KEEPING HEALTHY

COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS KEEPING HEALTHY A BALANCED DIET 1 Food Potatoes Chocolate Fish Oranges Milk 2 Energy Growth Repair When most people use the word ‘diet’ they mean they are eating less to try to lose weight. In the UK, 20% of the people are ‘on a diet’ almost all the time! When scientists use the word diet, they mean all of the food you eat every day - whether you are trying to lose weight or not. Doctors recommend that we should all have a balanced diet. This means we eat a selection of foods in the correct amounts to keep us healthy. To keep material flowing through the gut. Food types Carbohydrates Fats Proteins Vitamins Minerals 3 4 IS MY DIET OK? 1 2 Eat more of these Fruit Starchy vegetables Fish Eat less of these Salt Fats Sweets a) Any sensible answers acceptable. b) Vitamins, fibre, minerals. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 3 Diet problem High fat and sugar diet High salt diet Damage in body Can lead to obesity Can cause an increase in blood pressure leading to heart attacks and strokes Not enough vitamins to keep the body healthy Not enough variety to give a balanced diet A diet with no fruit or vegetables Only eating one type of food, say chips! 4 a) Eating breakfast helps to stop you feeling hungry during the morning and so eating lots of snack foods instead (which are often high in calories). b) Salt raises blood pressure which can lead to strokes and heart and kidney disease. EATING FOOD 1 a) 12 hours b) The fibre adds bulk to the food, so giving the muscles something to push against as it squeezes the food along the gut. From mouth to anus: Mouth Gullet Stomach Small intestine Large intestine Anus Digestion is the breakdown of food into simpler chemicals which can be absorbed into the body. Food must be broken down before it can enter the body. Breaking down foods is called digestion. It starts in the mouth where teeth break large lumps into smaller lumps. These smaller particles are passed through the gut where enzymes act on them. These enzymes split large molecules up into smaller molecules. The smaller molecules then pass through the gut wall into the body. a) Breakdown of protein begins in the stomach. Acid and enzymes there split large protein molecules into simpler chemicals. The half-digested food passes along the gut where more enzymes break it down 2 3 4 5 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS further. It is eventually absorbed into the blood lower down in the gut. b) Large food molecules are too big to pass across the gut wall into the body. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS DO I HAVE ENOUGH ENERGY? 1 Growth Repair Movement Keeping the body alive joule 2 3 Least to most energy needed: A pensioner in an home who cannot get around much A male office worker A teenage girl who plays a lot of sport A labourer building the Olympic village in London A professional athlete training for a marathon 4 Respiration happens in every cell in the body. Respiration reacts glucose and oxygen to give carbon dioxide and water and release energy. This energy keeps us alive. Without respiration cells die very quickly. Oxygen is taken out of the air by the lungs and passed around the body in the blood. The carbon dioxide made by respiration must be removed so it is passes to the lungs in the blood and breathed out. a) People tend to do less physical exercise as they get older and are not growing taller. However they tend to eat the same amount of food so have more energy than they need and get fatter. b) If you keep exercising, you tend to keep healthy and this slows the aging process. If you stop exercising, your muscles and bones start to weaken, which makes the body look and feel older (so you find exercise more difficult). 5 A BREATH OF FRESH AIR 1 2 3 a) Use in respiration Gas exchange is the taking in of oxygen and the passing out of carbon dioxide by the lungs or gills. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 4 The lungs produce a layer of liquid called mucus that covers all the inner surfaces. Dust, smoke and microbes are trapped in this liquid. Tiny hairs called cilia push the liquid, with the trapped rubbish, over the surface of the cells towards the throat. It enters the throat and is swallowed. In the stomach any dangerous organisms are destroyed. Smoking stops the cilia working properly. This is why smokers often have a bad cough – they are clearing the dirty mucus from their lungs! 5 a) All animals need oxygen to break down sugar to release energy to stay alive. b) Oxygen and carbon dioxide swap over at the surface of the alveoli in the lungs. A HEALTHY HEART 1 a) An artery carries blood away from the heart. TRUE b) A vein carries blood towards the heart. TRUE c) Veins have muscles to push the blood along them. TRUE d) A vein has a pulse. FALSE e) You only bleed if you cut an artery – blood cannot come out of veins. FALSE 2 Match the substance transported by the blood to its destination. Substance Oxygen Carbon dioxide Glucose Wastes 3 Going to... All cells Lungs All cells Kidneys Athletes depend on their blood to get oxygen to their muscles at a very high rate when they are competing. Their heart rate will rise very high and their breathing rate can be five or six times their resting rate! One way some athletes train for this is to work at very high altitude for a few months before the event. Their bodies respond to the low levels of oxygen at high altitude by producing more red blood cells and increasing the network of vessels that supply blood to the muscles. When they come back to sea level to compete they have an extra advantage. a) The muscles of the heart are working every second of the day, so need lots of oxygen 4 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS and food energy and produce a lot of carbon dioxide as waste. Therefore, they need a large supply of blood to both supply what they need and then take away the wastes. b) Valves in the heart only allow the blood to flow one way. MEASURING YOUR PULSE 1 2 3 Exercise, smoking, fear. Accept any three from: wrist, neck, groin, ankle. a) A line graph (similar to that shown below) would be most appropriate though a bar chart is also acceptable. 95 90 Pulse rate (beats per minute) 85 80 75 70 65 60 0 5 10 15 20 25 30 Time since smoking (minutes) b) c) in be 4 25 or 30 minutes acceptable. The regular smoker would probably show a smaller increase pulse rate than the non-smoker because his/her body would used to the cigarettes. a) By the time the blood has reached a vein, the pumping action of the heart has been smoothed out into a continuous flow. b) Fitter people tend to have lower pulse rates than unfit people. HOW DO YOU KNOW IF YOU ARE FIT? 1 To build muscles in the legs. To improve his/her breathing and heart. To make sure their running technique is good. 2 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS Show someone is fit Low levels of exercise hardly change the pulse rate. Lungs are very large. Heart rate at rest is low. Show someone is not very fit Low levels of exercise produce a big change in pulse rate. The body has a high fat level. Pulse rates take a long time to return to normal after exercise. 3 Very fit athletes show small changes in their pulse rate during low levels of exercise. After stopping exercise their pulse rates returns to normal very quickly. Unfit people find they need longer to recover after exercise and might strain muscles during an event. This is why you should always get a health check before starting a training program. If you do not and you try to do too much too quickly you could damage your joints and muscles. In the worst instances you might even suffer a heart attack caused by over-straining an unfit heart. a) A fit person is healthy, takes a lot of exercise and may also be a good athlete. A healthy person is well and free of disease, but may not take as much exercise as a very fit person. b) Better diet Stop smoking and drinking to excess Train regularly 4 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS STUDYING DISEASE HISTORY OF DISEASE 1 Table 1: Deaths from cholera in London 1851 District London (all districts ) West North Central East South b) South c) An area total than 100 000 of deaths per 2 Population in 1851 2 362 236 Deaths from cholera in 14 weeks ending Oct 14 10 367 Deaths per 10 000 residents 44 376 427 490 396 393 256 485 522 616 635 1 992 735 612 1 461 5 567 53 15 16 30 90 with a large population may have more deaths in an area with a low population but fewer deaths per the population. Converting all the figures to 100 000 makes it a fair comparison. a) A bar chart is most appropriate here (example below). 