Biology for CSEC 3rd Edition

Macmillan Educalion 4 Crinan Street, London, NI 9XW A division o f Macmillan Publishers Limited Compan ies and representatives throughou t Lhe world. www.m acmillan-caribbean .com ISBN 9780-230-43883 -5 Text© Linda Atwaroo-Ali 2014 Design a nd illustration © Macmillan Publishers Limited 2014 The auLhor has assened her rights to be identified as the author/s or this work in accordance wiLh the Copyright, Design and Patents Act 1988. This edition publ ished 20 14 First edition published 2003 All rigbts reserved; no pare of chis publication may be reproduced, stored in a retrieval system, transmitted in any fom1, or by any means, electron ic, m echanical. photocopying, recording, or otherwise, with out the prior wriuen permission or the publishers. Note to Teachers Photocopies may be made, for classroom use. or pages 332-367 without the prior written permission of Macmillan Publishers Limited. 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Printed and bound in Spain 20 17 2016 2015 2014 109 8765 4 32 1 Contents Series Preface vii About this Book viii Section A: Living Organisms in the Environment 1 2 3 4 5 2 The Variety of Living Organisms Characteristics of life The major groups of organisms Classification of organisms on the basis of visible characteristics The binomial system Chapter summary Answers To ITQs Examination-style questions 9 10 12 13 13 Ecology and the Impact of Abiotic Factors on Living Organisms Ecology Environmental factors Ecosystem, habitat, population, community Distribution of species Chapter summary Answers To ITOs Examination-style questions 15 15 16 17 21 22 24 Feeding Relationships between Organisms Producers and consumers Herbivores, carnivores and omnivores Predators and prey Food webs Decomposers and detritivores Special relationships Chapter summary Answers To ITQs Examination-style questions Ecosystem, Habitat, Population, Community Trapping the Sun's energy Pyramids of energy Pyramids of numbers Pyramids of biomass Bioaccumulation Chapter summary Answers To ITQs Examination-style questions The Cycling of Nutrients Biogeochemical cycles The carbon cycle The nitrogen cycle Acid rain Chapter summary Answers To ITOs Examination-style questions 3 3 15 6 7 24 Population Growth, Natural Resources and their Limits Growth of natural populations Resources and their limits Chapter summary Answers To ITQs Examination-style questions The Effects of Human Activity on the Environment Humans and the environment Endangered and vulnerable organisms Other effects of human activity Impact of human activities on marine and wetland environments Impact of increase in greenhouse gases Conservation and restoration of the environment Chapter summary Answers To ITQs Examination-style questions 24 25 26 27 Section B: Life Processes and Disease 28 29 8 Cells Why we need microscopes 30 Plant and animal cells 30 Unicellular microbes 31 33 33 37 37 38 39 9 40 40 40 42 42 43 46 49 50 50 51 52 52 55 60 60 62 63 63 64 66 70 72 72 74 74 75 Cell specialisation in multicellular organisms Movement of substances into and out of cells Chapter summary Answers To ITQs Examination-style questions 78 78 79 80 81 83 87 88 89 Photosynthesis Plants are the food supply for animals Photosynthesis Products of photosynthesis Limiting factors in photosynthesis Etiolation Chapter summary Answers To ITQs Examination-style questions 91 92 96 96 97 98 98 99 91 iii 10 Feeding and Digestion 11 100 16 Excretion, Osmoregulation and Homeostasis 181 Diet A balanced diet Malnutrition Holozoic nutrition Digestion and absorption along the alimentary canal Assimilation Functions of the liver Chapter summary Answers To ITQs Examination-style questions 101 106 107 108 111 116 117 117 118 119 181 182 183 184 189 189 192 Respiration Aerobic respiration Anaerobic respiration Chapter summary Answers To /TQs Examination-style questions 122 12 Gaseous Exchange The importance of transport in plants Transport systems of plants Movement of water through a plant Transpiration Adaptations in plants to conserve water Uptake and movement of mineral salts Transport of manufactured food Chapter summary Answers To ITQs Examination-style questions 15 Storage in Plants and Animals Why do organisms store food? Food storage in plants Food storage in animals Chapter summary Answers To ITQs Examination-style questions iv 196 196 197 199 205 205 206 130 18 Irritability, Sensitivity and Coordination 208 122 125 127 128 128 Irritability Stimulus The sense organs of humans The nervous system The endocrine system Drugs and the effects of drug abuse Chapter summary Answers To /TQs Examination-style questions 142 19 The Eye, the Ear and the Skin The need for a transport system 142 143 The circulatory system of humans Blood 149 Hypertension 152 The role of blood in defending the body against disease153 Chapter summary 156 Answers To ITQs 157 Examination-style questions 159 14 Transport in Plants 17 Movement 1~3 194 The importance of movement in animals Movement in plants The skeleton of humans Chapter summary Answers To ITQs Examination-style questions Importance of gaseous exchange in humans 130 Mechanism of gaseous exchange in humans 131 Importance and mechanism of gaseous exchange in plants 135 Characteristics common to gaseous exchange surfaces 135 The effects of smoking 137 Chapter summary 139 Answers To ITQs 140 Examination-style questions 140 13 Transport and Defence in Animals Metabolism Excretory products in animals Excretory products in plants The human excretory system Osmoregulation Homeostasis Chapter summary Answers To ITQs Examination-style questions 160 The eye How we see Sight defects and their corrections The ear How we hear Balance The skin Temperature regulation in humans Temperature regulation in birds Skin care Chapter summary Answers To ITQs Examination-style questions 160 161 163 166 167 20 Reproduction in Animals 168 Reproduction 168 Reproduction in humans 170 The male reproductive system 170 The female reproductive system 172 Hormones of the gonads Fertilisation 173 Development of the embryo, fetus and placenta 173 Birth 173 The role of contraception 178 HIV/AIDS and other STDs 179 Chapter summary 179 Answers To /TQs 180 Examination-style questions 209 209 210 211 217 219 222 223 224 225 226 227 230 232 233 234 235 237 239 239 240 240 242 244 244 246 246 247 248 250 250 252 253 254 256 256 258 21 Reproduction in Plants Life cycle of a plant Structure of a flower Pollination Fertilisation and development of seed Dispersal Chapter summary Answers To ITQs Examination-style questions 22 Disease and Humans Health and disease Pathogenic diseases and vectors Social and economic implications of disease Chapter summary Answers To ITQs Examination-style questions 259 24 Meiosis 259 The importance of meiosis 261 The process of meiosis 262 Significance of meiosis 263 Chapter summary 264 Answers To ITQs 267 Examination-style questions 267 25 Heredity and Genetics 269 23 Mitosis Chromosome number The cell cycle Importance of maintaining species chromosome number The process of mitosis Mitosis and asexual reproduction Chapter summary Answers To ITQs Examination-style questions Genes Examples of genetic effects Pedigree charts Chapter summary Answers To /TQs Examination-style questions 296 297 302 304 306 306 309 Genetic variation Importance of genetic variation DNA testing and forensic science Natural selection Artificial selection Mutation Genetic engineering Chapter summary Answers To ITQs Examination-style questions 310 310 312 313 313 317 319 321 323 324 325 Practical work in Biology School-Based Assessment contents 328 328 332 271 271 273 275 275 276 26 Variation and Evolution 276 Section C: Continuity and Variation 278 278 279 290 290 291 293 294 295 295 281 282 282 287 287 Section D: School-Based Assessment 288 27 School-Based Assessment Index 368 v Series Preface, 3rd edition Macmillan's textbooks for the Caribbean Secondary Education Certificate (CSEC) Science subjects have been written by teachers with many years' experience of preparing students for success in their examinations. These revised third editions have been written to align with the new CXC syllabuses (to be first examined in 2015). Additional practical activities have been included to reflect the new emphasis on practical work, and new [eatures (such as group work and discussion activities) will help teachers to cater to a variety of different learning styles within the classroom. These books are specially designed to stimulate learning, whatever the reader's needs. Students starting a topic from scratch may need to be led through the explanation one step at a time, while those with prior knowledge of a topic may need to clarify a detail, or reinforce their understanding. Others may simply need to cl1eck that they understand the material. Each CSEC science syllabus specifies the areas to be used for the School-Based Assessment (SBA). Each book in the series has a section designed to help students with their SBA, by offering advice on how to approach the task, presenting examples of good SBA work or suggesting suitable material to use within it. Teachers are free to photocopy these pages. The CSEC Science series covers everything a student needs pass their CSEC examination, as well as providing a firm foundation for more advanced study at CAPE level. Dr Mike Taylor -<:~~ ~'°~ Series Editor vii About this Book This book isn't just words o n a page. This book conra ins a range of different features to introduce, tea ch and highlight key information throughout the course. These pages explain h ow to use them. The larger column contains the main text and diagrams; you can read straight down it without interruption. The smaller column contains other useful facts, so make sure you use it to check your understanding. You sh ould remember to spend time stud yi ng the figures and diagrams as well as the text. This icon shows how you can make links be1ween lhis concept and other topics in Biology. 