Cambridge IGCSE Biology Coursebook (3rd Edition) PDF

Cambridge IGCSE Biology, Third edition Coursebook with CD-ROM Mary Jones and Geoff Jones Cambridge IGCSE Biology Third edition Cambridge IGCSE Biology, Third edition matche...

Cambridge IGCSE Biology, Third edition Coursebook with CD-ROM Mary Jones and Geoff Jones Cambridge IGCSE Biology Third edition Cambridge IGCSE Biology, Third edition matches the requirements of the latest Cambridge IGCSE Biology syllabus (0610). It is endorsed by Cambridge International Examinations for use with their exams. The Coursebook content has been revised and rearranged, ensuring that it is up to date and comprehensive in its coverage, with supplementary material clearly marked. A Workbook and Teacher’s Mary Jones and Geoff Jones Cambridge IGCSE® Resource are also available. The Coursebook contains: total coverage of the syllabus Biology language accessible to students of a wide range of abilities a clear indication of the chapter content at the beginning of each chapter activities to help students develop practical and investigative skills study tips throughout to aid with understanding highlighted definition boxes covering every definition required by the syllabus in-chapter questions and end-of-chapter questions, including exam‑style questions to test students’ knowledge summaries at the end of each chapter a glossary of key biological terms. Coursebook The accompanying CD-ROM contains: Coursebook advice on how to revise for and approach exams self-assessment check lists for making drawings, constructing and completing results tables, drawing graphs and designing experiments Third edition revision check lists for each chapter answers to the end-of-chapter questions, including the exam‑style questions model exam papers and mark schemes multiple-choice self tests and answers expanded notes on the activities from the Coursebook with full teacher/technician notes for the activities a series of animations to aid understanding. Other components of Cambridge IGCSE Biology, Third edition: Workbook ISBN 978-1-107-61793-2 Jones and Jones Teacher’s Resource ISBN 978-1-107-61496-3 Completely Cambridge – Cambridge resources for Cambridge qualifications Cambridge University Press works closely with Cambridge International Examinations as parts of the University of Cambridge. We enable thousands of students to pass their Cambridge exams by providing comprehensive, high-quality, endorsed resources. To find out more about Cambridge International Examinations visit www.cie.org.uk Visit education.cambridge.org/cie for more information on our full range of Cambridge International A Level titles including e-book versions and mobile apps. Original material © Cambridge University Press 2014 IGCSE_Biology_Coursebook_Cover.indd 1 29/08/2013 11:38 Mary Jones and Geoff Jones Cambridge IGCSE® Biology Coursebook Third edition Original material © Cambridge University Press 2014 i University Printing House, Cambridge CB2 8BS, United Kingdom 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/9781107614796 © Cambridge University Press 2002, 2014 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. 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Original material © Cambridge University Press 2014 Contents Introduction v 7 Animal nutrition 73 7.1 Diet 74 1 Classification 1 7.2 Digestion 78 1.1 Characteristics of living things 1 7.3 Teeth 80 1.2 Classification 2 7.4 The alimentary canal 82 1.3 The kingdoms of living organisms 6 7.5 Assimilation 89 1.4 Viruses 9 1.5 Classifying animals 9 8 Transport in plants 93 1.6 Classifying plants 12 8.1 Plant transport systems 94 1.7 Keys 15 8.2 Water uptake 96 8.3 Transpiration 97 2 Cells 18 8.4 Transport of manufactured food 102 2.1 Cell structure 19 2.2 Cells and organisms 25 9 Transport in animals 106 9.1 Circulatory systems 108 3 Movement in and out of cells 28 9.2 The heart 109 3.1 Diffusion 29 9.3 Blood vessels 113 3.2 Osmosis 30 9.4 Blood 117 3.3 Active transport 35 9.5 Lymph and tissue fluid 122 4 The chemicals of life 40 10 Pathogens and immunity 127 4.1 What are you made of? 41 10.1 Pathogens 128 4.2 Carbohydrates 41 10.2 Body defences 129 4.3 Fats 44 10.3 The immune system 133 4.4 Proteins 45 4.5 DNA 47 11 Respiration and gas exchange 140 11.1 Respiration 141 5 Enzymes 49 11.2 Gas exchange in humans 143 5.1 Biological catalysts 50 11.3 Breathing movements 146 5.2 Properties of enzymes 51 12 Excretion 153 6 Plant nutrition 58 12.1 Excretory products 154 6.1 Types of nutrition 59 12.2 Nitrogenous waste 154 6.2 Photosynthesis 59 12.3 The human excretory system 156 6.3 Leaves 59 6.4 Uses of glucose 64 6.5 Testing leaves for starch 65 6.6 Limiting factors 69 6.7 The importance of photosynthesis 70 Original material © Cambridge University Press 2014 Contents iii  13 Coordination and response 161 20 Organisms and their environment 264 13.1 Coordination in animals 162 20.1 Ecology 265 13.2 The human nervous system 162 20.2 Energy flow 265 13.3 Receptors 165 20.3 Nutrient cycles 270 13.4 The endocrine system 170 20.4 Population size 272 13.5 Coordination and response in plants 172 21 Biotechnology 280 14 Homeostasis 178 21.1 What is biotechnology? 281 14.1 Maintaining the internal environment 179 21.2 Using yeast 281 14.2 Control of body temperature 179 21.3 Making use of enzymes 282 14.3 Control of blood glucose concentration 184 21.4 Penicillin 284 21.5 Genetic engineering 286 15 Drugs 188 15.1 What is a drug? 189 22 Humans and the environment 292 15.2 Medicinal drugs 189 22.1 Food production 293 15.3 Misuse of drugs 190 22.2 Habitat destruction 296 15.4 Tobacco smoking 192 22.3 Pollution 299 22.4 Conservation 307 16 Reproduction in plants 197 16.1 Asexual reproduction 198 16.2 Sexual reproduction 198 Answers to questions 318 16.3 Sexual reproduction in flowering plants 200 16.4 Comparing sexual and asexual reproduction 208 Glossary 330 17 Reproduction in humans 212 Index 339 17.1 Human reproductive organs 213 17.2 Fertilisation and development 215 Acknowledgements 000 17.3 The menstrual cycle 220 17.4 Birth control 222 Terms and Conditions of use for 17.5 Sexually transmitted infections 225 the CD-ROM 000 18 Inheritance 230 CD-ROM 18.1 Chromosomes 231 Activities 18.2 Cell division 231 Notes on activities for teachers/technicians 18.3 Inheritance 235 Self-assessment checklists 18.4 DNA and protein synthesis 243 Answers to end-of-chapter questions Study and revision skills 19 Variation and natural selection 247 Revision checklists 19.1 Variation 248 Self-assessment tests 19.2 Adaptive features 250 Model papers and mark schemes 19.3 Selection 253 Help Notes Animations iv Cambridge IGCSE Biology Original material © Cambridge University Press 2014  Introduction This book has been written to help you to do well in There are two possible exams to test your practical your Cambridge International Examinations IGCSE skills, called Paper 5 and Paper 6. Your teacher will tell Biology examination (0610). We hope that you enjoy you which of these you will be entered for. They are using it. equally difficult, and you can get up to Grade A* on The book can also be used