IGCSE Biology PDF - Second Edition Edexcel

Edexcel International GCSE Biology Second Edition is available as a Student eTextbook. Student eTextbooks are downloadable versions of the printed textbooks that teachers can assign to students. Students can: Download and view them on any device or browser Add, edit and synchronise notes across...

Edexcel International GCSE Biology Second Edition is available as a Student eTextbook. Student eTextbooks are downloadable versions of the printed textbooks that teachers can assign to students. Students can: Download and view them on any device or browser Add, edit and synchronise notes across two devices Access their personal copy on the move Find out more and sign up for a free trial – visit: www.hoddereducation.co.uk/dynamiclearning  i IGCSE_biology_v4.2.indd 1 28/04/2017 14:36:43  In order to ensure that this resource offers high-quality support for the associated Pearson qualification, it has been through a review process by the awarding body. This process confirms that this resource fully covers the teaching and learning content of the specification or part of a specification at which it is aimed. It also confirms that it demonstrates an appropriate balance between the development of subject skills, knowledge and understanding, in addition to preparation for assessment. 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ISBN 9781510405196 ii IGCSE_biology_v4.2.indd 2 28/04/2017 14:36:43   Contents Contents Acknowledgements v Getting the most from this book vi Section 1 Living organisms: variety and common features 1.1 Characteristics of living organisms 2 1.2 Variety of living organisms 7 1.3 Cells and their organisation 11 1.4 Biological molecules 19 1.5 Movement of substances into and out of cells 32 Summary 42 Example of student response with expert’s comments 44 Exam-style questions 46 Extend and challenge 48 Section 2 Nutrition and respiration 2.1 Nutrition in flowering plants 51 2.2 Human nutrition 60 2.3 Respiration 70 Summary 76 Example of student response with expert’s comments 78 Exam-style questions 81 Extend and challenge 83 Section 3 Movement of substances in living organisms 3.1 Gas exchange in flowering plants 86 3.2 Gas exchange in humans 92 3.3 Transport in living organisms 100 3.4 Transport in flowering plants 104 3.5 Transport in humans (1) – blood, structures and functions 112 3.6 Transport in humans (2) – heart and blood circulation 118 Summary 126 Example of student response with expert’s comments 129 Exam-style questions 132 Extend and challenge 135 Section 4 Coordination and control 4.1 Excretion in flowering plants 138 4.2 Excretion in humans 140 4.3 Coordination and response in living organisms 146 iii IGCSE_biology_v4.2.indd 3 28/04/2017 14:36:43  Contents 4.4 Coordination and response in flowering plants 150 4.5 Coordination and response in humans 155 Summary 166 Example of student response with expert’s comments 169 Exam-style questions 171 Extend and challenge 173 Section 5 Reproduction and inheritance 5.1 Reproduction in living organisms 176 5.2 Reproduction in flowering plants 180 5.3 Reproduction in humans 190 5.4 Genes and chromosomes 198 5.5 Patterns of inheritance 206 5.6 Variation, change and evolution 217 Summary 226 Example of student response with expert’s comments 231 Exam-style questions 233 Extend and challenge 236 Section 6 Ecology and the environment 6.1 The organism in the environment 239 6.2 Feeding relationships 247 6.3 Cycles within ecosystems 255 6.4 Human influences on the environment 261 Summary 271 Example of student response with expert’s comments 274 Exam-style questions 279 Extend and challenge 281 Section 7 Use of biological resources 7.1 Using crop plants to produce food 283 7.2 Using microorganisms to produce food 290 7.3 Producing food in fish farms 297 7.4 Selective breeding 301 7.5 Genetic modification (Genetic engineering) 305 7.6 Cloning 313 Summary 321 Example of student response with expert’s comments 323 Exam-style questions 326 Extend and challenge 329 Experimental design (CORMS) 332 Index 334 iv IGCSE_biology_v4.2.indd 4 28/04/2017 14:36:43   Acknowledgements Acknowledgements Every effort has been made to trace the copyright holders of material reproduced here. The following material is reproduced with kind permission: Earth System Research Laboratories, Graph of monthly mean CO2 at Mauna Loa from http://www.esrl.noaa.gov/ gmd/ccgg/trends US Department of Commerce, National Oceanic and Atmospheric Administration. ‘Bleeding Canker of Horse Chestnut’, map of geographical locations reported to Forest Research Disease Diagnosis Advisory Service from http://www.forestry.gov.uk/fr/INFD-6KYBGV. © Crown copyright 2012. Anne Bebbington, Table 6.5, data extracted from SAPS-FSC Plants for primary pupils 6 (Plants in their natural environment) from http://www.saps.org.uk/attachments/article/1378/SAPS_book_6_-_Plants_in_their_natural_ environment_-_2016.pdf Fred Pearce, Graph (Mann, Bradley & Hughes, Nature 1998) from ‘Variations of the Earth’s surface temperature’, from http://www.guardian.co.uk/environment/2010/feb/02/hockey-stick-graph-climate-change,The Guardian (2 February, 2010). Climate Choices & Children’s Voices, Graph of ‘Northern hemisphere. Departures in temperature (celcius) from the 1961 to 1990 average’ (adapted) from http://climatechoices.co.uk/pages/cchange3.htm Permission for re-use of all © Crown copyright information is granted under the terms of the Open Government Licence (OGL). v IGCSE_biology_v4.2.indd 5 28/04/2017 14:36:43  Section Getting 1the Living mostorganisms: from this book variety and common