11 is important to remember that you arc not just learning facts in isolation but 10 think about how they relate to your world and your experiences . Where you see this icon, you will find an In-Text Question (ITQ). These are spread throughout each chapter and will help you to check your progress. If you can't answer the ITQ, you should refresh your knowledge by rereading the relevant paragraphs in the main text. Answers to the ITQs are found at the end of each chapter. This symbol means that you can find additional practice for this topic on the Macmillan CSEC Science digital resources. These stand-alone components will help you to learn and revise key areas of the course. For more information please visit: http://www.macmillancaribbean.com/pages.aspx/educationalbooks/ secondary/science. interactive_science_csec/. . .Anaerobic respiration in humans Human cells respire nonnally <1erobicall}'· However, during strcnuuu~ cxcrci.M!. mm.de cells need much more energy for lhc extra work that the)' arc doing. Thl' hrcathlng rate and hcJrt r.11c increase in an attempt lO i:et more oxygen to 1hc~c cells. Sweatin)? occurs to helµ lose some of 1he extra enNgy a~ heat. With im.l'cast<d rl-spir.ulon. ,, Im of heat ls produced which ls lost from the skin jchaptl'r 19). After a period of SUSI.lined exercise, 1he oxygen sup1>ly becomes inadequat('. even wi1h panting ror air and 1he increased hl'.in r.lte. The muscle cell~ 1hcn respire anaerobia lly. Encrg) h )lill produced when cell) respire anaerobicall y, although h Is a much ~mailer amount for each molecule of glucose. Thi~ means that they c m con1lnue 10 dn work (cuntr.1C1 and rdax). Anaerobic respiration in bacte L~ Sometimes bacteria can be found In canned foods or tins, desp1te the lact that the cans and tins are sealed so that no air can enter. How Is this possible? Some baocria a lso respire anaerobically. LikC' ani acid as a wastl' 1noduct. We make use of 1hb in 1 and cheese (Og urc 1 1.9 ), lnoculatlon ClCOtd 10 40°C n a 'statttt' CUii.i'ii of • nat'mhic fC'\J,l ~1lon e.g.~toboc:lb~ }:lurosc - -- -- - l actic acid+ energy In musclt- cdl~ .~ \;'-' Humans respire mosUy aerobically. When do humans respire enaeroblcally? f9f?Mnt11Uon n::uoeraa in twge Yd1lt (.CO cc tar lltX)I Lactic acid is a waste produa of th.ls reaction. It builds up In the muscles and a u ses 1hem to ache (rig ure 11 .6). This is often called fallgue . A her cxcrdsc:, rho bod1 ha> to gel rid of 1hc lact ic acid as quickly as pos<iblc. This is done by usin~ o xygen lO changr II bad~ 10 a chemical like glucose c;o tha1 ii can be IJro~cn down completely in .u:robic respiration. When anaerobic rcspir<Jllon occ:ur11 in muscles his in addition 10 aerobic respiration and not in phlCL' of ii. A perso n continucc; to 'bre011hc: hard ' or p.lnl for some time a her exerd~e .n oxy gen Is needed 10 get rid of the lactic acid. The oxygen required to gel rtd o( the lactic acid i< called 1hc o.><ygen debt (figure 11.7). ~ a>nYlrted IO lllct.c acid orodl.a1Q cool, tldd frurtt. etc. package and distribute 814..5°CthltllCtenltll'T'l8#\lllvebl. lerm!rutJOn OCCU'I al liw lemp ~ stont •2°C \;'-' What is alcoholic fennentation and what are two of its uses? Rgute II 9 Ch a p ter s umma ry All cells respire lo release energy to carry out the P' • Resp1ration takes place In the mitochondria of cells. Food Is oxidised dunno respiratioo. and carbon diox11 waste products: C,H110, + 60, - energy+ 6H,O+ 6CO, Energy Is stored In phosphate bonds In ATP (aclenosl • There are many advantages to storing energy as sm • There are two types of respiration: aerobic and anae Aerobic respiration uses oxygen and releases a lot DI • Anaerobic respiration releases a small amount of II'" Humans usually respire aerobically but tflelr muscle during prolonged exercise. • Lactic acid Is produced during anaerobic respiration oxygen debt which has to be repaid. Anaerobic respira11on in ~t produces ethanol whu and carbon tfiOxlde which is used In making bread. • Anaerobic respiration In bacferta is used In the makl1 f1a.1;r.1914•..14e1mm1 - · sugar--~ Anaerobic respiration in yeast ·-IO----·--.... - Rarc:h 'Mldl • btoMr1 doM'I • .,._ a.-1he maru:.. ... ..,.. of ~ and fenreltEl101 oc:an · ~N91SblCJbles OCC0i gMCll.ght ..... _ · ~~ltw~lnd ~- lhlleetw1QI During an.Jcrohic respiratio n in yc<i st. c1hanol and carbon dioxide arc produced as wash~ produas. EthJ:nol is an alcohol .ind the process b known as a lroholk fermenta1ion . Yeast h vc:ry lmponant m the makint-: nr alcohol and bread (figure 11 .8 ). The c1hanol can be prod u ced In man y ways to make .1 \\id~ rnngc ol alcoholi c drinks. indudlnJ.: beer and wine. which arc enjoyed by humans. The produc1lon of carbon dioxidt' h used in bread·maklng 10 make dough rise . The carbon dioxide produced by lhc ycae>t a~ ii rt.''§:p1res .u cumula1es inside the do ugh in '\mall pocl.l·t~. The d ough is e>een IO get bigger ur ri~ a s 1hc gas l"xpands with warm1h. E1hanol is also produced but in s mall quanlilics - i i evaporates when 1he bread is OOking in the: oven. The first time an important new word appears in lhe text, it is highlighted at the side. A definition or in-depth explanation is given in the main text. viii As you can see on pl26. lhe smaller column can contain key details. It is good practice to spend time reading this column as well as lhe main text so that you don't miss any important information. Each image has a caption and a figure number to help v. ith cross-referencing. Summaries of the key facts from each chapter will help you check your understanding. A list of objectives at the beginning of each chapter tells you what topics you will be covering. They will help you to plan and measure your learning. I understand the terms 'ecology', 'ecosystem' and •environment' (/ distinguish between abiotlc and biotic fact ors I/ distinguish between habitat and niche '7l distinguish between community and population tfj distinguish between population and species ./) relate the distribution of species to abiotic factors Q'i describe the components of soll (I Tables and definitions are printed in coloured boxes for easy recognition. understand the advantages and disadvantages o f th e use of natural and chemical fertilisers ITQ1 Ablotlc factors Biotic factors The temperature ol water. Feeding relatlooshlps, e.g. betWeen the lizard and Insects tnat are l1s prey, The amount of light available to the orvanlsms. Be!laviour of scad When attached by dolphin. You ma}' haVl' noted 01hcr examples from 1he pictures. ITQ2 A home.- aquariu m is a limit~i.1 ecosystem; ii <loan '1 contain tht· divcr-.:ity of species that would be found in 1he na u1e. A l:k1cky.ird pond is more likely IO be a compl ete eco;;ystcm wi1h ~1ll 1he divcrslly ncCt"~sary to sustain itself. JTQ3 (l) A habltiit Is 1hc place where an nrganism Jives. 1\ niche Is the role 0111 cells. 1hcv make lac1it 11a11ufoctu rc of yoghurt 0 •r ·1 This is the style of question you may come across in your exaill. Your teacher will suggest how you can use them. but they will measure what you have learnt and help to identify any gaps in your knowledge so you can revisit the relevant sections of the book. The School-Based Assessment pages contain activities which enable you to explore the theoretical concepts in the chapter. They will test your investigative and problem-solving skills and show realworld applications of the facts you are learning. ~es of life. nd water are produced as riphosphate), 1ackets of ATP. C, ergy. 'without the use of oxygen. s can respire anaerobically o Examination-style questions 0) Explain, using examples. the meaning of the terms: (a) abiotic factor. (bl biotic factor. 01) Define: (a) environment: (b) habtla~ (c) population: (d) community. (iii) Describe. using examples, how ablotlc factors of the envirooment affect the distribution of species. (iv) (a) Amoebae live In fresh and sat! water habitats. Describe a major problem of ' in I 27 • School-Based Assessment 1.1 To observe visible characteristics of animals and plants Chapter l The Variety of Living Organisms ' Syllabu s skills : O/R/R Procedure: an imals 1. Visit a backyard garden, a nearby cocoa estate, a nature centre, foothills of forest (anywhere a range of organisms can be seen). 2. Copy the table below into your lab book and observe five animals ~nclude three insects). Describe what ' ' ' " k.oUwJJll!!JJ..D'"""~-----" .nlmals and creates an ; used in the alcohol Industry 1f yoghurt and cheese. 127 ix Section A: Living Organisms in the Environment 9ihe Variety of Living Organisms 0 understand why there exists a range of living organisms on Earth 0 list and define the characteristics of life .,() describe the major groups of organisms 0 0 understand how a classification system is used to group all living organisms observe and classify living organisms according to visible similarities and differences range of living organisms characterisics of life growth respiration irritability movement nutrition excretion reproduction Prokaryota Protoctista Fungi Plantae Animalia classified according to common features Kingdom Phylum Class Order Family Genus Species species - can interbreed with each other breeds varieties races The plan et Earth, the third planet from the Sun, has all the conditions necessary to su pport life as we know it. Our pla net is position ed at such a distance from the Sun that living organisms ca n survive in th e range of temperatures on its surface (a lthough it is a fairly wide range). The presence of water in all its forms (solid, liquid and gas) a nd the combination o f gases whi ch make up the a tmosphe re (including n itrogen, oxygen and ca rbon dioxide) a re all conditions that a re essential to life on Earth. A h uge variety of living forms exist on the planet Earth . Th ey can inhabit most of the Earth 's surface, land, air and water. They show an e normous range in size a nd comp lexity - from the microscopic, which cann ot be seen by the naked eye and are as simple as one cell, to giant whales which must live in wa ter since th ey are too heavy to support themselves and move on la nd. Characteristics of life characteristics of life > ~ IT:.Q-1 V'-1 List three characteristics of the planet Earth that enable it to sustain life. Biology is the study of life and how living things stay alive. All Living organisms, microscopic to gigantic, possess certain characteristics. These are the characteristics of life that distinguish living things from non-living things. There are seven of these characteristics. Growth - Living organisms increase in mass, size and numbers. 2 Respiration -The energy released during respiration is needed to carry out all life processes. 