with the Cambridge ‘O’ either of them. You should try to do the Activities no level Biology syllabus (5090). matter which of these papers you are entered for. Core and Supplement Summary Your teacher will tell you whether you are studying just At the end of each chapter, there is a short list of the the Core part of the Biology syllabus, or whether you main points covered in the chapter. Remember, though, are studying the Supplement as well. If you study the that these are only very short summaries, and you’ll Core only, you will be entered for Papers 1 and 3 and need to know more detail than this to do really well in either Paper 5 or 6, and can get a maximum of Grade C. the exam. If you also study the Supplement, you may be entered The CD-ROM for Papers 2 and 4, and either Paper 5 or 6, and will be There is a CD-ROM in the back of the book. You’ll also able to get a maximum of Grade A*. The Supplement find the Summaries on the CD-ROM. You can use the S material in this book is marked by a letter ‘S’ and brown revision checklists on the CD-ROM to check off how far bars in the margin, like this. you have got with learning and understanding each idea. Definitions The CD-ROM also contains a set of interactive There are quite a lot of definitions in the IGCSE syllabus multiple-choice questions testing whether you know that you need to learn by heart. These are all in this and understand the material from each chapter. book, at appropriate points in each chapter, inside boxes You’ll find some self-assessment checklists on the with a heading ‘Key definition’. Make sure you learn CD-ROM too, which you can print off and use to assess these carefully. yourself each time you observe and draw a specimen, Questions construct a results chart, draw a graph from a set Each chapter has several sets of Questions within it. of results or plan an experiment. These are all very Most of these require quite short answers, and simply important skills, and by using these checklists you test if you have understood what you have just read (or should be able to improve your performance until you what you have just been taught). can do them almost perfectly every time. At the end of each chapter, there are some longer There are some suggestions on the CD-ROM about questions testing a range of material from the chapter. how you can give yourself the very best chance of doing Some of these are past questions from Cambridge exam well in your exams, by studying and revising carefully. papers, or are in a similar style to Cambridge questions. There are also some practice exam papers. Activities Workbook Each chapter contains Activities. These will help you to There is a workbook to go with this textbook. If you develop the practical skills that will be tested in your have one, you will find it really helpful in developing IGCSE Biology examination. There are more Activities your skills, such as handling information and solving on the CD-ROM. These are marked with this symbol: problems, as well as some of the practical skills. Original material © Cambridge University Press 2014 v  Acknowledgements Cover xxxx p. 1 Alamy; 2 Geoff Jones; pp. 7t, 7b Alamy; p. 11 Ian Esland xx; p.15 Geoff Jones; p. 17 Geoff Jones; p. 18 Kenneth Ingram; pp. 20t, 20b Eleanor Jones; p. 21 Biophoto Associates/SPL; p.22t, 22b,22br SPL; p. 26 SPL; p. 28 Alamy; p. 34 Geoff Jones; p. 40 SPL; p. 42 SPL; p. 43 SPL; p. 44 Alamy; p.45 SPL; 46t, 46b SPL; p. 49 Alamy; p. 58 SPL; p. 61t Biophoto Associates/SPL; p.61b SPL; p. 61r Andrew Syred/SPL; p. 65 Nigel Cattlin/Alamy; p. 67 Alamy; p. 73 SPL; p. 75 7.3-7.6 Geoff Jones; p. 77l Alex Segre/Alamy; p. 77r Images of Africa Photobank/Alamy; p. 87 Biophoto Associates/SPL; p. 88l SPL; p.88r SPL; p. 93 Alamy; p. 94 Andrew Syred/SPL; p. 95 J.C. Revy/SPL; p.96t SPL; p. 96b SPL; p. 106 Alamy; p. 110 Alamy; p. 112 Alamy; p. 114 Janine Photolibrary/Alamy; p. 115 Prof. P. Motta/Dept. of Anatomy/University “La Sapienza”, Rome/SPL; pp. 118, 120, 121 Phototake Inc./Alamy; p. 127 Alamy;p. 129t Alamy; p. 129b Alamy; p. 130 Alamy; p. 131 Alamy; p. 132l Alamy; p. 132r Alamy; p. 136 Alamy; p. 137 Alamy; p. 140 Alamy; p. 150 Rick Rickman/NewSport/Corbis; p. 153 Alamy; p. 161 SPL; p. 164 Wendy Lee; p. 165 Visual Ideas/Nora/Corbis; p. 175 SPL; p. 178 Alamy; p.185l SPL; p. 186r SPL; p. 188 Alamy; p. 189t CNRI/SPL; p.189b Alamy; p. 191l Zuma Press/Zuma/Corbis; 191r St Bartholomew’s Hospital/SPL; p. 192 XXXX; pp 194l, 194r Biophoto Associates/SPL; p. 195 SPL; p. 197 Alamy; p. 201 Geoff Jones; p. 202t Alamy: p. 202b Pictox/Alamy; p. 204 SPL; p. 208 Alamy; p. 212t SPL; p. 212b SPL; p. 215 Alamy; p. 219 Alamy; p. 225 SPL; p. 230 Alamy; p. 231l Chery Power/SPL; 231r CNRI/SPL; p. 232 Leonard Lessin/FBPA/SPL;p. 239 Alamy; p. 247l Alamy; p. 247r Alamy; p. 248 tr Wendy Lee; p. 248t Imagebroker/Alamy; p. 248b Sam Sangster/Alamy; p. 251l Alamy; p 251tr Alamy; p. 251br Geoff Jones; p. 253l Jayanta Dey/epa/Corbis; p 253r Mary Evans Picture Library/Alamy; p.254 Pat & Tom Leeson/SPL; p. 255 Stephen Dalton/NHPA; p. 257 Agence Nature/NHPA; p. 259tb Geoff Jones; p. 259br Terry Matthews/Alamy; p. 262 Alamy; p. 264 SPL; p. 278 SPL; p. 280 SPL; p. 281 SPL; p. 282l SPL; p. 282r SPL; p. 283 SPL; p. 287 SPL; p. 292 Alamy; p. 293bl David South/Alamy; 293tr David R. Frazier Photolibrary, Inc/Alamy; p. 294tl SPL; p. 294tr Alamy; p. 294bl SPL; p. 295t Alamy; p295b Alamy; p. 296l Gideon Mendel for Action Aid/Corbis; p. 296r Alamy; p. 297tl Alamy; 297bl Sylvia Cordaiy Photo Library Ltd/Alamy; p. 297tr Geoff Jones; p.297br Geoff Jones; p. 301l Lou Linwei/Alamy; p. 301r Jim West/Alamy; p. 303 Blickwinkel/Alamy; p. 305 Nigel Cattlin/Alamy; p. 306 Alamy; p. 308 Alamy; p. 312 Alamy; p. 313 Alamy; p.314l Alamy; p. 314tr Alamy; p. 314br Alamy; p. 315 Alamy Abbreviations SPL = Science Photo Library t = top, b = bottom, l = left, r = right Layout and illustration by Greenhill Wood Studios vi Cambridge IGCSE Biology Original material © Cambridge University Press 2014 1 Classification In this chapter, you will find out about: ♦ the characteristics of living things ♦ naming organisms using the binomial system ♦ how living organisms are classified ♦ how to use dichotomous keys to identify organisms. The puzzle of the platypus word means ‘nose like a bird’ and the second means In 1788, British settlers arrived in Australia. They ‘puzzling’. This is the Latin name that is used for the were amazed by many of the animals that they saw, animal today. and a strange animal with fur, webbed feet and a Although the Latin name Platypus could not be beak was among the most puzzling (Figure 1.1). used, people still called the animal a platypus. In People had already been living in Australia for the following years, proof was found that platypuses almost 50 000 years, and different groups of these lay eggs, rather than giving birth to live young. indigenous people had various names for this However, they feed their young on milk, which animal, such as dulawarrung. But the British arrivals is a characteristic feature of mammals. Scientists were not satisfied with just giving the animal a name. eventually decided