features Getting the most from this book Welcome to the Edexcel International GCSE (9−1) Biology Student Book. This book has been divided into seven Sections, following the structure and order of the Edexcel specification, which you can find on the Edexcel website for reference. Each Section has been divided into a number of smaller Chapters to help you manage your learning. The following features have been included to help you get the most from this book. TO THINK ABOUT... Try the activity before you start, and then have a look at it again once you have completed the Section, to see if your responses are different before and after learning more about the topics. PRACTICAL Practical boxes provide hints on key things to remember, or alternative practical work that you can do to help you learn more about that topic. STUDY TIP Study tips throughout the book will guide you in your learning process. TIP MATHS MATHS TIP Maths tips and skills give you additional help with the maths in the book so you can avoid losing valuable marks in the exam. vi IGCSE_biology_v4.2.indd 6 28/04/2017 14:36:50  Getting the most from this book Expert comments and tips for success At the end of each ­Section, you will find a summary checklist, highlighting the key facts that you need to know and understand, and key skills that you learnt in the Section. You will find Exam-style Before you try the questions at the end of each Exam-style questions, look Section covering the content at the sample answers and of that Section and the expert's comments to see ­different types of question you how marks are awarded and will find in an examination. common mistakes to avoid. EXTEND AND CHALLENGE When you have completed all the Exam-style questions for the Section, try the Extend and Challenge questions. ANSWERS Answers for all questions and activities in this book can be found online at www.hoddereducation.co.uk/igcsebiology STUDY QUESTIONS At the end of each Chapter you will find Study Questions. 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Seeing inside living organisms The two images of cells and their internal structures were obtained Make a list of things you know occur using different microscopes. The first microscope is one that you might inside cells. use in your biology course and it gives an image of a plant cell with Name some organisms that are chloroplasts. With this microscope, a beam of light is shone through made up of one cell only. the specimen, and then the light passes through a system of lenses that Make a list of some of the different magnify the specimen and let you see inside the cell. The maximum types of cells that are found in plants and in animals. useful magnification with this light microscope is around 1500. If the magnification is any higher, the image becomes too blurred to see any detail. The second image of a cell was taken with an electron microscope, shown with two people using one. The electron microscope uses a beam of electrons rather than light and magnifications of 100 000 are quite common. That is how the detail inside a chloroplast can be revealed. A disadvantage of the electron microscope is that specimens have to be killed and sliced, so living material cannot be observed. By using microscopes, we know that living organisms are made up of ‘cells’ TO THINK ABOUT... and scientists have also learnt about the smaller structures inside the cells, such as the chloroplasts you see in these images. But are all cells the same? Try to answer these questions at the Or are there different kinds of cells in the diverse range of living organisms start of this section, then come back we can observe: plants, animals, fungi protoctists and bacteria? How do to them when you have completed cells work together within an organism and how do cells connect with each the section to see how far you have other, allowing materials to move progressed in your understanding. between them? 1 IGCSE_biology_v4.2.indd 1 28/04/2017 14:37:03  Section 1 Living organisms: variety and common features 1.1 Characteristics of living organisms Is it alive? Biology is the study of life. But what exactly do we mean when we say that something is living? Imagine for a moment, that you are an intelligent alien species visiting planet Earth – but with no humans to talk to. How would you decide whether an object was alive (like a mouse) or not (like a pebble)? You might decide that movement is a characteristic of life – but does that mean that a falling snowflake is alive? Or you might decide that growth is a characteristic of life – but does that mean that a growing crystal of salt is alive? In these images the snowflake is not living but the human egg cell and flower are both parts of living organisms. This problem faces space scientists who wonder whether life has ever existed on nearby planets like Mars. Just because a sample of Martian soil absorbs oxygen, this does not by itself prove that there are living organisms using up the oxygen in the soil – the oxygen might just be reacting with minerals in the rocks. How can we be sure that something is living? Introducing living organisms One solution to the problem of what we mean when we say that something is ‘living’ is to produce a list of characteristics which is true for all forms of life on planet Earth. Unless an object does all of the things on the list, it cannot be considered alive. It is either dead or it was not a living organism in the first place. Section 1.1 acts as an introduction to the rest of the book. It provides a list of what makes living organisms different from non-living things and