3 Irritability - Living organisms can respond to changes in their internal environment and the world around them. These responses usually increase their chances of survival. 4 Movement - Most living organisms can move. Plants show growth movements such as growing towards the light. Most animals can move from place to place to find food or a mate. 5 Nutrition - All living organisms need food which is used as a source of energy. Plants make their food during photosynthesis. Animals get their food by eating plants or other animals. 6 Excretion - All living things make waste products during metabolism. These must be removed from the body. 7 Reproduction - This is the production of new organisms. Living organisms are able to carry out all these processes on Earth. Most organisms are adapted to live on land or in water, more or less close to sea level. Some survive in 'extreme' places such as: • in hot sulfur springs where chemical conditions are toxic to most living things; • in extreme cold, such as at the North and South Pole; • in deep parts of the ocean where no light can reach, such as the Marianas Trench; • in the upper atmosphere; • in extremely hot deserts, such as the Gobi desert; • inside other living organisms. Wherever they live, as long as they are able to carry out the processes of life living organisms survive and produce offspring. Most places on Earth can support life. ~ IT:.Q2 V'-1 Animals and plants are able to carry out certain processes which distinguish them from non-living things. Describe briefly how a plant (i) feeds (ii) moves. The major groups of organisms All organisms used to be classified or placed in two kingdoms or main groups - animals and plants, depending on whether they get their food from other organisms or make their own food. However, living things are more diverse than this and a classification system of five kingdoms is now used. These kingdoms are the Prokaryotes, Protoctists, Fungi, Plants and Animals (figure l. l ). Living organisms ___________,__ ------------ -- ---------------- - Prr l .. ~ (chromosomes not enclosed in a nucleus) Eukaryotes (chromosomes enclosed in a nucleus) Fungi unicellular - -- Viruses Piart, multicellular Figure 1.1 Living organisms are placed in five major kingdoms (shown In red). Anirm:1.. d - - - Living Orge111jsm_s·-iG.'1!.tle~£11vii:_~l)_rfla!J!1__- _ The kingdoms have scientific names that are slightly different from their common names. Prokaryota Protoctista Fungi Plantae Animalia _ _ __ _ _ ~-- _o ~ Viruses do not fil into this dassi.fication. They are the smallest organisms, though it is difficult to think of them as living because they can only 'live' inside anoth er living cell. They also do not have a tru e cellular structure Like other organisms (figure l.2). Viruses that attack humans HIV or human immunodeficiency virus Influenza virus 0 protein/ lipid coat ~ virus RNA IT:Q3 1....l'-1 What are the five major groups of lifeforms or organisms? Viruses that attack bacteria are called bacteriophages or simply phages Phage 2 bacteriophage phage DNA ~ IT:Q~ 1....l'-1 Bacteria are described as being microscopic and unicellular organisms. What do these terms mean? Phage DNA Is Injected into the bacterium where it makes copies of itself (20-1000) which are released to infect further bacteria. surface of bacterium Rgure 1.2 The structure of some viruses. Billions of viruses 'exist' around us and it is only when they enter the cells of an organisms that they sh ow some of the d1ara cteristics of life. There they can reproduce and grow in numbers. Viruses have a great impact on life on Earth because they can live inside every type of Uving organism, from bacteria to plants and animals. It is believed that they have changed the course of human history because of diseases like smallpox, measles and now AIDS. Rgure 1. 3 Eschenchia coliis a rodshaped bacterium which is part of the normal gut 'flora' of humans and other vertebrates. Rgure 1.4 Anabaena is a bacterium where the cells stick together in long chains. 4 Prokaryotes The prokaryotes are orga nisms that are commonly called bacteria. They occupy many en viromnents such as soil. dust, water. air. and in or on animals and plants (figure 1.3). Some are found Lu hot springs where temperatures may be higher than 78 °C . Some can survive freezing in ice. Some ha ve been found in deep cracks in the ocean floor, at very high pressures and temperatures of 360 °C. They can be found in every part of the living world. They are the most ancient group cytoplasm of organisms. They are also the smallest organisms that have a cell ular _......... cell wall structure. Man y exist as single cells, others are found in groups (figure 1.4). Their cells have a m uch simpler stru cture than those of the eukaryotes strand of DNA (figure 1.5). Rgure 1.5 Structure of a typical bacterium, Prokaryotes are vital to all other e g. Eschenchia co/1. The chromosomes are organisms sin ce th ey cause decay not enclosed in a nucleus and there is little of dead plant and animal material whi ch releases nutrients back into the structure in the cytoplasm. 1 · The Variety of Living Organrsrns CHAPTER 16, CHAPTER 22 environment. They are essential to the nitrogen cycle. They are also important co humans because they cause disease (e.g. cholera and TB - chapter 22 ) and are used in biotechnology (e.g. in insulin production - chapter 16). Protoctists Most protoctists are unicellular, that is made of one cell. This ce ll shows all the characteristics of life. Algae and protozoa are two kinds of protoctist. • Protozoa are unicellular and feed on other organisms (heterotrophlcally). They are found in all environments, especia lly in water, and examples include Amoeba and Paramecium (figure 1.6 and figure 1.7). They are important to humans because diseases such as malaria and sleeping sickness are ca used by protozoan parasites. • Algae live in the sea and in fresh water, and some live on land where the Figure 1.6 Amoeba proteus (x200). surface is damp. They make their own food by photosynthesis (figure 1.8). Some live as single cells, others are found in groups or colonies. A few, such cytoplasm as the seaweeds, can grow extremely large. These have structures that look cell membrane nucleus like stems, roots and leaves, but they are much simpler than true planes. Rapid growth (blooms) of algae can form scums on the surface of ponds, food lakes and rivers, turning them green. p seudopodia contractile vacuole Ma laria infects millions of people each year and it is estimated that 2.7 million people worldwide ?ie from this disease each year. Fungi Figure 1.7 The structure of Amoeba. ~ flagella Fungi range in size from unicellular yeasts to large toadstools. Some are used by humans for medicinal and dietary purposes. They are heterotroph ic organisms and obtain their food from the environment. However, they do not tak e in large particles of food that need to be broken down. They digest their food outside the body using enzymes which make it soluble. Then they absorb the food. So, they are usually found living in or on their food, whlch can be a dead or living organism (figure 1.9). cytoplasm spore body light-sensitive spot chloroplast r---+.--~ starch storage Figure 1.8 Ch/ore/la. a photosynthetic alga Note the presence of the chloroplast, where photosynthesis takes place. mycelium absorbed into fungus vesicles release enzyme and food is digested soluble food Ill enzymes insoluble food Figure 1.9 The hyphae of fungi extend into their food u.:JliSllOn occurs outside Lhe bod;. 5 ~ IT:QS l/'-1 Using one named example of each, describe one similarity and one difference between algae and protozoans. Figure 1.1O Penicillin spores are made in sexual reproduction (x600). Fungi reproduce by producing spores asexually or sexually (figure 1.10). These are dispersed by the wind and water and some rely on animals to take them to new environments. Common fungi are: • moulds (figure 1.10); • yeasts (figu re 1.11 ); • mushrooms and toadstools (figure 1.12). Figure 1.11 Yeast cells bud to make new cells 1n asexual reproduction. Importance of fungi to humans • Important in the making of the antibiotic penicillin. • Essential to many fermentation processes, such as those used in making bread, wine, beer and other alcoholic beverages. • Used to make a range of chemical products, such as anaesthetics, birth control pills and meat tenderiser. • Moulds and ru st are fungi that are important in damaging growing crops. • Ca use of spoilage of food. • Source of food and used to make food, such as sufu in Ease Asia. Plants (Plantae) Figure 1 12 Mushrooms are 11.; oor bodies of some fungi. ~ IT:Q6 l/'-1 Name three kinds of fungi and a possible use of each. 6 The plant kingdom includes mosses, liverworcs, ferns, coni fers and fl owering plants. Almost all p lants are photosynthetic. Many plants are a source of food for humans and other animals (figure 1.13). Some provide a rich ad diverse habitat (figure 1.14) . Some plants can be used as medicines. Bidens is a weed which has a small dajsy- Rgure 1. 13 Bananas a food source for many animals. Rgure 1.14 Mangroves a rich habitat 1 · Tite Variety of Living Organisms like flower (figure 1.1 5). The leaves and fl owers are steeped and u sed to 'cool the blood' (prickly h eat) and to relieve a sick stoma ch. Sometimes it is given to children to cure worms. Flowering plants angiosperms > .~ Rgure 1.15 Bidens - Shepherds needle, Spanish needle, The fl owering plants have Beggar-ticks, st1cktight. true fl ow ers and so m ake seeds. They are a lso called angiosperms and are divided into two groups: • the m onocotyledons; • the dicotyledons. Table L. l shows the distinguishing features of monocoi:yledons and dicotyledons. l/'-1 (i) Plants range in size from unicellular to giant. Put these plants in order of size starting from the smallest: fern, mango tree, croton, moss and lettuce. (ii) List five reasons why plants are important. Feature Monocotyledons Dicotyledons seed has one cotyledon or seed leaf has two cotyledons or seed leaves leaf has parallel veins has net-like or branching veins example corn (Zea mays) Hibiscus Table 1. 