to classify the platypus as a They wanted to classify it – to decide which group of mammal, despite its odd beak and the fact that it animals it belonged in. lays eggs. It was put into a new group of mammals, And this was where the problem began. The called monotremes, which also includes the echidnas animal had a beak and webbed feet, like a duck. It (spiny anteaters). had fur, like a mole. No-one knew whether it laid eggs or gave birth to live young. So was it a bird? Was it a mammal? No-one could decide. In 1799, a dead specimen of this strange animal was taken to England, where it was studied by Dr George Shaw. To begin with, he thought it was a hoax. He looked very carefully to see if someone had stitched the beak onto the head, but no – it was clearly a genuine part of the animal. Dr Shaw gave the animal a Latin name, Platypus anatinus. ‘Platypus’ means ‘flat-footed’ and ‘anatinus’ means ‘like a duck’. However, someone then pointed out that the name Platypus had already been taken, and belonged to a species of beetle. So another name was suggested by a German scientist, who gave it the name Ornithorhynchus paradoxus. The first Figure 1.1 The platypus is superbly adapted for hunting prey in water. Original material © Cambridge University Press 2014 Chapter 1: Classification 1  1.1 Characteristics of living things objects that are not alive (Figure 1.2). The definitions of Biology is the study of living things, which are often these characteristics are shown in the boxes below and called organisms. Living organisms have seven features on the opposite page. You should learn these definitions or characteristics which make them different from now, but you will find out much more about each of them later in this book. Growth All organisms begin Movement All organisms are able to move Sensitivity All organisms pick up small and get larger, by the growth to some extent. Most animals can move their information about changes in their of their cells and by adding new whole body from place to place, and plants can environment, and react to cells to their bodies. slowly move parts of themselves. the changes. Excretion All organisms Reproduction Nutrition Organisms Respiration All organisms produce unwanted or toxic waste Organisms are able to take substances from their break down glucose and products as a result of their make new organisms environment and use them to other substances inside their metabolic reactions, and these of the same species as provide energy or materials cells, to release energy that must be removed from the body. themselves. to make new cells. they can use. Figure 1.2 Characteristics of living organisms. Key definitions movement – an action by an organism causing a reproduction – the processes that make more of the change of position or place same kind of organism respiration – the chemical reactions in cells that excretion – removal from organisms of toxic break down nutrient molecules and release energy materials and substances in excess of requirements sensitivity – the ability to detect and respond to nutrition – taking in of materials for energy, growth changes in the environment and development growth – a permanent increase in size 2 Cambridge IGCSE Biology Original material © Cambridge University Press 2014  Key definitions S movement – an action by an organism or part growth – a permanent increase in size and dry mass S of an organism causing a change of position by an increase in cell number or cell size or both or place excretion – removal from organisms of the waste respiration – the chemical reactions in cells that products of metabolism (chemical reactions in break down nutrient molecules and release energy cells including respiration), toxic materials and for metabolism substances in excess of requirements sensitivity – the ability to detect or sense stimuli in nutrition – taking in of materials for energy, growth the internal or external environment and to make and development; plants require light, carbon appropriate responses dioxide, water and ions; animals need organic compounds and ions and usually need water In addition to these seven characteristics, living that lived long ago. The ancestor that they all share organisms have another feature in common. When we is called a common ancestor. The common ancestor study living organisms under a microscope, we can see that gave rise to all the mammals lived more than 200 that they are all made of cells. These cells all have: million years ago. ♦ cytoplasm We would therefore expect all mammals to have ♦ a cell membrane bodies that have similar structures and that work in ♦ a chemical called DNA, making up their genetic similar ways. If we find a new animal that has hair and material suckles its young on milk, then we know that it belongs S ♦ ribosomes, which are used for making proteins inside in the mammal group. We will already know a lot about the cell it, even before we have studied it at all. ♦ enzymes that are used to help the cell to carry out anaerobic respiration. Using DNA to help with classification S You can find out more about the structure of cells in In the past, the only ways that biologists could decide Chapter 2. which organisms were most closely related to each other was to study the structure of their bodies. They looked 1.2 Classification carefully at their morphology (the overall form and Classification means putting things into groups. There shape of their bodies, such as whether they had legs or are many possible ways in which we could group living wings) and their anatomy (the detailed body structure, organisms. For example, we could put all the organisms which could be determined by dissection). We still use with legs into one group, and all those without legs into these methods of classification today. But we now have another. Or we could put all red organisms into one new tools to help to work out evolutionary relationships, group, and all blue ones into another. The first of these and one of the most powerful of these is the study ideas would be much more useful to biologists than of DNA. the second. DNA is the chemical from which our chromosomes The main reason for classifying living things is to are made. It is the genetic material, passed on from make it easier to study them. For example, we put one generation to the next. You can read more about humans, dogs, horses and mice into one group (the its structure in Chapter 4, where you will find out that mammals) because they share certain features (for each DNA molecule is made up of strings of smaller example, having hair) that are not found in other molecules, containing four different bases. These bases, groups. We think that all mammals share these features called A, C, G and T, can be arranged in any order. because they have all descended from the same ancestor Biologists can compare the sequences of bases in the Original material © Cambridge University Press 2014 Chapter 1: Classification 3 S DNA of organisms from two different species. The more Species are grouped into larger groups called genera similar the base sequences, the more closely related