules in the cow’s milk. This is why the cream (the fat) doesn’t come to the top on standing. Although it is easy to see fogs, foams and emulsions, it is often hard to tell the difference
between solutions and some types of colloids. One way to do this is to shine a beam of light through them. The beam can be seen in the colloid because it bounces off the tiny particles. This is why you can see the headlights of a car in fog. However, the beam cannot be seen in a solution. Colloid
Type
sol or gel
solid in liquid liquid in gas liquid in liquid liquid in solid gas in liquid gas in solid
liquid aerosol liquid emulsion solid emulsion foam solid foam
Examples most paints, starch in water, clay in water, jelly fog, clouds, sprays from spray cans mayonnaise, milk cheese, butter, face cream whipped cream, beer froth, soap suds pumice, marshmallows, meringues
Activity A Forming an emulsion Shake up some olive oil with vinegar in a stoppered test tube, and let it stand for a while. Do the olive oil and vinegar mix? Now add a pinch of mustard powder and shake. Allow the mixture to stand again. What do you observe now? (Salad dressing is made this way.) Write an inference to explain your observations. B Solution or colloid? Dissolve a few crystals of hypo (sodium thiosulfate) in a beaker of water and shine a strong beam of light through it. Can you see the beam in the solution when looking from the side? Now add a few drops of dilute hydrochloric acid and observe what happens to the beam. Try to explain what has happened.
Chapter1 Mixingandseparating
Check!
Skillbuilder The concentration of a solution is often given as a percentage. For example, a 5% hydrochloric acid solution is dilute. A 30% solution is concentrated. If you have a dog at home, you may sometimes wash it in a dog shampoo or flea-killing liquid. These chemicals can be dangerous, and have to be mixed with water in the correct proportions. Suppose you have to make up a 5% dogwash solution. This means you need 5 parts of dogwash dissolved in enough water to make up a total of 100 parts. That is, you mix 5 parts of dogwash with 95 parts of water. This is a 5% solution.
1
Copy and complete these sentences. a When sugar is mixed with water, it ______. This shows that sugar is ______ in water. b Sand is ______ in water. c In salt water, the salt is the ______, and the water is the ______. d The solute in a solution does not settle out, but the solid in a ______ does. e A mixture with properties in between a solution and a suspension is a ______. f A solution that can dissolve no more solute is ______. g Most solids are more ______ in hot water than in ______. h A ______ solution is one which contains a small amount of solute. When more solute is added, the solution becomes more ______.
2
Which of the following statements are true, and which are false? a Water dissolves everything. b Solutions are always coloured. c Some gases dissolve in water. d Emulsions settle out on standing. e A solute can be a solid, a liquid or a gas. f More solute can be dissolved in an unsaturated solution. g Adding more water to a dilute solution will make it more concentrated.
3
Explain in your own words the difference between a solute and a solution.
4
How can you tell the difference between a solution and a suspension?
5
Imagine that while doing Investigate 1 (page 6) you noticed the following: a Nathan put his thumb over the mouth of a test tube to shake it. b Donna used her fingers to put a pinch of salt into a test tube.
Questions 1 How could you tell the difference between a 1% red food colouring solution and a 5% solution? 2 The label on a bottle of cleaner says it contains 15% ammonia. If the bottle contains 200 mL of cleaner, how much ammonia is in the bottle? 3 You want to fill a 50 litre bath with dogwash solution. The instructions say to make up a 0.5% solution. How much dogwash should you use?
Explain to Nathan and Donna why their methods were unsafe.
9
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ScienceWorld8forNSW
6
In your notebook, complete the table below by putting in the names of the solute and solvent for each solution.
Solution
Solute
Solvent
a sea water b hot chocolate c turpentine in which you have just cleaned a paint brush d bath water e soft drink 7
The photo below shows three different solutions of Condy’s crystals in water. a What clue in the photo suggests that the solutions contain Condy’s crystals? b How do the three solutions differ? c How can you explain this difference?
8
The instructions on jelly crystals say to dissolve them in boiling water. Suggest a reason for this.
challenge 1 Youhavepaintedsomethingwithanoil-based paint.Whycan’tyoucleanthebrusheswith water? 2 Isfogasolution,asuspensionoracolloid? Explainyouranswer. 3 Katyshoneabeamoflightthroughsome muddywater.Shecouldseethebeam.When shetriedthisagainthenextdayshecouldnot seethebeam.Explainherobservations. 4 Thefollowingsolutionsvaryinconcentration. Arrangethemfromthemostconcentratedtothe least concentrated. a aglassofmilkwithoneteaspoonof lavouring b aglassofmilkwithhalfateaspoonof lavouring c aglassofmilkwithtwoteaspoonsof lavouring d halfaglassofmilkwithtwoteaspoonsof lavouring 5 Ajugcontainsfourglassesofmilk.Youwantto makelavouredmilkwiththesame concentration as cabove.Howmuch lavouringwouldyouneedtoadd? 6 Whichoneofthefollowinggeneralisationsisthe mostgeneral? a Thehotterthesolventthemoresoluteit dissolves. b Thehotterthewaterthemoresugar dissolves. c Sugardissolvesbetterinhotwaterthanin cold. d Thehotterthewaterthemoreasubstance dissolves. Explainyourchoice. 7 Describehowyouwouldmakeasaturated solutionofsugarsolution.Ifsomeoneaskedyou tochecktheirsolutiontoseeifitwassaturated, how would you do it? 8 Designyourownexperimenttoinvestigate thefactorsthataffecthowquicklysugarwill dissolve in water. 9 Theoceansatthepolescontain2.9%salt,but theoceansattheequatorcontainabout3.5%. Suggestareasonforthis.
Chapter1 Mixingandseparating
1.3 Separating mixtures Separating suspensions Suppose you are in the kitchen and have boiled some peas in water, but you don’t want the water. You gently tip the saucepan so that the water runs out, leaving the peas in the saucepan. Pouring off the liquid like this, while keeping the solid in the container, is called decanting. It is a way of separating the liquid part of a suspension from the solid part. If a suspended solid settles very slowly you can speed up the separation by using a centrifuge. This is a machine designed to separate mixtures by a spinning motion. A spin-drier is one type of centrifuge.
Fig 16
A high-speed centrifuge is used at the blood bank to separate the components of blood.
Centrifuges are also used to separate cream from milk, and red blood cells from plasma at the blood bank. When test tubes of blood are spun in a centrifuge (Fig 16) the heavier red blood cells settle to the bottom, leaving the pale yellow liquid plasma on top. The plasma and red blood cells can then be separated by decanting. Decanting is not a very good method for complete separation. Some liquid is usually left behind. Also, unless you are very careful, you are likely to pour off some solid with the liquid. A better way of separating suspensions is by filtering. Suppose you have a suspension of chalk in water. The chalk can be separated from the suspension using filter paper. The filter paper has microscopic holes in it. The water passes through these holes, but the suspended chalk cannot. This is similar to separating sand and gravel using a sieve. The small sand particles pass through, but the larger gravel particles do not. The solution that passes through the filter paper and collects in the beaker is called the filtrate. The solid material that remains in the filter paper is called the residue.
suspension of chalk in water
Normal blood
Centrifuged blood—the heavy blood cells have settled to the bottom
residue (chalk)
filtrate (clear water)
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ScienceWorld8forNSW In our day-to-day life we use filters to separate solids from liquids and gases. For example, vacuum cleaners have a special bag that filters dust and dirt from the air that is drawn in. The hairs in your nose filter the dust from the air you breathe. There are filters in a car to clean the petrol, air and oil. Filters are used to purify the water we drink, and to clean the water in swimming pools.
Investigate
2 FILTERING AND DECANTING Aim Toseparateasoil–watermixturebyilteringand bydecanting.
Materials • • • • • • • •
soil three250mLbeakers 2or3piecesofilterpaper ilterfunnel retortstandandringclamp glassstirringrod teaspoon washbottle
Planning and Safety Check ReadthroughPartAanddescribe to yourpartnerwhatyouhavetodo.Your partnerwillthendescribePartBtoyou.
2 Setuptheiltrationapparatusasshownbelow. Adjusttheheightofthestandsothatthespout ofthefunneltouchestheinsidewallofthe beaker.Thisallowsthewatertolowoutevenly, withoutsplashing.
stirring rod
ring clamp
beaker
filter paper soil–water mixture filter funnel
PART A
Fi l te r i ng Method 1 Makeasuspensionbystirring about4teaspoonsofsoilina beakerofwater.Pourhalfofthis suspensionintoasecondbeaker andletitstandforaboutaday.
wash bottle
retort stand filtrate
Fig 19
Filtration apparatus
Chapter1 Mixingandseparating
3 Foldtheilterpaperandopenitoutintoacone as shown. 1
Neatlyaddthefollowinglabels:
ilterfunnel residue
ilterpaper stirringrod
PART B
Pull this single flap away from the other three.
Dec a nt in g
Then fold again.
1 Lookatthebeakercontainingthesoil–water mixturethathasbeenstandingforaday.
4 This forms a cone.
4 Placetheconeintothefunnel.Usethewash bottletowetthepapersothatitstickstothe sidesofthefunnel.
What do you notice? 2 Carefullydecantthewaterintoasecond beaker.Todothis,holdastirringrodoverthe mouthofthebeakerasshownbelow.Thisway theliquidrunsdowntherodwithoutsplashing.
5 HoldthestirringrodasshowninFig19,withits lowerendalmosttouchingtheilterpaper.This willallowthewatertolowgentlyintotheilter paper.
iltrate
2 Fold in half.
3
Carefullypoursomeofthesoil–watermixture downtherodintothefunnel.Don’tletthewater levelreachthetopoftheilterpaper.
6 Usethewashbottletorinsetheremainingsoil fromthebeakerintotheilterfunnel.Keepthe iltrateforPartB. 7 Drawadiagramoftheiltrationapparatus.Draw asimpletwo-dimensionalviewasshownonthe right.Noticehow muchsimpleritis than the threedimensionalview inFig19.For example,there is no line across thetopofthe beakers,andthe ringclamphas beensimpliied.
Decanting
soil
water
Comparethedecantedwaterwiththe iltratefromPartA.Isitasclear? 3 Filter the decanted water.
Discussion 1 Howeasywasittoilterthedecantedwater, comparedwiththeoriginalsoil–watermixture? Suggestareasonforthis. 2 Explainwhyyou: a wettheilterpaperinPartAStep4 b usedthewashbottleinStep6 c pouredthesuspensiondownastirringrod whenilteringanddecanting.
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Fig 23
At this salt plant, sea water is run into large ponds. Heat from the sun causes the water to evaporate, leaving the salt behind.
Separating solutions Once a solute has dissolved in a solvent to form a solution, you cannot separate it by filtration. The solution simply passes through the filter paper in the same way that water does. If a solution consists of a solid dissolved in water, you can separate them by heating. The water evaporates—turns into a vapour and seems to disappear into the air—leaving the solid behind. Salt can be obtained from sea water by this method. If you want the liquid you must somehow trap it as it evaporates and condense it back to a liquid. This process is called distillation. In a solar distillation plant, the sunlight passes
through glass plates and the heat causes salty bore water (from underground) to evaporate. The water vapour condenses on the glass roof, and the water droplets run down the inside of the glass plates into the collection gutter. The water is pure, because the salty solutes have been left behind. Distillation can also be used to separate two or more liquids with different boiling points, eg water and alcohol. This process is used in the making of whisky and brandy, and in the separation of crude oil into petrol, kerosene, diesel fuel and lubricating oil.
heat from the sun glass plates
< WEB watch > To find out how to make a simple solar still, go to www.scienceworld.net.au and follow the links to Solar still.
water condenses water evaporates
salty water
Fig 24
How a solar distillation plant works
collection gutter (pure water)
Chapter1 Mixingandseparating
Investigate
3 EVAPORATING AND DISTILLING Aim
Method
Toseparatethesoluteandthesolventina solutionbyevaporationandbydistillation.
1 Putthetripodandgauzematonaheatproof matasshownbelow. 2 Halfillthebeakerwithwater.Addsomeboiling chipstopreventbumping(violenteruptionof bubblesfromthebottomofthebeaker).
PART A
Evap or at i o n Materials • • • • • • • •
Toxic
copper sulfate solution(0.5M) boilingchips(brokenporcelain) 250mLbeaker Bunsenburner heatproofmat watchglass gauzemat Wear safety glasses. tripod
Planning and Safety Check ReadtheMethodforPartA. • Suggestwhyyouputthewatchglasson topofthebeakerofboilingwater,instead ofdirectlyonthegauzematoverthe burner. • Suggestwhyyoudon’tevaporatethe coppersulfatesolutioncompletelyover the burner.
3 One-thirdillthewatchglasswithcopper sulfatesolution.Placethewatchglassontopof thebeakerasshown. 4 Lighttheburnerandadjusttothebluelame. Thenputitunderthetripodandboilthewater inthebeaker.Thecoppersulfatesolutionwill evaporateslowly. 5 Whenalmostallthecoppersulfatesolutionhas evaporated,turnofftheburnerandletthe apparatuscool.(Ifyouheatthesolutionany longeritwillstarttosplutter.) 6 Leavetheremainingsolutioninthewatch glassinawarm,protectedplaceto inishevaporating.Thisprocessiscalled crystallisationandmaytakeadayortwo.
watch glass
copper sulfate solution
water
E OF A BURNER RULES FOR SAFE US from books, and away 1 Keep the burner away ch. from the edge of the ben the burner. der un 2 Use a heatproof mat . h r wit the air hole closed 3 Always light the burne ety flame when not 4 Switch to a yellow saf heating. r gets very hot. If you 5 The barrel of the burne turn it off first. Move have to move the burner, the gas hose—not the it by holding the base or barrel. off properly when you 6 Check that the gas is have finished.
boiling chips
gauze mat
tripod Bunsen burner
heatproof mat
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Discussion 1 Whatwasleftinthewatchglassafteradayor two?
3 Whatwasthepurposeofthegauzematwhen heating?
2 Inyourownwords,explainhowevaporation causedthesolutetobeseparatedfromthe solvent.
4 Whyisitessentialtowearsafetyglassesfor thisinvestigation?
PART B
Dis t illa t ion Materials SameasforPartA,plus: • conicallask • one-holedstoppertoitlask • lengthofglasstubing(atleast40cm longandbentasshownatright) • 2retortstandsandclamps • testtube
Planning and Safety Check
retort stand one-holed stopper glass tubing
clamp conical flask copper sulfate solution
Read the instructions and study the diagram. • Whatdoyouthinkisthepurposeofthe glasstubing? • Whatsafetyprecautionswill youneedtotake?
distilled water
Fig 26
Method 1 Setupthedistillationapparatusasshown. 2 One-quarterillthelaskwithcoppersulfate solution.Addsomeboilingchips. 3 Putonyoursafetyglasses.LighttheBunsen burner,adjustittothebluelame,andheatthe solutioninthelask. 4 Asthewaterboils,observe: a thewatervapourrisinginthelaskand movingthroughtheglasstubing b thewatervapourcondensingbackto liquidanddrippingfromtheglasstubing into the test tube.
Distillation apparatus
5 Collectasampleofdistilledwaterinthetest tube,thenturnofftheburner.
Discussion 1 Explainwhathappenedin: a theconicallask b the test tube. 2 Theliquidyoucollectedinthetesttubeis called the distillate. Why is it clear, not blue? 3 Theglasstubingiscalledanair-cooled condenser.Suggestareasonforthisname. 4 Designawater-cooledcondenser.
Chapter1 Mixingandseparating 3
Separating solids Sometimes we need to separate a mixture of solids from each other. The four methods below all depend on differences in the properties of the solids. 1 If one solid is soluble in water and the other is insoluble, you can add water. When you filter the mixture, the residue is the insoluble solid. The filtrate contains the soluble solid in solution. It can be recovered by evaporation. The process can be summarised in a flowchart. MIXTURE OF SOLIDS
Add water to mixture
Filter
INSOLUBLE SOLID (residue)
Evaporate filtrate
SOLUBLE SOLID
2
If one solid is attracted to a magnet and the other is not, you can use magnetic separation. This method is used in industry to separate the magnetic minerals in mineral sands. Fig 27
A magnet will separate the magnetic minerals in sand.
If one insoluble solid floats on water and the other sinks, you can add water to the mixture and skim off the floating solid. For example, you can separate sawdust and sand this way. Sometimes this method can be used even if both solids normally sink in water. A special chemical is dissolved in the water, and air is bubbled into it. A froth of bubbles floats to the top, taking one of the solids with it. This method is called froth flotation. It was invented in Australia, at Broken Hill, and is often used to separate valuable minerals from rock. To see how froth flotation works, open the Froth Flotation animation on the CD.
4 If one solid is heavier than the other, you can use gravity separation. A good example of this is gold panning. Here the water is swirled about in the pan, allowing the heavy gold to sink and the lighter mud and sand to be washed off the top. This is like decanting. Fig 28
When you pan for gold, you use gravity to separate heavy gold particles from ‘lighter’ sand.
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Experiment
WATER PURIFICATION 4 Decidehowyouwillattacktheproblem.
The problem to be solved
• Whichtechnique(s)willyouuse?
Thenormalwatersupplyhas brokendown.Theonlywater availableiscreekwater,which isgreenishincolour,smells, andhasallsortsofthings init,egtwigsandmosquito wrigglers.Howcanyoumake thiswaterpureenoughtodrink?
• Whatequipmentwillyouneed? •
Who will do what?
• Howmuchtimewillyouneed? 5 Whenyouandyourteacherarehappywith yourplan,putitintoaction. Keeparecordofwhatyoudid.
Method
Whatwasthewaterlikeafteryoupuriiedit?
1 Formagroupwithotherstudents.Yourteacher willgiveyouasampleofabout200mLof impurecreekwater.Yourtaskistorecoveras muchpurewateraspossible.
Howmuchpuriiedwaterdidyourecover? 6 Ifyourtechniqueisn’tsuccessful,tryanother. Youmayneedtodiscusstheproblemwithyour teacher.Youmayalsoneedtousethelibrary.
2 Observethecreekwaterandrecordwhat impuritiesareinit.
Writing your report Writeareportdescribingwhatyoudid,for someoneelsetoread.Youcouldprepareaposter forpresentationtotherestoftheclass.Include a discussionofhowsuccessfulyourmethodwas.
3 Inyourgroup,discusswaysofpurifyingthe water. Whichoftheseparationtechniquesyou havelearntinthischaptercouldyouuse?
• Isyourmethodpractical?
Thelowdiagrambelowshowshowwater ispuriiedinawatertreatmentplant.Couldyou modifythisforuseinthelaboratory?How?
screening (water passes through mesh)
• Howlongdidittake? • Wouldyourmethodworkforlargervolumesof water?
alum
sedimentation (letting the suspension settle) filtration
sand
pump
storage tank
flocculation (alum causes colloids to settle)
gravel sludge
drinking water
chlorine added to kill germs
Fig 30
A water treatment plant
Chapter1 Mixingandseparating Separating colours Chromatography (CROW-ma-TOG-ra-fee) can be used to separate a mixture of coloured substances. (Chromos is the Greek word for ‘colour’.) For example, this method will separate the coloured substances in black ink, as shown below.
rs How to separate the colou in black ink pen filter paper
1
Science in action Gas chromatography is used in industry and in scientific research to detect very small amounts of chemicals in mixtures. It is used to test the purity of medicines and to see if harmful pollutants are being released into the air. Forensic scientists use it to detect poisons and drugs in blood or traces of chemicals at crime scenes. The peaks on the graph on the monitor in the photo are the different chemicals in the sample being tested.
Use a black pen to place a spot in the centre of a piece of ilter paper.
beaker
colours begin to separate
2
yellow ring
blue ring
red ring
Drip water onto the spot, one drop at a time. The ink spreads out into coloured rings.
3 With this ink there are three rings—blue, red and yellow. This shows that the ink contains three different substances, coloured blue, red and yellow. The yellow substance is the most soluble in water. The blue is the least soluble.
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Investigate
4 PAPER CHROMATOGRAPHY Aim Toplanandcarryoutaninvestigationtoseparate thedifferentcolouredsubstancesininksorfood colouringsusingpaperchromatography.
Materials • variouscolouredinksfrombiros,feltpensor markingpens(Indianinkworkswell.) • foodcolourings • 250mLbeaker • ilterpaperorblottingpaper • dropper • scissors • adhesivetape • jellybeans,Smartiesorsimilarsweets • smallpaintbrush
Method UsethePlanningandSafetyCheckandthe diagramsbelowtoplanwhatyouaregoingtodo andhowyouaregoingtodoit.
Planning and Safety Check • Youcanuseoneormoreofthethree methodsbelow. • Blackanddarkcoloursusuallygivegood results. • Forsomeinks,egbiro,youmayneedto usealcoholormethylatedspiritsinsteadof water as the solvent. • Toremovethefoodcolouringsfromajelly beanorsimilar,putitinawatchglassand addthreedropsofwater.Brushthejelly beanwithasmallpaintbrushuntilthe colouringdissolvesinthewater. • Allowtheilterpaperstodry,thenlabel themandsticktheminyournotebook. • Whenyouhaveinishedtheinvestigation, writeareportdescribinginafewsentences whatyoufoundout.Forexample,whichink orjellybeancontainsthemostcolours?
You could use a digital camera to take photos of your results and use them in a PowerPoint presentation.
Method A Add solvent a drop at a time. spot of ink or food colouring
Method C beaker
Method B
filter paper
Tape strip onto pencil
filter paper strip solvent (1 cm below spot)
spot (2 cm from end of strip)
spot of ink or food colouring
solvent
Make two cuts in the filter to create a tongue.
Chapter1 Mixingandseparating
Check! 1
2
Work with a partner and give each other a spelling test of these words. Correct any mistakes. apparatus filter funnel beaker laboratory dilute solubility distillation solute evaporation solution
C D A
Look at the food strainer below. Explain how it works.
3
Why is filtering usually a better method of separation than decanting?
4
Suppose you filter river water which contains mud, sand, dissolved salt and some plant materials. Which of these materials will be present in: a the residue? b the filtrate?
5
What is a centrifuge? Where is a centrifuge found in most homes?
6
Write a sentence or sentences using these words correctly: condensation, distillation and evaporation.
7
The diagram at the top of the page shows the apparatus used to distil salt water. Write down the correct letter for each of the following: a Bunsen burner b where evaporation takes place c where the vapour changes to a liquid d distilled water e where the salt stays.
8
B
Go back to the three problems in Getting Started on page 3. Can you now suggest other solutions?
E
9
Which method would you use to do each of the following? a separate iron filings from sawdust b make fresh water from sea water c remove the water from wet clothes d remove the dust from the smoke going up a factory chimney e separate the coloured dyes in an ink f separate cream from milk g separate a mixture of salt and pepper
10
A dye is known to be a mixture. When a spot of the dye was put on a strip of filter paper and placed in alcohol, three coloured spots appeared, as shown. a Why have the parts of the mixture separated? b Which coloured substance do you think is the most soluble in alcohol? Why?
11
solvent reached here green
blue red original spot
Draw a simple diagram of the apparatus needed to separate a mixture of sea water and sand so that you obtain clean sand. On your diagram label at least three pieces of equipment, and show where the salt and sand end up.
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challenge 1 InInvestigate2(page12)youusediltration apparatus.Whatisthedifferencebetween equipmentandapparatus? 2 Whyisitimportanttoreplacetheiltersusedin carsfromtimetotime? 3 UsingFig16onpage11,explainhowa centrifugeworks. 4 Achemistusedpaperchromatographyto investigatesomeink.Herresultsareshown below. a Whichdifferentcoloureddyesdidtheink contain? b Inferthecolouroftheink.
8 Thephotobelowshowsaseparatingfunnel. Itcanbeusedtoseparatetwoliquidsthatdo notmix,forexampleoilandwater.Explainhow youthinkitworks.
Solvent reached this far.
pure red dye
pure blue dye
pure yellow dye
pure green dye
ink mixture
5 Kirk,Nathan,PatsyandJadeeachhada mixturetoseparate.Thefourmixtures(notin order)were: a mudandwater b mudandsalt c salt and water d mud,saltandwater. Patsy’sirststepinherseparationwastoadd somewatertohermixture.Kirkseparatedhis mixturebydecantingit.Jadehadmorestepsin herexperimentthanNathandid. Whichstudentseparatedwhichmixture? 6 Afterusinganelectrickettlewithhardwaterfor sometimeaninsolublesubstancebuildsup insideit.Inferwherethiscomesfrom. 7 Lookatthephotooftheswimmingpoolilteron page12.Describehowyouthinkitworks.
9 Imagineyouareawastemanagement engineer.Youhavebeensuppliedwitha mixturethatcontainssand,sawdust,iron ilingsandleadshot. Yourtaskistoseparate asmuchofeach componentas you can, so that they can be recycled.
10 Supposeyouownalollyshop.Yoususpectyour supplierissellingyouacheap,inferiorbrand insteadofSmarties,butchargingyouforthe realthing.Howcouldyoucheckthis?
Chapter1 Mixingandseparating
Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
chromatography
1 A ______ is a substance that dissolves in a ______ to form a
concentrated
colloids
______.
decanting
2 When a substance ______, it is said to be soluble. Substances
dilute
which do not dissolve are ______.
dissolves
3 In a ______ (eg muddy water), the solid settles to the bottom
distillation
when left standing. Solutions do not settle.
filtering
4 Many everyday substances are ______, with properties in
insoluble
between solutions and suspensions.
mixture
5 A ______ solution contains only a small amount of solute in a
properties
given volume of solvent. A ______ solution contains a larger amount of solute.
solute solution
6 Separation techniques depend on differences in the ______ of
solvent
the substances in the ______.
suspension
7 Suspensions can be separated by ______, using a centrifuge or by ______.
8 A dissolved solid can be separated from a solvent by evaporation or by ______. 9 A mixture of coloured substances can be separated by paper ______. Try doing the Chapter 1 crossword on the CD.
1 If you dissolve instant coffee in hot water, the water is the: A solvent B solute C solution D suspension 2 If more water is added to a coloured solution it becomes: A more concentrated B more dilute C saturated D a darker colour 3 Water can be separated from alcohol by: A chromatography B filtration C evaporation D distillation
4 Four liquids—water, kerosene, alcohol and petrol—were used to test the solubility of three unknown solids, A, B and C. Georgia did the tests and recorded the mass of solid that dissolved in equal volumes of the liquids. Solvent
water kerosene alcohol petrol
Grams of solid that dissolved Solid A Solid B Solid C
5 1 4 1
6 1 3 0
0 5 4 6
a Which liquid is the best solvent for solid B? b If solid A was accidentally mixed with solid C, which liquid could you use to separate them? Explain your answer.
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c Is there any way of separating a mixture of A and B?
REVIEW
5 Look at the diagram below. a What are the pieces of equipment labelled A–E? b Label the filtrate and the residue. c There are two mistakes in the diagram. What are they? d Redraw the diagram correctly.
8 a Write one complete and scientifically correct sentence using these words: colloid emulsion milk b Do the same for these words: concentrated dilute solution 9 The police receive a ransom note written using a felt pen. They also have felt pens from three suspects. How could they use paper chromatography to find out who wrote the ransom note?
C
E
B
A D
6 The apparatus below can be used to obtain pure water from salt water. a What is this separation method called? b Explain how the method works. c What is the purpose of the ice-cold water? You have a mixture of salt and dirt that Ken collected on his recent trip to Lake Eyre. Your task is to separate the salt by removing the dirt.
ice-cold water salt water
heat
pure water
7 When a can of fruit juice is left to stand, a sediment forms on the bottom of the can. Is fruit juice a solution, a suspension, a colloid or a combination of these? Explain.
1 Work out a way of separating the salt. 2 Make a list of the equipment you will need. 3 Do the separation correctly and safely. For Step 3 work with a partner, who will watch what you do and note any errors you make. They will discuss these with you when you have finished. Then swap jobs and check your partner’s skills.
Check your answers on pages 276–277.
Chapter1 Mixingandseparating Learning focus: Possible career paths in science
US AREA C O F D E B I R C PRES
Forensic science A 16-year-old girl has been killed in a hit-and-run accident. The police send the victim’s clothing to the police crime laboratory, where a forensic scientist finds a tiny chip of dark-green metallic paint on the right leg of the jeans. She subjects the paint chip to extreme heat and allows the vapours to pass into a gas chromatograph. A stream of inert carrier gas pushes the vapour through a long capillary tube which is heated in an oven. The inside of this tube is coated with a liquid solvent. The different components of the paint vapour dissolve in the solvent to different extents. The ones that dissolve most are held back on the column. The ones that dissolve least are carried through by the gas. In this way the different components of the paint are separated. The components reach the end of the tube at different times, as indicated by the peaks of the chromatogram on the computer monitor. See the diagram below and the photo on page 19.
2005 Pajeros registered within a 20 km radius of the accident. They also visit panel beaters in the area. Eventually they find a red 2005 Pajero with damage to the front. In the police garage they discover that the Pajero has been freshly painted and there is dark-green paint underneath the red. They send a sample of the dark-green paint to the forensic scientist. When she runs it through the gas chromatograph she obtains the same chromatograph as from the chip from the victim’s jeans. On the basis of this evidence the owner of the Pajero is arrested for the hit-and-run.
Questions 1 Chromatogram A is of the paint from a victim’s clothes. Chromatogram B is of the paint from a suspect’s car. Are the paints the same? Explain your answer. 3 5
1 4 2
paint chip crucible heater
Paint A
6
capillary tube carrier gas
2 Time (min)
4
2 Time (min)
4
oven
computer monitor
Paint B
detector
Different car paints produce different chromatograms. By contacting car manufacturers the scientist is able to identify the model (a 2005 Pajero) that used the paint found on the victim. The police then use this information to search for
2 How is gas chromatography similar to paper chromatography (page 20)? How is it different? 3 Would you like to be a forensic scientist? Why or why not?
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2 Science
atwork Planning page Getting started Skillbuilder page 29 Writing reports Experiment Paper bridges
2.1 What is science? page 28
Activity page 32 Experiment Which filter? Skillbuilder pages 35–36 Drawing graphs
TRB 2.2 Experimenting page 32
Assessment task 2 Types of scientists
Activity page 36 Investigate 5 Dissolving time Investigate 6 Stopping distance
2.3 Solving problems page 40
Experiment Science at work
Main ideas Chapter 2 crossword
Review
TRB Chapter 2 test
Learning focus: Carrying out investigations
Prescribed focus area Experimenting
Chapter2 Scienceatwork r you wil In this chapte
t…
l learn abou
LearningFocus ●
carrying out investigations (page 50)
Skills ● ● ● ● ●
planning and performing first-hand investigations (Activity page 32, Experiments pages 30 & 34, Investigate 5 & 6) processing information—identifying relationships (Activity page 36) presenting information (Skillbuilders pages 29 & 35–36) thinking critically—inferring and generalising (Experiments pages 30 & 34, Investigate 5) working individually and in teams (Investigate 6, Experiment page 42, Doing a project page 43)
You and your friends sit down to watch a movie on DVD. You slide the DVD into the machine and nothing happens. Work in a small group to complete the following tasks.
● Make a list of all the possible reasons why your DVD doesn’t play. ● For each reason, discuss how you could test whether it is right or wrong, and suggest how the problem could be fixed.
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2.1 What is science? Finding out why your DVD doesn’t play involves asking questions like Is the DVD player plugged into the TV?, testing the question, asking more questions if the DVD still doesn’t work and doing more tests.
Science is all about asking questions, testing, asking more questions and doing more tests. Science is a way of finding out how or why things happen. You learnt previously that an experiment is a well thought out test. The test has a series of steps involving several different skills as shown below.
Generalising Observing
Observing is when you us e your senses to fin d out as muc h as you can about an obje ct or event. O bservations can lead to tw o different ty pes of description. One is record ed in words, and is called qualitative (Q UAL-i-tateive) observa tion. Other o b servations involve takin g measurem ents. These are called qu antitative (QU ANT-i-tateive) observa tions. Both o b servations are called da ta.
u write a Generalising is where yo e in most statement that seems tru many cases after you have made may be observations. Since there tion, words exceptions to a generalisa often used. like ‘most’ and ‘many’ are ks Often a generalisation lin am ex ple, two different factors. For s that ‘the when a painter generalise the paint warmer the day the faster time to dries’, he is linking drying temperature.
Recording
rite down where you w Recording is this often record u o Y . ta a d r you le. in a data tab
Inferring Inferring is trying to explain your observations. For example, to explain why the DVD doesn’t load, you might say that there is a faulty connection between the DVD player and the TV. This inference may not be correct, but it could be tested by making further observations.
ng a ing t f maki n c o i s d s e e c io Pr the pro servat
ure ob ting is ur Predic of what a fut based on yo now. e st foreca redictions ar you already k .P at will be ions and wh t a observ
Chapter2 Scienceatwork
Investigations and experiments In Chapter 1 you did some laboratory investigations involving filtering, solubility, evaporating and distilling and paper chromatography. In this chapter you will be doing experiments where you have to design tests to answer questions or solve problems. What’s the difference between an investigation and an experiment? The terms mean much the same thing. Both involve carefully planned laboratory or field work. However, an experiment is based on solving a problem or answering a question. Experiments involve designing tests, observing and recording data, then writing full reports. The Skillbuilder below shows you how to write up a report.
Skillbuilder Writing reports A report is organised using seven headings. TITLE
AIM
MATERIALS
METHOD
A very brief description of the investigation, your name and the date. You say why you did the investigation—sometimes this is a question. A list of the equipment and chemicals you used in the investigation You say what you did in the investigation in numbered steps. Whenever possible include a large, neat diagram of the apparatus.
You record the data. Data includes qualitative observations (words) and measurements (numbers). Usually these are recorded in a data table. This makes the data easier to read. DISCUSSION You try to explain your results, and list any problems that you experienced. You might also explain how you could improve the investigation. CONCLUSION You answer the question posed in the aim. Often your conclusion will contain a generalisation—one that seems true in most cases. For example, a student investigating paper bridges concluded: The more folds the paper bridge has, the more weight it can support. RESULTS
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Experiment
PAPER BRIDGES Suppose you suspend a piece of A4 photocopy paper between two blocks. How much weight will the paper support? None, you say! Well look at the paper bridge in the photo.
Writing your report The paper has been folded many times. It is a paper bridge, and it can support a container with stones in it.
1 Write a full report of your experiment, using the headings: Title, Aim, Materials, Method, Results, Discussion and Conclusion.
The problem to be solved
2 Your discussion should contain an inference that tries to explain your observations.
If we increase the number of folds in a piece of paper, will it support more weight? Your task is to work in a small group to design an experiment that will answer this question.
3 Your conclusion should contain a generalisation that links weight and the folds in the paper.
Designing your experiment 1 Discuss what tests you will do to answer the question. 2 Make a list of the equipment you will need. 3 Discuss how you are going to record your observations. Will you take quantitative observations? 4 When you and your teacher are happy with your plan, get started.
4 You might like to take a digital photo of your set-up and include it in your report.
Extending the experiment You might like to extend your experiment by testing these predictions: 1 Two layers of folded paper will support twice the weight supported by a single piece of paper. 2 Heavier paper will support more weight than ordinary paper. 3 Dry paper is much stronger than damp paper.
Chapter2 Scienceatwork
Check! 3
You placed a young mouse in a cage with dishes containing three different foods. After observing her for 30 minutes you noticed that she had eaten nothing. What inferences could you make from this?
4
Cameron has a mouse in a cage. The mouse has an exercise wheel with a counter on it. Cameron wrote down the counter reading each morning, but the bottom of his results sheet has been torn off. a Predict what the counter reading for Day 4 should be (approximately). b Explain how you made this prediction.
1
Use the following words to complete the sentences below. A generalisation… Predicting… An experiment… a ______ is a scientific test. b ______ is a statement that is true in most cases. c ______ is saying what may happen in the future. 2 For each statement below say whether it is an observation, inference, prediction or generalisation. a It tends to rain more in winter than in summer. b She must have eaten something that doesn’t agree with her. c There should be a full moon next week. d The leaves on this plant are turning yellow. e That colourless liquid must be an acid.
challenge 1 Heidi dropped a ball from two different heights and measured how high it bounced each time. She used her data to draw a graph. 70
Bounce height (cm)
60 50 40 30 20 10 0
50
100
Drop height (cm)
a Predict how high the ball will bounce if she drops it from 75 cm.
day
counter reading
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b Predict the bounce height for a drop height of 150 cm. 2 Mick peeled a banana for lunch and left it in his bag when he went to play soccer. Later he discovered that the banana had turned brown and soft. a Pose a question based on Mick’s observations. b Suggest an inference that tries to answer this question. 3 Ask other students in your group these questions: • Willitraintomorrow? • Willitbeafullmoontonight? • Howfastcanyouswim50metresfreestyle? a Decide whether the answers they gave you are predictions (based on observations and knowledge), or just guesses. b What information would you need to turn the guesses into proper predictions?
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2.2 Experimenting In the paper bridges experiment, you tried to find out if the number of folds in the paper affected the weight the paper could support. Was your experiment a fair test? Did you consider the other factors that might have affected the result?
Controlling variables There are other factors that could have affected the results of your paper bridge experiment. Look at the photos below.
There are at least three factors that could affect the results of this experiment: 1 the number of folds in the paper 2 the length of the paper between the supports 3 the shape of the weight container. These factors that could change the results of an experiment are called variables. You should test only one variable at a time. If you want to increase the number of folds in the paper, then you must keep the other two variables the same: use the same type of container, and keep the length of the bridge the same. This is then called a fair test. The test becomes a fair test when you control the variables. You keep all the variables the same, except one.
Activity
Fig 7
One paper bridge is longer than the other. The shorter bridge can support more weight.
You can make a pendulum by suspending a steel nut on a paper clip tied by cotton to a metal clamp and stand. Suppose your group wants to find out whether the mass of a pendulum makes any difference to the time it takes to do a complete swing (from start back to start again). Use the questions below to design an experiment that will test the statement above. What are the variables in this experiment? Which variables will we purposely change? Which variables will we need to keep the same? How will we measure the swing time? Do the experiment, if you have time.
Fig 8
The containers are different shapes. The paper bridge supports the rectangular container better than the circular one.
Chapter2 Scienceatwork Testing a hypothesis A hypothesis (high-POTH-e-sis) is a generalisation which can be tested. It explains a set of observations or gives a possible answer to a question. Note that the plural of hypothesis is hypotheses (highPOTH-e-sees). An example of a hypothesis is given on this page.
3
Based on his results he made this generalisation. I can generalise that the things made of metal are magnetic. That’s my hypothesis.
Rosco recorded his observations of the effect of a magnet on various materials.
1
Material tested
Magnetic ( ) Non-magnetic ( )
nail
✓
piece of glass
✗
wooden pencil
✗
knife paperclip
2
✓ ✓
4
From this generalisation he was able to make a prediction that could be tested.
If my hypothesis is correct, I predict that a pin, a one dollar coin and a piece of aluminium foil will be attracted to a magnet.
He looked through his results.
The nail, knife and paperclip are attracted to the magnet, and they are all made of metal.
5
Rosco experimented further. Because his prediction turned out to be wrong, he had to modify (change) his hypothesis. Only the pin is attracted to the magnet. I’ll have to modify my hypothesis. Things made of iron and steel are magnetic.
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Experiment
WHICH FILTER? In Investigate 2 on page 12 you learnt how to filter some muddy water. In this experiment you will design tests to see whether folding a filter paper in different ways has any effect on the time it takes to filter some muddy water.
5 Which variables will you control? Which variable are you going to change? 6 Discuss how you are going to record your observations. 7 When you and your teacher are happy with your plan, get started.
The problem to be solved To compare the time it takes to filter muddy water using filter papers folded in different ways. Refer to page 13 to recall how to make a folded filter paper. Follow the instructions below for making a fluted (folded many times) filter paper.
Writing your report 1 Write a full report of your experiment, using the headings: Title, Aim, Materials, Method, Results, Discussion and Conclusion. 2 Your discussion should contain an inference that tries to explain your observations.
Designing the experiment 1 Work in a small group and discuss the tests you will do.
3 Do your results support your hypothesis? If not, write a better hypothesis.
2 Write a hypothesis for the experiment. 3 Make a list of the equipment you will need.
Extending the experiment
4 Make a list of the safety precautions you will take.
You might like to test this prediction: A sixteen-fold fluted filter paper filters twice as fast as an eightfolded one.
Making a fluted filter paper
Fold here. Unfold the filter paper.
Fold into quarters ...
... then fold three more times.
Adjust the folds so that the filter paper forms an eight-pointed star.
Chapter2 Scienceatwork Independent and dependent variables
Graphing A line graph is a way of displaying data so that it can be interpreted easily. It may be a straight line or a curved line. A line graph shows you the relationship between two variables. Look at this data from the side of a milk carton. The data was obtained by storing milk at various temperatures and recording the average time before it ‘went off’.
The temperature was changed on purpose. It is called the independent variable, because you can select any value for it. The number of days the milk lasted is called the dependent variable, because it depends on the temperature. All other variables, eg brand of milk and type of container, were controlled (kept the same).
Skillbuilder Drawing graphs 1 On a piece of graph paper draw the horizontal axis and the vertical axis. 2 On a line graph, the dependent variable is plotted on the vertical axis. The independent variable is plotted on the horizontal axis. Label the horizontal axis ‘Temperature (°C)’. Label the vertical axis ‘Time (days)’.
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x
title for graph
vertical axis 8
How long milk lasts at various temperatures
7
dependent variable
Time (days)
6 5
x
smooth pencil line through points
4 3 2
To see a step-by-step drawing of the line graph on this page, open the Drawing a line graph animation on the CD.
x
x
1
horizontal axis 2
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independent variable
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Temperature (°C)
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Activity 3 Select suitable scales for the two axes so that the graph fills most of the page. 4 Look at the first pair of numbers in the data table. They are: temperature 4°C time 9 days In pencil, mark the point where the grid lines meet with a small neat cross, as shown on the previous page. Then do the same with the other pairs of numbers. 5 By looking at the four crosses you have drawn, you can see that this graph is a curved line. Use a pencil to draw a smooth curve through the crosses, as shown. (This may take some practice.) Don’t join the crosses with straight lines. 6 Finally, write a title for the graph at the top. This tells others what the graph is about.
Science in action Elaine Perriman is a food technologist. She works in the laboratory of a country milk factory that makes a range of full fat, reduced fat and skim milks, cream and flavoured milks. She routinely samples the pasteurised milk from the factory and tests for the presence of disease-causing bacteria. In this way she can tell that the pasteurisation process is working correctly. She also samples the raw milk that comes in from dairy farms to make sure there are no antibiotics in the milk. When farmers treat sick cows with antibiotics, the antibiotics pass into the milk. Some people are allergic to certain antibiotics, so it is Elaine’s responsibility to make sure that the raw milk does not contain antibiotics. Milk is a very important food in most people’s lives. Most states have milk factories, but 61% of all the milk produced in Australia comes from Victoria.
Use the graph on the previous page to answer these questions. 1 How long does milk last when stored at 8°C? 2 A carton of milk lasted 1½ days. At what temperature was it probably stored? 3 Describe in your own words what the shape of the graph tells you about the relationship (link) between the temperature of the milk and how long it lasts. 4 Complete this hypothesis. The lower the temperature…
Chapter2 Scienceatwork
Investigate
5 DISSOLVING TIME Aim To write and test a hypothesis about how temperature affects the time it takes an antacid tablet to dissolve in water.
2 Drop in an antacid tablet. Do not stir. Time how long it takes for the tablet to dissolve: that is, how long before it disappears completely. Record this time in your data table.
Materials • • • • • • •
beaker,eg250mL thermometer stopwatchorwatchwithasecondhand 4antacidtablets,egAlka-Seltzer hotwater(fromhottap) icewater Note: Clear aspirin sheetofgraphpaper
tablets can be used instead of Alka-Seltzer.
Planning and Safety Check 1 Write down your hypothesis about how you think temperature affects dissolving time. (Base your hypothesis on your previous experience of making hot and cold drinks or doing the washing up.) 2 Prepare a data table like the one below in which to record your results. Temperature (°C)
Time to dissolve (seconds)
Ice water Room temperature Warm water
3 Repeat Steps 1 and 2 for the other temperatures. Remember to control the variables you listed in the Planning and Safety Check. Record your results. 4 Plot a graph with water temperature on the horizontalaxisanddissolvingtimeonthe vertical axis. Draw a smooth curve through the four crosses. This line shows how the dissolving time depends on the temperature of the water. 5 Write a report of the investigation using the usual headings.
Hot water
Discussion Write down all the variables that could affect the dissolving time. Which ones will you need to keep the same?
Method 1 Fill the beaker with water from the tap. Use the thermometer to measure the temperature of the water. Record this temperature in your data table.
1 Which is the independent variable, and which is the dependent variable in this experiment? 2 What does your graph tell you about the relationship between temperature and dissolving time? 3 Do your results support (agree with) your hypothesis from the Planning and Safety Check? If not, write a better hypothesis.
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Check! 6 1
Rebecca, Alistair and Ian compared the hardness of three different types of wood. They did this by measuring how far a dart went into the wood, as shown below. Was this a fair test? If not, explain how the test could be improved.
Paul’s parents measured his height every year, starting when he was two. They recorded these measurements on a graph. a How old was Paul when he was 100 cm tall? b Predict how tall he will be when he is eight. c Can you predict how tall he will be when he is 20? Explain.
Rebecca
120 Alistair
Height (cm)
38
Ian
110 100
x x
90 x
x
80 2
2
What are the variables that affect how long it takes you to get to school?
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You have three different powders. You want to find out which one dissolves most rapidly in water. a Which variables will you need to control in your test? b Which variable will you purposely change? c What will you measure?
4
Which of the following are inferences and which are hypotheses? a This piece of iron must be a magnet. b All things fall towards the Earth because of gravity. c Plants grow more in summer than in winter. d I think the wet road caused this accident. Justify your answers (explain why they are inferences or hypotheses).
5
Dan used a decibel meter to measure the noise given off by a car travelling at different speeds. a Design a data table for Dan’s results. b Which measurement is the independent variable? And which is the dependent variable?
4
Age
6
8
7
Rebecca and Megan want to test whose bike has better brakes. Design a fair test for them. Remember, when designing fair tests you: • changesomething • measuresomething • keepeverythingelsethesame.
8
Ace planted 2 bean seeds in each of 4 pots of soil. Every three days he added water to the pots as shown below. Pot 1 no water Pot 2 10 mL of water Pot 3 20 mL of water Pot 4 40 mL of water a Write a hypothesis for Ace’s experiment. b Why did he plant 2 bean seeds in each pot and not just one?
Chapter2 Scienceatwork
challenge
4 Use the graph below to answer the following questions. a What is the graph about? b Which is the independent variable? c Which is the dependent variable? d By what amount do the numbers on the vertical axis increase? e How much mass does each small grid line on the vertical axis represent? f By what amount do the numbers on the horizontalaxisincrease? g What was the mass of the baby at birth? h When did the baby reach a mass of 4000 grams? i What was the baby’s mass at the end of the seventh week? j During which week did the baby’s mass decrease?
1 The following questions refer to Investigate 5 Dissolving time on page 37. a Suppose you wrote Antacid tablets dissolve faster in hot water for your hypothesis. What would you need to do to test this hypothesis? b Use the graph you drew to predict how long a tablet would take to dissolve in water at 35°C. c What temperature would the water need to be for a tablet to dissolve in exactly one minute? 2 A group of students was investigating the growth of seedlings. They measured the average height of the seedlings every day. a Draw a graph of their data. b Is the graph a straight line or a curve?
0 1 2 3 4 5 6
Height (cm) 0 1.0 2.1 2.6 3.8 5.0 5.8
0 2 4 6 8 10
x x
5000
x
4500
3 Mark and Dylan used a datalogger and temperature probe to find out how quickly the temperature of ice-cold water changed as it was heated. They obtained the data list below on their calculator screen. a Draw a graph to display their results. b Use the graph to find out approximately how long it took the melted ice to reach a temperature of 70°C. c What was the approximate temperature of the heated ice after three minutes? Time (min)
Baby‘s mass
Temperature (ºC) 0 5 30 75 93 98
Mass (grams)
Time (days)
x
x
x 4000
x 3500
x
x x
x
3000
2500 0
2
4
6
8
10
Time (weeks)
Use the ideas from Investigate 5 on page 37 to design an experiment to test the effect of stirring on dissolving time.
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2.3 Solving problems Josh is playing a computer game in which he has to find the buried treasure. He is using his science skills to solve this problem. Read carefully through the six steps on this page. Note that at Step 6 you should be prepared to change your hypothesis if necessary. You cannot ignore some data or change it to fit in with what you think should happen. Also, not all problems are easy to solve. And you may have to do many experiments. In Investigate 6 you can try to solve a problem yourself.
STEP 1: THE PROBLEM How do I find the hidden treasure?
STEP 2: HYPOTHESIS This could be the answer to the problem. If it is, what predictions can I make?
Try other tests I can't tell whether the results agree with my hypothesis.
STEP 3: TEST How can I test my hypothesis? I must be careful to control variables.
STEP 4: RESULTS Record my observations.
STEP 5: CHECK HYPOTHESIS Interpret the data.
STEP 6: THINK AGAIN
My results agree with my hypothesis. BINGO!! What else can I predict?
Back to the beginning! My results don't agree with my hypothesis. I need to modify it.
Chapter2 Scienceatwork
Investigate
6 STOPPING DISTANCE Aim To investigate the variables that affect the distance it takes a moving vehicle to stop (stopping distance).
Method Step 1: The problem Form a group with other students, and make a list of all the variables you think may affect a moving vehicle’s stopping distance.
Step 2: Hypothesis Decide which one of the variables from Step 1 you are going to test. Write a hypothesis that says how this variable will affect the stopping distance. (Make sure your hypothesis is testable.) Using your hypothesis, write a prediction you can test. (See Step 4 on page 33 for an example.)
Step 3: Test (experiment) In your group, decide what equipment you will need to test your prediction. For the vehicle you could use a toy car or truck. Or you could build one out of Lego or a similar building kit. To get the vehicle moving you could run it down a ramp. Write a brief plan for your experiment. Remember to control all variables except the one you are purposely changing. Show your plan to your teacher.
Step 4: Results Do your experiment. You may need to do some trial runs before making any measurements. Record all your results in a data table. Which is the independent variable and which is the dependent variable? You may want to display your results on a graph. (This would be useful for showing to the rest of the class.)
rement
Repeating the measu
ment of the stopping If you repeat a measure bly get a slightly distance, you will proba because there are some different value. This is control, eg whether the variables you cannot not. For this reason it vehicle runs straight or ch measurement three is a good idea to do ea average. times and calculate the nts you make, the The more measureme ge will be, but three more reliable the avera ually enough. measurements are us
Step 5: Check hypothesis Do your results support your hypothesis? That is, was your prediction in Step 2 correct? Write a conclusion, giving an answer to the question you investigated. Which variables did other groups investigate? What did they find? How do their results compare with yours?
Step 6: Think again How accurate do you think your results are? Can you think of ways to improve your experiment? Write a report of your experiment using the usual headings.
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Experiment
SCIENCE AT WORK It is fun to solve everyday problems by experimenting. Choose one or more of the problems below or think of your own problem.
In designing your experiment, use the six steps in investigating you used in Investigate 6, starting with a hypothesis you can test.
PROBLEM A
PROBLEM B
What sorts of liquids flow through the funnel most easily? Liquids you could try are water, glycerine, cooking oil, sugary water …
thistle funnel
Does the shape of a boat’s hull affect its speed?
stopwatch
pulley
cup for weights boat shapes plastic tubing dropper
blocked section of drain
PROBLEM C
PROBLEM D
Which colour cloth is the coolest in summer? Which is the warmest in winter? no cloth (control)
black cloth
white cloth
Florists say that a vase of flowers will last longer if the stems of the flowers are crushed and if you add a little sugar to the water. Do these variables really affect the life of the flowers?
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t c je o r p h c r a e s e r a g Doin Any of the problems on the previous page would make a good student research project. Here are the steps you need to follow in doing a project.
1 Choose a topic Pick something you are interested in. There are project ideas in some of the Challenges and Try this activities in this book, and many of the experiments can be extended into projects. Check the websites on this page to see what other students have done. Make sure your ideas are feasible. Are there experiments you can do on this topic? Can you get the equipment and materials you need? Can you finish it in the time available? Talk with other people about your ideas.
2 Plan your project Write a brief outline of what you plan to do and discuss it with your teacher before you start.
3 Do it
Use the skills you have learnt in this chapter to carry out your project. Put your notes straight into a special project logbook so that they are not lost. It is important to record your failures as well as your successes. After each experiment ask yourself What would happen if … ? then try it. Repeat your experiments to make sure you always get the same results, and be prepared to change your ideas in the light of your results, as you may not always get the answers you expect.
4 Prepare a report This may be a written summary, a poster display, a short talk using overhead transparencies or a PowerPoint presentation. The websites below give information if you want to enter your project in a science contest.
< WEB watch > Go to www.scienceworld.net.au and follow the links to the websites below.
BHP Billiton Science Awards The site includes what you can win, entry requirements and details of last year’s winners. Science Talent Search (Victoria) Young Scientist Awards (NSW) CREST CREST stands for Creativity in Science and Technology. You can look up current and past projects and CREST schools in your state. Science Fair Links This site has links to many other sites that have ideas for projects. Sci-Journal On this site you can browse through research projects done by other students. You can also publish your own.
Fig 28
Michael Morris won a BHP Billiton Science Award when he was in Year 8 for investigating ways of controlling house dust mites with tea tree oil. He has since gone on to win other awards for his science projects.
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ScienceWorld8forNSW Science in action Scientists are ordinary people who solve problems using the skills you have learnt in this chapter. Over the years scientists have made many important discoveries which affect our daily lives. Five of these are described on the following pages. Select at least one of these and answer the questions about it.
Post-it self-stick notes Some discoveries in science are made by accident, or serendipity. Art Fry was in church one Sunday in 1974. He sang in the choir but he had a problem. The bits of paper he had put in his book to mark the hymns kept falling out. Suddenly he had an inspiration. Several years ago the 3M company where he worked had made a glue that was thrown out because it wasn’t sticky enough. Perhaps it would be sticky enough to make sticky bookmarks for his choir book. Fry went back to his laboratory at 3M and tried the old glue. It worked, but he spent a year and a half modifying and testing it. When he took it to the advertising department they weren’t very keen on his idea for sticky note pads. However, they put them on the market, and soon people around the world were buying Post-it self-stick notes.
Questions 1 Use a dictionary to find the meaning of the word serendipity. 2 Did Art Fry work scientifically to make self-stick notes? Explain. 3 Suggest uses for Post-it self-stick notes. 4 For information on Art Fry go to www.scienceworld.net.au and follow the links to Inventions at play.
Dung beetles Cattle were introduced to Australia over 200 years ago. We now have a problem of too much cattle dung. It covers grazing land and flies breed in it. George Bornemissza, who came to Australia from Hungary, started studying the problem in 1951. He found that Australia has dung beetles that can break down the dung of native animals such as kangaroos. However, very few of these beetles can break down cattle dung. He therefore suggested bringing dung beetles from other parts of the world to Australia. The first of these beetles were released in 1967, and today dung beetles are well established in some areas. However, they have not spread far enough, and flies are still a problem throughout Australia. Scientists from CSIRO, Australia’s largest scientific research organisation, are therefore still working on the problem.
Questions 1 Why is cattle dung such a problem? 2 Why was it necessary to introduce dung beetles to Australia when there were some here already? 3 How can the spread of dung beetles throughout Australia reduce the number of flies? 4 Suggest a plan to spread dung beetles more evenly across Australia. 5 What precautions must be taken when a foreign animal or plant is planned to be introduced to this country?
Chapter2 Scienceatwork
Twin lambs
Medicines from frogs
Dr Helen Newton Turner was experimenting with the breeding of sheep. In 1951 someone sent her some ewes that produced twins much more often than usual. She knew that twin lambs were rare, and wondered whether she could use the ewes to breed whole flocks of sheep that produce twins more often. She therefore set up a series of experiments with ewes that had produced twins and rams that had been twins. At the same time she did similar experiments with single-bearing ewes mated with single-born rams. Her results showed that ‘twinned’ parents produced three times the number of sets of twin lambs as the ‘single’ parents. She then worked with a farmer near Cooma (NSW) and by 1972 his merino flock was producing 210 lambs each year for every 100 ewes! The sheep industry has benefited enormously from Dr Turner’s work.
Dr Michael Tyler from the University of Adelaide has been studying frogs for 30 years. The secretions produced by the skin of frogs contain many different chemicals. Some of these are toxic, but others have been found to be useful as medicines. For example, scientists have recently isolated a pain-killer 200 times more powerful than morphine. Dr Tyler wanted to find a way of extracting the secretions from the frogs without harming them. One day he was having acupuncture for a headache. The acupuncturist inserted needles in his skin and passed a small electric current through him, causing his skin muscles to twitch slightly. This caused him to wonder whether frogs would release their secretions when their skin muscles were twitched using a small electric current. Back in his laboratory Dr Tyler found that his idea worked, without harming the frog, and without using needles. From a single ‘milking’ he could obtain up to 100 milligrams of secretions. He found that these secretions contain as many as 30 different chemicals. The secretions kill several different bacteria, fungi and viruses, and his recent work has been to find out which secretions kill which organisms.
Questions 1 Why do sheep farmers like twin lambs? 2 What is meant by ‘twinned’ parents and ‘single’ parents for sheep? 3 How did Dr Turner control the variables in her sheep breeding experiments?
Questions 1 Dr Tyler discovered a new laboratory technique. What is it? 2 He repeated his tests several times. Why do you think he did this? 3 Suggest how he could find out which of the 30 chemicals in the secretions kills a particular virus. 4 Suppose he identifies the virus-killing chemical. What do you think he should do next?