1 D1stmgwshmg features of monocotyledons and dicotyledons. Angiosperms a re th e la rgest group of plants. They include most crop plants, orna men tal pla nts and plants used as he rbs or m edicin al plants. They vary in size fro m the very sm all to gigan tic (over 90 m ta ll) and are ofte n very bea utiful (figu re 1.1 6). They can live in a wide variety of habitats, from deserts to ra inforests. Figure 1.16 Flame tree. Phyla is the plural of phylum. Animals (Animalia) The animal kingdom conta ins multicellular, heterotrop hi c orga nisms. Th ey a re grouped in phy la as sh own in figure 1.17. Animalla Cnidaria Platyhelminthes • lh. Annelida invertebrates Nematoda vertebrates Figure 1. 17 Animals are placed in phyla. (Tho:;e .>hown mred are described in more detail overleaf.) 7 Living Organisms 1n the Environment Table I .2 shows examples of each animal phylum. Phylum Examples Cnidaria jellyfish, sea anemone, coral Platyhelminthes flatworms, e.g. tapeworm Mollusca slug, snail, mussel, octopus Annelida roundworm , earthworm, leech Arthropoda insect, spider, lobster, millipede, centipede Nematoda roundworms Chordata fish, amphibian , reptile, bird, mammal Table 1.2 Example:s of the animal phyla. Arthro'pods (Arthropoda) Figure 1.18 An invertebrate that lives on land , a snail. Arthropods dominate life on Earth. They include the crustaceans, millipedes, centipedes, arachnids and insects. They all have an exoskeleton (outer skeleton of chitin) and jointed limbs. • The cru stacea n s a re aquatic or live in damp pla ces . They include woodlice, crayfish, crabs, lobsters a nd barnacles. • The arachnids include spide rs, scorpions, mi tes and ticks. They have four pairs of wa lking legs and are mainly terrestrial and carnivorous. • The insects have a distinct head, thorax and abdomen, and three pairs of walking legs. They include locu sts, bees, ants, beetles, aphids and fleas. Molluscs (Mollusca) Rgure 1. 19 An invertebrate that lives in water, a sea cucumber. The molluscs have a soft body which is often covered by a shell. They include con ch, sna ils, slugs, cockles, mussels, octopus, squid, clams and oysters. Figures 1. 18 a nd 1.19 show examples o f mollusccs. Some molluscs like conch and oysters are important to Caribbean people as a source of food and an exotic trea t to loca ls and tourists. Farming of mo ll uscs is pra ctised on some islands as demand exceeds supply from wild pop ula tions. These a nimals are a renewable resource but popula tions can decline rap idly because of over- harvesting from their natural habitat. Chordates (Chordata) Most ch ordates are also vertebrates because t hey have a vertebral column. The vertebra tes include the fishes (ca rti laginous and bony), amphibians, reptiles, birds and mammals (figure 1.20). 8 1 · The Variety of Living Organisms frog (ampilibian) lizard (reptile) scarlet ibis (bircf) monkey (mammal) Figure 120 There are five groups of vertebrates: fish amphibians. reptiles. birds and mammals. Birds (Aves) have the fo llowing ch aracte ristic [ea tures: • front pair o[ limbs modified to form wings; • skin covered with [eath ers; • produce hard-shelled eggs (reproduction); fish • are warm-blooded. Q9.:., l:tQ8 vv Name the five groups of vertebrates, giving two examples of each. Mammals (Mammali a) have the followin g chara cteristics: • four limbs; • sk in covered with hair; • most give birth to live you ng; • feed their yo ung with milk made by the mother (suckle); • are warm-blooded. Classification of organisms on the basis of visible characteristics :X Practical activity SBA 1.1 : To observe visible characteristics of plants and animals. page 333 artificial classification > natural classification > The simplest way co classify organisms is according to similariti es in their visible ch aracteristics. For example, if we see a number of organisms, we could stan to group them by putting those with w ings together. We can make another group of those with eight legs. We cou ld also put the ha iry ones together. And so on . However, where do we put those th at are both h airy and winged? There are two types of classification, artificia l and natural. Artificial classification is based on easily observed ch a racteristics, like colour, shape or number of legs. This is a convenient and easy method of groupi ng organisms and is designed for a practica l purpose. However, worms and snakes have the sam e sh ape, but snakes have a backbone while worms do not. Natural classification tries to use natural relation ships between organisms using both internal and external characteristics. For example, organisms with backbones are grouped together because th ey all have backbones and many other similarities. Similarities in anatomy, physiology and behaviour may all be considered when grouping organisms in a natural classification. Organisms are grouped by similarities that sh ow descent from shared ancestors. For example, a bird wing and a human arm show descent from a ve rtebrate ancestor. A bird w ing an d an insect wing are derived from different stru ctures. 9 Similarities in DNA (deoxyribonudeic acid) sequ ences are increasingly being relied on to determine ancestry. The more alike the DNA sequences a re for two types of organisms, the recently they diverged from a shared ancestor. Remember that each organism has its own DNA 'fingerprint'. Biologists can now construct new evolution ary tree diagrams that sh ow how existing orga nisms are related to one another using their DNA . ~ IT:Q9 l..)'...J Classify these organisms according to similarities in their visible characteristics into three groups. Dichotomous keys A dichotomous key is a tool that enables classification of organisms. It works by asking a series of qu estions in a step-by-step fashion until you are led to the name of the orga nism. Dichotomous mea ns 'divide d into two parts' and a dichotomous key always offers two answers to each question. Sii:nple example of part of a dichotomous key Does it have wings? 2 3 yes - go to question 2 no - go to question 5 Does it have feathers? yes - it is a bird no - go to question 3 Are the wings brightly coloured? yes - it is a moth or butterfly no - go to qu estion 4 And so on. Dichotomous keys can be used to dassify organisms according to both artificial or n atural criteria, including DNA information where it is available. The binomial system Carl Linnaeus was a scientist in the 18th cen tury who first grouped organ isms together by a natural classification. Many people had tried grouping o rganisms before, but they ha d all used artificial classification. Linnaeus' classification 10 binomial system > Genera is the plural of genus. made it easier to study organisms, since the enormous variety is organised into closely related groups. Carl Linnaeus also put forward a system for naming each species of organism with a biological name, which is called the binomial system. He did this because organisms may have many common names. For example the plant called shadow benny, bandania and cilantro in Trinidad and Tobago, is called sit weed or spirit weed in Jamaica, and in Martinique and Guadeloupe it is known as bandanie. Each biological name has two parts which are the sa·me in all these countries and all over the world - the biological name for the pla~ t is Eryngium foetidum. Th e first word of this name is the genus name and always starts with a capital letter. If you are writing it several times, the first word may be shortened. Fo r exa mple Eryngiumfoetidum may be abbreviated to E.foetidum. The second word is the species name. Every known species has a place in this classification . It starts with major groups of general features, which are broken down into smaller and smaller groups that get more and more specific. Look at the example of the classification of humans in figure 1.21. Living organisms Placed In five main groups (kingdoms) Kingdom Prokaryotes Protoctista Phylum Fungi Plantae Animalia Annelida Arthropoda Chordata invertebrates Sub-phylum Class Order Vertebrata (possess a vertebral column) Reptilia (reptiles) Aves (birds) Mammalia (hairy, warm-blooded, suckle young) Primates (monkeys) Carnivora I Family Hominidae (human-like apes) Genus Homo I ------- I Species erectus I ..,.,.. (-II-developed brain) Agure t .21 The classification of humans. 11 Human beings belong in the kingdom Animalia because we are multicellular and heterotrophic. We belong in the phylum Chordata and the sub-phylum Vertebrata because we have a backbone. We are in the class Mammalia because we have hair, are warm-blooded and suckle our young. We are in the order Primates with all the other monkeys and apes. We belong to the family Hominidae which are the human-like apes. In the past, this family bas included several genera including the genus Homo, grouped by the structure of the skull and teeth . There have also been other species of Homo in th e past, for example Homo erectus. However, that species is separated from the modern Homo sapiens . because they had more body hair and a smaller brain . AJI people today belong to the species H omo sapiens because they all have the same characteristics. Table 1.3 sh ows how the ocelot starts in the sam e large groups as humans but is pla ced in a dillerent group from the level of Order down. It is grouped with all the other kinds of cat. Classification group Humans Ocelot Kingdom Animalia Animalia Phylum Chordata Chordata Sub-phylum Vertebrata Vertebrata Class Mammalia Mammalia Order Primates Carnivora Family Hominidae Felidae Genus Homo Leopardus Species sapiens pardalis Table 1.3 Classification of humans and ocelot. 1Chapter summary - ------ • A huge variety of living forms exist on planet Earth . • All living organisms show the seven characteristics of life: growth, respiration, irritability, movement, nutrition, excretion and reproduction. • Living organisms are grouped into five kingdoms: prokaryotes, protoctists, fungi, plants and animals. · • The prokaryotes are bacteria. • The protoctists include algae and protozoa. • The fungi include yeasts and toadstools. • The plants are mostly photosynthetic (make their own food). • The animals need to get their food by eating plants or other animals. • The phyla of animals are cnidarians, platyhelminths, molluscs, annelids, arthropods, nematodes and chordates. • The chordates include fish, amphibian, reptiles, birds and mammals. • Each major group or phylum is broken down into smaller groups. • Organisms can be classified according to similarities in their visible characteristics. • A dichotomous key is a tool for classifying organisms by asking a series of yes/no questions in a step-by-step fashion until you are led to the name of the organism. • Each species has a common name and a scientific name. • A species is a group of similar organisms that can interbreed. 