Cambridge Lower Secondary Science Workbook 8 (2021) PDF

9781108742856 Jones, Fellowes-Freeman & Smyth Lower Secondary Science Workbook 8 CVR C M Y K...

9781108742856 Jones, Fellowes-Freeman & Smyth Lower Secondary Science Workbook 8 CVR C M Y K Cambridge Lower Secondary Cambridge Lower Secondary Science These workbooks are full of activities to help you practise what you have learnt and encourage you to think and work scientifically. Focus, Practice and Challenge exercises provide clear progression so you can see what you have achieved. Your teacher may use them in the classroom, or to set your homework. Cambridge Lower Secondary Active learning opportunities help you apply your knowledge to new contexts Three-tiered exercises in every topic help you see and track your own learning Write-in for ease of use Science Science Answers for all activities can be found in the accompanying teacher’s resource WORKBOOK 8 For more information on how to access and use your digital resource, please see inside front cover. Mary Jones, Diane Fellowes-Freeman & Michael Smyth WORKBOOK 8 This resource is endorsed by Cambridge Assessment International Education Completely Cambridge ✓ Provides learner support as part of a set of Cambridge University Press works with Cambridge resources for the Cambridge Lower Secondary Assessment International Education and experienced Science curriculum framework (0861) from 2020 authors to produce high-quality endorsed textbooks and digital resources that support Cambridge teachers ✓ Has passed Cambridge International’s and encourage Cambridge learners worldwide. rigorous quality-assurance process To find out more visit cambridge.org/ ✓ Developed by subject experts cambridge-international ✓ For Cambridge schools worldwide Registered Cambridge International Schools benefit from high-quality programmes, assessments and a wide range of support so that teachers can effectively deliver Cambridge Lower Secondary. Visit www.cambridgeinternational.org/lowersecondary to find out more. Second edition Digital access www.frenglish.ru  Cambridge Lower Secondary Science WORKBOOK 8 Mary Jones, Diane Fellowes-Freeman & Michael Smyth www.frenglish.ru University Printing House, Cambridge CB2 8BS, United Kingdom One Liberty Plaza, 20th Floor, New York, NY 10006, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia 314–321, 3rd Floor, Plot 3, Splendor Forum, Jasola District Centre, New Delhi – 110025, India 79 Anson Road, #06–04/06, Singapore 079906 Cambridge University Press is part of the University of Cambridge. It furthers the University’s mission by disseminating knowledge in the pursuit of education, learning and research at the highest international levels of excellence. www.cambridge.org Information on this title: www.cambridge.org/9781108742818 © Cambridge University Press 2021 This publication is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2012 Second edition 2021 20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Printed in ‘country’ by ‘printer’ A catalogue record for this publication is available from the British Library ISBN 978-1-108-74281-8 Paperback Additional resources for this publication at www.cambridge.org/delange Cambridge University Press has no responsibility for the persistence or accuracy of URLs for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Information regarding prices, travel timetables, and other factual information given in this work is correct at the time of first printing but Cambridge University Press does not guarantee the accuracy of such information thereafter. NOTICE TO TEACHERS IN THE UK It is illegal to reproduce any part of this work in material form (including photocopying and electronic storage) except under the following circumstances: (i) where you are abiding by a licence granted to your school or institution by the Copyright Licensing Agency; (ii) where no such licence exists, or where you wish to exceed the terms of a licence, and you have gained the written permission of Cambridge University Press; (iii) where you are allowed to reproduce without permission under the provisions of Chapter 3 of the Copyright, Designs and Patents Act 1988, which covers, for example, the reproduction of short passages within certain types of educational anthology and reproduction for the purposes of setting examination questions. www.frenglish.ru  Contents Contents 1 Cells 1.1 Plant cells 1 1.2 Animal cells 5 1.3 Specialised cells 7 1.4 Cells, tissues and organs 11 2 Materials and their structure 2.1 Solids, liquids and gases 16 2.2 Changes of state 21 2.3 Explaining changes of state 26 2.4 The water cycle 30 2.5 Atoms, elements and the Periodic Table 32 2.6 Compounds and formulae 34 2.7 Compounds and mixtures 38 3 Forces and energy 3.1 Gravity, weight and mass 42 3.2 Formation of the Solar System 49 3.3 Movement in space 53 3.4 Tides 56 3.5 Energy 60 3.6 Changes in energy 64 3.7 Where does energy go? 67 4 Grouping and identifying organisms 4.1 Characteristics of living organisms 71 4.2 Viruses 75 4.3 What is a species? 77 4.4 Using keys 82 4.5 Writing keys 87 iii www.frenglish.ru Contents 5 Properties of materials 5.1 Metals and non-metals 90 5.2 Comparing metals and non-metals 93 5.3 Metal mixtures 98 5.4 Using the properties of materials to separate mixtures 100 5.5 Acids and alkalis 105 5.6 Indicators and the pH scale 107 6 Earth physics 6.1 Sound waves 111 6.2 Reflections of sound 114 6.3 The structure of the Earth 120 6.4 Changes in the Earth 122 6.5 Solar and lunar eclipses 124 7 Microorganisms in the environment 7.1 Microorganisms 127 7.2 Food chains and webs 131 7.3 Microorganisms and decay 135 7.4 Microorganisms in food webs 142 8 Changes to materials 8.1 Simple chemical reactions 144 8.2 Neutralisation 149 8.3 Investigating acids and alkalis 154 8.4 Detecting chemical reactions 163 9 Electricity 9.1 Flow of electricity 166 9.2 Electrical circuits 168 9.3 Measuring the flow of current 170 9.4 Conductors and insulators 172 9.5 Adding and removing components 174 iv www.frenglish.ru  How to use this book How to use this book 4 Grouping and identifying organisms 4.3 What is a species? Exercise 4.3A Different species This workbook provides questions for Focus This exercise will help you to check that you understand what the term you to practise what you have learned ‘species’ means. in class. There is a topic to match each Complete the sentences. Choose from these words or phrases. topic in your Learner’s Book. Each topic You can use each word or phrase once, more than once or not at all. contains the following sections: different to exactly the same as fight fertile healthy horn horns infertile kingdoms reproduce species The drawings show a white rhino and an Indian rhino. Focus: these questions help you to master the basics Indian rhino White rhino 4 Grouping and identifying organisms Practice 2 Scientists do not all agree about whether viruses are living 76 organisms. Secondary_Science_WB_7_9781108742818_Unit_04 Page 76 22/04/20 4:52 PM I do not agree that viruses should be classified as living Practice: these questions help you to organisms. Viruses are living organisms. become more confident in using what you have learned a Write down one piece of information about viruses that supports the view of Scientist A. 4.3 What is a species? Exercise 4.3C A new frog species Challenge b Write down two pieces of information about viruses that In this task,support you willthe useview yourof Scientist B. understanding of what makes a separate species. You will suggest how scientists could decide how to classify a newly discovered kind of frog. Challenge: these questions will make In 2016, a team of you think very hard researchers from India and the National University of Singapore discovered an unusual frog in a rocky habitat near the coast of southwest India. The frog is tiny – only about 16 mm long. It looks similar to other little frogs that are classified in the genus Microhyla. This frog is pale brown and has black and orangey-red markings on its back, feet and sides. The males make a call that sounds like 74 a cricket chirping. The researchers thought that the frog looked different from the eight species of Microhyla known to live in India. They thought it might be a Secondary_Science_WB_7_9781108742818_Unit_04 Page 74 22/04/20 4:52 PM new species, not known about before. Suggest what the researchers should do to decide whether or not their frog really is a new species. You could think about these things. How many specimens of the new frog should they collect? (Think about how much evidence they need, as well as the fact that this species might be rare.) v What evidence should the researchers collect? www.frenglish.ru How should the researchers use this evidence to make a decision about whether or not the frog belongs to a new species? 