Collins Concise Revision Course for CSEC® Biology PDF

CONCISE REVISION COURSE CSEC ® Biology Anne Tindale CONCISE REVISION COURSE CSEC ® Biology Anne Tindale HarperCollins Publishers Ltd The News Building 1 London Bridge Street London SE1 9GF © HarperCollins Publishers Limited 2016 Collins® is a registered trademark of HarperCollins Publishers Limited Concise Revision Course: CSEC ® Biology is an independent publication and has not been authorised, sponsored or otherwise approved by CXC. ® CSEC® is a registered trade mark of the Caribbean Examinations Council (CXC). www.collins.co.uk/caribbeanschools Typeset by QBS All rights reserved under International and Pan-AmericanCopyright Conventions. By payment of the required fees, you have been granted the non-exclusive, non-transferable right to access and read the text of this e-book on screen. 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Author: Anne Tindale Publisher: Elaine Higgleton Commissioning Editor: Peter Dennis and Tom Hardy Managing Editor: Sarah Thomas Copy Editor: Rebecca Ramsden Proofreader: Tim Jackson Artwork: QBS Cover: Kevin Robbins and Gordon MacGilp Acknowledgements p4tl: 3Dalia/Shutterstock, p4tr: Wire_man/Shutterstock, p4bl: Noppharat46/Shutterstock, p4br: Bayanova Svetlana/ Shutterstock, p10l: PRILL/Shutterstock, p10r: R Kristoffersen/Shutterstock, p12: Eric Isselee/Shutterstock, p12: Robert_s/Shutterstock, p12: Tatiana Belova/Shutterstock , p12: Feathercollector/Shutterstock, p12: Stephen Mcsweeny/Shutterstock, p12:Vitalii Hulai/Shutterstock, p12: Wim van Egmond/Visuals Unlimited, Inc./Getty Images, p12: Anat Chant/Shutterstock, p12: Matt9122/Shutterstock, p12: Roland Birke/Getty Images, p13: Robert L Kothenbeutel/Shutterstock, p14: Juan Gaertner/Shutterstock, p15tr: Alfredo Maiquez/Shutterstock, p15cr: Nicolas. voisin44/Shutterstock, p15cbr: Nigel Cattlin/Visuals Unlimited/Corbis, p15br: Peter Leahy/Shutterstock, p18l: Hywit Dimyadi/Shutterstock, p18r: Fabien Monteil/Shutterstock, p20: Donovan van Staden/Shutterstock, p21: Rich Carey/ Shutterstock, p22: Lodimup/Shutterstock, p23: M. Shcherbyna/Shutterstock, p24: Mikadun/Shutterstock, p25l: Rich Carey/Shutterstock, p25r: Trusjom/Shutterstock, p25c: Rich Carey/Shutterstock, p34l: Dr.Jeremy Burgess/Science Photo Library, p34r: Don W Fawcett/Science Photo Library, p43: Anne Tindale, p48: Dimarion/Shutterstock, p53: Dr.M.A. Ansary/Science Photo Library, p54: Brian A Jackson/Shutterstock, p55: Mila_1989/Shutterstock, p71: Wikrom Kitsamritchai/Shutterstock, p73: Jose Luis Calvo/Shutterstock, p83: Jubal Harshaw/Shutterstock, p86l: Biodisc/ Visuals Unlimited/Corbis, p86c: John Clegg/Science Photo Library, p86r: Max Topchii/Shutterstock, p89: Dourleak/ Shutterstock, p105: Eranicle/Shutterstock, p126tl: Addyvanich/Shutterstock, p126tr: Southern Illinois University/ Science Photo Library, p126bl: Image Point Fr/Shutterstock, p126br: Areeya_ann/Shutterstock, p151: Daimond Shutter/ Shutterstock, p159t: Michael W. Tweedie/Science Photo Library, p159b: Sergey Goryachev/Shutterstock, p160: Nicky Rhodes/Shutterstock, p161: Jian Hongyan/Shutterstock eBook Edition © September 2018 Print book Edition ISBN 9780008157876 eBook Edition ISBN 9780008326258 Version: 2020-03-20 Contents The pathway to success vi Movement of substances into and out of cells 37 1 An introduction to living Revision questions 40 organisms 1 6 The chemistry of living The characteristics of living organisms 1 organisms 41 Classification of living organisms 1 Carbohydrates 41 Revision questions 4 Lipids 42 Proteins 42 2 Living organisms in their Recognising carbohydrates, environment 5 proteins and lipids 43 Definitions 5 Enzymes 44 Carrying out an ecological study 5 Revision questions 45 The impact of abiotic factors on 7 Nutrition 46 living organisms 8 Revision questions 11 The types of nutrition 46 Photosynthesis in green plants 46 3 Interrelationships between Mineral nutrition in plants 50 living organisms 12 Revision questions Heterotrophic nutrition in 50 Feeding relationships 12 humans 51 Symbiotic relationships 14 A balanced diet 51 Other interrelationships 16 Diet and the treatment and Energy flow in ecosystems 16 control of disease 55 Recycling 17 Vegetarianism 56 Revision questions 19 Revision questions 56 4 The impact of humans Digestion in humans 56 Absorption 60 on the environment 20 Egestion 61 The impact of human activities on Assimilation 62 natural resources 20 Control of blood glucose levels 62 The negative impact of human Revision questions 63 activity on the environment 21 Conservation and restoration 8 Respiration and gaseous of the environment 27 exchange 64 The growth and survival of Respiration 64 populations 28 Revision questions 66 Revision questions 29 Gaseous exchange and breathing 66 Exam-style questions – Breathing and gaseous exchange Chapters 1 to 4 30 in humans 66 The gaseous exchange surface 5 Cells 33 in a fish 69 Plant and animal cells 33 Gaseous exchange in flowering Microbe cells 35 plants 70 Cell specialisation 35 The effects of smoking 71 Revision questions 37 Revision questions 72 Contents iii 9 Transport systems 73 12 Irritability 100 Transport systems in multicellular Definitions 100 organisms 73 Responses of green plants to The circulatory system in stimuli 100 humans 73 Responses of invertebrates 100 Blood 73 The nervous system of humans 101 Blood and defence against Simple reflex actions 102 disease 76 The human brain 104 Blood vessels 77 Physiological effects of drug The heart 79 abuse 104 Circulation 80 Social and economic effects Revision questions 82 of drug abuse 106 Transport systems in flowering Revision questions 106 plants 82 The human eye 107 Movement of water through a Sight defects and how they are flowering plant 83 corrected 109 Water conservation in plants 86 The human skin 110 Movement of organic food Revision questions 112 through a flowering plant 86 Movement of mineral salts 13 Growth 113 through a flowering plant 88 Methods of measuring growth 113 Storage of food in living Growth in plants 114 organisms 88 A comparison of growth in plants Revision questions 89 and animals 117 10 Excretion and Revision questions 117 osmoregulation 90 14 Reproduction 118 Excretion 90 Asexual and sexual reproduction The kidneys and excretion in compared 118 humans 91 Sexual reproduction in humans 119 Osmoregulation in humans 93 Sexually transmitted Kidney failure and dialysis 93 infections (STIs) 127 Revision questions 94 Revision questions 128 Sexual reproduction in flowering 11 Movement 95 plants 129 Types of movement 95 Fertilisation in flowering plants 130 The human skeleton 95 Revision questions 134 Functions of the human skeleton 97 Movement in humans 97 Movement of the human forelimb 98 The importance of locomotion in animals 99 Revision questions 99 iv Contents 15 Disease 135 Vectors and the spread of pathogenic diseases 135 Treatment and control of disease 137 Physiological diseases 138 Social, environmental and economic implications of disease 139 Revision questions 139 Exam-style questions – Chapters 5 to 15 140 16 Inheritance and variation 145 An introduction to chromosomes and genes 145 Cell division 145 Revision questions 149 Inheritance 149 Co-dominance 151 Pedigree charts 153 Mechanism of sex determination 154 Sex-linked characteristics 154 Some important genetic terms 155 Variation 156 Revision questions 157 17 Species, selection and genetic engineering 158 Species 158 The formation of new species – speciation 158 Extinction of species 158 The role of natural selection in biological evolution 159 Artificial selection 160 Genetic engineering 161 Other applications of gene technology 163 Revision questions 164 Exam-style questions – Chapters 16 to 17 165 Index 167 Contents v The pathway to success About this book This book has been written primarily as a revision course for students studying for the CSEC® Biology examination. The facts are presented concisely using a variety of formats which makes them easy to understand and learn. Key words are highlighted in bold type and important definitions which must be learnt are written in italics and highlighted in colour. Annotated diagrams and tables have been used wherever possible and the relationship between structure and function is continually emphasized. Questions to help test knowledge and understanding, and provide practice for the actual examination, are included throughout the book. The following sections provide valuable information on the format of the CSEC® examination, how to revise successfully, successful examination technique, key terms used on examination papers and School-Based Assessment. The CSEC® Biology syllabus and this book The CSEC® Biology syllabus is available online at http://cxc-store.com. You are strongly advised to read through the syllabus carefully since it provides detailed information on the specific objectives of each topic of the course, School-Based Assessment (SBA) and the format of the CSEC® examination. Each chapter in this book covers a particular topic in the syllabus. Chapters 1 to 4 cover topics in Section A, Living Organisms in the Environment Chapters 5 to 15 cover topics in Section B, Life Processes and Disease Chapters 16 and 17 cover topics in Section C, Continuity and Variation At the end of each chapter, or section within a chapter, you will find a selection of revision questions. These questions