establishes the special features (characteristics) of living organisms. It emphasises the common features possessed by all living organisms (plants, animals and microorganisms) that make them distinct from non-living things, such as a rock. These common characteristics link living organisms together, through a common origin and shared history since life began on Earth 3.5 billion years ago. 2 IGCSE_biology_v4.2.indd 2 28/04/2017 14:37:14  1.1 Characteristics of living organisms This introduction aims to give a brief view into the extended and more detailed discussions in the later sections of the book, in which you explore how living things work – first within individual cells, then (for multicellular organisms) inside larger whole organisms. Later you have a chance to look at ecological relationships, which STUDY TIP show how living organisms interact with each other in the places where they live In Biology, you have to understand (their habitats). In the final sections of the book, you take a closer look at human the links between sections. beings – their influence on the natural environment and how humans use biological resources. We see how humans now (and in the past) use and apply biological principles – for example, in the production of food. In Section 1.1, the focus is on green (flowering) plants and humans, though the STUDY TIP characteristics apply to the whole range of living organisms (outlined in Note that the Study tips in Section 1.2). As you work through Section 1.1, you can use the Study tips to guide Section 1.1 all direct you to other you forwards to the relevant sections where the particular topics are discussed in parts of the book where the topics more detail. Or, when you have studied other sections in the book, you can refer are developed in greater detail. back to this introduction and see how far you have improved your understanding of what living organisms are and how they work. Nutrition Nutrition is the means of obtaining food, which provides the energy that living organisms need for the processes they carry out. It also provides the molecules that are built into other molecules that make up the substances of living material. Green plants obtain their food by taking in simple molecules. They take in carbon dioxide from the air and water and mineral ions from the soil. Green plants trap energy from the Sun and use this to build complex molecules from these simple molecules. This process is called photosynthesis and is of fundamental importance as the route by which energy is captured by living organisms then distributed through the living world to allow life as we know it. Plants are described as autotrophic because they build up their own food (‘auto’ = ‘self’ and ‘trophic’ = ‘feeding’). Animals eat other living organisms (plants or animals) and derive their energy from this food. The food contains complex molecules so the animal has to break STUDY TIP these down into simpler units before building them up again into the complex Refer to Section 2.1 for nutrition molecules that form part of the animal. Animals are described as heterotrophic in flowering plants, Section 2.2 for because they obtain food from a range of different sources (‘hetero’ = ‘different’). human nutrition and Section 6.2 Originally, the energy contained in the food comes from the Sun through plants, for feeding relationships between as indicated above, though often there is a food chain (or food web) that connects organisms in an ecosystem. the plant and the animal (or human). Respiration Respiration is the process that releases the energy locked within substances such as glucose. Chemical energy has been stored in the glucose and is released when the molecular bonds are broken. Respiration takes place in the cells of all living organisms. It is a series of chemical reactions and usually oxygen is required and carbon dioxide and water are produced as waste products. The energy released is transferred to a molecule (such as ATP) that acts like an energy battery, which stores the energy until it is needed to power some process in the living cell. 3 IGCSE_biology_v4.2.indd 3 28/04/2017 14:37:14  Section 1 Living organisms: variety and common features Respiration must not be confused with gas exchange, which describes the STUDY TIP processes involved in getting oxygen from the air to the cells and getting Refer to Section 2.3 for the topic of waste carbon dioxide out of the organism. In humans, breathing is part of the respiration in plants, animals and mechanism for gas exchange and is the way of getting air in and out of the some microorganisms. lungs. You must be clear that breathing is not part of the process of respiration. Excretion of waste Many chemical reactions take place inside the cells of living organisms. These are described as metabolic reactions. These reactions form pathways in which each step involves changing substances into other materials. Many of these metabolic reactions that take place in cells produce waste products that are not required by the cells and may even be toxic if they accumulate. Excretion describes the processes by which these substances are eliminated from the plant or animal. Examples of waste products include carbon dioxide from respiration and oxygen from photosynthesis. Water is also produced as a waste product in many reactions. In humans (and other animals), when proteins break down they produce a waste product that contains the element nitrogen – usually as urea. In humans, urea is eliminated from the body from the kidneys in urine. STUDY TIP Refer to Section 4.1 for excretion in In