1 Respiration 1.1 The human respiratory system Exercise 1.1 Structure and function in the respiratory system This exercise helps you to recognise the parts of the respiratory system on a diagram. You can then try describing their functions, and think about what it would be like to travel down through the system. Focus The diagram shows the human respiratory system. J H G F E D C B A 2 www.frenglish.ru  1.1 The human respiratory system 1 Complete the table by naming each of the parts shown on the diagram. Choose from these names. air sacs  bronchiole  bronchus  diaphragm  lung larynx (voice box)  intercostal muscles  rib  trachea Letter Name A B C D E F G H I Practice 2 Describe the function of each of the labelled parts listed in this table. Letter Function C D E F G H I 3 www.frenglish.ru 1 Respiration Challenge 3 In your own words, describe the pathway that air takes as it travels from outside your body into the air sacs. 1.2 Gas exchange Exercise 1.2 Lung surface area and body mass This exercise provides you with data about six different mammals. You will practise looking for correlations in data, and suggesting explanations for the patterns that you find. Focus The table shows the body masses of six mammals. It also shows the total surface area of the air sacs in the mammals’ lungs. 4 www.frenglish.ru  1.2 Gas exchange Total surface area Mammal Body mass in g of air sacs per m2 human 80000.1 70 mouse 20.2 0.1 rabbit 400.3 8 rat 300.4 0.8 sheep 68000.5 60 fox 20000.5 40 1 The entries in the table are not in a very helpful order. Complete the table by reorganising the entries in a way that makes it easier to see any patterns in the data. Total surface area of Mammal Body mass in g air sacs per m2 Practice 2 Describe the relationship between body mass and total surface area of the air sacs. 5 www.frenglish.ru 1 Respiration Challenge 3 Suggest an explanation for the relationship you have described. 1.3 Breathing Exercise 1.3A Measuring lung volumes Focus In this exercise, you complete a results table. Then you calculate mean values and draw a bar chart. Sofia and Zara want to know if learners who play wind instruments in the school orchestra can push more air out of their lungs than learners who play stringed instruments. The girls take a large, empty bottle. They mark a scale on the side to show volumes. 6 www.frenglish.ru  1.3 Breathing 1 Describe how Sofia and Zara can make the scale on the bottle. Sofia and Zara fill the bottle with water. They turn the full bottle upside down, with its open top in a large container of water. Marcus plays a wind instrument. The girls ask Marcus to blow into the bottle as hard as he can. They use the scale to record how much water Marcus can push out of the bottle. They then test eight more musicians. Here are the results that Sofia and Zara collect. boys who play wind instrume nts: 2100cm 3 1965cm 3 2005cm 3 girls who play wind instrume nts: 1950cm 3 boys who play stringed instru ments: 1865cm 3 1950c 3 m girls who play stringed instru ments: 1905cm 3 1910c 3 m 1885cm 3 7 www.frenglish.ru 1 Respiration 2 Complete Sofia and Zara’s results table. Person Boy or girl Wind or string player Volume displaced in cm3 1 boy wind 2100 3 Calculate the mean volume displaced (pushed out) for the boys who play wind instruments. Remember: To calculate the mean of three values, add them up and divide by 3. Show your working. cm3 4 Calculate the mean volume displaced for the boys who play stringed instruments. Show your working. cm3 8 www.frenglish.ru  1.3 Breathing 5 Calculate the mean volume displaced for the girls who play stringed instruments. Show your working. cm3 6 Complete the bar chart to show Sofia and Zara’s results. 2030 2020 2010 2000 1990 1980 1970 Mean volume displaced in cm3 1960 1950 1940 1930 1920 1910 1900 boys, girls, boys, girls, wind wind stringed stringed 9 www.frenglish.ru 1 Respiration Exercise 1.3B Looking at data on lung volumes Practice In this exercise, you will look for patterns in data. Then you think about how to improve an experiment. Look at the experiment that Sofia and Zara did, which is described in Exercise 1.3A. Sofia and Zara discuss what their results show. I think our results show I think our results show that boys can push out that people who play larger volumes of air wind instruments can than girls. push out larger volumes of air than people who play stringed instruments. 1 Is Sofia right? Explain your answer. 2 Is Zara right? Explain your answer. 10 www.frenglish.ru  1.3 Breathing 3 The girls’ teacher says they cannot draw any definite conclusions from their results. She asks them to try to improve their experiment. What will improve the girls’ experiment? Tick (✓) two boxes. Collecting more results from more people in the orchestra. Finding out whether playing a percussion instrument affects lung volume. Making three measurements for each person. Measuring how fast each person can run. Exercise 1.3C Lung volume at different ages Challenge In this task, you will practise finding information on a graph. You will do a simple calculation, and use evidence from the graph to make predictions. Scientists measured the lung volumes of several hundred men and women of different ages. The people were asked to push out as much air from their lungs as they could, in one breath. The mean values of the volume of air pushed out for each age group were calculated. 11 www.frenglish.ru 1 Respiration The graph shows the results. 5.0 men 4.0 Mean volume of air pushed out with one breath in dm3 3.0 women 2.0 1.0 5–9 10–19 20–29 30–39 40–49 50–59 60–69 70–79 Group in years 1 Suggest why the researchers collected results from several hundred men and women, rather than just a few in each age group. 2 State the mean volume of air pushed out for women in the 20–29 age group. Remember to give the unit with your answer. 3 Calculate the difference between the mean volumes of air pushed out for men and women in the 40–49 age group. Show your working. 12 www.frenglish.ru  1.4 Respiration 4 Describe how the mean volume of air that can be pushed out by women changes with age. 5 Use the graph to predict a value for the mean volume of air that can be pushed out by men aged between 70 and 79. 1.4 Respiration Exercise 1.4 Respiration by yeast In this exercise, you think about how to choose apparatus, and the correct way to use a thermometer. You make a prediction about temperature change and also think about using this apparatus to plan an experiment to test a hypothesis. Focus Yeast is a living micro-organism. Sofia wants to find out what happens to the temperature of yeast when it respires. She has some yeast mixed with water. She measures 25 cm3 of it and puts into an insulated cup. Then she adds 25 cm3 of sugar solution. 