test your knowledge and understanding of the topic covered in the chapter or section. At the end Chapters 4, 15 and 17 you will find a selection of exam-style questions which also test how you apply the knowledge you have gained and help prepare you to answer the different styles of questions that you will encounter in your CSEC® examination. You will find the answers to all these questions online at www.collins.co.uk/caribbeanschools. The format of the CSEC® Biology examination The examination consists of two papers and your performance is evaluated using the following three profiles: Knowledge and comprehension Use of knowledge Experimental skills vi The pathway to success Paper 01 (1 ¼ hours) Paper 01 consists of 60 multiple choice questions. Each question is worth 1 mark. Four choices of answer are provided for each question of which one is correct. Make sure you read each question thoroughly; some questions may ask which answer is incorrect. Some questions may give two or more correct answers and ask which answer is the best; you must consider each answer very carefully before making your choice. If you don’t know the answer, try to work it out by eliminating the incorrect answers. Never leave a question unanswered. Paper 02 (2 ½ hours) Paper 02 is divided into Sections A and B, and consists of six compulsory questions, each divided into several parts. Take time to read the entire paper before beginning to answer any of the questions. Section A consists of three compulsory structured questions whose parts require short answers, usually a word, a sentence or a short paragraph. The answers are to be written in spaces provided on the paper. These spaces indicate the length of answer required and answers should be restricted to them. Question 1 is a data analysis question which is worth 25 marks. You will be provided with some form of data, such as the results obtained during a practical investigation, which you will be expected to answer questions about. The data might be in the form of a table or a graph. If you are given a table, you may be asked to draw a graph using the data and may then be asked questions about the graph. The question might also test your planning and designing skills. Questions 2 and 3 are each worth 15 marks. They usually begin with some kind of stimulus material, very often a diagram, which you will be asked questions about. Section B consists of three compulsory extended response questions, each worth 15 marks. These questions require a greater element of essay writing in their answers than those in section A. One or more questions may require a drawing as part of your answer. It is important that you can reproduce the drawings you have been taught. The marks allocated for the different parts of each question are clearly given. A total of 100 marks is available for Paper 02 and the time allowed is 150 minutes. You should allow about 35 minutes for the data analysis question worth 25 marks and allow about 20 minutes for each of the other questions. This will allow you time to read the paper fully before you begin and time to check over your answers when you have finished. The pathway to success vii Successful revision The following should provide a guide for successful revision. Begin your revision early. You should start your revision at least two months before the examination and should plan a revision timetable to cover this period. Plan to revise in the evenings when you don’t have much homework, at weekends, during the Easter vacation and during study leave. When you have a full day available for revision, consider the day as three sessions of about three to four hours each, morning, afternoon and evening. Study during two of these sessions only, do something non-academic and relaxing during the third. Read through the topic you plan to learn to make sure you understand it before starting to learn it; understanding is a lot safer than thoughtless learning. Try to understand and learn one topic in each revision session, more if topics are short and fewer if topics are long. Revise every topic in the syllabus. Do not pick and choose topics since all questions on your exam paper are compulsory. Learn the topics in order. When you have learnt all topics once, go back to the first topic and begin again. Try to cover each topic several times. Revise in a quiet location without any form of distraction. Sit up to revise, preferably at a table. Do not sit in a comfy chair or lie on a bed where you can easily fall asleep. Obtain copies of past CSEC® Biology examination papers and use them to practise answering exam style questions, starting with the most recent papers. These can be purchased online from the CXC® Store. You can use a variety of different methods to learn your work. Chose which ones work best for you. Read the topic several times, then close the book and try to write down the main points. Do not try to memorise your work word for word since work learnt by heart is not usually understood and most questions test understanding, not just the ability to repeat facts Summarise the main points of each topic on flash cards and use these to help you study. Draw simple diagrams with annotations, flow charts and spider diagrams to summarise topics in visual ways which are easy to learn. Practise drawing and labelling diagrams that you have been given. Copy them from the book at first and then try to redraw them without the book. At least one question usually tests your ability to reproduce a drawing. Use memory aids such as: - acronyms, e.g. GRIMNER for the seven life processes; growth, reproduction, irritability, movement, nutrition, excretion, reproduction. - mnemonics, e.g. ‘some men never play cricket properly’ for the six major mineral elements required by plants; sulfur, magnesium, nitrogen, phosphorus, calcium, potassium. viii The pathway to success - associations between words, e.g. tricuspid - right (therefore the bicuspid valve must be on the left side of the heart), arteries - away (therefore veins must take blood towards the heart). Test yourself using the questions throughout this book and others from past CSEC® examination papers. Successful examination technique Read the instructions at the start of each paper very carefully and do precisely what they require. Read through the entire paper before you begin to answer any of the questions. Read each question at least twice before beginning your answer to ensure you understand what it asks. Underline the important words in each question to help you answer precisely what the question is asking. Reread the question when you are part way through your answer to check that you are answering what it asks Give precise and factual answers. You will not get marks for information which is ‘padded out’ or irrelevant. The number of marks awarded for each answer indicates how long and detailed it should be. Use correct scientific terminology throughout your answers. Give any numerical answer the appropriate unit using the proper abbreviation/ symbol e.g. cm3, g, °C. If a question asks you to give a specific number of points, use bullets to make each separate point clear. If you are asked to give similarities and differences, you must make it clear which points you are proposing as similarities and which points as differences. The same applies if you are asked to give advantages and disadvantages. Watch the time as you work. Know the time available for each question and stick to it. Check over your answers when you have completed all the questions. Remain in the examination room until the end of the examination and recheck your answers again if you have time to ensure you have done your very best. Never leave the examination room early. Some key terms used on examination papers Account for: provide reasons for the information given. Annotate: add brief notes to the labels of drawings to describe the structure and/or the function of the structures labelled. Compare: give similarities and differences. Construct: draw a graph, histogram, bar chart, pie chart or table using data provided or obtained. The pathway to success ix Contrast: give differences. Deduce: use data provided or obtained to arrive at a conclusion. Define: state concisely the meaning of a word or term. Describe: provide a detailed account which includes all relevant information. Discuss: provide a balanced argument which considers points both for and against. Distinguish between or among: give differences. Evaluate: determine the significance or worth of the point in question. Explain: give a clear, detailed account which makes given information easy to understand and provides reasons for the information. Give an account of: give a written description which includes all the relevant details. Give an illustrated account of: give a written description which includes diagrams referred to in the description. Illustrate: make the answer clearer by including examples or diagrams. Justify: provide adequate grounds for your reasoning. Outline: write an account which includes the main points only. Predict: use information provided to arrive at a likely conclusion or suggest a possible outcome. Relate: show connections between different sets of information or data. State or list: give brief, precise facts without detail. Suggest: put forward an idea. Tabulate: construct a table to show information