humans, you must not confuse egestion and excretion. Egestion describes flowering plants and Section 4.2 for the way that faeces are eliminated from the body. Most of the materials in faeces excretion in humans. have never been absorbed from the intestines into the cells of the body. STUDY TIP Refer to Section 4.3 for general Response to surroundings information about coordination Living organisms share the characteristic of sensitivity to different stimuli in their surroundings and an ability to respond. This means that living organisms and response, then to Section 4.4 can avoid problems (such as being eaten or becoming dried out) and can gain for response in flowering plants access to resources (such as light or food). and Sections 4.3 and 4.5 for details relating to response in humans. Plants and animals differ in the way that they respond to a stimulus. As examples, humans have special organs (known as receptors) that detect the stimulus (such as the eye for light or the ear for sound). They have a nervous system that coordinates a quick response, using muscles (that enable the person to run away from danger). Plants often respond much more slowly, by growing in a particular direction in response to the direction of light or gravity. STUDY TIP Refer to Sections 3.3 to 3.6 for details about movements of substances Movement within organisms under the heading All living organisms move in some way, though we more often associate movement from one place to another with animals. of ‘transport’ and to Section 4.4 for ways that parts of flowering plants In plants, movement usually involves a part of the plant, rather than the whole move. There is no further discussion organism. Some plants (such as climbing beans or peas) produce tendrils. These of locomotion in animals. may twist around until they make contact with an object, like a stick, to which they can anchor. Most animals are able to move from place to place and this is known as locomotion. Some do not move very far, but for many we are familiar with characteristic movements such as an athlete running, a bird flying, a worm wriggling or a fish swimming. 4 IGCSE_biology_v4.2.indd 4 28/04/2017 14:37:14  1.1 Characteristics of living organisms Control of internal conditions The conditions inside an organism, such as temperature and water content, must be kept within strict limits. If these limits are exceeded, the processes that occur in the organism may suffer, having an effect on its health. The term homeostasis is used to describe the maintenance of the internal environment of an organism within the required limits. For example, in the human body, if the internal temperature gets too high, there are mechanisms for losing heat and allowing the body to cool. Similarly, if the body loses too much water without taking in enough to compensate or if the level of carbon dioxide in the blood is too high, there are systems in the body to control these situations, bringing the internal environment back to normal. STUDY TIP In plants, various mechanisms exist that help control the internal Look in Section 4.3 for details about environment. On a very hot day, a plant might lose a lot water from its leaves control of internal conditions, and then begin to wilt. The stomatal pores on the leaves may close as a result though this refers mainly to humans. and this prevents any further loss of water vapour. On the other hand, in a You can find more details (for plant with a good water supply, the stomata remain open encouraging water humans) in Sections 4.2 loss from the leaf. This process cools the leaves in the same way as sweating and 4.5. cools the skin of a mammal. Reproduction Every living thing ultimately dies. But if they can reproduce first, they ensure that there are some offspring to take their place in the world. Living organisms all share the ability to reproduce and make more like themselves and so continue the species from one generation to the next. The information that controls an offspring’s characteristics is contained in the DNA. This essential information divides when a cell divides, so that some is passed on to each of the cells that build up into the next generation. For some, particularly for microscopic organisms, reproduction occurs simply by dividing into two. In other organisms, a piece breaks off and is able to grow into a new individual. This can occur in many plants and some animals. These are methods of asexual reproduction. STUDY TIP Most plants and animals reproduce by sexual reproduction. This occurs Refer to Section 5.1 then to Section as a result of two special cells joining together. These special cells are the sex 5.2 for flowering plants and Section cells – one from the male and one from the female. The offspring receive some 5.3 for humans. Section 5.4 gives DNA from the male parent and some from the female parent and this DNA details about DNA. determines the characteristics of the offspring and ensures there is continuity to the next generation. Growth and development In sexual reproduction, the new individual starts as a single fertilised egg cell (zygote). The zygote divides to form the many different types of cells that make up the tissues and organs of an adult individual. During development from zygote to adult, the organism gets larger and usually changes in shape and proportion. Animals reach a maximum size and then generally do not increase further, nor do they continue to develop new structures in the way that plants do. 5 IGCSE_biology_v4.2.indd 5 28/04/2017 14:37:14  Section 1 Living organisms: variety and common features Plants continue