13 www.frenglish.ru 1 Respiration yeast and sugar water mixture solution thermometer 1 One piece of apparatus that Sofia needs is missing from the diagram. State what this apparatus is, and why Sofia needs it. 2 Sofia measures the temperature of the mixture of yeast and sugar solution in the cup. How should Sofia measure the temperature? Tick (✓) all the correct statements. Hold the thermometer in the liquid and then take it out to read it carefully. Stand the thermometer in the cup so it is resting on the bottom. Hold the thermometer in the liquid and stir gently. Make sure her eyes are level with the meniscus to read the temperature. 14 www.frenglish.ru  1.4 Respiration Practice 3 Predict what will happen to the temperature of the mixture in the cup. Explain your prediction. Prediction Explanation 4 Sofia has missed out something very important from her experiment. What has she missed out? Look at what Sofia is trying to find out. Think about what she needs to do to be sure any temperature change she measures is due only to the yeast respiring. Challenge 5 Describe how Sofia could use her apparatus to test this hypothesis: The more sugar the yeast is given, the faster it will respire. 15 www.frenglish.ru 1 Respiration 1.5 Blood Exercise 1.5A The components of blood Focus In this exercise, you will think about the three components that make up blood. Human blood has three components: plasma red blood cells white blood cells. 1 Which of these three components is a liquid? 2 Which of these three components have nuclei? 3 Which component has each of these functions? a transporting oxygen from the lungs to all the respiring cells in the body b protecting against pathogens that have got into the body c transporting blood cells, nutrients and carbon dioxide 16 www.frenglish.ru  1.5 Blood Exercise 1.5B Functions of blood components Practice In this exercise, you will think about suitable words to complete sentences about blood. Choose the best words to complete the sentences. antibodies  bacteria  carbon dioxide   cytoplasm glucose  haemoglobin  least  like  most nucleus oxygen  plasma  unlike Blood contains a pale yellow liquid, called. This liquid carries red blood cells and white cells around the body. It also transports several different substances in solution, including and. Red blood cells are the abundant cells in the blood. Their function is to transport from the lungs to all the cells in the body that are respiring. To help them to do this, they contain a red pigment called. White blood cells, red blood cells, contain a nucleus. Their function is to destroy pathogens, such as , that get into the body. Some of them do this by producing chemicals called , which attach themselves to the pathogens and kill them. Other white blood cells kill pathogens by taking them into their and digesting them. 17 www.frenglish.ru 1 Respiration Exercise 1.5C Rats at altitude Challenge In this challenging task, you will use information to make a prediction. You will draw a graph to display a set of results, and think about the design of an experiment. Red blood cells carry oxygen around the body. At high altitudes, there is less oxygen in the air. A team of scientists did an experiment to find out how the number of red blood cells in rats changed when the rats were taken to high altitude. 1 Make a prediction about what might happen to the number of red blood cells when the rats were taken to high altitude. Explain your prediction. This is what the scientists did. They kept one group of rats at sea level, and took another group to high altitude. They took blood samples from each rat on days 1, 3, 7, 15 and 20. They measured the number of red blood cells in a certain volume of blood from each rat. This is called the red blood cell count. They calculated the mean red blood cell count for each group of rats. 18 www.frenglish.ru  1.5 Blood The table shows their results. Mean red blood cell count Time in days Rats at sea level Rats at high altitude 1 6.5   6.5 3 7.0   8.5 7 6.5 10.0 15 6.5 10.5 20 7.0 11.5 2 On the grid, construct line graphs to show these results. Draw two lines on the same pair of axes. Tip: Take care with the scale on the horizontal axis. 19 www.frenglish.ru 1 Respiration 3 What was the independent variable in the experiment? 4 What was the dependent variable in the experiment? 5 Suggest two variables that the scientists should have kept the same. 6 Calculate the increase in red blood cell count for the rats at high altitude from day 1 to day 20. Show your working. 7 Use your answer to question 6 to calculate the mean rate of increase per day. Show your working. 8 After 20 days, the rats at high altitude were taken back down to sea level. Predict what would happen to their red blood cell count over the next few weeks. Explain your answer. 20 www.frenglish.ru 2 Properties of materials 2.1 Dissolving Exercise 2.1A Using the correct scientific term Focus This exercise will help you to use the correct scientific terms. Use the terms given below to label the diagrams. Each term may be used once, more than once or not at all. dissolves solution filtrate solute mixture solvent solid volume C A D E B 21 www.frenglish.ru 2 Properties of materials A B C D E Exercise 2.1B What is the difference between these terms? Practice In this exercise, you will practise explaining the difference between terms. 1 Explain the difference between the terms transparent and opaque. 2 Explain the difference between the terms dissolving and melting. 3 Distinguish between the terms solute, solvent and solution. 22 www.frenglish.ru  2.2 Solutions and solubility Exercise 2.1C Explaining observations Challenge In this exercise, you will explain the reasons behind some observations. When 20 g of salt is added to a beaker containing 100 g of water the salt dissolves and seems to disappear as a solution is formed. 1 What is the mass now? 2 Explain your answer. 2.2 Solutions and solubility Exercise 2.2A Using the correct scientific term Focus This exercise will help you to use the correct scientific terms. Use the terms given below to complete the sentences. Each term may be used once, more than once or not at all. 23 www.frenglish.ru 2 Properties of materials concentrated solubility saturated solution soluble insoluble diluted 1 A substance that will not dissolve in water is. 2 Solution A has more solute particles in it than solution B. Solution A is more than solution B. 3 Sofia has added more and more copper sulfate to a beaker of water until no more will dissolve. She has made a of copper sulfate. 4 Copper sulfate dissolves in water so it is said to be in water. 5 Marcus has added 50 cm3 water to a solution of sodium chloride. He has the solution. Exercise 2.2B Looking at the solubility of three solutes Practice This exercise will help you to interpret results. Zara, Arun and Marcus have investigated three solutes, A, B and C to find out how soluble they are. They put water in their test tubes and measured how many spatulas of the solute they could add until no more would dissolve. 24 www.frenglish.ru  2.2 Solutions and solubility Zara has her test tubes ready, with the water added before she starts to add the solutes. Marcus has his test tubes ready, with the water added before he starts to add the solutes. Arun has his test tubes ready, with the water added before he starts to add the solutes. 25 www.frenglish.ru 2 Properties of materials They each use the solutes in the same order and add them to their set of test tubes, working from left to right Here are their results. Number of spatulas of solute used until no more Solute used would dissolve Zara Marcus Arun A 3 3 9 B 1 3 3 C 2 3 6 1 Which solute did Zara find was the most soluble? 2 Which did she find the least soluble? 3 Look carefully at Arun’s results. He has a different number of spatulas of solute added compared to Zara but do Arun’s results agree with Zara’s findings? 