the (singular: genus). Each genus contains several species species are to one another. They have a more recent with similar characteristics (Figure 1.3). Several genera common ancestor than species that have DNA base are then grouped into a family, families into orders, sequences that are less similar. orders into classes, classes into phyla and finally phyla into kingdoms. Some of the more important groups are The classification system described in this chapter. The first person to try to classify organisms in a Figure 1.3 shows five animals that all belong to the scientific way was a Swedish naturalist called Linnaeus. mammal order. You can see that they all have hair, He introduced his system of classification in 1735. which is a characteristic feature of mammals. The He divided all the different kinds of living things into animals have been classified into two groups – groups called species. He recognised 12 000 different horse-like mammals and dog-like mammals. (What species. Linnaeus’s species were groups of organisms features do you think differ between these two groups?) that shared the same appearance and behaviour. We still The horse-like mammals all belong to the genus Equus. use this system today. Biologists do not always agree The dog-like ones belong to the genus Canis. on exactly how to define a species, but usually we say that organisms belong to the same species if they can breed together successfully, and the offspring that they produce can also breed. pony dog jackal zebra wolf Dog-like mammals Horse-like mammals genus Canis genus Equus species species Canis Canis species Canis lupus species species familiaris mesomelas Equus caballus Equus burchelli Figure 1.3 The binomial naming system. 4 Cambridge IGCSE Biology Original material © Cambridge University Press 2014 The binomial naming system Linnaeus gave every species of living organism two Key definition names, written in Latin. This is called the binomial species – a group of organisms that can system. The first name is the name of the genus the reproduce and produce fertile offspring organism belongs to, and always has a capital letter. The binomial system – an internationally ageeed second name is the name of its species, and always has a system in which the scientific name of an small letter. This two-word name is called a binomial. organism is made up of two parts showing the For example, a wolf belongs to the genus Canis genus and species and the species lupus. Its binomial is Canis lupus. These names are printed in italics. When you write a Latin name, you cannot write in italics, so you should Study tip underline it instead. The genus name can be abbreviated like this: C. lupus. Do take care to write Latin names (binomials) correctly. You will often see them written wrongly in the media! You should always use a capital letter for the first name and a small letter for the second name. Question 1.1 The table shows how two organisms – a monarch butterfly and a giant pangolin – Kingdom animal animal are classified. Phylum arthropods vertebrates a Use the informatiton in the table to suggest Class insects mammals whether these two organisms are not related at all, distantly related or closely Order Lepidoptera Pholidota (butterflies and moths) related. Explain how you made your decision. b Write down the genus of the giant pangolin. Family Danaidae Manidae c Use the Internet or a textbook to find out Genus Danaus Manis how a human is classified. Write it down in a Species Danaus plexippus Manis gigantea table like the one shown on the right. Monarch butterfly Giant pangolin Original material © Cambridge University Press 2014 Chapter 1: Classification 5  1.3 The kingdoms of living organisms Animals Animals (Figure 1.4) are usually easy to recognise. Most animals can move actively, hunting for food. Under the Centipede microscope, we can see that their cells have no cell walls. Some animals have, in the past, been confused with plants. For a very long time, sea anemones were classified as plants, because they tend to stay fixed in one place, and their tentacles look rather like flower petals. Now we know that they are animals. Characteristics: ♦♦ multicellular (their bodies contain many cells) ♦♦ cells have a nucleus, but no cell walls or chloroplasts ♦♦ feed on organic substances made by other living organisms. Black- headed gull Earthworm Figure 1.4 Some examples of animals. Plants Shepherd’s purse The plants that are most familiar to us are the flowering plants, which include most kinds of trees. These plants flower have leaves, stems, roots and flowers (Figure 1.5). However, there are other types of plants – including ferns and mosses – that do not have flowers. What all fruit of them have in common is the green colour, caused by a pigment called chlorophyll. This pigment absorbs energy from sunlight, and the plant can use this energy to make sugars, by the process of photosynthesis. leaf As they do not need to move around to get their food, plants are adapted to remain in one place. They often have a spreading shape, enabling them to capture as much sunlight energy as possible. Characteristics: ♦♦ multicellular ♦♦ cells have a nucleus, cell walls made of cellulose and often contain chloroplasts root ♦♦ feed by photosynthesis ♦♦ may have roots, stems and leaves. Figure 1.5. An example of a plant. 6 Cambridge IGCSE Biology Original material © Cambridge University Press 2014  Questions Fungi S For a very long time, fungi were classified as plants. 1.2 The photograph below shows a sea anemone. However, we now know that they are really very a Explain why people used to think that sea different, and belong in their own kingdom. Figure 1.6 anemones were plants. shows the characteristic features of fungi. b Explain how using a microscope could help We have found many different uses to make of fungi. you to confirm that sea anemones are animals. We eat them as mushrooms. We use the unusual fungus yeast to make ethanol and bread. We obtain antibiotics such as penicillin from various different fungi. Some fungi, however, are harmful. Some of these cause food decay, while a few cause diseases, including ringworm and athlete’s foot. Fungi do not have chlorophyll and do not photosynthesise. Instead they feed saprophytically, or parasitically, on organic material like faeces, human foods and dead plants or animals. Characteristics: ♦ usually multicellular (many-celled) ♦ have nuclei ♦ have cell walls, not made of cellulose 1.3 The photograph below shows a plant called a ♦ do not have chlorophyll liverwort. Liverworts do not have roots or proper ♦ feed by saprophytic or parasitic nutrition. leaves. They do not have flowers. Suggest how you could show that a liverwort belongs to the plant kingdom. Bread mould sporangium containing spores aerial hypha feeding hypha bread Edible mushroom cap gills, bearing spores mycelium Figure 1.6 Some examples of fungi. Original material © Cambridge University Press 2014 Chapter 1: Classification 7 S Protoctista Prokaryotes S The kingdom Protoctista (Figure 1.7) contains quite a Figure 1.8 shows some bacteria. Bacteria