to grow throughout their lives. For example, every year a tree puts out new growth from its buds, including new shoots and new leaves. STUDY TIP This means it grows in size and complexity each year. In flowering plants, Section 5.2 includes some flowers develop into fruits and seeds and these may be dispersed to start the information for flowering plants and next generation. Section 5.3 for humans, though you You could try to find some photographs of yourself at different ages, and use might also make links with Section these to trace your own growth and development from the time you were quite 2.2 (human nutrition). small to see how have you changed throughout your life so far. STUDY QUESTION 1 The table below lists some descriptions or statements about processes carried out in living organisms. Some are carried out only by plants and some only by animals. Some processes are carried out by both plants and animals. Copy and complete the table. Tick in the boxes to show whether the processes are carried out by plants or by animals (or both). In the final column, name the process involved. (It will help you to think of a bean plant and a human as examples of a plant and an animal.) Description or statement Plants Animals Process synthesise sugars and give out waste oxygen release energy from sugars and use oxygen grow faster on one side when exposed to light from one side eat other living organisms as food get rid of waste nitrogenous material from the breakdown of protein molecules produce more organisms that are the same or similar to themselves use muscles to run and jump get larger and change during life 6 IGCSE_biology_v4.2.indd 6 28/04/2017 14:37:14  1.2 Variety of living organisms 1.2 Variety of living organisms From simple origins to the diversity of today’s living organisms The sweep through history and pre-history gives an overview digestive nutrition of life from its possible origins, = kingdom multicellular perhaps 3.5 billion years ago. It photosynthetic nutrition shows what scientists have pieced animals together from the probable multicellular beginnings of life to the diversity plants of living organisms we see on fungi Earth today. The timescale is photosynthesis evolved approximate but is backed by in some bacteria – and protoctists geological evidence in the rocks oxygen became abundant and later by fossil evidence in atmosphere of the Earth showing the forms of some first life forms probably unicellular or multicellular ancestors of plants and animals absorbed and digested more complex cells other life forms (digestive nutrition) with DNA that exist today – and some that bacteria in nucleus evolved have become extinct. 500 million years ago Today’s world has an enormous last universal diversity of living organisms. To help unicellular life forms common ancestor us make sense of all this information, 3.5 billion years ago we find it useful to sort (or classify) them into groups. If you were in charge of a library, how would you organise the books? Would you arrange them according to the colour of their covers or when they were published or would you classify them on the basis of their authors or topics? Which would be most useful and what would you do if new books were added – where would you fit them in? For living organisms, the diagram can be described as an outline of a sequence with branches, reflecting relationships between different groups and how they have changed or diverged over time. In present-day organisms, those with similar features are considered to be closely related, having at one time shared common ancestors. A widely accepted classification is the ‘Five kingdom’ classification and the ‘groups’ described in this section are based on this, but what other systems of classification have been used in the past or are currently considered? Who did a lot to establish the binomial system for naming organisms (into genus and species)? Why do classification systems change and have to be altered as new species are found? And how do modern DNA studies confirm or raise questions about existing classification systems? 7 IGCSE_biology_v4.2.indd 7 28/04/2017 14:37:15  Section 1 Living organisms: variety and common features Eukaryotic and prokaryotic organisms and their features Cells that contain a nucleus with a distinct membrane are described as eukaryotic (see page 11). Eukaryotic organisms may be multicellular or single-celled. Plants, animals, fungi and protoctists are all eukaryotic organisms. Prokaryotic cells do not have a nucleus and the nuclear material (a single circular chromosome) lies in the cytoplasm of the cell. Prokaryotic cells are much smaller (they have a thousand-fold smaller volume) than eukaryotic cells. In fact they are too small to contain chloroplasts or mitochondria (see page 12). Bacteria are prokaryotic organisms. Eukaryotic organisms Plants and animals are two of the five main groups of living organisms. Both are multicellular. Some key features that distinguish plants from animals are listed. Plants n contain chloroplasts (and so carry out photosynthesis) n have cellulose cell walls n store carbohydrates as starch or sucrose. Plants: Maize (a cereal) Plants: Pea (a herbaceous legume) Animals n do not contain chloroplasts (so cannot carry out photosynthesis) n do not have cellulose cell walls n often store carbohydrates as glycogen n usually have nervous coordination n are able to move from place to place. Animals: A human Animals: A housefly (an insect) Fungi n cannot carry out photosynthesis n have cell walls made of chitin n some are single-celled (e.g. yeast) n the body, for most, is made up of thread-like hyphae, containing many nuclei and organised into a mycelium (e.g. Mucor) n feed by secreting extracellular digestive enzymes (outside the mycelium) onto the food and then absorbing the digested molecules Fungi: Mucor (bread mould), showing Fungi: Yeast (a single-celled fungus), n this method of feeding is described as saproptrophic mycelium, seen with a light microscope. seen with a light microscope. (feeding on decaying matter) The hyphae are between 10 and 25 µm The yeast cells are between 2 and 10 µm n some fungi are parasitic (feeding on living material) in diameter. in diameter. n may store carbohydrate as glycogen. 