Fig 34
Dr Tyler with one of his frogs
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Rabbit plague Thomas Austin liked to go shooting at the weekends. So in 1859 he imported 24 rabbits from England to his property near Geelong in Victoria. A female rabbit can produce 40–50 young in one year, and with few natural enemies there was soon a plague of rabbits. In one year Tom Austin shot over 14 000, and within 20 years or so the rabbits had spread to almost all parts of Australia. Fences didn’t seem to keep them out. They ate every blade of grass and stripped the bushes they could reach, turning once green areas into deserts. Many of Australia’s wallabies and native rodents became extinct or endangered. In 1919 a Brazilian scientist said he knew about a virus called myxoma which infected rabbits and gave them a disease called myxomatosis (MIX-a-mat-toe-sis). However the Australian government ignored his advice because people were making lots of money selling rabbit meat and using the fur to make hats. By the 1940s the rabbit plague was out of control and Jean MacNamara, an Australian expert on viruses, eventually convinced CSIRO to try the myxoma virus. At first CSIRO scientists couldn’t get the virus to spread, but they found that it spread more
quickly in wet weather, because the disease is carried from one rabbit to another by mosquitoes, which breed when it is wet. Myxomatosis killed up to 80% of the rabbits in most of Australia and as a result beef and wool production increased. However, as the years passed the virus was less effective. So in 1991 the CSIRO found another weapon against the rabbits—the calicivirus (cal-LEE-sea-virus) which doesn’t need mosquitoes to spread it. It was released in 1996 and one year later about 100 million of Australia’s 300 million rabbits had died. For the first time in living memory there was lush vegetation across the Nullarbor Plain and in the Simpson Desert.
Questions 1 Why was the rabbit plague such a disaster for sheep and cattle farmers, and for native plants and animals? 2 The rabbit plague resulted in severe soil erosion, with soil washed away during heavy rain. Why did this happen? 3 Suggest why the Australian government was reluctant to introduce the myxoma virus into Australia.
Check! 1
2
d
When you are doing an experiment, what is the usual order for the following?
e
check hypothesis hypothesis predict
f
results test think again
Which of the following are true, and which are false? a An experiment is a test containing a series of steps used to solve problems. b Hypotheses are always correct. c Scientists don’t know the answers to some questions.
3
a
b c
In an experiment all variables must be kept the same. You should ignore data that does not agree with your hypothesis. A good hypothesis allows you to make predictions. When you write a report of an experiment, what should the section headed ‘Aim’ tell the reader? What should the conclusion of a report tell you? Under which heading would you describe how you carried out the experiment?
Chapter2 Scienceatwork
4
Sometimes you have to modify a hypothesis. When would you need to do this?
5
While cooking on the barbecue Tammy was annoyed by all the insects that were attracted to the light. Then she remembered reading that insects are less attracted to yellow light. Use the steps on page 40 to design an experiment to test Tammy’s idea. Discuss your design with others.
6
An oil company claims you get more kilometres per litre from their petrol. They say this is because of an additive called Z. How could you test this claim?
7
A group of students collected the equipment shown below. They wrapped can A in four layers of aluminium foil each 0.25 mm thick. They wrapped can B (identical to can A) in a single layer of foil 1 mm thick. They filled both cans with hot water and recorded the temperature of each can every two minutes for 10 minutes. (The data table is shown below.) a b c
What hypothesis were the students testing? Look at the students’ data and decide whether it supports their hypothesis. Write a conclusion for the experiment.
Times (minutes)
Can A (°C)
Can B (°C)
0 2 4 6 8 10
90 87 85 84 84 83
90 87 84 82 80 78
< WEB watch > For the websites listed below, go to www.scienceworld.net.au and follow the links. 1 What does CSIRO stand for? If there is a branch of CSIRO in your city or town, see if you can find out what scientists do there. Your teacher may be able to arrange a visit or a scientist may visit your school to talk with you. Visit the CSIRO website. 2 Join a science club such as CSIRO’s Double Helix Science Club. Visit their website. Perhaps your teacher could help you set up one at school. 3 During the next few weeks check newspapers and magazines. Collect articles about new discoveries in science and technology. You can also check out the latest science news at these websites: Science Daily New Scientist Nova CNN 4 Use a library to find out about the life and work of one particular scientist. Once you have collected your information, prepare a three minute talk to the class about your scientist. You may like to use the plan below. Name of scientist: Dates born (and died): Country of birth: Details of work: Any other interesting information: The Bright Sparcs site has information on more than three thousand Australian scientists.
Try doing the Chapter 2 crossword on the CD.
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Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
controlling
1 ______ is a way of finding answers to questions by doing
generalising
experiments.
experiments
graph
2 Solving ______ by doing experiments involves using skills such as observing, inferring, predicting and ______.
hypothesis problems
3 A ______ is something which can change the results of an experiment.
relationship same
4 In an experiment you purposely change one variable and keep all the rest the ______. This process is called ______ variables.
science variable
5 A ______ is a generalisation which explains a set of observations or gives a possible answer to a question.
6 Hypotheses can be tested by doing ______. If necessary they can be modified to explain further observations.
7 A ______ is a way of displaying data. It can also be used to show the ______
REVIEW
between two variables.
1 What name is given to a generalisation which a scientist can test? A experiment B hypothesis C inference D observation 2 Lim is checking the burning of a candle. He finds that after 2 hours, one-quarter of the candle has burnt. Predict how long it will take the whole candle to burn. A 1 hour C 4 hours B 2 hours D 8 hours 3 Sally and Bonita both bought the same kind of rubber ball. Sally said: My ball will bounce better than yours. Bonita answered: I’d like to see you prove that. What should they do to find out which ball bounces better? A Drop both balls from the same height and see which ball bounces higher. B Hit the balls against a wall and see how far each bounces off the wall.
C Throw the balls against the floor and see how high they bounce. D See which ball can be squeezed the most. 4 Tamika tested a number of substances to see whether or not they conduct electricity (allow an electric current to pass through them). She also noted whether the substances were metals or non-metals. Her results are shown below. Substance
Metal or non–metal?
sulfur zinc copper iodine lead phosphorus steel
non-metal metal metal non-metal metal non-metal metal
Does it conduct electricity?
✗ ✓ ✓ ✗ ✓ ✗ ✓
a Use Tamika’s results to write down two specific observations about steel.
c In which range was the UVB reading at 10 am? d How could you explain the dip in the graph around 12 noon?
Tamika tested two more substances: Substance
Metal or non–metal?
carbon tin
non-metal metal
Does it conduct electricity?
✓ ✓
c Do these results support your hypothesis? If not, modify it. 5 The amount of salt that will dissolve in 100 mL of water is called its solubility. This solubility was measured at different temperatures and the results graphed.
extreme
Intensity of UVB
b Write a hypothesis about metals and non-metals and electricity.
very high high moderate 8
9
10
11
12
1
2
3
4
Time of day
7 You see this advertisement on TV. 600 Solubility 400 (g/100 mL) 200 0
SUDSO 20 40 60 Temperature (°C)
80
Which of the following statements best describes this graph? A As the temperature changes the solubility stays the same. B As the temperature increases the solubility decreases. C As the temperature increases the solubility increases slowly. D As the temperature increases so does the solubility, slowly at first, then more quickly.
6 The graph above right is from a TV news weather report. It shows the amount of UVB radiation received on a particular day. a At what time did the UVB radiation reach its peak? b During what times of the day was the UVB reading in the very high range?
washes brighter in hot or cold water
You decide to do an experiment to see if Sudso is in fact better than other washing powders. a Write a brief plan for your experiment. b Which variables will you need to control? c Which variable will you purposely change? d Which variable will you measure?
Check your answers on page 277.
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REVIEW
Chapter2 Scienceatwork
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ScienceWorld8forNSW Learning focus: Carrying out investigations
US AREA C O F D E B I R C PRES
Experimenting Food poisoning
Rice flow
The Browns were on holidays when Mr Brown and the two children, Ryan and Lia, became ill. Mrs Brown took them to the hospital where they saw Dr Singh. Mr Brown, who had had a recurring stomach ulcer, complained of pains in the stomach. Ryan had been sick in the car and was badly sunburnt because he hadn’t put any sunscreen on that morning. Lia said she was dizzy and had a headache. Mrs Brown was worried because Lia had been stung by a bee earlier in the day. Dr Singh listened to the Browns’ problems and made notes. He also asked a lot of questions, including what they had eaten that day. Mrs Brown didn’t think that had anything to do with the fact that all three of them were sick, but she told the doctor they had fish at a café on the beach. Mrs Brown didn’t have any—just a salad. Dr Singh thought their symptoms were like those of several other patients he had seen. He suspected food poisoning from the fish they had eaten for lunch. He ordered several tests on the Browns and on samples of fish from the cafe. When he got the tests back it was fairly obvious that they did have food poisoning. Copy and complete the table below to show how Dr Singh used science skills to solve the problem.
Lachlan saw his little sister pouring rice through a funnel. He wondered whether the size of the hole in the funnel makes any difference to how fast the rice flows out. So he designed an experiment with a paper cone, as shown below. He used scissors to cut a bit off the bottom of the cone to make different-sized holes. For each cone he used the same amount of rice, and measured the time for it to flow through. Here are his results.
Science skills 1 Identify the problem 2 Make observations 3 Make a hypothesis 4 Test the hypothesis 5 Make a conclusion
What Dr Singh did
Add rice. paper cone
0 mm
10
20
30
Measure hole diameter. rice flowing through
Diameter of hole (mm) 4 6 8 10 12
Time taken (s) Trial 1 Trial 2 Trial 3 38 28 18 11 5
41 24 16 9 4
39 26 16 11 5
1 Which variable did Lachlan purposely change? 2 Which variable did he measure? 3 Which was the independent variable and which was the dependent variable? 4 List two variables that Lachlan controlled. 5 Use graph paper to draw a line graph of Lachlan’s results. 6 Write a generalisation that Lachlan could use as a conclusion for his experiment.
3 Whatare
thingsmadeof ? Planning page Getting started Activities page 54 Investigate 7 Measuring density
3.1 Properties of matter page 53
Activity page 58 Activity page 64 Activity page 65
3.2 Solid–liquid–gas page 61
Animation Particle theory
Investigate 8 Melting and boiling
TRB Assessment task 3 A particle model
Activities page 70 Activities page 71
3.3 Using the particle theory page 70
Activity page 73
Main ideas Chapter 3 crossword
Review Learning focus: An idea can gain acceptance in the scientific community as either theory or law
Chapter 3 test
Prescribed focus area From idea to theory
TRB
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l learn abou
r you wil In this chapte
LearningFocus ●
an idea can gain acceptance in the scientific community as either theory or law (page 76)
KnowledgeandUnderstanding ● ● ●
the particle theory of matter (Sections 3.2 and 3.3) properties of solids, liquids and gases change of state (Section 3.2)
Skills ● ● ● ●
planning and performing first-hand investigations (Investigate 7 and 8) processing information—using mathematics (Investigate 7) and identifying trends in data (Investigate 8) presenting information—tables and graphs (Investigate 8) thinking critically—inferring, predicting and generalising (Investigate 8 and Activities pages 71 and 73)
Use the three photos on this and the previous page to help you to answer these questions. ● Which of the things in the photos are solids? Which are liquids? Which are gases? ● Can you change the shape of solids, liquids and gases?
● Can you compress a solid, that is, squeeze it into a smaller volume? Can you do this for liquids and gases? ● What do solids, liquids and gases have in common?
Chapter3 Whatarethingsmadeof?
3.1 Properties of matter What is matter? Everything around you is made up of matter—the desk, your shirt, the water in a swimming pool, the hair on your head, even the air you breathe. Most matter can be classified into one of three main groups: solids, liquids and gases. These are usually called the three states of matter. Solids, liquids and gases have two important properties—they all have mass and they all take up space. To find the mass you use a balance. To find the amount of space occupied by something you measure its volume. So all matter has mass and occupies space.
Gases The air around us is a gas. In fact, it is a mixture of gases, mainly nitrogen and oxygen. Other common gases are helium and carbon dioxide. All these gases have mass and occupy space. Gases do not have a fixed shape or volume. A gas fills its container, no matter what the shape or size of the container. For example, helium gas fills a metal gas cylinder. The gas can be let out through the tap to fill balloons of various shapes and sizes. If the balloon bursts, the gas will escape and spread out into the air. Gases can also be compressed (squeezed into a smaller volume like the helium in the cylinder). You cannot do this with liquids and solids.
Solids Solids include such things as steel girders, this book, and most of the objects you can see. They all have mass and occupy space. The shape of most solids cannot easily be changed, and nor can their volume. Powders are also solids but their shape can be changed.
Liquids Water, milk and oil are all examples of matter in liquid form, and they all have mass. The volume of a quantity of liquid does not change, but its shape can. For example, pour some milk from a carton into a glass. The volume of the milk doesn’t change, but its shape does. And if the milk is spilt, it has another shape (Fig 4). Fig 5
Fig 4
The volume of a liquid does not change, but its shape may.
Gases do not have a fixed shape or volume.
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Activities A Crumple a tissue, and fit it tightly into the bottom of a glass. Push the glass, mouth down, into a large container of water until most of the glass is under water. What do you observe? Pull the glass out of the water and check whether the tissue is wet. Write an inference to explain your observations.
tissue
glass water
B Use a balloon and an electronic balance to test whether air has mass.
C Place your finger over the end of a syringe containing air. Try to push the plunger in. Can air be compressed? Push in.
Draw some water into the syringe. Can water be compressed?
D To summarise what you know about solids, liquids and gases, copy the following table. Complete it by putting a 4 or a 8 in each box.
State of matter
Have mass
solids
✓
liquids
✓
gases
✓
Occupy space
Properties of matter Fixed Fixed shape volume
Can be compressed
Chapter3 Whatarethingsmadeof? Density
I don’t care if they DO weigh the same. I’m not swapping!
Similarly, iron is denser than wood. Suppose you have a 1 cm cube of iron and a 1 cm cube of wood. Both cubes take up the same amount of space, so they both have the same volume (1 cubic centimetre). However, their masses are very different. The iron cube has more mass packed into one cubic centimetre. The density of iron is therefore greater than the density of wood. Density is how much mass is packed into a measured volume. It is usually measured in grams per cubic centimetre (g/cm3). The table at the top of the page shows the densities of some common substances. Notice that the density of water is 1 g/cm3, and that gases are much less dense than solids and liquids. Anything will float in water if its density is equal to or less than the density of water, that is 1 g/cm3. For example, a piece of pine wood (density 0.4 g/cm3) floats in water, but a piece of granite (density 2.7 g/cm3) sinks. Fruit and vegetables sometimes float and sometimes sink. For those that float, the lower their density the
0.00018 0.0013 0.002 0.1 0.2 0.4 0.7 0.9 0.9
water
1.0
sea water aluminium granite iron nickel lead gold osmium
FLOAT IN WATER
helium gas air carbon dioxide gas polystyrene foam cork pine wood petrol polythene plastic ice
1.03 2.7 2.7 7.8 8.9 11.3 19.3 22.5
SINK IN WATER
An important property of matter is its density. Which is heavier, a kilogram of feathers or a kilogram of gold? The answer is neither—they both have the same mass. The difference is that a one kilogram bar of gold would be about the size of a Mars bar, while one kilogram of feathers would fill a very large pillow. The mass of the gold is packed into a much smaller volume than the feathers. A small volume of gold has a large mass. We say that gold is much more dense than feathers.
Table of densities (g/cm3)
more they stick out above the water. You can try this at home with a bowl of water. Humans, like most animals, float in water, but only just. This is because we are mostly water. However, we have a layer of fat under our skin, and this has a density less than water. There are also air spaces, such as lungs, inside our bodies. Sharks are unusual in that they are denser than water. If they don’t keep swimming they sink to the bottom.
Why don’t we stop here for a bit and give these surfers a scare?
Fig 9
It’s tempting Shazza, but we have to keep swimming.
Anything will float in water if its density is equal to or less than the density of water.
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ScienceWorld8forNSW Measuring density To find the density of something you must first measure its mass and volume. You then divide the mass by the volume to find the density. density (g/cm3)
=
mass (g) volume (cm3)
Measuring the volume of a regular solid such as a cube is easy, but how would you measure the volume of an irregularly shaped object such as your body? The secret is to drop the object into water, and measure the volume of water it displaces (pushes out). This method was discovered by Archimedes in Greece about 250 bc. In Investigate 7 you can use this method to find the density of a small object.
Fig 10
One way to measure your volume
Investigate
7 MEASURING DENSITY Aim To measure the density of two different objects.
Recordthemassesinthedatatable.
Materials • • • •
Checkwithyourteacherifyouhaveforgotten how to do this.
measuringcylinder,100mL balance pieceofwire 2smallobjects—onethatloats(egwooden cube)andonethatsinks(egmarble)
Planning and Safety Check
2 Abouthalfillthemeasuringcylinderwithwater. Itisbestifyouillittoasetmark,say30mL. Make sure the bottomofthemeniscus(the curvedwatersurface)isexactlyonthemark. Recordthisinitial volume(V1) in the data table.
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40
Readthesixstepscarefullyanddrawup adatatableliketheonebelow.
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20
10
Method 1 Usingthebalance,indthemassofeachobject.
Object
Mass (g)
Initial volume of Final volume of water, V2 (mL) water, V1 (mL)
Volume of object V2 – V1 (cm3)
Density (g/cm3)
Chapter3 Whatarethingsmadeof?
3 Holdingthecylinderatanangle,carefullyslide intheirstobject.Ifitloatsyouwillhaveto holditunderthewaterwithapieceofwire,as shown.
5 Calculatethevolumeofeachobjectby subtractingtheinitialvolumeofwater(V1) from theinalvolume(V2). Recordyourresultsinthedatatable. (Note:1millilitre=1cubiccentimetre.)
Recordthewaterlevelinthecylinderwith theobjectcompletelyunderwater(V2).
volume of object
= V2 – V1
6 Calculatethedensityofeachobjectusingthe formula:
density thin wire
=
mass of object (g) volume of object (cm3)
Giveyouranswertothenearest0.1gramsper cubic centimetre.
Discussion
4 Taketheobjectoutofthecylinder,andrepeat Steps2and3fortheotherobject. Recordthewaterlevelforthesecond object.
Using materials All the materials around us are taken from or made from the Earth’s natural resources. For example, we use cotton, wood and rubber from plants and wool, leather and silk from animals. We breathe the air and extract various gases from it, eg oxygen, nitrogen and argon. We use the rocks of the Earth and extract metals such as iron, copper and gold, and other useful materials like coal, oil and limestone. We eat seafood from the oceans and extract salt from seawater. Some of these materials we use in their natural state. For example, a gold nugget can be made into jewellery and wool can be woven into clothing. Often we process these materials to improve or alter their properties. For example,
1 Compareyourresultswiththosefoundbyother students.Iftheyaredifferent,suggestpossible reasons. 2 Which object is more dense? 3 Suggestanotherwayofindingthevolumesof theobjects.Tryit,andcheckyourresults.
we may treat the wool to make it shrink-resistant, and we grind up corn to make flour, which we use to make bread. These are processed materials. Over the years, however, we have made many totally new materials. For example, 2000 years ago the Chinese discovered how to make paper from wood. In recent times we have made an incredible range of materials such as concrete, glass, plastics, paints and pesticides. These materials do not occur naturally, and are said to be synthetic.
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ScienceWorld8forNSW Science in action The properties of a material determine what it can be used for. Wool is used for winter clothes because it keeps your body heat in. Aircraft are made of aluminium metal because it is light. Copper is used to make electric wires because it is a good conductor of electricity, and because it can be shaped to form wire. Drills are sometimes diamond-tipped, because diamond is much harder than most other substances. Synthetic materials are continually being developed with special properties to do particular jobs. Here are four examples. 1 Since 1996 Australia’s banknotes have been made from polypropylene plastic. These last longer than paper notes, stay cleaner and are very difficult to counterfeit. They can also be recycled to make compost bins, plumbing fittings and other useful household and industrial products. 2 In 1999 CSIRO developed a new sunscreen called Sunsorb. It is similar to zinc cream, but because the powder it is made from is so fine, it is virtually invisible.
Activity For this activity you will need some peanutshaped starch packing beads. How many starch packing beads do you think will ‘disappear’ in two teaspoons of water? To test this, add one starch bead at a time, stirring well to form a suspension. Observe how the beads change and how the water changes. Could you get the beads back again? How?
3 If you break open a disposable nappy, you will find a white powder called WaterSorb. It forms a gel when water is added to it. It can soak up a large volume of urine, keeping the baby’s bottom dry. It is also used to prevent pot plants drying out. egan Ken b tific ien his sc ents at m i r expe arly age. e y a ver
4 Polystyrene packing beads are being replaced by ones made from wheat or corn starch. This makes sense because wheat and corn are renewable, unlike polystyrene which is made from oil and is non-renewable. These beads cause less damage to the environment since they form a suspension in water and are biodegradable.
< WEB watch > Go to www.scienceworld.net.au and follow the links to the websites below. The secret of the disposable nappy This site has an experiment to test the superabsorbent powder in a disposable nappy. Reserve Bank of Australia This site has information on the famous Australians on our notes, how the notes are made and recycled, and how to detect counterfeit notes. Try searching under the trade names of some of the newer synthetic materials, eg Kevlar, Mylar, Nomex, Teflon, Tyvek. Keep notes on the properties and uses of each material you research.
Chapter3 Whatarethingsmadeof?
Check! 1
2
4
In which state would a substance be if it had: a no fixed volume? b a fixed volume and shape? c a fixed volume but took the shape of its container? Each of the cartoons below illustrates at least one property of matter. Which shows that: a a solid has a fixed shape? b a liquid can be made to have any shape? c a gas can be compressed? d a gas does not have a fixed volume?
Look at the data table below.
Object A Object B Object C a b 5
a b
How many kilograms are there in 2000 g, 100 000 g, 1530 g? How many grams are there in 2 kg, ½ kg, 6.7 kg?
volume (cm3)
39 54 6
6 20 5
Which object has the greatest mass? Which object has the greatest density?
Look at the diagrams below. Suppose you keep your finger over the end of the syringe, starting in position A. You push in the plunger to B, then pull it back to C. In which position is the air in the syringe most dense? Explain your choice. A
3
mass (g)
B
C
6
It is easier to float in sea water than in fresh water. Use your knowledge of density to explain this.
7
A balloon filled with helium rises when you let it go. A balloon filled with carbon dioxide sinks. Explain the difference.
8
In each of these pairs, which is the object, and which is the material it is made from? Describe the properties of each substance that make the object useful. Record your answers in a table with three columns. a window / glass b styrofoam / coffee cup c plastic / ruler d aircraft / aluminium e bank note / polypropylene plastic
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9
Classify the following materials as natural, processed or synthetic: concrete milk petrol flour natural gas soft drink marble nylon superphosphate marijuana oxygen uranium
challenge 1 Manypeopleincorrectlysaythatleadisheavier thansteel.Whatshouldtheyreallysay? 2 Whichpropertiesallowyoutodistinguish between the substances in each of the followingpairs? a steelandaluminium b lemonadeandwater c saltandsugar d woodandplastic e polystyreneandstarchpackingbeads 3 Whichofthefollowingwouldyouusetomake thebaseforastand-upsignoutsideashop— concrete,aluminiumorgold?Explainyour answerintermsofthepropertiesofthethree substances. 4 a Apieceofcopperhasamassof50gand avolumeof5.6cm3. What is its density? b Anotherpieceofcopperhasavolumeof 7 cm3. What is its mass? 5 Arectangularblockofwoodhassides8cmby 4cmby5cm.Ithasamassof120g. a What is its density? b Wouldthisblockofwoodloatinwater?
10
Make a table listing the properties of the four synthetic materials described on page 58.
11
What is the difference between a renewable material and a non-renewable one? Give examples, in addition to the ones on page 58.
6 Whatisthemassofairinaroommeasuring 10m×5m×3mifthedensityofairis 1.3kg/m3? 7 Suggestsomeusesforaplasticthatdissolves in water. 8 Theballoonsinthephotoaremadeofamaterial calledMylar.Theyareilledwithheliumgas andstayinlatedformonths.Suggestwhich propertiesofMylarmakeitsuitableforusein thesespecialballoons.
t r y t his 1 One-third fill a glass vial with glass vial glycerine. Carefully pour an equal volume of coloured water down the inside of the vial so that it flows gently onto the glycerine, as shown. Drop a small piece of perspex into the vial. Observe what happens, and try to explain it in terms of density.
coloured water glycerine
2 Does a fresh hen’s egg sink or float in water? Try it. Now add salt to the water, while stirring carefully, and observe what happens. Explain your observation. A rotten egg floats in fresh water. Suggest why.
Chapter3 Whatarethingsmadeof?
3.2 Solid–liquid–gas The three different states of matter can be changed from one to another by adding or removing heat. These changes are called changes of state. If you heat a solid it will form a liquid. For example, ice melts to produce liquid water. Metals such as iron and gold also melt if you heat them enough.
sublimation melting
solidification or freezing
ENERGY OUT (cooling)
condensation
Heating also causes evaporation of liquids to produce gases. For example, when water is heated it evaporates to form water vapour, which is a gas. The hotter the water gets, the more quickly it evaporates. When bubbles of water vapour appear in the water it is said to be boiling. The water vapour forms more quickly, and is now called steam. This occurs at 100°C, the boiling point of water. Water can evaporate at any temperature, but boiling occurs only at the boiling point. Cooling causes gases to condense and form liquids. For example, steam is invisible, but when it meets cooler air it forms a cloud. This is because the steam condenses to form tiny droplets of water. A similar thing happens in the bathroom when you have a hot shower. Some of the hot water evaporates and changes into water vapour. Because the air in the bathroom is cooler, the water vapour condenses to form tiny
evaporation or boiling
Solid gold melts at about 1000°C. The liquid gold can then be poured into moulds.
ENERGY IN (heating)
Fig 18
drops of water which float in the air and ‘fog up’ the mirror. Similarly, as water from the Earth’s surface evaporates it forms water vapour. As this water vapour rises it becomes cooler and may condense to form clouds and perhaps rain. Cooling also causes water to freeze or solidify. This occurs naturally when snow and hail form. We use the same process to make ice blocks and ice-cream. Molten metal can be poured into moulds to solidify into various shapes (see Fig 18). Some solids do not change to a liquid when they are heated. Instead they turn straight into a gas in a process called sublimation. For example, ‘dry ice’ is solid carbon dioxide. When it sits on the bench it soon warms up and changes directly into gaseous carbon dioxide, which is invisible. Another way to look at changes of state is to think of the three states of matter as rungs on an energy ladder. To change state by climbing up the ladder, energy must be added to the matter—it must be heated. To change state by going down the ladder, energy must be taken from the matter—it must be cooled.
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ScienceWorld8forNSW The particle theory More than 2000 years ago in ancient Greece a philosopher called Democritus suggested this hypothesis: all matter, living and non-living, is made of tiny particles too small to be seen. His idea was that if you kept cutting something into smaller and smaller pieces you would eventually come to the smallest possible particles—the building blocks of matter. He used the word atomos (which in Greek means ‘cannot be divided’) to describe these tiniest particles. This is where the word ‘atom’ comes from. (You will learn about atoms in Chapter 8.) Since then scientists have done many tests with matter, and the results have always agreed with Democritus’ hypothesis. Such a hypothesis that is supported by many experimental results is called a theory. So the hypothesis that matter is made up of tiny particles too small to see is now called the particle theory of matter. This particle theory can be used to explain the properties of solids, liquids and gases.
The particle theory of matter 1 All matter is made up of tiny particles too small to see. 2 There are spaces betw een the particles. 3 There are attractive fo rces between particles. The weaker thes e forces are, the further apart the particles are. 4 The particles are alway s mo
ving.
5 At high temperatures the particles move faster than they do at low temperatures.
Solids
The particles in a solid (eg steel) are packed tightly in a fixed pattern. There are strong forces called chemical bonds holding them together, so they cannot leave their positions. The only movements they make are tiny vibrations to and fro. We cannot see these invisible particles, but we can use a model. For example, we can represent the particles by the students in your class. When
everyone is sitting down, the class is a model for a solid. The word model has a special meaning in science. It is not the latest model car or a fashion model. It is a way of representing something that is too small to be seen, or too large or complicated to be studied easily. A model is not the real thing. It is only a representation that helps you understand or explain something.
Chapter3 Whatarethingsmadeof?
Liquids
HEAT
The particles in a liquid (eg water) can move about and slide past each other. They are still close together but are not in a fixed pattern. The forces (bonds) that hold them together are weaker than those in a solid.
When the students are moving about busily doing practical work, the class is a model for a liquid.
HEAT Gases
The particles in a gas (eg air) are far apart, and they move about very quickly. There are still attractive forces between them but they are very weak. The particles collide with each other and the walls of the container, and bounce off in all directions.
When the lesson is over students go in many different directions. Some may stay in the room, while others go to different parts of the school.
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Activity 1 Make a model for matter by putting some ball bearings in a flat dish or box. What do the ball bearings represent? What does the dish or box represent? Draw the arrangement of the ball bearings. What state of matter does this represent? 2 Shake the dish gently so that the ball bearings move about. Describe the new arrangement of ball bearings. What state of matter does this represent? 3 Shake the dish vigorously. Describe the new arrangement. What state of matter does it represent? Your teacher may demonstrate this model using a dish on an overhead projector.
Explaining melting We can use the particle theory to explain changes of state. When a solid is heated, its particles gain more energy and vibrate more. This makes the solid expand—get bigger. At the melting point the particles vibrate so much that they break away from their positions. When this happens the solid becomes a liquid.
solid
heat
The particles vibrate more.
heat at melting point
A liquid is formed.
Teacher note: It is possible to buy special magnetic marbles for this activity. Fig 24
The particle theory can be used to explain the melting of a solid.
Chapter3 Whatarethingsmadeof?
Activity Explaining boiling When a liquid is heated, its particles have more energy and move faster. They bump into each other more energetically and bounce further apart. This makes the liquid expand. At the boiling point, the particles have enough energy to break the bonds holding them together. They break away from the liquid and form a gas.
At low temperatures the particles in the liquid move slowly.
Set up the apparatus shown below and observe carefully what happens. Where does evaporation occur? Where does condensation occur? Where does water exist in: a a solid state? b a liquid state? c a gaseous state? ice cubes
watchglass
beaker heat
gauze mat Bunsen burner (or hotplate)
water
tripod
As the liquid gets hotter, the particles move more quickly. Some have enough energy to break the bonds holding them together and escape (evaporate).
heat at boiling point
Science in action To see how this works, open the Particle theory animation on the CD.
At the boiling point all the particles have enough energy to evaporate.
Fig 25
The particle theory can be used to explain the evaporation and boiling of a liquid.
If you are fascinated by the weather, you may be interested in becoming a meteorologist. Meteorologists study how water evaporates from the Earth’s surface to form water vapour which rises into the atmosphere where it condenses to form tiny water droplets which we see as clouds. Meteorologists analyse and interpret weather data collected around Australia, including satellite photos. They then prepare weather reports for TV and newspapers, and issue warnings for storms, cyclones, floods and droughts. They work in field stations throughout Australia and its territories, from the tropics to Antarctica.
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Investigate
8 MELTING AND BOILING stopper with hole
Aim Tomeasureandgraphthetemperature asicemeltstowaterandthenboils.
Materials
For information on
using dataloggers, • smallbeaker,eg250mL open the ICT • crushedice skillsheet on the CD. • thermometer (–10to110°C)or dataloggerandtemperatureprobe • burner,tripod,gauzeandheatproofmat • stopwatch • stirringrod • retortstandandclamp • stopperwithholetoholdthermometerinclamp • graphpaper
stirring rod
thermometer
crushed ice
Wear safety glasses.
Planning and Safety Check ReadthroughtheMethod. • Whatsafetyprecautionswillbenecessary? • Whichistheindependentvariableand whichisthedependentvariable?Howdo you know which is which? Designadatatable,withcolumnsforthe twovariablestobemeasured.
Method 1 Setuptheapparatusasshown. 2 Half-illthebeakerwithcrushedice,and measureitstemperature.(Remembertowait untilthereadingissteady.) Recordthetemperatureoftheiceinyour datatable. 3 Lighttheburnerandadjustittoamediumlame. Putitunderthebeakerandimmediatelystart timing. 4 Measurethetemperatureeveryminute.Usethe stirringrodtostirgentlybeforeeachreading. Continueyourmeasurementsuntilthewaterhas beenboilingfor3or4minutes. Recordthedatainthedatatable.
5 Graphyourresultsorprintthemfromthe datalogger.
Discussion 1 Whatcausedtheicetomelt? 2 Whatdidyounoticeaboutthetemperatureas theicemelted? 3 Whatdidyounoticeaboutthetemperatureas thewaterboiled? 4 Yourgraphhastwolatsectionsjoinedbya slope.Whatdoesitmeanwherethegraphis lat?Onthegraph,markwhentheiceismelting. Alsomarkwherethewaterisboiling. 5 Useyourgraphtoindthetemperatureofthe water10minutesafteryoustartedheating. 6 Predictthetemperatureofthewater 10minutesafteritstartedtoboil. 7 Thetemperaturedidnotincreasewhiletheice wasmeltingandwhilethewaterwasboiling— eventhoughtherewasaconstantsupplyof energyfromtheburner.Usetheparticlemodel toexplainwherethatenergywasgoing.
Chapter3 Whatarethingsmadeof?
Check! LIQUID freeze
1
Copy the diagram above. Put one word in each box and on each arrow to summarise what you know about changes of state.
2
Complete these sentences: a The melting point of ice is the temperature when it changes from a ______ to a ______. b The melting point of ice is ______°C. c The boiling point of water is the temperature when it changes from a ______ to a ______. d The boiling point of water is ______°C. Choose from the words solid, liquid or gas to say what type of substance will be formed when: a a gas condenses b a liquid freezes c a solid melts d a liquid boils
3
5
Changes of state
a b c d e
Name the change of state that occurs when— a dew forms on the grass b a bottle of perfume is opened and can be smelt on the other side of the room. c a puddle of water on the road disappears when the sun shines. d moth balls placed in a suitcase of clothes are gone after a few months. e lava flows from a volcano and slowly forms a rock called basalt.
Heating
Cooling
solid to liquid liquid to gas gas to liquid liquid to solid solid to gas
6
Indicate whether each of the following statements is true or false. If the statement is false, rewrite it so that it is true. a Melting occurs when a solid changes to a liquid. b All matter consists of particles. c To change a liquid to a gas you have to cool it. d Solids have a definite shape because their particles are free to move around. e Water can evaporate at any temperature. f If water boils for a long time, its temperature rises above 100°C. g Condense is the opposite of evaporate. h The particles of a gas are so far apart that they do not attract each other at all. i The particles of a solid do not move.
7
a
Write your answers in complete sentences. 4
The table below lists five changes of state. For each change decide whether heating or cooling is needed. Copy the table and tick the correct columns.
b c
d
In which state do the particles move fastest? In which state are the particles closest together? In which state are the particles close together but not arranged in a regular pattern? In which state of matter are the bonds between particles greatest?
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challenge
6 Belowisagraphshowingthechangein temperatureovertimeaswaxisheated.
1 Luigiwearsglasses.Heindsithardtosee when he enters a hot steamy bathroom. Use whatyouhavelearntinthischaptertoexplain this.
D
100 Temperature (ϒC)
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B
C
A 0
2 Ifgasesandliquidsarebothmadeofparticles, whyaretheirpropertiessodifferent?Explainin termsofparticlesandbonds. 3 Answerthesequestionsincompletesentences. a Howcanyoumaketheparticlesinasolid move faster? b Whataretheparticlesdoingifaliquidis evaporating? c Whatcanhappentoagasifitsparticles slowdown? 4 Whenyoucookfoodinasaucepanwithalid on,youmaynoticewaterontheinsideofthelid. Why is this? 5 Useyourknowledgeoftheparticletheoryto explaineachchangeinthediagramsbelow.
10
20 Time (min)
30
a Whichpartofthegraphshowsthatachange ofstateistakingplace? b Whatisthemeltingpointofthewax? c Whatisthestateofthewaxduringtheirst 10minutesofheating? d What is the state of the wax between C and D? e Inwhichpartofthegrapharethebonds betweenthewaxparticlesgreatest? 7 Hexaneisusedasanindustrialsolvent.Ithas ameltingpointof–94°Candaboilingpointof 69°C. a Ishexaneasolid,aliquidoragasatroom temperature(20°C)? b Ifhexaneisheatedto90°Cwouldyou expectittobeasolid,aliquidoragas? 8 Whichwouldevaporatemorequickly:waterina lattray,orwaterinanopenbottle?Explainyour answerintermsoftheparticletheory. 9 Whydoclothesdryfasteronawindydaythan theydoonacalmday?
Chapter3 Whatarethingsmadeof?
10 Angiewantedtokeepheryoghurtcool,soshe putitinajarwithsomeiceandscrewedthelid ontightly.Whenshewenttoputitinherlocker 15minuteslater,shesawthattheoutsideofthe jarwasquitewet. Everyonehadagoatexplainingwhathad happened(seethecartoon). a Whoseinferencedoyouagreewith?Why? b Canyousuggestabetterinference? 11 Dryiceissometimesusedtocreatefogand mistonstage.Ifcarbondioxideisinvisible,how canyouseethedryicefog? 12 Onahotdayyouperspire(sweat).Asthis perspirationevaporatesitcoolsyou.Usethe particletheorytoexplainhowevaporation producescooling.
A fourth state of matter We are familiar with the three states of matter we find on Earth—solids, liquids and gases. However there is a fourth state of matter called plasma which makes up 99% of the universe. Plasma consists of charged particles that are even further apart than the particles in a gas. You don’t see much plasma on Earth because it requires very high temperatures. However the sun is made of plasma, as are all the stars. Lightning is a type of plasma that occurs naturally on Earth. You may have seen a plasma sphere in a science centre. The glass sphere contains a gas at a very low pressure and when very high voltage passes through it, it glows and looks like ‘bottled lightning’. Plasmas also occur in neon signs and fluorescent bulbs. Because the particles in a plasma are charged, they are affected by a magnetic field. Loops of plasma erupt from the surface of the sun and follow the curved magnetic field of the sun. Scientists are experimenting with plasmas as hot as 100 million degrees. They are trying to make a
The jar must have leaked.
Water from the ice has come through the jar.
Water in Coldness comes the air through the glass sticks to and turns to water. the glass.
Jan
an
Se An
gie
h Ko
fusion reaction that produces energy as the sun does. They use powerful electromagnets which create a ‘magnetic bottle’ to contain the superhot plasma.
< WEB watch > To find out more about plasmas, go to www.scienceworld.net.au and follow the links to Amazing Plasmas.
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3.3 Using the particle theory We have used the particle theory to explain solids, liquids and gases, and how they can change from one state to another. In this section we will try to use it to explain some other properties of matter.
Diffusion If someone opens a bottle of perfume in the middle of the classroom you soon smell it in other parts of the room. The fragrance spreads through the air in all directions. This gradual mixing of substances is called diffusion.
Let’s explain how perfume diffuses. When the lid is on, the gas particles remain inside the bottle. When the lid is taken off, the liquid perfume evaporates easily. Since there are only weak forces between the particles, they can spread out, moving away from the crowded bottle to places where there are fewer particles of perfume. Eventually the particles spread evenly throughout the air in the room.
Activities A Put a beaker on a sheet of white paper and half fill it with water. Let it stand for a while to let the water become perfectly still. Use a pair of tweezers to drop a single crystal of potassium permanganate (Condy’s crystals) down a drinking straw as shown. Then leave the dish undisturbed overnight. Explain what you observed in terms of particles. potassium permanganate crystal tweezers drinking straw
B This activity involves the poisonous gas nitrogen dioxide and can only be done as a teacher demonstration—in a fume cupboard. Place a few pieces of copper in a small beaker. Pour a few drops of concentrated nitric acid on the copper and immediately cover the beaker with a larger beaker, as shown. Observe what happens to the brown gas. (It helps to put a piece of white cardboard or paper behind the beakers.) white Use a fume cupboard.
cardboard
beaker water white paper
copper + nitric acid
Chapter3 Whatarethingsmadeof? As you saw in the activity on the previous page, when a crystal of potassium permanganate is placed in water, the water slowly turns purple. Both the crystal and the water are made of particles. Being in the liquid state, the water particles are moving and bump into the particles The water particles are continuously moving.
in the crystal. This causes some particles to leave the crystal and move into the spaces among the water particles, as shown below. This is the process of dissolving. As the particles continue to move, they diffuse throughout the water and the purple colour spreads evenly.
Particles leave the crystal.
Because the particles are all moving, they become evenly mixed.
crystal
Activities Your teacher may demonstrate the following activities. For each activity, predict what you think will happen, then observe what happens and finally explain what happened. A Using a ball and ring apparatus (or other metal shapes), put the ball through the ring. Then heat the ball strongly and try to put it through the ring again. What do you predict will happen if you heat the ring and try again? Try it. B Fill a flask with coloured water and fit a stopper with a piece of glass tubing through it. The coloured water in the tube should reach just above the stopper. Mark this level with a marking pen. Put the flask in a container of hot water for a few minutes. Now put it in a container of cold water. How could you use this apparatus to measure temperature? C Put a balloon over the mouth of a flask. Heat the flask gently using a Bunsen burner. Write a generalisation to explain the results of all three activities.
ball
ring
glass tube coloured water
hot water
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ScienceWorld8forNSW Expansion and contraction
Air pressure
As you saw in the activity, solids, liquids and gases all expand (get larger) when they are heated. That is, they occupy more space. Similarly, when they are cooled they contract (get smaller) and occupy less space. In solids the particles vibrate in fixed positions. As the solid is heated the particles absorb energy, vibrate more violently and start to bump into each other. This causes them to move further apart so that they have more room for their violent vibrations. As a result, the solid as a whole expands. When the solid is cooled, energy is lost. The particles slow down again and occupy less space (contract). Expansion and contraction of liquids and gases can be explained in a similar way.
When Rhys pulls into the service station, he discovers his car has a flat tyre. What keeps the tyre inflated is air pressure. The invisible particles of air are only tiny but they move very rapidly— about the speed of a rifle bullet. These tiny bullets bombarding the walls of the tyre cause the air pressure. What has happened to Rhys is that some of the air has escaped from the tyre and there are not enough particles to give the pressure needed to keep the tyre inflated. Rhys gets the tyre fixed and pumps it up with compressed air. Now the air pressure is back to normal.
HEAT (expansion)
COOL (contraction)
Fig 43
Fig 42
In the cool balloon the air particles move slowly. In the warm balloon the faster-moving particles hit the walls of the balloon more violently, pushing them out and causing the balloon to expand.
A flat tyre contains few air particles and the air pressure is low. An inflated tyre contains many air particles and the pressure is high.
It is a hot day and Rhys drives non-stop for two hours to get to the beach. When he checks the tyre pressure, he finds it has gone up. There can’t be any more air particles in the tyre. What has happened is that friction between the tyre and the road has caused the air inside the tyre to heat up. This means the particles have more energy and are moving faster and hitting the walls of the tyre harder. Hence the air pressure is higher. When the tyre cools down, the particles will lose energy and slow down, and the pressure will return to normal. You have seen how the particle theory (page 62) can be used to explain changes of state, diffusion, expansion and contraction, and air pressure. You can now try to explain some other properties of matter for yourself.
Chapter3 Whatarethingsmadeof?
Activity For each observation below write an inference to answer the question in terms of the particle theory. Draw a model to explain what is happening to the invisible particles. 1 Observation: Lead is four times denser than aluminium. Question: How can you explain this? 2 Observation: Add a teaspoon of sugar to a glass of water and stir. Question: Explain what happens. 3 Observation: You can pour water from one container to another, but honey is much harder to pour, especially when it has been in the fridge. Question: How can you explain this? 4 Observation: Crystals have a definite shape, with straight edges and sharp corners. For example, salt crystals are cubes, while quartz crystals (below) are like pointed columns. Question: How can you explain these different shapes?
5 Observation: Hold your finger over the end of a bicycle pump and push in the plunger. Let go of the plunger and it moves back to where it came from. Question: What pushed the plunger back?
6 Observation: Make a soap film on a frame like the one shown below. Pull the thread to stretch the film. When you release the thread the film contracts, pulling back the thin wire. Question: Why does this happen?
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Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
attract
1 Matter has ______ and takes up space (its ______).
heat energy
2 There are three common ______ of matter on Earth: solids, liquids
mass
density
moving
and gases.
3 ______ is how much mass is packed into a measured volume. 4 Materials may be natural, processed or ______. What you use a material for depends on its ______.
5 Matter can be changed from one state to another when ______ is added or removed.
6 The particle ______ of matter states that all matter is made of
properties spaces states synthetic theory volume
particles too small to see. These particles: • have______betweenthem • ______eachother • areconstantly______ • movefasterasthetemperatureincreases.
REVIEW
Try doing the Chapter 3 crossword on the CD.
1 The statement All matter is made of particles is: A an observation B an inference C a prediction D a generalisation
3 A substance has no fixed shape. From this information it would be correct to say that the substance is a: A gas B solid or liquid C liquid or gas D solid or gas
2 Copy the diagrams below and label them by replacing the letters (A–G) with one of these words: condensation, evaporation, gas, liquid, melting, solid, solidification.
4 Give three examples of how the use of a substance depends on its properties.
D
E
G A
F B
C
Chapter3 Whatarethingsmadeof?
Table of densities (g/cm3)
aluminium lead platinum polystyrene foam petrol water
2.7 11.3 21.5 0.1 0.7 1.0
6 Archimedes was asked to find out if the crown belonging to the king of Syracuse (in ancient Greece) was made of pure gold. The king thought some silver may have been added to reduce the amount of gold needed. Archimedes decided to use his knowledge of density to solve the problem. He found the volume and mass of the crown. He also found the mass of an equal volume of pure gold. Here are his results. volume of crown = 100 cm3 mass of crown = 1500 g mass of 100 cm3 of pure gold = 1930 g
a What is the density of pure gold in g/cm3? b What was the density of the crown? c Was the crown made from pure gold? 7 Write a paragraph describing the advantages and disadvantages of plastic, paper and cotton canvas for making supermarket bags. In your answer use these words: processed, non-renewable, renewable and synthetic.
SALE
8 The questions below refer to the following list of some of the possible properties of particles. Rate of movement A vibrating or moving very slowly B moving around freely but slowly C moving freely and rapidly Spaces between particles D very close together, almost touching E fairly close together F wide spaces between them Forces between particles G very strong bonds H held together to some extent but free to move around I very weak bonds
a Aluminium is a solid. Which three properties listed above would probably be true of its particles? b Ozone is a gas. Which three properties would probably be true of its particles? c Petrol is a liquid. Which three properties would probably be true of its particles? d Steel cannot easily be compressed. Which description in Spaces between particles would best explain this? e Diamond is a very hard substance. Which two properties above would best explain this? f Property E in the above list can sometimes be changed to property F by: A heating the substance B cooling the substance C putting it in another container D compressing the substance 9 Use the particle theory to explain each of the following questions: a Why do gases have much lower densities than solids and liquids? b Why do gases condense to form liquids when cooled? Check your answers on pages 277–278.
REVIEW
5 Mercury is a liquid with a density of 14 g/cm3. Use the table below to find something that would sink in water but float in mercury.
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ScienceWorld8forNSW Learning focus: An idea can gain acceptance in the scientific community as either theory or law
US AREA C O F D E B I R C PRES
From idea to theory
Democritus (de-MOK-rit-us) was a Greek philosopher who lived from 460 to 357 BC. He had the idea that everything is made of atoms.
John Dalton (1766–1844) turned Democritus’ idea into a scientific theory. There is more about Dalton on page 181.
Use the internet and other resources to research the following questions about Democritus and Dalton. You could search under ‘atomic theory history’. Do this individually or in a group. Because there are so many questions you may need to divide the task between different individuals or groups. 1 Why did Democritus use the Greek word atomos to describe invisible particles of matter? (see page 62). 2 Were Democritus’ particles all the same? Explain. 3 How did Democritus explain the difference between a solid and a liquid? 4 Who was Leucippus? 5 Did the ancient Greeks do scientific experiments? Explain. 6 We know very little about Democritus and his ideas. Suggest a reason for this. 7 Aristotle was a famous Greek philosopher. Did he agree with Democritus’ ideas? Explain? 8 Were the Greeks the only ancient people to come up with the idea of atoms? 9 In the Middle Ages the church associated atomic thinking with Godlessness. Suggest a reason for this. 10 Suggest why Democritus’ idea was not developed any further for 2000 years. 11 When did people start doing proper scientific experiments? 12 What experiments were done by Dalton and other scientists around 1800? 13 What was Dalton’s atomic theory? Once you have finished your research, share your findings with the class. Then use what you have found out to discuss these final questions. 14 Why was Dalton able to convert Democritus’ idea into a scientific theory? Why did this process take more than 2000 years? 15 Do you think the atomic theory has changed since the time of Dalton? Explain.
4 Building
blocksoflife Planning page Getting started Activity page 79 Skillbuilder page 80 Using a microscope Activity page 81 Skillbuilder page 83 Drawing cells
4.1 Cells page 79
TRB Assessment task 4 A model cell
Investigate 9 Observing cells Activity page 87 Activity page 90
Investigate 10 Observing flowers Activity page 96
4.2 Growth and reproduction page 89 4.3 Reproduction and survival page 93
Main ideas Chapter 4 crossword
Review and Lab review
TRB Chapter 4 test
Learning focus: The place of social and ethical considerations in science
Prescribed focus area Stem cell research
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l learn abou
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LearningFocus ● ●
the place of social and ethical considerations in science (page 101) positive and negative impacts of recent applications of science (page 101)
KnowledgeandUnderstanding ● ●
cell theory unicellular and multicellular organisms (page 79)
Skills ● ● ●
safely use a microscope (Skillbuilder page 80, Activities pages 81 & 87, Investigate 9 and 10) presenting information—drawing cells (Skillbuilder page 83) presenting information—using tables (Activity page 96)
x100
● You are using a magnifying glass to look at a tiny insect on a stick. The magnifying glass has x2 on it. What does this mean? ● Another magnifying glass has x4 on it. How is this different from the first one? What will you see if you look at the insect with this magnifying glass? ● The organisms in this photo live in freshwater ponds and creeks. What does the x100 mean on the photo? Can you think of a way to find out how big these organisms are?
Chapter4 Buildingblocksoflife
4.1 Cells All organisms are made of small building blocks called cells. Your body contains over 3 billion of them. Most cells are very small and can be seen only with a microscope. However some cells, such as birds’ eggs, are large enough to be seen with your eye. The emu egg is the largest single cell of all! Some organisms are unicellular. These single cells are complete organisms. The photo below shows unicellular organisms called euglena (you-GLEEN-a), which live in fresh water and contain chlorophyll to make their own food by photosynthesis.
x4000
Fig 4
Red blood cells are specialised cells that carry oxygen around your body.
flagella
x500
Fig 5
Nerve cells have an irregular shape. They carry nerve messages throughout your body.
Activity x200
Fig 3
Euglena live in freshwater lakes and ponds. Long, whip-like ‘hairs’ called flagella at one end of the cell help it move through the water.
Multicellular organisms contain many different types of cells and each type of cell is specialised. This means that each type of cell has a different job to do in the organism. For example, in humans, red blood cells carry oxygen, muscle cells contract and relax to move bones and organs, nerve cells conduct nerve messages, and stomach lining cells make substances which help in the digestion of foods.
The photos of the cells on this page are many times larger than the actual size of the cells. Each photo shows the number of times that the cell has been magnified. For example, the x200 on the euglena photo means that the cells have been magnified 200 times. You can use this information to find the actual sizes of the cells. Measure an average-sized euglena cell with your ruler. Then divide this by 200 (the magnification) and give your answer in millimetres. Use this method to find the sizes of the other cells in the photos.
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Skillbuilder Using a microscope In this chapter you will be using a microscope to view different types of cells
Parts of the microscope Study the diagram below which shows the parts of a microscope. Your microscope may be slightly different from this one. However, the basic parts will be the same. If you are in doubt, ask your teacher for advice.
eyepiece lens
body tube
Setting up a microscope 1 Rotate the objective lenses until the low power lens clicks into position directly above the hole in the stage. (The low power objective lens is usually the shortest one, and has the lowest number stamped on it, eg ×4.) 2 Place a hair on a microscope slide and put it on the stage. 3 Looking from the side, turn the focusing knob to move the lens very close to the slide. 4 Now look through the eyepiece lens and move the objective lens away from the slide until the hair is in focus. Rotate the higher power objective lens into place. (You may need to use the fine focus knob to make the image clearer.)
objective lenses stage clips
stage focusing knobs— coarse adjustment fine adjustment light source
base
Chapter4 Buildingblocksoflife
Observing prepared slides
What x10 means
of a A microscope magnifies things. Each lens ked microscope has its magnifying power mar on it. the Look at the eyepiece lens. You may see lens this number ×10. This means that inal size. magnifies things to 10 times their orig same way. The objective lenses are marked in the roscope The total magnifying power of the mic eyepiece is found by multiplying the power of the . If the lens by the power of the objective lens then the ×10, is e eyepiece is ×10 and the objectiv es. tim microscope will magnify the object 100
Your teacher will give you a microscope slide containing some cells for you to practise your microscope technique. Observe the shapes and features of the cells.
Questions 1 A microscope has a x4 eyepiece and a x10 objective. What is the total magnification of the microscope? 2 When focusing, why do you turn the focusing knob so that the objective lens moves away from the slide? 3 A hair is 0.005 mm wide. How wide would it be if you looked at it with the lenses in Question 1?
Activity Making a wet-mount slide 1 Place a drop of water in the middle of a microscope slide. 2 Cut out a small lower case ‘e’ in the piece of newspaper and place it on the drop of water on the slide. Cover the ‘e’ with another drop of water. 3 Place the edge of the cover-slip on the edge of the drop of water, and lean it on a pencil, as shown. 4 Lower the pencil slowly and let the coverslip fall flat on the slide. (This stops air bubbles forming under the cover-slip.) You should do this a few times to master the skill. Show your slide to your teacher.
e
5 Place the slide on the stage and observe the letter under low power. Record your observations. Is the ‘e’ the right way up? Move the slide to the left. Which way does the ‘e’ move when viewed through the lens? Questions 1 Suppose you place the number ‘5’ under the microscope. Draw what you would expect to see through the lenses. Explain your drawing. 2 A cell is 0.01 mm long and 0.02 mm wide. How big would it be if you viewed it under a microscope with a ×10 eyepiece lens and ×4 objective lens?
e
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ScienceWorld8forNSW Cells in organisms The cells of living things vary in shape and function, but they do have features in common. All cells are surrounded by a thin covering called a cell membrane, which acts like a fence controlling the movement of substances into and out of the cell. The cell membrane also helps to hold the cell together and to give it shape. The round, dark-coloured object in the cells in the photos below is the nucleus (NEW-klee-us). This controls all the cell’s activities, and without it the cell eventually dies. The inside of cells is filled with a jelly-like substance called cytoplasm (SIGH-toe-plaz-um). This is where many chemical reactions take place. The cytoplasm also contains many other small bodies and structures called organelles
(OR-gan-els). These help to keep the cell functioning correctly. How are plant cells different from animal cells? Plant cells have a cell wall on the outside of the cell membrane. This is a thick, tough layer that protects the softer parts inside the cell and also provides stiffness that helps support the plant. Plant cells also contain large liquid-filled spaces called vacuoles (VAK-you-oles) where water and dissolved substances are stored. Some animal cells have small vacuoles, but most have none at all. Inside the cytoplasm of plant cells there are organelles called chloroplasts. These contain the green pigment chlorophyll, which is needed for photosynthesis. Photosynthesis occurs in the chloroplasts.
Animal cells
Plant cells
These cells are from the inside lining of a human cheek. The diagram below will help you interpret the photo.
These cells are from the leaf of a plant. The diagram below will help you interpret the photo.
×600
×1200
cell wall nucleus cell membrane
cell membrane vacuole cytoplasm chloroplasts
cytoplasm
nucleus
Chapter4 Buildingblocksoflife Science in action Shane is a baker. He makes different kinds of bread with the help of a unicellular organism called yeast. When making bread, Shane adds the basic ingredients—flour, sugar, water and yeast—and mixes them together to form dough. The dough is then left for a while in a warm place. During this time, the yeast cells grow and multiply rapidly using the sugar as a food. Yeast cells get the energy needed for growth and reproduction by breaking down the sugar. Carbon dioxide and alcohol are produced as waste products. This process is called fermentation. glucose
carbon dioxide + alcohol
The carbon dioxide gas given off by the yeasts causes the bread to rise and makes the holes in the bread. When the bread is baked, the heat of the oven quickly evaporates the alcohol from the dough.
Skillbuilder Drawing cells In the next investigation you will be using the microscope to observe some animal and plant cells. In these observations, you should include drawings in your report.
How to draw cells 1 Always use a sharp HB pencil, and have a clean eraser handy. 2 The cells you see under the microscope are fairly complicated. Try to keep your drawings as simple as posssible. 3 Choose 2 or 3 cells to draw. Draw the lines and shapes. Don’t shade or colour the drawing. 4 Make the drawing as large as possible. Include only the structures you can identify. Label these structures.
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Investigate
9 OBSERVING CELLS Aim To use a microscope to observe plant and animal cells.
Materials • • • • • •
microscope 2microscopeslidesandcover-slips pieceofonion methylenebluestain leaffromafreshwaterplant(egelodea) smallpiecesofapple,mincemeat,fresh chicken, moss, potato, spirogyra etc
Planning and Safety Check • CarefullyreadthroughPartsA,BandC, and make a list of the materials you will need for each part. • Askapartnertodescribewhattheyare going to do in Part A. Then you describe whatyouaregoingtodoinPartB.
4 Observe both slides under low power, then under higher power. Record the differences between the two slides. In which one are the cells more easily observed? Which parts of the cell can you easily see? Draw two or three stained cells. Label the cell wall, the nucleus and the cytoplasm.
PART B
L ook in g a t chloroplasts Method 1 Tear a small leaf from the top of the freshwater plant. 2 Prepare a slide as you did for the onion skin, butthistimeusetheleaf.(Youcanuseadropof waterorthemethylenebluestainifyouwish.)
PART A
O n i o n ski n ce lls Method 1 Remove one layer from the onion. Then peel a small piece of the very thin skin from inside the layer. 2 Put a drop of water on a slide then place the piece of onion skin on the drop. Add another drop of water on top of the onion skin. Then add a cover-slip as shown below.
onion skin drop of water
3 Repeat Steps 1 and 2 with a second slide, but instead of adding water, add one drop of methylene blue stain. Then place a cover-slip over the onion skin.
3 Observe the leaf under low power, then under higher power. Use the photo of the plant cells on page 82 to help you identify the round chloroplasts, the cell wall, the nucleus and the cytoplasm. Draw a labelled diagram of what you observe. How do these cells compare with the onion cells from Part A?