have cells that mixture of organisms. They all have cells with a nucleus, are very different from the cells of all other kinds of but some have plant-like cells with chloroplasts and organism. The most important difference is that they do cellulose cell walls, while others have animal-like cells not have a nucleus. without these features. Most protoctists are unicellular You will meet bacteria at various stages in your (made of just a single cell) but some, such as seaweeds, biology course. Some of them are harmful to us and are multicellular. cause diseases such as tuberculosis (TB) and cholera. Characteristics: Many more, however, are helpful. You will find out ♦♦ multicellular or unicellular about their useful roles in the carbon cycle and the ♦♦ cells have a nucleus nitrogen cycle, in biotechnology, in the treatment of ♦♦ cells may or may not have a cell wall and chloroplasts sewage to make it safe to release into the environment ♦♦ some feed by photosynthesis and others feed on and in making insulin for the treatment of people organic substances made by other organisms. with diabetes. Some bacteria can carry out photosynthesis. The Paramecium oldest fossils belong to this kingdom, so we think that they were the first kinds of organism to evolve. Characteristics: ♦♦ often unicellular (single-celled) ♦♦ have no nucleus ♦♦ have cell walls, not made of cellulose ♦♦ have no mitochondria. nucleus cytoplasm cell membrane Cross-section of the bacterium Escherichia coli strand of DNA flagellum Chlamydomonas cell wall plasmid cytoplasm cell wall cytoplasm containing chloroplast cell membrane ribosomes cell membrane capsule nucleus External view of cholera bacteria Vibrio cholerae Figure 1.7 Some examples of protoctists. Figure 1.8 Some examples of bacteria. 8 Cambridge IGCSE Biology Original material © Cambridge University Press 2014 S 1.4 Viruses 1.5 Classifying animals You have almost certainly had an illness caused by a Figure 1.10 shows some of the major groups into which virus. Viruses cause common diseases such as colds and the animal kingdom is classified. influenza, and also more serious ones such as AIDS. Viruses are not normally considered to be alive, kingdom because they cannot do anything other than just exist, animals until they get inside a living cell. They then take over the phylum arthropods cell’s machinery to make multiple copies of themselves. class phylum insects nematodes These new viruses burst out of the cell and invade others, where the process is repeated. The host cell is usually killed when this happens. On their own, viruses phylum vertebrates phylum cannot move, feed, excrete, show sensitivity, grow or annelids class class reproduce. fish reptiles Figure 1.9 shows one kind of virus. It is not made of class class a cell – it is simply a piece of RNA (a chemical similar birds amphibians phylum to DNA) surrounded by some protein molecules. It molluscs class is hugely magnified in this diagram. The scale bar mammals represents a length of 10 nanometres. One nanometre is 1 × 10−9 mm. In other words, you could line up Figure 1.10 Classification of the animal kingdom. more than 15 000 of these viruses between two of the millimetre marks on your ruler. Phylum Vertebrates These are animals with a supporting rod running along the length of the body. The most familiar ones have a protein backbone and are called vertebrates. Class Fish The fish (Figure 1.11) all live in water, except for one or two like the mudskipper, which can spend short periods genetic of time breathing air. material Characteristics: (RNA) ♦ vertebrates with scaly skin ♦ have gills ♦ have fins. 10 nm Figure 1.9 An influenza virus. dorsal fin streamlined body operculum covered in scales Questions covering gills S 1.4 Why are viruses not generally considered to be living things? 1.5 State one similarity and one difference between the cells of a fungus and the cells of a plant. 1.6 How do the cells of bacteria differ from the cells of caudal fin anal fin pectoral fin plants and animals? pelvic fin Figure 1.11 A fish. Original material © Cambridge University Press 2014 Chapter 1: Classification 9  Class Amphibians Class Birds Although most adult amphibians live on land, they The birds (Figure 1.14), like reptiles, lay eggs with always go back to the water to breed. Frogs, toads and waterproof shells. salamanders are amphibians (Figure 1.12). Characteristics: Characteristics: ♦ vertebrates with feathers ♦ vertebrates with moist, scale-less skin ♦ forelimbs have become wings ♦ eggs laid in water, larva (tadpole) lives in water ♦ lay eggs with hard shells ♦ adult often lives on land ♦ endothermic ♦ larva has gills, adult has lungs. ♦ have a beak. thin, moist skin beak visible ear drum body covered with feathers Figure 1.12 A frog. Class Reptiles Figure 1.14 A bird. These are the crocodiles, lizards, snakes, turtles and tortoises (Figure 1.13). Reptiles do not need to go Class Mammals back to the water to breed because their eggs have a This is the group that humans belong to (Figure 1.15). waterproof shell which stops them from drying out. Characteristics: Characteristics: ♦ vertebrates with hair ♦ vertebrates with scaly skin ♦ have a placenta ♦ lay eggs with rubbery shells. ♦ young feed on milk from mammary glands ♦ endothermic ♦ have a diaphragm scaly skin ♦ heart has four chambers ♦ have different types of teeth (incisors, canines premolars and molars). Figure 1.13 A snake. Figure 1.15 An ocelot, an example of a mammal. 10 Cambridge IGCSE Biology Original material © Cambridge University Press 2014 Chapter 1: Classification Phylum Arthropods Crustaceans Arthropods are animals with jointed legs, but no These are the crabs, lobsters and woodlice. They breathe backbone. They are a very successful group, because through gills, so most of them live in wet places and they have a waterproof exoskeleton that has allowed many are aquatic. them to live on dry land. There are more kinds of Characteristics: arthropod in the world than all the other kinds of ♦ arthropods with more than four pairs of jointed legs animal put together. ♦ not millipedes or centipedes Characteristics: ♦ breathe through gills. ♦ several pairs of jointed legs ♦ exoskeleton. Edible crab exoskeleton containing Insects calcium salts Insects (Figure 1.16) are a very successful group of animals. Their success is mostly due to their exoskeleton eye and tracheae, which are very good at stopping water from evaporating from the insects’ bodies, so they can live in very dry places. They are mainly terrestrial 2 cm claw (land-living). antenna jointed leg Characteristics: ♦ arthropods with three pairs of jointed legs Figure 1.17 An example of a crustacean. ♦ two pairs of wings (one or both may be vestigial) ♦ breathe through tracheae Arachnids ♦ body divided into head, thorax and abdomen. These are the spiders, ticks and scorpions. They are land-dwelling organisms. Locust Characteristics: ♦ arthropods with four pairs of jointed legs head thorax wing jointed leg ♦ breathe through gills called book lungs. Spider, antenna eye abdomen Moth cephalothorax pedipalp 2 mm abdomen 4 pairs