4 Explain the difference in the reading that Zara and Arun got. 5 Marcus has the same number of spatulas for all three solutes. Explain why his results are so different from those of Zara and Arun. 26 www.frenglish.ru  2.2 Solutions and solubility Exercise 2.2C Making up a solution Challenge This exercise will help you to work out how to make solutions of the correct concentration. Arun has a solution of copper sulfate labelled X. 1 Explain how he can make up a 100 cm3 solution of copper sulfate that is: a half as concentrated as solution X b a quarter as concentrated as solution X c half as concentrated as the solution in part b. 2 What steps can Arun take to ensure that his solutions are made up as accurately as possible? 27 www.frenglish.ru 2 Properties of materials 2.3 Planning a solubility investigation Exercise 2.3A Dissolving salt Focus If we use more In this exercise, you will interpret a graph and spot mistakes. water I think more Marcus and Sofia are investigating how much salt they can dissolve salts will dissolve. in different volumes of water. The volume of water they use is the independent variable. This is what they do. Sofia measures out the volume of water. Marcus places the beaker of water on a top pan balance and adds salt, one spatula at a time, until no more dissolves. He measures the mass of salt added. Here is their table of results. Volume of water Mass of salt in cm3 in g 10 4 20 9 30 13 40 16 50 20 60 26 70 26 80 30 90 32 100 36 28 www.frenglish.ru  2.3 Planning a solubility investigation Marcus plots this graph from their results. 36 34 32 30 28 26 24 22 20 Mass of salt in g 18 16 14 12 10 8 6 4 2 0 0 10 20 30 40 50 60 70 80 90 100 Volume of water in cm3 1 What was Sofia’s prediction? 2 Which reading is plotted incorrectly? Draw a red circle around it on the graph. 3 Which other point does not fit the pattern of the graph? Draw a blue circle around this mass reading in the table, and around the point on the graph. 4 Draw a line of best fit. 29 www.frenglish.ru 2 Properties of materials 5 Describe what the graph shows. 6 Was Sofia’s prediction correct? Exercise 2.3B Comparing the solubility of two salts: part 1 Practice In this exercise, you will plan an investigation and interpret some results. Arun and Marcus are asked to compare the solubility of two salts in water at room temperature. The two salts are labelled X and Y. 1 Name the independent variable in the investigation. 2 Name the dependent variable in the investigation. 3 List the control variables in the investigation. 30 www.frenglish.ru  2.3 Planning a solubility investigation 4 Describe how Arun and Marcus will carry out this investigation. They have access to normal laboratory equipment. You may draw a diagram if this helps your description. 31 www.frenglish.ru 2 Properties of materials Exercise 2.3C Comparing the solubility of two salts: part 2 Challenge Arun and Marcus carry out the experiment described in Comparing the solubility of two salts: part 1. They find that more of salt X than salt Y can be dissolved in water at room temperature. The boys then investigate the solubility of these two salts at different temperatures. The graph shows the results of their investigation. 100 salt Y 90 salt X 80 70 60 Solubility in g per 50 100g of water 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 190 Temperature in °C 5 At what temperature do the two salts have the same solubility? 6 Which salt is less soluble at 50 °C?. 7 Describe what the graph shows about the solubility of salt X. 32 www.frenglish.ru  2.4 Paper chromatography 8 Describe what the graph shows about the solubility of salt Y. 2.4 Paper chromatography Exercise 2.4A Wordsearch Focus This wordsearch contains words that are used throughout this unit. M O L E N R O C E L O J F L B S O L U T E T S C G W T X S O L A Y A L K A S L P I E N L C H R O M A T O G R A M I U T I O N G I U L R K C K E T U D E R M O R P A I M T D I L U T E B R A E P A T E S O L V E N T A T M H S E A U N P R Y R N X E L F K S K V D E M S A W C D S J A S H D I K D I S S O L V E T M T F L O D B I B C A C L H I X 33 www.frenglish.ru 2 Properties of materials Exercise 2.4B Paper chromatography Practice This exercise will give you practice in interpreting a chromatogram. A food scientist is testing the food colouring used in drinks sold for children. She has to check that any colouring used does not contain any banned chemical. She places drops of the drink on chromatography paper. She uses water to allow the colouring to separate. She also makes another chromatogram of all the permitted chemical colourings. If she finds anything that does not match with these colourings, she will have to carry out further tests. The diagrams show her two chromatograms. chromatogram from the drink chromatogram of the permitted chemicals 1 Why is the spot of drink placed above the water line at the start of the process? 2 How many different colourings has the scientist found in the drink? 3 Draw a circle around the dye in the drink that is not on the permitted list of colourings. 34 www.frenglish.ru  2.4 Paper chromatography 4 Explain why the scientist should carry out further tests on this colouring found in the drink. Exercise 2.4C Paper chromatography with plant material Challenge This exercise will give you practice in interpreting a chromatogram. Sofia has been given some liquid that has been extracted from the petals of a flower. She wants to find out if it is a pure substance or if it is a mixture. She places drops of the liquid on a piece of chromatography paper. The diagram shows what she did. chromatography paper pipette pencil line She was careful to allow each drop of liquid to dry before adding another drop. She placed the paper into a beaker containing water and waited to see the result. After about 15 minutes she saw that the water had moved up the paper but the drop of liquid had not. 1 Explain why this happened. 35 www.frenglish.ru 2 Properties of materials 2 What should Sofia try now? After Sofia changed her investigation, she produced this chromatogram. 3 Label the chromatogram. A B C D E F 4 Why did Sofia dry the drops of liquid before she added more? 5 Is the colour from the petals pure or a mixture? How do you know this? 36 www.frenglish.ru  2.4 Paper chromatography 6 Explain how the liquid was separated. 37 www.frenglish.ru 3 Forces and energy 3.1 Forces and motion Exercise 3.1A Balanced forces Focus In this exercise, you will describe balanced forces. 1 What is needed for two forces to be balanced? Tick (✓) two statements in the table. Statement Needed for forces to be balanced? Two forces must be the same size. Two forces must be different sizes. Two forces must be in the same direction. Two forces must be in opposite directions. 2 A box sits on the ground. The box is not moving. Write ‘true’ or ‘false’ after each statement. a There are no forces acting on the box. b There are balanced forces acting on the box. c There is an unbalanced force acting on the box. 3 Sofia is riding her bicycle. The driving force on the bicycle is balanced with the force of friction on the bicycle. Draw arrows on the diagram to show these forces. Write the names of the forces on the arrows. 38 www.frenglish.ru  3.1 Forces and motion Exercise 3.1B Unbalanced forces Practice skills In this exercise, you will be thinking about the effects of unbalanced forces. 1 Which of these can happen because of unbalanced forces? Tick (✓) all correct statements. A car will move at a constant speed. A boat will slow down. A football will change direction. A book will not move on a desk. 2 The diagram shows the forces on a car. contact force driving friction force weight State: a which forces are balanced and b which forces are unbalanced and c what will happen to the car. 39 www.frenglish.ru 3 Forces and energy Exercise 3.1C Changing direction Challenge In this exercise, you will describe how unbalanced forces can cause a change in direction of movement. 1 The diagram shows the forces, A–D, acting on a bird when it is flying. A D B C a Describe the effect of these forces on the movement of the bird. b Describe one change needed to the forces for the bird to go higher. c Describe two changes to the forces that would make the bird go slower. 