or data which has been given or obtained. Drawing tables and graphs Tables Tables can be used to record numerical data and observations. When drawing a table: Neatly enclose the table and draw vertical and horizontal lines to separate columns and rows. When drawing numerical tables, give the correct column headings which state the physical quantities measured and give the correct units using proper abbreviations/ symbols, e.g. cm3, g, °C. Give the appropriate number of decimal places when recording numerical data. x The pathway to success When drawing non-numerical tables, give the correct column headings and all observations. Give the table an appropriate title which must include reference to the responding variable and the manipulated variable. Graphs Graphs are used to display numerical data. When drawing a graph: Plot the manipulated variable on the x-axis and the responding variable on the y-axis. Choose appropriate scales which are easy to work with and which use as much of the graph paper as possible. Enter numbers along the axes and label each axis, including relevant units, e.g. cm3, g, °C. Use a small dot surrounded by a small circle to plot each point. Plot each point accurately. Join the points with a sharp continuous line. Give the graph an appropriate title which must include reference to the responding variable and the manipulated variable. Biological drawings Drawing is one of the skills assessed for SBA. Any biological drawing should be: Large enough to show all structures clearly, however, space must be left at one or both sides for labels. Drawn using a sharp HB pencil, preferably a mechanical pencil with a 0.5 mm lead. Drawn with single, sharp, continuous lines which are all of even thickness. Lines should not be sketchy and drawings should not be shaded or coloured. An accurate representation of the specimen. It must show structures typical of the specimen but should not contain unnecessary detail. If a large number of small, repetitive structures are present, only a few should be drawn to show accurate detail. Correctly proportioned. Labelled fully. Label lines should be drawn using a pencil and ruler. As far as possible label lines should be horizontal, they should not cross and should begin in or on the structure being labelled. Labels should be neatly printed in pencil and appropriately annotated. If only a few structures are labelled, all labels should be on the right. Appropriately titled. The title must be neatly printed in pencil below the drawing and be underlined. The title should include the view or type of section, the name of the specimen or structure, and the magnification of the drawing. The pathway to success xi School-Based Assessment (SBA) School-Based Assessment (SBA) is an integral part of your CSEC® examination. It assesses you in the Experimental Skills and Analysis and Interpretation involved in laboratory and field work, and is worth 20% of your final examination mark. The assessments are carried out at your school by your teacher during Terms 1 to 5 of your two-year programme. The assessments are carried out during normal practical classes and not under examination conditions. You have every opportunity to gain a high score in each assessment if you make a consistent effort throughout your two-year programme. Assessments are made of the following five skills: Manipulation and Measurement Observation, Recording and Reporting Planning and Designing Drawing Analysis and Interpretation As part of your SBA, you will also carry out an Investigative Project during the second year of your two-year programme. This project assesses your Planning and Designing, and Analysis and Interpretation skills. If you are studying two or three of the single science subjects, Biology, Chemistry and Physics, you may elect to carry out ONE investigation only from any one of these subjects. You will be required to keep a practical workbook in which you record all of your practical work and this may then be moderated externally by CXC®. xii The pathway to success 1 An introduction to living organisms Biology is the study of living organisms. All living organisms from the simplest unicellular organisms to the most complex multicellular organisms share certain characteristics. The characteristics of living organisms Living organisms have seven characteristics in common: Nutrition (feeding): the process by which living organisms obtain or make food. Animals take in ready-made food and are called heterotrophs. Plants make their own food and are called autotrophs. Respiration: the process by which energy is released from food by all living cells. Aerobic respiration requires oxygen and takes place in most cells. Anaerobic respiration takes place without oxygen in certain cells. Excretion: the process by which waste and harmful substances, produced by the body’s metabolism, are removed from the body. Movement: a change in the position of a whole organism or of parts of an organism. Most animals can move their whole bodies from place to place. Plants and some animals can only move parts of their bodies. Irritability (sensitivity): the ability of organisms to detect and respond to changes in their environment or within themselves. Growth: a permanent increase in the size and complexity of an organism. Reproduction: the process by which living organisms generate new individuals of the same kind as themselves. Asexual reproduction requires only one parent. Sexual reproduction requires two parents. Classiﬁcation of living organisms Using similarities and differences between living organisms they can be classiﬁed into groups. Simple classiﬁcations can be done based on visible characteristics such as number of legs, number of body parts, number of wings, presence or absence of antennae, hairiness, shape, arrangement of veins in a leaf or an insect’s wing. Scientists also use internal structures, developmental patterns, life cycles and electron microscopic techniques to classify organisms. In addition, the modern classiﬁcation uses the molecular structure of deoxyribonucleic acid (DNA) to assist in grouping organisms; the greater the similarity in their DNA structure, the more closely related are the organisms. The basic category of classiﬁcation is the species. A species is a group of organisms of common ancestry that closely resemble each other and are normally capable of interbreeding to produce fertile offspring. Closely related species are then grouped into genera (singular genus). Related genera are then grouped into families, related families into orders, orders into classes, classes into phyla and phyla are grouped into kingdoms. i.e. species genera families orders classes phyla kingdoms There are ﬁve kingdoms in the modern classiﬁcation. Members of the kingdom Prokaryotae have cells that lack true membrane-bound nuclei, so their DNA is free in the cells. Members of the other four kingdoms have cells that contain true nuclei surrounded by membranes (see Chapter 5). These are known collectively as eukaryotes. Viruses make up a group of organisms without any cellular structure. They are particles made up of a piece of DNA or RNA surrounded by a protein coat and they can only reproduce inside other living cells. Viruses are not included in the ﬁve kingdom classiﬁcation. 1 An introduction to living organisms 1 Prokaryotae Bacteria and blue-green algae Unicellular organisms Cells have a cell wall Cells lack a true nucleus, the DNA is free in the cell Cells lack other membrane-bound organelles, e.g. mitochondria, chloroplasts Most feed by absorbing food e.g. tuberculosis (TB) bacterium Protoctista Includes the protozoa and algae Most are unicellular, some are simple multicellular organisms that lack any complex development of tissues and organs Cells have a true nucleus surrounded by a membrane and other membrane-bound organelles Protozoans are animal-like and ingest food or absorb food Algae are plant-like, contain chlorophyll and make their own food by photosynthesis e.g. Amoeba, Paramecium, Euglena, Sargassum (seaweed) The living world Fungi Includes yeasts, moulds and mushrooms Most are multicellular with a body composed of microscopic threads called hyphae, a few are unicellular Cells have cell walls that contain chitin Cells lack chlorophyll Most reproduce by spores Feed by absorbing food e.g. pin mould Plantae (plants) Multicellular organisms Cells have cell walls made of cellulose Cells contain chlorophyll Make their own food by photosynthesis Stationary organisms (see Figure 1.2, below) Animalia (animals) Multicellular organisms Cells lack cell walls and chlorophyll Feed by ingesting food Most move their whole bodies from place to place (see Figure 1.3, below) Figure 1.1 The five kingdoms Bryophytes Have simple stems and leaves Have root-like ﬁlaments called rhizoids Produce spores for reproduction Live in damp, shady places e.g. moss, liverwort Ferns Have proper roots, stems and leaves called The plant fronds kingdom Produce spores on the underside of fronds for reproduction Monocotyledons e.g. breadfruit fern, maidenhair fern Leaves have straight, parallel veins and are usually long and narrow Conifers Seeds contain one cotyledon (seed leaf) Have proper roots, stems and leaves Flower parts are in multiples of three Leaves are usually needle-shaped e.g. sugar cane, guinea grass Produce seeds inside cones for