2500 2000 Deaths from cholera 1500 1000 500 0 Southwark and Vauxhall Lambeth Kent Company Water company Pumps Not ascertained COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS b) The water in the centre of London was polluted with sewage which carried the typhoid bacteria. Water from outside London was cleaner because it did not receive sewage from the many people living in the city. THE INFECTION CYCLE 1 Disease AIDS Food poisoning Flu Malaria Typhoid How you catch it Unprotected sex with an infected person or exchange of blood Eating food that has gone off Breathing in microbes in the air From an insect bite Drinking contaminated water 2 a) b) An …………. is a disease caused by a microorganism entering and multiplying within the body. 3 a) The incubation period is the time between someone being infected with a microorganism and the first signs of the disease. b) If they are infected they can pass on the microorganism even if their body is preventing them from showing any signs of the disease. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS PREVENTING DISEASE 1 TRUE d) An open wound is an easy way for microbes to get into the body. TRUE e) Tanned skin is better protection against germs than pale skin. FALSE 2 Start to finish: Cut finger with dirty knife Bacteria enter cut Scab forms to seal off cut Bacteria multiply in body Antibodies produced to destroy bacteria Skin repairs itself and scab falls off a) Superstrip is waterproof but Silverstick is not. Silverstick has antiseptic but Superstrip does not. b) A bar chart is most appropriate here (example below). 160 140 a) Skin acts as a barrier to microbes entering the body. TRUE b) Washing hands makes infection more likely. FALSE c) Our tears contain a chemical that can destroy some germs. 3 Bacterial growth (per square cm) 120 100 80 60 40 20 0 Superstrip Wonderplaster Sticking plaster Silverstick c) Silverstick is not waterproof. It may be that the wound dried out more quickly than with the other plasters and this prevented the growth of microorganisms. 4 a) A scab helps to stop blood leaking out of the body and stops microorganisms getting in. b) Antibodies act against invading cells but antitoxins act against the toxins these invaders produce. SEXUALLY TRANSMITTED DISEASES COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 1 2 Disease Syphilis Gonorrhea Thrush Genital herpes AIDS 3 How you catch it Bacteria Bacteria Fungus Virus Virus Smallpox Chlamydia is an increasing problem in the UK. It is caused by a bacterium and is spread by sexual activity. Unfortunately the infection often produces no symptoms so the sufferer does not seek treatment. The long term effects can be devastating though. Chlamydia infection can lead to infertility in women. Using a condom can help to reduce the chance of catching chlamydia. a) HIV is a virus. AIDS is the disease it produces after it has lived in the body for some time. b) People can become infected with HIV by unprotected sex with an infected person or by transfer of blood from an infected person. BIOLOGICAL WARFARE 4 1 2 The smell of dead bodes Changes in the phases of the Moon a) To be ‘in quarantine’ means that you are kept away from other people for a time until it has been proved that you are not carrying any infections. b) Any sensible answers acceptable, e.g. import of animals into the country following an event where someone might have become infected with a disease. Anthrax is a serious disease caused by a virus. It kills humans very quickly and can be spread easily by tiny spores that are breathed in with the air. Military planners have tested ways to produce large stocks of the anthrax spores and spray these into the air over opposing armies or towns. One problem with this technique is that even after the enemy has been killed the invading army cannot enter the area because of the anthrax contamination. 3 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 4 a) An outbreak of a dangerous disease might be controlled by keeping people in quarantine, treating them with drugs, vaccinating uninfected people if possible and killing any animals or microbes that could spread the disease. b) Salmonella can be added easily to cooked food which is kept warm and never reheated enough to kill the bacteria. People who eat the food would then take in the salmonella. VACCINATION 1 Edmund Jenner 2 a) A line graph is best here although a bar chart is also acceptable (example below). 350000 300000 250000 Smallpox deaths 200000 150000 100000 50000 0 1950 1955 1960 1965 Year 1970 1975 1980 India World b) 1975 c) Smallpox vaccines prevent the virus from growing in the human body. If everyone can be vaccinated the virus has nowhere to live and multiply so it dies out. a) He tested it on a small boy by scratching the skin and adding some cowpox pus. The boy did not then catch smallpox. b) To inoculate means to put a weakened type of a virus into someone. WHAT ARE VACCINES? 1 a) 13 months b) Diphtheria, tetanus, whooping cough, polio, measles, mumps, rubella c) 12 3 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 2 Correct order: Vaccine created in laboratory - this is a specially weakened strain of the virus. Vaccine injected into person. Person’s immune system reacts to vaccine by destroying the invading virus and creating memory cells that can quickly react when the virus reappears. Live virus gets into body. Memory cells in the immune system quickly recognise the virus – the body reacts to produce antibodies. Antibodies destroy virus before it has a chance to establish itself. 3 a) A side effect is something that happens as well as the main, desired effect of a treatment. For example, the flu vaccine may cause a slight temperature and aching muscles for a few days after the injection. b) The general health of the child, whether the child has reacted badly to any vaccines in the past and how high the risk of contracting the disease is in the area where the child lives. HOW TO GET RID OF MICROBES 1 Use a disinfectant Wash down a lab bench before doing any microbiological work. Destroy old microbiological cultures. Clean the floor in an operating theatre. Use an antiseptic Wash an open cut. Gargle with a sore throat. Wipe the skin before giving a patient an injection. 2 a) The one with the largest clear area around it. b) Incubate means to give the bacteria time to grow. The plates were incubated to give the bacteria time to grow and see how the chemicals affected their growth. a) Washing your hands with an antiseptic gel is a good way to prevent infections being spread from ward to ward in a hospital because any microorganims picked up in one ward are killed before you go into the next one. b) Surgeons use special gowns that can be boiled to sterilise them between operations. Ordinary clothes might carry in microorganisms from the street that could get into the patient’s body. 3 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS ARE MICROBES USEFUL? 1 Made by microbes Cheese Yoghurt Bread Beer No microbes needed Ice cream Pancakes Chocolate Coffee 2 a) Correct sequence: Milk is heated to boiling to kill all microbes in it. Milk cooled to 45oC in a covered container. Special bacteria added to the cooled milk. Mixture of milk and bacteria left overnight in a warm place. Your yoghurt is ready! b) To kill any bacteria naturally present. c) To give the bacteria time to grow. d) To stop the bacteria from spoiling the yogurt. 3 As with most microbes, yeast grows more quickly in warmer conditions. Cooks know this and keep dough warm while it is rising. The rising is caused by yeast in the mixture producing carbon dioxide gas as it grows. The little bubbles of gas give the bread its light texture. During cooking the bread temperature rises so high that the yeast is killed. That is why bread does not continue to rise after it has been cooked! 4 a) Microbes do many useful things from making foods to breaking down wastes in the soil. b) The low temperature in the fridge keeps the yeast from working but does not kill it. TOPIC QUIZ – Keeping healthy 1 Any sensible suggestions acceptable. For example: Food type carbohydrates protein Foods pasta, potatoes, wheat, bread meat, fish, eggs, beans COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS Food type fats Foods butter, margarine, chocolate, nuts 2 Eat less salt, eat more green vegetables. 3 Can lead to high blood pressure and obesity, both of which put a strain on the heart. 4 5 6 7 8 9 10 Joules (calories acceptable) a) Oxygen b) Carbon dioxide In the neck. Your muscles need more oxygen so blood is pumped more quickly round the body to supply this. Neck, wrist. Their hearts tend to be larger and so need to pump less often to get enough blood to the body than unfit people. The chemicals in cigarette smoke stop the small hairs in the lungs (cilia) that normally clean mucus away, from working. The only way to clear out the lungs is then to cough it up.       11 Fresh fruit and vegetables are a good source of vitamins. TRUE If you take in more energy in your food than you use up you will get fat. TRUE Small hair-like cells in the lung push mucus and dust towards the throat so that they can be swallowed. TRUE The heart is made of muscle. TRUE Office workers need less food than manual labourers to stay healthy. TRUE Eating only beefburgers and drinking only fizzy drinks is an excellent, healthy diet. FALSE – beefburgers are high in fat and fizzy drinks are high in sugar, so this is neither a balanced nor a healthy diet. Arteries take blood towards the heart, veins take blood away from the heart. FALSE – arteries take blood away from the heart, veins take blood towards the heart. Cigarette smoking lowers your pulse rate. FALSE – cigarette smoking raises your pulse rate.   COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS  To have a balanced diet, you only really need to worry about the amount of protein you eat. FALSE – to have a balanced diet, you need to make sure you are eating the right amount of all the food groups. TOPIC QUIZ – Studying disease 1 2 Any sensible suggestions acceptable, e.g. invading microorganisms, bad diets, drugs, genetic causes, poisons. a) Typhoid b) Contaminated water c) He looked at the prevalence of the disease in areas with clean and dirty water. 3 4 5 6 The immune system Any sensible suggestions acceptable, e.g. being vaccinated, keeping healthy, avoiding high risk areas for infections. A disease spread by sexual contact a) A weakened form of an infecting agent. b) The body can ‘practise’ against the vaccine so that when the real disease-causing organism enters the body it can react more quickly and so prevent the organism from setting up an infection and causing disease. An antiseptic can be safely used on the human body but a disinfectant is too strong to use on living things. Yoghurt, cheese, bread To prevent transferring germs from patient to patient. AIDS       7 8 9 10 11 Flies lay eggs in rotting meat. These hatch to form maggots. The meat does not produce the maggots itself. TRUE An antibody is a chemical made by the body when a microbe enters it. TRUE Smallpox has been eradicated from the Earth using vaccination to protect people. TRUE Boiling kills all microbes. TRUE Milk is boiled to kill off bacteria already present and then cooled before adding the yoghurt culture. TRUE Microbes are not needed to produce beer. FALSE – microbes are needed to produce beer. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS     The best time to vaccinate someone against polio is when they have the disease. FALSE – you need to vaccinate someone before they have the disease. Taking certain herbs can protect you against infection with HIV. FALSE – the only way to protect yourself against HIV is to practise safe sex. Toxins are harmless chemicals produced in the body by microbes. FALSE – toxins are chemicals that are harmful to the body. Your zodiac sign controls what sorts of diseases you will suffer from in your life. FALSE – your genes and the environment together control what sorts of diseases you will suffer from. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS SEPARATING MIXTURES DISSOLVING ROCKS 1 a) A solvent is something that can dissolve something else. b) Dissolve in water sugar table salt Do not dissolve in water tea leaves carbon diamond steel paper 2 3 Salt dissolves in water but sand does not. When water seeps through limestone very small amounts of the rock dissolve. As the water drips from the roof of a cave a tiny amount of the water evaporates. This makes the dissolved mineral, called calcium carbonate, come out of solution. The calcium carbonate sticks to the roof of the cave. Over hundreds of years these specks grow to form a stalactite. When the drop of water hits the cave floor the same thing happens. But here the small particles of calcium carbonate grow into a stalagmite. a) As the water passes over the object, it deposits tiny amounts of calcium carbonate that comes out of solution. Over time this builds up to make a stone layer over the object. b) The amount of calcium carbonate deposited by each droplet of water is very very small. SWEET TOOTH 1 2 3 4 You can taste it. If you boil the water away the sugar is left behind. Hot water dissolves sugar more quickly than cold water. 120 g a) A line graph is most appropriate here (example below). 4 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 70 60 Mass of salt dissolved (g) 50 40 30 20 10 0 10 20 30 40 50 60 70 80 90 Temperature (°C) b) 33–35° C. c) 8 g d) The result for 70°C looks too high compared with the ones on either side. 5 a) Hot water is better at dissolving away dirt than cold water. b) The dyes in the fabric dissolve in hot water and so leave the garment in the washing water. PURE SALT 1 a) A solution forms when something dissolves in a liquid. b) A solute is a substance that can dissolve in something to make a solution. 2 Rock salt contains impurities which give it a colour. 3 a) Correct sequence: Trap seawater in large, flat dishes or puddles. Let the sunlight evaporate the water. The salt crystallises out of solution. Collect the salt from the dried-up pool or dish. b) The sun provides the energy needed to evaporate the water. 4 Salt is a common mineral – but is often mixed with other substances. If we want to use salt in cooking it has to be purified to remove bits of grit or any substances that might taste bad or be dangerous. The easiest way to do this is to dissolve the salt in the rock salt in water and collect the salty water. This can be heated and the pure salt is left behind when all the water has evaporated. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 5 a) The larger surface area of the pool allows much quicker rates of evaporation. b) Some of the impurities are bits of stone and grit which would not be good to eat and some impurities may be dangerous. SUPER SOLVENTS 1 Would wash away in the rain. 2 If a substance is insoluble it will not dissolve in a solvent. 3 a) b) c) d) e) Water can dissolve sugar. TRUE Water can dissolve grease and oil. FALSE Alcohol can dissolve ballpoint pen ink. TRUE Oil paints can dissolve in water. FALSE White spirit can dissolve paint on a dirty paintbrush. TRUE 4 Solvent Sugar Nail polish Dried gloss paint Oils Scent from flowers Road tar 5 Water √ x x x x x Alcohol √ x x √ √ x Acetone x √ √ √ √ x White spirit x √ √ √ √ √ a) Some solvents give off highly flammable vapours. b) If the solvent dissolves the dye in the fabric it could spoil the T-shirt even if it removes a small stain. DISTILLATION 1. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 2 Distillation is heating a liquid and condensing the vapours in a separate container. 3 a) The ground. b) In the plastic cup. c) Makes the plastic sheet dip down over the plastic cup so that the water droplets collect in the cup. d) The Sun. 4 a) To change the flavour and to increase the level of alcohol in the drink. b) Because ordinary tap water contains other dissolved substances which might interfere in the reactions you want to do. BETTER BOILING 1 Any sensible suggestions acceptable, e.g. to boil away the liquid, to make a reaction go more quickly. 2 a) Packing ice around a container helps vapours to condense inside it. TRUE b) Heating a liquid increases the rate of evaporation. TRUE c) Cooling a liquid has no effect on its evaporation. FALSE d) Water only evaporates at 100°C. FALSE 3 a) (1) The cold water flowing around the central tube helps to cool the vapours and so increase condensation. (2) The tightly-fitting stopper in the flask stops vapours escaping without going down the condensing pipe. (3) The down-turned delivery pipe helps to direct condensed liquids into the collecting flask. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS b) The pressure inside the system could build up and it may explode. c) It would fall. 4 a) The long coiled delivery tubes give the vapours more time to condense than a short, straight one would. b) Copper metal is easy to work and does not corrode with the hot liquids and vapours. DRINKING WATER 1 a) milligrams b) 0 (zero) c) The bottled waters have been sterilised so do not contain any harmful bacteria. 2 Desalination is the removal of salt from a solution – usually seawater. 3 4 a) Boiled and cooled water still contains dissolved substances but dis b) To increase the rate of evaporation. CHROMATOGRAPHY 1 2 b a) b) c) d) e) a mixture of dissolved substances. A D B and E D i) The solvent is moving upwards from the bottom. ii) The lowest marked area. a) Chromatography separates the colours in a sample of black ink by allowing them to diffuse up a paper. The smaller molecules move faster and so spread away from the slower dyes behind them. b) Solids cannot diffuse so the substances have to be in solution. 3 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS ATOMS, ELEMENTS AND COMPOUNDS CHEMICAL ALPHABET 1 2 Symbol H O C Cl Na 3 Element Hydrogen Oxygen Carbon Chlorine Sodium b contains one type of atom. Scientists use chemical symbols to represent atoms. This helps because it is quicker than using the full name for each substance. It also shows how much of each atom is present in substances that contain more than one atom. For example, carbon dioxide is written as CO2. This shows that there are twice as many atoms of oxygen as there are of carbon. 