8 IGCSE_biology_v4.2.indd 8 28/04/2017 14:37:34  1.2 Variety of living organisms Protoctists n are a rather diverse group of organisms, held together by the fact that they don’t fit in any of the other groups n are microscopic and single-celled, though some aggregate into larger forms (such as colonies or chains of cells that become Protoctists: Amoeba, single-celled, size approximately 0.1 mm (just filaments) visible with the eye) n are usually aquatic n some have features like animal cells (e.g. Amoeba and Plasmodium, the parasite that causes malaria) n some have features like plant cells, including chloroplasts (e.g. Chlorella). Algae are included in this group. Prokaryotic organisms Protoctists: Chlorella, single- Protoctists: Plasmodium, a Bacteria celled, containing chloroplast (size parasite (size 15 µm in length) n are single-celled, though have different shapes (e.g. rod-shaped, 8 µm in diameter) spherical) n cell structure includes cell wall, cell membrane, cytoplasm, and plasmids n have no nucleus but contain circular chromosome of DNA n feed in different ways: n some can carry out photosynthesis n most feed off other organisms, living or dead. (If feeding off a living organism, the bacteria are described as parasites; if feeding off dead organisms, the bacteria are Bacteria: Lactobacillus (a rod- Bacteria: Streptococcus described as saprobionts or decomposers.) shaped bacterium), size 2 µm (a spherical bacterium) (2000 nm) in length Pathogenic organisms, including viruses The term pathogen is used to describe a microorganism that causes disease, for example in plants and animals. Fungi, protoctists and bacteria all include some pathogens. All viruses are pathogenic and can exist only inside a living cell. Viruses can reproduce but do not carry out other characteristics of living things. For this reason, often viruses are not included in a classification of living organisms. Features of viruses are listed below. Viruses n very small particles (smaller than bacteria), variety of shapes Viruses: Tobacco mosaic virus Viruses: HIV virus (causes AIDS), and sizes (prevents formation of chloroplasts in size 120 nm in diameter plants), size 300 nm in diameter n lack a cellular structure n consist of a protein coat that surrounds either DNA or RNA n live and reproduce only inside living cells n can reproduce (by instructing the host cell to make more of them), but do not carry out any other characteristics of living organisms n all are parasitic and infect every type of living organism (including plants, animals and bacteria; viruses that infect bacteria are called bacteriophages). Viruses: Influenza virus (causes ‘flu’), size 100 nm in diameter 9 IGCSE_biology_v4.2.indd 9 28/04/2017 14:38:15  Section 1 Living organisms: variety and common features STUDY QUESTIONS 1 Section 1.2 gives a broad picture of the range of living organisms and the common features that have led to a classification system and the recognition of groups within this system. In Section 1.2, very few named examples have been included from the enormous number of living organisms that exist today (and have existed in the past). For each group, list three more examples of organisms that would fit in that group. Check that your examples show the given features. Then include some information about each organism in your list (such as why they are important to humans or where they can be found). Give your information under the following headings: n Plants n Animals n Fungi n Protoctists n Bacteria n Viruses. For the last four groups (fungi, bacteria, protoctists and viruses) include at least one pathogen in your list. Explain why viruses are often not included in a biological classification of living organisms. 2 The Study tips are given in the box below as cross-references. These all make connections with topics in other parts of the book and which you study during your course. Follow each of the links to help you make the connections and understand about the range of living organisms and the common features they show. You can check the links either when you study Section 1.2 or as you study different topics of your biology course. Devise your own chart to summarise the groups of organisms and the connections with other aspects of their biology. Cross-references to other parts of the book For more information about plants look at Section 1.3 (cells and their organisation), Section 1.4 (biological molecules), and Section 2.1 (plant nutrition). For more information about animals look at Section 1.4 (biological molecules), Section 4.5 (coordination and response in humans), and Section 1.1 (characteristics of living organisms). For more information about fungi, read about glycogen in Section 1.4 (biological molecules), yeast in Section 7.2 (using microorganisms to produce food) for its role in fermentations, including making bread, and in Section 6.3 (cycles within ecosystems) for the role of fungi in extracellular