reproduction e.g. pine, ﬁr Dicotyledons Leaves have a network of veins and are Flowering plants usually broad Have proper roots, stems and leaves Seeds contain two cotyledons Produce seeds inside fruits that develop from Flower parts are in multiples of four or ﬁve ovaries of ﬂowers for reproduction e.g. pride of Barbados, ﬂamboyant Figure 1.2 The main groups of plants 2 1 Concise Revision Course: CSEC® Biology Porifera (sponges) Crustaceans Stationary organisms Have two pairs of antennae Lack tissues and organs Usually have ﬁve or seven pairs of legs Body contains a single cavity with many Body is divided into head, thorax and abdomen pores in its walls making a system of water or cephalothorax and abdomen canals e.g. lobster, shrimp, crab, woodlouse e.g. barrel sponge, vase sponge Arachnids Cnidaria Have no antennae Have a bag- or umbrella-shaped body Have four pairs of legs Gut has only one opening, the mouth Body is divided into cephalothorax and abdomen Have a ring of tentacles around the mouth e.g. spider, tick, scorpion e.g. sea anemone, coral, jellyﬁsh Insects Platyhelminthes (ﬂatworms) Have one pair of antennae Have a long, ﬂat, unsegmented body Have three pairs of legs e.g. tapeworm, liver ﬂuke Body is divided into head, thorax and abdomen Nematodes (roundworms) Have a pair of compound eyes Have an elongated, round, unsegmented Most have two pairs of wings body with pointed ends e.g. cockroach, moth, ant, house ﬂy e.g. hookworm, threadworm Myriapods Annelids (segmented worms) Have one pair of antennae Have an elongated body divided into Have many pairs of legs The animal segments Body is elongated and divided into many segments kingdom e.g. earthworm e.g. centipede, millipede Arthropods Have a waterproof exoskeleton (external skeleton) made mainly of chitin Pisces (ﬁsh) Have a segmented body Have a waterproof skin covered with scales Have several pairs of jointed legs Have gills for breathing Molluscs Have ﬁns for swimming Have a soft, moist, unsegmented body e.g. barracuda, ﬂying ﬁsh, shark Have a muscular foot Amphibians Many have shells Have a soft, moist, non-waterproof skin without e.g. slug, snail, octopus scales Echinoderms Eggs are laid in water, larvae live in water, adults Have a body based on a radial pattern live on land of ﬁve parts Larvae have gills, adults have lungs Body wall contains calcium carbonate e.g. frog, toad, newt plates, often with projecting spines Reptiles Have tube feet with suction pads for Have a dry, waterproof skin with scales movement Lay eggs with a rubbery shell on land e.g. starﬁsh, sand dollar, sea urchin e.g. snake, lizard, iguana, turtle Chordates Aves (birds) Have a notochord (rod) running down the Have a waterproof skin with feathers body, most have a backbone Have a dorsal nerve cord with the anterior Have a beak and no teeth end usually enlarged forming the brain Forelimbs are modiﬁed to form wings Most have an internal skeleton of bone Lay eggs with a hard shell and cartilage Are homeothermic (warm blooded) e.g. sparrow, cattle egret, hawk Mammals Have a waterproof skin with hair and sweat glands Have different types of teeth Young feed on milk from their mother Are homeothermic e.g. mouse, whale, human Figure 1.3 The main groups of animals 1 An introduction to living organisms 3 Kingdom Prokaryotae: bacteria Kingdom Protoctista: Amoeba and Paramecium Kingdom Protoctista: Sargassum (seaweed) Kingdom Fungi: pin mould on bread Revision questions 1 Identify FIVE ways you could use to determine if something is living. 2 What methods do scientists use to classify living organisms? 3 a What makes members of the kingdom Prokaryotae different from members of the other four kingdoms? b Name the other FOUR kingdoms into which organisms can be classified. 4 State THREE differences between plants and animals. 5 What is a species? 6 Give TWO ways to distinguish between a monocotyledon and a dicotyledon. 7 Give TWO characteristics of the members of EACH of the following groups: a insects b fish c mammals d arthropods. 4 1 Concise Revision Course: CSEC® Biology 2 Living organisms in their environment Living organisms constantly interact with each other and the environment in which they live. Deﬁnitions Ecology: the study of the interrelationships of living organisms with each other and with their environment. Environment: the combination of factors that surround and act upon an organism. These factors can be divided into two groups: Biotic factors: all the other living organisms that are present such as predators, prey, competitors, parasites and pathogens. Abiotic factors: all the non-living chemical and physical factors (see page 8). Habitat: the place where a particular organism lives. For example, the habitat of an earthworm is the upper layers of the soil. Species: a group of organisms of common ancestry that closely resemble each other and are normally capable of interbreeding to produce fertile offspring. Population: all the members of a particular species living together in a particular habitat. For example, all the sea urchins living in a sea grass bed form a population. Community: all the populations of different species living together in a particular habitat. For example, a woodland community consists of all the plants, animals and decomposers that inhabit the wood. Ecosystem: a community of living organisms interacting with each other and with their abiotic environment. Examples of ecosystems include a pond, a coral reef, a mangrove swamp, a grassland and a forest. Niche: the position or role of an organism within an ecosystem. For example, an earthworm’s niche is to burrow through the soil, improving its aeration, drainage and fertility. Carrying out an ecological study The aim of studying any ecosystem is to identify the different species of plants and animals present, to ﬁnd out where they live, determine their numbers, and ﬁnd out about the relationships they have with each other and with the abiotic factors. Ecosystems studied could include a pond, a piece of wasteland, a small area of woodland, an area of grassland, a sand dune or a rocky shore. Collecting organisms To identify organisms, they may need to be collected. Organisms must never be collected or destroyed unnecessarily; as few as possible should be collected and returned to their original positions if possible, and their habitat should be left as undisturbed as possible. Pooters, pitfall traps, nets, plankton nets and a Tullgren funnel may be used. 2 Living organisms in their environment 5 intake suck here fine net – traps plankton as it is pulled through the water string gauze over tube specimen jar sample jar – collects plankton small animals wire frame are sucked into the jar Pooter for small animals, especially those Plankton net for plankton in small places ﬂat stone to keep rain out reflector light bulb – light and heat supporting stone cause animals to move soil sample downwards through the or leaf litter soil or leaf litter container, e.g. jam jar funnel or plant pot – sunk in the ground wire mesh – small animals crawling animals fall fall through into the container collecting jar – may contain water or alcohol Pitfall trap for walking or crawling animals Tullgren funnel for small animals in soil wire frame samples or leaf litter handle net – traps flying insects or aquatic animals Net for ﬂying insects or aquatic animals Figure 2.1 Methods to collect organisms Sampling techniques It is not practical to ﬁnd and count all members of all species present, so sampling techniques are used to sample small areas from which conclusions can be drawn about the ecosystem as a whole. Observation The ecosystem should ﬁrst be observed and the common species of plants and animals recorded. Any adaptations that enable the organisms to survive in the ecosystem should be noted, together with any interrelationships between the organisms. 6 2 Concise Revision Course: CSEC® Biology Quadrats A quadrat is a square frame whose area is known, e.g. metal or 0.25 m2 or 1 m2. It is placed, at random, several times wooden frame within the ecosystem. The number of individuals of each species of plant and stationary or slow-moving 1m animal found within the quadrat is counted. If it is not string or wire possible to distinguish individual plants of a species, e.g. grass, the quadrat can be made into a grid using string and the percentage of the quadrat area covered can be estimated. Quadrats are used to study the distribution and Figure 2.2 A grid quadrat abundance of plants and stationary or slow-moving animals in uniform ecosystems, e.g. an area of grassland. Line transects A line transect is usually a measuring tape or string that has marks at regular intervals, e.g. 10 cm or 25 cm. It is placed in a straight line across the ecosystem and the species of plants and stationary or slow-moving animals touching the line, or touching the line at each mark, are recorded. Line transects are useful where there is a transition of organisms across the ecosystem, e.g. down a rocky seashore. They give a quick idea of the species present and how they change across the ecosystem. Key: species A species B species C species D 0 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 horizontal distance along the ground/cm Figure 2.3 Displaying the results of a line transect for four species, A, B, C and D Belt transects A belt transect is a strip of ﬁxed width, e.g. 0.5 m or 1 m, made by placing two parallel line transects across an ecosystem. The species found between the lines are recorded. Alternatively, a quadrat can be placed alongside one line transect and the number of individuals of each species found within its boundaries is counted. The quadrat is then moved along the line and counting is repeated at regular intervals. Estimating population sizes Population sizes can be estimated by using the results from quadrats or by using the capture– recapture method. Using results from quadrats Results from quadrats can be used to obtain: Species density This is the average number of individuals of a given species per m2. If the quadrat is 1 m2, it is obtained by dividing the total number of individuals of the species by the number of quadrats used. Total population This is the total number of individuals of a given species in the area under study. It is obtained by multiplying the species density by the total area of the ecosystem studied. 