12 ~ ·Jiii The presence of water, suitable temperature range, the presence of gases in the atmosphere, like oxygen and carbon dioxide. ITQ2 (i) Most plants are able to make their own food in a process called photosynthesis. (ii) A plant moves by growing towards light from the environment. ITQ3 Prokaryotes (bacteria) , protoctists (algae and protozoans), fungi (moulds, yeasts and mushrooms} , plants (mosses, liverworts, ferns, conifers and flowering plants), animals (invertebrates and vertebrates). ITQ4 Microscopic means cannot be seen with the eye without the use of a microscope because they are so small. Unicellular means made up of one cell. A bacterium is a single cell which can carry out all the processes of life. ITQS Algae: Chlorella; protozoan: Amoeba. Both orgarusms have 'true' nuclei; the chromosomes are enclosed in a membrane which is called a nucleus (so they belong to the eukaryotes). (Bacteria differ from this and are prokaryotes.) A difference between Ch/ore/la and Amoeba is that Chlorella has a chloroplast and is able to photosynthesise or make its own food, while Amoeba cannot photosynthesise and must feed on other organisms. ITQ6 Yeast: to make bread. Mushrooms: for food. Moulds: to make the antibiotic penicillin. ITQ7 (i) Moss, lettuce, fern, croton and mango tree. (ii) They produce oxygen which is need by anima ls for respiration. They are a food source. They can be used for medicinal purposes (herbs). They hold topsoil in place. They provide homes for animals. ITQ8 Fish: shark, guppy. Amphibian: frog, toad . Reptile: snake, lizard. Bird: parrot, duck. Mammal: lion, goat. (You may have thought of many other examples.) ITQ9 Two pairs of wings, three pairs of legs, body divided into three parts. ITQ1 Examination-style questions (i) (a) List the characteristics of life. (b) Describe the importance of two of these characteristics. (ii) Explain the difference between: (a) the growth of a crystal and the growth of a plant. (b) the movement of a cloud and the movement of an animal. (iii) Robots have been built that move, detect and respond to various stimuli. (a) In what ways is a robot similar to a human? (b) What are some differences between a robot and a human? 2 (i) Living organisms can be classified into five kingdoms. List these five groups giving a named example of each. (ii) Describe two differences between vertebrates and invertebrates. .. (iii) List the main characteristics of dicotyledons and monocotyledons in order to distinguish between them. (iv) Discuss the importance of microorganisms to humans. 13 (i) 3 Animals can be found almost anywhere on Earth. Describe how: (a) a bird is adapted for flying. (b) a fish is adapted for swimming. (c) a bird is similar to a fish. (d) a bird is different from a fish. (ii) Humans are said to be closely related to chimpanzees. (a) Explain why this is so by comparing visible differences and similarities between humans and chimpanzees. (b) Are there any similarities in their behaviour? Explain fully. 4 (i) List two features common to the organisms shown below. (ii) Using each feature, classify the organisms. List the members of each group. D B E G H :; .' •' 14 5 cology and the Impact of Abiotic Factors on Living Organisms 0 understand the terms 'ecology', 'ecosystem' and 'environment' 0 0 0 distinguish between abiotic and biotic factors 0 distinguish between population and species 0 0 0 relate the distribution of species to abiotic factors distinguish between habitat and niche d istinguish between community and population describe the components of soil understand the advantages and disadvantages of the use of natural and chemical fertilisers ecology ( I ) ecological study { biotic factors environmental I abiotic factors ecosystem I r distribution of plants and animals ' community r population I species I ' habitat niche Ecology Ecology is the study of the relationsh ips of organisms with each other and their environment. Togeth er, all the external con diti ons in which an organism lives con stitute its en vironment. Environmental factors Environmental factors may be of two kinds: • abiotic or ph ysical factors (non -living); • biotic factors (living) . 15 Abiotic or physical factors edaphic factors > ~ IT:Q1 V'--J Examine figure 2.1 and its caption. List: (i). two abiotic factors (ii) two biotic factors you can deduce from the images. biotic factors > (a) • Cli matic factors such as light, temperature, rainfall, wind and availability of water. • Edaphic factors (associated with the soil) such as pH, texture, temperature, organic and mineral content. • Aquatic factors such as salinity, wave action and dissolved oxygen. • Topographic factors (associated with physical features of the Ea rth's surface) such as the angle of the slope. Biotic factors Biotic factors result from the activities of Jiving organisms in the environment. Factors like predation, symbiosis, competition and disease ail involve rhe living elements of the environment. All the relationships that exist between the living organisms, including the feeding relationships (food chains and food webs), camouOage, pollina tion and dispersal make up the biotic part o( the environment. (b) ~ IT:Q2 V'--J Why is a home aquarium not selfsustaining while a backyard pond might be? 1;mmmu ecos stem > (C) Rgure 2. 1 (a) The white-lip anole lizard lives in tropical rainforest and feeds on insects. (b) The bottle-nosed dolphin is a fast-swimming marine mammal that feeds on big-eye scad. The scad swim in big shoals and dart back and forth when attacked to try to confuse the dolphin. (c) The Caribbean flamingo feeds on tiny algae and shrimp which it filters from soda lake water with its specialised bill. Other birds cannot feed in these lakes because soda is caustic. Ecosystem, habitat, population, community An ecosystem is a sell-sustaining system of organisms interacting w ith each other and their environment. It is made up of all the plants and animals ~ sharing an environment. It is self-sustained wh en it can take care of itself - no IT:Q3 V'--J human imervenrion is needed to keep it going. Distinguish between (i) habitat and The area in which an organism lives is called its habitat, for example a small niche (ii) population and community. pond, a swamp or a rocky shore. A very small habitat is called a microhabitat, for example the soil at the bottom of a pond, the roots of a mangrove tree, leU3ftJ the crevice of a rock. A niche describes the role an organism plays within the ecosystem. It how the organism lives in its habaitat. population > A population is a group of organisms of the same species which live in a particular habitat. For example, in a pond ecosystem, there may be a community > population of beetles and a population of snails. A community consists of ~ all the populations which live in the same place and interact with each other. IT:Q4 V'--J The community in the pond ecosystem is made up of populations of different Using figure 2.2, describe: (i) a species of organisms, feeding on each other, competing with each other, population (ii) a habitat (iii) a niche (iv) hiding and protecting each oth er and also communicating with each oth er a community. (figure 2.2). 16 Abiotic factors Biotic factors Water's edge Water column Bottom Water surface Water column B ottom Water's edge Waterlogged soil Variable light Variable light Birds - red seal coot Variable 0 2 0 2 maybe low Insects - water strider Temperature may vary Dead/decaying matter Variable sediments Plants - water lettuce Microscopic organisms zooplankton, phytoplankton Insects - water boatman, diving beetle Fish - guppy, molly, tilapia, tarpon Bacteria including blue-greens micro- and macro-algae Shrimp Snails Dragonfly larvae Flowering plants grasses, sedges Crabs - land crab, fiddler crab Birds - egret, sandpiper Figure 2.2 The biotic and abiotic factors in a pond habitat, including the community and populations of organisms living in the pond habitat. Distribution of species The distribution of species is related to the physical or abiotic fa ctors of the environment as well as the availability of food or prey. A species is adapted t0 live in its environment. For example, camels are adapted to survive and live in the desert, an extremely harsh environment. Other species simply cannot live there. On ly animals that can tolera te dehydration and survive extremes of temperature can be found there. Effects of water on distribution ~ IT:QS \./'-I What are some factors or qualities of water that determine the types of organism that live in water? Water is an abiotic factor that affects the distribution of species. Organism s like fish and jellyfish that live in water must be able to use oxygen dissolved in water or take their oxygen from the air above the water, like whales. If they do not attach themselves to rocks or bury themselves in the seabed, they must also be adapted to move in water. There are two main kinds of water found on Earth : • fresh water found in lakes, rivers and ponds; • salt water found in the ocea ns and seas. 17 Living Organisms in tha Environment Fresh water is low in salt and mineral content, but salt water can be very concentrated. Where these two kinds of water meet, such as in estuaries, the waters m ix to give brackish water. Most anima l species are adapted to Live in either fresh water or salt water (figure 2.3). Only a very few that live in estuaries or regularly migrate from sea to river or back again (s uch as salmon and ee ls), can cope with the different conditions. Fish in a marine environment Fish in a freshwater environment gills actively excrete salt to the water passing over them gills actively ab sorb salt from the water passing over them drinks sea water t does not drink fresh water water constantly enters the organism and collects in a vacuole small amounts of concentrated urine produced too much salt is a problem and is actively gotten rid of l large amounts of dilute urine produced too much water is a problem it is not actively taken in and is actively gotten rid of Agure 2.3 Adaptations of bony fishes to live in marine or freshwater environments. Freshwater