Chapter4 Buildingblocksoflife
PART C
O t her ce lls Method 1 For this part you will look at cells in apple, mince meat, chicken, moss, potato, spirogyra, duckweed etc. 2 Place a small amount of material on the end of a toothpick. Scrape it onto a slide. 3 Addadropofwaterandacover-slip.Youcan add a drop of stain if you wish.
Discussion 1 Why is a stain used when observing cells? 2 What general shape are the onion cells? Do other types of cells also have a regular shape? Do other cells have the same shape as onion cells?
Video microscope: Your teacher may connect a camera to a microscope to show you different types of cells.
Observe the cells. Draw and label two or three of the cells.
Bacteria
Sizes of cells You have seen that cells have a variety of shapes depending on their function. Most animal and plant cells are about 0.005 mm to 0.02 mm in diameter. The largest single cell is the ostrich egg, which is about 15 cm long. However, the longest cell is a type of nerve cell found in the giant squid and can be up to 7 metres in length.
Bacteria are unicellular organisms and have a much simpler cell structure than animal and plant cells. A bacteria cell is usually smaller than other cells, ranging in size from 0.0005 mm to 0.003 mm. Bacteria are usually classified by their shape. There are rod-shaped ones (bacilli), spherical ones (cocci) and spirals (spirilli). Bacteria have a cell wall, but no nucleus. This is the major difference between a bacterial cell and a plant or animal cell.
Questions 1 What is the main difference between an animal cell and a bacterial cell? 2 What is the average diameter of an animal or plant cell? What is the average diameter of a bacterial cell? How much larger is an average animal cell than an average bacterial cell?
< WEB watch > Go to www.scienceworld.net.au and follow the links to Bacteria. Use the websites to find out about different types of bacteria: the ones that cause disease and the ones that are useful to us.
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ScienceWorld8forNSW Cells, tissues and organs Unicellular organisms such as euglena contain all the structures necessary to exist on their own and be independent from other cells. However, the cells in large, multicellular organisms are generally specialised, and therefore need to work together with other cells for the survival of the organism. For example, a single cheek cell cannot exist on its own for very long and will die after a short time outside the body. Cells of the same type are generally found together in tissues. A tissue is a group of similar cells organised to do a particular job. For example, the muscle tissue in the wall of your stomach and gut is made from muscle cells. The nerve tissue in your brain and spinal cord is made from nerve cells. In multicellular organisms, various tissues are arranged into a structure called an organ. An organ is a collection of specialised tissues that has a particular function. For example, a leaf whose main function is to make food, contains food-making tissue, transport tissue, support tissue and lining tissue.
muscle cell
nerve cell
Fig 17
muscle tissue
nerve tissue
Many cells of the same kind combine to form tissues in the body.
The leaf—a plant organ
Food-making tissue The cells in this tissue contain many chloroplasts and are generally found underneath the top surface of the leaf.
Lining tissue The cells in this tissue act as a ‘skin’ for the leaf. They are flat and have a waxy coating to stop the leaf from losing water.
Transport tissue These cells form the tubes that carry water up from the roots, and nutrients from the leaves to other parts of the plant.
Support tissue The cells in this tissue have an irregular shape and act like a framework to support the leaf and help form its shape.
Chapter4 Buildingblocksoflife
Activity You will need a microscope and slide, some prepared slides of various tissues, some clear nail polish and a leaf. A Looking at tissues Set up a microscope and ask your teacher for a prepared slide of a tissue. Draw a sketch of the cells in a small section of the tissue (about six to ten cells). Write down the name of the tissue (this will be written on the slide). B Observing the cells on a leaf’s surface Brush some nail polish on the underside of a leaf, so that it covers an area about the size of a 20 cent piece. Let it dry for a few minutes.
The stomach is an organ whose function is to break down (digest) food. It contains glandular tissue which produces substances that chemically break down foods, muscle tissue which churns the food, and connective tissue which holds the other tissues together.
Peel the dried nail polish from the leaf and look at it under a microscope. You will see a copy of the surface cells on the leaf. You will also see cells that form holes or pores in the surface of the leaf. Find out from the library what these pores are called. What is their function?
Connective Tissue This tissue is found between other tissues and helps to hold these tissues together.
from the mouth
Muscle Tissue The cells in this tissue contract and relax, thus helping to mix and move the digestive food in the stomach.
stomach
to small intestine
Fig 20
stomach cut open to show lining
The tissues in the stomach have a number of functions. Cells in the gland tissue make chemicals that help digest foods, and muscle tissue moves the stomach to help mix the food.
Gland Tissue The cells in this tissue make substances that help break down the food in the stomach.
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Check! 1
5
Copy the following sentences into your notebook, then complete them using the words you have learnt in this section. a Organisms are made of building blocks called ______. b Cells in large organisms are called ______ cells, because they perform a particular function. c The lens that you look through at the top of a microscope is called the ______. d Organelles are found in the ______ of a cell. e Chloroplasts are organelles that contain ______.
6
Explain the difference between a tissue and an organ. Give an example and use the words cells and function in your answer.
7
On page 79, the word multicellular was used. Explain what this word means.
8
Look at the diagram of the leaf on page 86. Make an inference for each of the following observations. a The lining cells are very flat and fit together like tiles. b There are many chloroplasts in the food-making cells. c There are holes or pores in the underside of the leaf. d The cells in the support tissue fit together like trusses in a house frame.
9
You are an illustrator for a Year 8 science textbook. Try to explain, using labelled drawings, how to make a wet-mount slide.
Draw up a table similar to the one below and list the features of plant and animal cells so you can compare them. One feature has been done for you.
Plant cells
Have a nucleus
Animal cells
Have a nucleus
2
A microscope lens has ×10 marked on it. What does this mean?
3
Copy the drawing of a cell below into your notebooks. Use the information in the table above to determine whether it is a plant cell or an animal cell, then label the cell. 1 2 3
5 4
4
Describe the function of each of the five parts of the cell in Question 3.
challenge 1 A microscope has two eyepiece lenses, ×4 and ×10, and three objective lenses, ×4, ×10 and ×40. a What combination of lenses gives a ×160 magnifying power? b What are the lowest and highest magnifying powers of the microscope? c A specimen was photographed using the ×10 and ×10 lenses. On the photo the specimen measured 55 mm in diameter. What is the actual size of the specimen?
2 a What does the letter ‘F’ look like through a microscope? b Under a microscope you observe a tiny insect moving diagonally across a slide, as shown in the diagram. Where should you place your finger to prevent it from escaping from the slide?
Chapter4 Buildingblocksoflife
4.2 Growth and reproduction When a bean seed is planted in moist soil, the roots begin to grow and become larger and longer. This growth occurs because certain cells in the roots multiply and make more cells by a process called cell division.
Producing new life All organisms reproduce to make more of their own kind. Unicellular organisms do this by cell division. They simply split in two to produce offspring that are identical to the original organism. This is called asexual reproduction.
cell division
cell growth
Fig 24
Fig 23
All living things grow when cells divide to make new cells. Each of these new cells then grows in size and becomes a mature cell.
All living things grow by making new cells. Your body grows rapidly in stages up to the age of about 15. During this time your bones grow thicker and longer. For example, your thigh bone (femur) grows to about three times the length it was when you were born. Bone cells in the enlarged rounded ends of the femur divide to make new cells. Your skin grows in much the same way. Certain cells below the surface of the skin divide to make new cells. So, as the bones and other parts of your body grow larger, your skin also grows. However, unlike bones, which stop growing at adulthood, cell division continues in your skin until death. The skin continually loses cells from its surface and replaces them with new ones.
Microscopic organisms, like these paramecia, reproduce by splitting in two.
Larger organisms reproduce sexually. To do this, the two parents (one male and the other female) produce sex cells. These cells are different from other cells. They can combine to make a cell that eventually becomes a new and independent organism. The female sex cell is called an ovum or egg cell. Ova (plural of ovum) are made in organs called ovaries (OH-var-ees). The male sex cell is called a sperm cell and is much smaller than ova. Sperm are made in organs called testes (TES-teez). When a sperm and ovum meet, the nuclei of the two cells join together, and a new living thing is formed. This process is called fertilisation (FUR-til-eyes-AY-shun). Fertilisation can occur externally or internally. For example, in humans internal fertilisation occurs. The male deposits the sperm inside the female’s body. They then swim towards the ovum, where fertilisation occurs. Female frogs, on the other hand, release their eggs in the water, and sperm released by the male swim to the eggs.
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Fig 25
Human sperm cells (×2500) look like miniature tadpoles. They use their tail to swim through liquid. The head of the sperm contains the nucleus and a small amount of cytoplasm.
The sex cells of organisms are not all the same size and shape. Fig 27 shows the actual sizes of ova from five different animals.
Fig 26
A human ovum (×1000) with sperm cells on its surface. The ovum is much larger than a sperm cell, because it has much more cytoplasm. The cytoplasm contains food for the fertilised egg during the first few days of cell division and growth.
Activity mullet
frog
hen
human mouse
Fig 27
The sizes and shapes of five different ova
The eggs of mammals are small compared with the eggs of birds, reptiles, amphibians and fish. They have only a small quantity of cytoplasm, because the eggs develop internally and receive nourishment from the mother within a few days of fertilisation. In birds and many other animals, the fertilised egg develops outside the mother’s body and must contain enough food for the whole period of growth.
Break open a hen’s egg in a flat glass dish or petri dish. Notice the yellow yolk and clear albumen (the ‘white’). These make up the cytoplasm of the cell. Look at the yolk carefully and you should see a tiny white patch. This is the nucleus of the egg. It is this part of the egg that develops into a young chicken. Observe the ‘ropes’ in the albumen. These keep the young chicken in place in the egg and stop it albumen ‘ropes‘ egg shell from rolling over.
yolk nucleus of egg
albumen
Chapter4 Buildingblocksoflife Dogs
Eggs and life cycles Humans In humans, a baby girl at birth has ovaries that each contain about 200 000 eggs. These eggs do not begin to mature until certain changes take place in a young girl’s body. These changes occur during a stage called puberty (PEW-ber-tee). In girls, this occurs somewhere between the ages 10 and 14. From the onset of puberty, a woman’s ovaries will produce usually one egg a month for about the next 40 years. At about age 50, the ovaries stop producing eggs. This is called menopause.
The ovaries in a female dog contain thousands of immature eggs when it is born. At about 6 months old, the female dog starts producing mature eggs. This is the period the female is said to be ‘on heat’, and it is a sign that she is ready to mate with a male dog. Unlike in humans, the ovaries in dogs can release many eggs during this period, and the female can give birth to as many as 15 puppies. Female dogs go ‘on heat’ about every 6 months, so it is possible for dogs to have two litters of puppies in a year. The pregnancy lasts just over two months.
Chickens Like humans and dogs, hens are born with many thousands of immature eggs in their ovaries. At 3 months of age, hens start laying eggs. They have been bred to lay up to 200 eggs a year. However, these eggs are usually used for food and not for producing more chickens. The eggs you buy at the supermarket have not been fertilised by a rooster and therefore cannot develop into chickens. The ancestor of the modern hen was the red jungle fowl, found in South-East Asia. It is believed that this bird was domesticated about 4000 years ago. The present-day jungle fowl lays between 3 and 12 eggs a year, which is similar to the number of eggs laid by other birds.
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Check! 1
2
3
Copy and complete the following sentences. a ______ ______ is a process in which cells split into two. b In organisms that reproduce sexually, the male produces ______ and the female produces ______. c Fertilisation occurs when the ______ of sex cells combine. d In males the ______ produce sperm, and in females the ______ produce eggs. Name two places in the body of a 1-year-old child where cell division occurs. Would this be the same for a 50-year-old person. Give a reason for your answer. Look at the Term and Meaning lists top right. Match the terms in the left-hand column with the meanings in the right-hand column. To do this, draw up a table like the one below.
Term
Meaning
challenge 1 Celldivisioninmicroscopicorganismscan occur rapidly if the conditions are suitable. For example, bacteria can divide every 20 minutes. Assuming one bacterium divides every 20 minutes, and none die, how many bacteria would there be after six hours? 2 Women usually give birth to one child at a time, but multiple births do occur. Identical twins occur when the egg splits into two just after fertilisation and each develops separately. Fraternal twins occur when two eggs are released from the ovary and each is fertilised by a different sperm. Use the information above to answer the following questions. a Identical twins are always the same sex and look almost exactly alike. Why?
Term
Meaning
ovary
where sperm are made
semen
when the nuclei of a sperm and ovum join
fertilisation
a liquid containing sperm
ova
the organ that produces eggs
testes
female sex cells
4
Look at Figs 25 and 26 on page 90. Use a ruler and the information given in the captions to calculate the sizes of a sperm cell and an ovum.
5
Why do sperm cells have tails while eggs do not?
6
External fertilisation occurs in frogs and mullet. Suggest why these animals produce many more eggs than humans or mice do.
7
A male usually releases millions of sperm when it is mating with a female. a How many of these sperm do you think usually fertilise the female’s ovum? Suggest a reason for your answer. b Suggest why the male makes and releases so many sperm.
b Why is it possible to have fraternal twins with quite different features? c Suggest why twin births are much less common than single births.
Chapter4 Buildingblocksoflife
4.3 Reproduction and survival All organisms reproduce, but not all organisms do this in the same way. In animals, sperm can fertilise eggs inside the female’s body (internal fertilisation) or outside the female’s body after she has laid her eggs (external fertilisation). In mammals, birds and reptiles fertilisation takes place internally, while in most other animals the eggs are fertilised externally.
Fig 33
Fig 32
Fertilisation occurs externally in frogs. However, in some types of frogs, to make fertilisation more effective, the male clasps the female’s back and produces sperm while she lays her eggs.
Newly hatched turtles scramble towards the water. Many of the hatchlings die because there is no parental care and therefore no protection from enemies.
Birds and mammals produce considerably fewer eggs than reptiles, frogs and other animals. Young birds and mammals are generally dependent on their parents for food, warmth and protection from enemies. This increases the chances of survival of the young. For example, newly hatched birds cannot fly and cannot feed themselves and would certainly die without the protection of one or both parents. The table at the top of the next page compares the method of reproduction and the parental care of four different types of animals.
Caring for offspring The young animals that hatch from eggs which are laid and fertilised externally are completely independent of each other and of their parents. For example, when a frog’s eggs hatch, the tadpoles swim away from the leftover egg mass and have to find their own food and protect themselves from enemies. The eggs of reptiles are fertilised internally, but most reptiles do not care for their young after the eggs hatch. For example, sea turtles lay their eggs in the sand on the beach. The eggs are covered up and left to incubate. When the young turtles hatch, they dig their way to the surface and then scramble down the beach to the water. On their journey to the water, many of the young turtles are eaten by birds and other animals.
Fig 34
These newly hatched birds are completely dependent on their parents for food, warmth and protection from enemies.
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Bream (fish) Number of eggs produced each year How eggs are fertilised Parental care
Green tree frog
Magpie (bird)
Common wombat (mammal)
about 5 million
up to 2000
three or four
one
externally in water (sea) None—the eggs are left in the water, the young hatch and have to find food and protection.
externally in water (ponds and creeks) None—the eggs are protected by a mass of jelly, but after hatching the tadpoles have to find food and protection.
internally
internally
The female sits on the eggs until they hatch, then feeds and protects the young until they can fly.
A bean-sized baby is born, which develops inside the mother’s pouch for up to 10 months. It is then protected by the mother for another 10 months.
Parental care in seahorses Many animals have peculiar reproductive behaviours—the seahorse is one such animal. The seahorse is a bony fish (as distinct from non-bony fish such as sharks and rays), and in most bony fish fertilisation occurs externally. The female seahorse has a long, hollow appendage called an ovipositor. In some types of seahorses, she uses this to place her eggs in the male’s front belly pouch. Here he fertilises the eggs and protects them until they hatch (note the belly pouches on the two male seahorses in the photo).
< WEB watch > Go to www.scienceworld.net.au and follow the links to Wildlife Africa. This is a commercial website, but it has interesting information on the habits and behaviour of many African animals.
Reproduction and survival in flowering plants Trees, shrubs, bushes, palms and grasses are examples of flowering plants. All these plants reproduce sexually. Flowers contain the reproductive organs that make the sex cells. Pollen contains sperm cells and is made in the anthers. The ova, or eggs, are made in the ovaries. Pollen lands on the stigma of the flower (part of the female reproductive organs). The pollen tubes carrying the sperm then grow down the style and the sperm eventually fertilise the ova in the ovary.
Asexual reproduction
Some flowering plants are able to repr oduce asexually as well as sexually. For example, a stra wberry plant has flowers and produces fruit (strawb erries) containing seeds. The plant can also send out runners from which new strawberry plants grow . This form of asexual reproduction produces new plants with features identical to the original plan t.
Chapter4 Buildingblocksoflife
Investigate
10 OBSERVING FLOWERS Aim
PART B
To dissect a flower and identify its parts.
Di s sect in g a f lowe r
Materials • • • • • • •
afewdifferenttypesoflowers,eghibiscus petridish smallbrushortoothpick microscopeandmicroscopeslide cavitymicroscopeslide single-edgedrazorblade stereomicroscopeorhandlens
Method 1 Touch the end of the stigma with your finger or a pencil. Notice that it is sticky. 2 Use forceps to gently hold a flower while you cut it in half by cutting down the stem.
Planning and Safety Check CarefullyreadthroughPartsAandB,and make a list of the materials you will need for each part. Make a list of the safety precautions you will need to take in this experiment.
PART A
O bs er vi ng flo w er s Method 1 Use the diagram of a flower below to identify the following parts of one of your flowers— petal, sepal, stigma, anther, filament and ovary.
pollen on stigma
petal anther stamen filament
style
4 Use a stereomicroscope or hand lens to observe the ovary and ovules. Record your observations. Draw the arrangement of the ovules in the ovary. 5 Cutanantherinhalfandobservethepollen grains with the stereomicroscope. Repeat this for other flowers.
2 Repeat for other flowers. stigma
3 Look at the ovary. It contains a number of rounded objects called ovules. Each ovule containsanegg(ovum).
Record your observations.
Discussion 1 Why is the stigma sticky? 2 Different types of flowers have different shapes and sizes of pollen. Suggest a reason for this. 3 Infer the functions of the sepals.
ovary containing ova
sepal
pollen tube growing down towards ova
4 The petals on most flowers are brightly coloured. Suggest a reason for this. 5 What is meant by the word ‘pollination’. How is it different from ‘fertilisation’?
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ScienceWorld8forNSW Seeds and dispersal After the ova have been fertilised and the seeds develop, the petals, sepals and stamens of the flower wither and fall off. The ovary becomes a fruit with the seeds inside it (or sometimes on the outside of it, eg a strawberry). In some fruits, such as apples, the wall of the ovary thickens to form an edible fruit. In others, such as eucalypts, it is hard and woody. Seeds must be spread away from the adult plant to give the plants that grow a better chance of survival. This is called dispersal. There are four main methods by which fruit disperse their seeds. 1 The seeds fall out of the fruit and are carried away by the wind. 2 Animals eat the fruit, and the indigestible seeds pass out of the animal in its droppings. In this way the seeds can be spread many kilometres away from the adult plant. 3 Some seeds are sticky or have hooks or spikes which get caught in the fur or hair of animals. These seeds may be carried a long way before they fall off or are rubbed off. 4 Some fruit explode, throwing out the seeds.
Science in action Nick Hansa operates a large native plant nursery. For many years he has studied plants, and their methods of reproduction and seed dispersal. He often goes looking for the seeds of rare or endangered native plants. To do this, he needs to know the type of seeds the plants produce. For plants whose seeds are very small and are normally dispersed by wind, he covers the seed pods with special bags before the seeds mature. When the seed pods open, the seeds fall into the bag and are collected. Larger seeds are collected on the ground after they have fallen from the plants.
Activity 1 Collect about 10 different types of fruit or the seeds from the fruit. 2 Draw up a data table and classify the seeds into groups, depending on the way you infer they are dispersed. Include a brief description of the way each group of seeds is dispersed in your data table. 3 Find more fruits or seeds, classify them and add them to your table. 4 Take digital photos of the seeds or fruit and present your report in a PowerPoint presentation. Or design a poster to record and display your results and talk about your findings to the class.
< WEB watch > Go to www.scienceworld.net.au and follow the links to the websites below. Fruit and seed dispersal Has great photos and interesting descriptions. Seed dispersal Contains video clips showing types of seed dispersal.
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Growing plants from cuttings Many plants, including flowering plants, are able to reproduce from parts of the adult plant. This is a form of asexual reproduction called vegetative reproduction. Strawberry plants send out runners which produce new strawberry plants with leaves and roots. Potatoes are actually underground stems called tubers. The buds (‘eyes’) that develop on a potato can grow into new potato plants. The advantages of vegetative reproduction are that a plant can multiply quickly in a place which suits it, and that it stops other plants from growing near it. You can try growing plants from cuttings using the instructions opposite and the hints below.
Leaf cutting 1
sealed plastic bag— not touching the leaf
leaf stalk moist propagating mix
Helpful hints 1 Plants that are suitable for leaf cuttings are the ones which have soft, furry or velvety leaves: for example, African violet and coleus. You could also try begonia and snowflake (Euphorbia leucocephala). 2 Many types of shrub or small tree are ideal for growing plants from stem cuttings. 3 Daisies, fuchsias and native correas propagate easily from cuttings. For best results use a good quality propagating mix. 4 When growing plants from stem cuttings, dip the stem into some plant cutting powder (root growth powder). This will promote root growth on the cutting. 5 Do not over-water the propagating mix. It is best to add a little water often. 6 The plastic bag stops the plants from drying out and dying from water loss. You can also buy mini-hothouse trays at plant nurseries to grow your plant cuttings in.
Place the cut end of the leaf stalk in a pot of moist propagating mix. Then tie a large clear plastic bag over the pot. Make sure the bag does not touch the cutting.
2
If the leaf has large veins, use a sharp knife to cut three or four of them as shown. Lay the leaf flat on a pot of moist propagating mix. sealed plastic bag moist propagating mix leaf small cut in leaf vein
Stem cutting Cut a stem about 10 cm long and remove all but 2 or 3 of the leaves at the top of the stem. Dip the cut end of the stem in plant cutting powder. Then tie a large clear plastic bag over the pot. Make sure the bag does not touch the leaves.
bamboo stake for support
sealed plastic bag— not touching the leaf moist propagating mix
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Check! 1
Some of the following statements are false. Choose the false ones and rewrite them to make them correct. a Pollen contains the male sex cells and is produced in the ovary. b Fertilisation in most reptiles occurs externally. c Young reptiles are dependent upon their parents for food and protection. d All flowering plants reproduce sexually.
2
Describe the degree of care given to their young by most: a fish b frogs c birds d mammals
3
Suggest why the number of eggs produced per year by different types of animal decreases as the degree of parental care increases.
4
About 3 in every 100 000 eggs laid by a bream grow to be adult fish. a Suggest why the survival rate of the eggs is so low. b Use the table on page 94 to work out how many adult bream would be produced from the eggs laid by a bream in a year.
5
Use your own words to describe what the word ‘disperse’ means on page 96.
6
Suppose a particular type of plant can reproduce sexually (by seeds) as well as asexually (by sending out runners). List the advantages and disadvantages of each type of reproduction for the plant.
7
The coconut is a fruit with a very hard covering. It is hollow and does not sink in water. Suggest how coconut seeds are dispersed.
8
The photo shows a close-up of the seeds of the plant called cobblers pegs. Suggest how these seeds are dispersed.
challenge 1 Suggest why plants with bright flowers are mainly insect-pollinated, while grass flowers are usually wind-pollinated. 2 The seeds below are drawn at their actual size. a Whichone(s)doyouthinkwouldbe dispersed by the wind? Give a reason for your answer. b Whichone(s)mightbecaughtonthefur of animals. Give a reason.
seed A
seed B seed C
seed D
3 In most types of frogs, the eggs are laid in the water together in a mass of foul-tasting jelly, whereas fish lay their eggs individually in the water. Suggest how these two reproductive behaviours help in the survival of each type of animal. 4 Many types of animals show courtship behaviour before they mate and produce offspring. Use the internet and other library resources to find out what courtship behaviour means. Write a report of what you find out, giving examples. How does courtship help in the survival of each animal? 5 The ‘most devoted parent’ award for caring for offspring should go to the male emperor penguin. Use library books or the internet to find out why the emperor penguin would win this award.
Try doing the Chapter 4 crossword on the CD.
Chapter4 Buildingblocksoflife
Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
cell division
1 All organisms are made of ______. There are many different
cells
types of cells, with different shapes and different functions.
2 A ______ can be used to identify the various parts of a cell: the nucleus, cell membrane, cytoplasm and organelles. A ______, chloroplasts and vacuoles can be observed in plant cells.
3 Cells of the same type are generally found together in ______. Each type of tissue has a particular ______ in an organism.
4 Tissues are arranged in structures called ______ in multicellular organisms. Each tissue has a specific function in an organ.
5 An organism grows in size by making new cells in a process
cell wall
disperse fertilisation function mammals microscope organs reptiles sperm tissues
called ______.
6 In sexual reproduction, ______ occurs when the nucleus of a ______ cell joins with the nucleus of an ovum.
7 Organisms that care for their young (birds and ______) generally produce fewer eggs than those whose young are independent (fish, ______ and frogs).
8 Flowering plants show a variety of methods to ______ their seeds away from the adult plant.
REVIEW
1
2
A cell is observed under a microscope to have a nucleus, cytoplasm and organelles. The cell is: A definitely an animal cell. B definitely a plant cell. C either a plant cell or an animal cell. Which one of the following statements about cells is false? A Plant cells have large vacuoles. B A nerve cell is an example of a specialised cell. C All cells are rectangular or brick-shaped. D Plant cells have cell walls.
3
Match the cell part in the list with the correct description below. cell membrane chloroplast
cytoplasm nucleus
vacuoles cell wall
a an organelle that is involved in the process of photosynthesis b the jelly-like material that fills a cell c the part of the cell that controls its activities and keeps it alive d a covering that controls the movement of materials into and out of a cell e a thick, tough layer that helps support and protect the cell f liquid-filled spaces found in some cells.
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1 00
A microscope has a ×10 objective lens and a ×4 eyepiece lens. How big would an object 0.05 mm in diameter appear through the microscope?
REVIEW
4
Kate labelled a drawing of a microscope, but she made some mistakes. In your book write the correct names of parts 1 to 7.
5
1 2
4 5
Kate’s list 1 objective lens 2 body tube 3 focusing knob 4 eyepiece lens 5 stage 6 light 7 stage clips
10 The fruits and seeds from various plants are shown in the diagrams below. Infer how the seeds are dispersed by each type of plant. seed
fruit
open cap
seeds wing
seeds
a pine
seed
b apple
c eucalypt
seeds
3 6 fruit
spikes
7
d burr
e paw paw
Microscope licence test 6
a A male fish externally fertilises the eggs laid by a female fish. Give two reasons why many of the eggs are never fertilised. b Less than 0.5% of eggs laid by a frog reach adulthood, but over 60% of eggs laid by birds reach adulthood. Suggest reasons for this.
You will be working in pairs and assessing each other’s work in this practical test of microscope skills. You will be given—a microscope, microscope slide and cover-slip and a small piece of newspaper which contains a few letters. Your teacher will also give you an assessment grid to help you assess your partner’s task.
7
Explain how a unicellular organism is different from a multicellular organism.
8
Why is your stomach called an organ? Use the words cells and tissues in your answer.
Your task—to make a wet-mount slide of some letters on a small piece of newspaper without any air bubbles or excess water, and then draw it under the microscope.
9
The two cells in the drawing below are found in different tissues in your body. The cell from tissue A is box-like and makes a watery substance called mucus. The cell from tissue B is very flat. Infer the function of each tissue and where it might be found in your body.
The test—your teacher and the class will discuss what you have to do to pass the licence test. Your partner will then assess the quality of your wet-mount slide and drawing and record your results on the assessment grid. Remember, you can only pass or fail this test. If you fail you must repeat the test until you pass. Your teacher may issue you with a microscope operator’s licence when you pass the test.
Check your answers on pages 278–279. cell from tissue A
cell from tissue B
Chapter4 Buildingblocksoflife Learning focus: The place of social and ethical considerations in science
US AREA C O F D E B I R C PRES
Stem cell research Imagine if scientists could produce…
Christopher Reeve, the star of the film, Superman (1978), was paralysed when he fell from a horse in 1995. He was confined to a wheelchair and for the rest of his life he lobbied politicians to approve stem cell research to find a cure for people with spinal cord injuries. But what are stem cells? Stem cells are unspecialised cells that can develop into any one of over 200 different types of cells in the body. They can also divide and make accurate copies of themselves (see page 89). Scientists see the possibility of using these stem cells to treat some diseases and to replace damaged tissue. Where do scientists get stem cells? They can be found in bone marrow, but unfortunately these stem cells have already started to become the cells they will replace. However, stem cells in human embryos (3–5 days old) have not yet started to develop, so they are much better to use. So far scientists have used donated embryos remaining after IVF procedures. However, the problem is
If they could do this they could treat…
nerve cells
spinal cord injuries and Parkinson’s disease
heart muscle cells
damage caused by heart attacks
insulin-producing cells
diabetes
skin cells
burns and ulcers
retina cells
some kinds of blindness
whether it is ethically correct to use these human embryos. With any scientific development there will always be people who are for it and people against it. Religious groups and right-to-life groups are against the use of embryonic stem cells because they believe that even though they are unborn, the embryos have the right to life. There is also a fear that the use of stem cells could lead to humans being grown in the laboratory. On the positive side, the potential medical benefits of stem cell research are enormous, as listed in the table above. As Christopher Reeve once asked ‘Is it more ethical for a woman to donate unused embryos that will never become human beings, or to let them be tossed away as garbage when they could help save thousands of lives?’
Corner discussion 1 Your teacher will put the following signs in the four corners of the room: ‘agree’, ‘disagree’, ‘unsure but I think I agree’ and ‘unsure but I think I disagree’. 2 Do you think leftover human embryos should be used for stem cell research? Move to the corner that applies to you. 3 People in each corner now try to convince the people in the two unsure corners to join them. Everyone should be given a chance to contribute to the discussion.
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5 Energyin ourlives
Planning page Getting started
Investigate 11 Energy from food
5.1 What is energy? page 104
Activity page 108
5.2 Forms of energy page 107
Animation Roller-coaster
Investigate 12 Observing energy changes Assessment task 5 Energy changes
Investigate 13 Where does the energy go?
TRB
5.3 Energy comes—energy goes page 116
Main ideas Chapter 5 crossword
Review Learning focus: Different groups use different criteria to make a decision about an issue
Chapter 5 test
Prescribed focus area Nuclear power station inquiry
TRB
Chapter5 Energyinourlives t…
l learn abou
r you wil In this chapte
LearningFocus ● ●
different groups use different criteria to make a decision about an issue (page 125) viewpoints about issues with a major scientific component (page 125)
KnowledgeandUnderstanding ● ● ●
the law of conservation of energy (page 117) natural resources—fossil fuels and renewable & non-renewable energy (pages 118–120) technology—energy transformations (Section 5.2)
Skills ● ● ●
gathering first-hand information using dataloggers (Investigate 13) processing information—using mathematics (Investigate 11) presenting information—using graphs (Investigate 13)
You have probably used the word ‘energy’ many times, but what is energy? And are your ideas about energy the same as other people’s ideas? A good way to sort out your ideas is by brainstorming. To do this follow these six steps. 1 Sit in a group of about six people, facing each other. 2 Select someone to write down all the ideas. 3 Everyone should try to give at least one idea about energy—the more ideas the better at this stage. If you can’t think of anything here are some suggestions: ● Think of a sentence with the word ‘energy’ in it.
● Draw something with a lot of energy. ● What do we use energy for? List the different types of energy and give examples. 4 Don’t discuss the ideas yet, and don’t criticise anyone else’s idea. 5 After 2 or 3 minutes of brainstorming, discuss the group’s ideas about energy. You might like to select some of these ideas, write or draw them on a large sheet of paper and present them to the class.
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5.1 What is energy? If you use a torch for a long time, the light gradually gets dimmer and dimmer until it no longer shines. We say the batteries are ‘flat’—they have run out of energy. In a similar way you can’t pedal a bicycle or dig in the garden for too long because your body runs low on energy. If you don’t eat food, your body becomes weaker and weaker. This is why we say that food gives us energy. Everything around us depends on energy. Plants need energy from the sun to make food. Cars depend on the energy stored in petrol. Energy is used in homes, offices and industry to run all sorts of machines. It is used for lighting and heating our homes, and for cooking and storing food. Obviously energy is very important to us, but you probably found in Getting Started that it is difficult to say exactly what it is. It is easier to say what energy can do. If you have a lot of energy, then you can do a lot of work. You do work when you use a force to move something. Energy is the ability to do work. The more energy something has, the more work it can do. A gale-force 100 km/h wind has more energy than a gentle 10 km/h breeze. It can therefore do more work, for example turning windmills or ripping off roofs. Also, a raised sledgehammer has more energy and can do more work than an ordinary hammer, because it is heavier (has more mass). Let’s see who can bang their nail in the fastest.
Anything that does work must have a supply of energy. A motorbike will not keep running unless it is supplied with petrol. Petrol provides energy that the engine uses to do work. When
you pedal a bicycle, the energy comes from the muscles in your body, and your muscles get their energy from the food you eat. If you have a higher intake of energy than you need, then the extra energy is stored in your body as fat. On the other hand, an inadequate energy diet will lead to a thin and unhealthy body. Energy source - petrol
Fig 3
Energy source - food
The bicycle and the motorbike both need energy to move them.
Measuring energy In talking about how much energy something has, it is important to have a unit for measuring energy. In the same way that the litre is the unit for measuring volume, energy has a unit called the joule (J). This unit was named after a British scientist called James Joule. You use one joule of energy to lift a 100 gram mass one metre. Because a joule is only a small amount of energy, it is common to use kilojoules (kJ) and megajoules (MJ). The table on page 106 shows you how much energy is involved in various everyday activities. = 1000 joules 1 kilojoule 1 megajoule = 1 000 000 joules To find how much energy is stored in food, you can turn it into heat and measure what that heat can do. In Investigate 11 you will burn some food to do that. Of course there are no fires burning inside you. The food combines with oxygen in your cells in the chemical reaction called respiration, and heat energy is released.
Chapter5 Energyinourlives
Investigate
11 ENERGY FROM FOOD Aim To find out how much energy is released when a small piece of food burns.
Wear safety glasses.
Materials • smallpieceoffood,egNutri-Grainor Tiny Teddy • Bunsenburner • wiretomakeholder Teacher note: When • smalltesttube selecting foods remember • thermometer some students may be • measuringcylinder allergic to burning peanuts. • standandclamp
thermometer
Planning and Safety Check • Readthroughtheinvestigation,then describe to your partners what you have todo,measureandrecord. • Whatdatawillyouneedtorecord? • Whatsafetyprecautionswillbe necessary?
Method
2 cm
piece of food
wire holder
1 Use the measuring cylinder to measure exactly 10 mL of water into a small test tube. 2 Clamp the test tube as shown. 3
Use a thermometer to measure the initial temperature of the water.
4 Usethewiretomakeaholderforthepieceof food. 5 LighttheBunsenburner.Thenputthefood inthelame.Assoonasitcatchesire,holdit about2cmunderthetesttube. 6
Whenthefoodstopsburning,stirthewater gentlywiththethermometer,andmeasurethe final temperature.
7 Ifyouhavetime,repeattheexperimentwith otherfoods,egpotatocrisps,nuts,bread,rice, spaghetti.
Discussion 1 Byhowmanydegreesdidthetemperatureof the water increase? 2 Ittakes4.2joulestoraisethetemperatureof 1mLofwaterby1°C.So,tocalculatetheheat energygainedby10mLofwater,multiplythe temperatureriseby42.Youranswerwillthen beinjoules. 3 Doyouthinkalltheenergyfromtheburning food went into heating up the water in the test tube? Explain. 4 Were there any problems with the investigation? Ifso,suggesthowtheseproblemscouldbe fixed.
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Check! 6 1
a
For each of the following words, write a sentence to show that you understand its scientific meaning. force
work
energy
2
How do you know if something has energy?
3
Why can a cricket ball do more work than a golf ball moving at the same speed?
4
How many joules are there in: a a kilojoule? b a megajoule?
5
Use the table below to answer these questions. a How much energy does the average person get from the food they eat in a day? b How many kilojoules of energy does a burning match produce? c Which has more energy stored in it—a car battery or one litre of petrol? d Is there enough energy stored in a battery to boil a kettle of water?
b
7
Where does the energy needed to start a car come from? If you leave the lights on while your car is parked for a few hours, you may have trouble starting it. Why?
In a science lab, Alex and Holly are doing an experiment on the chemical energy stored in foods. Look carefully at the illustration. List at least five things they are doing that are unsafe.
Energy involved in everyday activities (in kilojoules) Energy produced by a burning match
10
Energy you gain by eating a chocolate biscuit
300
Energy needed to boil a kettle of water
700
Energy you use in walking 5 km
1000
Electrical energy stored in a car battery
2000
One day’s hard work
7000
Average energy gained from the food you eat in a day
11 000
Electrical energy used by a family home each day
80 000
Energy stored in five litres of petrol Energy made by a power station every second
160 000 2 000 000
8
Why do you puff and pant after running quickly or exercising?
9
In Getting Started on page 103 a student said that whenever a change occurs, energy is involved. For example, a kettle boils when you supply heat energy. Give as many examples as you can to illustrate this idea.
Chapter5 Energyinourlives
5.2 Forms of energy There are many different forms (types) of energy.
Kinetic energy Any moving object has kinetic (kin-ET-ic) energy. When you run you have kinetic energy. A moving train has a large amount of kinetic energy. The kinetic energy of the strong winds in a cyclone or tornado can cause a lot of damage. As a moving object slows down, it loses kinetic energy. When it stops it has no kinetic energy.
Fig 6
Gravitational potential energy Much of the energy around us is stored energy. We notice it only when it changes to other forms. It has the potential to do work, so stored energy is called potential energy. For example, the stored energy that something has when it is high up is called gravitational potential energy. This energy is there ready to be used because of the pull of gravity. When you are at the top of a slide you have gravitational potential energy—you have the potential to slide to the bottom. The heavier you are, and the higher the slide, the more potential energy you have. As you slide down, this gravitational energy is changed to kinetic energy. Energy can easily change back and forth between potential and kinetic.
The winds in cyclones and tornadoes have a huge amount of kinetic energy.
The amount of kinetic energy an object has depends on its speed. The faster the object moves, the more kinetic energy it has. For example, a cricket ball bowled by a fast bowler has more kinetic energy than one bowled by a spin bowler. Kinetic energy also depends on the mass of the moving object. The larger the mass, the greater its kinetic energy. A cyclist and a bus may be travelling at the same speed, but the bus has much more kinetic energy because it has greater mass.
Fig 7
At the top of the slide you have gravitational potential energy.
To see how energy changes back and forth between potential and kinetic, open the Roller-coaster animation on the CD.
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ScienceWorld8forNSW Elastic potential energy When you jump on a trampoline, what pushes you into the air? Try to visualise what happens in slow motion. The trampoline consists of a frame with a flexible mat attached by springs. When you land on the mat, it moves down, stretching the springs and storing energy called elastic potential energy in them. As the stretched springs return to their original size and shape, they release their stored energy. The mat is pulled back up, and you are thrown into the air. A wind-up toy stores elastic potential energy. So does a stretched elastic band. The more it is stretched, the more elastic energy it has, and the more work it can do. Fig 8
The elastic energy stored in the stretched trampoline springs throws you into the air.
Activity Make a motormouse as shown. large cotton reel
nylon or metal washer
rubber band
Step 1 Thread a rubber band through the cotton reel.
pencil
Step 3 At the other end, put the washer over the rubber band, then put a pencil through the rubber band.
To make it go, simply wind up the pencil until the rubber band is tightly twisted. Then put the motormouse on the floor and let it go.
broken match
What type of energy does the motormouse have when you let it go? tape
Step 2 Put a piece of broken match through one end of the rubber band. Tape the match to the reel so it will not move.
What type of energy did it have before you let it go? Energy is needed to wind up the motormouse. Where did this energy come from? Investigate the relationship between the number of turns of the pencil and the distance the motormouse travels.
Chapter5 Energyinourlives Chemical energy
Sound energy
Energy is stored in chemicals as chemical energy. When fuels such as wood and petrol are burned, this stored energy is released as heat and light. Foods also contain chemical energy which can be used by our bodies.
Sound is a form of kinetic energy caused by vibrating objects. It travels from place to place as sound waves. The louder the sound is, the more energy it has, and the more work it can do by vibrating things such as your eardrums.
Nuclear energy
Heat energy
Energy is also stored inside atoms as nuclear energy. It can be released from some atoms, eg uranium atoms, in nuclear power stations.
Heat is a form of energy that hot objects have. If heat energy is taken away from an object, it becomes cooler. This is what happens in refrigerators and in air-conditioned rooms.
Fig 10
Nuclear energy stored in hydrogen atoms is the source of the Sun’s energy.
Light energy Burning chemicals, very hot objects and stars all release light energy. It travels through space in waves (as do radio and TV waves, microwaves and ultraviolet waves). Light energy from the sun, called solar energy, is used by plants to make their food.
Electrical energy Electrical energy is widely used because it is easily transmitted by wires to the place where it is needed. It can be changed into other forms of energy by the many electrical devices that have been invented. It can also be stored in batteries.
light energy
kinetic energy
Fig 11
Electrical energy can be converted to...
heat energy
sound energy
Electrical energy is very useful because you can easily convert it into other forms of energy. Four different energy converters are shown here.
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Energy can be transferred from one object to another. In golf, a ball at rest is made to move by a moving golf club. Some of the kinetic energy of the club is transferred to the ball.
KINETIC ENERGY
HEAT ENERGY
The club has kinetic energy, but the ball has none.
Some of the kinetic energy of the club has been transferred to the ball.
Fig 13
Rubbing your hands together converts kinetic energy into heat energy.
Fig 14
The energy conversions that occur when a candle burns.
CHEMICAL ENERGY
Another everyday energy transfer occurs when you heat water on a stove. Heat is transferred from the gas flame or the electrical heating element to the water, causing it to boil. Energy can also be converted or transformed from one form into another. For example, if you rub your hands together they become warm. You have converted the kinetic energy of your moving hands into heat energy. You can describe this change with an arrow, as shown top right. Sometimes more than one form of energy is produced when an energy change occurs. A candle is designed to convert stored chemical energy into light, but some of the stored energy becomes heat. When you use an electric drill, not all of the electrical energy is converted to the kinetic energy of the drill. Some is lost as sound energy and some as heat energy (the drill becomes hot).
LIGHT ENERGY + HEAT ENERGY
Chapter5 Energyinourlives
Investigate
12 OBSERVING ENERGY CHANGES Aim To observe the energy changes that occur in a variety of situations.
Part
Planning and Safety Check Discuss the safety issues for each part of the investigation. Drawupadatatableliketheoneshownbelow.Foreach part,youwillrecordtheenergyconversion(s)thatoccur,andany energytransfer(s)fromoneplacetoanotherwithoutanenergy conversion.(Youmayneedtodiscussthiswithothers.)
Observations
Energy conversion(s) that occurred
Energy transfer(s) that occurred
A B
PART A
PART B
Materials
Materials
• • • •
• • • • •
pieceofmagnesiumribbon1–2cmlong pairofmetaltongs Bunsenburner heatproofmat
6voltbattery 3connectingwireswithalligatorclips heatproofmat fewstrandsofsteelwool switch
Warning: Do not look directly at the burning magnesium. Look to one side. The light is very bright and could damage your eyes.
magnesium ribbon
steel wool
Wear safety glasses.
6V switch
Method Method Light the burner. Use the tongs to hold the magnesium in the flame until it starts to burn. Thentakeitoutofthelameandholditoverthe heatproof mat.
Use the wires to connect the battery and switch as shown. Put the steel wool on the heatproof mat. Connect the wires to it. Press down the switch for a few seconds. Observe what happens.
Do not leave the switch on.
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PART C Materials • pieceofnichromewireorironwireabout 50 cm long • 2piecesofcopperwireabout50cmlong • multimeter • Bunsenburner
Be careful not to touch the hot wires. multimeter
Method
copper wire
Sandpapertheendsofthecopperwire,then twist the ends of the three wires together tightly as shown. Connect the ends of the copper wires to the terminals of the multimeter.(Themultimeter detectssmallelectriccurrents.)Putonejunctionin thecrushediceandheattheotherjunctionuntilit gets red hot. Observe the multimeter carefully.
nichrome wire
crushed ice
What you have made here is called a thermocouple. It is used to measure temperatures in ovens and furnaces.
PART D
PART E
Materials
Materials
• solarcellkit(consistingofseveralsolarcells connectedtoanelectricmotor,preferablyitted withapropeller)
• beakerofwater • tuningfork
tuning fork
electric motor
solar cells
Method
Method Placethesolarcellkitinbrightsunshine.What happens if you cover all or some of the solar cells?
Striketheforkedendofthetuningforkgentlyon theheelofyourshoe(notonthebench).Holdthe forknearyourear.Striketheforkagain,butthis timelookcloselyattheprongs. Striketheforkathirdtime,andtouchthe surfaceofthewaterinthebeakerwiththe vibrating prongs.
Chapter5 Energyinourlives
Check! 1
2
Copy and complete each of these sentences. a A moving object has ______ energy. b Energy that is stored is called ______ energy. c A boulder rolling downhill is losing ______ ______ energy, but gaining ______ energy. d Burning a piece of coal changes ______ potential energy into ______ and ______ energy. e Springs can ______ energy which can be released later. Make two columns, one headed ‘kinetic energy’, and the other ‘potential energy’. Place each of the following in the correct column. a an archery bow ready to shoot an arrow b a running high-jumper just before leaving the ground c a jet plane at the point of take-off d at the top of your bounce on a trampoline e a spring-loaded popgun f a child’s swing at its highest point g a child’s swing at its lowest point
3
What are the two types of potential energy?
4
The two rocks below have the same mass. Which one has more potential energy? Why?
d e f g h i j k l 7
Main energy conversions
battery
electrical to sound
electric motor
electrical to light & sound
lift going up
chemical to kinetic
solar cell
chemical to heat & light
radio
nuclear to electrical
TV
chemical to electrical to light
torch
light to electrical
car
chemical to electrical
campfire
electrical to kinetic
nuclear power station
electrical to kinetic to gravitational
8
Maria connected a coil of wire to a milliammeter, as shown. When she pushed a magnet quickly into the coil, the ammeter showed that there was an electric current flowing. When she stopped moving the magnet, no current flowed. Write a sentence describing what happened in terms of energy changes.
9
Go back to Getting Started on page 103. How have your ideas about energy changed after working through this chapter?
B
6
What is the difference between an energy transfer and an energy conversion? Give examples. What form(s) of energy do the following have? a a diver standing at the top of a tower b a bent ruler c a block of chocolate
Pair up these lists correctly in your notebook.
Object
A
5
a burning log a glowing firefly a lightning flash ocean waves a slice of bread a TV set (turned on) a warm pizza the water in a waterfall a wound-up toy
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challenge 1 Copy and complete the table below. Energy used
Energy converter
Energy produced
light globe
3 4
electric fan
5
petrol engine kinetic
electric torch cell
6
steam engine atomic bomb electrical
heat slingshot or catapult
kinetic
7
waterwheel kinetic
sound
2 What energy changes are being described in eachofthefollowing?UsearrowsasinFig13 andFig14onpage110. a Thewindblewhard,turningthewindmill noisily as it pumped the water from deep underground into the trough. b Atthelickofaswitchthewashingmachine started turning and churning the clothes.
8
9
c ‘…two,one,zero.’Therocketbelchedire andsmoke,thegroundshookand,witha deafeningroar,therocketleftthelaunchpad. d Thelightninglashed,andthethunder crashed. The gum tree was split right down the middle. List at least three different things in which chemical energy is stored. Into what forms of energy does the human body convert the chemical energy in food? Ifaneonstreetlightconverts300Jof electricalenergyinto200Jofheatenergyand 90Joflightenergy,howmuchsoundenergyis produced?(Assumethesearetheonlyenergy conversionsthatoccur.) Giveanexampleofsomethingthathas: a gravitational energy due to its high position b elastic energy because it has been stretched c chemical energy In each case explain how the energy can be used to produce movement. Howcouldyoudemonstratethatsoundisa formofkineticenergy? Drawacartoonofajack-in-the-box.Discuss with another student how potential energy is involved,andhowthisenergychangeswhen the lid is opened. Write a caption to describe your cartoon in energy terms. Whatisthesourceofenergyforasolarpowered car? What energy conversion occurs whenthecarismoving?Howwouldsuchcars operate at night or on cloudy days?
Chapter5 Energyinourlives
t r y t his 1 Build a mousetrap racer as shown. To make it go, simply wind the string around the axle by turning the rear wheels. Then put it on the floor and release it. What energy changes occur?
3 To make a windmill you will need 2 empty soft drink cans, a wire coathanger, scissors and pliers. Carefully cut the bottom 4 cm off a soft drink can (A). Cut the top rim off a second can (B). Cut strips 2 cm wide to within 2 cm of the bottom of can B.
trapper arm string
cut
can A
Wrap string around axle.
mousetrap
< WEB watch > You could do a project on mousetrap racers. Go to www.scienceworld.net.au and follow the links to Mousetrap racers. 2 Make a working model of a waterwheel as shown below. In this device, the gravitational energy of the water is changed to kinetic energy which is then transferred to the spinning wheel. water
plastic blades
knitting needle
styrofoam wheel
plastic soft drink bottle with holes in bottom
can B
Put the base of can B into can A, then fold back the strips to form vanes, as shown in the photo. Make holes in the middle of the base of each can. Put the coathanger wire through these holes and bend it as shown. Find some moving air and watch it spin. Can you modify it to make it work better?
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5.3 Energy comes—energy goes Wasted energy When we use energy it often changes from one form to another. For example, the cyclist is using the chemical energy stored in her muscles to pedal her bike. So chemical energy is converted into useful kinetic energy. But as she pedals she gets hot. So some of her energy is wasted as heat energy. These energy changes can be shown by an energy arrow. The thickness of the arrow shows roughly how much energy is converted into the different types. Sometimes one energy change follows another. The series of steps is called an energy chain. For example, the energy chain for a moving car has three steps. 1 The stored chemical energy of the petrol is converted into heat energy when the petrol is burnt in the car’s engine. 2 Some of this heat energy is converted into kinetic energy of the moving engine parts. 3 This kinetic energy is then transferred through the gears to the wheels.
waste heat
chemical energy in muscles
Fig 27
kinetic energy of bike and rider
An energy arrow for riding a bike
The energy chain is not 100% efficient, since each step in the chain involves some loss of energy. Friction between the moving parts of the engine produces heat. This heat is transferred to the air around the car. Also, as the engine parts move they produce sound energy. Therefore, not all the stored energy in the petrol is used to make the car’s wheels turn. In fact, engineers have calculated that if you start with 100 joules of chemical heat energy kinetic energy chemical kinetic energy energy, you end up released of wheels and energy stored of moving with only 25 joules as petrol burns car in petrol engine parts of kinetic energy. The other 75 joules is waste heat and sound wasted as heat and sound. 80 J Note that the total amount of energy you end up with is the same as the amount you started chemical energy with. The 75 joules of waste heat and sound in petrol 100 J kinetic energy of car 20 J from the car is not useful, because it cannot be used again. All energy converters waste energy like this—usually as heat. The longer the energy Fig 28 Energy chain and energy arrow for a car chain, the more energy that is wasted.
Chapter5 Energyinourlives The efficiency of an energy converter is the percentage of the input energy which is turned into useful energy. Efficiency =
useful energy × 100 input energy
For example, the efficiency of a car is about 25%. Because there is always some waste energy, the efficiency of an energy converter is always less than 100%.
Fig 29
This label from a microwave oven shows that for every 1400 watts of electricity (1400 joules per second) the oven produces only 900 watts of heat. It is therefore 64% efficient.
Conservation of energy You have looked at examples of how energy is converted from one form to another. After thousands of such observations, scientists decided that there is a special rule or law that describes energy changes. The law of conservation of energy says that energy cannot be made or destroyed—it can only be converted from one form to another. This means that the universe always has the same amount of energy, even though this energy is constantly being converted from one form to another and being transferred from one place to another. To help you understand the law of conservation of energy, think about a board game such as Monopoly, where money can be used for buying and selling. The money is transferred between players and the bank, but the total amount is always the same. At the end of the game, if all the players add up their cash, the total should be the same as at the beginning, although it will be distributed differently. The same applies to energy. It moves around and changes its form, but the total amount is always the same.
Investigate
13 WHERE DOES THE ENERGY GO? Aim To find out what happens to the heat energy as a container of hot water cools down.
Materials • • • • • •
2Lice-creamcontainerorsimilar 250mLbeakerorsimilar 2thermometers boilingwater You could use a graphpaper datalogger with temperature probes. stopwatch
Method 1
Open the ICT skillsheet on using dataloggers on the CD.
Use one of the thermometers to measure the temperature of theair(roomtemperature).
Planning and Safety Check ReadthroughSteps1–6sothatyouknow exactly what you have to do. YouwillneedtodoSteps2,3and4quickly. Design and draw up a suitable data tabletorecordyourresults.Youwillbe measuring the temperature inside and outsideabeakerofhotwatereveryminute for at least 15 minutes. 2 Putthebeakerintheice-creamcontaineras shownonthenextpage.Add200mLofhot watertothebeaker—beingcarefulnottoburn yourself. 3 Pour1500mLofcoldwaterintotheice-cream container.
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hot water
Label the two curves and draw a third line on your graph to represent room temperature during the experiment.
cold water
Discussion 1 Copy and complete the following summary.
4 Placeonethermometerinthebeakerand theotherintheice-creamcontainer.Startthe stopwatch and measure the temperature inside andoutsidethebeaker. Recordthesetemperaturesinyourdata table(fortime=0). 5 Measure the inside and outside temperatures everyminute,usingthethermometerstostirthe watergently.(Don’ttakethethermometersout ofthewater.) Keeptakingtemperaturesfor15–20 minutes. 6 Plot both sets of results on a graph of temperature(verticalaxis)versustime (horizontalaxis).Drawasmoothcurveforeach setofpoints.(Thecurvedoesn’thavetogo througheachpoint—solongasitshowsthe generaltrendoftheresults.)
Where does energy come from? We use a lot of stored energy without really thinking about where it comes from. We get food from the supermarket, petrol from the service station, and electricity through power lines. But where does the energy in these things come from in the first place? Green plants store the energy of sunlight as chemical energy (food), using the process of photosynthesis. Animals that eat these plants use most of the energy for their body activities
Asthetemperatureofthewaterinthebeaker decreased,thetemperatureintheice-cream container______.Thewaterinthebeaker ______energy,whilethewaterintheice-cream container ______ ______.
2 Whichistheindependentvariable,andwhichis the dependent variable? 3 Calculate how much heat energy the water in thebeakerlost(volumeofwaterinmLxrisein temperature). 4 Calculate how much heat energy the water in theice-creamcontainergained. 5 Are the two amounts of heat energy the same? Ifnot,explainwhytheyaredifferent. 6 Describe the transfer of heat energy in this experiment.Doyouthinkthatthetotalamount of energy changed? Explain. 7 Onyourgraph,lookatthecurveforthewater insidethebeaker.Thecurveissteeptostart with,thenlevelsout.Suggestareasonforthis. 8 Predict what would happen to the temperatures insideandoutsidethebeakerifyoucontinued this experiment for an hour or more.
and store the rest. So animals that eat plants and other animals are using stored energy that came originally from the sun. Most of our electricity comes from power stations that burn coal to produce steam. This steam is then used to turn turbo-generators that produce the electricity. The petrol we use in our cars is produced by the distillation of crude oil. We also use natural gas for heating. Coal, oil and natural gas are called fossil fuels because they were formed from plant and animal remains.
Chapter5 Energyinourlives
How oil was formed How coal was formed When geologists examine the fossil plants in coal, they find that these remains come from plants that no longer exist on Earth. They infer that these plants probably grew in moist warm swampy forests about the time dinosaurs roamed the Earth. This suggests that present coal deposits probably formed from ancient plants that existed millions of years ago. Over a period of time the climate changed and the plants in these forests died, leaving layers of decaying wood and other plant material. Sediments such as sand and mud were then deposited on top of the old forest, trapping the plant material. As more and more sediments were deposited, the weight of these layers forced out much of the water and gases from the plant material, making it richer in carbon. Thus began the slow change over millions of years from wood to coal.
Geologists infer that oil was formed from microscopic plants and animals which died and then settled to the bottom of shallow seas and lakes. The remains of these marine organisms were covered quickly by sand and mud. After being buried by thick sediments and subjected to heat and pressure over millions of years, biochemical processes formed crude oil, various gases and water. At the same time the sediments hardened to form rock. Once formed, the oil and natural gas slowly seeped towards the Earth’s surface through porous rocks like sandstone which soak up the oil like a sponge. Sometimes the oil and gas were trapped (often under pressure) beneath a layer of non-porous rock like shale, through which they could not escape. To extract the oil and gas a pipe has to be drilled down through the rocks above. sea layer of dead marine life
swampy forest
sand
other layers remains of rotting forest
layer of mud containing droplets of oil, water and gases
sand
layers of sediments old forest
non-porous rock
rocks raised above sea level and folded ground level gas oil
weight of sediments layer of coal forms
water porous rock
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ScienceWorld8forNSW Renewable or non-renewable There is a major problem in using fossil fuels as a source of energy. They are non-renewable. They have taken millions of years to form from energy that came originally from the sun. Yet once they have been burnt in our cars or in power stations they are gone forever. This is why we say they are non-renewable. The process of obtaining energy from fossil fuels is also very inefficient, as shown below. In fact, there is more energy reaching the unused energy (light and heat)
energy used by plants
chemical energy stored in plants (photosynthesis)
Earth in 10 days of sunlight than in all the fossil fuels on Earth! It makes much better sense to use renewable energy sources that can be replaced as they are used. We now have the technology to capture the sun’s energy directly for our use. For example, solar cells are used to provide power supply systems for remote and rural areas. Hydroelectricity and wind power are other renewable energy sources. You will find out more about renewable and non-renewable energy in later studies. heat energy wasted as coal formed
chemical energy stored in coal
waste heat energy
coal burnt
electrical energy coal-burning power station
ancient forests coal mine
coal
Fig 33
Check! 1
Suppose you wind up a toy car and let it go. a Where did the energy needed to wind up the toy come from? b Where has this energy gone when the toy stops moving? spring
An energy arrow showing how the electrical energy we use came initially from solar energy. Notice how much energy is wasted at each step.