1 2 40 www.frenglish.ru  3.1 Forces and motion 2 An aeroplane is flying north, in a straight line, at a constant speed. The aeroplane needs to turn towards east. Draw an arrow on the diagram to show the direction of the unbalanced force needed to make the aeroplane turn east. North West East South 3 Tetherball is a game. A tennis ball is attached to a string. The string can rotate around a vertical pole. The tennis ball moves in a circle around the pole. direction of tennis ball tennis ball pole The tennis ball in the diagram has been hit by a player and is moving in the direction shown. a Draw an arrow on the diagram to show the direction of the force on the tennis ball. Label this arrow F. The string breaks when the tennis ball is at the position shown in the diagram. b Draw another arrow on the diagram to show the direction that the tennis ball will move when the string breaks. Label this arrow D. 41 www.frenglish.ru 3 Forces and energy 3.2 Working out speed Exercise 3.2A Units of speed Focus In this exercise, you will consider the units of speed. 1 a Which of these is the standard unit of distance in science? Circle one unit. metre   foot   mile   kilometre b Which of these is the standard unit of time in science? Circle one unit. day   hour   minute   second c Which of these is the standard unit for speed in science? Circle one unit. m s   m/s   m/s2   m2s 2 Speed can be measured in kilometres per hour, km/h. A motorcycle travels at 60 km/h. What does 60 km/h mean? Tick (✓) one box. It travels a distance of 60 m every second. It travels a distance of 60 m every hour. It travels a distance of 60 km every second. It travels a distance of 60 km every hour. 42 www.frenglish.ru  3.2 Working out speed 3 In the year 2016, a spacecraft reached a speed of 260 000 km/h. Calculate the distance this spacecraft would travel in 2 hours. Show your working. km Exercise 3.2B Calculating speed Practice In this exercise, you will calculate the speeds of some objects. 1 a Write the equation that links speed, distance and time. b Give the unit of speed when distance is in metres and time is in seconds. In each of these calculations, show your working and give the unit with your answer. 2 A car travels a distance of 70 m in a time of 2 s. a Calculate the average speed of the car. 43 www.frenglish.ru 3 Forces and energy The car changes speed to travel a distance of 30 m in a time of 2 s. b Calculate the new speed of the car. 3 Arun walks from home to school. School is a distance of 450 m from Arun’s home. Arun walks this distance in a time of 300 s. a Calculate Arun’s average walking speed. b Explain why your answer to part a is an average speed. 4 An aeroplane travels a distance of 5400 km in a time of 6 hours. Calculate the average speed of the aeroplane, in km/h. 44 www.frenglish.ru  3.2 Working out speed Exercise 3.2C Calculating distance and time Challenge In this exercise, you will use speed to calculate either the distance or the time of travel. 1 a  omplete the equation for calculating distance from speed C and time. distance = b Complete the equation for calculating time of travel from speed and distance. time = In each of these calculations, show your working and give the unit with your answer. 2 A train travels at a constant speed of 45 m/s. a Calculate the distance travelled by the train in: i 30 s ii 2 minutes. 45 www.frenglish.ru 3 Forces and energy 3 Zara runs at a constant speed of 4 m/s. Sofia rides her bicycle at a constant speed of 6 m/s. a Calculate the time taken for Zara to run a distance of 120 m. b Calculate how much further Sofia travels in one minute than Zara does. 4 Marcus’s father plans to travel by car. He needs to travel a distance of 50 km in a time of 2 hours. a Calculate the average speed at which the car must travel. b Explain why the car must go faster than your answer to part a for some parts of the journey. 46 www.frenglish.ru  3.3 Describing movement 3.3 Describing movement Exercise 3.3A Distance–time graphs 1 Focus In this exercise, you will decide what you can work out from a distance–time graph. 1 Which of these can be worked out from a distance–time graph? Tick (✓) one box. the force on an object the speed of an object the mass of an object the weight of an object 2 Look at the distance–time graph for a train. Distance Time a Which of these distance–time graphs shows the train going faster? Write the letter. Distance Distance Distance Distance Time Time Time Time A B C D b Which distance–time graph in part a shows no change in distance with time? Write the letter. 47 www.frenglish.ru 3 Forces and energy Exercise 3.3B Distance–time graphs 2 Practice In this exercise, you will sketch some distance–time graphs. When sketching a graph, you only label the axes with quantities. You do not need to scale the axes or put numbers on the axes. 1 Sketch a distance time graph for: a a stationary object b an object travelling at a constant speed away from a starting position c an object travelling at a constant speed towards a starting position. 48 www.frenglish.ru  3.3 Describing movement 2 Sofia walks from home to a shop. She walks at a constant low speed. She stops to talk to a friend. She continues walking at a higher speed than before. Sketch a distance–time graph of Sofia’s journey from home to the shop. 3 Marcus rides a bicycle at a constant speed from the park to a friend’s house. Marcus stays at his friend’s house for a short time. Marcus rides his bicycle at the same constant speed back again from his friend’s house to the park. Sketch a distance–time graph of Marcus’s journey from the park and back to the park. 49 www.frenglish.ru 3 Forces and energy Exercise 3.3C Distance–time graphs 3 Challenge In this exercise, you will draw a distance–time graph and work out values from the graph. 1 An aeroplane departs from airport A at time 0 hours. The aeroplane takes 4.5 hours to travel to airport B. Airport B is a distance of 3600 km away from airport A. The aeroplane spends 1.5 hours at airport B, before departing again for airport A. The journey back from airport B to airport A takes 4.0 hours. a Draw a distance–time graph of the journey on the grid below. b Use your graph to work out: i the total time of the journey ii the speed of the aeroplane going from airport A to airport B iii the speed of the aeroplane going from airport B to airport A. 50 www.frenglish.ru  3.4 Turning forces 3.4 Turning forces Exercise 3.4A Identifying turning forces Focus In this exercise, you will decide where turning forces are used. 1 Which of these actions needs a turning force to happen? Tick (✓) all that apply. pushing a door open pulling a chair across the floor twisting the top off a bottle pushing the hands of a clock around pushing a trolley up a ramp stretching an elastic band 2 Which of these objects needs a turning force to work? Tick (✓) all that apply. 3 What name is given to the turning effect of a force? Circle one word. minute moment rotate revolve 51 www.frenglish.ru 3 Forces and energy Exercise 3.4B Calculating moments Practice In this exercise, you will calculate moments and make predictions about moments. 1 Write the equation that links moment, force and distance. 2 The picture shows a crane supporting a 15 000 N weight. The weight is supported 5 m from the pivot of the crane. 5m pivot 15 000 N a Calculate the moment caused by the weight on the crane. Show your working. Nm 52 www.frenglish.ru  3.4 Turning forces b Explain the effect on this moment of: i moving the weight further from the pivot ii moving the weight closer to the pivot. 3 Some people use units that are not international standard units. One of these units of distance is the foot. One of these units of force is pounds. Write the unit of moment in these units. Exercise 3.4C Moments, force and distance Challenge In this exercise, you will calculate forces and distances for moments. 