of jointed legs Figure 1.18 An example of an arachnid. Figure 1.16 Some examples of insects. Original material © Cambridge University Press 2014 11  Myriapods Fern These are the centipedes and millipedes. frond Characteristics: ♦♦ body consists of many segments sporangia with spores ♦♦ each segment has jointed legs. Centipede long, thin rhizome – an segmented body underground stem roots jointed legs on each segment 0.5 cm Figure 1.20 An example of a fern. Figure 1.19 An example of a myriapod. Flowering plants These are the plants that are most familiar to us. They can be Questions tiny, or very large – many trees are flowering plants. S 1.7 List three ways in which all mammals differ Characteristics: from all birds. ♦♦ plants with roots, stems and leaves 1.8 Explain why bats are classified as mammals, ♦♦ reproduce by means of flowers and seeds even though they have wings. ♦♦ seeds are produced inside the ovary, in the flower Flowering plants can be divided into two main groups, the monocotyledonous plants and the dicotyledonous plants, 1.6 Classifying plants often abbreviated to monocots and dicots (Figure 1.21). We have seen that plants are organisms that have Monocots have only one cotyledon in their seeds. They cells with cell walls made of cellulose. At least some usually have a branching root system, and often have leaves parts of a plant are green. The green colour is caused in which the veins run in parallel to one another. Dicots have by a pigment called chlorophyll, which absorbs two cotyledons in their seeds. They frequently have a tap energy from sunlight. The plant uses this energy to root system, and their leaves are often broader than those of make glucose, using carbon dioxide and water from monocots, and have a network of branching veins. its environment. This is called photosynthesis. Plants include small organisms such as mosses, Corn Pea (monocot) (dicot) as well as ferns (Figure 1.20) and flowering plants (Figure 1.21). Ferns parallel veins Ferns have leaves called fronds. They do not produce flowers, but reproduce by means of spores strap-shaped broad produced on the underside of the fronds. leaves leaves Characteristics: ♦♦ plants with roots, stems and leaves network of ♦♦ have leaves called fronds branching veins ♦♦ do not produce flowers ♦♦ reproduce by spores Figure 1.21 Flowering plants. 12 Cambridge IGCSE Biology Original material © Cambridge University Press 2014 Chapter 1: Classification Activity 1.1 Making biological drawings Here are some points to bear in mind when you draw. ♦♦ Make good use of the space on your sheet of Skill AO3.3 Observing, measuring and recording paper – your drawing should be large. However, do leave space around it so that you have room Biologists need to be able to look closely at for labels. specimens – which might be whole organisms, ♦♦ Always use a sharp HB pencil and have a good or just part of an organism – and note significant eraser with you. features of them. It is also important to be able to ♦♦ Keep all lines single and clear. make simple drawings to record these features. ♦♦ Don’t use shading unless it is absolutely You don’t have be good at art to be good at necessary. biological drawings. A biological drawing needs ♦♦ Don’t use colours. to be simple but clear. ♦♦ Take time to get the outline of your drawing You will be provided with a specimen of an correct first, showing the right proportions. animal to draw. ♦♦ Now label your drawing to show the features of the organism that are characteristic of its classification group. You could also label any features that help the organism to survive in its environment. These are called adaptations. For example, if your organism is a fish, you could label ‘scales overlapping backwards, to provide a smooth, streamlined surface for sliding through the water’. Here are some points to bear in mind when you label a diagram. ♦♦ Use a ruler to draw each label line. ♦♦ Make sure the end of the label line actually 1 Look carefully at the specimen, and decide touches the structure being labelled. what group of animals it belongs to. Jot down ♦♦ Write the labels horizontally. the features of the organism that helped you ♦♦ Keep the labels well away from the edges of to classify it. your drawing. 2 Make a large, clear drawing of your organism. Original material © Cambridge University Press 2014 13  Activity 1.2 Calculating magnification The following are two very important things to notice. Skill ♦ You must use the same units for all the AO3.3 Observing, measuring and recording measurements. Usually, millimetres are the best units to use. Drawings of biological specimens are usually ♦ You should not include any units with the final made at a different size from the real thing. It is answer. Magnification does not have a unit. important to show this on the diagram. However, you must include the ‘times’ sign. If The magnification of a diagram is how much you read it out loud, you would say ‘times five’. larger it is than the real thing. Questions size of drawing A1 Measure the length of the lowest ‘tail’ (it is magnification = size of real object really called an appendage) on the centipede For example, measure the length of the spider’s below. Write your answer in millimetres. body in the diagram below. You should find that it A2 The real length of the appendage was 10 mm. is 40 mm long. Use this, and your answer to question A1, to calculate the magnification of the drawing of the centipede. The real spider was 8 mm long. So we can calculate the magnification like this: length in drawing magnification = length of real spider 40 = 8 = ×5 Study tip Be prepared to use the magnification equation organised in a different way: size of real object = size of drawing × magnification. 14 Cambridge IGCSE Biology Original material © Cambridge University Press 2014 Chapter 1: Classification 1.7 Keys 1 jointed limbs........................................... 2 If you want to identify an organism whose name you no jointed limbs...................................... earthworm do not know, you may be able to find a picture of it in a book. However, not every organism may be pictured, 2 more than 5 pairs of jointed limbs....... centipede or your organism may not look exactly like any of the 5 or fewer pairs of jointed limbs........... 3 pictures. If this happens, you can often find a key that you can use to work out what your organism is. 3 first pair of limbs form large claws....... crab A key is a way of leading you through to the name of your organism by giving you two descriptions at a no large claws.......................................... 