2 Living organisms in their environment 7 Species cover This is the percentage of ground covered by a given species. It is used if the percentage of the quadrat area covered was estimated. If the quadrat is 1 m2, it is obtained by dividing the total percentage of ground that the species covered by the number of quadrats used. Species frequency This is the percentage of quadrats in which the given species was found. These results can be recorded in tables and bar charts. Table 2.1 Displaying results obtained for four species using a 1 m2 quadrat Species Number of organisms or percentage cover in Total of 10 Species Species Species each quadrat (Q) quadrats density/ cover/% frequency/% Q1 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 number of individuals per m2 W 6 8 4 7 5 30 3 50 X 12 5 15 7 12 8 4 16 1 80 8 90 Y 10% 50% 45% 5% 40% 30% 5% 25% 210% 21 80 Z 15% 25% 5% 30% 10% 5% 90% 9 60 a species density b species cover 30 10 )2m rep slaudividni( )%( revoc seiceps ytisned seiceps 20 5 10 0 0 W X Y Z species species Figure 2.4 Bar charts displaying the results obtained from quadrats Capture–recapture method Capture–recapture is used to estimate population sizes of moving animals. A representative sample of animals of a species is collected, the animals are counted and each one is marked, e.g. with a dot of paint. The animals are released back into the same area and given time to mix with the original population. A second sample is collected, counted and the number of marked organisms counted. The population size is then estimated: number of organisms × number of organisms estimated population size = in ﬁrst sample in second sample number of marked organisms recaptured The impact of abiotic factors on living organisms The abiotic environment supplies living organisms with many of the requirements that they need to survive. Abiotic factors are important in determining the types and numbers of organisms that exist in a given environment, i.e. they inﬂuence the distribution and behaviour of living organisms. These factors can be divided into the following: edaphic factors climatic factors aquatic factors. 8 2 Concise Revision Course: CSEC® Biology Edaphic factors Edaphic factors are those connected with the soil. Soil is a mixture of inorganic rock particles, water, air, mineral salts, organic matter and living organisms including plant roots, small animals and micro- organisms. Soil provides organisms living in it with water, oxygen, nitrogen and mineral nutrients. Table 2.2 Edaphic factors and their impact on living organisms Edaphic factor Impact on living organisms Texture, i.e. composition of Inﬂuences the water content of the soil. The smaller the soil rock particles particles, the more water held by capillarity and chemical forces Rock particles form from and the higher the water content. rocks by weathering and are Inﬂuences the air content of the soil. The larger the soil particles, classiﬁed by size: the larger the air spaces and the higher the air content. Clay: less than 0.002 mm Inﬂuences the mineral ion content of the soil. The smaller the Silt: 0.002–0.02 mm soil particles, the harder it is to leach and the higher the mineral Sand: 0.02–2.0 mm content. Gravel: greater than 2.0 mm Inﬂuences how easy it is for plant roots to penetrate and animals The percentage of each to burrow through the soil. The larger the particles, the easier to determines the texture of penetrate and burrow through. the soil. Water Essential for photosynthesis in plants. Obtained from rainfall and Dissolves minerals so they can be absorbed by plant roots. held in a thin ﬁlm around soil Prevents the desiccation (drying out) of soil organisms without particles by capillarity and waterproof body coverings, e.g. earthworms. chemical forces. Air Oxygen in the air is essential for aerobic respiration in plant roots Present in the spaces between and soil organisms. the soil particles. Oxygen in the air is necessary for bacteria and fungi to decompose organic matter aerobically to form humus. Nitrogen in the air is necessary for nitrogen ﬁxing bacteria to form inorganic nitrogenous compounds, e.g. nitrates. Mineral nutrients Essential for healthy growth of plants (see Table 7.1, page 50) Formed from decomposing organic matter and by dissolving from the surrounding rock. Present as ions dissolved in soil water. pH Mainly affects mineral ion availability for plants. If the soil is too The optimum pH for most acidic or alkaline, mineral ions become less available. plants is 6.0 to 7.5 Humus Improves the air content by binding soil particles together in Formed by bacteria and fungi small clumps called soil crumbs. decomposing dead or waste Improves the mineral ion content by adding minerals, and organic matter. Humus is a absorbing and retaining minerals. dark brown, sticky material Improves the water content by absorbing and retaining water. which coats soil particles, mainly in the topsoil. 2 Living organisms in their environment 9 Climatic factors The climatic factors affecting terrestrial organisms include light, temperature, humidity, water availability, wind and atmospheric gases. Light Light intensity and its duration affect living organisms. Light is essential for plants to make food by photosynthesis and the rate of photosynthesis depends on light intensity. Light also synchronises activities of plants and animals with the seasons, e.g. ﬂowering in plants, and migration, hibernation and reproduction in animals. Temperature Most organisms can only survive within a certain, narrow temperature range. At low temperatures, ice crystals may form in cells and damage them. At high temperatures, enzymes are denatured. Temperature affects the rate of photosynthesis and germination in plants and the activity of animals, e.g. many animals become dormant in low temperatures. Humidity Humidity affects the rates of transpiration in plants and evaporation of water from some animals. Water availability Terrestrial habitats receive water by precipitation from the atmosphere as rain, snow, sleet and hail. Water is essential for life. Chemical reactions in cells and most life processes need water in order to take place (see page 54). It is also essential for photosynthesis in plants. Wind Wind is essential for pollination and seed dispersal in many plants and may also inﬂuence migration of birds. It can affect the rate of transpiration in plants, the rate of evaporation of water from animals and the growth of vegetation, e.g. branches on the windward side of trees in exposed places become stunted and deformed. Seed dispersing in the wind Tree exposed to the wind Atmospheric gases The air is a mixture of gases including nitrogen, oxygen, carbon dioxide, water vapour and pollutants. Oxygen is essential for aerobic respiration in almost all living organisms, carbon dioxide is essential for photosynthesis in plants and pollutant gases have a negative effect on living organisms. 10 2 Concise Revision Course: CSEC® Biology Aquatic factors Aquatic factors affect organisms living in aquatic habitats, e.g. ponds, lakes, rivers, oceans and coral reefs. Aquatic organisms are affected by light, temperature, water availability and pollutants in the same way as terrestrial organisms. They are also affected by other factors. Salinity Salinity refers to the concentration of salt in the water. Most aquatic organisms are adapted to survive in a speciﬁc salinity and can only tolerate small changes. Some are adapted to live in fresh water, some in salt (sea) water and others in brackish water, e.g. in estuaries. Water movement and wave action Organisms living in rivers and streams are affected by the constant movement of water, those living along ocean shorelines are exposed to wave action and to changing water levels as the tide changes, and those living in oceans are affected by currents. Dissolved oxygen Aquatic organisms use oxygen dissolved in the water for respiration. Oxygen levels in still or polluted water are often low, whereas habitats exposed to moving water usually have sufﬁcient oxygen. Revision questions 1 What is ecology? 2 Distinguish between the following pairs of terms: a habitat and niche b population and community c species and population. 3 Identify FOUR methods you could use to collect organisms from a habitat. 