animals, like Amoeba, have mechan isms to get rid of the excess water that enters their body by osmosis (figure 2.4). ~l vacuole moves to the cell --""-4 membrane The water is actively expelled from the contractile vacuole of the Amoeba. Figure 2.4 Amoebae can live 1n fresh water because they are adapted to get rid of the excess water m their bodies. (a) Some species do not Live in water, but it still determines their distribution . Toads and frogs Li ve and feed on land but must return to water to reproduce. They are always found near rivers, pon ds and lakes. Others return to water to cool down and are found in or around areas with water. The distribution of planes is also related to water. Plants n eed a constant suppl y of water from the soil. Some actually live in wa ter, like water lilies. Plants that live in areas where water is in shon supply are called xerophytes. They have special fea tures which help reduce transpiration and therefore water loss (figure 2.5). Some of these features are: • redu ction of leaves to fine spikes (e.g. cacti); • the stomata are sunken in grooves and reduced in number (e.g. oleander); • the leaves roll into a cylindrical shape (e.g. marram grass). (b) Figure 2.5 (a) Cacti have leaves reduced to spines to reduce transpiration (b) Tile leaves of oleander have stomata sunken in grooves to reduce water loss. 18 - - __-c- ~ • Ecology arid tt1e Impact of Abiotio Factors on Livin~ -011ganisiiis The change from water to land along the edge of wa ter can create very clear zones of vegetation. Plant species that are more tolerant of having their roots submerged in water for long periods of time, such as the red mangrove, are fo und at the edge of the water. These species are replaced further inland by th ose which can tolerate some su bmersion, such as the black mangrove, and even further inland by those whkh are adapted to cope with on ly a li ttle submersion, such as the white mangrove (fi gure 2.6). Red mangrove Black mangrove White mangrove pneumatophores that are wider, knobby and less dense thick stilt roots or prop roots support and spread the weight of the tree in the soft soil slender aerial roots hang from the trees nutritive roots absorb nutrients anchoring roots Excrete salt through their leaves An indication of drier, better soil. They have normal root systems. Excrete salt through glands in the petioles J Excrete salt through salt glands Low tide SEA (SALl) WATER Mangrove zonation Rgure 2.6 Zonation of vegetation along the edge of a mangrove swamp. 19 ,; . ~Living Organisms in the Environmer't _. Effect of light on distribution ~ ll!Q6 \../V Name some herbivores that come out at night to feed, hoping to escape their predators. (ii} Predators that hunt at night may use mechanisms other than light to detect their prey. Describe, using examples, two other means apart from light that can be used to detect prey. (i} Light also affects the distribution of plants and animals throughout the Earth. Animals use light mainly to see their prey (figure 2.7). Some use the absence of light to escape predators. Light is vita l to planes because it is needed for photosynthesis. Without light a plant w ill die. Plants are not found in those areas of the Earth without light, like deep caves and deep ocean fl oors. Two aspects of light, its duration and its intensity, are important for the distribution of species, particularly plants . . However, heat is usually associated with high light intensity or bright light, and temperature is also an abiotic factor that affects species distribution. Effect of temperature on distribution Temperature also affects the distribution of species. Poikilothermic animal s are particularly affected because their body temperature reflects the temperature of the surroundings. If it is too cold, they cannot generate eno ugh energy to move around to find food or escape predators; if it is too hot, the proteins in their bodies start to break down and they die. Homeotbermic animals, such as mamma ls and birds, may be able to live in a greater range of temperatures but they show adaptations to cope with extremes of temperature. Camels are adapted for desert life. Desert hares have long ears which give off heat to keep the animal cooL but arctic hares have very short ears to reduce heat loss. Other mammals that live in the polar regions, like the polar bear, have thick layers of body fat and fur to keep them warm. Mammals such as whales, walruses and seals, are also able to live in cold polar waters because they have a thick layer of fat, called Rgure 2.7 Chameleon actively hunts its prey. blubber, just beneath the skin. This insulates them Crom the cold: whale blubber can be up to 50 cm thick. Effect of heavy metals on distribution micronutrients > 20 Our environment, and in particular the sea, contains in large or smaller amounts almost every metal known to humans. Life began in the sea and so most living things, through the process of evolution, have acq uired a tolerance for sma ll concentra tions of these metals. Some of them, such as copper, are essential in trace quantities and are called micronut rients. Metals such as copper, mercury and lead (called the heavy metals) are not tolerated in more than trace amounts. In larger conce ntrations they become toxic to animal and plant life, and we think of them as pollutants. These large concentrations often arise as a result of human activities. For example, some slag heaps on the island of Anglesey in the United Kingdom are so rich in copper that nothing, except a few clumps of horsetail grass, will grow on them. Mercury and lead are particularly dangerous to humans. The poisonous effects of mercury have been known since Roman times. By the J 9th century, mercury was widely used for 'silvering' mirrors, and for treating sexually transmitted diseases. Makers of fe lt hats, who used mercury, suffered from various nervous and mental disorders - hence the phrase 'mad as a hatter' . As the chemical industry developed, organic compounds of mercury were discovered. These are even more toxic because they bind to proteins and fats in body cells. The cells of the brain and the nervous system appear to be more . affected by these compounds and nowadays many mercury compounds which were once commonly used, for example as seed dressings, are prohibited. Lead is hardly less dangerous. Lead compounds damage the brain, particularly in young children, and lead poisoning can ca use to serious mental disorders. Th e three main ways in which lead was released into the environment were from local water pipes, from lead compounds in paint and from additives in petrol. In many countries alJ three are now prohibited. Tolerance to heavy metals like lead, copper, zinc and mercury, is inherited and passed on to offspring. Random mutations can result in some organisms having greater tolerance to heavy metals th an others. Plants may be able to: • trap heavy metals in the cellulose cell walls; • confine the metals to the vacuoles; • excrete the metals back in to the environment. These heavy-metal tolerant plants are rarely found in unpolluted areas as they are less competitive than other plants. They flourish in polluted areas as the heavy metals kill the competing plants. Tolerant plants pass on th~ir tolerance to their offspring. Effect of soil on distribution ~ Practical activity SBA 2.2: Water-holding capacity of three types of soil, page 338 Practical activity SBA 2.3: Percentage of water in a soil sample, page 339 Practical activity SBA 2.4: Percentage of air in a soil sample. page 340 Soil supports terrestrial life. For plants, it provides an anchor for roots and is a medium for nutrients. It acts as a ·sponge for water, holding it for absorption by the roots of plants. Plants are able to grow where the soil can provide all their needs. This means that soil type is very important to the distribu tion of plants. Animals depend on plants which depend on soil. Thus soil is also and so important to the distribution of terrestrial animals. It provides shelter for subterranean animals, but more importantly, thousands of microbes exist in soil tl1at replenish the microbes that live in the digestive tracts of herbivores. Humans have adapted to life on land. We build homes on land and depend on agriculture for our food. All crops require special types of soil. The soil sustains all forms of life across the planet. . ,.Chapter summary I~ II • Ecology is the study of the relationships of organisms with each other and their environment. • There are two kinds of environmental factors: abiotic and biotic. • Abiotic factors make up the non-living part of the environment. • Biotic factors result from the activities of the living organisms in the environment. • An ecological study involves looking at the biotic and abiotic factors of an area. • Sampling methods include quadrats, line transects and sweep nets. • A habitat is a place or area where an organism lives. • A niche is the role an organism plays within the ecosystem. • A species is a group of organisms that can interbreed and are adapted to live in their environment. • A population is a group of organisms of the same species living in an area. • A community consists of all the populations living in the same area. • The abiotic factors of an environment affect the distribution of the species found there. • Water and light are examples of abiotic factors that affect the distribution of species. 