2
When using a hacksaw to cut a piece of metal, the blade and the metal both become hot. Explain in energy terms why this happens.
3
Classify the following energy sources as renewable or non-renewable: coal, diesel fuel, LPG gas, ocean waves, the sun, uranium, wind, wood.
Chapter5 Energyinourlives
4
Copy the boxes and complete the two energy chains below.
A
B
5
Draw an energy chain that shows the energy changes from the sun to the woman.
6
Explain in your own words how the petrol used in cars came originally from energy from the sun.
7
A hot water system is 65% efficient. If it is supplied with 3000 joules of electrical energy, how much heat energy does it produce?
8
To charge a battery you have to supply energy. But you never get as much energy from the battery as you use to charge it. Why is this?
9
The diagram on the right shows the energy changes in a coal-burning power station. a Draw an energy arrow to describe what happens in the power station. b How many joules of heat are lost to the environment for each 100 joules of chemical energy stored in the coal? c A small amount of energy is lost when the kinetic energy of the turbo-generator is converted to electrical energy. Infer how this energy is lost. d What is the efficiency of the turbogenerator? e What is the overall efficiency of the power station?
coal 100 joules of chemical energy
20 joules of waste heat energy (chimneys)
steam
80 joules of kinetic energy
44 joules of waste heat energy (cooling water) turbogenerator
36 joules of kinetic energy
35 joules of electrical energy
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challenge 1 Herearetheeficienciesofiveenergyconverters. torch battery 90% solar cell 10% electricmotor 60% filament light bulb 5% luorescentlight 20% a Draw a bar graph to display this data. b Draw a table that shows for each of the energyconverters: • thetypeofinputenergy • thetypeofoutputenergy • thetypeofwastedenergy. c Why is it cheaper to light schools with fluorescent lights rather than filament light bulbs? 2 What form of energy does a frictional force usually produce? 3 Peterburnthisingeronafrypan.He immediately put his burnt finger in some crushed ice. Explain in energy terms what happenedwhen: a he burnt his finger b he put his finger in the ice. 4 Twocarscollidehead-on.Whathappensto thekineticenergythateachcarhadbeforethe crash?
5 Machines that have moving parts can be made to run more efficiently. Use examples to explain how this can be done. 6 Thediagramshowssomeone’s idea of a perpetual motion machine(adevicewhich once started needs no more energytokeepgoing). Explain why it cannot supply electricity to the house. hydro-electric power station
pump
7 State the law of conservation of energy. Illustrate your answer by describing the energy changes thatoccurwhenaireworksrockettakesoff andexplodeshighintheair,emittingcoloured balls of light as the remaining pieces fall to the ground. 8 Writeastory(approximatelyapage)about‘The yearthesunstoppedshining’. 9 Lookatthediagrambelow.Drawanenergy chain tracing the energy changes from the sun to the energy user on the left.
electric whipper snipper
dam
hydro-electric power station
Chapter5 Energyinourlives
Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
chains
1 ______ is the ability to do work. It is measured in ______ (J).
conservation
2 ______ energy is the energy an object has because of its
converted
movement. Potential energy is ______ energy.
3 There are many different ______ of energy; for example, light, heat, ______ and sound.
coal and oil
electricity energy forms
4 Energy can be ______ from one object to another, and it can be ______ from one form to another.
heat joules
5 When an energy change occurs some energy is always wasted
kinetic renewable
as ______.
6 The law of ______ of energy says that energy cannot be made
stored transferred
or destroyed.
7 Most forms of energy (including fossil fuels) can be traced back to the sun using energy ______.
8 ______ energy sources such as solar energy can be replaced as they are used. Non-renewable sources such as ______ cannot be replaced when they are used.
REVIEW
Try doing the Chapter 5 crossword on the CD.
1
The electricity you use in your home is a form of energy that came originally from: A electricity in thunderstorms B coal C the potential energy of water stored in dams D the sun
2
Which one of the following is false? A If an object has energy it can do work. B A raised object has potential energy. C Energy can appear from nowhere and also disappear. D When you hit something you are transferring energy.
3
Which would require most energy? A riding a bicycle on level ground B riding a bicycle up a hill C walking D doing your homework
4
Which of the following involves a transfer of energy from one object to another, rather than a change in the form of the energy? A Hot tea poured into a cup makes the cup hot. B A hydro-electric power station uses running water to generate electricity. C The tyres of a moving car become hot. D Oil is burnt to heat a room.
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REVIEW
5
a In which position does the roller-coaster car have the most gravitational potential energy? b In which position does it have the most kinetic energy?
9
Bree found this data for Australia’s energy use in 2003–04. Substance
Percentage of total
coal oil natural gas hydro-electricity wood, bagasse and other renewables
41.8 33.8 19.6 1.1 3.7
a Draw a pie chart to display this data. b Which fossil fuels are used in Australia? c What percentage of Australia’s energy use is from renewable sources? d Use a dictionary to find out what bagasse is.
6
7
For every 100 joules of energy used by an electric light bulb, you get only about 5 joules of light energy. a What happens to the other 95 joules of energy? b What is the efficiency of the light bulb? A rock is held above a concrete path and dropped. Copy and complete the energy chain below, by putting the correct energy forms in the two empty boxes.
10 Write an energy chain to describe the energy changes that occur in a hydro-electric power station (shown below). dam
water intake
electric generator
turbine river
KINETIC
HEAT
8
11 A ball bounces because the kinetic energy it has when it hits a surface changes to elastic potential energy as the ball is pushed slightly out of shape. This elastic energy then changes back to kinetic energy as the ball leaves the surface. Design an experiment to compare the efficiency with which different types of balls change their kinetic energy into elastic potential energy when they bounce.
David said that electrical energy is made in power stations. Is he correct? Explain using the law of conservation of energy. Check your answers on page 279.
Chapter5 Energyinourlives Learning focus: Different groups use different criteria to make a decision about an issue
US AREA C O F D E B I R C PRES
Nuclear power station inquiry A chairperson will organise the inquiry and keep order. You will start with a speaker from the ‘for’ side, then one from the ‘against’ side, and so on. The undecided group will be given time to ask their questions. Finally, each of the members of the undecided group will vote for or against the power station, based on the arguments presented by the groups.
FOR Federal government Australia must reduce its greenhouse gas emissions, and nuclear power stations don’t produce carbon dioxide as coal-burning power stations do.
Australian Nuclear Science and Technology Organisation (ANSTO) Imagine there is a proposal to build Australia’s first nuclear power station at Nelson Bay, just north of Newcastle. There are individuals and groups who have many different viewpoints on this proposal. So a public inquiry is to be held in Newcastle to discuss the new power station, and to vote on whether it should be given the goahead. For the inquiry the class will be divided into seven different groups: • For—three groups are in favour of the nuclear power station. Against—another three groups are against the • power station. • Undecided—the rest of the class are undecided and it is their job to develop a set of questions to ask the speakers before they vote. Each of the groups is to prepare a 3-minute speech for the inquiry, using the brief notes in the box. You will need to do research to fill out the details of your argument for or against the proposal. You will also need to elect a speaker to present the case prepared by your group.
Coal-burning power stations produce sulfur dioxide gas and ash containing toxic heavy metals. Nuclear power stations don’t.
Economist Australia has huge reserves of uranium, and nuclear power could be produced at a competitive price. The use of nuclear power would also reduce the cost of the government’s emissions trading scheme.
AGAINST Australian Conservation Foundation (ACF) Nuclear wastes are radioactive for hundreds, sometimes thousands of years, and the nuclear industry does not have a long-term storage plan.
ACTU Any accident at the power station is likely to release dangerous radiation, and there is a risk of earthquakes in the Newcastle area.
People for a nuclear-free Australia (PNFA) Instead of funding a nuclear power station, the government should be encouraging the use of renewable energy sources such as wind and solar.
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6 Investigating heat
Planning page Getting started Investigate 14 Heat and temperature Skillbuilder page 131 Using maths equations
6.1 Heat and temperature page 128
Animation What effects the rate?
6.2 Heat transfer page 134
Animation Enzyme action
6.3 Heat in everyday life page 143
Assessment task 6 Methods of cooking
Activity page 134 Activity page 136 Investigate 15 Which absorbs more radiation? Experiment Which is the best insulator?
TRB
Main ideas Chapter 6 crossword
Review Chapter 6 test Learning focus: Models and theories that have been modified or rejected
Prescribed focus area How a theory was rejected
TRB
Chapter6 Investigatingheat t…
l learn abou
r you wil In this chapte
LearningFocus ●
models and theories that have been modified or rejected (pages 128 and 149)
KnowledgeandUnderstanding ● ●
heat energy the particle theory of matter (page 129)
Skills ● ● ● ● ●
planning first-hand experiences and choosing equipment or resources (Investigate 14 & 15 and Experiment page 140) gathering information from a histogram (page 131) processing information (Investigate 14, Skillbuilder page 131 and Experiment page 140) problem-solving (Experiment page 140) the use of creativity and imagination (pages 145–146)
The photo shows a glassworker. The molten glass inside the furnace is at a temperature of more than 1000°C. The furnace and glass give off a huge amount of heat. ● What do you notice about the end of the metal rod in the furnace?
● List the items of protective clothing the worker is wearing. ● Suggest why the glassworker’s clothing is silver-coloured. ● Describe two ways in which the heat moves from the furnace to the glassworker.
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6.1 Heat and temperature Heat is very important in our lives. Our body functions best at a temperature of about 37°C. If we get too hot or too cold we feel uncomfortable. If our body temperature rises too far above normal or too far below normal we can die. We use fans, heaters and air conditioners to keep us comfortable. The walls and ceilings of our homes are insulated to keep heat in during winter and out during summer. We use heat for cooking food and for heating water. Heat is used by industries to make new materials such as glass, steel and plastics. Our cars produce heat when they burn petrol. Heat from burning coal is used to generate electricity. But what is heat? And how is it different from temperature? Several hundred years ago, people thought of heat as a special fluid called caloric which flowed in and out of objects as they were heated or cooled. An American named Benjamin Thompson, who later moved to Germany and became Count Rumford, showed that this caloric idea was incorrect. He observed that when holes were drilled in brass to make cannons, so much heat was produced that water had to be poured over the cannons to cool them. From this
Fig 2
Drilling brass cannons produced considerable heat. From this, Count Rumford inferred that heat is a form of energy.
Rumford inferred that it was the movement of the drills that made the cannons hot. The kinetic energy of the drill had been converted into heat energy. People soon realised that some heat is always produced when energy changes from one form to another. In other words, heat is a form of energy (page 109). For this reason it is measured in joules (J). Heat and temperature are not the same, but there is a connection. Temperature is a measure of how hot or cold something is. It is measured in degrees Celsius (°C) using a thermometer. You have probably used ‘sparklers’. Each spark is actually a tiny piece of white-hot metal, and its temperature may be as high as 800°C. (The temperature of boiling water is only 100°C.) However, if a spark falls on your hand you don’t even feel it. This is because each spark contains only a small amount of heat energy. Some of this heat energy is transferred to your skin, but the resulting temperature rise is so small that you usually cannot detect it. Fig 3
Fig 3
Each tiny spark has a high temperature but contains very little heat.
Chapter6 Investigatingheat Heat and the particle theory We can use the particle theory to explain heat. When you heat an object, the particles in it move more rapidly and therefore have more energy. This is why the temperature is higher. When the particles lose energy and move more slowly, the temperature is lower. Look at the diagram below. When a hot object comes into contact with a cold object, heat flows from hot to cold until both objects are at the same temperature. The rapidly moving particles in the hot object transfer some of their energy to the particles in the colder object. The larger the temperature difference, the faster the transfer. Cool objects in warm places take in energy from their surroundings. For example, an ice block melts quickly on a hot day. Warm objects such as a cup of hot coffee lose heat energy to their cooler surroundings.
The particle theory states that all matter is made up of tiny little particles....
....and that these tiny particles are in a constant state of motion.
The more energy the particles have, the faster they move.
Did you know? If the temperature of a substance was lowered to –273°C, its particles would have no energy at all and would therefore be completely still. This temperature is called absolute zero, and scientists have come close to this in some experiments.
hot metal
cold water
direction of heat transfer
Heat transfer has stopped. Water and metal are at the same temperature.
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Investigate
14 HEAT AND TEMPERATURE Aim To find answers to these questions: A Does the mass of a substance influence how much its temperature rises? B Does the type of substance influence how much its temperature rises?
hotplate
Materials • • • • • • •
hotplateorburner,tripodandgauze 250mLbeaker thermometer measuringcylinder,100mL stopwatch Flammable olive oil papertowel
Planning and Safety Check Read through both parts of the investigation. • Discusswithyourteacherthesafestway to handle the hot beaker. • HowisPartBdifferentfromPartA? • Suggestwhyahotplateisusedinthis experimentinsteadofaBunsenburner. Draw up a data table like the one below. Temperature of Rise in the liquid (°C) temperature before after (°C) heating heating 50 mL water
2 Adjustthehotplateortheburnerto medium heat. Leave it at the same setting throughout the experiment. This is to make sure that the heater supplies heat at a constant rate. 3 Placethebeakerofwateronthehotplatefor exactly 2 minutes. Then remove the beaker from the hotplate, stir the water gently with the thermometer and read the temperature. Record this temperature in the data table. Calculate and record the rise in temperature. 4 Empty the beaker, cool it under running water, and dry it. 5 Add100mLofwatertothesamebeakerand measure the temperature before and after heatingfor2minutes.
100 mL water 60 mL olive oil
Record your results in the data table.
120 mL olive oil
Discussion
PART A
1 Which variable did you change in this investigation?
Method
2 Which variables did you keep the same?
1 Use the measuring cylinder to add exactly 50 mL of water to the beaker.
Conclusion
Use the thermometer to measure the temperature of the water, to the nearest degree. Record this in the data table.
Write an answer to the question How does the mass of a substance influence how much its temperature rises?
Chapter6 Investigatingheat
Discussion
PART B
WhichvariabledidyouchangegoingfromPartA toPartB?Whichvariablesdidyoukeepthesame?
Method RepeatPartA,butthistimeuseoliveoil—60mL and120mL.(Sixtymillilitresofoliveoilhasthe same mass as 50 mL of water.) Record all results in the data table.
From Investigate 14 you can conclude that— A The same amount of heat will raise the temperature of 50 mL of water twice as much as it raises the temperature of 100 mL of water. B The same amount of heat will raise the temperature of olive oil more than it raises the temperature of an equal mass of water. In other words, olive oil heats up more quickly than water does. The bar graph below shows the amounts of heat needed to 4.2 J warm 1 gram of various materials by 1°C. You could also predict that if you supply twice as much heat to water or olive oil you raise 2.0 J the temperature twice as much. 0.9 J
0.7 J 0.4 J
e
m
Fig 7
ry
er
pp co
Write an answer to the question How does the type of substance influence how much its temperature rises?
Skillbuilder Using maths equations The amount of heat energy needed to raise the temperature of 1 gram of a substance by 1°C is called its specific heat capacity. For example, the specific heat capacity of water is 4.2 joules per gram per °C. To calculate the heat needed to change the temperature of something, you can use this mathematical formula: heat (J) = mass (g) x specific heat capacity x change in temperature (°C) So, the heat needed to raise the temperature of 50 mL (50 g) of water by 10°C can be calculated as follows: heat
=
50 g x 4.2 x 10°C
=
2100 joules
Use the specific heat capacities from the bar graph on the left to answer these questions.
0.1 J u rc
Conclusion
s as gl a
m lu
i
u ni
l
m o
e liv
oi
er
at w
The heat needed to raise the temperature of 1 gram by 1°C. You will notice that solids generally heat up more easily than liquids.
To summarise, the amount of heat gained or lost by an object depends on three variables: • its mass • the temperature change • what it is made of. You can calculate the amount of heat that is transferred if you know these three variables.
1 How much heat is required to: a raise the temperature of 100 mL of water by 10°C? b raise the temperature of 60 mL of olive oil by 10°C? 2 A 5 gram block of aluminium was heated from 30°C to 100°C. How much heat energy was needed? 3 How much heat is given out when 60 g of copper cools from 100°C to 20°C? 4 Using your results from Investigate 14, calculate the amount of heat transferred to 50 mL water, 100 mL water, 60 mL olive oil and 120 mL olive oil. Are they all the same?
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Check! 1
2
Decide which of the following statements are true and which are false. Rewrite the false ones to make them true. a Heat is a form of energy. b When you strike a match, you convert kinetic energy into heat energy. c When an energy change occurs, some heat energy is always produced. d A block of ice contains no heat energy. e Heat is measured in degrees Celsius. f As an object becomes hotter, its particles move more rapidly. g Heat travels from cold objects to hot objects.
5
Josh heats two identical iron nails together until they are red hot. He drops one into 50 mL (50 g) of water and the other into 60 mL (50 g) of olive oil. If both liquids are at the same temperature to start with, predict which will be hotter one minute after the nails are dropped in? Explain your answer.
6
Explain why heat energy can be considered a form of kinetic energy.
7
Eva had four identical beakers containing different amounts of water, as shown. She heated them for different lengths of time and none of them boiled.
When Faith used an electric hair dryer to dry her hair, the hair dryer became quite hot. What energy change has occurred?
a b c
3
a b
4
B
half full
half full
5 minutes
8 minutes
C
D
full
full
5 minutes
10 minutes
Which beaker of water received the most heat? Which beaker would you predict had the highest temperature after heating? Which beaker would have the lowest temperature after heating?
8
Samples of 50 g of aluminium, copper, glass and water all initially at 20°C are heated for 5 minutes on a hotplate with a constant setting. Predict the order (from highest to lowest) of the final temperatures of each sample. See the bar graph on the previous page.
9
Suggest why mercury is used in thermometers. (Hint: see the bar graph on the previous page.)
Which is hotter—a cup of water at 50°C or a bathtub full of water at 50°C? Which contains more heat energy?
A cold saucepan is put into a sink containing hot dishwashing water. a What will happen to the temperature of the saucepan? b What will happen to the temperature of the water? c Does heat flow from the water into the saucepan, or from the saucepan into the water?
A
10 On a hot summer’s day the dry sand at the beach can be almost unbearable to stand on, while the water is cool. Try to explain this temperature difference.
Chapter6 Investigatingheat
challenge
2 Harrydidanexperimentanddrewthese diagrams to show his method.
1 Ramone was making some ice blocks from fruitjuice,anddecidedtoinvestigatetheir temperatureastheycooledinthefreezer.He put a thermometer in one of them and measuredthetemperatureevery10minutes. Hisresultsareinthetablebelow. a Was heat being added to the ice blocks during Ramone’s experiment, or being taken away from them? b PlotRamone’sresultsonalinegraph. c Suggestareasonforthelatpartofthe graphbetween40minand60min. d Suggestareasonforthelatpartbetween 90minand100min. e Atwhattemperaturedidtheiceblocks freeze? Time (min) 0 10 20 30 40 50 60 70 80 90 100
X
thermometers
100 mL water methylated spirits
kerosene Heat for 5 minutes.
a WhichvariablesdidHarrycontrolinthis experiment? b Which variable did he purposely change? c Which variable did he measure? d WhatdoyouthinkwastheaimofHarry’s experiment? 3 Nicky measured the temperature of a saucepan ofhotwaterasitcooled.Sheplottedherresults as shown in the graph. a What was the temperature of the water after 10minutes?After40minutes? b Why is Nicky’s graph steep to start with but flatter near the end? c What do you think the temperature of the room was when Nicky did her experiment? Explain your answer.
Temperature (˚C) 25 15 8 1 –1 –1 –1 –4 –8 –10 –10
Temperature (°C)
X Temperature as hot water cools (Challenge 3)
X 50
X X X
20
40 Time (min)
60
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6.2 Heat transfer Heat energy can be transferred in three different ways. The direction in which it flows is always from a higher temperature to a lower temperature. 1 Conduction This is how heat energy is transferred through solids. Some solids conduct heat better than others.
3 Radiation This is how heat energy is transferred from the sun to Earth. No matter is necessary.
2 Convection This is how heat energy is transferred in liquids and gases.
Activity 1 You will need a glass rod about 20 cm long, and a metal rod the same length and thickness as the glass one. 2 Use wax or grease to stick a paperclip about 5 cm from the end of each rod. Then lay the rods across a tripod so that the paperclips hang down as shown. 3 Heat the end of both rods equally. Which paperclip falls off first? What does this mean?
Conduction A metal rod in contact with a hot flame quickly becomes hot. The heat is transferred along the rod by the process of conduction. The particles in the end of the rod gain energy from the flame. This causes them to vibrate faster and collide more energetically with each other. This process continues like a chain reaction from particle to particle along the rod. As a result, heat energy is transferred from the hot end of the rod to the cooler end. Heat energy is transferred along the rod.
wax To see how meat is cooked by conduction, open the Cooking animation on the CD.
glass rod
metal rod paperclip
tripod
As you saw in the activity, some solids conduct heat better than others. Substances that conduct heat well are called good conductors, and most metals are good conductors. Substances like glass, which are poor conductors of heat, are called insulators. Most plastics are poor conductors of heat, so those that do not melt easily are used to make handles for saucepans, kettles, frying pans and irons.
Chapter6 Investigatingheat Examples of conduction Insulating handles allow you to pick up hot objects without the heat being conducted to your hand. Plastic foam is a good insulator, and is used in the walls of refrigerators to keep heat out. aluminium saucepan (good conductor)
bakelite plastic handle
You may have seen birds fluffing up their feathers on cold days. This is to trap air between their feathers. Because air is an insulator, it slows down the loss of heat from the bird’s skin to the surrounding cooler air. Woollen jumpers, sleeping bags and the batts used to insulate houses also work by trapping air. The wetsuits worn by surfers and divers are made of foam rubber. A thin layer of water warmed by body heat is trapped between the suit and the diver’s skin. Being a poor conductor, this water helps to prevent the diver’s body heat from escaping. waterproof neoprene wetsuit
heat from stove
Liquids do not conduct heat very well. The set-up below shows that water is a poor conductor of heat. Even though the water boils at the top of the test tube, the ice at the bottom melts only slowly. If water was a good conductor of heat, the ice would melt quickly.
boiling water
tongs
iceblock weighted with wire
Gases are also poor conductors of heat. You can demonstrate this by holding your hand beside a burner flame. If air was a good conductor of heat, your hand would quickly be burnt, but it isn’t.
body of diver
body heat
water caught under wetsuit
water
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Activity 1 Fill a large beaker with water and allow it to stand until the water is completely still. 2 Carefully drop half a teaspoon of used tea leaves down one side of the beaker, making sure not to disturb the water. 3 Heat underneath the tea leaves as shown. Suggest why the tea leaves rise. Draw a diagram showing the movement of the tea leaves.
Hot water systems work by convection. The heater at the bottom warms the water which moves upwards as the cool water takes its place, setting up convection currents. The hot water is drawn off from the top. When a hot water tap is turned on, more cold water flows in at the bottom.
Hot water rises...
hot water taps
...and cool water takes its place.
water tea leaves
heater cold water
Convection The movement of the tea leaves in the activity above demonstrates the movement of heat energy by the process of convection. This process can be explained using the particle theory. When water particles at the bottom of the beaker are heated, they gain more energy and move more rapidly. Because of this, they move further apart than the particles above them. Hence the warm water near the bottom is less dense than the water above it. This warmer water therefore rises, and colder water moves in to take its place. This movement of particles is called a convection current. It continues until all the water in the beaker is at the same temperature.
Convection currents also occur in air. When you turn on a heater in winter, the warm air rises above the heater. A convection current is then set up as the cooler air sinks. The same thing happens on a larger scale to form a sea breeze. During the day the land is warmer than the sea, because the sea takes a long time to warm up. Warm air rises above the land, and cooler air blows in from the sea to take its place.
Warm air rises.
cooler air (sea breeze)
Land warmer than sea
Fig 21
How a sea breeze is caused by convection
Chapter6 Investigatingheat Radiation The Sun’s rays heat the Earth. However, the space between the Sun and the Earth does not contain matter, so heat energy cannot be transferred by the processes of conduction or convection. Instead, the Sun transfers heat energy by the process of radiation. All objects transfer some heat by radiation. The hotter the object, the more heat it radiates. The radiation itself is not hot, but when it is absorbed by an object it causes the particles in the object to move more rapidly, thus heating it. radiation absorbed
Fig 22
infra-red radiation
The curved silver mirror at the back of an electric radiator reflects the radiation.
Warm objects radiate heat mainly in the form of infra-red radiation, which we cannot see but which can be detected by special infra-red scanners. People are usually warmer than their surroundings and give off more infra-red radiation. This is why infra-red scanners are used at night by air–sea rescue helicopters to help find people who are lost. If a metal object becomes hot enough it will glow, giving off visible light as well as infra-red radiation. Light, infra-red and other forms of radiation all travel as extremely high-speed waves which can pass through a vacuum, such as the vacuum of space. In a vacuum the speed of radiation is 300 million metres per second or 3 × 108 m/s. Different types of radiation have different wavelengths. The waves travel in straight lines, and they can be reflected, absorbed or transmitted by matter. All of these properties of radiation are applied in microwave cooking. Microwaves are reflected off metals, so they reflect from the
TRANSMITTED (passes through transparent material)
ABSORBED (taken in)
REFLECTED (bounces off)
Fig 23
Heat and light can be transmitted, reflected or absorbed.
inside of the oven onto the food being cooked. The microwaves penetrate the food to a depth of between two and four centimetres, where they are absorbed. This causes the molecules in the food (mainly water molecules) to move more rapidly, and hence the food heats up. The heat is then transferred to other parts of the food by conduction. This process may continue for a short time after the food is removed from the oven. The microwaves are transmitted through the glass dish, which remains relatively cool because it absorbs very little radiation. (Microwaves will also pass through paper and most plastics.) ‘stirrer’ to reflect waves
waveguide
source of microwaves
glass dish food
turntable
Fig 24
How a microwave oven works. You can see through the glass door, but the microwaves cannot pass through the metal lattice behind the glass.
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Investigate
15 WHICH ABSORBS MORE RADIATION? Aim To compare the amount of radiation absorbed by a shiny silver can and a dull black can.
Materials • 2thermometersordataloggerand 2temperatureprobes • portablespotlightorelectricradiator • 2metalcans—oneshinysilverandonedull black
NOTES 1 Instead of using a spotlight, you could use a microscope lamp, or you could put the cans in direct sunlight. 2 If you use empty food cans, you could blacken one by holding it in the smoke from a burning candle. Painted soft drink cans work well. 3 To cut down on heat loss by convection, you need lids.
5 Plotthetemperatureforbothcansonasingle graph.(Adataloggerwilldothisforyou.)You could use a different colour for each can, but make sure you label the two curves.
Discussion and conclusion 1 Which was the independent variable, and which was the dependent variable? 2 Which variables did you control? 3 Whichcanabsorbedmoreradiation?Howdo you know? Was your prediction correct? 4 Look at your graph. What does the slope of each line tell you about the warming rate of the can? 5 Basedontheresultsofthisexperiment,writea generalisation saying how the amount of heat absorbedbyanobjectdependsonthetypeof surface. 6 Could the experiment be improved? If so, how?
Planning and Safety Check Read the Method carefully and discuss with your teacher what equipment you will use. • Whatsafetyprecautionswillbenecessary?
Design a similar experiment to find out which can cools more quickly.
• Whichcandoyoupredictwillabsorbmore radiation? Why? In your notebook design a data table in which to record the temperature of each can everyminutefor15minutes.
thermometer
dull black can
hole in lid
Method 1 Addequalvolumesofcoldwatertobothcans. 2 Positionthespotlightorradiatoratanequal distance from each can. 3
portable spotlight
Record the initial temperature of the water ineachcan.(Theseshouldbethesame.)
4 Turn on the lamp and at the same time start timing. Record the temperature in each can every minutefor15minutes.
shiny silver can
Chapter6 Investigatingheat Absorbing and emitting radiation Dark-coloured surfaces are better absorbers of radiation than light-coloured ones. This is because light-coloured surfaces reflect more of the radiation. Bright shiny surfaces are the best reflectors and the poorest absorbers. This is why aluminium foil is used in ceilings and walls of houses to reflect heat. On the other hand, the absorbing panels of solar water heaters are painted black so that the copper pipes inside them absorb as much of the sun’s radiation as possible. Dark-coloured cars become much hotter than light-coloured cars when left in the sun. And dark-coloured clothes are hotter in summer than light-coloured clothes. light car (good reflector, poor absorber)
dark car (good absorber)
Fig 28
The cooling fins on an air-cooled motorcycle engine have a large surface area to increase radiation of heat.
Controlling heat transfer An object that is warmer than its surroundings will lose heat until it is the same temperature as its surroundings. Similarly, an object that is cooler than its surroundings will gain heat from its surroundings. We use insulators to control this transfer of heat. Eskys and thermos flasks (see page 144) are insulated containers to keep food and drink at the temperature we want it—either hot or cold. Pizza delivery people put their pizzas in special insulated boxes to keep them warm.
All objects emit (give out) infra-red radiation if they are at a higher temperature than their surroundings, but some radiate heat more readily than others. Dark-coloured objects radiate heat more effectively than light-coloured objects. Rough surfaces also radiate heat more effectively, due to their greater surface area.
silver teapot (poor emitter)
cooling fins
black teapot (good emitter)
Is the pizza still hot?
Why did I ask for triple chilli?
We insulate the walls and ceilings of our homes. This keeps them cool in summer by preventing heat from coming in from outside. It also keeps them warm in winter by preventing heat from escaping. (See page 146.)
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Experiment
WHICH IS THE BEST INSULATOR? The problem to be solved Yourtaskistodesignanexperimenttosolve the problem Which type of material keeps you warmest in winter?
Designing your experiment The design of the experiment is up to you, but here are some questions to guide you. • Whatwillyouuseasamodelforahuman body? One idea is to use a can filled with hot water. • Howwillyouclotheyourmodelbodies?What materialswillyouuse?Somepossibilitiesare wool,cotton,nylon,polyester,lannelette.How many model bodies will you need? • Howwillyoumeasurethetemperature?How often will you do this, and how long will you continue the experiment? • Howwillyoumakeyourtestfair(asinChapter 2)?Youarevaryingthetypeofclothing,but whatothervariablesarethere?Howwillyou keep these other variables constant? • It would be a good idea to use an experimental control—amodelbodywithno clothes.Youcanthencomparetheclothed bodies with it to see how effective the different types of clothes are.
• If possible, repeat your experiment to improve the accuracy of your measurements. If you get the same results, then you can be more confident your conclusion is correct. If someone else repeats your experiment and gets the same results you can be even more confident. Results like this are said to be reliable.
Results Howwillyourecordanddisplayyourresults?Ifa datalogger is available you could use it. Would a graph be useful? Computer programs such as Excel can be used for drawing graphs. Open the ICT skillsheet on the CD to see how this can be done.
Writing your report Look carefully at your results and write a report of your findings, giving your answer to the problem. Youcouldtakeadigitalphotoofyourset-upto include in your report. Could you improve your design?How?
Instead of keeping something warm you often want to keep something cold. Design an experiment to find out which is the best insulator for this.
Chapter6 Investigatingheat
Check! 1
What is the advantage of a copper bottom on a saucepan?
2
The four beakers shown are identical and contain the same volume of water at 80°C. After 10 minutes the temperature of each is measured again.
A
B
C
5
Refrigerators and freezers are painted white. Yet the coils at the back are painted black. Why is this?
6
Predict the effect that a chocolate coating would have on the rate at which an icecream melts. How could you test your prediction?
7
Polar bears have white fur and black skin. In winter their fur is fluffed up, and in summer it sits down flat. Suggest how these adaptations allow the bears to control their temperature.
8
In a supermarket the doors of vertical refrigerators must be kept shut, yet the freezer unit in the foreground of the photo has no lid. How can you explain this?
9
There are similarities and differences in the way light, heat and sound are transmitted, reflected and absorbed. a Can heat travel through space where there is no air? What about light and sound? b Can heat, light and sound be reflected? Give examples. c Can heat, light and sound be absorbed? Give examples.
D
plastic foam
a b c 3
Which beaker do you think will be the hottest after 10 minutes? Why? Explain why the water in B will probably be a little warmer than that in A. What happens to the heat energy lost from the beakers?
An ordinary gas or electric oven is more correctly called a convection oven. Why? Draw a diagram showing how it works by convection.
heating element
4
You put a can and a glass bottle of ginger beer into the refrigerator at the same time. They both contain 375 mL and are both at room temperature. Predict which one will cool more quickly. Why?
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challenge 1 What colour would you paint large petrol storage tanks? Why? 2 Look at the cartoon showing Jason thinking abouthowheattravels.Isheright?Howwould you answer him?
Wool is a very good insulator. So, why not wear a woollen jumper on a hot day? Surely this would reduce the amount of heat reaching your body.
3 AnsaandTammyilledtwopapercups,one with water and the other with soil. They placed them in the refrigerator overnight. The next morning they took both cups, put them in the sun, and measured their temperature every 15minutes.Herearetheirresults. Time
Water
Soil
9.00am
10°C
10°C
9.15am
10°C
11°C
9.30am
12°C
13°C
9.45am
13°C
16°C
10.00am
14°C
20°C
10.15am
15°C
25°C
10.30am
15°C
30°C
a Plottheseresultsonagraph. b Whichabsorbsheatmorereadily—water or soil? c Duringtheday,whichbecomeshotter—the land or the sea? d Where would a glider pilot look for thermals (risingair)—abovelandorabovealake?
4 Hot-airballoonsworkbyusingaburnerthat heatstheairbelowtheballoon.Howdoes this make the balloon rise? 5 Use the particle theory to explain the following. a Conduction occurs much more rapidly in solids than in gases. b Convection currents can occur in liquids and gases, but not in solids. 6 Design an experiment to compare the insulating properties of four different house bricks. Try it if you have time. 7 One end of a long glass rod is heated to 100°Candtheotherendiscooledto0°C. a What will happen to the temperature at each end if the rod is left at room temperature? b Sketchgraphstoillustratethetemperature changes at the two ends of the rod. 8 Using what you have learnt in this chapter suggest: a four ways of preventing heat loss from your house in winter b four ways of preventing your house from getting hot in summer.
Chapter6 Investigatingheat
6.3 Heat in everyday life This section is different from other sections of the book. Instead of working through it page by page, you can select any of the six activities on the following pages. You will need to apply what you have learnt in the first two sections and work
things out for yourself. In some of the activities you will be designing your own experiments to solve a problem. If you need help with this, see Chapter 2.
1 Firewalking each coal is actually burning. When a firewalker’s foot touches a burning coal, a small amount of heat is transferred to the foot by conduction. This loss of heat is enough to temporarily reduce the surface temperature of the coal below ignition temperature, causing it to stop burning. The secret to firewalking is that charcoal is a poor conductor of heat, and it takes about a second before enough heat is transferred through the dead outer layer of skin on the foot to the living tissue beneath, thereby causing a burn. So,providedthatthefootisincontactwithany one hot coal for less than a second, it will not be burned. Despite all this, firewalking is still dangerous, and you should not try it yourself! Firstly, burns can occur where the skin is thinnest; for example, underthearchandbetweenthetoes.Secondly, if there is any burning wood mixed with the coals itmayproducehotgasjetscapableofburning. Thirdly, small bits of coals can sometimes stick to the firewalker’s feet. When this occurs the coal is in contact with the foot for longer than a second and a burn will result.
Exercises YoumayhaveseenirewalkingonTV,where peoplewalkbarefootacrossapitofred-hot coals.Somepeoplethinkthatthisshowshow themindcaninluencethebody.Butitcanbe explained in terms of heat transfer. Even when you walk barefoot on a hot bitumen road your feet can be burned as heat is transferredtothembyconduction.Sohowcan youwalkonred-hotcoalsatabout800°C? Thecoalsarecharcoal—formedbythepartial combustion of wood. Only the outer layer of
1 Whatisthetemperatureofred-hotcoals? 2 What are coals made of? 3 Arecoalsgoodconductorsofheatorpoor conductors? 4 What is the main way heat is transferred in firewalking? 5 What is meant by the term ‘ignition temperature’?
>
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6 Abouthowlongdoesittakebeforeliving tissue beneath dead skin is burned? 7 Why is it a problem if small bits of coals stick to the firewalker’s feet? 8 Given the maximum contact time of one second, is it safe to walk across the coals at normal walking pace? Explain. 9 Suggestwhythemaximumcontacttimeis slightly different for different people. 10 Howdoesirewalkingillustratethe difference between temperature and heat?
2 How does a thermos work? Studythelabelleddiagram.Thenwritean explanation of how a thermos keeps liquids hot or cold. Make sure you explain how the various parts work to prevent heat flow by conduction,convectionandradiation.Your teacher may be able to show you the inside of a thermos.
cover
well-fitting plastic stopper double-walled glass or stainless steel container
silvered walls
hot or cold liquid
heat radiation air space
air pumped out to create a vacuum
rubber, plastic or cork supports
Chapter6 Investigatingheat
3 Which is the coolest colour to wear? Which is the coolest colour to wear in summer? Designanexperimenttoindout.You could use a method similar to that in Investigate15onpage138,oryoucould workoutyourowndesign.Adatalogger with several temperature probes would be very useful here. Write your report, giving your conclusion and commenting on the accuracy and reliability of your method and results. Include a recommendation to people wanting to keep cool in summer.
Phew! It’s so hot! You must be absolutely roasting in those dark clothes.
4 Does white coffee cool faster than black coffee? One evening as Mahdi was making coffee for Kyle and herself the telephone rang. Mahdiwasjustabouttoaddthemilkto Kyle’s coffee when he said, ‘The coffee will probably stay hotter if you add the milk after I’ve finished on the phone.’ Mahdi knew Kyle would be on the phone for ages, so she said, ‘Wouldn’t it be better if I added themilknow?Ilearntatschoolthatdarkcoloured things like coffee give off more heatandcoolfasterthanlight-coloured things like milk.’ Who is right? Write a hypothesis about the cooling of coffee. Then design and carry out an experiment to test your hypothesis. Youwillneedtomakecareful measurements and record your results onagraph.(Youmaybeabletousea datalogger with temperature probes.) Is Mahdi’s explanation correct? Is it to do with colour, or is it to do with the relative temperaturesofthecoffeeandmilk?How could you find out?
Don’t add the milk to my coffee ‘til I’ve finished on the phone.
Wouldn’t it be better if I put it in now?
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5 Why use a lid? Youhavebeenglancingthroughabookcalled 101 ways to save energy in the home. One of the tips is to always put a lid on a saucepan whencooking.Youwonderwhether this is in fact true. Basedonwhatyouhavelearnt in this chapter, write a hypothesis that you think is correct. Make sure that the hypothesis is written in such a way that you can test it. For example, you need to say what will be measured. Now go ahead and test your hypothesis. If possible, repeat your experiment to make sure your conclusion is reliable.
lid
steam
boiling water food
stove
6 Designing a house Yourtaskistodesignahouseforyourareathat is cool in summer and warm in winter, using what you have learnt in this chapter about heat transfer. Take into account how heat is gained and lost by an average house, as shown in the diagram. In your design you should consider:
roof 25%
• thepositionofthehouse • thetypeofbuildingmaterialsused for the floor, walls and roof
walls 35% windows
10% • designfeaturessuchasalator slopingroof,typesofwindows(eg single-ordouble-glazed)andventilation
• thesurroundsofthehouse,includingthe types of trees
< WEB watch > To find out more about energy-efficient house designs, go to www.scienceworld.net.au and follow the links to Sustainable energy info (fact sheets on building) and Energy Smart house design.
floor 15%
Fig 43
draughts & ventilation 15%
The percentages of the total heat transfer in various parts of an average house
Chapter6 Investigatingheat
Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
absorb
1 Heat is a form of ______ which can raise the ______ of an object.
conduction
2 The temperature of an object depends on how fast its ______
convection
are moving. The faster they move, the higher the temperature.
3 The amount of heat gained or lost by an object depends on its ______, the temperature ______ and what it is made from.
4 ______ is the transfer of heat through a material by the collision of particles. Metals are the best conductors of heat. Poor conductors are called ______.
5 Heat energy flows from places where the temperature is ______ to where it is ______. Insulators are used to reduce the amount of heat ______.
change
energy high insulators low mass particles radiation temperature transfer
6 ______ is where heat is transferred by circulating currents in liquids or gases.
7 Heat energy can be transferred across empty space by means of ______. 8 Dark-coloured surfaces ______ and emit radiation better than light-coloured surfaces. Try doing the Chapter 6 crossword on the CD.
REVIEW
1 If one end of a copper rod is held in a burner flame, heat travels quickly along the rod to the other end. Substances like copper which behave in this way are called good: A absorbers B insulators C radiators D conductors 2 A building is heated by running hot water through a number of radiators. The most efficient colour for these radiators would be: A silver B white C black D red
3 Copy and complete the diagrams below to show the convection currents you would expect to form in the water. a
b
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4 Which of the following statements are true, and which are false? Rewrite the false ones to make them correct. a A cold object eventually heats up to the same temperature as its surroundings. b Conduction is fast in insulators. c Heat transfer by conduction is very slow in liquids and gases. d The sun transfers heat energy to the Earth by the process of convection. e The hotter an object is, the less radiation it emits. f When an object absorbs radiation its temperature rises. g Heat radiation travels at the speed of light. 5 If two objects are at different temperatures, what can you say about the movement of the particles in the hotter one? 6 Which has more heat energy—a teaspoon of water at 80°C or a bucket of water at 80°C? Explain. 7 If you hold your hand above a burning candle, you will burn yourself. Yet you can quite comfortably hold your hand beside the flame. Why is this? 8 Look at the diagram of a toasted cheese sandwich being cooked in a griller. a How does heat travel from the heating element to the sandwich? b Why can’t the heat travel by conduction or convection?
heating element
9 Rory and Trent poured equal volumes of cold water into two identical styrofoam cups, then put identical thermometers in each. They put one cup in the sun and the other in the shade, and recorded the temperatures every 10 minutes. Here are their results. Temperature (°C)
Times (minutes)
in sun
in shade
0 10 20 30 40 50 60
15 16.5 18 20 21 23 24
15 16 17 17.5 18.5 19.5 20.5
a Plot the results on a graph. b What conclusion can you draw from the graph? c What variables did Rory and Trent control in this experiment? d Which method of heat transfer caused the increase in temperature of the water in the cups? e What would be the effect of painting the cup in the sun black? 10 A manufacturer claims that a certain insulating material is good ‘to keep the cold out’. Is this expression accurate? Explain using a diagram. 11 Do sheep get colder when it is raining and their wool is wet? Design an experiment to find out, listing the steps you would need to take to make it a fair test.
toasted cheese sandwich
Check your answers on pages 279–281.
Chapter6 Investigatingheat Learning focus: Models and theories that have been modified or rejected
US AREA C O F D E B I R C PRES
How a theory was rejected Activity 1 Measure 50 mL of cold water into a beaker and record its temperature. Then measure out 50 mL of hot water and record its temperature. 2 Add the hot water to the cold water and stir carefully with a thermometer. Record the temperature. 3 Use what you have learnt about heat to explain your results. To explain the results of the activity did you write a hypothesis that heat is transferred from a hotter substance to a colder one? Scientists test a hypothesis like this by carrying out more experiments. Other scientists then repeat these experiments. If all the experiments support the hypothesis, and none have shown it to be false, the hypothesis is accepted as a theory. This theory is accepted until new evidence is found that doesn’t support it. In 1783, Antoine Lavoisier proposed the theory that heat is a special fluid called caloric that flows
from warmer to colder objects. Unfortunately Lavoisier was beheaded in the French Revolution in 1794. Four years later Count Rumford did his experiment with drilling brass cannons (see page 128), and suggested that the caloric theory was incorrect. However, scientists were reluctant to reject the caloric theory since it successfully explained many experiments. In 1842 James Joule carried out a famous experiment that meant the caloric theory had to be rejected. He made the apparatus shown below in which a falling weight turned a paddle in a tank of water. The friction caused by the paddle caused the temperature to rise slightly. From this he was able to show that heat is just a form of energy and can be explained in terms of the motion of particles (see page 129). 1 How does a hypothesis become a theory? 2 Draw a time line showing the events outlined on this page, as well as Dalton’s particle theory in 1803. How long did the caloric theory last? 3 Why was the caloric theory rejected? pulley pulley thermometer
falling weight
fixed paddle water
rotating paddle
Lavoisier, in the red coat, is carried to the guillotine during the French Revolution.
Joule’s experiment
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7 Exploring space
Planning page Getting started Activity page 153 Skillbuilder page 155 Timelines
Activity page 163 Activity page 164
Activity page 173
7.1 Observing the night sky page 152
7.2 Exploring the solar system page 157
7.3 Stars and galaxies page 169
TRB Assessment task 7 An astronomy survey
Main ideas Chapter 7 crossword
Review Learning focus: Distinguishing between scientific, economic and legal argument
TRB Chapter 7 test
Prescribed focus area Colonising Mars
Chapter7 Exploringspace t…
l learn abou
r you wil In this chapte
LearningFocus ●
distinguishing between scientific, economic and legal argument (page 177)
KnowledgeandUnderstanding ● ●
the solar system components of the universe (Section 7.3)
Skills ● ● ● ●
gathering information from secondary sources (Activities pages 163–164, Science Bits page 166) processing information (Activities pages 163–164) presenting information (Skillbuilder page 155, Activity page 164) thinking critically—generalising and predicting (Activity page 153)
Do aliens exist? If so, where do they come from? How much do you know about the solar system and the universe? Form a group and discuss the questions below. ● If aliens exist somewhere in the universe, where are they likely to live? Describe the body features they would have to have to live in these places. ● The nearest star is 4.3 light-years away. What does this mean? Could we get to this star using our present methods of space travel? Suggest other ways of travelling to stars. ● It has been suggested that humans might one day live on Mars. Why Mars and not one the other planets in our solar system?
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7.1 Observing the night sky When you gaze into the night sky you are looking at part of the universe. Astronomers (scientists who study objects in space) describe the universe as space and everything in it. However, they are not sure how big the universe is. They do know that it is made up of billions of stars, millions more than the few thousand that you can observe by looking at the night sky.
Inferences from observations Most cultures throughout history have had very important beliefs about the visible objects in the universe. The Egyptians, 4000 years ago, believed that the sky was the body of the goddess Nut. The stars were shiny jewels on her dress, while the planets were shiny boats that drifted across the sky. At about the same time the Babylonians thought that the Earth was the centre of a huge sphere, with the Sun, Moon and planets moving around the Earth. Many people also thought that the Earth was flat. In most cultures the beliefs were based on a central Earth with the other objects moving
around it. These beliefs or inferences were based on the observations that the Sun, Moon, planets and stars all move in a westerly direction around the Earth. In AD 140 the Greek astronomer Ptolemy (TOLL-em-ee) wrote an encyclopaedia of astronomy detailing the motion of the moon, the five known planets (Mercury, Venus, Mars, Jupiter and Saturn), the sun and the stars all revolving around the Earth. Ptolemy and other astronomers of his time were very influential, and their ideas went unquestioned for about 1400 years. In 1543, Nicholas Copernicus (ko-PER-nickus) published a book containing the idea that the Earth was not the centre of the universe. Using very detailed observations gathered over 40 years, he inferred that the planets revolve around a central sun. Even though his inference was not new, it proved to be a bombshell because it was contrary to the traditional belief that the Earth is the centre of the universe.
(only half the sphere shown) stars Mars
Earth
Jupiter Saturn
Sun Venus Mercury
Fig 2
Moon
The Babylonians thought that the Earth was at the centre of a huge sphere, with the stars set like jewels on its inner surface.
Fig 3
In 350 BC most people believed that the Earth was flat. But the Greek mathematician Aristotle inferred that the Earth was a sphere after observing its circular shadow on the Moon during an eclipse.
Chapter7 Exploringspace
Activity For this activity you will need a pencil, a large sheet of stiff paper or cardboard, a compass and some Blu-tack. a Place the paper on some flat, level ground. Use the compass to find north and position a long side of the paper to face north. Mark north in the corner of the paper. b Put a piece of Blu-tack on the blunt end of the pencil, and place the pencil about 5 cm in from the north edge of the paper, as shown in the photo.
Another breakthrough in astronomy occurred in 1609 when Johannes Kepler published his First Law of Planetary Motion. This supported Copernicus’ inference and suggested that the planetary paths are ellipses rather than circles. These paths are called orbits. His inference was based on incredibly accurate planetary observations collected over 30 years by his teacher, Tycho Brahe (pronounced Bray).
Invention of the telescope In 1610 Galileo built a telescope using lenses, and observed the surface of the Moon for the first time. He saw mountains, craters and large flat plains. He also observed the planets Mars, Venus and Jupiter, and discovered that they were round and disc-like, unlike stars, which were just points of light in the sky. When observing Jupiter, Galileo also noticed four moons revolving around the planet. He used these observations to support the inference that the Sun was at the centre of the solar system.
N c Place an at the end of the shadow, and write the time next to it. d Do this every half an hour for as long as you can. (If you only have a lesson, mark the shadow every 5 minutes.) e Join up the s on the paper and show in which direction the shadow moved. What shape is the line joining the s? How does the movement of the shadow relate to the rotation of the Earth? Predict how the line would change throughout the year.
Fig 5
Some of Galileo’s observations of the moons of Jupiter. The date is on the left and the moons that were visible on each night are marked beside Jupiter (the circle).
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ScienceWorld8forNSW After Galileo’s small telescope, larger and more powerful telescopes were built to scan the night sky. In 1781 William Herschel discovered the planet Uranus using a very large telescope. In the early 1800s astronomers observed unusual changes in Uranus’ movements and inferred that they were caused by an unknown planet. After many years of careful observation, the new planet’s position in the sky was predicted by English and French astronomers. Then in 1846 the new planet was discovered by the German astronomer, Johann Galle. It was called Neptune. The American astronomer Percival Lowell had predicted the presence of a ninth planet in 1905. However, it was difficult to observe with a telescope because it was so far away from Earth. Eventually Pluto’s existence was confirmed when it was observed in 1930 using newly invented photographic methods. Pluto was officially declared a planet in 1999 by the International Astronomical Union, but in 2006 the Union reclassified it as a dwarf planet.
Fig 6
William Herschel’s telescope used in the discovery of Uranus in 1781.
Fig 7
The arrangement of the planets and Pluto in the solar system. The planets revolve around the Sun in orbits that are roughly in the same plane. However Pluto’s orbit is tilted and crosses the orbit of Neptune. Because of this, Pluto was closer to the sun than Neptune between the years 1979 and 1999.
Pluto Saturn Uranus
Jupiter
Sun
Mercury
Neptune
Venus Earth
Mars
Asteroid belt
The diagram is not to scale.
Chapter7 Exploringspace
Skillbuilder The history of motion pictures
Timelines A timeline is a visual way of representing the sequence of historical events, and can be drawn horizontally or vertically. Notice in the diagram below the vertical timelines can start at the top or the bottom. The line has intervals marked on it to indicate the units of time. It is like the scale used on the axis of a graph. The timeline on the right shows the events in the history of motion pictures (movies). Look at the three timelines below. What is the time interval for each?
Digital projectors replace film projectors in cinemas 2000 Digital surround sound used in cinemas 1980 First IMAX cinema 1960
Where would you mark 1985, 7 pm and 925 BC? 1940
Cinerama movies made using three projectors, a wide curving screen and stereo sound
Colour movies first made
1980
1990
10 am
800 BC
12 noon 2 pm
850 BC
4 pm 6 pm 8 pm
900 BC
1900
First public screening of a motion picture (Waves on the shore)
950 BC
1890
10 pm 12 midnight
First talking motion picture 1920
1000 BC
2000
Drawing timelines Your task is to draw a timeline for the events that led to the discovery of all nine planets in the solar system. To do this you need to read through the information on pages 152–154 carefully. 1 Draw a vertical line down the long side of a large piece of paper. The arrow on the line can point up or down. 2 Your timeline will go from 2000 BC to AD 2100. Work out a suitable scale for the timeline and draw it. (Hint: To save time, mark every 500 years on the timeline.)
Thomas Edison shows a 15 second film in New York
3 Read through the information in the text and in the captions underneath the photos and drawings. From this information, select each event and the date on which it occurred. Summarise the event into a sentence. 4 On the right-hand side of the timeline, write the event that occurred, draw a box around it, then rule a line from the event to the year in which it occurred. (Use the motion pictures timeline above as a guide.) 5 Discuss the timeline with your group. You may be asked to present it to the class.
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Check! 1
How does the ancient Egyptian model for the universe differ from that of the Babylonians?
2
Ptolemy’s ideas about the structure of the solar system are based on an incorrect inference about the movement of the Sun, Moon and planets. What is this inference?
3
In the late 1600s people began to accept a new idea about the arrangement of the solar system. What was this new idea?
4
What is an orbit? What general shape is it? What is so unusual about the orbit of Pluto?
5
Which planets cannot be seen with the naked eye? When was each one discovered?
6
The word ‘planet’ comes from the Greek word meaning ‘wanderer’? Suggest why this is a good term to describe these bodies in space.
7
Suggest why it took so long to discover Pluto.
8
Suppose you were observing the stars in the Southern Cross one clear night. You recorded the position of the stars and the time. Two hours 8 pm later you observed the Southern Cross again and recorded its position. Make an inference to account for the difference in the observations. 10 pm
challenge 1 Look at Fig 5 on page 153. This is Galileo’s record of his observations of the moons around Jupiter. a On the night of the 10th he observed four moons, but on other nights he observed three and sometimes two. Make an inference to account for the differences in these observations. b Over how many nights did Galileo make observations? What assumptions did you make to answer this question? 2 Galileo observed four moons orbiting Jupiter. In 1908 astronomers recorded seeing the eighth moon. Today, astronomers have ‘seen’ 63 moons, some of which are only 20 km in diameter. From 1610, it took 300 years to find four more moons, and from that date only 90 years to find another 57. a Suggest why this occurred. b Do you think that astronomers have actually ‘seen’ the smaller moons of Jupiter? Give reasons for your answer. 3 Below is a 14th century woodcut of Ptolemy’s map of the universe. The names are written in Latin. a What is at the centre of the universe? b The first seven circles represent the objects in the solar system. What are the English names for these seven objects? Name them in order from closest to furthest. c What do you think is represented by the outer three circles?
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7.2 Exploring the solar system Look back at the diagram of the solar system on page 154 showing the planets orbiting a central sun. We know at present that there are eight planets in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune The planets are usually divided into two groups: the inner planets and the outer planets.
Inner planets These are sometimes called the rocky planets and include Mercury, Venus, Earth and Mars. They are the ones closest to the Sun, they have rocky surfaces and are all relatively small.
Outer planets The outer planets, Jupiter, Saturn, Uranus and Neptune, are much bigger than the inner planets, and make up 99 per cent of the total mass of all the planets. They are often called the giant planets or the gas planets. They all have rings around them and a large number of moons. They consist mainly of the gases hydrogen and helium. Below their surface these gases are in liquid form, and at the centre is a rocky core. Fig 12
Mercury is the smallest planet in the solar system, and is closest to the sun. Like our Moon, much of its surface is covered by impact craters.
You can use the following memory jingle (or mnemonic) to help you remember the order of the planets. My Very Educated Mother Just Served Us Nachos The two groups of planets are separated by hundreds of thousands of tiny chunks of metallic rock called asteroids. They orbit the sun between Mars and Jupiter in what is called the asteroid belt. There are so many asteroids in this belt that there is always a danger of collision for passing spacecraft. Most planets have a layer of gas, called an atmosphere, covering them. The inner planets have a relatively thin atmosphere, while the gas planets have a much thicker atmosphere. Earth’s atmosphere is a mixture of nitrogen and oxygen and smaller amounts of carbon dioxide and water vapour. Jupiter’s thick atmosphere, on the other hand, consists mainly of hydrogen and helium. The gases in the atmosphere are held close to a planet by its gravity. On a large planet like Jupiter, where the gravity is 2.6 times greater than on Earth, the lightest gases (hydrogen and helium) are held in the atmosphere. On Earth, however, these gases escape into space. Mercury is so small and hot that it has no atmosphere at all.
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Theinnerplanets The Earth’s two neighbours, Venus and Mars, have been the most observed and studied of all the planets in the solar system. In the next 20 years many spacecraft will land on Mars’ surface and gather information for a possible human landing. Venus, on the other hand, has a very thick, acidic atmosphere and may be unsuitable for a human landing.
Fig 15
Fig 13
The Mars Exploration Rovers Spirit and Opportunity landed on Mars in 2004 and have sent thousands of high-quality images back to Earth.
Fig 16
Fig 14
The thick clouds of Venus’ atmospher e can be seen swirling ar ound the planet.
enor on Mars is an Olympus Mons across. volcano 600 km
mous
The Tick volcano on Venus is 66 km across and has radiating ridges on the side s. The rim at the bottom seems to have been brok en by a dark lava flow.
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Theouterplanets Each of the four outer gas planets has a feature that makes it different from the other planets. Jupiter is the giant planet and is over twice as heavy as all the other planets put together. Saturn has distinctive rings around it. Uranus is a pale green-blue colour and has faint rings. Its axis of rotation is nearly at right angles to the other planets, which means that the planet is lying on its side. Neptune is also a green colour, but its most striking feature is its Great Dark Spot.
Fig 17
Fig 18
d Spot Jupiter’s Great Re a distance m photographed fro one of , Io . of 21 million km n be seen ca , Jupiter’s moons top right.
Fig 19
A composite vi ew of Saturn and six of its moons. The ph otos were taken by the Vo yager 2 spacecraft in 19 80.
An artist’s impression of Uranus with its faint rings from one of its moons (Miranda) in the foreground.
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Whatisaplanet? The discovery of Pluto After the 1846 discovery of Neptune, astronomers were expecting to find another planet beyond Neptune. However, even after 60 years of searching, no new planet was found. The unknown planet was called ‘Planet O’, and was actually photographed in 1919 but not noticed because it was smaller than astronomers had expected. In February 1930, the American astronomer Clyde Tombaugh identified a new planet in photographs taken a month earlier. The new planet was called Pluto after the Roman god of the dead and ruler of the underworld.