4 time, and asking you to choose between them. Each 4 3 pairs of limbs....................................... locust choice you make then leads you on to another pair of descriptions, until you end up with the name of your 4 pairs of limbs....................................... spider organism. This kind of key is called a dichotomous key. To use the key, pick one of the animals that you are ‘Dichotomous’ means ‘branching into two’, and refers to going to identify. Let’s say you choose organism B. the fact that you have two descriptions to choose from Decide which description in step 1 matches your at each step. organism. It has jointed limbs, so the key tells us to go Here is a key that you could use to identify the to step 2. Decide which description in step 2 matches organisms shown in Figure 1.22. organism B. It has more than 5 pairs of jointed limbs, so it is a centipede. D A B C E Figure 1.22 Organisms for practising using a key. Original material © Cambridge University Press 2014 15  Constructing keys be the same size – you could have two in one group and Using a key is quite easy, but writing your own key is two in the other, or perhaps one in one group and the much more of a challenge. rest in the other. Let’s say you want to write a key to enable someone to Now concentrate on a group that contains more than identify each of the four flowers in Figure 1.20. one flower. Choose another feature that will allow you to First, make a list of features that clearly vary between split the flowers into two further groups. the flowers. They should be features that cannot possibly Keep doing this until each ‘group’ contains only be mistaken. Remember that the person using the key one flower. will probably only have one of the flowers to look at, so Now go back and refine your key. Think carefully they cannot necessarily compare it with another kind about the wording of each pair of statements. Make sure of flower. So the number of petals or the colour is a that each pair is made up of two clear alternatives. Try good choice, but the size (large or small) is not, because to reduce your key to the smallest possible number of different people might have different ideas about what is statement pairs. ‘large’ or ‘small’. Finally, try your key out on a friend. If they have any Now choose one of these features that can split the problems with it, then try to reword or restructure your flowers into two groups. The two groups don’t have to key to make it easier to use. Limnanthes Viola Potentilla Erodium Figure 1.23 Can you write a key to identify these flowers? Summary You should know: ♦♦ the seven characteristics that distinguish living things from non-living objects ♦♦ why it is important to classify organisms ♦♦ about the binomial system of naming organisms S ♦♦ how DNA base sequences help with classification ♦♦ the characteristic features of animals (including arthropods and vertebrates) and plants S ♦♦ the features of bacteria, fungi and protoctists, and the problems of classifying viruses ♦♦ how to make good biological drawings and calculate magnification ♦♦ how to use a dichotomous key to identify an unknown organism ♦♦ how to construct a dichotomous key. End-of-chapter questions 1 a Without looking back at the beginning of this chapter, decide which five of these characteristics are found in all living things. movement blood system sight growth photosynthesis nutrition sensitivity speech excretion b List the other two characteristics of all living organisms. 16 Cambridge IGCSE Biology Original material © Cambridge University Press 2014 Chapter 1: Classification  2 Three species of tree have the following binomials: Carpodiptera africana, Commiphora africana, Commiphora angolensis Which two of these species do biologists consider to be the most closely related? Explain your answer. 3 Construct a table to compare the characteristic features of animals and plants. S 4 Construct a dichotomous key to help someone to identify five of your teachers. Try to meet these criteria: each pair of characteristics describes one contrasting feature each person could be identified without having to compare them with another person the key contains no more than four pairs of points (you may be able to do it with just three pairs). When you have finished, swap your key with someone else to check if it works. If not, make adjustments to it. 5 The photograph shows a section through a fruit. Magnification × 0.6 a Make a large diagram of the fruit. You do not need to label your diagram. b Calculate the diameter of the actual fruit at the point indicated by the dotted line. Show your working, and remember to include the unit. S 6 The diagram shows a virus. protein DNA (genetic material) 100 nm a With reference to the diagram, and your own knowledge, discuss whether or not viruses can be considered to be living organisms. b 1 nm (nanometre) is 10−9 m. Measure the length of the scale bar. Use this, and the label on the scale bar, to calculate the magnification of the diagram. Show your working. Original material © Cambridge University Press 2014 17  2 Cells In this chapter, you will find out about: ♦ the structure of plant cells and animal cells ♦ the functions of the different parts of cells ♦ tissues, organs and organ systems. Cells from deep time nothing else can live there. These organisms are If a long, thin spike of limestone hanging down from called extremophiles, which means ‘lovers of extreme the roof of a cave is called a stalactite, what do you conditions’. call a long, thin drip of bacteria-filled slime? Snottites are found in caves where the atmosphere Caver Jim Pisarowicz decided to call them contains large amounts of the smelly, toxic gas snottites, and the name stuck (Figure 2.1). Snottites hydrogen sulfide. The bacteria in the slimy threads, are studied by biologists interested in organisms far from being poisoned by the gas, actually use it to that can live in environments so strange that almost make their food. In the middle of the threads, there is virtually no oxygen, yet some kinds of bacteria live even here. Similar conditions – a lot of hydrogen sulfide, almost no oxygen – were found in the Earth’s very early atmosphere, more than 3.5 billion years ago, and this is probably when these extremophile bacteria first evolved. At that time, the cells of all organisms were much less complex than those of plants and animals (which did not appear on Earth until around 2 billion years ago). They had no nucleus, for example. Yet bacteria made of these seemingly simple cells are clearly very successful, if they have managed to survive almost unchanged through such an unimaginably long period of time. Figure 2.1 Snottites hanging from the roof of a cave. 18 Cambridge IGCSE Biology Original material © Cambridge University Press 2014 2.1 Cell structure cell membrane All organisms are made of cells. Cells are very small, so large organisms contain millions of cells. Some organisms are unicellular, which means that they are made of just a single cell. Bacteria and yeast are examples of single-celled organisms. Microscopes To see cells clearly, you need to use a microscope (Figure 2.2). The kind of microscope used in a school laboratory is called a light microscope because it shines light through the piece of animal or plant you are nucleus small vacuole looking at. It uses glass lenses to magnify and focus the image. A very good light microscope can magnify about nuclear envelope cytoplasm 1500 times, so that all the structures in Figures 2.3 and Figure 2.3 A typical animal cell – a liver cell – as seen with a 2.4 can be seen. light microscope. Photomicrographs of plant and animal cells are shown in Figure 2.5 and Figure 2.6. A photomicrograph is a picture made using a light microscope. Questions To see even smaller things inside a cell, an electron 2.1 How many times can a good light microscope microscope is used. This uses a beam of electrons magnify? instead of light, and can magnify up to 500 000 times. 