21 Living Organisms Jrr:t11 e~_En_1.1i_r:onn1e_n~, - . _· __ ~ ITQ1 J Abiotic factors Biotic factors The temperature of water. Feeding relationships, e.g. between the lizard and insects that are its prey. The amount of light available to the organisms. Behaviour of scad when attached by dolphin. You may have noted other examples from the pictures. A home aquarium is a limited ecosystem; it doesn't contain the diversity of species that would be found in the naute. A backyard pond is more likely to be a complete ecosystem with all the diversity necessa ry to sustain itself. ITQ3 (i) A habita t is the place where an orga nism li ves. A niche is the role an organism plays in an ecosystem. (ii) population is a group of organisms of one species living together in one habitat. A community is all the populations of all the organisms living together in an ecosystem. ITQ4 (i) A population is a group of organisms, all of the same species living together in one habitat. In this pond there are populations of many different species of fish and plants. (ii) A habitat is the place where an organism lives. The habitat is the pond. (iii) A niche is the role an organism plays in an ecosystem. Each organism in the pond has its own niche. (iv) A commun ity is all the populations Jiving together. This pond community includes the populations of au the plants, fish and other animals found there. ITQS Water may be salt water or fresh water. Salt water makes up the oceans and seas. Fresh water includes the lakes, rivers and ponds. Water can be stagnant or fast-fl owing and all the stages in between. Rocky shores have strong curren ts and wave action . Mangrove swamps have brackish water, which is a mix of salt and fresh. Orga nisms are adapted to live in these different habitats. ITQ6 (i) Examples are fruit-eating bats, and agouti which feed on fruits and seeds; there are many others that you might have thought of. (ii) Snakes have heat sensors found in pits on their face which can determine the presence of other living organisms. Snakes also use their forked tongue to pick up tiny particles left by an organism in the air. The tongue is then pushed into the pits of the mouth, and the snake 'tastes' the organism. Many other organisms use scent to find food. Insect-eating bats use sonar, or sound, to determine exactly what is around them and help them catch prey. ITQ2 Examination-style questions (i) Explain, using examples, the meaning of the terms: (a) abiotic factor; (b) biotic factor. (ii) Define: (a) environment; (b) habitat; (c) population; (d) community. (iii) Describe, using examples, how abiotic factors of the environment affect the distribution of species. (iv) (a) Amoebae live in fresh and salt water habitats. Describe a major problem of amoebae living in fresh water. 22 (b) Explain how Amoeba is adapted to live in fresh water. An ecological study was conducted in a cocoa estate and the data collected by a student are seen below. 2 Animals caught in the sweep net Animals seen Plants seen spider beetle caterpillar grasshopper other (unidentified) frog kiskadee lizard worm squirrel dog iguana millipede grass mango tree cocoa tree unknown shrubs coffee tree pea plant pomerac tree Quadrat throw Millipedes Spider 1 40 4 2 30 0 3 10 0 4 5 0 5 23 6 28 2 7 51 3 8 19 4 9 37 0 10 40 { (i) Construct a possible food web from the plants and animals recorded. (ii) These organisms interact with each other in a number of ways. Suggest two possible relationships that may exist between the organisms recorded. Using names examples, describe fully each example. (iii) Suggest some sources of error when using sweep nets. (iv) Calculate the population density of the millipede and spider. (v) The area studied was approximately 12 m wide and 20 m long. Calculate the population size for the millipede and spider. (vi) Describe fully how a quadrat can be used to estimate the number of organisms present in an area. (vii) Compare the use of the quadrat for these two organisms, millipede and spiders. Which do you think are the more accurate results? Explain why. 23 Fieeding Relationships betvveen Organisms 0 understand the meaning of the terms producers and consumers in a food chain and relate the position in the food chain to the mode of feeding 0 0 0 0 understand the terms herbivore, carnivore and omnivore 0 0 identify a food chain identify predator/prey relationships construct a food web that includes different trophic levels explain the role of decomposers understand that special relationships ex ist and discuss the advantages and disadvantages of such relationships food chain first trophic level second trophic level third trophic level fourth trophic level producer primary consumer secondary consumer tertiary consumer plants herbivore carnivore carnivore l ) symbiosis - relationships between organisms of different species decomposers food web - interlinking of food chains I parasitism commensalism mutualism predator/prey CHAPTER 9 Phytoplankton are microscopic organisms, like algae and blue-green bacteria that live in the oceans. They are seen in rivers, lakes and puddles of water. They are important since they start food chains in the world 's oceans or seas. Around deep-ocean hot water vents, there are bacteria wh ich get their n utrients and energy from the wa ter. These bacteria are the food for animals, an d these food ch ains are the only ones we know on Earth which do not depend on the Sun for th eir energy. Life depends on photosynthesis which is carried out by planes (chapter 9). Most animals get their n utrients (their source of energy) either directly or indirectly from p lants. Plants photosynthesise or make food from water and carbon dioxide, using light energy from the Sun to carry out the process. So the Su n is the ultimate source of energy for almost all life on Earth. Producers and consumers Plants are called producers because they produce or make their own food. They include mosses and green plants on land, and algae, aquatic planes and phytoplankton in water. Organisms that consume the plants or producers, ma in ly the animals, are ca lled consumers (figure 3. 1). Decomposers feed on dead o rganic matter (figure 3.2). nutrients (humus) made available by decomposers ! producer consumer consumer plant - - - - - - caterpillar - - - - - + small bird ~ 1 / they all die and their bodies are eaten ~i/ decomposers ~turn nutrients to the soil / Figure 3.2 dead fruit. Mould (a fungus) feeding on producer in the form of humus consumer etc ..... . Figure 3. 1 The relat1onsh1p between producers, consumers and decomposers Herbivores, carnivores and omnivores herbivores > Herbivores are organisms that feed only on plants. Examples are some insects (like grasshoppers, locusts, butterflies, bees), some birds (such as seed-eating and fruit-eating species) and some mammals (cows, horses, elephants, giraffes). In water, herbivores may be very large like the manatee or very small like a shrimp. carnivores > Carnivores are organisms that feed only on anima ls. They may hunt and kill other animals for food. Examples include some insects (like the praying mantis), some reptiles (such as snakes), some birds (eagles and hawks) and some mammals (lions, dolphins and leopards). lelulm1•li4-tl Omnivores feed on both plants and animals. Examples are pigs and humans. Food chains food chain > A food chain is a simple diagram that shows how the food or nutrients (the energy source) pass from one organism to another. For example: leaf-+ caterpillar-+ small bird -+ hawk The arrows show the movement of energy along the food chain. The leaf is a part of a green plant that is photosynthesising and is a producer. The caterpillar eats the leaf to get food (energy) to live and is thus a consumer. The sma ll bird and the hawk are also consumers because they are getting their food or energy from eating other organisms. Indirectly, their food comes from the leaf, since the food made by the leaf is first taken into the caterpillar, then into the sma ll bird as it feeds on the caterpillar and fina lly to the hawk. So all the consumers in the food chain ultimately get their food from the producer. We can also describe the food chain in terms of herbivores and carnivores. Herbivores feed on the plants or producers and then the carnivores feed on the herbivores. An omnivore may feed on the producer or herbivore (and even carnivore in some cases). producer -+ herbivore -+ carnivore (grass)\ (chi:ken) (mongoose) omnivore (h uman ) 25 Herbivores can only feed on the producers and are called the primary consumers. Carnivores which feed on herbivores are secondary consumers. Tertiary consumers feed on the secondary consumers and so on. producer --+ primary consumer --+ secondary consumer --+ tertiary --+ consumer Example: waterweed Producer trophic level > A food chain is composed of trophic levels. --+ tadpoles --+ small fish --+ bigger fish primary secondary tertiary (1°ry) (2°ry) (3°ry) consumer consuITier consumer Each organisITI in the food chain represents a trophic level. The three food chains below each consist of four trophic levels. These are examples of terrestrial food chains. Food chain I leaf --+ caterpillar -+ toad -+ snake Food chain II grass --+ grasshopper -+ insect-eating bird --+ hawk This is an example of an aquatic food chain. Food chain ill algae -+ sna il -+ leech -+ fish Table 3.1 Shows how the organisms of these three different food chains can be classified. Food chain I Food chain II Food chain Ill Type of feeder Consumer level Trophic level leaf producer producer first trophic level · herbivore primary consumer second trophic level carnivore secondary consumer third trophic level carnivore tertiary consumer fourth trophic level grass t caterpillar t t t insect-eating leech bird t snake t grasshopper snail t toad algae t hawk t fish Table 3. 