Why Pluto isn’t a planet Astronomers discovered two very odd things about Pluto’s orbit. Firstly, all the other planets orbit the sun in approximately the same plane. Pluto’s orbit, however, is inclined at 17° to that plane. Secondly, Pluto’s orbit is much more elliptical than the orbits of the other planets, and actually overlaps Neptune’s orbit. But is Pluto a planet? Pluto is 6 times smaller than Earth and also smaller than our moon. Pluto’s moon Charon, discovered in 1978, is larger in proportion to its planet than any other in our solar system.
Fig 20
Photos taken on 23 January 1930 (top) and 29 January 1930 show how Pluto had moved relative to the stars.
Pluto was always thought to be a planet until the mid 1990s when hundreds of Plutolike objects were discovered in a region beyond Neptune known as the Kuiper Belt (see the next page). Many of these objects are greater than 100 km in diameter. So, in August 2006 astronomers decided to reclassify Pluto as a dwarf planet.
The day our solar system got bigger In early January 2005, Mike Brown from the Californian Institute of Technology was analysin g photographs of objects in the far reaches of th e solar system when he found a planet-like object. Fu rther analysis showed that th is ‘planet’ is larger than Pluto and is about 97 times further from the Sun th an Earth. This Kuiper belt objec t is called Eris, the large st of the dwarf planets. It has an odd elliptical orbit like Pluto’s but its exact size is unkn own at present. It is ve ry bright, but its greyish surface colour may reflect more light than Pluto’s reddish surface . In September 2005, ot her astronomers discove red a moon around Eris.
An artist’s impression of Eris with our Sun in the distance
Chapter7 Exploringspace
The Kuiper Belt In the early 1990s astronomers began discovering many objects in space beyond Neptune. These objects were found in a band orbiting the sun. The band was named the Kuiper Belt after the Dutch-American astronomer Gerard Kuiper (pronounced KY-per). He had suggested in the 1950s that comets and asteroid-like matter existed beyond Neptune.
Kuiper’s hypothesis Using the results of astronomical investigations, Kuiper hypothesised that when the planets were forming, strong gravitational forces swept up all the matter and formed the planets as we know them. In the region beyond Neptune, the gravitational forces were weaker and there should be lots of smaller bodies including comets.
Missions in space The very first spacecraft, an artificial satellite called Sputnik 1, was launched by the then USSR in 1957. Since then spacecraft have landed on our Moon, and the planets Venus and Mars. They have also flown close to and photographed all the planets and their moons in the solar system.
In the late 1990s, using terrestrial and space telescopes, astronomers found many Kuiper Belt Objects. These observations supported Kuiper’s hypothesis.
Questions 1 Explain in your own words why astronomers thought there might be many objects beyond Neptune. 2 Do you think Pluto should be called a dwarf planet rather than the ninth planet? Give reasons for your opinion. 3 Suggest why Gerard Kuiper did not actually observe any Kuiper Belt Objects.
< WEB watch > Go to www.scienceworld.net.au and follow the links to the website below. The Kuiper Belt and Oort Cloud You can also search the internet under Kuiper Belt.
The first major missions into space were two Voyager missions launched in 1977. They sent back an incredible amount of new information on Jupiter, Saturn, Uranus and Neptune. Prior to these missions it was thought that Jupiter had 13 moons; now more than 60 have been observed. Uranus was thought to have five moons but Voyager 2 discovered another 10. The spacecraft also discovered rings around Uranus similar to, but much fainter than, those around Saturn. The cameras on board Voyager were able to send close-up images of Uranus’ moon, Miranda, showing deep canyons. These cameras were so good that they could photograph a newspaper headline about one kilometre away! Fig 21
The Voyager 2 spacecraft was launched in 1977. In 1979 it travelled past Jupiter, then past Saturn in 1981. Now 30 years later, it is passing the outer edge of the solar system and into the empty space beyond.
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ScienceWorld8forNSW Getting information on space Our knowledge about the solar system constantly changes as space missions reveal new information about planets and their moons. A very good source of up-to-date information is the internet. Newspapers, magazines and journals are another source. To do the activities on the following two pages you will need current information about the planets and their moons, as well as about past, current and future space missions. The websites listed in the box below are just some of the many that are available, and many of these websites also have links to other sites. You can find other websites using a search engine. For example, if you type in Jupiter’s moons, a number of sites will be listed, of which some may be suitable. When you write a report, make sure you list the websites you use. In this way, other people can check the accuracy of your information.
Go to www.scienceworld.net.au and follow the links to the websites below. NASA Solar System Exploration Current information on the planets as well as news, missions, science and technology reports. NASA Human Spaceflight Gives up-to-date information and news about the space shuttle, the International Space Station and other space missions. Mars News Information on past, current and future space missions to Mars. The Nine Planets A multimedia tour of the solar system. Good information on the planets and space missions. Science@NASA Headline News Excellent site for current news on space science and astronomy.
Helpful hints on units
Some of the technical information you will find on the websites below contains units that may be unfamiliar to you. Websites from the USA often use miles and miles per hour (mp h). The conversions are listed below. 1 mile = 1.6 km 1 mph = 1.6 km/h Some temperatures are given in the Fahrenheit (°F) scale. To convert degrees Fahrenheit to degrees Celsius, subtrac t 32 then multiply by 0.56. That is: °C = (°F – 32) x 0.56 Astronomers often use the Kelvin scal e to measure temperatures. To convert Kelv in to degrees Celsius subtract 273. °C = K – 273
< WEB watch > Voyager Information on the Voyager missions and images of Jupiter, Saturn, Uranus and Neptune and their moons. Has an excellent Planetary Tour animated movie. Windows to the Universe Information on the planets, space missions, and myths about the planets and the universe. Has links to other sites. Welcome to the planets Profiles on the planets and a link to the planetary photojournal. Solar system exploration Has answers to questions on the planets, comets, asteroids and space missions.
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Activity In this activity you will work in a small group of three or four people to complete the tasks below. You will need to use the library (including the internet) to find information on the solar system. Task 1 Prepare a planetary facts sheet. The facts sheet should list the planets, their average distance from the sun, their diameter, the number of moons, the surface temperature, the composition of the atmosphere and any other interesting information. Remember to list the names of the books, magazines, articles or websites you used to find your information. Prepare a rough draft first, discuss it with your group, modify it where necessary, then prepare your final copy. Use a computer database such as Excel to make your facts sheet.
Task 3 Compare the length of a day and the length of a year for each planet in the solar system. Record the information in a table. What pattern can you see in the lengths of the years of the planets as you move away from the Sun? Task 4 Gravity is the force of attraction between two bodies. It is this force which keeps you on the Earth, and it is the force that keeps planets and their moons in orbit. The table below gives the mass of each planet and the gravity on the planet’s surface, compared with Earth.
Planets Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
Mass Gravity (Compared with Earth = 1) 0.06 0.8 1 0.1 318 95 14.6 17.0
0.4 0.9 1 0.4 2.5 1.1 0.9 1.1
Task 2 Use the data to plot the following graphs. Draw a bar graph to show the planets in order on the horizontal axis and the diameter of the planets on the vertical axis.
Write a generalisation about the mass of the planet and the gravity on its surface.
Draw a line graph to link the diameter of the planets (horizontal axis) and the number of moons around each planet (vertical axis).
As the gravity decreases so does your weight. On which planets would your weight be less than on Earth?
Use the graphs to answer the following questions. Write a generalisation linking the diameters of the planets with their distances from the Sun. Write a generalisation linking the diameter of the planet with the number of moons.
Task 5 Find out about the origin of the names of the planets. Choose any five planetary moons and find out about the origins of their names. You may also like to research the myths and legends of the solar system from different groups or cultures around the world.
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Activity Other objects in our solar system The interplanetary travel agency You are a travel agent with Interworld Travel who specialise in taking people to Mercury, Venus and Mars, and on flybys of Jupiter and Saturn. The travel agent was right. It IS worth a million bucks!
Asteroids In 1989 the spacecraft Galileo was launched to study the atmosphere of Jupiter and its moons. One year later it entered the Asteroid Belt and came close to the asteroid Gaspra. Gaspra is a small asteroid about 19 km long. It is composed of rock and metal typical of most of the many other thousands of asteroids that are found orbiting the sun in a wide belt between Jupiter and Mars. About 100 000 asteroids are large enough to be seen from Earth. The largest is Ceres, which is 800 km in diameter, and is classified as a dwarf planet.
Write an itinerary for tourists who wish to travel to these planets. Use the guidelines below to do this. Use library research to find out approximately how long it would take to reach each of the planets. (Your Space SuperBus travels at 200 000 km/h.) Write a brochure about the surface conditions of the planets. For those planets on which the tourists are to land, give information about the special equipment they need to wear or take with them. In your itinerary, write about some of the planetary features you think that the tourists would find interesting. You may think that some of the moons are also worth mentioning. Write a list of safety points (similar to a current airline safety list) which you think all passengers should know before they land on planets or moons.
Fig 23
The 19 km long asteroid Gaspra photographed in 1991 by the spacecraft Galileo from a distance of 16 000 km.
Astronomers once thought that the asteroids may have formed from the collision of planets which shattered into small pieces. However, when added together, the mass of the asteroids is less than half the size of our moon. A more widely accepted idea is that they are debris left over after the formation of the planets billions of years ago.
< WEB watch > Search the internet under Gaspra. You will find many interesting Gaspra websites. Try searching asteroid to find out about other asteroids.
Chapter7 Exploringspace Meteorites The craters on many of the planets and moons in the solar system are caused by collisions with meteorites. These pieces of rock or iron vary in size from millimetres to thousands of kilometres in diameter. In space these objects are called meteoroids and in a planet’s atmosphere they are called meteors. If they strike a planet they are called meteorites. The atmosphere around a planet protects it from meteorite strikes. The Earth and Venus have fairly thick atmospheres and very few craters. Mercury, with an extremely thin atmosphere, has thousands of craters on its surface.
Comets
gases and is reflected, giving the comet a glowing tail sometimes millions of kilometres long. This tail always points away from the sun. Sometimes comets collide with planets. In 1994 Comet Shoemaker-Levy 9 crashed into Jupiter. The core of this comet shattered into 20 fragments following a close approach of Jupiter in 1992. As each fragment hit the planet, it exploded in the atmosphere releasing an enormous amount of energy.
< WEB watch > Search the internet under Comet ShoemakerLevy. You will find a number of websites with information, images and movies.
Other members of our solar system which we occasionally see in the sky are comets. These objects orbit the Sun in long, narrow elliptical orbits. Many have orbits which go beyond Pluto, but some have very small orbits. The most famous is Halley’s comet which orbits the Sun every 76 years, but the Great Comet of 1864 will not come back for another 2.8 million years! The core of a comet is made of rock and dust stuck together with ice and frozen gases such as ammonia and methane. The core is usually quite small—about 10 km in diameter—but when it approaches the Sun, the frozen gases warm up and evaporate. The light from the Sun hits the
Fig 24
Fig 25
This photo shows the giant fireball that erupted when a fragment from Comet Shoemaker-Levy 9 hit Jupiter in 1994.
Halley’s comet was photographed for the first time in 1910. It was last seen in 1986 and will be back in 2062. It was seen by Julius Caesar in 87 BC, Genghis Khan in 1222 and William Shakespeare in 1607.
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First look inside a comet Wilhelm Tempel, a German astronomer, observed a small comet in 1867 and again in 1873 and 1879. This comet was named Comet Tempel 1 in his honour. Comet Tempel 1 is a periodic comet which orbits the sun every 5.5 years. This made the comet a good target for the Deep Impact mission, whose aim was to probe beneath the surface of the comet.
Liftoff The Delta II rocket carrying the spacecraft was launched in January 2005. The spacecraft was the size of a small car. It was a combination of a flyby spacecraft, which was to stay close to the comet, and a smaller impactor spacecraft, which was to crash into the comet.
Impact In July 2005 the spacecraft approached Comet Tempel 1. The impactor was released into its path and relayed images of the comet’s nucleus to Earth until just seconds before impact. Meanwhile, the high-precision tracking telescopes on the flyby spacecraft took many high resolution photos of the impact. The impact had little effect on the comet’s orbital path around the Sun, even though the 370 kg impactor created a house-sized crater.
Comet Tempel 1 profile Your task is to prepare a profile on Comet Tempel 1 which you can present to your teacher, another group or the whole class. Use a selection of websites to prepare a computer report on an aspect of Comet Tempel 1. You can write about its discovery, the structure of the comet, its place in the solar system, the Deep Impact mission and/or the Deep Impact technology. Remember to include the website addresses in your report.
Fig 26
The impactor being released from the flyby spacecraft (top), the impactor just before impact (middle) and Comet Temple 1 after impact (bottom).
< WEB watch > Search the internet under Comet Tempel. You will find many websites with information, images and animations.
Chapter7 Exploringspace
Check! d Use the information about the planets which you gathered for the activities on pages 163 and 164 to answer questions 1 to 9. 1
The planets can be divided into two main groups: the inner planets and the outer planets. Place the eight planets into these two groups.
e
In 1976 a spacecraft landed on my surface, took soil samples and sent close-up television images back to Earth. I am named after the Roman god of the sea because of my sea-green colour caused by the methane in my atmosphere.
10 The photo below shows a plains region on Venus. Apart from a few volcanoes, there are no major craters on the surface. Suggest why Venus has fewer craters than Mercury or Mars.
2
Which is the smallest planet and which is the largest planet in the solar system?
3
Decide which of the following statements are true and which are false. Correct the false ones to make them true. a Saturn is between Jupiter and Neptune. b Venus is larger than Mercury but smaller than Uranus. c Mars takes about twice as long as Earth to orbit the Sun. d Some of the moons of Jupiter are larger than the dwarf planet Pluto. e The atmosphere of Venus contains hydrogen, methane and ammonia.
4
Which planet has the largest number of moons, and which have no moons at all?
5
On which planets have spacecraft landed? Why would it be difficult to land a spacecraft on Jupiter?
6
Suppose you are 13 years old on Earth. How old would you be in Jovian (Jupiter) years? How old would you be in Mercurian years?
11 The gravity on Mars is about two-fifths that on Earth, while Jupiter’s gravity is 2.5 times greater. How could the gravity affect humans and spacecraft?
7
Suggest why Pluto is called a dwarf planet.
8
Most planets rotate from west to east, but one of our near neighbours rotates the other way. Which planet is it? In which direction would the Sun rise on this planet?
9
Which planet am I? a I am very hot. People think I am mysterious because of the clouds that cover my surface. b I am lying on my side with my south pole pointing towards the Sun. c I have a very large number of moons and small particles of rock and dust that form thousands of spectacular rings.
12 Sir William Halley (1656–1742) used mathematics and his observations through telescopes to calculate the orbits of 24 comets, one of which is named after him. Use the data in the text and in the caption of Fig 25 on page 165 to find out whether Halley observed this comet in his lifetime. Was it Halley’s comet that King Harold saw just before the Battle of Hastings in 1066? (Why did the English think comets were bad luck and the French think they were good luck?)
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challenge 1 The photo below shows a number of meteorite craters. Four of these are labelled A, B, C and D.
B A
b Astronomers think that both moons were asteroids that came close to Mars and were captured by Mars’ gravity. What evidence may have led to this inference? 3 The table below shows information about 17 of the currently known moons of Jupiter. a Can you identify the four groups of Jovian moons? Write a description for each of the four groups of moons. b Is there a relationship between the size of the moon and the date of discovery? Write a generalisation for this. c Compare the sizes of the largest moons of Jupiter with the three smallest planets in the solar system. Some of the moons of Jupiter
C
D
a Which crater was caused by the largest meteorite? b Infer which is the oldest crater. Give reasons for your inference. 2 The two moons of Mars—Deimos and Phobos— both have an irregular shape and are composed of a rocky material which is quite different from the material on the surface of Mars. Both moons are quite small. Deimos has a diameter of 12 km, while Phobos (below) is 23 km across. a What is the origin of the names Deimos and Phobos? Suggest why the moons were given these names.
Moon
Discoverer
Diameter Distance from (km) Jupiter (km)
Metis
Voyager, 1979
49
127 600
Adrastea
Voyager, 1979
35
134 000
Amalthea
Barnard, 1892
166
181 300
Thebe
Voyager, 1979
75
222 000
Io
Galileo, 1610
3632
421 600
Europa
Galileo, 1610
3126
670 900
Ganymede
Galileo, 1610
5276
1.1 million
Callisto
Galileo, 1610
4820
1.9 million
Leda
Kowal, 1974
8
11.1 million
Himalia
Perrine, 1904
170
11.5 million
Lysithea
Nicholson, 1938
19
11.7 million
Elara
Perrine, 1905
80
11.7 million
Ananke
Nicholson, 1951
17
20.7 million
Carme
Nicholson, 1938
24
22.4 million
Pasiphae
Melotta, 1908
27
23.3 million
Sinope
Melotta, 1914
21
23.7 million
Callirrhoe
Spacewatch, 1999
5
24 million
< WEB watch > Go to www.scienceworld.net.au and follow the links to the website below. Jupiter: Moons Contains information about Jupiter’s known moons and links to other websites.
Chapter7 Exploringspace
7.3 Stars and galaxies The few thousand stars which you can see with your eyes belong to our galaxy called the Milky Way. It contains more than 100 000 million stars, but it is just one of millions of galaxies in the universe. A galaxy is a collection of stars and dust held together by huge gravitational forces. Galaxies are separated from each other by vast regions of space. Until the turn of the 20th century, the Milky Way was thought to be the whole universe. A giant spiral called Andromeda, which can be observed with a small telescope, was thought to be in the Milky Way. However, in 1923 the American astronomer Edwin Hubble showed that Andromeda was in fact another galaxy about 2.2 million light-years away, well outside our own galaxy. Hubble’s discovery encouraged other astronomers to search for galaxies and now more than 100 million have been identified! Fig 31
This spiral galaxy is similar in shape to our Milky Way galaxy and the Andromeda spiral. Over half the galaxies in the known universe are spirals.
Star distances
Sun, is The distance to our closest star, the ut 3 months abo e 150 000 000 km. (It would tak a current to reach the sun if you travelled in is spacecraft.) The next closest star 270 000 times or 41 000 000 000 000 km away, the distance to the sun. rmous, and The distances to the stars are eno sure in the numbers are far too large to mea e called the kilometres. Instead, a unit of distanc ance light travels light-year is used. This is the dist in one year. metres per Light travels at about 300 000 000 t travels ligh r 8 yea second (3 x 10 m/s), so in one x 1012 km. about 9 500 000 000 000 km or 9.5 look back When you look at stars you actually the in star in time. The light from the closest years ago. In Southern Cross left that star 220 as it used to other words, you are seeing the star be in the 1780s! Galaxies can be classified into three main types—spiral, elliptical and irregular. There are three galaxies that we can see easily from Earth— the Andromeda spiral and two irregular galaxies called the Large and Small Clouds of Magellan near the Southern Cross. Fig 32
Elliptical galaxies are egg-shaped with a bright central core of densely packed stars. Only the stars in the outer regions of the galaxy can be distinguished from others.
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Direction of rotation of the Milky Way Galaxy.
Our Sun is 32 000 light-years from the centre of the galaxy. Sun
Fig 33
Irregular galaxies have no definite shape and appear as fuzzy clouds. They are the least common and make up only three per cent of all known galaxies.
Sun
In 110 million years time the Sun and our solar system will have moved through one half-turn.
< WEB watch > Go to www.scienceworld.net.au and follow the links to the websites below. The Anglo-Australian Observatory Good images and information about stars and galaxies. Search galaxies or Andromeda galaxy in your internet search engine. You will find a number of websites with information, images and movies.
Diameter = 110 million light-years
Fig 34
The Milky Way rotates slowly about its centre. This view of the Milky Way was produced from data gathered by a satellite orbiting the Earth.
The Milky Way galaxy The Milky Way galaxy is a flat spiral shape and the ‘milky’ band appearance is due to the fact that you are looking through the central part of the spiral which contains the most stars. The areas to the side of the band have very few stars. The Milky Way has a diameter of about 110 000 light-years, which is smaller than our neighbouring spiral, Andromeda. Our Sun lies on one of the arms of the spiral, about 32 000 lightyears from the centre. The spiral rotates about its centre in space like a Catherine wheel firework.
Sun
Fig 35
A side view of our Milky Way galaxy as seen from space. Notice that most of the stars in the galaxy are concentrated in the centre.
Chapter7 Exploringspace The life of stars In the summer of the year 1054, Chinese astronomers recorded seeing a bright star appear in the sky. It was so bright that it could be seen during the day. What these astronomers had recorded was a supernova— a spectacular explosion which ended the life of a giant, hot star.
The birth of a star Astronomers believe that stars are born in clouds of gas (mainly hydrogen) and dust that occur throughout the universe. Sometimes a gas cloud collapses on itself, becoming hotter and denser as the gravitational force increases. This is the stage in the life of a star known as a protostar. Eventually the gas becomes hot enough to start nuclear reactions and the star begins to glow.
Middle age When a star about the size of our Sun forms, it initially glows very brightly. After about 10 million years, the star settles down to a long stable middle-life period of about 10 billion years. Our sun is now at midlife and has another 5 billion years to go before it runs out of fuel. Fig 37
The birth and death of a star similar in size to our Sun. Our Sun is in the middle of a stable period in its life and will last for another 5 billion years.
Fig 36
The Crab Nebula is a huge expanding cloud of gas that resulted from a supernova recorded by Chinese astronomers in 1054.
Old age and death When all the hydrogen fuel is used up, the outer layers of the star expand and cool, and the star forms a red giant. After this, the gases in the outer regions drift into space and the remaining gases collapse into a very small, very dense object known as a white dwarf. Eventually the white dwarf cools down and fades away leaving a mass of gases in space.
�
� protostars form
Our Sun is at this stage in its life.
gaseous cloud
white dwarf white dwarf gradually dies
red giant
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Nebulas
Stars many times the size of the Sun have a much shorter but spectacular life. These stars live for only about one million years. The mass in large stars creates enormous gravitational forces in the core of the star. The nuclear reactions use fuel very rapidly, creating very hot bright stars which appear a bluish-white in the night sky. When the fuel runs out, there is a tremendous outburst of energy which we see as a supernova. Much of the star’s matter is blown into space, leaving a mass of expanding cloud which is called a nebula (NEB-you-la). When such an explosion takes place the brightness of the star increases a billion times. The brightness lasts for a few days then fades over a number of years, but usually the star remains bright enough to be seen with the naked eye for a few months.
Fig 39
Fig 40
The Ring Nebula is the sort of nebula that our Sun will probably produce in about 5 billion years time. The red colour is due to the large amounts of hydrogen gas in the clouds.
This type of nebula is ma de up of clouds of very high temperature gases.
Fig 38
In 1987 David Malin, an Australian astronomer, photographed the star arrowed on the left which exploded to form the supernova on the right.
Fig 41
This is the Horsehead Nebula. It is a dark nebula and is made of clouds of dust which block the light from the stars behind it.
Chapter7 Exploringspace
Activity Up to the end of the 20th century the furthest humans had travelled in space was to the moon, a short 110 hours by rocket! Is it possible to travel further into space? Work in a small group and discuss the following questions. You will need to refer to the table and you may need to use information in the websites listed below. Using present technology, which destination could be the furthest a human might reach? Suggest why humans would want to visit other planets in our solar system. Is it practical for humans to visit the gas planets?
Destination from Earth
Could a planetary system exist around Alpha Centauri, our nearest star? Why would a planetary system be difficult for astronomers to detect? If aliens do exist, which planet or star system do you think they would come from? Is it possible for one of today’s space-craft to travel to our closest galaxy, Andromeda? How could it be made possible? (Creative ideas needed here!) Develop an argument for (or against) spending millions of dollars on space research and travel. Could the money be better spent on getting rid of poverty?
Using current spacecraft (40 000 km/h)
At light speed (300 000 km/s)
Venus
1.4 months
2.3 minutes
Mars
2.6 months
4.4 minutes
Jupiter
22 months
35 minutes
Uranus
7.8 years
2.5 hours
16.4 years
5.5 hours
113 600 years
4.3 years
176 million years
6 500 years
Pluto Alpha Centauri Crab Nebula Andromeda
10
6 x 10 years
Go to www.scienceworld.net.au and follow the links to the websites below. Space Travel Guide Detailed information about types of rocket propulsion, space shuttle and future space travel. SpaceWander Animated journey from Earth to other galaxies.
2.2 million years
< WEB watch > Space Exploration (Wikipedia) Information on the history of space travel, future developments and criticisms of space exploration. Human Space Flight (NASA) Information about missions, space stations, astronaut training and space shuttle.
Try doing the Chapter 7 crossword on the CD.
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Check! 1
a
b
Describe the shape of the Milky Way galaxy. Which other galaxy has the same shape? Which type of galaxy is the most common in the universe? Which is the least common?
2
Explain the difference between a galaxy and the universe so that a 7-year-old child could understand the terms.
3
The bright star Canopus, which can be seen due south during autumn, is 98 light-years from our solar system. a How far away is Canopus in kilometres? b During which Earth year did the light you see from Canopus actually leave the star?
challenge 1 Astronomers think that some protostars, which have very small masses, do not form stars. Suggest a reason for this. 2 The Hubble Space Telescope was placed in orbit around the Earth in 1990. Suggest why this telescope has detected objects in space that were previously unknown. 3 Data collected using the Hubble Space Telescope suggests that the Crab Nebula is about 6500 light-years from Earth. Use the information on page 171 to work out when, in Earth years, the actual supernova took place. 4 a The Sun is 1.5 × 108 km from Earth. How long does the light from the Sun take to reach the Earth? b Pluto is about 5.9 × 109 km from the Earth. Why don’t we use light-years to measure the distance to Pluto? 5 a What is the connection between a supernova and a nebula? b Suppose you are an astronomer and you are asked to predict whether a particular star will form a supernova or a red giant. What answer would you give?
4
A cosmic year is the period of time it takes for the Milky Way to complete one revolution. How many Earth years are there in a cosmic year?
5
There is a vast amount of interstellar dust and gas (mainly hydrogen) in galaxies. a What do you think the word ‘interstellar’ means? b Astronomers believe that the interstellar dust and gas is the birthplace of stars. Describe the life cycle of a star about the size of our Sun.
6
From our observations on Earth, the Sun appears to move across the sky from east to west. However, how would you observe the movement of the Sun and the planets from a neighbouring galaxy? (A diagram will help.)
6 Groups of stars are called constellations. Astronomers call the brightest star in a constellation the alphastar, the next brightest the beta-star, then the gammastar, then the delta-star and so on. The four main stars of the Southern Cross all appear to be the same distance away from Earth. However, the table below shows that they are not. Star
gamma delta
beta alpha
Distance from Earth (in light-years)
alpha-star
370
beta-star
490
gamma-star
220
delta-star
570
a Which star is closest to Earth? b If the beta-star and gamma-star were the same distance from Earth, would the betastar still look the brighter? Give reasons for your answer. c Does the information in the table tell you which star is the largest?
Chapter7 Exploringspace
Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
core
1 Ancient astronomers incorrectly inferred that the _____ was the
galaxies
centre of the _____. This inference was replaced by the idea of a central ____ with the planets revolving around it.
planets
2 Spacecraft have considerably increased our knowledge about the eight _____ in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
3 Asteroids, comets and dwarf planets like Pluto are also parts of our solar system. Asteroids are made from _____, while comets have a small frozen _____ and have a large tail when they approach the sun.
earth
rock and metal solar system spiral stars sun supernova
4 _____ are groups of millions of stars held together by gravitational forces. They have three basic shapes: _____, elliptical and irregular.
5 _____ form in clouds of dust and gas. Some stars glow for billions of
REVIEW
years, but larger stars have much shorter lives and end their lives in a _____.
1 Until the early 1600s, most people believed that: A the sun was the centre of the solar system. B all the planets revolved around Jupiter. C all the planets revolved around the Earth. D the solar system contained eight planets. 2 Which of the following is in the correct order? A Mercury–Mars–Venus–Jupiter B Mercury–Venus–Earth–Mars C Mars–Venus–Jupiter–Saturn D Venus–Earth–Jupiter–Saturn 3 a Into which two main groups can the planets in our solar system be classified? Describe the features of each group. b Why is Pluto not considered to be one of the outer planets?
4 A light-year is: A the distance light travels in one year. B the distance from the Sun to the nearest star in our galaxy. C the distance the Earth travels in one year. D the distance from the Milky Way galaxy to the nearest galaxy. 5 The Earth has very few meteorite craters compared with Mercury and Mars. Which of the following inferences best explains this? A These planets are smaller than the Earth. B These planets attract meteorites from space. C These planets are in the paths of meteorites. D These planets have little or no atmosphere to protect them from meteorites.
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ScienceWorld8forNSW 6 Spacecraft have landed on Venus and Mars. Why would it be difficult for spacecraft in the future to land on Jupiter or Saturn, but relatively easy to land on Mercury? 7 The table below shows the distance of each of the planets from the Sun and the speed at which they travel through space as they orbit the Sun (orbital speed). Planet
Distance from the Sun (million km)
Orbital speed (km/s)
58 108 150 228 778 1249 2871 4504
48 35 30 24 13 10 7 5
Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune
a Write a generalisation about the orbital speed of the planets and their distance from the Sun. b Compared with Venus, Jupiter takes: A the same time to orbit the Sun B a longer time to orbit the Sun C less time to orbit the Sun Give a reason for your answer.
–150°C
170°C
8 The object in the photo below is found deep in space and was photographed by a space telescope. The object is called: A an asteroid B a nebula C a comet D a spiral galaxy
9 The object in the photo above resulted from a supernova of a star. Explain why this is unlikely to happen to our Sun. 10 The diagram below is a cross-section of the planet Jupiter showing its inferred composition. a Write a description of the composition of Jupiter. Which element do you think is the most abundant? b How thick do astronomers believe Jupiter’s solid rocky core is? c Which is the thickest layer? How thick is it? d Make a generalisation about the temperature changes from the core to the outer edge of the planet. 10 000°C 19 000°C
mainly hydrogen gas atmosphere
atmosphere
REVIEW
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liquid hydrogen
24 000°C
liquid metallic hydrogen
water ammonia ice
rock 6400 km
13 300 km 30 000 km (drawing not to scale) 71 000 km
Check your answers on page 281.
Chapter7 Exploringspace
US AREA C O F D E B I R C PRES
Learning focus: Distinguishing between scientific, economic and legal argument
Colonising Mars Imagine it is the year 2030. The Earth’s population continues to grow and there have been major climate changes due to global warming. You have been invited to be part of an international Mars group to investigate the possibility of establishing a colony on the planet Mars. Form a group of about six, and appoint people to the following roles: • Leader—to get things started and complete the task on time Recorder—to write down • what the group has found out and decided Presenter—to present the • group’s findings to the class. You may want to take turns at these roles, and of course all members of the group should participate in all discussion and research. Your task is to consider all aspects of establishing a colony on Mars—including the scientific, economic and legal aspects. You are then to present your findings and recommendations to the class. To structure your investigation you should answer the following questions. You could search on the internet under ‘terraforming Mars’. Discuss with your teacher how much time you will need to complete this task. 1 Is Mars the most suitable planet for colonisation? Why? 2 What does it mean to terraform Mars? 3 The average temperature on Mars is –60°C. Is it scientifically possible to warm up the whole planet? How? 4 Can humans breathe the atmosphere of Mars? Could it be made breathable? How?
5 6 7
8
9
10
Are there minerals on Mars that could be used to construct the colony? Is there any life on Mars? Could food for the colony be grown there? How? Is it economical to develop a Mars colony? Could one country afford to do it on its own, or would it need to be an international effort? What legal aspects are there in colonising Mars? Who owns the planet? Who owns the minerals? Even if it is scientifically and economically possible to terraform Mars, should we do it? Is it ethically OK? What does your group recommend? Should we colonise Mars now, wait until a later time, or not colonise it? Explain your recommendations fully.
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8 Buildingblocks ofmatter
Planning page Getting started
8.1 Atoms and molecules page 180
Activity page 183 Investigate 16 Flame tests
8.2 Elements and compounds page 182
Activity page 188
Investigate 17 Making a compound Investigate 18 Breaking a compound
Assessment task 8 Minor elements
8.3 Chemical reactions page 191
TRB
Animation Water reaction
Main ideas Chapter 8 crossword
Review Learning focus: Observations depend on the understanding of the observer
Chapter 8 test
Prescribed focus area Inside the atom
TRB
Chapter8 Buildingblocksofmatter
179
t…
l learn abou
r you wil In this chapte
LearningFocus ●
observations depend on the understanding of the observer (page 198)
KnowledgeandUnderstanding ● ●
elements (Section 8.2) compounds and reactions (Sections 8.2 and 8.3)
Skills ● ● ● ●
choosing equipment or resources and performing first-hand investigations (Investigate 16 and 17) gathering first-hand information (Investigate 16) processing information—identifying patterns in data (Activity page 183) presenting information—using symbols (pages 182–183 and 187)
Meet Super-Sci. She can make herself smaller and smaller until she is not much bigger than the tiny invisible particles in all matter. These are called atoms and molecules. Super-Sci travels through the air where she sees nitrogen and oxygen molecules. These are ‘double atoms’, made of two atoms stuck together. They are whizzing past at about 1800 km/h, all moving in different directions. Occasionally they collide with each other. When Super-Sci dives into the harbour, she finds herself surrounded by water molecules. Each molecule consists of three atoms. The molecules are much closer together than they are
in the air. They often touch each other and are constantly moving past one another, continually changing their positions. Finally Super-Sci tries to push her way into the steel in the bridge, but the ball-like iron atoms are so close together she can’t crawl through. The iron atoms stay in their places, but they are constantly vibrating. Super-Sci counts the atoms and calculates that about eight million of them placed side by side would fit across the head of a pin! Imagine you are a TV news or current affairs presenter. Prepare a news item on Super-Sci’s fantastic voyage.
iron atoms AIR water molecules
oxygen molecule
WATER
nitrogen molecule
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8.1 Atoms and molecules In Chapter 3 you learnt about the tiny particles that make up all matter. For example, if you could break a piece of gold into smaller and smaller bits you would eventually end up with a single atom of gold. Atoms are the basic building blocks of all matter—both living and non-living. They are incredibly small. To give you some idea of their size, there would be 10 000 000 000 000 000 atoms in the dot at the end of this sentence. This means that there are about 2500 times more atoms in the dot than there are people in the world! Atoms are not usually found on their own. Two or more atoms joined together is called a molecule. For example, an oxygen molecule consists of two oxygen atoms held together by a chemical bond.
oxygen atoms
Fig 2
An oxygen molecule is made up of two oxygen atoms bonded together.
oxygen atom
Fig 3
A water molecule is made up of an oxygen atom combined with two hydrogen atoms, one on each side, a bit like Mickey Mouse’s ears.
A water molecule is made up of two hydrogen atoms bonded to one oxygen atom. This means water contains two different types of atoms. Molecules vary in size from tiny hydrogen molecules up to the huge protein molecules in your body. Each of these protein molecules contains about half a million atoms. Only in recent years have scientists been able to use special microscopes to ‘see’ atoms and molecules.
Fig 4
In this photo taken using a scanning tunnelling microscope, each little ‘mountain’ is a molecule.
Chapter8 Buildingblocksofmatter
Science in action John Dalton (1766–1844) John Dalton was born in 1766 and spent his childhood in a small English town. He soon became interested in mathematics and science, and when he was 12 he started a school of his own. This school seems to have been quite a success, despite the difficulty he had keeping the other children in order, especially those who were older than he was. Dalton continued teaching and lecturing throughout his life. He never married, and he said this was because his head was ‘too full of triangles, chemical processes, and electrical experiments to think much of marriage’. Dalton was a Quaker, and Quaker men and women had to dress in dark clothes. He was also colour-blind. The story is told that he once bought his mother a pair of bright scarlet stockings. He thought they were ‘bluish-drab and Quakerish’, and was very upset when his mother said she could not wear them because they were too bright. She had to call in a neighbour to convince her son that the stockings were bright scarlet and not bluishdrab. Dalton made over 200 000 recorded weather observations during his life. However, his greatest achievement was his atomic theory. He did a series of experiments and hypothesised that the atoms of any one element are identical to each other but different from those of all other elements. He also suggested that chemical reactions take place through rearrangements of atoms. Dalton imagined his atoms to be like pool balls, and he devised symbols for the different atoms. Some of his ideas later proved to be incorrect. For example, he inferred that a water molecule is made up of one oxygen atom and one hydrogen atom, instead of two hydrogen atoms. However, the atomic theory used today is basically the same as the theory Dalton proposed 200 years ago.
Questions 1 Which nationality was John Dalton? 2 What did he do for a living? 3 In your own words, explain why Dalton never married. 4 What was Dalton’s atomic theory? 5 How did he explain chemical reactions? 6 Suggest why Quakers wore drab clothing. 7 How does a hypothesis like Dalton’s become a theory? 8 Is Dalton’s atomic theory the same as the particle theory you learnt about on page 62? Explain.
ogen
Hydr c
in z Z
Sulf
Nitrogen
ur
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8.2 Elements and compounds Elements If you could look inside a piece of iron like Super-Sci did on page 179, you would find that it is made of millions and millions of tiny iron atoms—all the same. Similarly, a piece of copper is made of copper atoms only. But the piece of copper is different from the iron, because the copper atoms are different from iron atoms. Pure substances like iron and copper, whose atoms are all the same, are called elements. The photo below shows children building with Lego blocks. Thousands of different models can be built from a small number of different types of blocks. In a similar way, everything in the world around us is made from just over one hundred different elements. The first elements discovered were the metals gold, tin, copper and iron. Over the years more and more elements were discovered. In total, 90 elements have been found in the Earth’s rocks, soil, air and water. Another 20 or so elements, Fig 6
From just a few different Lego blocks you can build many different models.
which do not occur naturally, have been made by nuclear scientists, and more will almost certainly be made in the future. The radioactive substance plutonium is one of these synthetic elements. Some elements, like gold and silver, are very rare. Other elements are very common. For example, oxygen makes up about half of the mass of the Earth’s crust. Some common elements are listed in the table opposite. They can be classified into two main groups—metals and non-metals. (Metals conduct electricity, and most non-metals do not.) The elements can also be classified according to whether they are solids, liquids or gases at room temperature (20°C). Each element is represented by a symbol. This is a shorthand way of writing the name of the element. Sometimes the symbol is the first letter of the English name of the element: for example, carbon C. However, some elements have the same first letter: for example, carbon and calcium. In these cases a second letter is used: calcium Ca. Note that the first letter is a capital, but the second letter is not. In some cases the symbol comes from a Greek or Latin name. For example, the symbol for gold is Au. This comes from the Latin word aurum, which means ‘shining dawn’. Some elements are named after famous people or places: for example, einsteinium and francium. er... it seems Miss Jenkins actually asked us to bring in an example of an ELEMENT....
Chapter8 Buildingblocksofmatter
Activity Use the table below to answer these questions. 1 Write down the symbols for the following elements: calcium iron nitrogen carbon lead oxygen hydrogen magnesium sodium 2 Which elements have the following symbols? Al Au Br Cl Cu Hg K P S Zn 3 Which one of the elements in the table has the highest melting point? 4 Which is the most recently discovered element in the table? When was it discovered?
Element aluminium argon bromine calcium carbon chlorine copper gold hydrogen iodine iron lead magnesium mercury nitrogen oxygen phosphorus plutonium silver sodium sulfur zinc
Symbol Al Ar Br Ca C Cl Cu Au H I Fe Pb Mg Hg N O P Pu Ag Na S Zn
5 Which of the elements are solids, which are liquids, and which are gases? solids:
melting point and boiling point above 20°C (room temperature)
liquids:
melting point below 20°C, but boiling point above 20°C
melting point and boiling point below 20°C Put your answers in a table. gases:
6 Are metals usually solids, liquids or gases at room temperature? 7 Which is the lightest gas?
Metal or Melting Boiling 0 non-metal point ( C) point (0C) metal non-metal non-metal metal non-metal non-metal metal metal non-metal non-metal metal metal metal metal non-metal non-metal non-metal metal metal metal non-metal metal
660 –189 –7 850 3500 –101 1080 1060 –259 114 1540 327 650 –39 –210 –219 44 640 961 98 119 419
2060 –188 58 1440 4200 –35 2500 2700 –253 183 3000 1744 1110 357 –196 –183 280 3230 2200 890 444 910
Density (g/cm3) 2.7 0.0017 3.1 1.6 2.2 0.003 9.0 19.3 0.00008 4.9 7.9 11.3 1.7 13.6 0.00117 0.00132 1.8 19.8 10.5 0.97 2.1 7.1
Date of discovery 1825 1894 1826 1808 ancient 1774 ancient ancient 1766 1811 ancient ancient 1808 ancient 1772 1774 1669 1940 ancient 1807 ancient 1700
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Science in action Marie Curie (1867–1934) Marie Curie was born in Poland in 1867. At school she was always top of her class, and she went to university in Paris. Marie and her husband Pierre, who was also a scientist, became interested in pitchblende, an ore of uranium that was radioactive. It gave off a strange new radiation, including the newly discovered X-rays. They found that it was even more radioactive than pure uranium. So what else could be in the ore that gave out radiation? Marie thought she was on the track of a new element. Marie bought a tonne of pitchblende and had it dumped outside the shed where she worked in Paris. She and her husband ground the heap of ore to a powder, 20 kilograms at a time. They dissolved each lot of powder in acid, and evaporated the solution to form crystals. After four years of backbreaking work, Marie and Pierre had a tiny pile of white crystals a little bigger than the head of a pin. These crystals contained a new element called radium. In the dark it glowed with a bluish light. Whenever Marie worked with radioactive radium, her hands became covered with sores, burns and blisters. This led to the discovery that radium can be used to kill diseased cells in cancer tumours. Even though the gram of radium she had extracted was worth millions of dollars, she gave it to her university. During World War I, Marie organised mobile X-ray vans so that pieces of shells in wounded soldiers could be found and removed. In 1934 Marie Curie died of leukaemia, a disease probably caused by the radioactive materials she had worked with. She was the first woman to receive a Nobel Prize—one in physics and one in chemistry. During her life she had discovered two new elements—radium and polonium. In 1946 American scientists discovered another radioactive element. It was called curium in honour of Marie and Pierre Curie.
Questions 1 When and where was Marie Curie born? 2 What was radium used for?
Fig 8
Marie Curie in her laboratory
3 What was the name of the ore from which she obtained radium? 4 Suggest why Marie named one of the elements she discovered polonium. 5 Which new element was named in honour of Marie and Pierre Curie after their deaths? 6 Suggest how Marie could have protected herself from radiation.
< WEB watch > Research Marie Curie on the internet. Here are two sites to get you started: Marie Curie and the science of radioactivity Her life in detail, well-illustrated Marie Sklodowska Curie Her life presented as a series of simulated news articles that might have been written during her life
Chapter8 Buildingblocksofmatter
Investigate
16 FLAME TESTS Aim Different metals produce different colours in a flame. The aim of this investigation is to identify various metallic elements using flame tests.
Materials • Bunsenburner • smallatomiserbottlescontaining0.5Msolutions ofthefollowingorothersolublemetalsalts: bariumchloride potassiumchloride calcium chloride sodium chloride copper sulfate strontium chloride • unknownmetalsolution(Step4)
vaporises.(Youmayneedtorepeatthisifyou didnotseethecolourclearly.) 3 Repeat the procedure with the atomisers of the other solutions. Record the flame colours for the different metalsinyourdatatable. 4 Nowthatyouknowthecoloureachmetal producesinalame,yourteacherwillgiveyou anunknownmetalsalt.Testitandinferwhich metal it contains. Wear safety glasses.
Planning and Safety Check • Drawupasuitabledatatabletorecord your results. • Whatsafetyprecautionswillbe necessary?
Method 1 Lighttheburnerandadjustittothebluelame. 2 Holdtheirstatomiserbottlejustbelowthetop oftheburner,about20cmawayfromthelame. Spraythemistsothatitgoesupintothelame and observethelashofcolourasthesolution
Particles in elements
carbon atom
Metals, such as gold, are composed of collections of single atoms. In non-metals the atoms are bonded together. For example, diamond consists of carbon atoms, each linked to four other carbon atoms, as shown in Fig 10. Some gaseous elements contain separate molecules. For example, the molecules hydrogen (H2), nitrogen (N2), oxygen (O2) and chlorine (Cl2) each contain a pair of atoms. The gas ozone (O3), which protects us from UV radiation from the sun, has a molecule containing three atoms of oxygen. Fig 10
Part of a crystal of diamond
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Fireworks The Chinese were probably the first to use fireworks when they discovered how to make the black powder we call gunpowder about AD 850. They wrapped the black powder in bamboo or paper tubes to make crude missiles and flares that could be used to frighten away potential invaders. This was the beginning of pyrotechnics, which means ‘the art of making fireworks’. The Italians were probably the first to experiment with coloured fireworks in the early 1700s. The white colours of fireworks are due to the metals aluminium and magnesium burning at about 3000°C. The gold colours are due to iron and charcoal at a lower temperature. The other colours are produced by adding small amounts of other metals. For example, barium gives you a green colour, copper gives you blue and strontium gives you red. A fireworks shell is a cardboard sphere filled with hundreds of little black balls called stars, which contain the colour-producing elements. The stars are surrounded by the bursting charge. Multiple-burst shells are designed with several separate compartments. At the bottom of the main fuse cylinder time-delay fuse cardboard shell stars bursting charge side fuse black powder lift charge
Fig 11
The design of a fireworks shell
shell is a compartment that contains the black powder lift charge. To set off the firework, pyrotechnicians place the shell in a plastic cylinder and light the main fuse. This in turn lights the main fuse that ignites the lift charge at the bottom. This propels the shell high into the sky, where the time-delay fuse ignites the bursting charges to propel the stars out of the shell. Andrew and Christian Howard are brothers. They are directors of Howard and Sons Pyrotechnics, who light up our skies with spectacular fireworks displays. Andrew’s interest in fireworks was sparked at the age of seven, when his father took over the business from his grandfather. When asked how he got started, Andrew said ‘There are TAFE courses that specialise in high explosives, but not in fireworks. There are no textbooks covering our trade, so basically we learn from the dos and don’ts. We abide by some fairly strict safety regulations, particularly to ensure no spectators or staff are injured.’ Christian has arranged the special effects in movies such as The Matrix and live shows such as Metallica and Pink Floyd.
< WEB watch > For great fireworks photos, go to www.scienceworld.net.au and follow the links to Howard and Sons Pyrotechnics.
Chapter8 Buildingblocksofmatter Compounds If you look at Fig 3 on page 180 you will see that water molecules contain two different kinds of atoms—hydrogen and oxygen. Similarly, molecules of the poisonous gas carbon monoxide contain one carbon atom combined with one oxygen atom. And molecules of carbon dioxide (which plants use in photosynthesis) contain one carbon atom combined with two oxygen atoms. Substances that are made of two or more different kinds of atoms are called compounds. A chemical formula is a shorthand way of showing which elements are in a compound. It also tells you how many atoms of each element are present in one molecule of the compound. For example, water has the formula H2O. This tells you that each molecule of water contains two atoms of hydrogen (symbol H) and one atom of oxygen (symbol O). In other words, the hydrogen and oxygen are in the ratio 2:1. To read the formula aloud you say ‘H two O’.
Sodium chloride (common salt) has the formula NaCl. To read such a formula you say the letters in order: N-a-C-l. Sodium chloride is a solid compound and has the structure shown below, with sodium and chloride particles packed together tightly. There are no separate molecules, but the formula tells you that there are equal numbers of sodium and chlorine atoms. Iron oxide (rust) has the formula Fe2O3 (F-etwo-O-three). It has a similar structure to sodium chloride, but there are two particles of iron for every three particles of oxygen. (The iron and oxygen are in the ratio 2:3.) symbol for hydrogen
symbol for oxygen
WATER Each molecule contains two atoms of hydrogen and one of oxygen.
vinegar water
salt
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Activity Molecular models Because atoms and molecules are too small, we use models to represent them. There are two main types of molecular models. In both types the atoms are represented by coloured balls of different sizes. Different colours represent different atoms. In ball-and-stick models (see Fig 10 on page 185) the balls are joined by sticks to form molecules. There are no such sticks connecting atoms—they merely represent the bonds between the atoms. When you use these models you will notice that the bonds between atoms are at definite angles. The other type of model is the space-filling type (Fig 3 on page 180), where the atoms fit together at the correct angles. Make models to represent these molecules: ammonia (NH3) hydrogen (H2) methane (CH4) oxygen (O2) carbon dioxide (CO2) water (H2O)
Hey, you should be doing your science project - not playing about making models.
Draw a diagram of each molecule, labelling the different atoms. Examine the models to see how many bonds each type of atom can form. Record your results in a table.
Living and non-living All things, whether living or non-living, are made up of elements and compounds of these elements. Common non-living things like salt and sugar are usually compounds. For example salt (sodium chloride) is a compound of sodium and chlorine. Cane sugar is a compound of carbon, hydrogen and oxygen. Many substances, such as petrol, are a mixture of a number of different compounds. Living things contain a large number of different compounds, some very simple (eg water), and others very complex (eg proteins, fats and carbohydrates). These compounds are made up of about twenty essential elements, as shown in the diagram on the right. About 65% of your body mass is water (hydrogen and oxygen). The proteins, fats and carbohydrates all contain carbon. Hence the high proportion of oxygen, carbon and hydrogen in your body. Fig 16
O C H N Ca P
O O O O O O O O O O O O O O O O O O O O O O O O O O O O O oxygen 65% O O carbon 18% O O C C hydrogen 10% C C nitrogen 3% C C calcium 2% C H phosphorus 1% H other elements 1% H N Ca
The building blocks of the human body (percentage by mass)
O O O O O O O O O O C C C
O O O O O O O O O O C C C C H H H H N P
O O O O O O O O O O O O C C C C H H H N Ca
Chapter8 Buildingblocksofmatter The basis of life is a compound called DNA, which determines what you are like. It contains only the elements carbon, hydrogen, oxygen, nitrogen and phosphorus. However, DNA is very complex, and the various atoms can be combined in millions of different ways. The result is that there are millions of different types of DNA. What makes you different from everybody else is the way in which the atoms in the DNA in your body are put together. All matter can be divided into living and non-living things. Cells are the building blocks for living things. But cells and all non-living things are made of elements and compounds, which in turn are made of atoms and molecules. The salt in your body is the same as the salt on the kitchen table. And the calcium carbonate in an eggshell and in your bones is the same as the calcium carbonate in limestone. Just what gives a living thing life is not well understood. In the nineteenth century scientists said that living things contained a mysterious ‘vital force’. However, it is now known that living things contain very complex compounds. Somehow life is associated with these complex compounds. Scientists have been able to work out the structures of living substances. In fact, they have even been able to make quite complex substances in the laboratory. One such substance is insulin‚ one of the smallest proteins. Some day scientists may be able to create life itself! Fig 17
A model of a small section of the complex DNA molecule: oxygen—red carbon—black hydrogen—white nitrogen—blue phosphorus—purple
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Check! 1
2
3
4
Ask someone to check your spelling of these words: carbon dioxide
hydrogen
compound
molecule
element
sodium chloride
formula
symbol
What is the difference between— a an atom and a molecule? b an atom and an element? Which of the following are elements: aluminium, carbon monoxide, copper, iron oxide, kerosene, mercury, phosphorus, sand, sugar, water? Which element is present in all of the following compounds? SO2
5
challenge
H2S
H2SO4
CuSO4
Suppose you represent the atoms in three different elements by ●, and . How many different molecules could you form by linking these atoms together: a two at a time? b three at a time?
Select an element and use library resources to find out what you can about it. Here are some things you might look up: 1 Name of discoverer, date of discovery, how the element was named. 2 Properties and uses of the element. Go to www.scienceworld.net.au and follow the links to these websites: Web Elements Select an element for a range of information including photos, cartoons and audio descriptions.
1 UseFig16onpage188todrawabargraph and a pie chart of the elements in the human body. 2 Whyaretheresomanymorecompoundsthan elements? 3 Drawupatablewithtwocolumnsheaded ‘Elements’ and ‘Compounds’. Put each of the followingintothecorrectcolumn:
Al
SiO2
CO2
Cu
N2
NH3
H2SO4
O3
4 Writetheformulaforeachofthefollowing molecules: a nitrogen dioxide contains one nitrogen atom and two oxygen atoms b propanecontainsthreecarbonatomsand eight hydrogen atoms c glucosecontainssixcarbonatoms,twelve hydrogen atoms and six oxygen atoms. 5 A tiny crystal of magnesium chloride contains 2billionmagnesiumatomsand4billionchlorine atoms.Whatistheformulaforthecompound?
< WEB watch > CHEM4KIDS Simple information on the first 36 elements, with puzzles and help with pronouncing their names. The Visual Elements Periodic Table Very colourful and interactive It’s elemental Below the table you can click on a number of online games based on the elements. The Periodic Table of Comic Books Click on an element to see a list of comic book pages involving that element.
Chapter8 Buildingblocksofmatter
8.3 Chemical reactions Over the years scientists have experimented with substances—mixing them, heating them and passing electricity through them. For example, a chemical reaction occurs when sugar is heated. It splits into two simpler substances—water and carbon (which is black). Scientists discovered that carbon and other elements cannot be split into anything simpler by chemical reactions. They cannot be split because they contain only one sort of atom. Using chemical reactions, scientists are also able to make many new compounds. For example, when carbon is heated it reacts with the oxygen in the air to form the compound carbon dioxide. As you learnt in Chapter 1, most substances
are not pure, but are mixtures of two or more different substances (elements or compounds) which are not chemically combined. Air is a good example of a mixture. It contains many different elements and compounds, whose proportions are not always the same. all substances
mixtures
pure substances
compounds
elements
In Investigate 17 you can use a chemical reaction to make a compound. Then in Investigate 18 you can break a compound down into its elements.
Investigate
17 MAKING A COMPOUND Aim Tomakeacompoundfromtheelementsironand sulfur.
Planning and Safety Check • Read through the experiment and note the placeswheresafetyprecautionswillbe necessary. • Discuss the experiment with your teacher. Onlyonegroupatatimecanusethefume cupboard,andyourteachermaypreferto demonstrate all or part of the experiment.
PART A
Te s ti ng ir on & s ulfur Method 1 Place a small amount of iron powder in a test tube.Useamagnetasshowntotestwhether you can pull the iron powder up the side of the testtube.Ifyoucan,thentheironpowderis magnetic. Test some sulfur in the same way.
Materials • • • • • • • •
powderedsulfur ironpowder dilutehydrochloric acid(1M) spatula barmagnet • smalltesttube • Bunsenburner tripodandheatproofmat •
magnet Corrosive
aluminiumfoil crucible pipeclaytriangle
iron powder
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2 Add a few drops of dilute hydrochloric acid to someironpowderinatesttube.
Wear safety glasses.
Observewhathappens. Do the same with the sulfur. 3 Puttwospatulasofsulfurinanothertesttube, thentwospatulasofironpowder.Mixthemwell byshakingthetesttube. Testthemixturewiththemagnet.Whatdo you notice?
iron powder + sulfur crucible
aluminium foil
pipeclay triangle
Discussion 1 Did the properties of the iron and sulfur change when you mixed them? 2 Wasthereachemicalreactionwhenyoumixed them? 3 Have the iron and sulfur formed a mixture or a compound? Explain your answer.
PART B
Makin g iron s ul f ide Method 1 Linethecruciblewithsomealuminium foil and pour in the mixture of iron and sulfur. (Thealuminiumfoildoesn’treact—itsimply stopsthehotmixturestickingtothecrucible.)
4 Add some dilute hydrochloric acid to a small pieceofthesubstanceinthecrucible.(This shouldalsobedoneinafumecupboardasthe ‘rottenegg’gasgivenoffispoisonous.) Recordyourobservations.
Caution: The fumes from burning sulfur are poisonous. It is essential to use a fume cupboard so that you don’t breathe in any of the fumes. 2 Putthecrucibleinapipeclaytriangleona tripod,asshown.HeatitwithaBunsenburner. Assoonasthemixturebeginstoglow,turnoff theburner. 3 Whenthecruciblehascooledexaminethenew substancethathasformed. Describethepropertiesofthenew substance. Isthesubstancemagnetic? Can you separate the iron and sulfur?
Isthisthesamegasthatwasformedwhen you added hydrochloric acid to iron powder? How could you tell?
Discussion 1 Did the properties of the iron and sulfur change when you heated the mixture? Explain. 2 Wasthereachemicalreaction?Howdoyou know? 3 Whatwasneededtomakethereactionoccur? 4 Have the iron and sulfur formed a mixture or a compound? Explain your answer. 5 The compound you have made is called iron sulfide.Whataretheelementsinit?
Chapter8 Buildingblocksofmatter
Investigate
18 BREAKING A COMPOUND Aim Toindoutwhatsubstancesareproducedwhen waterisdecomposed(splitup)bypassing electricity through it.
3 Connectthevoltametertoapowerpackseton 6 volts DC. Turn it on. 4 Allowthecurrenttolowforabout15minutes, andobservethegasesthatcollectinthetubes.
Corrosive
Compare the volumes of the gases in the twotubes.
Materials • • • • •
dilutesulfuric acid(1M) voltameter(vol-TAM-e-ter) 2pyrextesttubes woodensplint,egpaddle-popstick distilledwater • powerpack
5 Invertadrytesttubeoverthetubewiththe most gas in it. Then open the tap and collect the gas. • taper
Planning and Safety Check
Lightataper,tiltthetesttubeupwards,andput theburningtapernearitsmouth. A ‘pop’ indicates the gas is hydrogen.
Read through the investigation. A voltameter is an expensive piece of equipment and theschoolprobablyhasonlyone.Soyour teacherwillprobablysetuptheequipment for you.
Method 1 Setupavoltameteras shown.
Wear safety glasses.
water
Afterthe‘pop’,lookforwaterdroplets insidethetube.Inferwheretheycamefrom.
tap voltameter
6 Collectatesttubefullofgasfromtheother voltametertube.Lightthewoodensplint,then blowitoutsothatithasaglowingtip.Putthe glowingsplintintothetesttube.Ifitburstsinto flame this indicates the gas is oxygen.
power pack
Discussion 1 Whatwerethetwogasesproducedwhen electricity was passed through water?
–
+
2 Openthetapsatthetopandaddwater containing a few millilitres of dilute sulfuric acid tothemiddletube.(Theacidmakesthewater conductelectricitymoreeasily.)Whentheside tubesarefull,closethetaps.