4 a) There are more elements than there are letters in the alphabet. b) H = hydrogen, O = oxygen, H20 = water, CO2 = carbon dioxide, Au = gold. GETTING SORTED 1 Describe metals Conduct electricity well Solid at room temperature Bend but do not break easily Shiny, often silvery, colour Can stretch to make wires 2 a Mystery element B C √ Metal? Nonmetal? √ Describe non-metals Conduct heat badly Tend to snap when they are bent COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS Mystery element D E √ Metal? Nonmetal? √ b) It conducts heat and electricity like a metal but is a liquid at room temperature. c) Mercury 3 a) If it conducts electricity and heat well, and if it is a solid at room temperature and can be beaten into flat sheets or drawn into wires it is probably a metal. b) Semi-conductors conduct electricity better than non-metals but not as well as metals. They are halfway between so are difficult to put into either group. ALL MIXED UP 1 Pure substances water sugar hydrogen Mixtures pure orange juice ice cream honey instant coffee powder two things does not have to have the same thing all the time. TRUE the substances are chemically bonded always cheaper than pure substances. TRUE be separated by physical methods. TRUE 2 A) A mixture of amounts of each B) In a mixture together. FALSE C) Mixtures are D) Mixtures can 3 a) Specks of gold and sand: swirl in a shallow pan of water, the heavier gold collects nearer the bottom of the pan. b) Oxygen and nitrogen in the air: by fractional distillation. c) Sugar and salt: chromatography. d) Tea from tea leaves: filtering the tea leaves from the liquid tea. a) Scientists need to know exactly what each thing they add to a reaction contains and the composition of mixtures can vary. b) You actually put a lot of different things into them when they are made. 4 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS WHAT ARE COMPOUNDS? 1 2 d a) Elements C H2O CH4 C2H5OH NaCl H2 Compounds Two or more elements join together chemically. 3 Element 1 Carbon Zinc Iron Iron 4 Oxygen Oxygen Sulphur Oxygen Element 2 Compound formed Carbon dioxide Zinc oxide Iron sulphide Iron oxide Compounds form when two or more elements join together chemically. Compounds have completely different properties from the elements that make them up. For example, sodium is a dangerous inflammable metal and chlorine is a poisonous gas. When they react together they make sodium chloride – the same salt that you put on your chips! a) The pile of sulphur and iron particles are a mixture of two different substances but the pile of iron sulphide is a single substance. b) Heat magnesium in air. UNDERSTANDING EQUATIONS 5 1 a) b) c) d) e) Calcium + oxygen → calcium oxide Sodium + oxygen → sodium oxide Hydrogen + oxygen → water Sulphur + oxygen → sulphur dioxide Zinc + sulphur → zinc sulphide 2 Symbol Chemical COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS Symbol H O CO2 CH4 NaCl 3 Chemical Hydrogen Oxygen Carbon dioxide Methane Sodium chloride Chemists use equations to quickly describe what happens in a reaction. An equation using the correct symbols shows which chemicals were involved in the reaction and the elements these chemicals are made from. It even shows how many chemicals of each sort were involved! So the equation below shows that two atoms of sodium react with one oxygen atom to make a new compound, sodium oxide with two sodium atoms to every one oxygen atom. 2 Na + O → Na2O a) The number of atoms is written after the symbol for the element as a small number just below the line. b) On the Periodic Table. COMBINING ELEMENTS 4 1 2 1:1 Nitrogen-containing compounds NO2 – a poisonous brown gas N2O – laughing gas: used as an anaesthetic NO3 – nitrogen trioxide: used to make nitric acid 3 Oxygen : nitrogen ratio 2:1 1:2 3:1 Atoms do not join up randomly to make compounds. They join in simple ratios and any part of the compound has that same ratio. So, in a pile of pure table salt, it is the same ratio of sodium to chlorine throughout the pile. Lead can form a number of different oxides. All of the oxides contain just lead and oxygen but they are different because they have different ratios of lead to oxygen. This means that the atoms are arranged differently in the different oxides. Therefore, they have different chemical and physical properties. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 4 a) Because if the ratio changed it would be a different compound. b) Most chemicals are made of a fairly small number of atoms. TOPIC QUIZ – Separating mixtures 1 2 3 4 a) Dissolve the salt in water and filter off the sand. b) No, because both salt and sugar dissolve in water. Increasing temperature increases the rate of dissolving. Rock salt is a mixture and not safe to use; table salt is a pure substance and has a stronger salt taste. a) acetone b) acetone (or white spirit) c) white spirit To improve the taste and to make it stronger. a) A glass tube used to condense liquids. b) The outer glass jacket is filled with cold running water. To produce fresh water from seawater. Dissolved substances. It does not get the clothes clean enough. Calcium carbonate.         5 6 7 8 9 10 11 Dissolved salts in a stream in a limestone area can petrify objects left in the stream. TRUE Alcohol is a useful solvent but needs to be handled carefully because it gives off vapours that catch fire easily. TRUE A solar still can produce clean drinkable water from river water in an emergency. TRUE Chromatography is used to check the colours in inks to detect forgeries. TRUE Mineral water contains no dissolved substances at all. FALSE – mineral water contains dissolved minerals. Water-soluble means something that water can dissolve. TRUE Distillation reduces the amount of alcohol in a drink. FALSE – distillation increases the amount of alcohol in a drink. The symbol mg stands for many grammes. FALSE – it stands for milligrammes. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS  Solubility of salt goes down as the temperature is raised. FALSE – the solubility of salt increases as the temperature is raised. TOPIC QUIZ – Atoms elements and compounds 1 a) b) c) d) e) Na: sodium O: oxygen C: carbon Mg: magnesium Fe: iron 2 3 4 5 6 7 8 Solid, liquid, gas. Metals conduct heat and electricity well, non-metals do not. The chemical elements Burns with a purple flame. A pure substance contains only one substance but a mixture contains more than one substance. A compound must be pure because if it is not pure it is a mixture of more than one substance. a) Magnesium oxide b) Sodium chloride c) Lithium hydroxide and hydrogen a) 2 b) 3 Any sensible answers acceptable, e.g. it is quicker, it shows the proportions of the elements present.         9 10 11 Metals conduct heat and electricity better than non-metals. TRUE An element contains only one type of atom. TRUE Elements in the same group in the Periodic Table have similar chemical properties. TRUE A compound contains atoms that are joined chemically. TRUE Mixtures can usually be separated by physical means. TRUE Ca is the symbol for carbon. FALSE – it is the symbol for calcium. All metals are solid at room temperature. FALSE – mercury for example is liquid. Carbon dioxide forms when carbon reacts with nitrogen. FALSE – it forms when carbon reacts with oxygen. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS   The numbers in symbolic chemical equations are not important. FALSE – they show you how many of each atom are present. The formula for common table salt is NaCl2. FALSE – it is NaCl. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS MAGNETISM MAGNETIC MATERIALS a) Iron is a magnetic material. TRUE b) Magnets can repel or attract other magnets. TRUE c) A more powerful magnet has a larger magnetic field. TRUE d) Magnetic materials are not affected by gravity. FALSE e) If you pass an electric current through a magnet it demagnetises it. FALSE 2 3 4 The two poles. The magnetic field near a powerful magnet may affect the magnetic recording on the tape. The north pole of a compass should really be called the north-seeking pole. If the compass needle is allowed to turn, this pole will point towards the north. It is actually a south pole because unlike poles attract each other. The part of the needle that points south is actually a north pole! In a bar magnet it is slightly different. Here the pole that is labelled north (it is usually red in colour) is actually a north pole! 1 5 a) Any sensible suggestions acceptable, e.g. electric bell, electric motor, electric generator. b) A magnet may damage the magnetic information in the strip down the centre of the card. MAGNETIC FIELDS 1 a) A magnetic field is an area where magnetic forces can be detected. b) A magnetic field will affect the direction that a compass needle points. 2 a) b) At the poles. 3 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS Experiment Two magnets are brought together with their north poles closest. Two magnets are brought together with their south poles closest. Two magnets are brought together with their north and south poles closest. A magnet is brought near an iron nail. A magnet is brought near a copper nail. Objects repel Objects attract each other each other √ √ √ √ √ No effect 4 a) The magnets could repel each other but a magnet will always attract a magnetic material. EARTH’S MAGNETIC FIELD 1 (1) Compasses always point north-south. (2) Magnetic fields around the Earth protect us from some dangerous radiations from space. 