1 A spanner will turn a nut. The nut needs a moment of 40 Nm to turn. The spanner is 0.2 m long. spanner nut 0.2 m 53 www.frenglish.ru 3 Forces and energy a Calculate the force that must be exerted on the spanner. Show your working and give the unit. b Explain why using a longer spanner will make the nut easier to turn. 2 An engine exerts a moment of 350 Nm 0.35 m when measured at a wheel. The engine drives a wheel that has a radius of 0.35 m The pivot of the wheel is at the centre. Calculate the force at the outside of the wheel. Show your working and give the unit. 3 Sofia weighs 500 N. She sits on a seesaw at a distance of 2 m from the pivot. 54 www.frenglish.ru  3.5 Pressure between solids a Calculate the moment that Sofia exerts on the seesaw. Show your working and give the unit. The seesaw will balance when the moments on both sides are equal. Zara weighs 400 N. b Calculate the distance from the pivot to where Zara should sit to balance the seesaw. Show your working and give the unit. 3.5 Pressure between solids Exercise 3.5A Describing pressure Focus In this exercise, you will describe what affects pressure in solids. 1 Which of these is used to work out pressure? Tick (✓) one box. force pressure = _____ ​​  area ​​ pressure = mass × area mass pressure = _____ ​​  area ​​ pressure = force × area 55 www.frenglish.ru 3 Forces and energy 2 Zara has four different styles of shoes. Which shoes will exert the greatest pressure on the floor when Zara wears them? Tick (✓) one box. 3 The picture shows a box. The areas of three faces of the box, A, B and C are shown. A = 40 cm2 B = 15 cm2 C = 60 cm2 a Which face of the box will exert the smallest pressure on the floor? Write the letter. b Explain your answer to part a. 56 www.frenglish.ru  3.5 Pressure between solids Exercise 3.5B Calculating pressure Practice In this exercise, you will calculate pressure in solids and think about the units of pressure. 1 A rock exerts a pressure of 20 N/cm2 on the ground. What does 20 N/cm2 mean? Complete the sentence. A force of acts on each of area. 2 A large book has a weight of 15 N. The area of one end of the book is 60 cm2. Calculate the pressure the book exerts when standing on this end. Show your working. N/cm2 3 A nail will go into wood if the pressure on the end of the nail is 60 N/mm2. The area of the end of the nail in contact with the wood is 0.5 mm2. Calculate the force needed on the nail to make it go into the wood. Show your working and give the unit with your answer. 4 Not all of the units used by people are standard scientific units. Some people use other units. One of these other units of force is pounds. One of these other units of area is square inch. State the unit of pressure in these other units. 57 www.frenglish.ru 3 Forces and energy Exercise 3.5C Variables affecting pressure Challenge In this exercise, you will consider the variables that affect pressure in solids. 1 The picture shows part of the stem of a plant called a rose. The stem has parts called thorns. stem thorns Explain why touching the thorns is more dangerous than touching other parts of the stem. 2 Cars can get stuck in sand when a wheel sinks down into the sand. Explain why putting a large piece of wood under the wheel can stop the wheel from sinking. 58 www.frenglish.ru  3.5 Pressure between solids 3 Arun is cutting bread. Explain why a sharp knife is better for cutting bread than a knife that is not sharp. 4 The picture shows a drawing pin. The two ends of the drawing pin are labelled A and B. A B Part A is pushed by your thumb. Part B goes into a wall or drawing board. Explain the shape of each end of the drawing pin. 59 www.frenglish.ru 3 Forces and energy 3.6 Pressure in liquids and gases Exercise 3.6A Trends in pressure 1 Focus In this exercise, you will describe what affects pressure in liquids and gases. 1 State what happens to the pressure in a liquid as depth increases. 2 Where is pressure in the air largest? Tick (✓) one box. at sea level at the top of a mountain at the top of clouds at the top of the atmosphere 3 A car tyre is filled with air. When the car is moving, the temperature of the tyre increases. State what happens to the pressure of the air in the tyre when temperature increases. 4 A plastic bottle is filled with air. The top is on the bottle so the air cannot escape. The bottle is squeezed so the volume decreases. State what happens to the pressure of the air in the bottle when the volume decreases. 60 www.frenglish.ru  3.6 Pressure in liquids and gases Exercise 3.6B Trends in pressure 2 Practice In this exercise, you will think in more detail about what affects pressure in liquids and gases. 1 The picture shows a small fish in deep water. The fish is not moving. The water is not moving. The arrows A, B and C show three directions from which pressure from the water acts on the fish. A B C Which statement is correct? Tick (✓) one box. The pressure in direction A is the largest. The pressure in direction B is the largest. The pressure in direction C is the largest. The pressure is equal in all directions. 2 The picture shows water coming out of three holes in a bottle. Describe the conclusion that can be made from this observation. 61 www.frenglish.ru 3 Forces and energy 3 A balloon is filled with air. The balloon is then sealed so that air cannot escape. a State what will happen to the pressure inside the balloon if the temperature decreases. b Explain your answer to part a. Exercise 3.6C Trends in pressure 3 Challenge In this exercise, you will demonstrate understanding of changes in pressure in gases. 1 A balloon is filled with air. The balloon is then sealed so that air cannot escape. The diameter of the balloon is 20 cm. Very cold liquid is poured over the balloon. The balloon becomes smaller until its diameter is 5 cm. Explain this observation. 62 www.frenglish.ru  3.6 Pressure in liquids and gases 2 The tyres on an aeroplane are filled with nitrogen gas. The aeroplane is at an altitude of 11 000 m. The temperature of the tyres is −50°C. The aeroplane lands on the ground 30 minutes later. The temperature of the tyres is now 25°C. a Sketch a graph of the atmospheric pressure outside the aeroplane during this 30 minutes. Atmospheric pressure Time b Sketch a graph of the gas pressure inside the tyres during this 30 minutes. Gas pressure in tyres Time 63 www.frenglish.ru 3 Forces and energy 3.7 Particles on the move Exercise 3.7A Diffusion in gases and liquids Focus In this exercise, you will describe what happens when gases mix and when liquids mix. 1 Two glass jars are kept apart with a seal. One jar contains a coloured gas. The other jar contains a colourless gas. gas jar seal gas jar The seal is removed. Draw the arrangement of particles in the jars some time after the seal was removed. 64 www.frenglish.ru  3.7 Particles on the move 2 A small volume of coloured ink is placed into a beaker of water. The diagram shows the particles in the ink just after adding to the water. Draw the arrangement of ink particles in the water a long time after the ink was added. Exercise 3.7B Diffusion Practice In this exercise, you will describe diffusion in terms of particle movement in gases and liquids. 1 Describe what is meant by diffusion. 65 www.frenglish.ru 3 Forces and energy 2 A small volume of blue ink is added to a beaker of water. There is blue colour only at the bottom of the beaker. a Explain why the water eventually all turns blue. b Explain why the water turns blue faster when the temperature of the water is higher. 3 Bromine is a brown liquid that evaporates easily at room temperature. When a container of bromine is opened, brown gas comes out of the container. Explain why the colour of the brown gas becomes less intense as it gets further away from the container. 4 A green gas is added to a bottle that contains air. A short time later, the green colour has spread to fill the bottle. Write true or false next to each statement. When the green colour fills the bottle, the movement of particles has stopped.. When the green colour fills the bottle, diffusion has stopped.. 