2.2 If an object was 1mm across, how big would it look This means that a lot more detail can be seen inside a if it was magnified 10 times? cell. We can see many structures more clearly, and also some structures that could not be seen at all with a light microscope. The human eye cannot see most cells. A hand lens magnifies The light microscope magnifies × 400 about × 10. Cells can to × 1500. With a light microscope often be seen as dots. you can see some structures inside a An electron microscope magnifies cell, such as a nucleus. × 40 000 to × 500 000. With an electron microscope much more detail can be seen. Figure 2.2 Equipment used for looking at biological material. Original material © Cambridge University Press 2014 Chapter 2: Cells 19  cell wall cell membrane nucleus nuclear envelope cytoplasm chloroplast large vacuole containing cell sap membrane around vacuole starch grain inside Figure 2.5 Many plant cells contain green structures, called chloroplasts. Even if it does not have any chloroplasts, you can still identify a plant cell chloroplast because it has a cell wall around it (× 2000). Figure 2.4 A typical plant cell – a palisade mesophyll cell – as seen with a light microscope. Cell membrane Whatever sort of animal or plant they come from, all cells have a cell membrane (sometimes called the cell surface membrane) around the outside. Inside the cell membrane is a jelly-like substance called cytoplasm, cell in which are found many small structures called membrane organelles. The most obvious of these organelles is usually the nucleus. In a plant cell, it is very difficult to see, because it is right against the cell wall. nucleus The cell membrane is a very thin layer of protein and fat. It is very important to the cell because it controls what goes in and out of it. It is said to be partially permeable, which means that it will let some substances cytoplasm through but not others. Cell wall All plant cells are surrounded by a cell wall made mainly Figure 2.6 Cells from the trachea (windpipe) of a mammal, seen through a light microscope (× 300). of cellulose. Paper, which is made from cell walls, is 20 Cambridge IGCSE Biology Original material © Cambridge University Press 2014  also made of cellulose. Animal cells never have cell Chloroplasts walls made of cellulose. Cellulose belongs to a group of Chloroplasts are never found in animal cells, but most substances called polysaccharides, which are described of the cells in the green parts of plants have them. in Chapter 4. Cellulose forms fibres which criss-cross They contain the green colouring or pigment called over one another to form a very strong covering to the chlorophyll. Chlorophyll absorbs energy from sunlight, cell (Figure 2.7). This helps to protect and support the and this energy is then used for making food for the cell. If the cell absorbs a lot of water and swells, the cell plant by photosynthesis (Chapter 6). wall stops it bursting. Chloroplasts often contain starch grains, which Because of the spaces between fibres, even very large have been made by photosynthesis. Animal cells never molecules are able to go through the cellulose cell wall. contain starch grains. Some animal cells, however, do It is therefore said to be fully permeable. have granules (tiny grains) of another substance similar to starch, called glycogen. These granules are found in Cytoplasm the cytoplasm, not inside chloroplasts. Cytoplasm is a clear jelly. It is nearly all water; about 70% is water in many cells. It contains many substances Nucleus dissolved in it, especially proteins. Many different The nucleus is where the genetic information is metabolic reactions (the chemical reactions of life) take stored. This helps the cell to make the right sorts of place in the cytoplasm. proteins. The information is kept on the chromosomes, which are inherited from the organism’s parents. The Vacuoles chromosomes are made of DNA. A vacuole is a space in a cell, surrounded by a Chromosomes are very long, but so thin that membrane, and containing a solution. Plant cells have they cannot easily be seen even using the electron very large vacuoles, which contain a solution of sugars microscope. However, when the cell is dividing, they and other substances, called cell sap. A full vacuole become short and thick, and can be seen with a good presses outwards on the rest of the cell, and helps light microscope. S to keep it in shape. Animal cells have much smaller Table 2.1 compares some features of plant cells and membrane-bound spaces, called vesicles, which may animal cells. contain food or water. Plant cells Animal cells have a cellulose cell wall have no cell wall outside the cell membrane have a cell membrane have a cell membrane have cytoplasm have cytoplasm have a nucleus have a nucleus often have chloroplasts have no chloroplasts containing chlorophyll often have large vacuoles have only small vacuoles containing cell sap often have starch grains never have starch grains; sometimes have glycogen granules Figure 2.7 Cellulose fibres from a plant cell wall. This picture was taken often regular in shape often irregular in shape using an electron microscope (× 50 000). Table 2.1 A comparison of plant and animal cells. Original material © Cambridge University Press 2014 Chapter 2: Cells 21 S Mitochondria Mitochondria are the powerhouses of the cell. Inside S Photographs of cells taken using an electron them, oxygen is used to release energy from glucose, in microscope, called electronmicrographs, show the process called aerobic respiration. You will find out tiny structures that are almost invisible with a light more about aerobic respiration in Chapter 11. microscope. They are called mitochondria (singular: Not surprisingly, cells that use a lot of energy have mitochondrion). Mitochondria are found in almost all a lot of mitochondria. Muscle cells, for example, are cells, except those of prokaryotes. Figures 2.8 and 2.9 tightly packed with mitochondria. Sperm cells, which show electronmicrographs of mitochondria. need energy to swim to the egg, and neurones (nerve cells), which need energy to transmit impulses, also nucleus nuclear envelope cytoplasm have large numbers of mitochondria. The black spots in the electron micrograph in Figure 2.8 are granules of a carbohydrate called glycogen. This is similar to starch. (Starch is never found in animal cells – they store glycogen instead.) Glycogen is a reserve fuel. When required, it can be broken down to glucose, to be used as a fuel by the mitochondria in the liver cell, or transported in the blood to other cells that need it. Ribosomes Even tinier structures than mitochondria can just be seen with an electron microscope (Figure 2.10). They