4 Explain how you would estimate: a the total population of a small, named plant growing in an area of wasteland b the total number of snails in a garden. 5 Define the term ‘environment’. 6 Distinguish between the biotic environment and the abiotic environment. 7 Discuss the importance of EACH of the following edaphic (soil) factors to organisms living in the soil: a water b air c mineral nutrients. 8 Discuss the importance of EACH of the following climatic factors to living organisms: a light b temperature c atmospheric gases. 2 Living organisms in their environment 11 3 Interrelationships between living organisms Many kinds of relationships exist between living organisms. These relationships may be beneﬁcial or harmful, close or loose. Feeding relationships Food chains Organisms within any ecosystem are linked to form food chains based on how they obtain organic food. Energy from the sun enters living organisms through photosynthesis occurring in green plants, also known as primary producers. This energy is incorporated into organic food molecules produced by the plants and is passed on to consumers through food chains. A food chain includes: A primary producer, i.e. a green plant. A primary consumer which eats the primary producer. A secondary consumer which eats the primary consumer. A tertiary consumer which eats the secondary consumer. Some food chains may also include a quaternary consumer which eats the tertiary consumer. Consumers can also be classiﬁed according to what they consume: Herbivores consume plants, e.g. cows, grasshoppers, snails, slugs, parrotﬁsh, sea urchins. Carnivores consume animals, e.g. lizards, toads, spiders, centipedes, eagles, octopuses, sharks. Omnivores consume both plants and animals, e.g. hummingbirds, crickets, humans, crayﬁsh. The levels of feeding within a food chain are referred to as trophic levels. Trophic level Organism’s status A terrestrial food chain An aquatic food chain 5 quaternary consumer (carnivore) hawk tiger shark 4 tertiary consumer (carnivore) snake barracuda 3 secondary consumer (carnivore) lizard ﬂying ﬁsh primary consumer 2 (herbivore) grasshopper zooplankton primary producer 1 (green plant) grass phytoplankton Figure 3.1 Examples of food chains 12 3 Concise Revision Course: CSEC® Biology Predator/prey relationships A predator is an organism that kills and feeds on another organism, e.g. a lion. The prey is the organism that the predator eats, e.g. a zebra. Predators are often the prey of other organisms and prey are often predators themselves. An apex predator is at the top of a food chain and has no predators, e.g. killer whales, tiger sharks, hawks, owls. Table 3.1 Predator/prey relationships from Figure 3.1 Habitat Predator Prey Terrestrial hawk snake snake lizard lizard grasshopper Aquatic tiger shark barracuda barracuda ﬂying ﬁsh ﬂying ﬁsh zooplankton A hawk swooping towards its prey A predator and its prey evolve together. The predator must evolve characteristics to catch its prey, e.g. speed, stealth, camouﬂage, highly developed senses, sharp and piercing mouthparts, poison to kill its prey, immunity to the prey’s poison. At the same time, the prey evolves characteristics to avoid being eaten, e.g. speed, camouﬂage, highly developed senses, rapid responses, poison, protective body coverings. Predator/prey relationships serve as biological controls and keep the numbers of organisms in an ecosystem relatively constant. If a predator overhunts its prey, the prey population will decrease and this will cause the predator population to decrease. The prey population will then begin to increase again, which will allow the predator population to increase. Humans can use predator/prey relationships to control pests. This is known as biological control. It involves introducing a natural predator of the pest into the environment, e.g. mongooses were introduced into Barbados to control the snake population. Food webs Any ecosystem usually has more than one primary producer and most consumers have more than one source of food. Consequently, food chains are interrelated to form food webs. quaternary consumers mongoose hawk tertiary consumers snake kingbird secondary consumers lizard frog mouse primary consumers caterpillar grasshopper primary producers hibiscus leaves grass seeds Figure 3.2 An example of a terrestrial food web 3 Interrelationships between living organisms 13 Detritivores and decomposers Detritivores and decomposers are organisms that are present in ecosystems. They are essential for the recycling of chemical elements within all ecosystems (see page 17). Detritivores are animals, e.g. earthworms, woodlice, millipedes and sea cucumbers, which feed on pieces of decomposing organic matter, breaking them down into smaller fragments. Decomposers are micro-organisms, i.e. bacteria and fungi, which feed saprophytically on dead and waste organic matter causing it to decompose. They secrete digestive enzymes that breakdown complex organic compounds into simple organic compounds which they absorb. During this process, they release carbon dioxide and inorganic mineral nutrients in the form of ions, e.g. nitrates and sulfates, into the environment. These can then be reabsorbed and re-used by plants. organic compounds in producers absorbed by producers consumed by consumers carbon dioxide inorganic mineral organic compounds in the air ions in the soil in consumers death and decomposition by decomposers Figure 3.3 Cycling in a terrestrial ecosystem Symbiotic relationships Symbiosis is any close relationship between two organisms of different species. Symbiotic relationships can be divided into the following types: parasitism commensalism mutualism. Parasitism In parasitism, one organism, the parasite, gains beneﬁt and the other organism, the host, is harmed. The parasite lives in or on the host and often has a vector or intermediate host which is unharmed by the parasite. The parasite usually reproduces inside the intermediate host and this increases the parasite’s chances of survival and transmission. Lice and ticks live on certain mammals, e.g. humans, dogs and cows, sucking their blood. Ticks on cattle cause damage to the hide, weakness, anaemia and tick paralysis. Tapeworms live in the intestines of humans. The tapeworm absorbs digested food from the intestines and also gains shelter and protection. The infected person may suffer from abdominal pains, loss of appetite, weight loss and nausea. A pig is usually the intermediate host. Plasmodium is the parasite that causes malaria in humans. After initially reproducing in the liver, the parasites enter red blood cells where they live and reproduce. A tapeworm in human intestines 14 3 Concise Revision Course: CSEC® Biology A high fever develops when the cells burst and release the parasites and subsides as the parasites enter more red blood cells. It then recurs as the cells burst and the cycle continues resulting in a recurrent fever. The Anopheles mosquito is the intermediate host. Dodder (love vine) is a parasitic plant with long yellow stems that twist around other plants from small shrubs to tall trees. Outgrowths from the stems penetrate into the host’s phloem and absorb sugars and amino acids. This causes reduced growth of the host. Commensalism Bromeliads growing on tree trunks In commensalism, one organism, the commensal, gains beneﬁt while the other organism neither gains nor is harmed. Epiphytes are plants, e.g. orchids and bromeliads, which grow non-parasitically on other plants, usually trees, which they use for support since their roots do not enter the soil. They usually grow high up on the branches where they are close to sunlight, have very little shade and are out of the reach of herbivores on the ground. Cattle egrets are commensals that perch on the back of cows. They gain food by eating ticks from the cow’s skin and insects that the cow disturbs as it Remora attached to a shark moves through the grass. Remoras are small ﬁsh that attach themselves onto the skin of sharks by suction cups on their heads. They gain food scraps left by the sharks as they feed. Mutualism In mutualism, both organisms gain beneﬁt, and in many cases, they cannot survive without each other. Leguminous plants, e.g. peas and beans, have nitrogen ﬁxing bacteria living in swellings on their roots called root nodules. The bacteria use nitrogen in the air in the soil to produce inorganic nitrogenous compounds. The plants gain nitrogenous compounds Root nodules of a leguminous plant which they use to manufacture proteins. The bacteria gain food, which the plants produce during photosynthesis, and protection. Coral polyps have green algae living within the tissues lining their digestive cavities. The polyps gain food and oxygen as the algae photosynthesise. The algae gain carbon dioxide as the polyps respire, nitrogenous compounds excreted by the polyps, and protection. Termites have protozoans living in their intestines. Termites are unable to digest the cellulose in the wood they eat; however, the protozoans can digest this cellulose into sugars. The termites gain digested food. The protozoans are supplied with food and Coral polyps protection. 