66 www.frenglish.ru  3.7 Particles on the move Exercise 3.7C Variables affecting diffusion Challenge In this exercise, you will think of variables that affect the speed of diffusion. 1 A purple crystal is added into the bottom of a large beaker of water. When the crystal dissolves, the liquid turns purple. Eventually, all the liquid is purple. a Explain why the purple colour is more intense when the crystal first dissolves and less intense when it has spread through all the liquid. Stirring speeds up the spreading of the purple colour. b List two other changes that would speed up the spreading of the purple colour. 1 2 2 Sofia makes two cups of coffee. One is cold and the other is hot. The cups and the coffee are the same in all other ways. Zara says that the hot coffee has a stronger smell than the cold coffee. Explain why this is the case. 67 www.frenglish.ru 3 Forces and energy 3 Many animals use smell to find food. Explain how these animals know what direction to move to get to the food. 68 www.frenglish.ru 4 Ecosystems 4.1 The Sonoran desert Exercise 4.1 The Sonoran desert ecosystem In this exercise, you will practise finding and using information in a written passage. You will think about different habitats in an ecosystem. You will also consider how different species interact with each other in an ecosystem, and how the loss of one species could affect others. Focus Saguaro cacti are found only in the Sonoran desert in Arizona, USA. They can live to be 200 years old. Saguaro cacti grow in dry places, where it rains only occasionally. Their roots spread out widely, just below the soil surface. This means that they can capture a lot of water when it rains. They do not have leaves, because water would evaporate from them. The plant would dry out. Instead, the cactus uses its green stems to make food by photosynthesis. Saguaro cacti cannot grow in places where the temperature falls below 0°C. Their cells are killed if they freeze. There are sharp spines on the cactus stems, which protect them from being eaten by animals. 69 www.frenglish.ru 4 Ecosystems 1 Describe the habitat of the saguaro cactus. 2 Describe two ways in which the saguaro cactus is adapted to live in this habitat. 3 It is much colder on the mountains than in the desert. Explain why saguaro cacti cannot grow on the high mountains. Practice Saguaro cacti provide habitats and food for other species in the desert. Some species of birds, including Gila woodpeckers and gilded flickers, use their beaks to make nest holes in their stems. After these birds have left the nest, other birds such as elf owls use the holes. Harris hawks make their nests of sticks where the arms of the cactus branch from the main stem. The cactus flowers produce pollen and nectar. These are eaten by bats, which pollinate the flowers. The flowers produce fruits after they have been pollinated. The fruits are eaten by birds, mammals and reptiles, such as desert tortoises. 70 www.frenglish.ru  4.1 The Sonoran desert 4 Use this information to suggest how the Saguaro desert ecosystem would be affected if: all the Gila woodpeckers and gilded flickers died out all the saguaro cacti died out. Challenge Many parts of Arizona have plenty of rainfall. They provide habitats for many different species of plant. 5 Suggest why saguaro cacti do not grow in these wetter areas. 71 www.frenglish.ru 4 Ecosystems 4.2 Different ecosystems Exercise 4.2A A tropical rainforest ecosystem Focus This exercise gives you practice in using the correct words when you are writing about ecosystems and habitats. Complete the sentences. Use each of these words once only. decomposers ecosystem  environment  habitats  nutrients Tropical rainforests grow where the temperature is always high and there is plenty of rainfall. Many different species of plant grow in the rainforest. The rainforests provide and food for many different species of animal. On the forest floor, fungi break down dead leaves and waste from the animals. These fungi are. The fungi release from the dead leaves and waste, which help the plants to grow. All of the plants, animals and fungi interact with one another. They also interact with the non-living parts of their. This network of interactions makes up the tropical rainforest. Exercise 4.2B Hydrothermal vents Practice In this exercise, you will think about a very unusual ecosystem. You will use information to construct a food chain, and think about the different habitats in the ecosystem. In 1977, a completely new ecosystem was discovered. In the deep ocean, below the surface, scientists found places where hot water rushes out from the sea bed into the water. 72 www.frenglish.ru  4.2 Different ecosystems These places are called hydrothermal vents. ‘Hydro’ means water, ‘thermal’ means heat, and a vent is an opening that things can pass through. No-one expected to find any life at a hydrothermal vent. It is completely dark. The water temperature can be as high as where it pours out, although it cools as it mixes with the sea water. But the scientists found many living organisms in this strange ecosystem. Instead of plants, tiny bacteria are the producers in the food chain. Instead of using energy from light to make food, they use energy in the chemicals dissolved in the hot water. The bacteria are able to survive in much higher temperatures than most living things. Giant tube worms also live at hydrothermal vents. Some of the bacteria live inside the tube worms. The worms provide a habitat for the bacteria, and use some of the food that the bacteria make. Other bacteria live in the hot water around the vent. They form thick mats on the sea floor. The bacteria are eaten by shrimps and tiny floating animals called zooplankton. The zooplankton are eaten by sea anemones. Crabs and octopuses eat sea anemones and tube worms. 1 Explain why plants cannot live at a hydrothermal vent. 2 Construct a food chain, containing four types of organism, that occurs at a hydrothermal vent. 3 Name the producer in your food chain. 73 www.frenglish.ru 4 Ecosystems 4 Where does this producer obtain its energy from? 5 Describe two different habitats in the hydrothermal vent ecosystem. Exercise 4.2C Mangroves and fish Challenge In this exercise, you will read about an experiment to find out how one ecosystem can affect another. The first ecosystem is a mangrove forest, and the second is a coral reef. You will also practise using data to draw conclusions. Mangroves are trees that grow on muddy seashores in tropical regions. Their roots are covered by sea water when the tide is high. Mangroves have unusual root systems that help to support them in the mud. The mangrove ecosystem provides habitats for many different animals. Baby fish often spend their early lives amongst the mangrove roots, safe from predators such as larger fish. Ecologists wanted to find out whether the presence of mangroves affected the numbers of fish in nearby coral reef ecosystems. They collected samples of four species of fish on several coral reefs where there were mangroves on the shore, and on several coral reefs where there were no mangroves. They measured the mass of each fish. The table shows their results. The mass is given in kg/km2. This means the number of kilograms of that kind of fish in an area of one square kilometre of coral reef. Mass of fish on coral reef in (kg/km2) Species of fish Mangroves on the No mangroves on shore the shore striped parrotfish 2170 1530 blue-striped grunt 447 288 yellowtail 6715 3098 schoolmaster 1898 1767 74 www.frenglish.ru  4.2 Different ecosystems 1 Explain the meaning of each of these words. habitat ecosystem predator 2 Which species of fish has the largest mass on coral reefs where there are mangroves on the shore? 3 Describe how the masses of fish on coral reefs where there are no mangroves on the shore differ from coral reefs where there are mangroves on the shore. 