digestion and in nutrient cycles and decomposition. For more information about bacteria, look at Section 1.3 to compare cell structure in bacteria with that of plant and animal cells, and read about DNA in Section 5.4 (genes and choromosomes) and use of plasmids in GM in Section 7.5 (genetic modification). You can also look at Section 7.2 for cultivation of bacteria in fermenters (for particular products), and make a link to pathogenic bacteria and immune response in Section 3.5 (transport in humans (1) - blood, structures and functions) and their role in decomposition in natural cycles in Section 6.3. For protoctists, make a link to eutrophication. For more information about viruses read about the use of bacteriophages as vectors for genetic modification in Section 7.5. Finally, you can look at Section 5.6 (variation, change and evolution) to help you understand how the variety of living organisms has arisen, and how species and groups have changed over time (and will continue to change). 10 IGCSE_biology_v4.2.indd 10 28/04/2017 14:38:15  1.3 Cells and their organisation 1.3 Cells and their organisation The importance of tiny cells The white cliffs of Dover, a well-known landmark in England, are enormous and easily visible from 30 miles away across the sea. Yet they are mainly built from the shells of single-celled organisms called phytoplankton. The second photo shows an example of one phytoplankton cell, covered in plates of calcium carbonate (chalk), and its name is Emiliania huxleyi. These tiny cells swirl around the oceans of the world and, if they are not eaten, they die and settle on the bottom as a white layer of chalk. The white cliffs of Dover were once on the floor of the sea, and their chalk is made up of such phytoplankton shells, only visible individually with the help of an electron microscope. The fundamental unit of all living matter is the cell, and life depends upon whole cells. A fragment of a cell cannot be regarded as living matter. So what are the key features shared by all cells? What are the differences between animal and plant cells? How do all the processes of living organisms go on inside cells? How are cells organised inside to make these living processes work and how do cells work together in larger multicellular organisms? Cells and their internal structures You need to use a microscope to see cells. With a simple light microscope you can see the outlines of cells and some of the structures inside. With more powerful microscopes (including electron microscopes), giving higher magnification, scientists are able to observe more details of the internal structures and find out a lot about these structures and how they function in a cell. The internal structures are described as organelles and they provide organised ‘compartments’ inside the cell. Each organelle carries out a particular task and it is important that they all work together to carry out the functions of the whole cell. Features of plant cells and animal cells Figure 1.1 shows key features of a generalised plant cell and a generalised animal cell. The plant cell is similar to a palisade mesophyll cell in a leaf and the animal cell is similar to a ‘cheek’ cell from the lining of your mouth. Some features are common to all cells, whereas some features are found only in plant cells or only in animal cells. Many cells differ from this generalised view as they are specialised to carry out particular functions. We look at some examples of specialised cells later in Section 1.3. 11 IGCSE_biology_v4.2.indd 11 28/04/2017 14:38:21  Section 1 Living organisms: variety and common features chloroplast vacuole cytoplasm cell membrane mitochondria nucleus ribosomes cell wall animal cell plant cell Figure 1.1 Features of a generalised plant cell (left) and generalised animal cell (right). The mitochondria are organelles where aerobic respiration takes place and are found in both plant and animal cells. The list below links features labelled in the diagram (Figure 1.1) with their functions in the cell. Features found in both plant and animal cells are given first. n Cytoplasm – This is like a thick watery liquid and many of the activities of cells take place in the cytoplasm. Important molecules here include enzymes, which catalyse many metabolic reactions, such as those of respiration and synthesis of proteins. A number of smaller structures, the organelles, are found floating in the cytoplasm – these look like particles STUDY TIP when viewed with a light microscope. The organelles are not fixed in Look in Section 1.4 for more details position and can move within the cytoplasm. Sometimes, for example, about enzymes. chloroplasts can be seen ‘streaming’ (i.e. moving round) in a cell. n Mitochondria – These are sausage-shaped organelles, scattered throughout the cytoplasm, where key reactions of aerobic respiration take place. They are just visible as small specks under the light microscope. n Ribosomes – These are very small complex particles (much too small to be seen with a light microscope), found in the cytoplasm. They are responsible for the synthesis of proteins, including enzymes, specified by genes in the nucleus of the cell (see Section 5.4). A single cell contains millions of ribosomes. n Nucleus – This contains the genetic information of the cell. This information is located in the DNA, which forms the chromosomes. The STUDY TIP chromosomes become visible as thread-like structures when the cell is You can find information about dividing, but most of the time the nucleus just appears denser than the DNA, genes and chromosomes and cytoplasm