3 Interrelationships between living organisms 15 Other interrelationships A variety of other interrelationships exist between living organisms: Camouﬂage: some organisms resemble others so they are concealed, e.g. stick insects resemble woody stems. Pollination: many plants depend on insects, small birds or bats to transfer their pollen from one ﬂower to another for reproduction. Support: some organisms use others for support, e.g. birds build nests in trees, vines use the support of other plants to grow closer to sunlight. Protection: some organisms use others for protection, e.g. grasshoppers live in long grass. Competition: members of the same species and of different species may compete with each other. Animals compete for food, space, a mate and shelter. Plants compete for light, water and minerals. Energy ﬂow in ecosystems During photosynthesis, primary producers absorb sunlight energy and convert it into chemical energy, which is stored in organic food molecules. Some of this energy is then released by the producers during respiration and some is passed on through food chains in the organic molecules. At each trophic level in a food chain, energy and biomass (amount of biological matter) are lost. Some organic matter containing energy is lost in faeces and some is lost in organic excretory products, e.g. urea. Some is used in respiration during which the stored energy is released and used, or lost as heat. The remaining energy containing organic matter is used in growth and repair, and is then passed on to the next trophic level when organisms are consumed. Organisms not consumed eventually die. The organic matter in faeces, excretory products and dead organisms is decomposed by decomposers and they release the energy during respiration. Energy, therefore, ﬂows from producers to consumers and decomposers in one direction through ecosystems, and is not recycled. In general, only 10% of the energy from one level is transferred to the next level. energy from energy lost energy lost energy lost energy lost energy lost the sun during respiration during respiration during respiration during respiration during respiration primary consumption primary consumption secondary consumption tertiary producer consumer consumer consumer faeces faeces faeces and excretory and excretory and excretory products products products death death death death decomposers Figure 3.4 Energy flow through an ecosystem 16 3 Concise Revision Course: CSEC® Biology Ecological pyramids trophic level Because there is less energy and biomass 5 quaternary consumer at each trophic level in a food chain, fewer 4 tertiary consumer organisms can be supported at each level. Energy, biomass and number of organisms 3 secondary consumer at successive levels can be represented 2 primary consumer by ecological pyramids. Due to the loss 1 primary producer of energy and biomass at each level, food chains rarely exceed four or ﬁve Figure 3.5 Pyramid of energy, biomass or numbers trophic levels. Recycling Recycling of materials in nature Materials are constantly being recycled and re-used in nature. The different chemical elements that make up the bodies of all living organisms, mainly carbon, hydrogen, oxygen, nitrogen, phosphorus, sulfur and calcium, are continually cycled through these living organisms and the physical environment. Decomposers are essential to the recycling of most of these elements. The cycling of water The cycling of water is essential to ensure that: Plants have a continuous supply of water to manufacture organic food by photosynthesis. All living organisms have a continuous supply of water to keep their cells hydrated and to act as a solvent (see page 54). Aquatic organisms have a constant environment in which to live. The cycling of carbon Carbon atoms are cycled by being converted into different compounds containing carbon, e.g. carbon dioxide and all organic compounds. The cycling of carbon is essential to ensure that: Plants have a continuous supply of carbon dioxide to manufacture organic food by photosynthesis. Animals and decomposers have a continuous supply of organic food. carbon dioxide (CO2) in the air – 0.038% combustion photosynthesis respiration respiration respiration organic compounds in fossil fuels organic compounds eaten by organic compounds in green plants animals in animals death and death and decomposition organic compounds decomposition in decomposers fossilisation fossilisation Figure 3.6 A simplified carbon cycle 3 Interrelationships between living organisms 17 The cycling of nitrogen Nitrogen atoms are cycled by being converted into different compounds containing nitrogen, e.g. nitrates and proteins. The cycling of nitrogen is essential to ensure that: Plants have a continuous supply of nitrates to manufacture proteins. Animals and decomposers have a continuous supply of proteins. Recycling of manufactured and other waste materials Recycling changes waste materials into new products. Recyclable materials can be divided into two categories: Biodegradable materials: these can be decomposed by the action of living organisms, mainly bacteria and fungi. They include waste from the food industry, farmyard and garden waste, most paper and bagasse from the sugar industry. Non-biodegradable materials: these cannot be decomposed by living organisms. They include glass, plastics, rubber, construction waste, synthetic fabrics such as nylon, and metals such as iron, steel, aluminium, copper and lead. Bagasse is biodegradable Plastics are non-biodegradable Recycling of manufactured and other waste materials is important because it: Prevents wastage of potentially useful materials. Conserves natural resources by reducing the quantity of fresh raw materials used in manufacturing. Reduces energy usage. Reduces the quantity of waste requiring disposal. Reduces pollution of air, land and water. Difﬁculties encountered in recycling manufactured materials Several difﬁculties are encountered when trying to recycle materials: It can be difﬁcult to persuade households and industries to separate their waste into different types. It is more difﬁcult to collect, transport and store waste items when separated into different types. It can be time consuming because items have to be cleaned before they are recycled. Also, different manufactured materials can have very different properties and they have to be sorted into their different types before recycling, e.g. there are many different types of plastics. It can be hazardous because recyclable materials have to be separated from any toxic materials before they can be recycled, e.g. the acid has to be removed from lead batteries before recycling the lead. 18 3 Concise Revision Course: CSEC® Biology It can be uneconomical in small countries such as the Caribbean islands because it is labour and energy intensive, and the quantity of recyclable materials generated by these countries is insufﬁcient to maintain the full-time operation of recycling plants. Most small countries do not have the facilities to use recycled raw materials. Revision questions 1 Some aphids were observed on the tomato plants in a garden and ladybird beetles were seen feeding on the aphids. The ladybirds were, in turn, being eaten by dragonflies which were, themselves, being fed on by toads. Use this information to draw a food chain for the organisms in the garden. 2 From the organisms in question 1, identify: a a carnivore b a herbivore c a primary producer d a primary consumer e a secondary consumer f a predator/prey relationship. 3 What are decomposers and why are they essential within any ecosystem? 4 What is a symbiotic relationship? 5 Give ONE example of EACH of the following symbiotic relationships: a mutualism b commensalism c parasitism. For EACH example, name the partners involved and discuss the impact of the relationship on BOTH partners. 6 Explain why food chains rarely contain more than four or five trophic levels. 7 With reference to water, carbon and nitrogen, explain why it is important to continually recycle materials in nature. 8 Suggest FOUR reasons why it is important to recycle manufactured and other waste materials in today’s world. 9 Suggest THREE difficulties encountered when trying to recycle manufactured and other waste materials in small countries such as the islands of the Caribbean. 