2 Copyandcompletethissentence.Waterisa compound of the elements ______ and ______. 3 Whenhydrogenburnsitcombineswiththe oxygenintheair.Inferwhatsubstanceis formed.(SeeStep5above.) 4 The volume of hydrogen produced was twice thevolumeofoxygen.Suggestareasonfor this.
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ScienceWorld8forNSW Chemical equations When you mixed iron and sulfur and heated the mixture, a chemical reaction occurred. The iron and sulfur were the reactants—the substances you started with. The iron sulfide was the product of the reaction. The equation for the reaction is: iron (Fe)
+
sulfur (S)
iron sulfide (FeS)
The reactants and products in a reaction can be solids, liquids or gases. For example, in Investigate 18 liquid water decomposed to produce hydrogen gas and oxygen gas. water (H2O) hydrogen (H2) + oxygen (O2)
During this reaction, molecules of water break apart and form molecules of hydrogen and oxygen.
Water molecules always contain two atoms of hydrogen bonded to every atom of oxygen. So when water decomposes, two molecules of hydrogen are formed for every molecule of oxygen, as Fig 22 shows. This is why the volume of hydrogen gas produced in Investigate 18 was exactly twice the volume of oxygen gas produced. Similarly, when a compound is made, exact quantities of the different elements react. The atoms in some molecules are more tightly bonded together than in other molecules. As a result, when molecules are rearranged during a chemical reaction, energy may be needed or energy may be released. The reaction between iron and sulfur needed heat to make it go, and the decomposition of water needed electricity. On the other hand, burning produces heat, and the reactions that occur inside batteries produce electricity. To see how this works, open the Water reaction animation on the CD.
H
H
O
H
H
1 94
H
O
O
O
H
Fig 22
Check! 1
State whether each of the following statements is true or false. Rewrite those that are false. a New substances are produced in a chemical reaction. b The rusting of iron is a chemical reaction. c Hydrogen is another name for water. d Hydrogen sulfide contains two elements—hydrogen and sulfur. e In a mixture, the parts can be separated only by a chemical reaction. f Compounds cannot be broken down into simpler substances. g The same elements can combine to form many different compounds.
H H
The compound water decomposes to form the elements hydrogen and oxygen.
2
Classify the following substances as elements, compounds or mixtures. air protein copper pure water hydrogen rust iron oxide soft drink mercury sulfur dioxide
3
Sodium is a soft silvery metal that reacts violently with water, and chlorine is a poisonous green gas. Sodium chloride (common salt) contains these two elements, but is safe to eat. How can you explain this?
4
Pure substance X is a green powder. When heated, it gives off a gas and changes to a black powder. Is substance X an element or a compound? Give reasons.
Chapter8 Buildingblocksofmatter
challenge 1 DiagramsAtoDbelowrepresenttheparticlesin differentsubstances.Whichrepresents: a an element? b a compound? c a mixture of elements? d a mixture of compounds?
A
andantiseptics,andinrocketfuel.Ifwater andhydrogenperoxidearebothmadeup ofhydrogenandoxygen,whyaretheyso different?Writeanexplanation. 5 Thediagrambelowillustrateshowammonia gas is made from nitrogen and hydrogen gases. ELEMENTS
B
hydrogen
C
nitrogen
D
MIXTURE
2 a Whatsubstancedoyoupredictwillbe formed when hydrogen and oxygen react together? Explain your prediction. b Writeawordequationforthereaction. 3 Tamaraheatedawhitepowder,andtwodifferent gasesweregivenoff.Onewasapoisonous browngascallednitrogendioxide,andtheother wasoxygen.Aredsubstancewasleftbehindin thetesttube. a Isthewhitepowderanelementora compound? b WhichelementscanTamarabesureare in the white powder? c WhenTamaracontinuedtoheatthered substance,shewasleftwithasilvery liquidcalledmercury.Moreoxygenwas alsoproduced.Whatarealltheelements in the white powder? 4 Hydrogen peroxide is a compound of hydrogenandoxygen.However,itisquite differentfromwater,andisusedinbleaches
COMPOUND
a Whatistheratioofnitrogenatomsto hydrogen atoms in the ammonia molecule? b Inwhatratiodothenitrogenandhydrogen react?Isthisthesameratioasinthe ammonia product? c Whatisthetotalnumberofatomsinthe product?Isthisthesameasthetotalnumber of atoms in the reactants? d Copy the diagram and draw the molecules in the boxlabelledMIxTURe. e Writeawordequationforthereaction.
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Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
1 ______ are the basic building blocks of all ______, both living and non-living.
2 Pure substances can be either ______ or compounds. Most substances are ______ of two or more pure substances.
3 A ______ is two or more atoms joined together by chemical
atoms bonds chemical reactions compound elements formula matter
______.
4 An element is a ______ made of atoms of only one type. It cannot be decomposed into simpler substances by chemical reactions.
mixtures molecule
5 There are over 100 different elements, each with its own ______.
pure substance
6 A ______ is a pure substance made up of two or more different
symbol
elements combined together.
7 The chemical ______ for a compound tells you what elements it contains. It also tells you the ratio of the atoms of these elements.
8 ______ can be used to make compounds from elements, and to break down compounds into elements.
Try doing the Chapter 8 crossword on the CD.
REVIEW
1 Which one of the following can you normally see without a microscope? A cells B elements C molecules D atoms 2 Copper, iron and chlorine are all: A compounds B mixtures C elements D metals
3 How many naturally occurring substances are there that cannot be broken down into simpler substances by chemical reactions? A ninety B hundreds C many thousands D not known 4 Which one of the following is a compound? A sodium B chlorine C sugar D hydrogen
5 Nitrogen dioxide is a compound which contains nitrogen and oxygen in the ratio of one atom of nitrogen to two atoms of oxygen. Its formula would be: A NO C NO2 B N2O D N2O2 6 If ● and ● represent two different atoms, which one of the following would best represent: a an element? b a compound c a mixture ●
A ● ●
C
●
B
●●
● ● ● ●
● ●
D
● ● ● ● ● ● ● ●
●● ●●
7 The formula for ammonia is NH3. How many atoms are there in a molecule of ammonia? 8 Nicholas knows that compounds containing sodium (a metal) produce a golden-yellow colour in a flame. He also knows that compounds containing iodine produce a purple gas when heated with concentrated sulfuric acid. He tests four chemicals and records his results. Substance
Yellow flame
Purple gas
1 2 3 4
✓ ✓
✓ ✓
a Which of these chemicals contain the element sodium? b Which contain the element iodine? c Which is likely to be the compound sodium iodide?
9 Jake pours some acid onto the element zinc. Hydrogen gas is formed and a colourless solution is left. He tests the colourless solution and finds that it contains only two different elements—zinc and chlorine. On the basis of these tests Jake can conclude that the acid contains: A hydrogen only B hydrogen and chlorine only C chlorine only D zinc and chlorine only 10 Write several complete sentences to explain the differences between an atom, a compound, an element and a molecule. 11 Stephanie passes an electric current through water in a voltameter, as in Investigate 18. She finds that the water slowly disappears and she is left with two gases—hydrogen and oxygen. She then mixes the two gases and puts a match to them. An explosion occurs and water is formed again. Knowing the structure of a water molecule, how can you explain Stephanie’s results? hydrogen atoms
oxygen atom
12 A scientist has two different compounds. She knows that the molecules in one can be represented by and the molecules in the other can be represented by . However she does not know which is which. How could she use chemical reactions to find out?
Check your answers on pages 281–282.
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REVIEW
Chapter8 Buildingblocksofmatter
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ScienceWorld8forNSW Learning focus: Observations depend on the understanding of the observer
US AREA C O F D E B I R C PRES
Inside the atom John Dalton (page 181) thought atoms were like tiny invisible pool balls. However, in 1897 an Englishman called JJ Thomson discovered tiny negatively charged particles much much smaller than atoms. These new particles were called electrons, and Thomson suggested a new model for the atom. It was like a round plum pudding of uniformly spread positive charge, with tiny negatively charged electrons scattered through it like raisins (or like the bits of chocolate in a chocolate-chip cookie). Ernest Rutherford, a New Zealander working in England, wanted to find out more about what is inside atoms. Obviously he couldn’t see inside atoms, so he used the tiny alpha particles emitted by the newly discovered radioactive element, radium. These particles were so small and moved so quickly that they passed through thin slices of matter—like X-rays through your body. Rutherford and two other scientists used a very thin piece of gold foil and around it they placed a special circular sheet that glowed when hit by an alpha particle. They found that most of the alpha particles fired at the foil passed straight through or were deflected only slightly. However about 1 in 20 000 was deflected by more than 90°. From Rutherford’s understanding of atoms, these observations didn’t make any sense. He said that, ‘It was quite the most incredible event that has ever happened to me in my life. It was almost as if you fired a 15 inch shell (40 cm in diameter) at a piece of tissue paper and it came back and hit you’. According to Thomson’s plum pudding model you wouldn’t expect the spread out positive charge or the tiny electrons to cause the large fastmoving alpha particles to bounce straight back. In 1911, after studying and thinking about the problem for a year or two, Rutherford proposed a new model in which the positive charge in the atom is concentrated in a small central core or nucleus. This nucleus would have a big enough positive charge to repel the positively charged alpha particles. Most of the particles, however,
did not bounce back because they went through the empty space inside the gold atoms. As a result of Rutherford’s careful experiments we now know that the atoms that make up planets, people, plastics and everything else are mostly empty space! • In a group discuss how Rutherford’s experiment illustrates that observations depend on the understanding of the observer. electrons
spread out positive charge
What Thomson’s plum pudding model predicted
electrons
large positive charge
What Rutherford’s new model predicted
Activity 1 Clamp a hula hoop vertically on a retort stand and use string to suspend a table-tennis ball in the middle of it. The hoop represents an atom and the ball represents its nucleus. 2 From several metres away, use a drinking straw to fire rice grains at the table-tennis ball. Count how many grains go straight through the ‘atom’ and how many hit the ‘nucleus’. 3 Is this a good model for Rutherford’s gold foil experiment? Explain.
9
Foodforlife Planning page Getting started Activity page 202 Skillbuilder page 204 Heating a liquid in a test tube
9.1 The need for food page 201
Investigate 19 Testing foods Experiment Enzyme action
9.2 Digesting food page 209
Animation Enzyme action
Investigate 20 Model intestines Assessment task 9 An energy budget
TRB
Activity page 215 Investigate 21 The blood system
9.3 Using food page 215
Animation The heart
Activities page 220
Main ideas Chapter 9 crossword
Review Learning focus: Choices need to be made when considering whether to use scientific advances
Chapter 9 test
Prescribed focus area GM foods Podcast
TRB
2 00
ScienceWorld8forNSW t…
l learn abou
r you wil In this chapte
LearningFocus ●
choices need to be made when considering whether to use scientific advances (page 225)
KnowledgeandUnderstanding ● ●
multicellular organisms—respiration, photosynthesis and plant structures humans—digestion, circulation and excretion
Skills ● ● ● ● ●
planning first-hand investigations and choosing equipment (Try this page 210, Experiment page 211 and Investigate 20) performing first-hand investigations and gathering first-hand information (Skillbuilder page 204, Investigate 19–21 and Activities pages 215 & 220) processing information—using mathematics (Activity page 202) thinking critically—using a model (Investigate 20) working individually or in teams (Experiment page 211 and Investigate 21)
Work in a small group to discuss the following tasks. ● You have just prepared a ham, tomato and cheese omelette. You are pleased with it because the eggs came from your own hens which forage in a large paddock, and you grew the tomatoes in your garden. Draw a food web to show the source of the foods that made your omelette. ● How much do you know about your body? Draw an outline of a body on a piece of A4 paper. Mark on the paper the positions of the following parts of the body: heart, liver, stomach, kidneys, oesophagus, salivary glands, intestines, anus, lungs and brain. Then briefly list the functions of each part.
Chapter9 Foodforlife
9.1 The need for food
Energy Food is needed to supply the energy for many body functions such as muscle movement and keeping a constant body temperature.
You need food for three reasons: • for energy • for growth and repair • to keep your body healthy and functioning correctly
Keeping healthy Food is needed to keep the cells and organs in your body functioning correctly.
Growth Food is needed to supply the raw materials for cell growth and the replacement of old cells.
The energy in food When a nut or piece of spaghetti burns, the chemical energy stored in the food is converted to heat energy. A similar process occurs in your body, but the energy is not released in one chemical reaction. Instead, the food is broken down in a number of steps in chemical reactions in the cells of your body. This process of obtaining energy from food in your body is called cellular respiration, or simply, respiration. The chemical energy in the food molecules is converted to chemical energy in other molecules or transformed into other forms of energy. Some of this energy is used in sending nerve messages along nerves, and to supply energy for muscle activity. In all these energy transformations the inal energy product is heat, which is eventually given off to your surroundings.
chemical energy in food chemical energy in body stored chemical energy in cells electrical energy in nerve messages kinetic energy in movement
heat
heat
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ScienceWorld8forNSW The energy in food is measured in kilojoules (kJ). A kilojoule is quite a small amount of energy. It takes about 80 kJ of heat energy to boil a cup of water. The amounts of energy in some common foods are shown below.
can of soft drink 600 kJ slice of toast with honey 560 kJ
hamburger 1450 kJ
apple 250 kJ bowl of cereal with milk 750 kJ
Activity How much energy do you use? The amount of energy you use each day depends on three factors: how much you are growing, how active you are and how much you weigh. The table shows the approximate amounts of energy used per hour by a 60 kg person doing various activities. List the activities that you did yesterday and the amount of time you spent doing each of them. Then, using the table as a guide, work out yesterday’s energy usage over 24 hours. (Assume that you are 60 kg.) Calculate how much energy you would use on a very active day. Do the same for a very inactive day. On which day should you eat more? Why? Work out how much energy you would use if you stayed in bed all day? Suggest how this energy is used. Would you use more energy standing up? Why?
Activity aerobics cycling, slow cycling, fast dancing doing homework housework jogging lying still playing ball games running fast sitting in class sleeping standing using computer walking, slow walking, fast watching TV
Energy used (kJ per hour) 7 000 700 1 500 1 000 500 600 2 500 300 2 800 10 000 500 250 400 350 600 2 000 350
Chapter9 Foodforlife
Foodtypes
There are various substances in the food you eat. But the one thing that all food contains is water. For example, potatoes contain 77% water, lettuce 93% and eggs 75%, while peanuts contain only 5% water. The dry matter in foods is made of four main food types: • carbohydrates (sugars, starch and cellulose) • proteins • fats • vitamins and minerals.
Carbohydrates (sugars, starch and cellulose) Sugars and starch are used for energy. Sugars are found in fruits, honey and sweets. Starch is found in rice, potatoes, bread and pasta. Cellulose is also called ibre and is found mostly in fruit, vegetables and cereals. It helps keep the food moving in your gut.
Proteins Proteins provide the materials for the growth and repair of cells. They cannot be stored in the body, so some protein must be eaten regularly. Meat, ish, chicken, nuts, cereals, eggs and cheese are high in protein.
Fats Fats are high in energy, producing about 2.5 times more energy per gram than carbohydrates. Fats are stored by your body as an energy reserve and also to insulate your body from heat loss. Animal fats (eg butter) are usually solid at room temperature, while vegetable fats are usually oils (eg olive oil).
Vitamins and minerals These are found in very small quantities in foods, but are as important as the other food types. They are used in various cell reactions in the body. Vitamins are found in all fresh fruit, vegetables, beans, nuts and meats.
CHIPS CHIPS
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Skillbuilder
4 Light a burner and turn the collar so that the flame is just off the yellow flame and turning blue. Heating a liquid in a test tube 5 Turn the gas down at the tap to give a small In Investigate 19 you might do a chemical flame. test for glucose. In this test you use a 6 Hold the test tube with a test tube holder Bunsen burner to heat a liquid in a test tube. and heat the liquid gently. Remember to This sounds simple, but it is a very difficult point the mouth of the test tube away from laboratory skill. you and other people. For this Skillbuilder your teacher will give 7 Move the test tube to and fro while you are you the following equipment: heating.Don’theatthetubetoostrongly, • testtube(inatesttuberack) otherwise the liquid will quickly boil and Wear safety • testtubeholder splash out of the tube. glasses. • glucosesolutionindropperbottle Record the colour change. • Benedict’ssolutionindropperbottle • Bunsenburner • matches
Method 1 Wear safety glasses. 2 Add 2 dropperfuls of glucose solution to a test tube. Then add the same amount of Benedict’ssolution. 3 Use the technique shown in the diagram to mix the two liquids.
Move the test tube to and fro while heating.
Investigate
19 TESTING FOODS Aim To test various foods for glucose, starch, protein and fat.
Materials • • • • • •
glucosesolution(10%glucosesolution) starchsuspension(20gstarch/L) proteinsolution(10%gelatinesolution) butterordripping Benedict’ssolutionorClinistix iodinesolution(5gI2in100mL10%KI)
• coppersulfatesolution(0.1M)and sodium hydroxide(2M)solution Corrosive orUristix • brownpaper • spottingtile • testtubeholder • 4testtubes,astopperandarack • burnerandheatproofmat(or aboilingwaterbathfortheclass) • smallpiecesoffoods,egcooked rice,fruit,bread,chicken,eggwhite
Chapter9 Foodforlife
Planning and Safety Check • Readeachofthe4foodtypetestsin PartAverycarefully. • Usingdiagramsandlabelsonly,describe whatyouhavetodoineachofthefour tests.
SAFE USE OF CHEMICALS 1 Protein testing solution The sodium hydroxide solution is very drop any corrosive. Take care not to splash or tely with edia on your skin. If you do, wash it imm r safety water and tell your teacher. Always wea glasses. ing glucose with Benedict’s solution Test 2 aining If you are going to heat a test tube cont must Benedict’s solution with a burner, you page. first do the Skillbuilder on the previous ng boili a up set Alternatively, your teacher may water bath for the test tubes.
PART A
Te s ts fo r fo o d t yp es Testing for glucose
Testing for starch Use a spotting tile for this test. 1 Add5dropsofstarchsuspensiontoaspoton thetile.Add5dropsofwatertoanotherspot. 2 Thenadd2dropsofiodinesolutiontothe starchandtothewater. 3 Ablue–blackcolour indicates starch is present. starch suspension water
iodine
Testing for protein DipaUristixstripintotheproteinsolutionand watchforacolourchange,ordothechemical testasfollows: 1 Add a dropperful of protein solution to a test tube,andadropperfulofwatertoasecondtest tube. 2 Addadropperfulofsodiumhydroxidesolution (takecare)toeachtesttube.
DipaClinistixstripintotheglucosesolutionand watchforacolourchange,ordothechemical testasfollows: 1 Add2dropperfulsofglucosesolutiontoatest tubeand2dropperfulsofwatertoanothertest tube(thisisthecontrol tube).
3 Thenadd2dropperfulsofcoppersulfate solutiontoeachtube.
2 Thenadd2dropperfulsofBenedict’ssolution toeachtesttube.Shakeeachtubetomix.
Rubsomebutteronapiece ofbrownpaper.Then hold the paper up to the light. Fat leaves a see-through markonthe paper.
3 Useatesttubeholdertoheateachtesttube verycarefullyoverasmalllameuntilitboils. Remembertoconstantlymovethetesttubeto andfrowhileheatingit. Ifyourteacherhassetupaboilingwaterbath fortheclass,placethetesttubesinthewater bath. 4 Aredprecipitatewillformifglucoseispresent.
4 Thebluesolutionwillturnpinkifproteinis present.
Testing for fat
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PART B
Te st i ng fo o ds Method 1 WashandcleanthefourtesttubesfromPartA. 2 Selectapieceoffoodandmashitup.Keepa little of it for the fat test, and add the rest to a cleantesttubecontainingabout5mLofwarm water. 3 Todissolveasmuch of the food as possible,youneed to add a stopper to thetesttubeand shakevigorously. Shake to dissolve the food.
4 Pourequalamountsofthemixtureintothree cleantesttubes. 5 Testforglucose,starchandproteinasyoudid in Part A. Test the solid piece of food for fat. Recordyourresults. 6 Selectanotherfoodandrepeattheabovesteps.
Discussion 1 Withoutlookingatyourbook,brielydescribe howyoutestedforglucose,starch,proteinand fat. 2 Thewatertestthatyouusedforeachfoodtype in Part A is called an experimental control. What wasthepurposeofthis? 3 Whatfoodtypeswerefoundinthefoodsyou testedinPartB?
science bits Foods
You are what you eat! If you need food for energy, why can’t you just eat fatty food, which is high in energy? The answer is that your body needs many different nutrients in foods to supply a variety of needs in addition to its energy needs. If you have a balanced diet, you are supplying your body’s needs by eating foods in the correct proportions. The table on the right shows an example of a balanced diet with the recommended amounts of foods to be eaten each day.
What’s wrong with processed foods? Processed foods are ones that are manufactured and they include biscuits, pies, chips and most fast foods. The table includes few processed foods; bread and cereals are the only ones. Processed foods often contain a high proportion of fats and very little protein. Always check the packaging for information about the fat and sugar content.
Lean meat/chicken/fish/eggs Dairy foods Wholegrain bread/crispbread High-fibre cereal Fresh fruit Vegetables Fats and oil (added to food)
Daily amount 1–2 serves 2 serves 2–3 serves 1 serve 2 serves 1–2 cupfuls 3 teaspoons
Questions Work in a small group to discuss the following questions. 1 Use the table to plan your food intake for a day. 2 What foods have you eaten in the last few days that are not included in the table? Would you consider these foods to be high in fat or sugar? 3 Suggest how your plan from question 1 would change if you were an athlete in training.
Chapter9 Foodforlife Where does food come from? Look back at your Getting Started notes. Notice in the food webs you constructed, green plants are at the beginning of each of them. This is because green plants make their own food by the process of photosynthesis, and supply food to all the other organisms in the food web. The chlorophyll in green plants absorbs the energy in sunlight, which is then used to build up larger molecules such as carbohdrates, fats and proteins. The energy chain below shows the steps in the process.
Sunlight provides energy
Chlorophyll traps the energy in sunlight.
Energy is used to make carbohydrates from CO2 and H2O.
The foods plants make Carbohydrates contain carbon, hydrogen and oxygen atoms. These are made from carbon dioxide (CO2) and water (H2O). Fats also contain carbon, hydrogen and oxygen atoms. But the atoms are arranged in different ways from those in the molecules of carbohydrates. Proteins contain nitrogen as well as carbon, hydrogen and oxygen. Plants absorb nitrogen from the soil in the form of compounds called nitrates, which are soluble in water. These nitrates are absorbed by the roots and are transported to those cells which are photo synthesising. Here they are made into proteins.
Cells use the energy in carbohydrates to supply energy for growth etc.
Many other elements, such as phosphorus, calcium, potassium, sulfur and magnesium, are also absorbed by the plant’s roots. For example, magnesium is needed in quite large quantities since it is part of the chlorophyll molecule. Other elements, such as boron, are needed in very small amounts. Fertile soil contains an abundance of the elements needed for plant growth. These elements are called soil nutrients. In natural environments, animal wastes and dead organisms are decomposed by bacteria and fungi in the soil. The resulting nutrients dissolve in water and increase the fertility of the soil. These processes form a nutrient cycle. On the other hand, where farmers harvest plant crops before they die and decay, there is much less nutrient recycling. For this reason, fertilisers have to be added to the soil.
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Check! 1
3
Draw a table with 3 columns and label the columns CARBOHYDRATES, PROTEINS, FATS. In each column list at least 4 foods that would contain a high proportion of the food type. For example, eggs would go in the protein column.
5
Bronwyn and Leong sit down together to eat lunch. Bronwyn eats a roast chicken leg and two chocolate biscuits. Leong eats an apple, a banana, and some sultanas. a Whose lunch contains more protein? b Whose lunch contains more fibre? c What does nutritious mean? Who is eating the more nutritious lunch?
6
Plant A in the diagram below was grown in fertile soil. Plant B, on the right, was grown in soil poor in nitrates. Suggest why the plants are different.
For each of the words below, write a sentence to show that you understand its meaning. respiration nutrients
2
4
proteins carbohydrates
Some of the sentences below are incorrect. Choose the incorrect ones and rewrite them to make them correct. a Vitamins and minerals are needed in large amounts by your body. b Vitamins and minerals are found in fresh fruit and vegetables, nuts and meats. c Proteins are used to supply your body with energy. They can be stored by the body. d Plants absorb all of the raw materials for growth and energy from the soil. e Cellulose is called fibre and helps keep the food moving in your gut. f Dead organisms and wastes decompose and are a source of soil nutrients. Write a paragraph to explain to someone a couple of years younger than you why we need food.
challenge 1 TanLongweighs60kilograms.Sheworksas acomputeroperatorfrom8amto4pm.Toget toandfromwork,shewalksfor30minutesto gettothetrain,hasa30-minutetrainride,then walksforanother15minutes.Shedoesaerobics foranhouronthewayhomefromwork,does houseworkforanhour,eatsdinnerandwatches TVbetween7.15pmand8.30pm,readsuntil 10,thensleepstill6am.Shesitsandhas breakfastuntil6.45am. Usethisinformationandthetableinthe activityonpage202toestimatetheamountof energyTanLonguseseachday. 2 Drawanenergychaintoshowwhathappens totheenergyinsunlightthatisabsorbedby aplantleafandeventuallystoredaschemical energyinananimal’sbody.
plant A
plant B
3 Thegraphbelowshowstherateof photosynthesisoccurringinaleafover 24hours.Intermsofenergy,explaintheshape of the graph.
Rate of photosynthesis
2 08
midnight
6 am
noon
6 pm
Time of day
midnight
Chapter9 Foodforlife
9.2 Digesting food When you take a bite out of a hamburger, you chew the mouthful of food a few times, then swallow it. That is the last you see of the hamburger. How is the hamburger digested? The diagram of the digestive system or gut, will help answer this question. The job of the digestive system is to break down the food you eat into smaller molecules, which are then able to pass from the small intestine
into your blood. Digestion is both the physical breakdown of large lumps of food into smaller ones, and the chemical breakdown of food. The chemical breakdown occurs with the help of substances called enzymes (EN-zimes), which are made in special cells in your body. These substances speed up chemical reactions, which break down large insoluble food molecules into small soluble ones.
MOUTH Digestion begins here. Food is chewed and broken into smaller pieces. Starch is chemically digested by an enzyme in saliva.
OESOPHAGUS (uh-SOF-a-gus) Food is pushed down this tube by muscular contractions in the oesophagus wall.
LIVER Stores and distributes food.
LARGE INTESTINE Water and some minerals are removed and pass into the blood here. The remaining insoluble food becomes waste and passes out through the anus.
ANUS
STOMACH This large muscular bag churns and mixes the food. Proteins begin to be digested. Hydrochloric acid released from the stomach wall kills bacteria. Food can be stored here for about 4 hours.
SMALL INTESTINE Proteins and carbohydrates are finally digested into smaller molecules. Fats are also digested. The soluble food passes out of the small intestine and into the blood.
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ScienceWorld8forNSW Digestive enzymes and food Enzymes that break down carbohydrates into sugars such as glucose are called amylases (AMill-AY-zes). Amylases are made in the salivary glands in the mouth and in other glands in the digestive system. The diagram on the right shows how amylase helps break down starch to glucose. Enzymes called proteases (PRO-tee-AY-zes) break down proteins into amino acids. These molecules are essential for your body to build structures such as cell membranes. Proteases are made in glands in the stomach and the small intestine. The enzymes that break down fats (lipids) are called lipases (LIE-pazes). Fats are broken down to fatty acids. To see how enzymes work, open the Enzyme action animation on the CD.
Enzymes in detergents Some washing detergents contain enzymes. They are added to the detergent to remove stains made by proteins such as blood and eggs, and stains from other biological sources.
single glucose molecule
1
Starch is a large molecule made up of about 300 glucose molecules joined together.
2 Amylase in saliva helps break the links joining the glucose molecules.
3
Separate glucose molecules are produced.
Proteins are very large molecules, and many are insoluble in water. They are made up of many smaller units called amino acids. All amino acids are soluble in water. The enzymes in detergents work by attacking the protein in the stain and breaking it down into smaller, soluble amino acids. The stain gradually fades as the smaller particles are removed from the fabric by the agitation of the washing machine and dissolved in the washing water.
Design a test to show the effectiveness of enzymecontaining detergents on pieces of cloth stained by fresh meat, egg, grass or other plants. To make it a fair test, you will have to control a number of variables. Check the instructions on the packets of detergents and discuss your design with your teacher. (See Chapter 2 for designing fair tests.)
Chapter9 Foodforlife
Experiment
ENZYME ACTION Theenzymeamylase(foundinsaliva)breaks downstarchintoglucose.Thisreactionoccurs inthemouthandinthesmallintestine.Canthe reactionbedemonstratedinthelaboratory?
The problem to be solved Yourtaskistoworkinasmallgrouptodesign atesttoshowthatamylaseactsonstarchto produce glucose.
Designing your experiment 1 ReadtheinformationintheHintsandtipsbox. Thenworkinyourgrouptodesigntests. 2 Makealistoftheequipmentyouwillneed. 3 Discusshowyouaregoingtorecordyour observations. 4 Discussyourdraftdesignwithyourteacher. Whenyouandyourteacherarehappywithit, get started.
Writing your report 1 Writeafullreportofyourexperiment,using theheadings:Title,Aim,Materials,Method, Results,DiscussionandConclusion. 2 Your discussion should contain an inference thattriestoexplainyourobservations.
3 Youmightliketotakeadigitalphotoofyour set-upandincludeitinyourreport.
Hints and tips 1 Youwillneedthefollowingchem icalsfor yourexperiment. • starchsuspension(20gstarc h/L) • iodinesolution • glucosesolution(10%) • Benedict’ssolutionorglucoset est strips(Clinistix) • amylasesolution(yourteache rwill preparethisfromamylasepowde r) Checkwithyourteacherifyouthink you needotherchemicals. 2 Theactionofamylaseoccurs inthebody atabout35°C.Youwillneedtos ityour testtubesinacontainerofwater atabout thistemperaturetogetreliablere sults. 3 Youmustincludecontroltubesi nyour tests.Rememberyouhavetocomp are thecoloursofyourtestswiththec ontrol tubes. 4 Usealongdroppertotakeou tsamples ofliquidsinthetesttubesandtest them onaspottingtileorinsmalltesttub esas showninthephoto.
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ScienceWorld8forNSW Food for cells When it reaches the small intestine, the food is like thick, creamy soup. The soluble food is made up of small molecules that are able to pass through the small intestine wall. From here they
pass into the blood in the many blood vessels that surround the small intestine. This dissolved food travels to the liver and is then distributed to cells in all parts of the body. Here the soluble food particles leave the blood and pass through the cell membrane into the cytoplasm of the cell.
from stomach cells small intestine
blood vessel
The blood flows through the liver and heart.
Soluble food materials pass through the intestine wall and into the blood.
Wastes pass out through anus.
Fig 16
The inside of the small intestine has many tiny projections called villi (VIL-ee) to increase its surface area. This allows more food to come in contact with the intestinal wall.
x100
Food materials pass from the blood vessels into the cells.
In the cells, glucose reacts with oxygen, which is also carried by the blood. This reaction produces the energy needed for the many cellular processes. glucose + oxygen
carbon + water + dioxide
ENERGY
The energy produced during cellular respiration is used for many body processes and for the growth and repair of cells. For example, the small molecules from the digested protein molecules are joined together to make new proteins, which are used to make membranes, organelles and other cell structures. Enzymes are required for these reactions.
enzymes
protein building blocks (amino acids)
new proteins
Chapter9 Foodforlife
Investigate
20 MODEL INTESTINES Aim Toinvestigatethesortofmoleculesthatcanpass throughmembranes.
Materials • • • • • • • • • • • • •
3lengthsofcellophanetubing(15cm) three250mLbeakers Wear safety glasses. 3twist-ties 3droppers smallfunnel spottingtileortesttubes 3rubberbands glucosesolution(10%) starchsuspension(20gstarch/L) proteinsolution(10%gelatinesolution) iodinesolution Benedict’ssolutionorClinistix Corrosive coppersulfatesolution(0.1M)and sodium hydroxide(2M)solutionorUristix
Method 1 Pourabout150mLofdistilledwaterintooneof thebeakers. 2 Holdapieceofcellophanetubingunderwater untilitissoft.Tieaknotinoneend.
4 Placethetubinginabeakerandlabelit Glucose.Securetheopenendofthetubing witharubberbandontheoutsideofthe beaker. 5 RepeatSteps1to4forthesecondpieceof tubing,butthistimeusestarchinsteadof glucose. 6 Forthethirdpieceoftubinguseproteinsolution. rubber band PROTEIN GLUCOSE
STARCH
7 Leavethebeakersforatleast15minutes (betterifleftovernight). Transferadropofthewatersurroundingthe tubingintheirstbeakertoaspottingtileor testtube.Testitforglucose(seepage205). Testthewaterinthesecondbeakerforstarch andthethirdoneforprotein(seepage205). Recordyourresultsinadatatable.
Discussion 1 Whatdoyourresultssuggestaboutthesizes ofthemoleculesthatcanpassthroughthe cellophanetubing? 3 Rubyouringers backandforthon funnel the other end until thetubingopens. Useasmallfunnelto three-quartersillthe tubingwithglucose solution. Then rinse glucose the outside of the solution tubingwithwater.
2 Ifthecellophanetubingbehavesinthesame wayasyoursmallintestinewall,whatcanyou inferaboutthepassageofsubstancesacross thesmallintestinewall? 3 Usethisinvestigationtoexplainwhyfoodhas tobedigestedbeforeitisusedbyyourbody.
Doessalt(sodiumchloride)passacross membranes?Designatesttoinvestigatethis.
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Check! 1
g h
Copy and complete the following sentences. a The speed of breakdown of foods into smaller particles is increased by ______. b Digested food passes through the ______ ______ wall and into the blood. c The oesophagus joins the ______ to the ______. d In the large intestine ______ and ______ are removed and absorbed by the blood.
2
What is cellular respiration? In your description, list the substances that are used and produced. Then write a word equation.
3
Look at the simple diagram of a human gut on the right. In which numbered part: a does protein digestion first occur? b is most of the digested food absorbed by the blood? c do wastes and insoluble material pass out of the body? d does food enter from the mouth? e is acid released to kill bacteria? f are fats digested?
2 1
3 4
5 4
The inside of the small intestine is not smooth but is folded and contains many tiny projections. What is the reason for this?
5
How does the function of the stomach differ from that of the small intestine?
6
Describe two functions of the mouth in digestion.
challenge 1 Inanexperimentonstarchandsaliva,the equipmentbelowwassetup. glass tubing
2 3
4 warm water amylase (saliva) + starch solution
Adropwasremovedfromthetesttubeusing theglasstubingandplacedonaspottingtile. Iodinewasaddedtothisdrop.Thisprocedure wasrepeatedevery10minutesforonehour. a Whatresultswouldyouexpect?
is food stored for short periods? are water and some minerals removed? (Youmayhavetousesomenumbers morethanonce.)
5 6
b Whatwasthepurposeofsamplingat 10-minuteintervals? Supposeyouwereahamsandwich.Writea fantasystoryofwhatwouldhappentoyouifyou wereeatenanddigestedbyahuman. Whenapieceofbreadisplacedonyour tongue,nothingcanbetasted.Afterashort while,asweettastecanbedetected.Inferthe reason for this. Supposeyouwantedtotesttheeffectof temperatureontheactivityoftheamylase enzymeinsaliva.Describehowyouwoulddo this. Somecellsinyourbody,egmusclecells,use moredigestedfoodmaterialsthanothers. Explainwhythisisso. Thereisanincreaseintheamountofmaterials carriedawayfrommusclecellsduringexercise. Suggestwhatmaterialstheseare,andexplain the reason for the increase.
Chapter9 Foodforlife
Activity 9.3 Using food In large multicellular organisms food has to be transported to all cells. These cells may be quite a distance from the places where the food was made or digested. For example, in a large eucalypt tree, the food that is made in the leaves may be as far as 30 metres from the cells in the roots. In a blue whale, the food digested in its intestine may have to be transported 20 metres to its brain cells. How do plants transport food? The photo of a leaf below shows the veins. These are the structures which transport materials around the plant.
Fig 23
A leaf showing the veins. The small photo, taken using an electron microscope, shows how the veins are made up of many microscopic tubes called conducting vessels.
In this activity you will observe the conducting vessels in the stem of a plant. You will need a soft stem with a few leaves (celery works well), a beaker, food colouring, a single-edge razor blade (or scalpel) and a microscope and slide. 1 Half fill the beaker with water and add some food colouring. 2 Cut the end off the plant stem and immediately place the stem in the beaker of coloured water. Leave it there for a few hours or overnight. 3 Take the stem out of the water and hold it up to the light. Can you see the colouring in the stem? 4 Use the razor blade to carefully cut a very thin cross-section of the stem. (This may take a bit of practice.) 5 Set up a microscope and view the crosssections. Draw a sketch of your stem crosssection.
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ScienceWorld8forNSW The conducting vessels you saw in the activity on the previous page were water-conducting vessels. Food-conducting vessels transport materials such as glucose and proteins. Food is made in the leaves. Food moves through foodconducting vessels.
Transport in humans Blood carries food and oxygen to all cells in your body and carries wastes away from them. Blood looks like a red liquid, but it is actually a suspension of red blood cells in a pale yellow liquid called plasma. Plasma is mainly water, but also contains dissolved food (mainly glucose), waste products, and minerals. The red blood cells carry oxygen from the lungs to the cells to be used in cellular respiration.
Water moves through waterconducting vessels. plasma water in soil
potatoes (starch storage)
The glucose that is made in photosynthesis is stored in the form of insoluble starch in the leaves. In some plants, such as carrots, sweet potatoes and turnips, a large amount of starch is stored in the main root, which swells as it stores the starch. Potatoes, yams and ginger store food in special underground stems called tubers. Fig 26
Carrots store food in the form of starch.
settled blood cells
Fig 27
Blood is a suspension of blood cells in plasma. When left, the blood cells settle out leaving the pale yellow plasma.
After the food has been digested in the small intestine and absorbed into the blood, it is carried to the liver. This is the largest organ in your body and functions as a warehouse and sorting-out or distribution centre for foods. When a meal is eaten and digested, a large quantity of glucose, amino acids and fatty acids is carried to the liver. Some of the glucose molecules are joined together with the help of enzymes to form a large molecule called glycogen, which can be stored in the liver. Some fats can be stored in the liver, but most are stored in special fat cells in tissue under the skin and around essential organs such as the heart and kidneys.
Chapter9 Foodforlife The heart and blood vessels Your heart is a muscular organ that keeps pumping blood to your body about 70 times a minute for the whole of your life. The blood vessels that carry blood away from the heart are called arteries. Veins carry blood back to the heart. Arteries and veins have the same layers of elastic and muscular tissue, but the layers in the arteries are much thicker (see Fig 28). As the heart contracts, blood is forced through the arteries. The heartbeat can be felt as a pulse near your wrist and in your neck. The large arteries and veins form many branches throughout the body. The narrowest arteries and veins branch into microscopic vessels called capillaries, which are very thin, usually only one cell thick. Food, oxygen and water pass through the capillaries to the cells, and wastes pass back as shown in the diagram below right.
ARTERY
muscle
VEIN
Fig 28
Arteries have thick muscular and elastic walls and carry blood away from the heart. Veins have thinner walls and take blood back towards the heart. blood from the heart
To see how blood flows through the heart and lungs, open The heart animation on the CD.
small artery
cells vein
blood supply to the brain
capillaries
artery blood supply to the lungs lung
heart
Food and oxygen pass to cells.
Wastes from cells pass into blood.
small vein
Large arteries take blood to the legs.
blood back to the heart
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Investigate
21 THE BLOOD SYSTEM Aim
PART B
Toinvestigateyourpulseandobservetheblood capillariesinaish’stail.
Materials • • • • •
awatchwithasecondhand,ordigitalwatch smallaquariumish,egguppy microscopeandmicroscopeslide cottonwool aquariumorpondwater
Planning and Safety Check • ReadthroughPartAanddecidewhois goingtodowhatsortofexercise.Designa datatablefortheresults. • Makealistofalltheprecautionsyouwill taketomakesuretheishinPartBisnot harmedinanyway.
Ca pillari es Yourteacherwilldothispartoftheinvestigation asaclassdemonstration. You can view the capillaries on a computer or TV monitor via a video camera fitted to a microscope.
1 Soaksomecottonwoolinpondwater,squeeze outmostofthewaterandlayitonamicroscope slide. 2 Carefullylaytheishonthecottonwooland placesomemorewetcottonwoolontopofthe ish.Thiswillholdtheishinplaceandstopit fromdryingout. 3 Makesurethetailisstickingoutofthecotton wool,asshown. wet cotton wool
PART A
fish
M e asur i n g puls e 1 Useyourindexingertoindyourpartner’spulse inthearteryintheirwrist. Recordthenumberofbeatsperminuteand call this the resting pulse rate. 2 Haveyourpartner exercise(egby standing and sitting rapidly)for2minutes. Immediatelyafterthe exercise,taketheirnew pulse rate.
I thought this was a science class - not a physical education class!
Recordyourresults. 3 Recordhowlongit takesforthepulserate to return to the resting rate. You might like to use a datalogger to measure and record your pulse rates using a pressure probe.
4 Lookatthetailthroughlowpowerona microscope.Thenswitchtohigherpowerto observethecapillariesandbloodcells. Useadiagramtorecordyourobservations.
Note: Take care of the fish and return it to the aquarium immediately after use. Discussion 1 Howdoesyourheart(pulse)respondtoa changeinactivityinyourbody? 2 Suggestwhythereisachangeinthepulserate withexercise.Includetheneedsofthebody cellsinyourexplanation. 3 Whyisitnecessaryforyourheartto continuebeatingwhenyouareasleep? 4 Doesaishhaveapulse?Suggestreasonsfor youranswer.
Chapter9 Foodforlife Getting rid of wastes Your body is like a factory. It takes in raw materials (food, water and air) and produces new products (cells and parts of cells). It uses energy in these processes and it also produces wastes. The wastes are gases, liquids and solids.
Gaseous wastes—carbon dioxide The most important cell reaction in your body is respiration, which produces carbon dioxide and water. Much of the water is reused by the body, but carbon dioxide is not used and has to be removed through your lungs. The two lungs are part of your respiratory system, and are large pink-coloured organs found inside the chest cavity. The lungs appear solid but are soft and sponge-like. The pink colour is due to the many blood capillaries in the lung tissue.
through the trachea and into smaller air tubes called bronchi (BRONK-ee), which end in minute air sacs called alveoli (AL-vee-OH-lee). The total surface area of the alveoli in the lungs is enormous—about 80 m2, or about half the size of a tennis court. The oxygen in the air breathed in passes through the thin walls of the alveoli and into the blood in the capillaries. From here the blood is pumped to cells throughout the body. The blood coming into the lungs from the body contains a lot of carbon dioxide. This passes from the blood into the alveoli and is breathed out.
nasal cavity
throat trachea ribs
Fig 33 alveoli air tubes (bronchi) diaphragm
Fig 32
Oxygen from the air passes into the blood in the lungs, and waste carbon dioxide passes from the blood and is breathed out.
Air enters the lungs from the nose or mouth and then the trachea (track-EE-a) or windpipe. The air is moved in and out of the lungs by the movements of the muscles around the ribs and the large muscular diaphragm. The air moves
A microscope view of lung tissue showing many thin-walled alveoli
Liquid wastes—urine Most of the wastes produced by cell reactions are soluble in water and are therefore able to be transported away by the blood. Many of these waste products are taken to the liver for processing. The liver is a very important organ in the body. It not only stores and distributes digested food, but it also breaks down many substances including amino acids and harmful substances such as alcohol. Urea is one of the substances produced by the liver when it breaks down amino acids. Urea is soluble and so is carried in the blood from the liver to the kidneys where it is then removed.
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Activities Blood is supplied to each of the two kidneys by a large artery called the renal artery (renal means ‘of the kidney’). About one litre of blood passes through the kidneys each minute. This blood is iltered, and the wastes and some water pass out of the kidney to the bladder. The liquid waste is called urine. The removal of wastes from the body is called excretion (ex-KREE-shun). The kidneys and liver are part of the excretory system. Sweat on your skin also removes salts and other soluble substances. But the skin is not considered part of the excretory system because the main purpose of sweat is to lower your body temperature.
Solid wastes—faeces The solid wastes are called faeces (FEE-seas) and consist of leftover material from the food you eat (mainly ibre), as well as bacteria (about 30% of the mass), water and other products of cell reactions. The faeces pass out of your body through the anus. The brown colour of faeces is due to substances produced in the liver when blood is broken down. large artery from heart
large vein to heart
renal vein
kidney
renal artery
Fig 34
Part A Looking at lungs Your teacher will show you a pair of sheep’s lungs attached to the trachea. Observe the colour and texture of the lungs and the trachea. Infer the function of the bands of cartilage in the trachea. Observe what happens when the lungs are inflated with air. Part B Looking at kidneys You will need a sheep’s kidney, a single-edge razor blade (or scalpel), scissors and gloves. 1 Peel off the fat around the kidney and look for the blood pelvis cortex vessels attached to the concave renal vein side of the kidney. 2 Use the razor blade to cut the kidney in half. renal The outer dark red artery region is called the cortex and is where the wastes are filtered. The lightto bladder coloured inner region is the pelvis and is where the urine collects. Infer the function of the fat around the kidney.
Urine flows down this tube to the bladder.
Use a library to find out the names of the various parts of the kidney, and how the kidney filters the blood.
bladder
Your teacher may supply you with a microscope. If so, cut a very thin piece of tissue from the lung and from the kidney and look at them under the microscope.
Kidneys are the main organs of excretion— the removal of wastes which are dissolved in water.
Note: Your teacher will tell you how to clean up and prepare the remains of the lungs and kidneys for disposal.
Chapter9 Foodforlife
Check! 1
2
Some of the sentences below are false. Select the ones that are false and rewrite them to make them correct. a Blood consists of blood cells suspended in plasma. b Lung tissue has very few blood vessels. c During exercise the amount of blood flowing to the body cells decreases. d Arteries have the same structure but much thicker walls than veins. e Urine is produced by the liver and is collected in the bladder.
5
What is urine? Where is it made and what happens to it in the body?
6
Bonnie had a pot plant that she kept in a sunny place on a veranda. She noticed that the plant had started to wilt. a What conditions made the plant wilt? b How could Bonnie save the plant?
7
The diagram below shows simplified blood vessels. a Match veins, arteries and capillaries to A, B, and C on the diagram. Explain your choices. b In which direction does the blood flow? How do you know?
Match the statements with the numbers on the diagram of the plant below. a This transports food and water to all cells in the plant. b Water and nutrients are absorbed here c Food and oxygen are made here. d This is where starch is stored.
B
A
1
2
C 8
What is the advantage to a plant such as a potato plant of storing food?
9
Why does the air you breathe out contain less oxygen and more carbon dioxide than the air you breathe in?
10
Suggest why your pulse rate increases when you see signs that you are in danger.
3
Delta 3 to base. (khhhk) Just noticed interesting phenomenon. (khhhk) Pulse rate seems to have increased. (khhhk) Over.
4 3
What is a pulse? Why does the pulse rate vary? What actions do you have to take to lower your pulse rate?
4
Suppose you analysed the blood in an arteryinyourarm.Youthendidthesame to the blood in a nearby vein. Which substances would you find more of in the artery than in the vein? Which substances would you find more of in the vein than in the artery?
11
During exercise your heart rate increases. Suggest why your breathing rate also increases during exercise.
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challenge 1 Whenatreeisringbarked,agrooveabout 2cmdeepiscutallthewayaroundthetrunk. Useyourknowledgeoftheplanttransport systemtosuggestwhyaringbarkedtree eventuallydies. 2 Yourbodycontainsabout5litresofblood. a Ifthekidneysilteronelitreofbloodinone minute,howmuchbloodisilteredinaday? b Howmanytimesisthe5litresofbloodiltered inaday? c Youproduceabout1500mLofurineeach day.Expresstheamountofurine produced as a percentage of the total amountofbloodilteredinaday. 3 Yourheartpumpsabout70mLofbloodwith eachbeat.Estimatethevolumeofblooditwould pumpin24hours.Whatassumptionshaveyou madeinyourcalculations? 4 Theveinsinyourbodyhavevalvesthatallow bloodtolowinonedirectiononly.
a Whatwastheaimoftheexperiment? b Whatequipmentwasneededforthis experiment? c Forhowlongdidtheexperimentrun? d Describetheresultsoftheexperiment. 6 Inafollow-upexperimentfortheonein Challenge5aplantwasplacedinameasuring cylinderofwater.Thetopwassealedbyacork. Thedropinthelevelofwaterinthemeasuring cylinderwasrecordedevery30minutes. Asimilarplantwassetupbutthistimeafanwas directed at the leaves of the plant. The graph showstheresultsoftheexperiment.
cork measuring cylinder
fan
valve
vein plant A
plant B
a Inwhichdirectionwouldthebloodlowinthe diagramabove?Howdoyouknow? b Suggestwhyarteriesdonothavevalves. 5 Aplantexperimentwassetupasshowninthe diagrambelow. bright light drops of water inside bag plastic bag moist soil
a Whatwasthepurposeofthecorkinthe measuringcylinder? b Whatvariableswerecontrolled? c Couldthenumberofleavesoneachplant affecttheresults?How? d Writeaconclusionforthisexperiment.
twist-tie
11 am 2 pm
Try doing the Chapter 9 crossword on the CD.
Chapter9 Foodforlife
Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
blood
1 All organisms need food for _____, for _____ and to keep their
carbon dioxide
bodies healthy and functioning correctly.
2 Foods contain four main food types: _____, proteins, _____, and vitamins and minerals.
carbohydrates
chlorophyll digestion energy
3 Carbohydrates include _____ and are used for energy. Fats are also an energy source, while proteins provide materials for the growth and _____ of cells.
4 Plants contain _____ and are able to make carbohydrates in photosynthesis.
fats growth kidneys photosynthesis repair
5 _____ is a process that breaks down large lumps of food into soluble materials containing small molecules which can dissolve in the blood.
sugars and starch transport
6 Plants _____ food, water and other materials in conducting vessels in stems, roots and leaves. Food made by _____ is stored as starch.
7 In humans, food, oxygen, water and wastes are carried to and from cells by the _____.
8 _____ is removed from the blood by the lungs, dissolved wastes are filtered from the blood in the _____, and solid wastes pass out of the body through the anus.
1 Which one of the following statements about respiration in animals and plants is incorrect? Respiration: A releases energy in cells. B requires oxygen. C needs sunlight. D uses up food. 2 Which one of the following statements about photosynthesis is incorrect? Photosynthesis: A uses up carbon dioxide and water, and gives off oxygen. B makes carbohydrates. C takes place in cells containing chlorophyll. D occurs 24 hours of the day.
3 Which of the following food types is used mainly for the growth of cells? A fats B proteins C vitamins and minerals D carbohydrates 4 Brad was testing various foods in an investigation. He added a few drops of a brown liquid to pieces of rice, chicken, bread and butter. He observed the rice and bread turn a blue-black colour. What substance was he testing for? A sugar C fat B protein D starch
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ScienceWorld8forNSW 5 The following questions refer to the diagram below.
The water in each of the beakers was tested for glucose at the start of the experiment and then after 30 minutes. The results are shown in the table below. Beaker 1
1
At the start After 30 mins
no glucose no glucose
Beaker 2
no glucose glucose
a Where did the glucose come from? b What was the aim of the experiment? c Why was beaker 1 included in the experiment? d Which variables were controlled?
2
3 4
8 The diagram below shows a simple model of a human heart. blood from body
a Where are most substances absorbed into the blood? b Where is food irst acted on by enzymes? c Where is food stored for short periods of time? d Where are carbohydrates irst digested? e Where are water and some minerals absorbed into the blood? 6 Which organs are responsible for the removal of solid, liquid and gaseous wastes from the body. 7 An experiment was set up using cellophane tubing. starch solution + saliva
starch solution
blood from lungs vessel C
vessel A chamber 1
chamber 3
chamber 2
chamber 4
blood to lungs vessel B
blood to body vessel D
a Which blood vessel, A or B, would have the thicker walls? Explain your answer. b Does the blood in chamber 1 contain more or less oxygen than the blood in chamber 3? Explain your answer. c Write a paragraph describing the low of blood through the four chambers and four blood vessels of the heart.
water Beaker 1
Beaker 2
Check your answers on page 282.
Chapter9 Foodforlife Learning focus: Choices need to be made when considering whether to use scientific advances
US AREA C O F D E B I R C PRES
GM foods podcast GM foods are genetically modified foods that are appearing on supermarket shelves. They are foods that contain genetically modiied ingredients. Sometimes the whole of the food is genetically modiied, for example soybeans and corn. Other foods contain varying amounts of GM ingredients. For example, 10% of a doughnut may be GM soybean meal. It is your decision— do you buy GM foods or not?
Podcast Get into a group of four and produce a podcast for other Year 8 students to answer the following questions about GM foods. 1 What do you think are the advantages and disadvantages of GM foods? 2 Do you think we should use GM foods? Why or why not? 3 Are there any risks in using GM foods? What are they? 4 Why do you think people have such different views about GM foods? 5 Do you think we can go too far with GM foods? Where would you draw the line? Two people in your group use the internet and other resources to research GM foods. The third person writes the script for the podcast and the fourth is the technician, producer and director of the podcast. Here are some hints on producing a good podcast. • Write the script so that it has a clear structure and direction, but you may want to want to allow for some ad-libbing and input from others in the group. Make sure your information is as reliable • as possible. Don’t rely on only one or two sources. Know when you have said enough and don’t • repeat yourself. • Choose ideas and vocabulary suited to your intended audience.
This fake crow was used in a demonstration against GM crops.
• Make sure the quality of the podcast is good, with a good quality microphone, recording software and a suitable place to record. • Speak clearly, audibly and at a reasonable pace. Make the podcast entertaining by being • enthusiastic and expressing your personality.
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10
Electricity Planning page Getting started
Investigate 22 Electric charges
Investigate 23 Simple electric circuits Investigate 24 Does it conduct?
10.1 Electric charges page 228
Animation Atoms
10.2 Electric currents page 235
TRB Assessment task 10 The history of electricity
Investigate 25 Series and parallel circuits Experiment Your invention
10.3 Electric circuits page 242
Main ideas Chapter 10 crossword
Review Chapter 10 test Learning focus: Developments in science have led to the development of new technologies
Prescribed focus area Conducting plastics
TRB
Chapter10 Electricity r you wil In this chapte
t…
l learn abou
LearningFocus ●
developments in science have led to the development of new technologies (page 251)
KnowledgeandUnderstanding ● ●
electrostatic force (Section 10.1) electrical energy
Skills ● ● ● ● ●
planning first-hand investigations and choosing equipment (Investigate 22–25) presenting information—electrical symbols (page 242) thinking critically—using models (pages 236 and 238) problem-solving (Try this page 234) the use of creativity and imagination, and working individually or in teams (Experiment page 248)
● How much do you know about electricity and electric circuits? Use this knowledge to explain how this mousetrap works. ●Why are two batteries needed? ● Keep your answer in mind for the Experiment ‘Your invention’ on page 248.
electromagnet
metal can
electric bell
aluminium pie dish
1.5 V battery
6V battery
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10.1 Electric charges In September 2005 Frank Clewer went for a job interview in Warrnambool. However, staff in the office heard loud crackling sounds and noticed the carpet was burnt where Frank had been. They called the fire brigade, and the building was evacuated. The firemen checked Frank and found that there was an electric charge of 30 000 volts on his synthetic jumper. Electric charges can build up on objects that are rubbed together, due to the friction between them. This build-up of electric charges on objects
Good morning. I was wondering if you had any vacancies in the electrical department.
is called static electricity, because the charges stay on the object. They are stationary.
Investigate
22 ELECTRIC CHARGES Aim To make and investigate electric charges.
Planning and Safety Check This investigation can be done only on dry days. Also, make sure everything (including your hands) is grease-free. Wash the equipment in soapy water and dry it thoroughly. You may need to warm some equipment in an oven. Read through the four parts. Note that Part B is a teacher demonstration.
PART A Materials 2 balloons and string
Method 1 Blow up a balloon and tie it. 2 Rub the balloon on a jumper or woollen cloth. Stand on a bench (be careful), hold the balloon up to the ceiling, then let it go. What happens? 3 Charge a second balloon in the same way. What happens when you hang the two charged balloons close together?
PART B If your school has a Van de Graaff generator, your teacher may demonstrate how it is able to generate a static electric charge on its dome. You may even be able to make your hair stand on end.
Chapter10 Electricity
PART C Materials • pieceoffurorsilk
charged rod
• plasticrod tap
Method Rub the plastic rod vigorously with fur or silk and bring it near (but not touching) a trickle of water. Describe what happens.
sink
trickle of water
Predict what will happen if you do touch the water with the rod. Give a reason for your prediction. Now try it.
PART D Materials • • • •
2perspexrods 2eboniterods pieceofwoolorfur pieceofsilk
• • • •
watchglass Blu-Tack cookingoil tile
Blu-Tack
ebonite rod
watch glass drop of oil tile
Method 1 Put a watch glass on top of a drop of oil on a tile. Place a small amount of Blu-Tack on either side of the watch glass, as shown. 2 Rub the ebonite rod (the black one) with wool and place it on the Blu-Tack. Bring the wool near one end of the rod. Try the other end as well. Record your observations. 3 Take the ebonite rod off the watch glass. Rub theperspexrod(theclearone)withsilk,place it on the watch glass, and bring the silk near one end. Record your observations. 4 Rub the ebonite rod with wool and place it on the watch glass. Rub a second ebonite rod with wool and bring it near one end of the rod on the watch glass. Repeat the test, but this time use twoperspexrodsrubbedwithsilk. 5 Repeat Step 4 but this time bring a charged perspexroduptoachargedeboniterod,and vice versa.
wool
Rod 1
Rod 2
Ebonite with wool Perspex with silk Ebonite with wool Perspex with silk
Ebonite with wool Perspex with silk Perspex with silk Ebonite with wool
What happened
Record the results for Steps 4 and 5 in a data table as shown above.
Discussion 1 Shannon tried to do the tests by placing the rods on the desk top instead of on a watch glass. She saw nothing happen. Suggest a reason for this. 2 Do both the charged rods behave in the same way?Explainyouranswer.
Conclusion Writeageneralisationtoexplaintheresultsofyour tests with charged rods.