and the chromosomes cannot be seen. Information about each protein synthesis in feature of the cell (and the whole organism) is held in the genes, along the Section 5.4. length of the chromosome. The nucleus (through the genes) determines the substances the cell makes and controls the activities of the cell. 12 IGCSE_biology_v4.2.indd 12 28/04/2017 14:38:22  1.3 Cells and their organisation n Cell membrane – This is the boundary between the cytoplasm of a cell and its surroundings. It keeps the cytoplasm and the organelles inside STUDY TIP the cell and the cell membrane also controls which materials enter and Look in Section 1.5 and make the leave the cytoplasm. Some materials may pass across the cell membrane link to diffusion and active transport. by diffusion and others by active transport. Many materials are kept inside the cell, while others are prevented from entering. These features are found only in plant cells. n Chloroplasts – These are green disc-shaped organelles found in the STUDY TIP photosynthetic cells of plants. (Chloroplasts are also found in some It is important to understand the role bacteria and in some protoctists.) This is where the chemical reactions of chloroplasts in photosynthesis of photosynthesis occur. The green colour is due to the presence of the (see Section 2.1 for flowering plants pigment chlorophyll. The chloroplast is the second largest organelle and Section 1.2 for a wider variety in the plant cell, after the nucleus, and is easily seen under the light of organisms). microscope. Many plant cells do not contain chloroplasts – such as those in roots. STUDY TIP n Cell wall – Plant cells are all surrounded by a tough cell wall. The plant Make a link to the cellulose molecule cell wall is composed of a polymer of glucose called cellulose. The cell in Section 1.4. wall provides strength and protection to plant cells. It is strong and resists forces that could change the shape of the cell. Cell walls make the outline of plant cells easy to see under the light microscope. Fungi and bacteria also have cell walls, but made of different materials. In STUDY TIP fungi, the cell walls are made of chitin, a substance also found in insects. In bacteria, the cell walls are made of a polymer of sugars and Look in Section 1.5 and Section 3.1 amino acids. to find out about the importance of n Vacuole – This is a large region at the centre of a plant cell, separated by turgid cells in plants. a membrane from the cytoplasm. It contains a watery solution known as cell sap. Often the cell sap pushes the cytoplasm outwards against the cell wall, giving the plant cell rigidity. Animal cells do not have a large vacuole though sometimes they contain small vacuoles. cell membrane – forms the outer boundary of the cytoplasm – jelly-like cell – regulating what enters transparent region where and leaves the cytoplasm much chemical activity takes place mitochondrion – site of aerobic respiration ribosomes – site of protein synthesis nucleus – transparent folds in the organelle containing flexible cell genetic material membrane (the chromosomes) Figure 1.2 Human cheek cells stained with methylene blue, seen with a Figure 1.3 Diagram showing structures of a human cheek cell. Compare this light microscope. Note the numerous with the microscope view (Figure 1.2). mitochondria within the cytoplasm. 13 IGCSE_biology_v4.2.indd 13 28/04/2017 14:38:27  Section 1 Living organisms: variety and common features chloroplast – bright green and cell wall – made of slightly smaller than the nucleus – site interwoven cellulose of photosynthesis fibres, giving the cell shape and protection cytoplasm – transparent region (a thick watery liquid), site of much chemical activity nucleus – transparent organelle, cell membrane – fatty containing genetic material layer inside the cell wall, (chromosomes) regulating what enters and leaves the cytoplasm vacuole – filled with watery cell sap that pushes the cytoplasm towards the cell wall Figure 1.4 Some palisade cells in a leaf, seen with a light microscope. The staining helps mitochondrion – the site of to show the chloroplasts. aerobic respiration Figure 1.5 Diagram of a palisade mesophyll cell, cut in longitudinal section and showing the structures of the cell. Compare this with the microscope view (Figure 1.4). Differences between plant and animal cells Common features in all cells have been listed above. Differences between plant and animal cells are summarised in Table 1.1. Table 1.1 Differences between plant and animal cells. Plant cells Animal cells have cellulose cell wall no cellulose cell wall some cells contain chloroplasts never contain chloroplasts usually have large vacuoles do not have large vacuoles though sometimes small vacuoles are present Diversity and specialisation of cells The generalised cells (Figure 1.1) show you the basic features of cells. But many cells, in both plants and animals, become specialised for the function they carry out. Here are just a few examples of specialised cells that you study in other parts of this book: STUDY TIP n root hair cell – an elongated ‘root hair’, increases the surface area for For more details about these cells, absorption of water look in Section 3.4 for root hair cells; n guard cells – shape alters when turgid and flaccid, controls the opening in Section 3.1 for guard cells; in and closing of stomata on the leaf surface Section 3.5 for blood cells; n red blood cell – has no nucleus, contains haemoglobin, carries oxygen in in Section 4.5 for nerve cells. the human body n nerve cell – an elongated ‘nerve fibre’, transmits nerve impulses.