2 a the core is too hot, iron is not magnetic above 77 o C. 3 Charged particles travelling through space. These are given out by the Sun. 4 The Earth cannot contain a giant bar magnet – so what causes the magnetic field? Scientists now think that molten, ironrich minerals in the outer core are constantly moving around by convection. This is similar to the way that liquids move in a saucepan on a stove. These movements create the magnetic field. This idea is known as the geodynamic theory. 5 a) Charged particles from space make the lights as they interact with the magnetic field. b) The solar wind distorts the shape of the Earth’s magnetic field so that it is not spherical. EXPLAINING MAGNETISM 1 (1) Stroke it with a permanent magnet (2) Store it near a permanent magnet. (3) Put it in a coil carrying electricity. A an iron nail. 2 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS B a steel bar 3 A You can magnetise an iron bar by stroking it with a permanent magnet. TRUE B You can demagnetise an iron bar magnet by heating it. TRUE C Magnets attract anything with iron in it. TRUE D Putting a magnet inside a solenoid carrying direct current demagnetises it. FALSE E All metals can be made into magnets. FALSE 4 If you place an iron bar in a coil of wire and pass direct current through the wire, the iron bar will be magnetised. Even when the current is switched off or the iron bar removed, the bar will still be magnetic. If you use alternating current in the coil a put a permanent magnet in it the magnetism will be destroyed. Even when the current is switched off the magnet will still be demagnetised. 5 a) A small crystal of iron in an iron bar that can be magnetised. b) They are orientated to align with the magnetic field lines. ELECTROMAGNETISM 1 A An electromagnet is made by passing electricity through a coil of insulated wire. TRUE B An electromagnet can be switched on and off. TRUE C Putting a soft iron core in the coil increases the power of an electromagnet. TRUE D All electromagnets are painted red. FALSE E Electromagnets do not have south poles. FALSE 2 a) S U COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS b) An ………………….. is formed when an iron bar is fitted inside a coil of wire carrying electric current. 3 a) Increase the number of coils, increase the current, add an iron core. b) Any sensible suggestions acceptable, e.g. using a compass. USING ELECTROMAGNETS 1 Any sensible suggestions acceptable, e.g. in an electric bell, an electric door lock, a crane for lifting iron or steel. Correct sequence: Visitor presses the doorbell and completes a circuit. Electricity flows along the circuit and magnetises the coil. The hammer is pulled away from the bell. The circuit is broken by the armature so the current stops flowing. The coil loses its magnetism. The springy steel strip forces the hammer against the bell and makes a sound. The circuit is remade so the coil becomes magnetic again and pulls the hammer away from the bell. 3 Relays are often used to control circuits that may carry many thousands of volts. A low-power circuit is completed when the operator presses a button. This magnetises a coil which flips a switch to start current in a much more powerful circuit. There are two advantages to this. One is that the operator’s button can be a long way from the actual switch so all of the switches in a large factory can be controlled from a single control room. The second is that people do not need to go near circuits carrying very large voltages. 2 4 a) The rise in electric current creates a magnetic force which breaks the circuit. b) Any sensible suggestions acceptable, e.g. it can be reset, it is faster. MOTORS AND GENERATORS 1 2 A It moves. Any sensible suggestions acceptable, e.g. a washing machine, an electric drill, an electric fan. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 3 (1) Increase the number of coils. (2) Increase the current. (3) Put an iron bar in the middle. A generator is a device that converts movement into electricity. A wire is moved in a magnetic field and this creates a current in the wire. The current passes out of the generator and can be use to power devices or charge a battery. To increase the power output from a generator you can move the wire more quickly, increase the strength of the magnetic field or increase the length of the wire. Most generators have coils of wire so that you can pack a long wire into a small space. 4 a) The stronger the magnets the more movement is created. b) Increase the voltage to increase the speed, reduce the voltage to lower the speed. POWER STATIONS 1 Correct sequence: Coal delivered to power station Coal is burnt to boil water Steam turns giant turbines Turbines turn generators Generators produce electricity a) clay b) wood a) (1) As heat (2) In friction in the moving parts of the generators. b) Any sensible suggestions acceptable, e.g. pollution from burning fuels, use of large amounts of ground to build it, damage caused by vehicles delivering the fuel, radiation leakage and waste from nuclear plants. a) Electricity is a very useful type of energy. b) Accept any sensible suggestions, e.g. reduce heating, fit energy-efficient bulbs, switch off devices when not in use. BURNING PROBLEMS 1 b A chemical made by human activity that damages the environment. 2 Pollutant Problem caused 5 2 3 4 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS Pollutant Carbon dioxide Sulphur dioxide Smoke and soot Other chemicals 3 Problem caused Global warming Acid rain Breathing problems Allergies a) Motor vehicles b) (1) Fit catalytic convertors (2) Use more energy-efficient cars. a) People are less likely to take their cars into the city and so less pollution is produced in the city. b) Acid rain, global warming, use of oil for energy rather than making useful products like plastics. RENEWABLE ENERGY RESOURCES 4 1 Renewable solar tidal bio-fuel 2 Energy resources Renewable Non-renewable Advantage Will never run out. Easy technology to manage. Disadvantage Can sometimes produce small amounts of energy. Will run out. Non-renewable oil coal nuclear COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 3 Device A wind-up torch An electricity-generating windmill A bicycle A solar-powered door bell A water mill for grinding corn 4 movement wind human muscles sunlight moving water Energy supplied by... a) Any sensible comments acceptable. b) Any sensible answers acceptable, e.g. can take up lots of land, birds can be hurt by windmills, building the power stations can use up energy and may produce pollution. WHAT ABOUT NUCLEAR POWER? 1 2 uranium Nuclear powers stations produce radioactive waste. TRUE Uranium reserves will last forever. FALSE Nuclear power stations produce very little carbon dioxide while they are working. TRUE Nuclear power stations are much more expensive to build than oil-fired power stations. TRUE 3 Nuclear power uses heat from nuclear reactions to boil water to make steam. This steam turns giant turbines. These turbines turn generators to make electricity. Nuclear power stations do not produce much carbon dioxide when they are working. However, building and dismantling these power stations needs a lot of energy and this comes from burning fossil fuels. Wastes made by nuclear power stations have to be stored for hundreds of thousands of years before they are safe. a) We need to explore all possible ways to generate electricity given that fossil fuels will run out one day. b) Accept any sensible suggestions, e.g. pollution, terrorist threat, proliferation of nuclear technology with links to weapons production. 4 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS SOUND AND HEAT WHAT IS SOUND? 1 A back and forward movement where the thing vibrating does not change its overall position. 2 Instrument Drum Trumpet Violin Guitar Sound is made by... hitting something blowing down a tube scraping two things across each other plucking a taut string 3 Sounds are vibrations in the air. These vibrations can be made by a vibrating surface in a drum or a vibrating string on a guitar. Wind instruments like the flute make a column of air in a tube vibrate. How quickly the air particles vibrate controls the pitch of the note. More vibrations per second gives a higher pitched sound. The distance the particles vibrate controls the loudness of the sound – the bigger the distance the louder the sound. a) Depends on choice of musical instrument. b) Plucking the string harder to produce greater movement. DESCRIBING SOUNDS 4 1 a) Lowest to highest: A note on a bass guitar A typical telephone ring A soprano in an opera The sounds bats use to find their way around b) Quietest to loudest: A whisper Normal speech A car horn A rock concert A jet plane taking off COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 2 3 a) An oscilloscope can show the volume, pitch and composition of a sound as a graph on a screen. b) The longer the wavelength the lower the frequency. SPEED OF SOUND 1 Slowest to fastest: A snail Sound in air Sound in metal A rocket taking off for the Moon A beam of light Density is the mass of an object divided by its volume. a) About 990 m b) About 330 m c) Getting closer 330 m 2 3 4 5 a) Because sound travels faster and further in solid ground than in air. b) The sound of the underground explosion passes through the Earth. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS SOUND WAVES 1 Scientific word Compression Rarefaction Longitudinal wave Meaning Moving closer together Moving further apart A wave that moves particles closer together and further apart in line with its direction. A wave that moves particles side to side along its direction Spreads out Transverse wave Dissipates 2 a) b) Arrow should be drawn moving horizontally to either the right or to the left. 3 a) The moving cone sets up vibrations in the air. b) High-pitched, quiet note c) Low-pitched, loud note 4 a) They return to their original positions when the vibration dies down. b) The particles push against each other. SOUNDS IN SOLIDS, LIQUIDS AND GASES 1 2 A vacuum a) The sound makes the yoghurt pot vibrate. This passes into the string which pulls on the yoghurt pot at the other end to recreate the same vibrations in the air. b) Pulled tight. The slack string will not pick up the vibrations of the yoghurt pot well or pass them on at the other end. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 3 4 A vibration is a back and forward movement but does not change the position of the object that is vibrating. The particles in gases are quite far apart. They move easily but the energy in the sound wave spreads out very quickly in every direction. In a liquid the particles are closer together. The vibrations pass easily between particles so the sound travels even more quickly. In a solid the particles are close together and held more tightly in place. It is more difficult to move them but because they are so close together even a small movement in one particle can affect the one next to it. For this reason the sound passes very quickly and can travel further than in a liquid or gas. a) There is nothing to pass on the vibrations. b) Air does not carry sound well. ULTRASONIC SOUNDS 1 2 b too high-pitched for humans to hear 5 A Human beings cannot hear sounds above 20 000 Hz. TRUE B Bats and dogs can hear sounds above 20 000 Hz. TRUE C Sounds with frequencies above 1 000 000 Hz are called ultrasonic. TRUE D A piano produces ultrasonic sounds at the top end of the keyboard. FALSE E Small children can hear ultrasonic sounds. FALSE 3 Sound can make things vibrate. A loud bass note at a concert can make your body tingle! Ultrasonic sounds are good at making small particles vibrate very quickly. This is used to clean bits of dirt from the surface of things like machinery or even human teeth. Doctors can also focus bursts of ultrasound on kidney stones. These stones are very painful but if they are made to vibrate by ultrasound they split up and the small pieces pass out of the body with the urine. a) Breaking up kidney stones, medical scanning, cleaning. b) It does not have any side effects (unlike radiation). THE EAR AND HEARING 1 Because you could scratch or perforate the ear drum. 4 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 2 3 Correct order: Outer ear collects sounds in the air around us. Sounds pass along the ear canal and make the ear drum vibrate. Eardrum passes vibrations onto the ear ossicles. The ear ossicles pass vibrations into the cochlea. Sense cells in the cochlea converts vibrations into nerve impulses. Nerve impulses pass to the brain which interprets them as sounds. 4 The ears also help us to balance. The semi-circular canals are three tubes bent into half circles in the inner ear. They contain a liquid which swirls around when we move our head. Small paddle-like sense cells detect the movement of the liquid. They send impulses to the brain and it interprets these to keep us balanced. 5 a) The ear ossicles pass vibrations from the ear drum to the inner ear. b) The mucus damps the vibrations of the ear ossicles so sounds seem quieter. DAMAGING OUR HEARING 1 a) b) c) d) deciBels 7 minutes Probably To protect their hearing a) Wear ear defenders, avoid areas with very loud noises. b) The sense cells in the inner ear are damaged so they cannot detect the sounds. HEAT AND TEMPERATURE 1 a) Coldest to warmest: 2 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS Liquid air The snow on top of Everest A supermarket freezer A nice cup of tea The boiling point of water The flame on a gas cooker b) A supermarket freezer. c) Celsius 2 Ice cubes in a cup of tea A metal rod in a Bunsen flame An explorer on the ice in Iceland The surface of the road in the summer sun A beef burger on a barbecue Ice cubes Metal rod Explorer Road surface Beef burger Tea Bunsen flame The ice Summer sun Barbecu e coals 3 4 Thermometer a) Heat is a form of energy but temperature is a measure of how hot something is. Two things that have the same temperature might contain different amounts of heat energy. b) Heat energy flows from where it is hotter to where it is cooler. GETTING WARMER 1 Any sensible answers acceptable, e.g. to cook it, to make a hot drink, to melt it, to increase the rate of a chemical reaction. Any sensible answers acceptable, e.g. gas fire, barbecue, electric cooker, Bunsen burner, sunlight, microwave. a) b) c) d) A block of ice: it melts to form water. An iron nail: glows red, may melt. A plastic cup: burns or melts. A bar of chocolate: melts, may burn. 2 3 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 4 a) The gloves reduce the loss of heat from your hands so they do not cool down so much. b) Microwave radiation produced by the oven hits the water in the food and heats it up. CONDUCTION 1 Good conductors an iron bar a gold bracelet a steel nail 2 Poor conductors a woolly jumper a plastic cup a polar bear’s fur coat a) Any sensible suggestions acceptable, e.g. to add heat to an object (e.g. a saucepan) or to conduct excess heat away from something (e.g. a computer chip). b) Any sensible suggestions acceptable, e.g. clothing for polar explorers, jackets for firefighters to wear in a burning building. Solids tend to be good conductors of heat energy. This is because the particles they contain are close together. When one starts to vibrate it makes the ones near it vibrate. In this way the heat energy passes through the solid. In liquids and gases the particles are further apart. The vibrations do not pass from particle to particle so easily. This is why liquids and gases are good insulators. 3 4 a) The heat is conducted away more quickly by the tin mug than by the plastic one. b) The plastic container is a poor conductor so heat cannot get into the ice cream to make it melt. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS CONVECTION 1 2 a) M O V E E N T b) . Warm currents of air in the atmosphere are called ……………. 3 a) Hot air is less dense than cold air so it rises as colder air pushes it upwards. b) The particles in a solid cannot move around. RADIATION 1 a) Beaker colour Temperature at start in oC 15 15 15 Temperature at end in oC 18 19 26 Change in temperature in oC 3 4 11 White Silver Black COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS b) A bar chart is most appropriate here (example below). 12 10 Temperature rise (°C) 8 6 4 2 0 White Silver Beaker Black c) Darker surfaces absorb heat radiation better than lighter ones. The nearer to the source of radiation, the greater the rise in temperature. b one way heat travels through empty space 2 3 Absorbers are surfaces that are good at absorbing energy but reflectors tend to bounce it back without absorbing it. TOPIC QUIZ – Magnetism 1 2 3 4 5 (Any three from) Steel, iron, nickel, cobalt. a) At the ends. b) North pole and south pole. A space where a magnetic force can be detected. An electromagnet can be switched on and off. A powerful electromagnet can pull magnetic metals like steel and iron from a mixture of metals containing aluminium and other wastes. It is demagnetised. 6 7 Increase the number of coils, increase the current flowing, add a soft iron core. 8 Movement of iron-containing liquid rocks in the centre. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 9 Crystals in an iron bar which can be aligned by a magnet field. 10 11          The magnetic field is strongest near the poles of a magnet. TRUE Iron filings arrange themselves along the lines of magnetic force in a magnetic field. TRUE The Earth’s core cannot be a permanent magnet because it is too hot. TRUE An electric bell contains an electromagnet which can be switched on and off very quickly. TRUE Stronger electric currents produce more powerful electromagnets than weaker currents. TRUE Aluminium is a magnetic material. FALSE – it is not a magnetic material. Electromagnets are always weaker than permanent magnets. FALSE – the strength of an electromagnet depends on the strength of the current and the number of coils. Generators convert electricity into movement. FALSE – generators convert movement into electricity. Magnetic fields cannot pass through paper. FALSE – they can pass though paper. a) They repel. b) They attract. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS TOPIC QUIZ – Sound and heat 1 2 3 4 5 How high the note is. Amplitude Light They move closer together and further apart. 6 7 The volume of the sound and the length of exposure to it. When using loud machinery or in very noisy environments. 8 Particles in the solid move back and forth against each other as the sound wave passes. 9 10 Hammers hitting the strings. They are at the same temperature. 11 a) Movement of heat through solids where the solid does not move. b) An insulator. 12        Sound cannot travel through the vacuum of space. TRUE Ultrasonic sounds are too high pitched to be heard by humans. TRUE Frequency is measured in Hertz. TRUE Sound is a form of energy. TRUE Sound travels at roughly 330m/sec. TRUE The frequency of a sound controls its loudness. FALSE – the frequency of a sound controls its pitch. Monocles are small bones in the human ear. FALSE – ossicles are small bones in the human ear. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS      You can improve your hearing by eating lots of carrots. FALSE – eating carrots will not affect your hearing. Sound travels faster in gases than in solids. FALSE – sound travels faster in solids than in gases. Sound waves are transverse waves. FALSE – sounds waves are longitudinal waves. In radiation hot particles move to carry the heat energy. FALSE – radiation does not involve the movement of particles. Some materials get colder if you add heat energy to them. FALSE – heat energy always increases the temperature of an object. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS LIFE AND DEATH DESIGN A PREDATOR 1 2 Feature a leopard’s ability to run very fast an owl has large eyes to see in the dark a rattlesnake produces poison a shark has backward facing teeth 3 Helps it to survive to catch prey to see prey in dark environments to kill its prey to stop its prey slipping out of its mouth A an animal that hunts and eats other animals A predator like a lion needs to be able to catch and kill its prey. The lion is camouflaged to creep through the bush without its prey noticing. Strong jaws can kill the prey quickly and the sharp teeth can cut into its flesh to remove all the meat from the body. The lion’s prey has other adaptations to avoid being eaten. 4 a) The predator will have no food to eat once all the prey are gone. b) Any sensible suggestions acceptable, e.g. sharp teeth and claws to kill prey, camouflage to creep up on prey, fast runner to catch prey. WHERE HAS THE OX GONE? 1 (1) In respiration in the predator (2) Undigested parts of the prey body (3) In energy required to actually catch the prey 2 An animal that eats dead animals rather than hunting and killing them. 3 All living things need a supply of energy. Plants get this from the sun by photosynthesis. All animals get it from their food – either plants or other animals. Because energy is always wasted when an animal eats, the total amount of energy available goes down as there are more links in the food chain. This is why there are always fewer lions in an area than zebras. a) A pyramid of numbers shows the number of organisms present at each feeding level in an ecosystem. b) A dung beetle eats dung. 4 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS POPULATION MODELS 1 Any sensible suggestions acceptable, e.g. Physical factors Temperature Oxygen levels Shelter Water supply 2 3 A Catastrophes Floods Volcanoes Biological factors Availability of food Diseases present in area Predators behaves in the same way as the thing it is modelling Scientists use models to investigate the way a population changes. Complex models use computers to predict what will happen according to certain rules. One advantage of computer models is that they can be run much more quickly than the thing they are modelling. Population changes in humans are modelled in large computers by scientists. They can even run them forward to predict the human population in 20 or 50 years time. 4 a) The model can investigate what would happen with different levels of fishing and so predict what the maximum take of fish could be without making the population crash. b) A simulation is a model, usually done on a computer, of a process. RECYCLING BY ROTTERS 1 Living organisms help these Living organisms cannot make things to decay these things decay leaf litter fish bones horse manure diamond car tyres tin cans 2 Any sensible suggestions acceptable, e.g. (1) The kitchen waste does not have to be dumped. (2) Kitchen waste makes very good compost. 3 Living things decay when they die. This decay is caused by a range of different organisms. Some can make wood decay. You may have seen mushrooms growing on fallen logs. The mushrooms release chemicals which dissolve parts of the wood. Other microbes then take over and break the wood down even further. Eventually the wood is converted to water, carbon dioxide and minerals in the soil. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 4 a) A biodegradable material can be broken down by living things. b) Plastic is not biodegradable. It is broken down into a powder by physical action and the particles produced can survive for a very long time and be carried around the planet in the oceans. POPULATIONS 1 A population is the number of organisms of a particular species living in a particular area. a) (1) b) (1) food supply 3 2 Improved food supply, (2) loss of predators Increase in predator population, (2) reduction in Animals produce many more young than they need just to replace themselves. However, their population remains pretty stable over many years. This means that many of the young do not survive to become adults. Only the fittest or the luckiest survive. If there is a massive increase in population of a species this can actually damage their environment and the large population will crash back to low numbers while the environment recovers. 4 a) The extra predators will take more prey animals to eat and so the population will fall. b) The lack of prey for the predators to hunt and eat will reduce their food supply and fewer predators will survive. BIOLOGICAL CONTROL 1 Any sensible suggestions acceptable, e.g. Plant Lettuce Cabbage Roses 2 Pest Slugs, caterpillars, snails Slugs, caterpillars, snails Aphids a) Pesticides will kill the pests that are damaging the crop. b) Pesticide residues may remain in the crop or the pest may develop resistance to the pesticide so it will not work. Biological control uses living organisms to kill pests. The main advantage of this system is that no poisonous pesticides are needed. And if the number of pests goes up the organisms that feed on them also rise. Ladybirds act as biological 3 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS control organisms for greenfly on roses and whitefly in tomato greenhouses. The ladybirds do not damage the crops and help to keep the pests in check. 4 a) Pesticides start to work immediately whereas a biological agent will need to increase in population before it can have a large effect on the pests. b) No suitable organisms may exist that can prey efficiently on the pests or it may be difficult to supply the control agents to the crop. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS SPACE DAY AND NIGHT 1 2 The Sun. A The Earth takes 24 hours to spin once on its axis. TRUE B Half of the Earth is always pointing towards the Sun. TRUE C The Earth moves round the Sun roughly every 365 days. TRUE D The Sun moves around the Earth going from east to west across the sky. FALSE E All planets in the Solar System have the same day length as the Earth. FALSE 3 The Earth completes an orbit of the Sun every 365¼ days. The extra six hours isn’t much in a year but over a century the extra time would be 25 days. This means Christmas would not arrive until January 19th! To stop this happening every four years an extra day is added to February. These years are called leap years and help to keep our calendars in sync with the movement of the Earth. 4 a) Ships appearing over the horizon, pictures of Earth from space. b) Gravity pulls us down towards the centre of the planet. THE SEASONS 1 Times 24 hours Events Time for the Earth to spin once on its axis Time for the Earth to complete one orbit of the Sun Length of the day at the spring equinox Length of the longest day of the year in the UK Length of the day on December 21st in the UK 365.25 days 12 hours 16 hours 30 minutes 8 hours COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 2 a) and are of ……………. . 