4 Suggest reasons for the difference that you have described in your answer to question 3. 75 www.frenglish.ru 4 Ecosystems 4.3 Intruders in an ecosystem Exercise 4.3A Beavers in South America Focus This exercise is about an invasive species in South America. You need to read the information carefully, then write answers in your own words. Beavers are mammals that live in streams and rivers in North America. They have thick, soft, waterproof fur. Beavers make dams in rivers. The dams slow down the river water and form deep, wide pools. Beavers use their sharp teeth to cut down trees to build their dams. 1 What is the habitat of beavers? 2 Describe how beavers change the habitat that they live in. 76 www.frenglish.ru  4.3 Intruders in an ecosystem In 1946, some beavers were taken to Tierra del Fuego in South America, to breed for their fur. Today, no beavers are used for fur. But the beavers still live in Tierra del Fuego. The numbers of beavers have increased. Their dams have caused a lot of damage to local ecosystems. 3 In North America, beavers are killed and eaten by brown bears. Some people have suggested introducing brown bears to Tierra del Fuego, to control the beavers. Suggest why this might not be a good idea. 77 www.frenglish.ru 4 Ecosystems Exercise 4.3B Water hyacinth Practice This exercise is about a plant that has become an invasive species in many different countries. You will practise finding information in a passage. You will combine this information with your own knowledge to answer questions. Water hyacinths are South American plants that live in fresh water. They have tough, green leaves that float on the water surface. They also have beautiful blue flowers. In South America, several herbivores feed on water hyacinth. The herbivores help to stop the number of water hyacinth plants increasing too much. Water hyacinths have been introduced to many countries outside South America. They are an invasive species in many aquatic ecosystems. They have multiplied rapidly, covering vast areas of rivers and lakes. They make such a thick covering that light and oxygen cannot reach the water below. This kills native plants and fish. On Lake Victoria, in Tanzania and Uganda, there is so much water hyacinth that the fishing boats cannot move through it. The fishing nets catch water hyacinth, not fish. 78 www.frenglish.ru  4.3 Intruders in an ecosystem 1 Explain the meaning of each of these words. herbivore invasive species aquatic 2 Explain why water hyacinths are not an invasive species in South America. 3 Explain two ways in which water hyacinth is causing problems in Lake Victoria. Use your own words. First way Second way 79 www.frenglish.ru 4 Ecosystems Exercise 4.3C Cane toads in Australia Challenge This exercise is about a new, invasive species in Australia, and the effects that it has had on other organisms in the local ecosystems. You will plan an experiment to find out if a strategy that is trying to save a native predator is working. Cane toads are huge toads that live naturally in South America. In 1935, 101 cane toads were brought to northern Australia. This was done because the toads eat beetles that were destroying sugar cane. The toads bred rapidly. They have now spread to most parts of northern Australia. Cane toads are poisonous. In South America, they have many predators. These help to keep the numbers of cane toads under control. However, in Australia, predators that eat cane toads often die. This has reduced the numbers of many rare Australian animals, such as the northern quoll. Scientists in Australia are trying to teach wild northern quolls not to eat cane toads. They are making little sausages of cane toad meat and feeding them to the quolls. This makes the quolls vomit, but does not kill them. The scientists hope that the quolls will learn to avoid cane toads. 80 www.frenglish.ru  4.3 Intruders in an ecosystem 1 Suggest why the numbers of cane toads have increased rapidly in Australia, whereas in their native South America the numbers stay fairly constant. 2 Suggest an experiment that the scientists could do, to test this hypothesis: Feeding cane toad sausages to northern quolls helps to stop them eating cane toads. Remember to think about variables that the scientists should change, measure or keep the same. Predict the results that you would expect if the hypothesis is supported. 81 www.frenglish.ru 4 Ecosystems 4.4 Bioaccumulation Exercise 4.4A Microplastics In this exercise, you will learn about microplastics. You can try finding information in a bar chart. You will also think about bioaccumulation. Focus Microplastics are tiny pieces of plastic less than long. Some microplastics come from big pieces of plastic that people have thrown away, and that slowly break apart. Some microplastics come from healthcare and beauty products such as toothpastes and face creams. In the sea, microplastics can float in the water. They are accidentally taken into the bodies of living organisms when they feed. Some of the denser microplastics slowly fall to the sea bed. 1 What are microplastics? 2 Explain where microplastics come from. 3 Explain why some microplastics end up in the mud at the bottom of the sea. 82 www.frenglish.ru  4.4 Bioaccumulation Practice The graph shows the quantities of microplastics found in the mud at the bottom of the sea in four years between 1996 and 2008. 160 140 120 100 mean number of microplastic particles 80 in kg of mud 60 40 20 0 1996 2000 2004 2008 Time in years 4 Look at the graph. a State the mean mass of microplastics found in 1 kg of mud in 1996. b Calculate the increase in the mass of microplastics in 1 kg of mud between 1996 and 2008. Show your working. 83 www.frenglish.ru 4 Ecosystems 5 Zooplankton are tiny floating organisms that live in the sea. Some fish feed by sucking in sea water and filtering out the zooplankton. Explain why these fish may end up with microplastics in their bodies. Challenge 6 Microplastics cannot be broken down by living things. They show bioaccumulation. Explain what is meant by bioaccumulation. 7 Seals eat fish. Explain why the concentration of microplastics in a seal’s body may be greater than the concentration in a fish’s body. 84 www.frenglish.ru  4.4 Bioaccumulation Exercise 4.4B Bias In this exercise you will look at some information and decide if it could be biased. Focus Some farmers have noticed that their maize crop is being badly damaged by insect pests that are new to the area. Maize is a very important crop for these farmers as they make most of their money from it. Some agricultural chemical companies are advertising a spray that will kill these insects. The chemical company says that the success rate of killing the insects is 90% and that there is only a very slight risk to animals or humans eating the maize. The farmers do not want to use anything that could be harmful to any animal or person who eats the maize. The farmers are concerned that the information from the chemical company may be biased. 1 Why do they think the information may be biased? Practice There is another company that breeds and sells predators of these insect pests and they say there is a 100% success rate and that this method of pest control is “environmentally friendly”. They state that these predators are not harmful other insects and they only feed on this particular species. These predators are not local to the area. The farmers think this sounds a much better idea. 2 Could this also be biased information? Explain your answer. 85 www.frenglish.ru 4 Ecosystems 3 What do you think the company mean by term “environmentally friendly”? 4 If the predators of these insect pests do eat other insects what problems could this cause? Challenge The farmers contact the government agriculture department who give the farmers more advice. They explain that the chemical spray is being investigated as it has been link