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ScienceWorld8forNSW Attraction and repulsion You have seen that rods rubbed with different types of cloth can move one another by noncontact forces. But why do electric charges sometimes attract and sometimes repel? Let’s hypothesise that an electric force is something like a magnetic force—another type of non-contact force. With magnets, two like poles repel each other, while two unlike poles attract. So if two perspex rods rubbed with silk repel each other, you might expect them to have the same electric charge on them. Similarly, two ebonite rods rubbed with wool repel each other, so they should also have the same charge. However, a perspex rod rubbed with silk and an ebonite rod rubbed with wool attract each other, so they should have opposite charges. Remember that a magnet can attract some unmagnetised metals, so you might also expect that a charged rod can attract some uncharged objects. To sum up, there are three laws that describe electric forces.
1
2
Science in action Benjamin Franklin The great American scientist Benjamin Franklin was the first person to explain successfully the charging of an object by rubbing. He suggested that the two types of charge could be called positive and negative. He inferred that there was an ‘electric fluid’ that could be moved from one object to another. If this electric fluid was added to an object then it gained a positive charge. If electric fluid was removed then the object developed a negative charge. Franklin’s ideas were useful for explaining electric charges, but other observations do not support his inferences about an electric fluid. Scientists now use a different explanation (see the next page).
Charged objects attract uncharged objects. For example, a charged plastic rod will attract small pieces of paper or a stream of water (as in Investigate 22 Part C). Like charges repel each other. It does not matter whether they are both positive or both negative.
< WEB watch > force of repulsion
3
Unlike charges attract each other.
force of attraction
Benjamin Franklin is famous for flying a kite in a thunderstorm—an extremely dangerous thing to do. When lightning struck the kite, electricity flowed down the string to a key. Luckily he survived. Go to www.scienceworld.net.au and follow the links to:
Benjamin Franklin: An Enlightened American This website has Franklin’s illustrated life story, information on his inventions, things he said, interesting facts and humorous stories.
Chapter10 Electricity Inside atoms
Explaining electric charges
About 100 years ago scientists discovered that there are even smaller particles inside atoms. Ernest Rutherford, a New Zealander, inferred that most of the atom is empty space. There is a small central core or nucleus which is positively charged. It contains protons which are positively charged, and neutrons which are neutral (no charge). Moving around the nucleus are electrons, which are negatively charged. Normally there are equal numbers of protons and electrons. This means that the charges balance each other and the whole atom is uncharged. If some electrons are removed from an atom, it becomes positively charged. If extra electrons are added, the atom becomes negatively charged. When the number of positively charged atoms in an object just balances the number of negatively charged atoms, the whole object is uncharged. But if the numbers become unequal, then the object has an electric charge.
What happens when you rub a perspex rod with a silk cloth? The frictional forces of the rubbing cause electrons to be removed from atoms on the surface of the rod and to become attached to atoms on the silk. This leaves the rod with a positive charge and the silk ends up with a negative charge. A different type of cloth may give electrons to the rod and make it negatively charged. This cloth will, of course, then have a positive charge.
To learn more about atoms, open the Atoms animation on the CD.
positive protons (and neutrons) in nucleus
. . . so the rod has an excess of positive charges . . .
silk cloth
. . . and the cloth has an excess of negative charges.
perspex rod
Everyday static electricity -
+
+
-
+
-
negative electrons surrounding nucleus
Fig 8
Electrons move this way . . .
A picture of an atom. It is neutral, with no overall charge.
The tingle you get when you walk across a synthetic carpet and then touch something metallic is due to static electricity. The friction between your shoes and the carpet causes your body to become charged. When you touch a metal object, the static electricity is discharged (allowed to escape). As the electricity flows across your skin, you feel a slight electric shock. During World War I, pilots landing small rubber-tyred aircraft often received a powerful shock when they stepped onto the ground. Today aircraft have special tyres that have metal in them. This lets the static electricity pass harmlessly to the ground when they land and prevents shocks and electrical problems. The rapid movement of drops of water in thunderclouds can cause a separation of positive and negative charges. The tops of the clouds
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ScienceWorld8forNSW normally become positive, and the bottoms negative. If these charges become big enough, electrons can jump from one part of the cloud to another, causing a spark. The air is heated so much it glows, producing lightning. The intense heat also makes the air expand suddenly, causing the loud noise of thunder. Lightning can also spark to the ground, or to other clouds.
thunderclouds
What to do in a thundersto rm
Each year in Australia lightning claims up to 10 lives and causes over 100 injuries. Many of these injuries happen when people use telephones during thun derstorms. If you are caught outdoors in a thunderstorm:
• Seek shelter in a hard-top vehicle or solid building. • If swimming or suring, leave the wa ter immediately. • If in a boat, go ashore to shelter as so on as possible. • Never shelter under trees. • Don’t use a mobile phone. • Don’t handle ishing rods, umbrellas or golf clubs. • Stay away from metal poles, wire fence s, sheet metal, clothes lines etc. • Don’t ride a horse or bike, or drive an open vehicle. • If you are in a car, park away from tr ees and power lines. Close the windows and avoid touc hing metal parts of the car. • If caught in the open, crouch down wi th your feet together. If you are indoors during a thunderstorm:
• Don’t use the telephone. • Disconnect external aerials and power leads to radios, TVs and computers. • Draw all curtains and keep clear of windows, electrical appliances, pipes and other metal ixtures. • Don’t stand bare-footed on concrete or tiled floors. • Avoid taking a bath or shower.
th in k sa fe
be sa fe
Fig 10
Lightning can spark within a large cloud, from a cloud to the ground, or from cloud to cloud.
Fig 11
Lightning strikes the lightning conductor on the Q1 tower on the Gold Coast.
Chapter10 Electricity
Everyday static electricity Operating theatres
cotton gowns (not nylon)
In operating theatres the sudden movement of blankets, clothes or equipment can produce electrostatic sparks. (Electrostatic means ‘relating to static electricity’.) These sparks are very dangerous because of the large amount of oxygen in the air and other flammable gases used to anaesthetise the patient. Many precautions are therefore taken to make sure static charges do not build up anywhere.
patient is earthed
trolley wheels made from antistatic rubber
conducting tiles on floor
equipment earthed by chains
shoes are antistatic and conducting image to be copied (face down)
CS IE lamp
lens
SCIENCE lens
cartridge containing toner powder (–)
EN
CE
drum
+
SC I
Photocopiers work by an electrostatic process. The main part of the machine is a rotating light-sensitive drum onto which the image of the document is projected. The positively charged paper attracts the negatively charged toner from the drum, forming an image. The paper then passes between heated rollers that fuse (melt) the toner onto the surface of the paper.
CN E
Photocopiers
printed image heated rollers
Powder coating When objects are powder-coated they are charged so they will attract the powder. This gives a much more even coating than other methods of spraying, and the powder reaches all parts of the object’s surface. However, great care has to be taken to keep dust particles out of the air, or they too will be attracted onto the object’s charged surface.
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Check! 1
Why do you sometimes notice a crackling noise when you take off your clothes?
2
If a rod is rubbed with nylon cloth and the rod becomes positively charged, what charge will be on the nylon?
3
You may have been zapped as you touched the door handle when getting out of a car. Suggest how the car becomes electrically charged.
4
What type of charge is on: a an electron? b the nucleus of an atom?
5
a b
In your own words, describe what causes lightning.
7
Some tall buildings and tall chimneys have a lightning rod on top of them. What purpose does it serve?
8
A piece of plastic held in your hand can be electrified by rubbing it with a cloth, but it is impossible to electrify a piece of metal in the same way. Why?
9
A suspended, positively charged rod has a second rod brought near to it. What is the charge—positive, negative or no charge— on the second rod if it: a repels the suspended rod? b attracts the suspended rod (two answers)?
11
1 Five different rods (A, B, C, D, E) were given an electric charge by rubbing them with two different cloths. The rods were then tested in pairs to see whether they repelled or attracted. A attracted C and C attracted E. A repelled D and B repelled E. Predict what will happen if you bring D and E together and B and C together. 2 The photo below shows a light plane being refuelled. Suggest why there is a wire between the fuel hose and the plane.
Give two examples where static electricity is a nuisance. Give two examples where it is useful.
6
10
challenge
Look at the labels on the cartoon of the operating theatre on the previous page. a The equipment and the patient are earthed. What does this mean? b What does the word conducting mean? c What does antistatic mean? Have you noticed that computer and TV screens become dustier than the things around them? Suggest a reason for this.
12 Explain how static electricity and magnetism are similar. In your answer use the terms non-contact force and force field.
t r y t his 1 You have been asked to solve the problem of the two sides of a plastic bag sticking together. a Why do you think this problem occurs? b Design an experiment to show how the bags stick together. c Suggest experiments you could try to overcome the problem. 2 Which type of carpet is most likely to give you an electric shock when you walk about on it? Design and carry out an experiment to find out. 3 In a very dark room, rub a spare fluorescent tube with wool, fur or clear plastic wrap. Can you see it glow? 4 Bring a charged rod near the smoke from a burning mosquito coil. What happens?
Chapter10 Electricity
10.2 Electric currents Static electricity is electricity that is stationary. If, somehow, this electricity can be made to move
you have current electricity or an electric current. A torch battery provides the energy to drive the current. When the battery is connected by wires to a bulb, electrons flow to light up the bulb.
Investigate
23 SIMPLE ELECTRIC CIRCUITS Aim
PART B
To investigate different ways of connecting a torch battery and bulb.
Us i ng a swit ch Materials
PART A
Li ght i ng a b ulb Materials • 1.5volttorchbatterywithoutholder • torchbulb(2.5volt)withoutholder • 2connectingwires
Planning and Safety Check Read through Part A and describe to your partner what you have to do. Your partner can then describe Part B to you.
• • • •
1.5volttorchbatterywithholder(orpowerpack) torchbulb(2.5volt)withholder 3connectingwireswithalligatorclips switch
Method 1 Use the holders and the three connecting wires to connect the battery and bulb as shown. 1.5 volt size D
Method 1 Use the battery and one connecting wire to make the bulb light. Draw a diagram of how you connected the battery and bulb. 2 See if you can find at least one other way of making the bulb light. Draw diagrams of any ways that you discover.
2 Make the bulb go on and off by touching the alligator clips together. 3 Now connect the switch into the circuit as shown. Switch the bulb on and off. 1.5 volt size D
What special places must be touched on the bulb for it to light? What special places must be touched on the battery? 3 Can you make the bulb light using two connecting wires? Draw diagrams of your set-ups. Students could investigate electric circuits using the computer program Crocodile clips.
Does it make any difference if you reverse the connections to the battery?
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trons 2 The elec h the ro flow th ug wire and connecting lb. into the bu
1 The battery pro the en ergy to vides push the ele ct from t rons away he – t ermina l.
What is a circuit? In Investigate 23 you should have noticed these things: 1 Both ends of the battery must be connected to the bulb before it will light. These metal connection points are called terminals. The top of the battery is positive + and the bottom is negative – . 2 The bulb has to be connected in two special places. The metal side of the bulb is one terminal, and the bottom is the other. They are both the same. There is no positive or negative. 3 For the bulb to light, there has to be a closed path (or circuit) joining the battery and the bulb. This is called an electric circuit. When there is a gap in the circuit, the light is off. A switch lets you open and close the circuit. An electric current can be compared to water flowing through pipes. The battery is like a water pump—it gives energy to the electrons just as the pump forces the water through the pipes. (See Fig 19 on the right.) A water meter measures how many litres of water are flowing through a pipe each second. In an electric circuit, the electric current or number of electrons passing per second is measured using an ammeter (AM-eat-er). An ammeter measures electric current in amperes (abbreviation amps, symbol A) or milliamps (1000 mA = 1 A). Voltage is a bit like the pressure in the pipes. It is a measure of how much energy can be given to the moving electrons in a circuit. It is measured
h the roug me h t w lb. So ns flo ectro de the bu o make l e e 3 Th wire insi is used t ow thin r energy hen fl t y e i h of the lb glow. T ough ry thr u e b t t e a b th to the back terminal. the +
fountain
pump
water in pipes
Fig 19
An electric current flowing from a battery through a bulb can be compared to water flowing in pipes.
in volts (V) using a voltmeter. A torch battery has 1.5 volts. A 6 volt battery can push a larger current around the same circuit. If one of the connecting wires in the previous experiment was replaced by a piece of string, the light bulb obviously would not glow. String does not let electricity through and is called an insulator. A substance like wire that does let electricity through is called a conductor.
Chapter10 Electricity
Investigate
24 DOES IT CONDUCT? Aim Connect objects here.
To test various substances to see how well they conduct electricity. 1.5 volt size D
Materials • • • • •
1.5Vbatteryandholder(orpowerpack) torchbulbandholder ammeterormultimeter 4connectingwires varietyofobjects,egpaperclip,plasticand glass rods, nail, coin, carbon rod, copper rod, matchstick, rubber band, aluminium foil, strip of paper, piece of string
ammeter
Record whether the bulb glows.
Planning and Safety Check Discuss the investigation with your teacher. You may use a 6 volt battery or a power packinsteadofthe1.5voltbattery. Look at the ammeter. The red or + terminal must be connected to the + terminal of the battery. • Suggest why you use an ammeter in this investigation. • Draw up a data table like the one shown. Listatleast10objectsintheleft-hand column. Write down what material each object is made of. Object
Material
paperclip stirring rod
steel glass
Does bulb grow?
Ammeter reading (mA)
Method 1 Set up a circuit as shown. Ask your teacher to check your circuit before you go on to Step 2. 2 Touch the two alligator clips together. Observe what happens to the bulb. Record the electric current reading on the ammeter. 3 Connect one of the objects between the alligator clips.
Record the ammeter reading. (This tells you how much current passes through the object.) 4 Test each of the other objects. Record the results in your data table. 5 Is your skin a conductor or an insulator? Does it make any difference if your skin is wet or dry?
Discussion 1 Which materials are good conductors of electricity? How do you know? 2 Which materials are poor conductors (insulators)? 3 Use the ammeter readings to decide which one of the materials is the best conductor. 4 Why is it that some materials did not cause the bulb to glow, yet gave a reading on the ammeter? 5 Is air a conductor or an insulator? How do you know? 6 How could you test whether water is a conductor or an insulator?
Conclusion How are the materials that conduct electricity similar? Write a generalisation about the types of materials that conduct and do not conduct electricity.
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ScienceWorld8forNSW Conductors and insulators All metals are conductors, while most non-metals are insulators. Conductors
Insulators
carbon
plastic
salt water
glass
acids
cloth
silver
paper
copper
wood
gold
rubber
aluminium
air
Insulators are very important in the supply and use of electricity. The poles that carry electricity from power stations to cities need insulators to stop electricity from escaping to the ground (Fig 23 on the next page). The handles of screwdrivers and pliers are often coated with plastic insulation. The casings of electric plugs, sockets and switches are all made from plastic.
How can you explain the difference between conductors and insulators? An electric current is a flow of electrons. So a conductor is a material through which electrons can flow. A metal consists of an arrangement of positive nuclei in a ‘sea’ of electrons. These electrons are not strongly attracted to any one nucleus. So, when the metal is connected to a battery, the electrons can move easily through the metal to produce a current. In an insulator the electrons are held tightly by the positive charges. Because of this, the electrons cannot move, and no electric current can flow when the insulator is connected to a battery. If you charge an insulator such as a plastic rod by rubbing, the charge stays on the surface of the insulator. But the insulator slowly loses its charge to the air, especially in wet or humid weather. The charge is also lost quickly if you touch the insulator with your hand. This process allows the charge to flow to the ground, and is called earthing. You cannot charge a conductor by rubbing. Any charge you produce flows through the conductor to the ground immediately.
Conductor
Insulator no current flows
current flows electrons held only loosely by positive nuclei
electrons held tightly by positive nuclei
Note: Good conductors of electricity are also good conductors of heat (see page 134).
Chapter10 Electricity
heating element
fan
ON F OF
Fig 24
Fig 23
The insulators on power lines are made of glass or porcelain. The conducting wires are made of aluminium and steel.
In electric power lines there is always loss of energy due to the resistance of the metal in the wires. For this reason, scientists are trying to make cheap superconductors, which offer no resistance to the flow of electricity. The use of such materials would save billions of dollars. Superconductors could also be used in the maglev trains now being developed. These trains float above the tracks supported by the noncontact forces between large electromagnets. Fig 25
Resistance When an electric current moves through a conductor, there is always some electrical resistance to the current. This is because of the attraction of the electrons to the positive nuclei of the atoms in the conductor. This attraction is greater in some conductors than in others, giving them a greater electrical resistance. As the electrons are pushed through a conductor they lose some of their energy as heat. This waste heat can be a nuisance; for example, computers get hot when used. However the waste heat is sometimes useful. For example, because nichrome wire has a fairly high resistance, it is used to make the heating elements in many electrical appliances used around the home. It is usually coiled to take up less space. The filament of a light bulb is made from very thin tungsten wire. When a current is passed through it, the wire becomes so hot that it gives off a brilliant white light.
This hair drier contains a nichrome wire heating element.
The chilled superconductor (bottom) is acting like a magnet. It repels the magnet (top), making it hover in the air above the superconductor.
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Check! 1
2
Copy and complete the following sentences. a A path for electricity is called a ______. b A ______ lets you open and close a circuit. c Moving electrons in a wire are called an electric ______. d An ______ is an instrument used to measure electric current. e The unit for electric current is the ______. f ______ is a measure of the energy given to the electrons in a circuit. g Substances that do not allow an electric current to flow through them are called ______. h Metals are ______ because they allow an electric current to pass through them. i Opposition to the flow of current in a circuit is called ______. j If the resistance in a circuit is increased the current ______.
5
Lisa connected a bulb to a battery. The wires were connected properly, but the bulb did not glow. What could be wrong (two possibilities)?
6
Explain in your own words the difference between an insulator and a conductor of electricity.
7
Why are electrical connecting wires covered with plastic?
8
This ammeter measures current in two different ranges: 0 to 1 amp and 0 to 10 amp.
4 2
a
In which of these circuits will the bulb glow? For the other circuits, explain why the bulb won’t glow.
b 9
A B
C
4
Which battery can supply the most energy to electrons in a circuit: 1.5 volt, 6 volt or 9 volt? Why?
1.0
10
What is the reading if the 0–10 amp range (top) is used? What is the reading if the 0–1 amp range (bottom) is used?
Electric current (amperes)
4H HB 3B
0.03 0.10 0.70
b
10
pointer
Type of ‘lead’
D
Into what two forms of energy is electrical energy changed in a light bulb?
.8
A
Ngoc tested how well different types of pencil ‘lead’ of the same length and thickness conduct electricity. His results are shown:
a
3
8
.6
.4 .2
6
Which type of ‘lead’ has the greatest resistance? Pencil ‘leads’ contain graphite, which is a conductor. Which type of pencil ‘lead’ would you infer contains the most graphite?
Why is it safer to wear shoes than to go barefoot in an electrical storm?
Chapter10 Electricity
challenge 1 Explainwhythebatteryinatorcheventually goes flat. 2 When you push down the switch the torch producesabeamoflight.Explainindetailhow this happens. switch
handle
4 A company produces an all-metal electric kettle, but the government bans its sale. Suggest why it was banned. 5 Explainwhytheelementinatoasterbecomes red-hot, while the wires connecting the toaster to the mains power supply remain cool. 6 One of the things that ‘lie-detectors’ measure is skin resistance. Lying is supposed to make you sweat. How do you think this lie-detector works? I never done nothin’... honest!
reflector plastic case 6 volt battery
+ glass
3 What do you think is the most likely cause of the following? a Your radio starts to get quieter and quieter. Turning up the volume doesn’t seem to help much. b Your torch is very bright but suddenly goes out. c Your CD player stops working, but when you tap on the case it works again.
t r y t his
7 Why don’t the materials that conduct current electricity hold static electricity? 8 Usingwhatyouknowaboutresistance,explain why a long wire has more resistance than a short one, and why a thin wire has more resistance than a thick one.
2 Make your own switch. Here are some designs. Try out your switch in a circuit.
1 Find out whether tap-water will conduct an electric current. Set up the circuit shown, using a conductivity kit. You could also test rainwater, distilled water and salt water.
uncoated paperclip
thumbtack springy steel
6V
clothes peg conductivity kit
thumbtacks water
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10.3 Electric circuits Circuit diagrams Look at the two circuits on the right. They look different, but they are actually the same. If you wanted to tell someone how to set up this circuit, you might confuse them if you drew these sketches. Also, drawing diagrams like these takes time. So electricians have decided on a simple way to draw electric circuits with a symbol for each component (part). These symbols are listed below. The wires in a circuit are drawn straight and at right angles. For example, the circuit on the right can be drawn as shown. This is called a circuit diagram.
OR
mbols Electrical sy circuit diagram connecting wire light bulb
Fig 33
You may see the older symbol for a light bulb drawn like this:
Series and parallel circuits
battery (The long thin stroke is positive and the short fat stroke is negative.)
power pack (variable power supply)
or
How to draw a circuit diagram
The parts of a circuit can be arranged in two different ways. Take, for example, two torch bulbs. They can be connected one after the other as shown in Fig 34 below. This is called a series connection. Note that there is only one path for the electric current to flow, and the current is the same everywhere in the circuit. As you connect more bulbs in series, the current decreases, and the bulbs don’t glow as brightly.
resistor
switch open
series circuit
switch closed
A
ammeter
Fig 34
A series circuit
Chapter10 Electricity master switch
Many electrical appliances use several batteries connected in series. When you put in the batteries, the positive terminal of one battery must touch the negative terminal of the next. For example, a 3 volt toy usually has two 1.5 volt batteries arranged in series as shown in the cartoon.
parallel circuit
A
Click...whirrr...who? What? Hmm... must have dozed off for a bit.
Fig 36
A parallel circuit
Sometimes it is not easy to tell whether the components of a circuit are connected in series or in parallel. However, if you can trace the complete circuit using one finger, then the components are connected in series. Those parts of a circuit that branch and where you have to use more than one finger are connected in parallel. Note that a circuit may contain a mixture of series and parallel connections (Fig 37). Two bulbs can also be connected side by side. This is called a parallel connection. Look at Fig 36. At A the electric current splits and follows two different paths. The electrons flowing through each bulb get the full push from the cell—they don’t share it as in a series circuit. As a result, each bulb glows as brightly as if it was the only bulb in the circuit. A master switch can be used to turn off both bulbs together, or separate switches can be used to turn each bulb off independently.
2 1 3
Fig 37
Bulbs 2 and 3 are in parallel, but they are in series with bulb 1, the switch and the battery.
In Investigate 25 you can investigate series and parallel circuits for yourself.
Investigate
25 SERIES AND PARALLEL CIRCUITS Aim To investigate series and parallel circuits.
Materials • • • •
two1.5Vbatteriesandholders(orpowerpack) 3torchbulbsandholders 6connectingwires ammeterormultimeter
Planning and Safety Check • Carefullyreadthroughtheinstructionsfor the three parts on pages 244 and 245. • Towhichterminalofthebatterydoyou connect the positive (+) terminal of the ammeter?
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PART A
Li ght i ng a b ulb Method 1 Connect up a circuit with a battery, a switch and one bulb. Close the switch and observe the brightness of the glow of the bulb. 2 Connect a second bulb in series with the first bulb, as shown below.
In which two-bulb circuit do the bulbs glow more brightly? Suggest a reason for this. What happens if you unscrew one of the bulbs in the parallel circuit? 5 Add a third bulb in parallel with the other two. What happens?
Discussion 1 What is the effect of increasing the number of bulbs in series in a circuit? 2 If one bulb in a series circuit blows, the others also go out. Why? 3 Describe the effect of adding more bulbs in parallel in a circuit. 4 When one bulb in a parallel circuit fails, the others continue to operate. Why? 5 Parallel circuits are used in the electrical wiring of a house. Suggest reasons for this.
PART B Does each bulb glow as brightly as the singlebulbinStep1? Unscrew one of the bulbs from its socket. Record what happens. 3 Repeat Step 2 with three bulbs. 4 Connect up a second circuit with the two bulbs in parallel, as shown below.
B att er y pr oble m Research question: Can you make the bulb glow more brightly by adding a second battery? Experimenttoindoutwhetheryoushouldadd the second battery in series or in parallel. Write a brief report of your findings.
Notes for Part B 1 When connecting batteries in series, you must connect the positive of one to the negative of the other, as shown. +
2 When connecting batteries in parallel, you must connect the positive of one to the positive of the other.
+
+
+
Chapter10 Electricity
PART C
U si ng an am m et er Research question: How can you use an ammeter to find out whether the current is the same in all parts of a series and parallel circuit? Discuss the research question in a group and designanexperiment.Checkitwithyourteacher before you start. Don’t forget to connect the positive terminal of the ammeter to the positive terminal of the battery or power pack, as in the circuit on the right.
+
+
A
Write a report of what you find.
Check! 2 1
Copy and complete the sentences below by selecting the correct words to describe the circuit below. a In this circuit the electricity has ______ (one / two) paths to follow. b This circuit is ______ (open / closed). c If bulb A went out while the switch was closed, bulb B would (stay on / go out). d If more bulbs were added to the circuit, each bulb would glow ______ (more / less) brightly. e If the circuit had only one bulb, it would glow ______ (more / less) brightly. f The bulbs are connected in ______ (series / parallel).
Answer these questions about the circuit below. a How many paths can the electric current follow? b Does the current have to pass through bulb A for bulb B to glow? c If bulb B blew would bulb A continue to glow? d What would happen if you added a third bulb in parallel?
A
A B
B
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3
Write out a list of the equipment needed to set up circuit A. Do the same for circuit B.
5
What voltages are being used in these two electrical appliances? Torch 1.5 VOLT
AA SIZE
A
Battery compartment of radio top row 1.5 VOLT D SIZE
B
4
A
6
Draw a circuit diagram that has: a two batteries and a bulb in series b one battery and two bulbs in series c two batteries in parallel and a bulb in series d two batteries in parallel and two bulbs in series e a power pack and a string of eight decorative bulbs in parallel
7
Draw a circuit using two batteries and two bulbs that makes the bulbs glow most brightly.
8
In the circuit diagram below, what happens to each of the bulbs A, B and C when you: a close switch 1? b then close switch 2? c then open switch 3?
Draw a circuit diagram for each of the following.
A
bottom row
connecting wires
3 A
B
B
2 1
C
9
Give two reasons why lights in parallel are better than lights in series.
Chapter10 Electricity
challenge 1 Draw a circuit diagram with a battery, three lights and three switches so that each switch turns on only one light. Where would you place a fourth switch that could switch all three lights on and off (that is, a master switch)? 2 Consider the two circuits below. The resistor in the circuit is a piece of nichrome wire like that used in jug elements. If the nichrome wire has a greater resistance than a light bulb, which of the three identical bulbs (A, B or C) will have the dimmestglow?Explainyouranswer.
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4 How is adding an ammeter (very low resistance) to a circuit different from adding a light bulb or electric motor? 5 Suppose the latest portable CD player is wired with superconducting material. Would the batteries last a longer or a shorter time than in a normal CD player?Explainyouranswer. 6 Below is the circuit diagram for a caravan.
1
2
3
A
B
4
C
D
A
6 5
B
C
3 The bulbs in this circuit are both dimly lit when the switches are open. Predict what will happen when: a switch1isclosed(twothings) b switch 2 is closed as well.
A
1
B
2
E
F
a Which switches do you need to close so that only one light stays on? b Whichlightsareonwhenswitches1,4and 6 only are closed? c Are lights A and B in series or in parallel with each other? 7 Howwouldyouconnectsix1.5volttorchcells to give a voltage of: a 9 volts? b 6 volts? c 4.5 volts? Drawcircuitdiagrams.Youmustuseallsixcells. (Hint:Two1.5voltcellsinparallelhaveatotal voltageof1.5volts.) 8 Design a circuit with one battery, four switches and a bulb so that the light comes on when any one of the switches is closed. Draw a circuit diagram. (This circuit could be used to light the inside of a car with four doors. Opening a door closes a switch.)
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Experiment
YOUR INVENTION Aim To use what you have learnt in this chapter to invent a useful electrical device.
as well as your successes. Other students may be able to suggest ways of improving your design. (If your invention is good enough you may be able to enter it in a science contest.)
Method 1 Studythetwoinventionsontheright.Explainto
Traffic lights
another student how one of them works. Your partnerwillexplaintoyouhowtheotherone works. You could also have another look at the mousetrap on page 227.
2 Use your imagination to design your own invention, or use the ideas below.
• abatterytester
• acircuitwhereyoucanswitchalightonin one place and turn it off somewhere else
• aburglaralarmwhereabellrings,alight flashes or a trapdoor opens to catch the burglar •
a model house in which you can turn the lights on and off independently
•
an alarm to warn you of strong wind
•
a device to warn you when a water tank is about to overflow
•
an alarm clock using a candle
•
an electric maze
•
a way of dimming a light (Hint: A long wire has more resistance than a short one.)
•
a pinball machine (Hint: A rolling metal ball could be used to close a switch.)
3 Draw a sketch of your design before you start. Try to draw a circuit diagram too.
red
amber
green 3-way switch
Wiper glasses electric motor
wires to battery and switch on belt copper wire
4 Make a list of the things you will need to make your invention. 5 Check your design with your teacher, then go ahead and make it. (You may be able to work on your invention at home.) 6 Prepare a report of your invention for the rest of the class. Make sure you report any problems,
cotton ball
L-shaped aluminium
Chapter10 Electricity
Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
ammeter
1 Objects can be given an electric ______ by rubbing. Gaining
charge
attract
electrons makes an object negatively charged, and losing electrons makes it positively charged.
circuit conductors
2 Like charges ______ each other, while unlike charges ______ each
electrons
other.
energy
3 Electric current will flow only if it has a continuous path or ______.
insulators
4 Electric current is a flow of ______. It is measured in amperes,
parallel
using an ______.
repel voltage
5 Batteries supply the ______ to push electrons around a circuit. ______ is a measure of how much energy can be given to the moving electrons in a circuit. It is measured in volts.
6 ______ offer little resistance to the flow of electricity. ______ offer a great deal of resistance.
7 A series circuit has only one conducting path for electrons, whereas a ______ circuit has two or more alternative paths.
Try doing the Chapter 10 crossword on the CD.
REVIEW
1 What happens to two charged rods held near each other if they have: a the same charge? b opposite charges? 2 What charge is left on a material if it has been rubbed and: a loses electrons? b gains electrons? 3 Which of the following are conductors and which are insulators? a copper b plastic c steel d air e wood f salt water
4 Look at the diagrams below. a Which is the correct way to put two batteries in a torch? b Are the batteries connected in series or in parallel?
A
B
C
D
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REVIEW
5 Consider the circuits below.
A
Work with a partner. From the two circuits below, select the one you are going to set up. Your partner (or your teacher) will mark you on your performance.
B
C
a What will the brightness of the bulbs in circuit B be like compared with the bulb in circuit A? Why? b How bright will the bulbs in circuit C be compared with the bulb in circuit A? Why? c Without changing the number of bulbs, how could you make the brightness of the bulbs in circuit B the same as the bulb in circuit A? Draw a diagram of the new circuit. 6 Consider the circuit below.
First write down a list of the equipment that you will need to set up the circuit. Then set up the equipment correctly and promptly. How to score List of equipment: A chose the equipment perfectly B left out a small item, like a connecting wire C left out a major item, such as a bulb or a battery D was not sure of the equipment needed
B
C
Setting up the equipment: A set up the circuit correctly and promptly 1
A
2
When switch 1 is closed and switch 2 is open: A none of the bulbs lights up B only bulb A lights up C bulb A and bulb B light up D all the bulbs light up
7 Explain why you sometimes get an electric shock when you walk on a nylon carpet and then touch something made of metal.
B set up the circuit correctly, but took quite a while to do it C set up the circuit promptly, but with a slight error in it D set up the circuit slowly, but with a slight error in it E was not sure how to set up the circuit. Dismantle the circuit. Now swap roles, so that this time you mark the performance of your partner setting up the other circuit. (Don’t forget to return all equipment.)
8 Design a circuit with a cell, a switch and a bulb, so that the light goes off when the switch is closed. Check your answers on pages 282–283.
Chapter10 Electricity Learning focus: Developments in science have led to the development of new technologies
FOCU PRESCRIBED
S AREA
Conducting plastics On page 238 you learnt that plastics are insulators—they don’t usually conduct electricity. However, in the mid-1970s three scientists discovered a plastic that was somewhere between an insulator and a conductor. A Japanese scientist, Hideki Shirakawa, was trying to make a plastic called polyacetylene. By accident he added 100 times as much catalyst as he intended, and a shiny metallic-looking film appeared on the inside of his reaction vessel. At about the same time two other scientists, Alan MacDiarmid and Alan Heeger, were experimenting with metallic films at the University of Pennsylvania in the United States. MacDiarmid and Shirakawa met by chance during a coffeebreak at a seminar in Tokyo. When MacDiarmid heard about Shirakawa’s accidental discovery he invited him to work with him in his laboratory in the US. MacDiarmid, Heeger and Shirakawa did many experiments and found that if they exposed the polyacetylene to bromine vapour its electrical conductivity increased by a factor of 10 million! They immediately published their discovery of a conducting plastic, and in 2000 they were jointly awarded the Nobel Prize in Chemistry. In 1990 another group of scientists in England developed a conducting plastic which gave off light when sandwiched between two electrodes with electricity flowing between them. Scientists say that it won’t be long before ultra-thin television screens using this new plastic are available, as well as luminous traffic and information signs. Perhaps light-emitting wallpaper for our homes will also become a reality. Conducting plastics can also be used to make solar cells in a continuous roll. These are cheaper and more versatile than the present silicon-based solar cells. The solar cell plastic can also be made into fabric to make clothes which can convert light into electricity to run devices such as iPods.
The electronic reader being used by the student on the right is produced by Plastic Logic. It is the size of a sheet of paper and about 1 cm thick. It can store thousands of documents and save you carrying around heavy books and notes.
Other applications of conducting plastics that are availabe are: • rechargeable plastic batteries for use in portable electronic equipment such as Apple’s iPhone, and in hybrid electric cars • windows that you can darken during the day by passing a small electric current through them • antistatic material for use in offices and operating theatres, where it is important to avoid a build-up of static electricity (see page 233).
Questions 1 What is the important development in science described on this page? 2 What new technologies have been developed as a result of this development in science? 3 Which of these technologies do you think has the most potential for the future? Explain your answer.
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Livingsystems Planning page Getting started
Activity page 254 Activities page 255 Investigate 26 Colour adaptations
Investigate 27 Physical factors in water Investigate 28 Water loss in plants
11.1 Survival page 254
Animation Natural selection
11.2 Physical factors page 262
Assessment task 11 Sampling the environment
TRB
Main ideas Chapter 11 crossword
Review Learning focus: Why different groups and cultures may have different views in relation to scientific issues
Chapter 11 test
Prescribed focus area Murray River crisis
TRB
Chapter11 Livingsystems r you wil In this chapte
t…
l learn abou
LearningFocus ●
why different groups or cultures may have different views in relation to scientific issues (pages 259 and 275)
KnowledgeandUnderstanding ●
ecosystems
Skills ● ● ● ●
gathering first-hand information (Activities page 255 and Investigate 26) gathering information from secondary sources and processing it (pages 268 and 271–272) thinking critically—predicting, using models and using cause and effect (Investigate 27 and 28) working in teams and presenting information (Activity page 254, Investigate 26 and pages 271–272)
The four photos on this page and the previous page show a number of different Australian environments. ● For each photo think of some of the living things that might live in the environment. ● Make a list of the characteristics that the animals and plants would need to be able to survive in each type of environment.
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marinethemes.com/David Fleetham
11.1 Survival In previous studies you learnt that an ecosystem is the system of relationships between the living things and their interactions with the non-living things. The survival of an organism in an ecosystem depends on living as well as non-living factors. For example, the survival of an organism not only depends on its ability to get food and be protected from predators, competitors and disease-causing organisms, but also on the supply of water and air, a suitable temperature and weather conditions, and good soil. The biological factors in an ecosystem describe all the living things that interact with an organism—its food, predators, competitors and disease organisms. The non-living or physical factors include temperature, light, humidity, the availability of air and water, and soil fertility. These factors are extremely important for the survival of any organism. For example, microscopic algae (plankton) are found only in the surface waters of the ocean where there is sufficient light for photosynthesis.
Activity Work in a small group for this activity. Look at the photo of the coral reef community. Write a brief report on the survival of an organism on the coral reef using the following three points as your structure. 1 Choose an organism that lives on the reef. Make a list of all the biological factors that will influence its survival. Give examples if possible. 2 Construct a food web for the organism. 3 Describe the non-living factors that may affect the survival of your organism. Give examples. Check your report and rewrite it if necessary, so that another group can read it. Swap your report with another group. Read their report and assess its good points and poor points. Make some brief notes. Give the report back to the group and discuss your group’s opinion of the report.
Chapter11 Livingsystems Adaptations The survival of an organism also depends on the characteristics of the organism itself. For example, the organisms in the photos below live in quite different habitats, and each organism has characteristics that enable it to survive in its own particular habitat.These characteristics are called adaptations (ADD-ap-TAY-shuns).
Fig 3
Jabiru
Fig 4
For example, the jabiru in Fig 3 lives in wetland areas of northern Australia. It has very long legs to enable it to walk through the swampy areas where it finds food. Its beak is long and pointed so it can collect snails, worms and fish from the water and mud. It also has large, strong wings to help it escape from enemies.
Dolphin
Activities A Look at the animals in Figs 3, 4 and 5 above. For each animal, list all the physical and biological factors that may affect its survival in its habitat. Suggest how the animal’s adaptations help its survival. B Your teacher will supply you with three or four preserved animals (or photos of animals). Work in a group for this part of the activity. Use observations and your knowledge of the animals to make inferences about how well their characteristics help them survive. For each animal record your observations about its size, shape, colour and other characteristics that you think are important in its survival. Decide where each animal lives and describe its habitat. Then infer how the characteristics help it survive in its habitat.
Fig 5
Kookaburra
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Types of adaptations The katydid (KAY-tee-did) in the photo above is similar to grasshoppers. It eats the leaves and shoots of plants. Birds and carnivorous insects such as preying mantises feed on katydids. A katydid has a number of adaptations that ensure its survival. Its body is sideways flattened and is leaf-green in colour. This helps to camouflage it amongst plants. It also quivers,
making it appear like a leaf moving in the wind. It has very keen eyesight and long, strong legs that help it escape quickly when threatened by predators. The katydid lays a very large number of eggs in the soil. For convenience, we can classify adaptations into three groups—structural, functional and behavioural. Structural adaptations refer to the shape and size of the organism and how the various parts of its body are put together; for example, the katydid’s flattened body, its colour, and the shape and size of its legs. Functional adaptations refer to the working of an organism’s body; for example, the katydid’s egg-laying ability and the way it can digest plant leaves and shoots are functional adaptations. Behavioural adaptations are to do with how the organism behaves; for example, the quivering of the katydid mimics the movement of leaves and makes it hard to see in the bushes.
Investigate
26 COLOUR ADAPTATIONS Aim
Method
To use a model to explain the effect of colour on the survival of organisms in different habitats.
1 Measureouta3mx3mareaonyour selectedsurface.Markthecornersofthe squarewithpiecesofpaper,sticksorrocks. Youcouldmarktheareawithstringifyouhave some.
Materials • 60colouredtoothpicks,plasticdisksorbeads (20green,20redand20yellow)
Planning and Safety Check • Workingroupsofthree.Onememberwill bethescatterer,theothertwowillbethe predators. • CarefullyreadthroughtheMethodand prepare data tables for Steps 3 and 4. • Youwillneedtodothisexperimentonat leasttwodifferentsurfacesor‘habitats’; forexample,grass,dirt,sand,concrete, carpet or leaf litter.
3m
3m
Chapter11 Livingsystems
2 Askthe‘predators’nottolook,thenscatterthe toothpicksrandomlyoverthemarkedarea. 3 Givethe‘predators’15secondstoindasmany toothpicksastheycan. Countthenumbersofeachcolourof toothpickfoundandrecordthedata. 4 CollectallthetoothpicksthenrepeatSteps1to3 using other surfaces. Recordtheresultsinyourdatatable.
Discussion 1 For each colour calculate the survival rate as a percentageoftheoriginal20. % survival rate =
number remaining x 100 20
2 Drawabargraphofthepercentagesurvival rates for the three different colours. 3 Comparethesurvivalratesforthedifferent surfaces.Suggestwhytheyaredifferent.
Natural selection In the last Investigate you probably found that of the three colours of toothpicks, the green ones were the most difficult to find on grass, while the yellow or red ones were easily seen and picked up by the ‘predators’. As a result, the green toothpicks had a higher survival rate on grass. In any population of organisms there are variations among the individuals. For example, in a population of field mice, you might see dark-coloured ones and light-coloured ones, short ones and long ones, ones with larger ears and ones with shorter ears. In the toothpick model, there were colour variations in the toothpick population. When equal numbers were placed on grass, more of the green coloured toothpicks survived than either of the other colours. In this case, biological factors (the ‘predators’) caused a change in the make-up of the population. The green toothpicks had the most favourable characteristics for a grass habitat and are said to be selected.
4 Compareyoursurvivalrateswiththoseofother groups.Yourteachermayorganiseaclass discussion. 5 Supposethethreedifferentcolouredtoothpicks werepartofalargetoothpickpopulation inaparticular‘habitat’.Assumethesame ‘predators’werepresent.Predictwhatmight happentothetoothpickpopulationinthearea overaperiodoftime.Givereasonsforyour prediction. 6 Doyouthinkyourmodelwasagoodone? Suggestwaysinwhichyoucouldimproveit. 7 Usingtheresultsofyourmodel,writea generalisation about the effect of camouflage (colour)onthesurvivaloforganismsina particular habitat. 8 Youmayhaveheardofthetermselection or natural selection.Useyourgeneralisationfrom Question 7 to suggest a meaning for this term.
In a natural ecosystem, this selection of favourable characteristics is called natural selection. The organisms in a population that have favourable characteristics survive in a particular habitat, breed and pass their characteristics on to their offspring.
Fig 9
In a population of field mice you often see variations in colour, size and shape.
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ScienceWorld8forNSW What happens if the conditions change? Suppose there is a drought and the grass in our model dies, leaving bits of dead grass and sand-coloured soil. The green toothpicks will now be more easily seen by the ‘predators’ than the yellow ones. Under these conditions the yellow toothpicks have a higher survival rate than the a population of organisms
biological factors
green ones. The yellow toothpicks are better adapted to this habitat, and after some time the make-up of this population will be different from the toothpick population on the green grass. To see what happens to a population of organisms when factors change, open the Natural selection animation on the CD. Organisms with favourable characteristics survive.
Organisms breed and pass favourable characteristics to their offspring.
environmental changes
physical factors
Fig 10
How natural selection works.
science bits Adapted to fire During a hot, dry summer the chance of bushfires anywhere throughout Australia is quite high. Bushfires destroy houses and other property and burn out hectares of bush. The fires also kill animals which cannot escape from the flames. However, fire is part of the Australian environment and many native plants are firetolerant. Some even need fire for their survival. For example, the seeds of some wattles need the heat from fires to germinate, and the thick woody Banksia fruit (shown in the photo) open and release their seeds only when heated by fire. Many eucalypts have very thick, fire-resistant bark that protects the living cells inside the trunk from damage. The old leaves that are destroyed by the fire are quickly replaced by new shoots. In this way the eucalypt recovers from the fire damage
while other types of plants are killed. Eucalypts are adapted to fire and this helps in their survival. One species of eucalypt called the candlebark gum even spreads fires. Pieces of burning bark break off the trunk and are carried by the wind to start fires a long way away from the original trees.
Chapter11 Livingsystems
TheRiverRedGum ecosystem For thousands of years large forests of the River Red Gum have flourished along the Murray River and other large rivers that flow into it. However, over the last 200 years huge changes have occurred to these forests.
The Murray River floodplain The River Red Gums are well-adapted for the floods that once occurred regularly along the Murray. Under natural conditions, the river flooded every 1.7 years for about two to three months, as the snow melted in the Snowy Mountains. The floodwaters carry fertile soil, and branches and leaves from dead trees, which are caught around the roots of the trees. Over thousands of years, soil rich in nutrients has built up the floodplain.
The River Red gum ecosystem A River Red Gum forest can produce 250 million seeds per hectare! Most seeds fall in spring and early summer when the floods naturally recede, and the seeds germinate in the warm moist soil during summer. The seeds create food for ants and other insects as well as some birds. The flowers attract nectar-eating birds, insects and possums. These herbivorous animals attract echidnas, goshawks and water rats.
Human impact Farms established along the Murray river systems required a dependable water supply for crops. To regulate the water flow, over 100 dams and weirs have been built along the rivers. As a result, the following changes have occurred to the natual cycle: • flooding now occurs only every 10 years • flooding lasts for several days only instead of several months • the total volume of water has been reduced.
Questions Use the information on this page and from the websites below to complete the following. 1 Draw a food web for the organisms in the River Red Gum ecosystem. 2 Describe how the River Red Gum is well adapted for life on the floodplain. 3 What physical factors have changed since agriculture was established on the Murray River?
< WEB watch > Go to www.scienceworld.net.au and follow the links to the websites below. River Red Gum Click on the Redgum Forests icon and download the fact sheet, which contains information on the Redgum Forests, water management and timber production. River Red Gum Forests This website contains very good information about the human impact on the River Red Gum ecosystem.
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Check! 1
4
Classify the following statements according to whether they refer to structural, functional or behavioural characteristics. a Frill-necked lizards raise the large spiny layer of skin behind their head when they are threatened. b Sharks have a very streamlined shape. c Sea turtles lay up to one hundred eggs in the breeding season. d When sea turtle eggs hatch, the young turtles dig through the sand and head directly for the water. e Many plants that live on the rainforest floor have very large leaves. f Fungi release enzymes that are able to break down the dead organism they are growing on. g The large front legs of a preying mantis have spines on them.
2
Certain plants have prickles or thorns on them. a What is the advantage to the plant of having these structures? b Name three plants that have these structures.
3
Look at the three types of birds’ feet in the diagram below. a Describe the habitat in which each bird might live. b How does the structure of its feet help the survival of each bird in its habitat?
5
The diagram below shows four types of birds’ beaks. Three of them belong to the birds in Question 3. Can you match them? Give reasons for your choice.
A
B
C
D
The sugar glider is a small possum-like animal that lives in eucalypt forests. At night it feeds on the nectar in the flowers in the forest canopy. It has a thin layer of skin that stretches from its front legs to its back legs.
a
3
b
1
c
2
6
Suggest a reason for the skin between the sugar glider’s legs. Suppose the animal did not have the skin between its legs. What problems would the animal then have to face? Suggest why the animal feeds at night.
Explain the process of natural selection in your own words. Infer what might happen in the long term to a population of a particular type of animal whose individuals looked, functioned and behaved identically.
Chapter11 Livingsystems
challenge 1 Acertaintypeofmothcalledthepepperedmoth hastwomainvariations—alightformandadark form. dark form
3 Thebodytemperatureofbirdsandmammalsis fairlyconstantandchangesverylittleevenwhen thesurroundingtemperaturechangesgreatly. Otheranimalshavebodytemperaturesthat changewiththesurroundingtemperature. a Suggestwhyaconstantbodytemperature might be an advantage for the survival of a particular animal. b Whichtypeofadaptationisaconstantbody temperature?Explainyouranswer. c Explainthefollowingobservations. • Snakes,frogsandinsectsarerarelyfound inplaceswithsnowandice. • Snakesareveryslow-movingoncold mornings. • FishcanexistintheArcticandAntarctic regions. 4 Thediagrambelowshowsthedistributionof threetypesofplants.Usetheinformationinthe diagramtodecide,givingreasons,whetherthe statements are true or false.
light form
Fig 16
The light and dark forms of the peppered moth on a lichen-covered tree
Duringtheday,thelightformrestson light-colouredtreesandrocks,whilethedark formrestsincavitiesintreesandrocksand in caves. a Whatdoyouthinkwouldbethemain predatorsofthepepperedmoth? b Suggestwhythemothsrestduringtheday. Whichtypeofadaptationisthis? c Inanexperiment,studentscaughtand countedthemothsinaparticularplace.Over threenights,theycaught15light-coloured mothsand46dark-colouredones.Writean inference to explain their results. 2 Thedrainsinatownweresprayedfor mosquitoesusingapesticidecalledBBB. Aftertheirstspraying,mostofthemosquitoes died.Thepesticidewasusedagainstthe mosquitoesforthenextiveyears.However,the numberofmosquitoeskilleddecreasedeach year.Afterthetenthyearofspraying,veryfew mosquitoeswerebeingkilledbyBBB. a Suggestwhynotallthemosquitoesdied aftertheirstsprayingwithBBB. b Couldthisbecallednaturalselection? Explainyouranswer.
ferns
swampy area
eucalyptus A
rich loamy soil
eucalyptus B
sandy soil
a Eucalyptustreesdieinwater-loggedsoil. b Thedistributionoffernsdependsonlyonthe typeofsoil. c EucalyptusBisadaptedtodifferentsoil types.
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11.2 Physical factors Animals and plants that live in aquatic ecosystems need characteristics different from those that live on land. Let’s look at the physical factors that affect the survival of organisms that live in water and on land.
Living in water Of all the physical factors in the environment, water is one of the most important for the survival of organisms. Aquatic organisms are not faced with having to find water, but there are other physical factors which do affect their survival. These factors include: • the amounts of dissolved gases in the water • water temperature • intensity of light • currents and waves • the buoyancy effect of water.
Light The availability of light is very important for plants and algae. These organisms use light to make their food by photosynthesis. You might think that light passes freely through water. However, some light is absorbed by water, and in deep water very little light is available. Light penetration of water can also be reduced by the amount of material dissolved or suspended in it. For example, suspended materials such as silt cause a cloudiness in water, and very few plants can grow in water in this condition. 0 Organisms that photosynthesise live near the surface. 50 Depth of water (m)
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100 150 200 darkness—no light
Dissolved gases and water temperature Oxygen and carbon dioxide are the two gases essential for living things. Every living cell needs oxygen for respiration. Carbon dioxide is needed by organisms that photosynthesise. How do aquatic organisms obtain oxygen and carbon dioxide? Oxygen and carbon dioxide are both soluble in water, and there are two main ways in which these gases get into the water. Firstly, the gases dissolve in the water where the air touches it at the surface. Secondly, oxygen is produced by aquatic plants and algae during photosynthesis, and carbon dioxide is produced during respiration by all organisms. These gases, however, are not as readily available to aquatic organisms as they are to land organisms. The danger faced by aquatic organisms is that the amount of dissolved gas decreases with a rise in the temperature. Therefore, small bodies of water such as ponds or
rock pools which tend to heat up quickly contain smaller amounts of dissolved gases. The solubility of oxygen in water at various temperatures
Chapter11 Livingsystems Currents and waves Organisms that live in fast-flowing streams or on the rocky shore have to avoid being washed away. Many use mucus or a cement to attach to solid objects like rocks. Some use claws or hooks to hold on to rocks, branches or the submerged roots of trees. In the ocean, waves help to increase the amount of dissolved gases in the water. When waves crash over rocks the water traps bubbles of air, thus allowing more oxygen to dissolve in the water. In creeks and rivers, waterfalls and rapids churn up the water and allow more of the gases in the air to dissolve.
barnacle
Fig 20
chiton
Rocky shore animals have adaptations for attaching to rocks. Chitons are flattened, and use mucus and a strong muscular foot, while barnacles use a limestone cement.
Buoyancy effect of water Have you ever wondered why you feel almost weightless when you go swimming? The reason is the buoyancy effect of water—the upwards force experienced by objects placed in water. If you suspend a large rock from a spring balance and lower the rock into a bucket of water, you will find the the water will make the rock considerably lighter than it is in air. Fig 21
Whales can be crushed by their own weight when stranded on the beach.
Aquatic animals, particularly those that live in the ocean, are adapted to the buoyancy effect of water. The skeleton or exoskeleton that supports the body of an animal in water would not support its extra weight if it lived on land. This is why some large animals such as whales can be crushed by their own weight when stranded on the beach. The buoyancy effect of water also supports organisms such as jellyfish that don’t have skeletons. They can float around in the water but their weight on land tends to flatten them.
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Investigate
27 PHYSICAL FACTORS IN WATER Aim Toinvestigatethephysicalfactorsthataffectlifein aquaticecosystems.
Planning and Safety Check • Youcandothethreepartsofthis investigationinanyorder.Foreachpart, readthroughtheMethodandmakealist ofthematerialsyouneed.Selectthe materialsforeachpartinturnfromyour equipmentstoreortrolley. • Foreachpart,makealistofthesafety precautionsyouwillneedtotake. • Preparedatatableswhereappropriate.
Teacher note: Fill a few buckets with tap water at least three days before use. This will be enough water for the whole class. Materials • aquariumorlargeglassjar(sharewithclass) • methylenebluesolution • oxygen-removingsolution(50g/Lsodium dithionite/hydrosulfite,freshlyprepared) Toxic • pieceofstring(about30cmlong) • smallroundballoon • springbalance(newtons) • stirringrod • thermometer • 2smallplastictakeawaycontainers • 250mLbeaker • 250mLofine,drysand • 400mLjarwithscrewlid(orsoftdrinkbottle) • heatlamp(optional)
PART A
Te m pe ra tur e
dry sand
water
2 Placebothcontainersinthesunorundera heatlampfor20minutes. Measure the temperature near the top of thesandandthewaterandrecordyourdata.
Discussion 1 Whichshowedthegreatertemperature change—sandorwater?Whywoulditbebest to use the average of the class results to answerthis? 2 Whatdotheresultsmeanfororganismsthatlive inwater,comparedwiththosethatliveonland? 3 Predictwhatwouldhappentothesandand waterifthesurroundingscooleddown.Check yourpredictionbyputtingthecontainersina refrigeratorfor20minutes.
PART B
Dis s olved oxyg en Method 1 Carefully,withoutstirringupthewater,dipa beakerintoabucketofwaterthathasbeen sittingforseveraldays.Takeoutalittlemore than200mLofwater. 2 Pourtheexcesswaterdownthesinkuntilthe meniscusisonthe200mLmark. 250
Method
200
1 Pourthesandintoonecontainer.Pouranequal volumeofwater(atroomtemperature)intothe other container.
150
Record the initial temperature of the sand andthewater.
100 50 Make sure there is exactly 200 mL of water.
Chapter11 Livingsystems
3 Addthreedropsofmethylenebluetothewater andstirverygently.
3 Whyistheremoredissolvedoxygenin mountainstreamsthaninponds? 4 Whyareaeratorsusedinaquariums?
PART C
Buoyan cy Add 3 drops of methylene blue.
Stir very gently.
Method 1 Fillaballoonwithwaterandtietheend.Laythe balloon on the bench and observe its shape. Drawtheshapeoftheballoon.
250 200 150 100 50
4 Whilestirring,addoxygen-removingsolution a drop at a time untilthebluecolourjust disappears.
2 Tieapieceofstringaroundtheneckofthe balloonandsuspenditinthewaterinan aquarium. Howdoesits shapechange? Drawit.
Record the number of drops added. This is ameasureoftheamountofdissolvedoxygenin thewater. 5 WashoutthebeakerandrepeatSteps1and2. Thistime,pourthewaterintoajar,screwthelid onandshakevigorouslyfor10seconds.
3 Suspendarockorothermassfromaspring balance.Findtheweightoftherockinairand inwater. Shake the water vigorously for 10 seconds.
6 Pourthewaterbackintothebeakerandrepeat Steps 3 and 4.
Record the data in a table. Then calculate thebuoyancyforceontherock.
Discussion 1 Account for the difference in the shape of the ballooninandoutofwater. 2 Explainwhytheweightoftherockisdifferent inandoutofwater.
Recordyourresults.
Discussion 1 Explainanydifferenceinthetworesults. 2 Whydidyouusewateroutofthebucketand notfromthetap?
Is the buoyancy effect in salt water different from what it is in fresh water? Discuss this question in a group and design an experimenttoanswerit.
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ScienceWorld8forNSW Living on land Land organisms have plenty of air around them but water is often scarce. For organisms to survive on land they need: • lungs or other structures for obtaining oxygen • a strong supporting skeleton • methods of obtaining water and avoiding excess water loss • ways to keep warm in cold weather and cool in hot weather.
Obtaining oxygen Most land animals use lungs to obtain oxygen for respiration. Since the surface of the lungs has to be kept moist, these organs are internal. Oxygen first dissolves in the thin watery layer on the inside surface of the lungs and then passes through the lung wall and into the body. Without this water, oxygen would not pass through the lungs and the organism would suffocate.
Obtaining water and avoiding water loss Organisms cannot live without water. Aquatic organisms can easily obtain water, because they live in it, but for land organisms water is the factor that can determine their survival. Most land animals need to drink water to replace that lost in breathing and urinating and by evaporation. However, some land animals do not drink but obtain all their water from the food they eat. Land animals generally have a covering over their bodies to stop water loss by evaporation. For example, a reptile’s skin is waterproof and very little water can pass through it.
Fig 27
The dusty hopping mouse obtains all its water from the food it eats.
Water loss in plants Plants absorb water from the soil through their roots. The water travels up the stem to the leaves, where it is used in the process of photosynthesis. The remaining water is lost from the leaves. The leaves of plants have tiny openings on their surfaces which allow gases to enter and leave the leaf. These openings are called stomates (STOW-mates). Look at the diagram on the right. Water evaporates from the moist surfaces of the cells inside the leaf and passes out of the leaf through the stomates into the air. The stomates are able to open and close, and in doing so can control the loss of water vapour from the leaves. About 85% of the plant’s water loss occurs through the stomates. The remainder of the plant’s water loss occurs when water evaporates from the cells on the
surface of the leaf. This single layer of cells forms the ‘skin’ or epidermis on the top and bottom of the leaf. Many plants have a waxy, waterproof layer called the cuticle over the epidermis, which also helps to prevent water loss. epidermis
epidermis
cuticle (waxy layer over epidermis)
stomate
Chapter11 Livingsystems
Investigate
28 WATER LOSS IN PLANTS Aim
4 Repeat Step 3 for another leaf.
Toinvestigatewaterlossfromplants.
5 Observethepaperforabout15minutes.(While youarewaiting,goontoPartB.)
Materials • 5piecesofdriedcobaltchloridepaper (2cmx2cm)inasmalljarwithalid • forceps • 4piecesofclearpackagingtape • clearnailpolish • microscopeandslide
Planning and Safety Check • Carefullyreadthroughthemethodfor PartA.Makeaverybriefsummaryof whatyouhavetodo. • Discusswithyourgrouphowyouare goingtoanswerthequestioninPartB.