3 Interrelationships between living organisms 19 4 The impact of humans on the environment The human population is currently growing at about 1.2% per year. This growth, together with improved standards of living, is having a profound effect on all other living organisms, natural resources and the environment in general. The impact of human activities on natural resources Human activities are having a negative impact on both non-renewable and renewable natural resources, and in many cases, these resources are being rapidly depleted. Non-renewable resources Non-renewable resources are present in the Earth in ﬁnite amounts; they cannot be replaced, and consequently they are running out. These include: Energy resources such as fossil fuels, i.e. petroleum (crude oil), natural gas and coal, and radioactive fuels, e.g. uranium. Mineral resources such as iron ore, bauxite (aluminium ore), copper and tin. Renewable resources Renewable resources can be replaced by natural processes. However, many plant and animal species are being overexploited such that their numbers are decreasing, in some cases to the point of extinction. Many marine organisms are being overﬁshed for food, e.g. lobsters, whales, turtles, sea eggs and conch. Some terrestrial organisms are being overhunted for products such as fur and ivory, e.g. mink, seal and elephants. Illegal hunting endangers elephants 20 4 Concise Revision Course: CSEC® Biology Vast areas of forest are being cut down to provide land for housing and agriculture, and to provide materials for fuel, building and the manufacture of paper. This deforestation leads to: The loss of a habitat for plants and animals. The destruction of plants and animals living in the forests. Some of these may eventually become extinct. A reduction in photosynthesis resulting in a gradual increase in atmospheric carbon dioxide levels which is contributing to the greenhouse effect (see page 26). Disruption of the water cycle. Soil erosion caused by the absence of leaves to break the force of the rain and roots to bind the soil. Deforestation leaves soil exposed to soil erosion Soil is being eroded due to cutting down trees and not replanting, and bad agricultural practices such as leaving the soil barren after harvesting, using chemical fertilisers instead of organic fertilisers, overgrazing of animals and ploughing down hillsides instead of contour ploughing. The loss of soil leads to: A reduction in the number of trees and other plants that can be grown. A reduction in the quantity of agricultural crops that can be grown. The negative impact of human activity on the environment Many human activities such as agriculture, industry, mining and disposal of waste have a negative impact on living organisms and the environment. These activities: Cause the destruction and consequent loss of habitats and organisms living in them. Release waste and harmful substances into the environment which damage the environment, harm living organisms and have a negative effect on human health, i.e. they cause pollution. 4 The impact of humans on the environment 21 Pollution caused by agricultural practices and industry Modern agricultural practices and industry produce waste products that pollute the air, land and water. Pollution is the contamination of the natural environment by the release of unpleasant and harmful substances into the environment. Table 4.1 Pollution caused mainly by agricultural practices Pollutant Origin Harmful effects Pesticides, Used in agriculture to Become higher in concentration up food chains and e.g. control pests, diseases can harm top consumers. insecticides, and weeds. Can harm useful organisms as well as harmful ones, fungicides Used to control e.g. bees, which are crucial for pollination in plants. and vectors of disease, e.g. herbicides mosquitoes. Nitrate ions Chemical fertilisers Cause eutrophication, i.e. the rapid growth of green (NO3 ) and − used in agriculture. plants and algae in lakes, ponds and rivers, which phosphate Synthetic detergents. causes the water to turn green. The plants and algae ions (PO4 ) 3− begin to die and are decomposed by aerobic bacteria that multiply and use up the dissolved oxygen. This causes other aquatic organisms to die, e.g. ﬁsh. Eutrophication 22 4 Concise Revision Course: CSEC® Biology Table 4.2 Pollution caused mainly by industry Pollutant Origin Harmful effects Carbon Burning fossil Builds up in the upper atmosphere enhancing the dioxide (CO2) fuels in industry, greenhouse effect, which is leading to global warming motor vehicles, (see page 26). power stations and Some is also absorbed by oceans causing ocean aeroplanes. acidiﬁcation (see page 26). Carbon Burning fossil fuels in Combines with haemoglobin more easily than oxygen. monoxide industry and motor This reduces the amount of oxygen reaching body (CO) vehicles. cells which reduces respiration and mental awareness. Bush ﬁres and cigarette Itandcauses dizziness, headaches and visual impairment, can lead to unconsciousness and death. smoke. Sulfur dioxide Burning fossil fuels in Causes respiratory problems, e.g. bronchitis, and (SO2) industry and power reduces the growth of plants. stations. Dissolves in rainwater forming acid rain. Acid rain decreases the pH of the soil, damages plants, harms animals, corrodes buildings, and causes lakes, streams and rivers to become acidic and unsuitable for aquatic organisms. Combines with water vapour and smoke forming smog, which causes respiratory problems, e.g. bronchitis, asthma and lung disease. Pollution from industry Oxides of Combustion at Very toxic. Cause lung damage and even at low nitrogen high temperatures concentrations they irritate the respiratory system, (NO and NO2) in industry, motor skin and eyes. vehicles and power Reduce plant growth, cause leaves to die and dissolve stations. in rainwater forming acid rain (see above). Carbon Burning fossil fuels in Coat leaves which reduces photosynthesis, and particles industry. blacken buildings. (smoke) Bush ﬁres and cigarette Combine with water vapour and sulfur dioxide to smoke. form smog (see above). Dust and Industry. Cause respiratory problems, e.g. bronchitis, asthma other Mining and quarrying. and lung disease. particulate Coat leaves which reduces photosynthesis. matter Heavy metal Burning fossil fuels in May be directly toxic to organisms or become ions, e.g. industry. higher in concentration up food chains, harming top mercury, Extraction and consumers. cadmium, puriﬁcation of metals. Damage many body tissues and organs, especially the lead and nervous system. arsenic ions 4 The impact of humans on the environment 23 Pollution caused by the improper disposal of garbage A very small amount of human garbage is recycled; most is dumped in landﬁlls, garbage dumps, gullies, waterways, oceans, by the roadside, or is incinerated. Improper disposal of garbage is a threat to the environment: Toxic chemicals in the garbage can leach out and contaminate the soil, aquatic environments and water sources. Greenhouse gases, e.g. methane and carbon dioxide, can be released into the atmosphere where they contribute to the greenhouse effect (see page 26). Hydrogen sulﬁde gas can be released into the air. This gas is extremely toxic, and even low concentrations irritate the eyes and respiratory system. Plastics can enter waterways and oceans where they are harmful to aquatic organisms. Bacteria from untreated sewage can enter groundwater and cause disease, e.g. cholera. Garbage attracts rodents, which can spread disease. Garbage creates an eyesore, which impacts negatively on tourism, especially eco-tourism. Improper garbage disposal damages the environment Pollution of marine and wetland ecosystems Marine ecosystems are aquatic ecosystems where the water contains dissolved compounds, especially salts, i.e. it is ‘salty’. They include coral reefs, seagrass beds, rocky and sandy shores, mangrove swamps, estuaries and the open ocean. Wetland ecosystems are transitional ecosystems where dry land meets water and the water may be fresh, brackish or salt. They are areas of land that are covered with water for either part or all of the year, and are usually found alongside rivers, lakes and coastal areas. They include mangrove swamps, freshwater swamps, marshes and bogs. 24 4 Concise Revision Course: CSEC® Biology A coral reef A mangrove swamp A seagrass bed Because of their rich biodiversity and beauty, these ecosystems are major contributors to the economies of many small island developing states of the Caribbean through tourism, ﬁsheries and coastal protection. Many of these ecosystems are being polluted by untreated sewage, chemical fertilisers, pesticides, industrial waste, hot water, garbage and oil from oil spills. This pollution impacts negatively on both the overall health of the ecosystems and their aesthetic appeal. They are also being overﬁshed and destroyed for development purposes, e.g. to build harbours or marinas. Damage to coral reefs, mangrove swamps and other marine and wetland ecosystems results in a loss of: Biodiversity; coral reefs and mangrove swamps being some of the most biodiverse ecosystems on the planet. Habitats for many organisms, e.g. reef ﬁsh and mangrove oysters. Natural resources, e.g. ﬁsh, crabs, lobsters, oysters, seaweeds and wood. Attractions and recreational sites for tourists. Nursery grounds for reef ﬁsh which mangrove swamps provide, resulting in a reduction in population sizes of ﬁsh on reefs. Nesting and breeding grounds for birds, e.g. egret and scarlet ibis. Protection for shorelines against wave action and tidal forces, resulting in increased coastal erosion. Flood control provided by wetlands. Due to the pollution and destruction of marine and wetland ecosystems and the coastal erosion that often follows, the tourism and ﬁshing industries of Caribbean states are in danger of declining and this will have a negative impact on their economies. 4 The impact of humans on the environment 25 The greenhouse effect and global warming Carbon dioxide, water vapour, dinitrogen monoxide (N2O) and methane (CH4) are greenhouse gases. They form a layer around the Earth that lets radiation from the sun pass through but prevents much of it being reﬂected back into space. This radiation causes warming of the Earth which is known as the greenhouse effect. 2 The Earth reﬂects some radiation back into Sun space. 1 Radiation from the sun 3 Greenhouse gases absorb some passes through the Earth’s radiation and radiate it back to atmosphere and warms Earth. This also warms the Earth. the Earth. Earth’s atmosphere Earth containing greenhouse

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