3 b) Summer winter examples a) When the northern hemisphere is tilted towards the Sun, sunlight is spread over a smaller area than when it is tilted away. This means more energy is delivered per square metre of the area, producing more heat. b) A satellite is something that orbits a planet. THE MOON 1 A B C D E The Moon is Earth’s only natural satellite. TRUE The Moon takes 28 days to orbit the Earth. TRUE The Moon’s shape changes as it orbits the Earth. FALSE The Moon is about 1500 km from the Earth. FALSE Eclipses of the Moon only happen during the summer. FALSE 2 [Insert diagram – take from bottom of figure 2 on page 190 of SB2] 3 The Moon orbits the Earth every 28 days and sometimes it passes between the Earth and the Sun. If it lines up exactly it can block the light from the Sun coming towards the Earth. This is called a solar eclipse. Of course, there are times when the Moon is on the other side of the Earth to the Sun. In this case the Earth blocks the sunlight to the Moon. This is called a lunar eclipse. a) The Moon reflects light from the Sun. b) The shape the Moon appears to be in the sky. It depends on how much of the lit side of the Moon is facing towards the Earth. THE SOLAR SYSTEM Moving out from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. 1 4 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 2 Planet Mercury Mars Jupiter Saturn Description Takes about 72 days to orbit the Sun. Sometimes called the Red Planet, humans have landed a robot spaceship there. The largest planet in the Solar System Rings of debris spin around the middle of this planet. 3 The Solar System consists of one star and eight planets. The star, which we call the Sun, is by far the biggest object in the Solar System. Its diameter is 1000 times Earth’s. Nuclear reactions generate huge amounts of energy and we see these as sunlight. Planets are smaller and do not give out their own light. The distances between the planets are much bigger than the distances across the Sun. So the Solar System is largely empty. a) Any sensible suggestions acceptable, e.g. they allow us to see more details on the planet’s surface, we can see planets that are invisible with the naked eye. b) Mercury is very hot and rocky with no atmosphere. The Sun would be very large in the sky. Venus is cooler and has large clouds of gases (and possibly liquids). GRAVITY IN SPACE 4 1 2 3 4 c pulls two masses together. Isaac Newton b e Their mass The distance apart Gravity is the force that holds the universe together. It acts between any masses and always pulls them together. You are pulled towards the Earth because of the force of gravity. You also pull the Earth towards you. But your mass is so small compared with the planet that you move much more than the planet! That’s why you fall towards it. The force of gravity depends on the masses of the two objects and the distance between them. The larger the masses and the shorter the distance the bigger the force. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS 5 a) The Sun is larger than Earth and so exerts a gravitational force that is strong enough to keep Earth in its orbit and prevent it from ‘flying into space’. b) The force of gravity from the Earth is very strong so the rockets need large engines to push against it. These use up large amounts of fuel. GRAVITY AND WEIGHT 1 2 3 newtons a) a) the amount of material it is made of. b) The force that pulls masses towards each other. 4 a) Weight is the force of gravity acting on an object but mass is the amount of material an object contains. b) The Moon’s gravitational force is smaller than the Earth’s so the force acting on objects (their weight) is lower. SATELLITES 1 Any sensible suggestions acceptable, e.g. (1) communications, (2) weather forecasting, (3) mapping of the Earth. 2 The radio waves cannot go through the Earth so they have to go round it. They travel in straight lines so have to be passed from satellite to satellite to get round the Earth. The Moon. The very first satellite put into space was Sputnik 1 in 1957. Nowadays there are thousands of satellites in orbit around the Earth. Some change their positions. Others, called geostationary satellites, are always above the same spot on the planet’s surface. They move in step with the planet. 3 4 COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS These geostationary satellites are used for communications networks. Putting a satellite into orbit is not cheap! It needs a very large rocket to push it up against Earth’s gravitational pull. 5 a) Any sensible suggestions acceptable, e.g. for weather forecasting, mapping, scientific research, surveillance. b) To push against the force of gravity. SPACE TRAVEL 1 Any sensible suggestions acceptable, e.g. (1) people like to explore, (2) scientific research. 2 a needed to escape the pull of Earth’s gravity. 3 The gravitational force on the Moon is lower than the Earth’s because it has a smaller mass. (1) (2) (3) moons. 5 4 For engines to escape the Earth’s gravity For engines to change direction during flight To push against gravity when landing on other planets or Escaping from Earth is not easy! Gravity pulls objects down towards the planet and the larger the object the greater the force. Rockets are very large because they need a lot of fuel to power the engines to push against gravity. But more fuel means more weight! The Saturn V rocket that took humans to the Moon weighed over 2 700 000 kg but the capsule that made the trip to the Moon was less than 100 000 kg. Most of the rocket was fuel. Once the rocket got into space it needed much less fuel because the force of gravity is so much lower. a) This is when the engines have to work hardest to accelerate the giant rocket. As fuel is used up the rocket gets lighter and the attraction of gravity reduces as you get further away so less fuel is needed for the engines. b) Even the nearest star is far too far away. EXPLORING FURTHER 6 1 2 3 (1) Use telescopes (2) Send probes to land on the surface c Robot probes can be smaller and need fewer supplies. Probe Mars Jupiter Saturn Neptune Uranus COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS Probe Pioneer 10 Voyager 1 and 2 Pathfinder 4 Mars x x √ Jupiter √ √ x Saturn x √ x Neptune √ √ x Uranus x √ x The Hubble telescope 5 a) The Earth’s atmosphere absorbs and scatters some of the light so degrades the image. b) Any sensible suggestions acceptable, e.g. robot probe could analyse the composition of the soil. TOPIC QUIZ – Life and death 1 Camouflage, able to run quickly, good eyesight and hearing. 2 Hunting takes energy, not all of the prey is eaten and not all of it can be digested. 3 A diagram showing the numbers of individuals at different feeding levels in an ecosystem. 4 Any sensible suggestions acceptable, e.g. temperature, oxygen supply, water levels, light levels. 5 Animals moving long distances from one area to another, often as a result of a seasonal change. 6 7 Because they can run experiments more quickly. Any sensible suggestion acceptable, e.g. leave it out in the environment, say buried, in water etc. and see if the weight changed over a few months. If it fell it would be at least partially biodegradable. For microorganisms to respire. Natural selection 8 9 10 No pesticide residues in food or environment, less likely to develop resistance in the pests. 11  Camouflage helps animals to move around but not be seen by predators or prey. TRUE COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS          Energy is wasted when an animal eats another animal. TRUE An increase in food supply almost always leads to an increase in animal populations. TRUE A food web shows the feeding relationships in an area. TRUE If predators fall in number the prey population tends to rise. TRUE Only predators have adaptations, prey animals have none. FALSE – prey animals have adaptations to help them hide from and escape predators. 99% of the energy in grass is wasted when it is eaten by a cow. FALSE – more than 1% of the energy is usefully transferred to the cow. Leaf litter is broken down by cows and sheep. FALSE – leaf litter is broken down by decomposers. Greenfly are good organisms to control ladybird populations. FALSE – it is ladybirds that can control greenfly populations. Fungicides are used to kill weeds. FALSE – fungicides are used to kill fungi. TOPIC QUIZ – Space 1 2 3 4 5 a) 365 b) 12 The Moon. a) 8 b) 1 Gravity Newtons The gravitational pull on the Moon is lower than on a) b) Earth. 6 The speed you must travel at to escape the pull of Earth’s gravity. 7 8 9 10 11  Sputnik 1 was the first artificial satellite. TRUE A deep space probe. Mercury Saturn We can only see the part that faces towards the Sun and as the Moon orbits the Earth, and this changes. COLLINS KS3 SCIENCE WORKBOOK 2 ANSWERS          Satellites are used for communications and surveying the Earth. TRUE Copernicus was a Polish astronomer who suggested the Sun was at the centre of the Solar System. TRUE An eclipse occurs when the Moon passes in front of the Sun. TRUE Christmas day is warm in Australia but June can be cold and wet. TRUE An orbit is a square path around the Earth. FALSE – an orbit is an elliptical path around the Earth. Most of the weight of the Saturn V rocket was electronic computers. FALSE – most of the weight of the Saturn V rocket was fuel. Saturn is able to produce its own light. FALSE – Saturn reflects light from the Sun. The Earth is at the centre of the Sun and planets. FALSE – the Sun is at the centre of the Earth and other planets. The seasons are caused by the daily spin of the Earth. FALSE – the seasons are caused by the Earth’s tilted axis.