6 After15minutes,comparethecolourofthe paper on each side of the leaves. Recordyourresults.
Discussion 1 Whyisitimportanttouseforcepsandnotyour ingerstohandlethecobaltchloridepaper? 2 Onwhichleafsurfacedidthecobaltchloride paperchangecolourirst? 3 Wouldyouexpectmorewaterlossonahotday oronacoolerday?Why? 4 Whatresultswouldyouexpectifithadnot rainedformanydays?
PART A
PART B
1 Useforcepstotakeapieceofbluecobalt chloridepaperoutofthejar.(Don’ttouch thepaperwithyouringers.)Replacethelid immediately.Putadropofwateronthepaper.
Are there as many stomates on the top side of a leaf as there are on the underside? Usethenailpolishtechniquefromtheactivity onpage87todesignatesttoanswerthe question.YoucanusePVCwoodworkingglue insteadofnailpolish,butyouhavetolettheglue dryovernight.
Method
Recordyourobservations. 2 Takethejarofcobaltchloridepaper,forceps andpackagingtapeoutsideandindabroadleafed plant in the sun. 3 Use the forceps to place a piece of cobalt chloride paper on the top side of a leaf. Tape thepaperinpositionasshownbelow.Dothe same on the underside of the leaf.
cobalt chloride paper clear packaging tape
Discussion 1 Onwhichleafsurfacedidyouindmore stomates—toporunderside?Suggestareason for this. 2 Awaterlilyplanthasstomatesonthetop surfaceonly.Suggestareasonforthis.
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Desertecosystems Deserts are very harsh for living things. The two main factors that affect the survival of organisms here are the lack of water and the extreme temperatures. The daytime temperatures can sometimes be as high as 45°C, while the night-time temperatures can fall well below 0°C.
Most animals that live in desert ecosystems are active at night (nocturnal) and sleep in burrows or in caves during the day to avoid the heat. Many animals, like the bilby, do not drink, but obtain all their water from the food they eat. Some reptiles can change their skin colour to regulate their body temperature. A pale skin reflects the heat, while a darker skin absorbs heat on cool winter mornings.
Fig 32 Fig 31
In Central Australia, the average annual rainfall is less than 200 mm, but often no rain falls for years.
Desert plants have to control their water loss very carefully. These plants have relatively few stomates on their leaves, and in many types of plants the stomates close during the hottest part of the day. Most stomates are located on the underside of the leaf, away from the direct sunlight. Most desert plants have small, narrow leaves with a relatively thick waxy coating on them. And many plants have hairs on the leaf surface to reduce the sunlight hitting the leaf and thus evaporating water. The leaves of eucalypts hang vertically to avoid the direct heat of the sun.
The tough, impermeable skin of reptiles greatly reduces water loss.
Questions 1 Describe the ways in which desert plants are adapted for life in the desert ecosystem. 2 Bilbies and native mice are active at night and sleep during the day. How would you classify this type of adaptation? Why is it important for the survival of these animals? 3 List the ways in which animals lose water. Then suggest how animals that live in the desert could limit their water loss. 4 The leaves of some desert plants curl into a tube during the hottest part of the day. Suggest why this happens. 5 Use the internet to write a brief report about the life cycle of a native Australian desert plant.
Chapter11 Livingsystems
Check! 1
Some of the following statements are false. Select the false ones and rewrite them to make them correct. a Organisms that live in the ocean or in rivers are called aquatic organisms. b Temperature, predators and dissolved oxygen are physical factors in aquatic environments. c The buoyancy effect of water supports organisms without a skeleton, such as jellyfish. d Most of the water lost from a plant occurs by evaporation of water from the cuticle. e As the temperature of water increases, the amount of dissolved gases increases.
2
Why don’t water plants grow well in creeks and lakes that contain muddy water?
3
An animal was found in a very fast-flowing stream. From the list below, choose the adaptations it might have. • astreamlinedbody • long,thinlegs • alattenedbodyshape • largeheadandeyes • short,muscularlegs • largegillstoabsorbthesmallamountof dissolved oxygen • hooksontheendsofitslegs • around,ball-likebodyshape • asmooth,shinybody
4
Plants that live fully immersed in water do not have any stomates on their leaves. Suggest reasons for this adaptation.
5
The density of sea water is 1.03 g/cm3. Explain why it is easier to float in sea water than in fresh water.
6
List the biological and physical factors that may affect the survival of a fish in a lake. How are these different factors from those that affect the survival of a mouse in a wheat field?
7
Suggest why reptiles such as lizards and snakes are generally better adapted to living in arid environments than frogs.
8
Use the oxygen solubility graph on page 262 to answer the following questions a What does the word solubility mean? b What is the solute and what is the solvent? c How much oxygen can dissolve in 1 L of water at 15°C? d Kate has an aquarium with 10 L of water in it at 10°C. How much oxygen can this volume of water hold? e Kate turned on an aquarium heater and the water reached 30°C. How much oxygen can dissolve in the water now? f Kate tested her aquarium water and found the dissolved oxygen to be 5 mg/L at 25°C. However, the tropical fish require at least 7 mg/L dissolved oxygen. What could she do to successfully keep these fish?
9
Cacti grow in desert ecosystems. They are very slow-growing plants.
The green part is the stem, which contains a small number of stomates, and has a very thick, waxy cuticle. It also stores water for the plant. The prickles are modified leaves and contain no stomates. The cells in the stem contain less chlorophyll than the cells in most other plants. a What is the purpose of the waxy coating? b Use the information above to explain how cacti are well adapted to desert life. c Suggest why cacti are slow growing. d Some cacti have very deep spreading roots. Suggest a reason for this.
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challenge 1 Smallchildrenoftencollectishandother aquaticanimalsfromrockpoolsatthebeach. Iftheseanimalsareplacedinabucketofsea waterandleftinthesun,theyusuallydieaftera fewhours.Suggestareasonforthis. 2 Inanexperiment,Joeputaplantin200mLof waterinaglassandadded5mLofoiltothe watertostopevaporation.Hethenputthesetup on a balance. Joeduplicatedtheset-upbutthistimetieda plasticbagaroundtheplant.Heleftbothplants in the sun for 4 hours.
d Howdoyouaccountforhisresults? e Wouldaddingathirdglasswithnoplant improvehisexperiment?Explain. f WouldJoe’sresultsbedifferentwithdifferent weatherconditions(eghotandwindyinstead ofcoolandcalm)? 3 Thegraphbelowshowshowtheamountof dissolvedoxygeninalakeinsummerchanges withthedepthofwater. Dissolved oxygen (mg/L) 0.1
0.2
0.3
0.4
2 4
drops of water
plant
5 mL oil 200 mL water
5 mL oil 200 mL water
without bag with bag
ThetablebelowshowsJoe’sresults.Healso observeddropsofwaterinsidetheplasticbag at the end of the experiment. Initial mass (g)
Final mass (g)
without bag
220
204
with bag
230
230
Plant
a Suggestwhytherewasadifferenceinthe initialmassesofthetwoplants. b Accountforthedifferencebetweentheinal andinitialmassesoftheplantwithoutthe bag. c WhydidJoeusetwoplants?
6
Depth (m)
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8 10 12 14 16
a Writeageneralisationlinkingthedissolved oxygenandthedepthofwater. b Whatconcentrationofdissolvedoxygenis foundatadepthof3m? c Betweenwhichdepthsistherearapid changeintheamountofdissolvedoxygenin thewater? d Suggest reasons for the greater concentration ofdissolvedoxygeninthewaterabovea depth of 8 m. 4 Mostreptilesandamphibians(frogsandtoads) hideinburrowsduringwinter.Suggestwhyish, crayishandotheranimalsthatliveinwaterdo not do this. 5 Usetheparticletheorytotrytoexplain whygasesdissolvebetterinwateratlower temperatures. Try doing the Chapter 11 crossword on the CD.
Chapter11 Livingsystems
Problemsinecosystems When Captain James Cook sailed along the east coast of Australia in 1770, he wrote in his journal that this land was a ‘continent of smoke’. He was referring to the numerous bushfires he could see from his ship. Before humans came to this land, it seems that fires, which were started by lightning strikes, occurred only very occasionally. However, Aborigines, whose ancestors arrived about 50 000 years ago, used fire for their survival and changed the natural pattern and timing of fires. This in turn changed the relationships of the organisms in certain ecosystems. Major changes like bushfires, droughts and floods or large toxic chemical spills have a huge impact on the organisms in ecosystems.
Your task—impacts on ecosystems For each of the three topics, use the ideas to write a report about one of the natural or humancaused disasters and how it affects the paricular ecosystem.
What to do • •
•
•
•
Work in a small group. Choose a topic and decide what you are going to write about and how you are going to structure your report. That is, will you present your report as an essay-type report, a PowerPoint presentation, a newspaper-type article, a poster and oral presentation, a video presentation etc. You are not limited by the ideas under each of the topics or the order in which they appear. You can include other information as well. You can use information from past or recent disasters as well as models or predictions in your report. Document your report with the source of your information—website addresses, book titles and authors, titles of newspaper articles and dates etc.
Bushfires How do bushfires start naturally? What weather conditions cause bushfires? Some bushfires are called ‘low-heat fire s’ while others are very intense and destruc tive. Why does this occur? The Aboriginal method of burning actu ally protected their environment rather than destroying it. Explain what this stateme nt means. What changes occur to the populations of organisms in an ecosystem as a result of a bushfire? What emergency services are involved in fighting bushfires? What methods are used to reduce the risk of bushfires and to reduce the damage caus ed by them?
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Droughts and floods
How is a drought defined? Are some areas in Australia more likely to experience droughts than others? Why does this happen? What is the El Niño effect? Does it affect the weather in all parts of Australia? Can it be predicted? What changes occur to the populations lt of organisms in an ecosystem as a resu of a drought and flood? ly Are some areas of Australia more like Why rs? to experience floods than othe does this happen? Floods cause huge losses of property, crops and livestock. However there are benefits to the environment as a result of flooding. What are these benefits?
Chemical spills Damage to ecosystems from oil spills can occur when oil is transported from the oil fields to the refineries. Find out whe re in Australia oil is drillled and where it is transported to. Give an example of a major oil spill and document the damage it caused to the ecosystem. What methods are used to clean up oil spills? Heavy metals are very toxic to most organisms. What are heavy metals? Give examples of industrial processes that produce them. How do heavy metals get into natural ecosystems? The photo shows a fish kill. Why do they occur? What measures are taken to avo id fish kills in Australian waterways and seas?
Chapter11 Livingsystems
Copy and complete these statements to make a summary of this chapter. The missing words are on the right.
adaptations
1 An _____ is the system of feeding relationships between the living
buoyancy
things and their interactions with the non-living things.
2 The survival of an organism depends on _____ factors as well as
4
ecosystem drying out functional
physical or non-living factors.
3
biological
_____ are characteristics that help an organism survive in its particular living place. They can be classified as structural, _____ or behavioural. _____ is a process by which those organisms with characteristics best suited to their environment survive and reproduce.
light natural selection oxygen physical temperature
5 The _____ factors in an ecosystem include dissolved gases, _____, humidity and the availability of air and water.
6 The main environmental factors that affect organisms which live in water are the amount of _____, water temperature, light, currents or waves, and the _____ effect of water.
7 To live successfully on land organisms must obtain _____ from the air, and have ways of obtaining water and avoiding _____.
REVIEW
1 For each of the words below, write a sentence to show that you understand its meaning. stomates biological factors buoyancy adaptation 2 Which of the following would you class as a functional adaptation? (There may be more than one answer.) A Dolphins have a layer of fat under their skin. B Dolphins sometimes follow ships. C Female dolphins give birth to live young and produce milk on which to feed them. D A dolphin is able to make many sounds with its voice box. E Dolphins have a streamlined shape.
3 Which of the following would you class as a physical factor in an ecosystem? (There may be more than one answer.) A the number of predators in the area B the availability of light C the density of trees in the area D the amounts of nutrients in the soil 4 Which one of these statements is correct? A The solubility of gases increases as the temperature of the water increases. B The shape of a bird’s beak would be classed as a structural adaptation. C Waves and currents usually decrease the amount of dissolved oxygen in the water. D An object with a density greater than that of water will float.
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REVIEW
5 Plants can control water loss in a number of ways. Which of the following would help a plant reduce water loss? (There may be more than one answer.) A A large number of stomates on both surfaces of the leaves B Small, narrow leaves C A thick cuticle on the leaves D Stomates that open during the middle of the day E A waxy coating over the surface of the leaves 6 In an experiment similar to the one on colour adaptation, disks (20 of each colour) were scattered over an area 3 m by 3 m. The ‘predators’ found as many as they could in 10 seconds and the results were tabled. Colour of disk
blue green yellow red
Number found
20 17 4 8
a Draw a bar graph of the results. b Infer the type of surroundings over which the disks were scattered. c Explain how this experiment can be used as a model for natural selection.
Dissolved oxygen (mg/L)
7 The water-holding burrowing frog lives in the desert regions of central Australia. Suggest adaptations it might have to help it survive in this environment.
8 How would you explain to a class of young science students what the term buoyancy means? Describe any demonstrations you would use in your explanation. 9 Read each of the following questions and then answer them as fully as you can. a Why do land animals have to have some sort of skeleton whereas aquatic animals can survive without one? b Why does an oil spill kill aquatic animals and plants? c Why is natural selection often called ‘survival of the fittest’? d How do land animals avoid losing water from their bodies? 10 Kerrie used an oxygen meter to measure the changes in the dissolved oxygen in her aquarium at home. The aquarium was next to a window and contained many water plants, fish and snails. It was kept at 25°C, and had an aerator (bubbler) fitted to it. However, during her experiment, the aerator was accidentally switched off for 8 hours. The graph below shows her results. a When was the aerator switched off? Explain your answer. b What was the highest concentration of dissolved oxygen in the aquarium? What was the lowest? c Why was there a slight fall in the dissolved oxygen after 6 pm? d Predict the shape of the graph if no aerator had been used in the aquarium.
6 5 4 3 2 1 12 noon
6 pm
12 midnight
6 am
12 noon
Time (hours)
Check your answers on pages 283–284.
Chapter11 Livingsystems
US AREA C O F D E B I R C PRES QUEENSLAND
Murray River crisis
Bourke
Broken Hill
NEW SOUTH WALES
pipeline Morgan M
ur r
n hla La c
Mildura
Murrumb idge
ve Ri
Adelaide
ivid i ng
ng rl i Da
Moree
r
at D
SOUTH AUSTRALIA
e Riv
Ran ge
Brisbane
ay r
The Murray is Australia’s longest river, and its basin covers 1 000 000 square kilometres of Queensland, New South Wales, Victoria and South Australia. Most of its water comes from the Great Dividing Range in the east, and it then wanders across the western plains, reaching the ocean in South Australia. An Aboriginal legend says its wandering course was formed by a giant cod thrashing as it tried to escape a hunter’s spear. Forty per cent of Australia’s farms are in the Murray–Darling basin and they produce a third of Australia’s agricultural production—wool, cotton, wheat, sheep, cattle, dairy products, rice, oil-seed, wine, fruit and vegetables. The water used to irrigate these farms is taken from the river. Once 25 000 gigalitres flowed down the river each year, but today the flow is less than 3000 gigalitres! Dams and reservoirs have been built to control the flow of water. This means there is not enough water in places, and too much in other places. This has affected plants such as the River Red Gums (page 259) and animals such as the Murray Cod—Australia’s largest freshwater fish. In 1991 there was an outbreak of toxic blue-green algae along 1000 km of the Darling River. Too much water is being taken out of the Murray River, and too much pollution is being put back in. This is a major problem for the city of Adelaide, which draws its water from the Murray. Over the last 200 years, 40% of the natural vegetation has been cleared, and shallowrooted crops, such as wheat and pasture for livestock, have been planted. This has caused the underground water to rise, bringing salt to the surface and causing a major salinity problem. Obviously the Murray River needs more water, but where will it come from, if rainfall doesn’t increase? Australia is suffering a long-lasting drought, perhaps the worst in 1000 years, and climate change could reduce the flow in the river even further. The Federal and State governments are working together to try to solve the problem.
Toowoomba
Dubbo
Gre
Learning focus: Why different groups and cultures may have different views in relation to scientific issues
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er Riv
Sydney
Griffith eR ive
r
Wagga Wagga
Canberra Shepparton
VICTORIA
Melbourne Snowy Mountains Scheme
One obvious solution is to reduce the amounts of water that farmers are allowed to use for irrigation. Also, large amounts of water could be saved by improved irrigation systems, as up to 85% of water is now lost due to evaporation and leaks. Perhaps farmers could switch to crops that use less water. It has even been suggested that water could be piped from high-rainfall areas into the Murray–Darling.
Questions 1 How would the following groups differ in their views on what should be done about the Murray? • farmers in the Murrumbidgee Irrigation Area • people living in Adelaide • the Federal and State governments • the Australian Conservation Council • people living in Sydney 2 The Wiradjuri Aboriginal people who live along the river say, ‘Look after the land and rivers, and the land and rivers will look after you.’ Explain what you think this means. Try to correctly use the word sustainable in your answer.
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Answers to Reviews the right-hand test tube. The salt that was dissolved in the water is left behind in the left-hand test tube. c The ice-cold water lowers the temperature inside the right-hand test tube. This causes the water vapour in the tube to condense back to liquid water.
If your answer does not agree with the answer given here, go back to the chapter, and read the relevant section again. Your answers may be slightly different from the answers given here. If in doubt, check with your teacher.
Chapter 1 Mixing and separating 1
A
2
B—see page 7
3
D—see page 14
4
a Water—since it dissolves more of solid B than the other liquids do b Water—If you add water to the mixture of A and C, only A will dissolve. You can then separate them by filtration and evaporation. c A mixture of A and B could be separated using petrol. Some of A would dissolve, and this could be recovered by evaporation. However, this is not a good method, because A doesn’t dissolve very well in petrol.
5
7
The fact that a sediment settles out on standing indicates that some of the fruit juice is in suspension. However some is also in solution since the liquid is coloured. And if you don't get a clear solution on settling then the fruit juice is a colloid (see page 8). So fruit juice is a solution, a suspension and possibibly a colloid as well.
8
There are many possible sentences using these words. For example: a Milk is a liquid-in-liquid colloid called an emulsion (see page 8). b A concentrated solution contains more solute than a dilute solution (see page 7).
9
The ink in a felt pen is a mixture of several different colours. Different felt pens contain different ink mixtures, which can be separated using paper chromatography.
a and b C—beaker
To start with, the police would test a sample of ink from the ransom note. Then they would test the ink from the felt pens of each of the three suspects. If they get the same pattern of colours as in the ransom note, then the owner of this pen is probably guilty. (It is of course possible that the note was not written using this particular felt pen, but with another pen of the same type.)
B—filter paper
RESIDUE E—ring clamp
D—stand
A—filter funnel
FILTRATE
c
The mixture should be poured from the beaker down a stirring rod—as shown in Fig 19 on page 12. The stem of the filter funnel should be touching the inside of the beaker.
6
a Distillation—see page 16 b Heating causes the water in the lefthand test tube to boil. Water vapour travels along the tube and condenses to form pure water in
Lab review 1
Add water to the mixture and stir. The salt dissolves but the dirt does not.
2
Filter the mixture as in Investigate 2 on pages 12–13. The residue on the filter paper is the dirt, and the filtrate is the salt solution. Equipment needed: • piece of ilter paper • ilter funnel • stand and ring clamp • wash bottle • glass stirring rod • 2 beakers
AnswerstoReviews b The variables to control are: • how big and how dirty each piece of cloth is • amount of washing powder you use • volume of water you use • temperature of water • method of washing the cloth • how long you wash the cloth c You are purposely changing the type of washing powder. d You will measure the cleanness of the cloth.
Evaporate the salt solution as in Part A of Investigate 3 on page 15. Equipment needed: • watch glass • matches • Bunsen burner • metal tongs • heatproof mat • boiling chips • gauze mat • tripod
3
Chapter 2 Science at work 1
B
2
D—One-quarter of the candle burns in 2 hours, so you can predict that the whole candle will burn in 4 × 2 = 8 hours.
3
A—It is difficult to control how hard you hit (B) or throw (C) the balls.
4
a Steel is a metal and conducts electricity. b Metals conduct electricity, but non-metals don’t conduct electricity. c You would not expect carbon (a non-metal) to conduct electricity. You could modify the hypothesis as follows: Metals conduct electricity, but most non-metals don’t.
5
C (D is incorrect because the solubility increases with temperature at a uniform rate. In other words, the graph is a straight line.)
6
a about 1 pm b about 11.30 am and between 12.30 pm and 1.30 pm c at the top of the high range d Most probably there were clouds around 12 noon that blocked some of the UVB.
7
Chapter 3 What are things made of? 1
D—Because the statement says all matter, it is a generalisation rather than an inference.
2
See the diagram at the bottom of this page.
3
C
4
There are several examples on page 58 but you have probably thought of others.
5
Aluminium (density 2.7 g/cm3) and lead (density 11.3 g/cm3) will both sink in water. And because their densities are less than the density of mercury (14 g/cm3), they will float in mercury. mass of pure gold a Density of pure gold = volume of pure gold
6
=
b Density of crown
solidification
1500 g 1000 cm3
= 15.0 g/cm3 c No—the density of the crown is less than 19.3 g/cm3, therefore it is not pure gold.
evaporation
melting
solid
= 19.3 g/cm3 mass of crown = volume of crown =
a Cut a piece of dirty cloth into equal-sized pieces. Using the same quantities of soap powder and water, wash one piece of cloth in Sudso and the others in other types of washing powders for the same time. Compare the results. Do the experiment in both hot and cold water.
1930 g 1000 cm3
liquid
condensation
gas
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7
Your answer should be something like this: Shopping bags are normally made of LPDE plastic. These are cheap but are difficult to dispose of and at present cannot be recycled. However, the green shopping bags made of polypropylene can be reused many times. Plastic is a synthetic material made from coal. It is therefore non-renewable. The bags could be made from paper, a processed material made from wood, which is renewable. However, paper bags may not be as strong as plastic ones. Bags could also be made from cotton canvas. These are more expensive but can also be reused.
8
9
a A particles vibrating or moving very slowly D particles very close together, almost touching G very strong bonds between particles b C particles moving freely and rapidly F wide spaces between particles I very weak bonds between particles c B particles moving around freely but slowly E particles fairly close together H particles held together to some extent but free to move around d D particles very close together, almost touching e D particles very close together, almost touching G very strong bonds between particles f A a The particles in gases are much more spread out than the particles in liquids or solids. There are fewer particles packed into each cubic centimetre. Hence gases have lower densities than liquids or solids. b When a gas is cooled its particles lose energy and don’t move as quickly. They become closer together and attract each other more strongly. As a result the gas condenses to a liquid.
Chapter 4 Building blocks of life 1
C—All cells have a nucleus, cytoplasm and organelles.
2
C—Cells have many and varied shapes.
3
a chloroplast b cytoplasm
c d e f
nucleus cell membrane cell wall vacuoles
4
A ×10 objective and a ×4 eyepiece lens gives a total magnifying power of ×40. An object 0.05 mm in diameter would appear to be 40 × 0.05 = 2 mm in diameter.
5
Kate’s list should be: 1 eyepiece lens 2 body tube 3 focusing knob 4 objective lens
5 stage 6 stage clips 7 light
6
a Firstly, the eggs may be eaten by other animals, and secondly sperm from the male may not reach the eggs to fertilise them. b Fewer frogs’ eggs reach adulthood than birds because (1) the frogs’ eggs are fertilised externally, which means that many eggs may not be fertilised, and (2) the young tadpoles are not cared for by the adult frog, so many young may be eaten by other animals.
7
A unicellular organism consists of a single cell which contains all the structures necessary to live an independent life. On the other hand, a multicellular organism contains many different types of cells which work together for the survival of the organism.
8
The stomach is an organ because it is made up of many different types of tissues, eg gland tissue, muscle tissue and connective tissue. These tissues contain specialised cells which work together to digest food.
9
Tissue A could be found in the lining of the gut where its function would be to produce mucus that is slippery and allows the food to move smoothly through the gut. The cells of Tissue B could form a flat surface like paving stones, and this tissue could be found in the skin.
10 a The pine seed has a wing that allows it to be carried in the wind. b The apple has a sweet, edible fruit that is eaten by animals. The seeds pass through the gut of the animal and out in its droppings, and are spread this way.
AnswerstoReviews c The eucalypt has very small, light seeds which fall out of the ‘gumnut’ and are carried away by the wind. d The burr seed has spikes which stick to the fur, hair or feathers of animals. The animal may pick off the burr some distance from the plant. e The paw paw has edible flesh around its seeds. The seeds are spread in animal droppings in the same way as apple seeds.
8
People often say that electrical energy is made in power stations, but this is not scientifically correct. According to the law of conservation of energy, energy cannot be made—you can only change it from one form to another. In a power station you are converting the chemical energy in coal or the kinetic energy of falling water into electrical energy.
9
a
wood, bagasse and other renewables 3.7%
Microscope licence test 1
Making a wet-mount slide—see the Activity on page 81.
2
Setting up a microscope—see the Skillbuilder on page 80.
natural gas 19.6%
D
2
C—This is against the law of conservation of energy (page 117).
3
B
4
A—Heat energy is transferred from the hot tea to the cup.
5
a B b C
6
a The other 95 joules of energy are wasted as heat energy. This is why the bulb becomes so hot. energy × 100 b efficiency = input energy
coal 41.8%
oil 33.8%
Chapter 5 Energy in our lives 1
hydro-electricity 1.1%
b Coal, oil and natural gas c 4.8% (hydro-electricity + wood, bagasse and other renewables) d Bagasse is the crushed, juiceless remains of sugar cane left after extracting the sugar. It is used as a fuel and for making wallboard etc. 10 gravitational potential energy of water in dam kinetic energy of water in pipe
=
5 joules × 100 100 joules
= 5% 7
gravitational potential
electrical energy in electrical generator 11 The more efficiently a ball changes its kinetic energy into elastic potential energy (then back to kinetic energy), the higher it bounces. To compare different balls, you could drop them from the same height onto the same surface and measure how high they bounce. To make the test completely fair, the balls would need to be the same mass and size.
Chapter 6 Investigating heat
KINETIC
HEAT
kinetic energy of spinning turbine
sound
1
D
2
C—see page 139
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a Warming of a cup of water
25
x
Temperature (ϒC)
x
SUN 20
x
x
SHADE x x
15
4
a true b false—conduction is fast in conductors (or slow in insulators) c true d false—the Sun transfers heat energy to the Earth by the process of radiation e false—the hotter an object is, the more radiation it emits f true g true
5
According to the particle theory (page 129) the particles in a hot object move more rapidly than the particles in a cooler object.
6
The amount of heat in an object depends on its mass, its temperature and what it is made of. So a bucket of water has more heat energy than a teaspoon of water at the same temperature.
7
When your hand is above the candle, heat rises through the air by convection. When your hand is beside the flame, some heat travels to your hand by conduction, but air is a poor conductor of heat. The candle is not hot enough to produce a lot of radiation.
8
10
20
30 Time
40
50
60
b The cup of water in the Sun warms up more rapidly than the cup of water in the shade. c Same volume of water in each cup Identical cups Same initial water temperature Identical thermometers d Heat was transferred to the cups by radiation from the Sun. e If you painted the cup black it would absorb more radiation. However, as it warmed up it would probably lose heat more rapidly than an ordinary styrofoam cup. 10 Heat flows from warm places to cold places. So the insulation is to slow down the movement of heat from warm to cold. It is therefore better to say ‘to keep the warm in’ rather than ‘to keep the cold out’. cold
warm
convection
a Heat travels from the heating element to the sandwich by radiation. b Heat cannot travel downwards by convection, and conduction through the air would be very slow because air is a poor conductor.
insulation
11 You can base your experiment on Investigate 15 on page 138. 1 Make two model sheep, eg by wrapping wool around soft drink cans. 2 Wet the wool on one of the cans. 3 Fill both cans with warm water at the same temperature, and put a thermometer in each. 4 Record the temperature in each can every minute for 15 minutes.
AnswerstoReviews b Jupiter’s solid core is estimated to be 12 800 km in diameter (6400 km × 2). c The thickest layer is the liquid hydrogen layer which is 41 000 km thick. d The temperature decreases as the distance from the centre increases.
5 Plot the results on a graph and decide which ‘sheep’ cools more rapidly. This should give you some idea of whether sheep get colder when it is raining.
Chapter 8 Building blocks of matter dry wool
wet wool
Chapter 7 Exploring space 1
C—see page 152
2
B
3
a The inner planets and the outer planets. The inner planets have rocky surfaces and are relatively small. The outer planets are all relatively large and consist of gases. b Pluto is much smaller than any of the outer planets and its orbit is tilted (see Fig 7 on page 154). Also it is more like the inner rocky planets than the outer gas planets.
4
A
5
D—see page 165
6
Jupiter and Saturn are gas planets and have no known solid surface on which a spacecraft could land. Mercury, on the other hand, has a solid surface.
7
a As the distance from the sun increases, a planet’s orbital speed decreases. b B—Jupiter’s orbital speed is slower than that of Venus. It is also further from the sun, making its orbital path longer.
8
B—see pages 165 and 166
9
Supernovas occur to end the lives of giant, hot stars. Our sun is only a medium-sized star and will end its life as a red giant, then a white dwarf.
10 a Jupiter is composed mainly of hydrogen in gas and liquid states. It also contains some water and ammonia, with a small rocky core.
1
B—Only elements, eg the substances copper, mercury and chlorine, can be seen without a microscope.
2
C
3
A—There are only 90 elements found naturally, but they can combine to form many thousands of different compounds.
4
C—Sugar is a compound of carbon, hydrogen and oxygen.
5
C—Only NO2 has nitrogen and oxygen in the ratio 1:2. The ratios of nitrogen to oxygen are: A NO 1:1 B N2O 2:1 C NO2 1:2 D N2O2 2:2 or 1:1
6
B represents an element—atoms of one type only. (A represents a mixture of elements and compounds, C represents a mixture of elements and D represents a compound.)
7
Four (three hydrogen and one nitrogen)— although there are only two different types of atoms.
8
a 1 and 4 b 2 and 4 c 4—because it gives a yellow flame and produces a purple gas
9
B—The tests show that the elements hydrogen, chlorine and zinc are present. The zinc reacted with the acid, so the acid contains only hydrogen and chlorine.
10 Your answer should be something like this: Elements and compounds are substances but atoms and molecules are invisible particles. A compound is a substance containing two or more elements combined together. A molecule is two or more atoms joined together.
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sources such as the cellophane bag. It is called an experimental control. d The volume of water in each beaker, the volume of starch solution in each piece of tubing, and the time each was left.
11 The electric current causes the water to decompose into the elements hydrogen and oxygen (see page 193). electric current
8 When hydrogen and oxygen are mixed, a lighted match causes them to combine again. In both cases a chemical reaction occurs. lighted match
12 The scientist needs to use chemical reactions to break the compounds into their elements, as in Question 11. If she does this, the first compound ●■will give her equal amounts of ●and ■. The second compound ●■●will give twice as much ●as ■.
Chapter 9 Food for life 1
C
2
D—Photosynthesis needs the energy from sunlight, so it stops at night.
3
B—see page 203
4
D
5
a b c d e
6
Solid wastes (faeces) pass out of the gut through the anus. Liquid wastes are removed by the kidneys through the bladder. Gaseous wastes are removed by the lungs and breathed out through the trachea. (See pages 219 and 220.)
7
a The glucose came from the breakdown of starch by the enzyme in saliva. The glucose passed through the cellophane tubing and into the water in beaker 2. b The aim of the experiment was to test whether glucose is produced when saliva and starch are mixed together. c Beaker 1 was used as a comparison, and to check that glucose did not come from other
Chapter 10 Electricity 1
a Rods with the same charge repel each other. b Rods with opposite charges attract each other.
2
a If a material loses electrons it becomes positively charged. b If a material gains electrons it becomes negatively charged.
3 3—the small intestine (see page 209) 1—enzymes start digesting starch in the mouth 2—the stomach 1—the mouth 4—the large intestine
a Vessel B contains blood which is being pumped away from the heart. Therefore, it would have thicker walls. b The blood in Chamber 1 would have less oxygen since the blood has come from the body and is being pumped to the lungs to receive more oxygen. c The blood flows through vessel A into chamber 1, then into chamber 2. It is pumped from chamber 2 to the lungs in vessel B. It then returns from the lungs to chamber 3 in vessel C, and finally is pumped from chamber 4 to the body in vessel D.
Conductors
Insulators
copper steel salt water
plastic air wood
4
a A (Set-up D may or may not work, depending on whether the battery terminal touches the spring at the bottom. Because of this, torch batteries are usually put in with the + terminal nearest the bulb.) b The batteries are connected in series.
5
a The bulbs in circuit B will glow only half as brightly as the bulb in circuit A. This is because the electric current has to flow through two bulbs instead of one. b The bulb in circuit C will glow as brightly as the bulb in circuit A. This is because the three bulbs are in parallel, and each bulb glows as brightly as if it were the only bulb in the circuit.
AnswerstoReviews • Buoyancy is the upwards force when objects are placed in water. See page 263. • The biological factors in an ecosystem are all the living things that interact with an organism—its food, predators, competitors and disease organisms. See page 254. • An adaptation is a characteristic which enables an organism to survive in its habitat. See page 255.
c You would need to arrange the two bulbs in parallel. Alternatively you could add a second battery to give the current more ‘push’.
6
C (Current flows only in the left-hand part of the circuit—through bulbs A and B, but not through bulb C.)
2
C and D—Functional adaptations are those that refer to the functioning or working of an organism’s body.
7
As your shoes rub on the nylon carpet, static electricity builds up on your body. When you touch something which conducts electricity (eg a metal door knob), an electric current flows across your skin and you feel a slight electric shock.
3
B and D—All the others involve organisms.
4
B
5
B, C and E—see pages 266 and 268.
6
a
The battery, bulb and switch need to be in parallel, as shown. When the switch is open (off), current flows in the bottom half of the circuit, lighting the bulb. When you close the switch, virtually all the current flows through the top half of the circuit. This is because the switch has a much lower resistance than the bulb, and the current follows the path of least resistance. Hence the light goes off when the switch is closed.
Chapter 11 Living systems 1 • The leaves of plants have tiny openings called stomates on their surfaces which allow gases to enter and leave the leaf. See page 266.
20 18 16 14 12 10 8 6 4 2 Blue
Green Yellow
Red
b The yellow and red disks were similar in colour to the surroundings, since fewer of them were found than blue and green. The surroundings might have been a yellow-red coloured sand or soil. c The four different coloured disks represent the variations in a population. On this particular surface, the yellow and red disks have a better chance of survival. Over time the ‘predators’ will reduce the blue and green disks and the population will consist mainly of red and yellow disks.
Lab review The equipment needed is almost the same for both circuits: • 1.5 volt battery and holder • 3 bulbs and holders • switch • connecting wires (6 for the left-hand one, 7 for the right)
Disksfoundondifferentsurfaces Number found
8
7
As its name suggests, the frog stores water in its body and loses very little. It would also burrow into the soil to avoid the heat of the day and the cold of the night. The frog would probably lay eggs in pools after rain, the eggs would hatch and the tadpoles would mature quickly before the water dried up. (Your answer may be different from this. If you are in doubt ask your teacher.)
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Buoyancy is why you seem to float in water. The water seems to push up on your body. You could suspend a rock from a spring balance and slowly lower it into a bucket of water. The reading on the balance will decrease, showing the rock doesn’t weigh as much in water.
9
a Aquatic animals have the buoyancy effect of water to support their weight in water, whereas land animals need strong skeletons to support their weight on land. b Oil floats on water so a spill will cover the surface of the water, stopping oxygen from dissolving in it. Oil is also poisonous to living things. c Natural selection is called ‘survival of the fittest’ because only those organisms that have adaptations suited to their environment survive. They are said to be the ‘fittest’ and they produce offspring with the same adaptations. d To reduce water loss, land animals have a tough waterproof skin or covering, and organs such as lungs with moist surfaces inside their bodies.
10 a Between 2 am and 10 am, since the amount of dissolved oxygen decreased during this time. b The highest concentration was 5.6 mg/L. The lowest concentration was 2.1 mg/L. c It became dark after 6 pm, so photosynthesis in the water plants stopped, thus reducing the dissolved oxygen. d 6 Dissolved oxygen
2 84
with aerator
5 4 3 2
without aerator
1 12 noon
6 pm 12 midnight Time
6 am
12 noon
Glossary The words in this list occur in dark type throughout the book. The number after each entry gives the page where you will find more information. For some words the pronunciation is given. The syllable in capitals should be stressed; for example, bicycle (BY-sick-el).
adaptations (ADD-ap-TAY-shuns): the characteristics of an organism which enable it to survive in its habitat. 255 alveoli (AL-vee-OH-lee): minute air sacs in the lungs which allow the gases to pass into and out of the blood capillaries. 219 arteries: thick-walled blood vessels that carry blood away from the heart. 217 asteroids: tiny chunks of metallic rock found orbiting the sun in a wide belt between Mars and Jupiter. 157 atmosphere: the layer of gas surrounding a planet. 157 atoms: particles too small to see, that make up all matter. 180 behavioural adaptation: the way an organism behaves in order to survive in its environment. 256 buoyancy: the upwards force on objects when they are placed in water. 263 capillaries: microscopic blood vessels with very thin walls that allow substances in the blood to pass to and from the body cells. 217 carbohydrates: a food type that supplies energy for the body; carbohydrates include sugars and starches. 203 cell division: the process in which a cell divides to make two new cells. 89 cell membrane: the thin covering surrounding a cell which controls the movement of substances into and out of the cell. 82 cells: the building blocks of all living things. Cells are usually microscopic. 79 cellular respiration: the process that occurs in cells in
285
which food is broken down in chemical reactions to release energy. 201 cell wall: the tough outside layer of a plant cell. 82 change of state: a change from one state of matter to another, eg from solid to liquid. 61 chemical bonds: attractive forces between atoms. 62 chemical energy: the form of energy stored in chemicals, eg foods and fuels. 109 chemical formula: a group of symbols and numbers indicating the elements in a compound and the ratio of these elements; for example H2O. 187 chloroplasts: small structures containing chlorophyll, found in the cytoplasm of plants and algae. 82 chromatography (CROW-ma-TOG-ra-fee): a technique used to separate small amounts of soluble substances in a mixture; for example, the coloured substances in ink can be separated using filter paper. 19 circuit diagram: a standard way of drawing an electric circuit, using symbols. 242 colloid (COL-oid): a mixture which has properties in between a solution and a suspension; the particles in the colloid may be tiny bits of solid, liquid droplets or gas bubbles. 8 comets: small bodies that orbit the sun in elongated elliptical orbits; they usually have long glowing tails. 165 compound: a pure substance that contains atoms of two or more elements combined in a fixed ratio; it can be broken down into its elements by chemical reactions. 187 concentrated (CON-cen-TRAY-ted): describes a solution containing a large amount of solute, compared with other solutions. 7 concentration: the amount of solute dissolved in a certain volume of solution. 9 condense: to change from a vapour into a liquid; condensation is the opposite of evaporation. 14 conduction: the transfer of heat through a solid, or the passing of an electric current through a solid or liquid. 134 conductor: a substance that allows heat or electricity to move through it easily. 134, 236 conservation of energy: this law says that energy cannot be made or destroyed—it can only be changed from one form to another. 117
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ScienceWorld8forNSW control the variables: to keep all the variables the same, except the one you are purposely changing in an experiment. 32 convection: the transfer of heat in a liquid (or gas) by the movement of particles, when less dense liquid rises and more dense liquid flows in to take its place. 136 cytoplasm (SIGH-toe-plaz-um): jelly-like substance that fills most of a cell. 82 data: information gathered by observation, experiment or library research; it may be qualitative or quantitative. 28 decanting: gently pouring off a liquid, leaving the solid in the container. 11 density: how much matter is packed into a measured volume; it is measured in grams per cubic centimetre. 55 dependent variable: a variable that changes in response to changes in the independent variable; values for this variable are graphed on the vertical axis. 35 diffusion: the gradual mixing of substances caused by the random movement of particles. 70 digestion: the physical and chemical breakdown of food into soluble materials. 209 dilute (dye-LOOT): describes a solution containing a small amount of solute, compared with other solutions. 7 dissolves: when two or more substances mix completely, so that they appear as one; eg sugar dissolves in water. 5 distillation: a separation technique that involves evaporating a liquid, then condensing the vapour in a separate container. 14 ecosystem: a system of relationships among organisms and the way they interact with the non-living things in their habitat. 254 elastic potential energy: the energy stored in compressed or stretched springs or other elastic devices. 108 electrical resistance: resistance to the flow of electric current through a conductor; good conductors have low resistance. 239 electric charge: results when an object gains electrons (negative charge) or loses electrons (positive charge). 228 electric circuit: a continuous path around which an electric current can flow. 236
electric current: the flow of electricity around an electric circuit. 235 electrons: tiny particles carrying a negative charge; they surround the nucleus of an atom. 231 element: a pure substance made up of only one type of atom; it cannot be broken down into simpler substances by chemical reactions. 182 emulsion (ee-MULL-shun): a colloid with tiny droplets of one liquid spread through a second liquid; milk is an emulsion. 8 energy: the ability to do work; there are many different forms of energy. 104 energy chain: a series of steps in which energy changes form, eg chemical energy ➞ heat energy ➞ kinetic energy. 116 enzymes (EN-zimes): substances made by special cells in the body to speed up chemical reactions. 209 evaporate (e-VAP-or-ATE): to change state from liquid to gas; evaporation can be used to separate a solute from a solvent. 14 excretion (ex-KREE-shun): the process of removing wastes from the body by the liver and kidneys. 220 experiment: a well thought out scientific test, usually designed to test a hypothesis or prediction. 28 faeces (FEE-seas): solid waste produced by the body and removed through the anus. 220 fair test: an experiment where you change something, measure something and keep everything else the same. 32 fats: a food type that supplies a large amount of energy and which can be stored in the body. 203 fertilisation (FUR-til-eyes-AY-shun): the process in which the nuclei of a sperm and ovum join to make a new living thing. 89 filtering (filtration): a way of separating a solid from a liquid (or gas) using a filter. 11 fossil fuels: fuels obtained from material that was once living; for example, oil, coal and natural gas. 118 functional adaptation: the way an organism’s body works in order to survive in its environment. 256 galaxy: an enormous number of stars grouped together and having one of three basic shapes—spiral, elliptical or irregular. 169 generalisation: a statement or conclusion, based on many observations, that holds true in most cases: for example, most plants are green. 29
Glossary gravitational potential energy: the energy stored in a raised object. 107 heat: a type of energy that can raise the temperature of things; it is measured in joules. 128 hypothesis (high-POTH-e-sis): a generalisation that explains a set of observations or gives a possible answer to a question; it can be tested by experimenting. 33 independent variable: a variable that is purposely changed in an experiment; values for this variable are graphed on the horizontal axis. 35 insulator: a substance that does not allow heat or electricity to move through it easily. 134, 236 joule (J): the unit for measuring work and energy. 104 kidneys: organs that filter and remove waste materials from the blood. 219 kilojoule (kJ): a unit in which energy is measured; 1 kilojoule = 1000 joules. 104 kinetic (kin-ET-ic) energy: the energy that a moving object has. 107 light-year: an astronomical unit that is used to measure the huge distances between stars; it is the distance light travels in one year. 169 liver: a large dark red organ that stores and distributes digested food materials. 216 lungs: large organs which absorb oxygen from the air and remove carbon dioxide from the body. 219 matter: a term used to include anything that has mass and occupies space (has volume). 53 menopause: the period in the life of a woman when the reproductive cycle stops operating. 91 meteorites: pieces of rock or metal from space that crash into planets or moons. 165 mixture: two or more pure substances mixed together but not chemically combined. 4 model: a way of representing something that cannot be observed directly because it is too small, too large or too complicated; for example, a model of a molecule. 62 molecule: a tiny particle containing two or more atoms in a fixed ratio and joined by chemical bonds. 180 natural selection: the process in which organisms that have favourable characteristics survive in a particular habitat, and reproduce. 257 nebula (NEB-you-la): a huge expanding cloud made up of dust and gases formed after a massive star explodes (supernova). 172
non-renewable energy: energy resources that are not replaced as they are used; for example, coal and oil. 120 nuclear energy: the energy stored inside the nuclei of atoms. 109 nucleus (atom): the positively charged core of an atom; it contains protons and neutrons. 231 nucleus (cell): the small rounded object that controls the activities of a living cell. 82 orbit: the path followed by an object as it revolves around another object, eg the orbit of the Earth as it revolves around the Sun. 153 organ: a collection of tissues that has a particular function in the body, eg heart, kidney. 86 organelles (OR-gan-els): small structures found in the cytoplasm of cells, eg chloroplasts. 82 ovary (OH-var-ee): the female reproductive organ that makes ova (eggs). 89 ovum (plural ova): the female sex cell, also called an egg. 89 parallel connection: a method of connecting electrical components (eg batteries and bulbs), so that the current divides and part passes through each component. 243 particle theory: the theory that all matter is made up of particles (atoms or molecules) that are too small to see and that are always moving. 62 plasma (blood): the pale yellow liquid part of blood, which contains mainly water, dissolved food, minerals and waste products from cells. 216 plasma (matter): fourth state of matter that exists at very high temperatures; it consists of charged particles even further apart than the particles in a gas. 69 potential energy: stored energy, available to be converted to other forms of energy. 107 properties: the characteristics or features something has. 4 proteins: a food type that provides the materials for the growth and repair of cells. 203 puberty: the period of time (usually between the ages of 10 and 15) during which sexual development occurs. 91 pure substance: matter containing only one substance (either an element or a compound); it has a fixed composition and fixed properties. 4 radiation: the transfer of heat from a hot object through space (or air) to a cold object. 137
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ScienceWorld8forNSW red blood cells: small red-coloured, doughnut-shaped cells in the blood that carry oxygen to other cells in the body. 216 reliable: results are reliable if they are the same when the experiment is repeated many times. 140 renewable energy: energy resources that can be replaced as they are used; for example, solar energy. 120 saturated: describes a solution that contains the maximum amount of solute that will dissolve at that temperature. 7 series connection: a method of connecting electrical components (eg batteries and bulbs), so that the current passes through one then the other. 242 sex cell: a special cell for reproduction. The male sex cell is a sperm and the female is an ovum (egg). 89 solubility: the amount of solute that will dissolve in a measured volume of solvent at a particular temperature. 7 solute: a substance that dissolves in a solvent to form a solution. 5 solution: a liquid (or solid) containing one or more solutes dissolved in a solvent; for example, salt water. 5 solvent: a substance that can dissolve other substances. 5 specific heat capacity: the amount of heat needed to raise the temperature of one gram of a substance by one degree Celsius. 131 sperm cell: the male sex cell. 89 states of matter: there are three states of matter—solid, liquid and gas; a substance can exist in any of these three states. 53 stem cells: unspecialised cells that can develop into any one of many different types of cells in the body. 101 structural adaptation: a special body part that helps an organism survive in its environment. 256
supernova: an explosion of a massive star which scatters most of its matter into space. 171 suspension: a mixture in which tiny bits of solid (or liquid) are evenly spread through a liquid (or gas), but are not dissolved; if allowed to stand, the suspended matter slowly settles out. 5 symbols: signs, markings or letters that represent something else; for example, the symbol for copper is Cu. 182 temperature: how hot or cold something is; it is measured in degrees Celsius. 128 testes (TES-teez): the two male reproductive organs that make sperm. 89 theory: what a hypothesis becomes after it has been supported again and again by experimental results. 62 tissue: a group of similar cells organised to do a particular job in the body, eg muscle tissue. 86 trachea (track-EE-a): a cartilage-banded pipe that takes air from the throat to the lungs. 219 universe: space and everything in it. 152 vacuole (VAK-you-ole): a liquid-filled space found mainly in plant cells which is used to store water and dissolved food. 82 variable: any changeable factor that may influence the results of an experiment. 32 veins: tubes in plants that carry water, minerals and food materials. 215 : blood vessels that carry blood towards the heart. 217 vitamins and minerals: substances needed in very small amounts by your body to keep it healthy. 203 voltage: the electrical ‘push’ causing current to flow in an electric circuit. 236 work: the result of a force moving an object a certain distance; energy is needed to do work. 104
Index absolute zero 129 adaptations 255 in leaves 268 in rocky shore organisms 263 to fire 258 toothpick investigation 256–257 air pressure 72 alveoli 219 amino acids 210 ammeter (using) 237, 245 amylases 210 Andromeda galaxy 169 Archimedes 56 Aristotle 152 arteries 217 asexual reproduction 87, 94 asteroids 157, 164 atmospheres (planets) 157 atomic theory 76, 181 atoms 62, 76, 180–181, 231 inside them 198 bacteria 85 baking bread 83 balanced diet 206 ball and ring apparatus 71 banknotes 58 batteries 236 connecting them 243–244, 246 behavioural adaptations 256 Benedict’s solution 204–205 biological factors 254–255 blood 216 blood system 217–218 boiling 61, 65–66 bonds (chemical) 62 Bornemissza, George 44 brainstorming 103 bumping (in test tubes) 15 Bunsen burner (safe use) 15 buoyancy 263, 265 bushfires 258, 271 caloric theory 128, 149 capillaries 217 in fish 218 carbohydrates 203, 207
289
cell division 89 cell membrane 82 cell nucleus 82 cell wall 82 cells 79–82 drawing them 83 observing them 84–8 stem cells 101 cellular respiration 201, 212 centrifuge 11 changes of state 61, 64–65 chemical bonds 62 chemical energy 109, 201 chemical equations 194 chemical formulas 187 chemical reactions 191–194 chemical spills 272 chloroplasts 82, 84 chromatography 19 circuit diagrams 242–243 coal (how formed) 119 colloids 8 Comet Tempel 1 166 comets 165–166 compounds 187, 191–192 concentration 7, 9 conclusion 29 condensation 14, 61, 65 conducting plastics 251 conducting vessels (plants) 215–216 conduction (heat) 134 conductors electrical 237–238 heat 134–135 conservation of energy (law of) 117 control (experimental) 140, 205–206 controlling variables 32 convection 136 Copernicus, Nicholas 152–153 corner discussion 101 Crab Nebula 171 crystallisation 15 CSIRO 44–47 Curie, Marie 184 cytoplasm 82
Dalton, John 76, 181, 198 data 28 datalogger use 66, 117, 138, 145 decanting 11, 13 Democritus 62, 76 density 55 measuring it 56–57 dependent variable 35 desert ecosystem 268 diamond 185 diffusion 70 digestion 209 digestive system (gut) 209 discussion 29 disposable nappies 58 dissolved gases (in water) 262 dissolving 5, 71 dissolving time (effect of temperature) 37 distillation 14, 16 DNA 189 doing a project 43 drawing graphs 35–36, 39, 66 droughts and floods 272 dung beetles 44 Earth (place in universe) 152 ecosystems 254 coral reef 254 desert 268 problems in 271–272 River Red Gum 259 efficiency 117 eggs hens 90–91 other animals 93 elastic potential energy 108 electric charges 228–232 electric circuits 235–236, 242–245 series and parallel 242–245 electric current 235–236 electrical energy 109 electrical resistance 239 electrical symbols 242 electrons 198, 231, 236, 238 elements 182–183 in human body 188 library research 200 emulsions 8 energy 103–104 forms of 107 from food 105, 201 in everyday activities 106, 202 measuring it 104
2 90
ScienceWorld8forNSW renewable and non-renewable 120 wasted 116 energy arrows 116, 120 energy chains 116 energy changes 110–112 energy-efficient house 146 environments 253–254 enzymes 209–210, 212 in detergents 210 experiment 211 epidermis 266 euglena 79 evaporation 14–15, 61, 65 excretion 220 expansion and contraction 71–72 experimental control 140, 205–206 experiments 28–30, 32–34, 50 faeces 220 fair tests 32 fats 203, 207 testing 205 fermentation 83 fertilisation 89 internal/external 93 filter paper (folding) 13, 34 filtering 11–13, 18, 34 filters 12 firewalking 143–144 fireworks 186 flame tests 185 flocculation 18 flowers (parts of) 95 fluted filter paper 34 food technologist 36 food types 203 food processed 206 testing 204–205 why we need it 201 forensic science 25 formulas (chemical) 187 fossil fuels 119 Franklin, Benjamin 230 frog research 45 froth flotation 17 Fry, Art 44 functional adaptations 256 galaxies 169–170 Galileo 153 gas chromatography 19, 25 Gaspra (asteroid) 164 generalisation 28–29, 33
glucose test 205 GM foods 225 gold panning 17 graphing 35–36, 39 gravitational potential energy 107 gravity separation 17 heat and temperature 128, 130–131 heat energy 109, 128 heat experiments 138, 140, 145–146 heat transfer 117–118, 129, 134 controlling it 139 heating a test tube 204 Herschel, William 154 Horsehead Nebula 172 hydro-electric power station 122–124 hydrogen test 193 hypothesis testing 33, 40–41, 149 independent variable 35 inferences from observations 152 inferring 28, 152 infra-red radiation 137 ink (separating colours) 19 inner planets 157 insulators electrical 237–239 heat 134–135, 140 invention (electrical) 248 investigations 29 iron sulfide (making) 193–194 Joules, James 149 joules 104 Jupiter 159 moons of 153, 168 kidneys 219–220 kilojoules 104, 202 kinetic energy 107 Kuiper Belt 160–161 lambs (twin) 45 large intestine 209 Lavoisier, Antoine 149 leaf cells (observing) 86–87 light (in water) 262 light bulb 235–236 light energy 109 lightning 232 light-year 169 lipsases 210 lipstick 4 liver 209, 216 living and non-living 188–189
living in water 262–263 living on land 266 Lowell, Percival 154 lungs 219–220, 266 MacNamara, Jean 46 magnetic separation 17 magnifying power 78, 81 Mars 158 colonising 177 materials 57–58 matter 53 measurements (repeating them) 41 medicines from frogs 45 melting 61, 64, 66 Mercury 157 meteorites 165 meteorologist 65 microscope (using) 81–81, 84–85 microwave oven 137 milk 8, 36 Milky Way galaxy 169–170 mixtures 4 models 62–63 molecular models 188 molecules 180 motormouse (making) 108 mousetrap 227 mousetrap racer 115 Murray River 259, 275 myxomatosis 46 natural selection 257–258 nebulas 172 Neptune (discovery) 154 nitrates 207 nuclear energy 109 nuclear power station inquiry 125 nucleus (atom) 198, 231 observing 28 oesophagus 209 oil (how formed) 119 operating theatres 233 orbits of planets 153 organelles 82 organs 86 outer planets 159 ova (egg cells) 89–90 ovaries 91 oxygen in water 262, 264–265 oxygen molecule 180 packing beads 58 paper bridges 30, 32
Index paper chromatography 19–20 parental care 93–94 particle theory 62–65, 70–73 and heat 129 pendulum experiment 32 peppered moths 261 photocopiers 233 photosynthesis 118, 207 physical factors 254–256, 262–266 planets 152, 157, 163–164 gravity on 163 plant cuttings 97 plasma (blood) 11, 216 plasma (matter) 69 plastics (conducting) 251 Pluto (discovery) 154, 160 podcasts (producing) 225 post-it notes 44 potential energy 107 powder coating 233 predicting 28, 33 projects (doing one) 43 properties 4, 58 proteases 210 proteins 203, 207 testing 205 Ptolemy 152 puberty 91 pulse (measuring) 218 pure substances 4, 191 pyrotechnics 186 qualitative and quantitative 28 rabbit plagues 46 radiation 137 absorbing & emitting 138–139 radium 184 red giant 171 reliable results 140 reports (writing them) 29 reproduction 89, 93–94 asexual 89, 94 in chickens 91 in dogs 91 in flowering plants 94 in humans 89–90 vegetative 97 resistance (electrical) 239 respiration 201 respiratory system 219 River Red Gum ecosystem 259, 275 roller-coaster 107 Rumford, Count 128, 149
Rutherford, Ernest 198 saturated solution 7 Saturn 159 science at work 28 science contests 43 scientists at work 44–46 sea breeze 136 seahorses 94 seed dispersal 96 separating funnel 22 separating solids 3, 17 series and parallel 242–245 sex cells 89 small intestine 209, 212 model for 213 soap film 73 sodium chloride (salt) 187 soil nutrients 207 solar distillation 14 solar energy 120 solar system 154, 157 solids, liquids and gases 52–54, 61–63 sols (gels) 8 solubility 7 soluble and insoluble 5–7 solutions 5 separating them 14 solvents 5 solving problems 40–42 sound energy 109 space (library research) 162 space missions 161 space travel 173 sparklers 128 specific heat capacity 131 speed of light 169 sperm cells 89–90 stars (life cycle) 171 states of matter 53 static electricity 228–232 stem cell research 101 stomach 87, 209 stomates 266–268 stopping distance (investigation) 41 structural adaptations 256 sublimation 61 Sun’s shadow 153 Sunsorb 58 superconductors 239 supernovas 171–172 Super-Sci 179
suspensions 5 separating them 11 switches (electrical) 235, 241 telescope (invention) 153–154 temperature 128 terraforming Mars 177 thermocouple 112 thermos 144 Thomson, JJ 198 thunderstorms 231–232 timelines 155 tissues 86–87 trachea 219 transport in humans 216–217 in plants 215–216 Turner, Dr Helen Newton 45 Tyler, Dr Michael 45 universe 152, 169–172 Uranus 159 urine 219–220 vacuoles 82 Van de Graaff generator 228 variables 32, 35, 50 variation (biological) 257 vegetative reproduction 97 veins in animals 217 in plants 215 Venus 158 villi 212 vitamins and minerals 203 voltage 236 volume by displacement 56–57 Voyager 161 wasted energy 116 wastes (from body) 219 water (decomposing it) 193–194 water formula 187 water loss 266 in plants 267 water molecule 180, 194 water purification 18 WaterSorb 58 waterwheel (making) 115 wet-mount slide (making) 81 wetsuit 135 white dwarf 171 windmill (making) 115 yeast 83
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Macmillan Education Student CDs now come with great new interactive functionality, which makes teaching and learning even easier in a digital world! All you need is Abode Reader to access this great functionality.
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