1 Different ways to classify organisms in food chains CHAPTER 4 All food chains have certain characteristics in common, as seen in table 3.1. The number of trophic levels in a food chain is normally limited to four or five, since the amount of energy being passed on gets smaller and smaller at each level (d1apter 4). Predators and prey i•li§•F?U•li•-11 i!mlfJd Animals also show predator/prey relationships. Predators are carnivores that feed on other animals that are called their prey. Predators hunt, capture, kill and eat other anima ls and those that are hunted and eaten are the prey. Food chains therefore include predators. They are the higher order consumers. rosebush -+ aphid -+ ladybird -+ spider -+ insectivorous bird 26 Prey Predator aphid -+ ladybird ladybird -+ spider spider -+ bird Table 3.2 Predator/prey relationships in the rosebush food chain. In this food chain, while the spider is a predator because it kills and eats the ladybird, it is also prey to the insectivorous bird. The food chain shows three predator/prey relationships(table 3 .2) Animals that are prey have evolved to hide and escape predators, using characteristics such as camouflage, mirrticry and speed. Predators, on the other hand, have evolved characteristics to improve their chances of catching prey, like speed, lures and traps. When all these organisms die, decomposers return their nutrients to the' plants through the soil, and the nutrients return to other feeding animals in the food chains. Food webs A food chain shows one organism feeding on one other organism only, but feeding relationships are more complex than this. One organism may feed on a number of organisms and in turn may be eaten by a number of organisms. The interlinking of a number of food chains is called a food web (figures 3.3 and 3.4) . •?a7 \../'-) From the food web shown in figure 3.3: (i) name (a) two herbivores, and (b) two carnivores. (ii) give the name of an organism which is (a) a primary consumer; (b} a secondary consumer; (c) a producer; (d) a tertiary consumer; (e) both a secondary and tertiary consumer. (iii) name (a} two predators, and (b} two prey. (iv) name an organism found in: (a) the first trophic level; (b) the third trophic level. ~ IT:Q2 frog rat I butterfly caterpillar hibiscus plant grasshopper snail \) mango tree grass Rgure 3.3 A terrestrial food web. warbine l due' _ - cosf rob \../'-) Construct a food web seen in a (i} marine habitat (ii) a tree (such as a mango tree). ~ ~ water beetle mayfly nymph / water boatman water-flea ~ pond weed l algae Figure 3.4 A freshwater (aquatic) food web. 27 Decomposers and detritivores decomposer > CHAPTER 5 ~ IT:Q3 \../'--) Define the terms 'producer', 'consumer' and 'decomposer' and give two named examples of each. All living organisms eventually die. Their bodies are composed of complex compounds like carbohydrates, lipids and proteins that they stored when they were alive. T\.vo groups of organisms called the decomposers and detritivores obtain their food or energy from the remains of the dead organisms. As they feed on the dead organisms they cause their decay or decomposition (figure 3.5). They help in the recycling of nutrients (chapter 5) since they return the nutrients trapped in the dead organisms back to the environment. The nutrients become available again to living organisms. Dead organism fungi and bacteria simple substances complex compounds (proteins, lipids, - - - - - - - - - - - - • (carbon dioxide (CO:U. carbohydrates, etc.) compounds of ammonia (NH:i) from the proteins) carbon dioxide (C02) released into the air as the fungi and bacteria respire fungi and bacteria live f f / in the dead organism SOIL ammonia is released into the soil and combines with substances in the soil to form ammonium compounds / after some time the dead organism is broken down completely by the fungi and bacteria SOIL Agure 3.5 A dead organism decays or decomposes as fungi and bacteria feed on it. 1n11 ..11i.9 saprophyte > ~ IT:Q~ \../'--) Draw a diagram to show the feeding relationship between a producer, a consumer and a decomposer using examples from your answer to ITQ3. lullil!mH•i••U 28 Decomposers include bacteria and fungi. They secrete enzymes which break down dead plants and animal material into a substance called humus. Humus enriches and improves the structure of soils in which plants grow and from which they derive nutrients. Imagine the build-up of dead plants and animals on the Earth's surface if there were no decomposers. All the vital chemical elements or nutrients trapped in these dead organisms would not be able to return to living organisms or be recycled. Detritivores also help in the removal and recycling of dead o rganisms by feeding on small fragments of the dead material, which are called detritus. Examples of detritivores include woodlice and earthworms. Saprophyte is the name given to any organism that feeds on dead organic material, so decomposers and detritivores are all saprophytes. Special relationships The environment supports a host of organisms all living together. But some organisms live in very special relationships with each other. These relationships may be advantageous to all the organisms involved but, sometimes, one organism can cause harm to another. Symbiosis describes any relationship that exists when different species of organisms live together. There are three types of symbiosis: • mutualism; • commensalism; • parasitism. 3 · Feeding Relationsl1ips between Organisrns Mutual ism In this kind of association, CHAPTER 5 two organisms of different species Live closely together and both benefit. Here are some examples. • Some sea anemones and hermit crabs - The anemone attaches itself to the shell used by the hermit crab and obtains scraps of food as the crab feeds. The crab gains protection from predators as it is camouflaged by the anemone and protected Figure 3. 6 A hermit crab and sea anemone. from preda tors by the stinging tentacles (figure 3.6). • Leguminous plants and the bacterium Rhizobium (chapter 5) -The bacteria live inside swellings on the roots of the leguminous plants, like peas and beans. These bacteria convert nitrogen gas into ammonia, which is then con vened into arp.ino acids and used by the plants for growth. The plants benefit because they can thrive in a LI types of soil, even soil where nitrate is in short supply. The bacteria also benefit by having a place to live and an e nergy supply which they ger from the plant. • Egret and cow - The egret perches on th e cow's back as it feeds on insects and aradmids, especially ticks that can harm the cow. The egret is obtaining food and the cow benefits by having blood-sucking insects removed from its body. Commensalism commensalism > ~ IT:QS I../'-) Using named examples, distinguish between mutualism and commensalism. Commensalism is a relationship between two species in which one clearly benefits and the other is not harmed. Here are some examples. • Some orchids or ferns on trees - The orchids or fems are small plants that grow high on tbe tree to obtain sunligh t for photosynthesis (figure 3.7). They use the Rgure 3.7 An orchid growing on a tree. tree for support but n ot as a food source. The tree is not harmed, nor does it benefit. • Egret and cow - When the egret walks behind the cow, it feeds o n insects that fl y up as the cow sha kes the grass while it walks. The egret benefits but the cow does not. • Shark and remora - The remora attaches itself to the shark and moves around with it. As the shark feeds, the remora also feeds on scraps of food that are floating around. The remora obtains food wh ile the shark is not harmed, but nor does it benefit. 29 Living Organisms in the Environment Parasitism l•l§liU-1H51J ectoparasite > endoparasite > A parasite is an organism wh ich lives and feeds on or ins ide another o rganism , which is called the host. The parasite gains while the host is harmed. • Parasites wh ich live on the outer surface of their hosts are called ectopa rasites. For example, ticks, lice, fleas a nd leeches feed on th e blood of th eir h osts such as dogs, hwnans, cattle and fish (figure 3.8). • Parasites that live within a h ost are called endoparasites . An example in humans is th e o rganism which causes mala ria. A protozoan of the genus P/asmodium enters the human bloodstream through the bite of an infected female Anopheles mosquito. Once in th e body, the parasite multiplies, ca using bo uts of fever, pain, shivering and sweatin g. Millio ns of people die each year from malaria, although anti-malarial drugs like quinine and choroquinine have been developed. ,, Chapter summary Figure 3.8 A leech sucks blood from a human • • • • • • • • • • • • • • The Sun is the ultimate source of energy for most life on Earth. Plants make food and are called producers. Animals eat plants or other animals and are called consumers. A diagram which shows the sequence in which organisms feed on each other is called a food chain . A food web shows the interlinking of a number of food chains. Decomposers feed on dead plants and animals. Herbivores feed on plants alone. Carnivores feed on animals alone. Omnivores feed on both plants and animals. Symbiosis describes relationships between two different species. Mutualism describes a relationship where both species benefit. Commensalism is when one species benefits and the other is not harmed but nor does it benefit. In a parasitic relationship, one species benefits at the expense of the other. Predators are carnivores that feed on other animals which are called their prey. II II ITQ1 (i) (a) Aphid, butterfly, hummingbird, beetle, caterpillar, grasshopper or snail. (b) Ladybird, frog, kiskedee, tarantula, rar. snake, mongoose or hawk. (ii) (a) Aphid, butterfly, beetle, hu mm ingbird, caterpilla r, grasshopper or sna il (b) Ladybird, frog, kiskedee, tarantula, rat (c) Hibiscus, mango tree, grass (d) Frog, snake, mo ngoose, hawk (e) Frog, hawk (i ii) (a) Ladybird, frog, kiskedee, tarantula, ra t, snake, mongoose or h awk (b) Snake, frog, ladybird, kiskedee, ta rantula, rat hummingbird, aphid, beetle, caterpillar, grasshopper o r snail (1v) (a) Hibiscus, mango or grass (b) Ladybird, hawk, kiskedee, frog, tarantu la or rat 30 ITQ2 killer whale ' ( penguin seal \. J fish ' ( krill zooplankton \. J bachae phytoplankton mango tree Foodweb for a marine habitat Foodweb for a mango tree ITQ3 A producer is an organism tha t produces or makes organic food. A plant makes organic food during photosynthesis, so any plant is a producer. Examples are mango tree and hibiscus plant, bu t you may have thought of many others. A consumer is an organism that eats or consumes organic food. Animals cannot make their own food, so any animal is a consumer. Examples are caterpillars and humans. A decomposer is an organism that feeds on dead organic food (dead animals and plants). The food is said to be decaying or rotting as the decomposer feeds on it. Examples are bacteria, fungi. ITQ4 hibiscus plant -+ caterpillar bacteria/ Mutualism and commensalism are both relationships between two species or partners that are beneficial or good. In mutualism, both partners benefit. In commensalism, one partner benefits while the other, though not benefitting from the relationship, is not harmed in any way. An example of mutua lism is between the pigeon pea plant (leguminous plant) and Rhizobium bacteria that live in swellings of its roots. The pigeon pea plant gets amino acids for growth, and the bacteria obtain shelter and energy. An example of commensalism is seen with sharks and remora fish . The remora fish obtain food an d protection from the shark which benefits nothing from the relationship and is also not harmed. ITQ5 Examination-style questions (i) Construct a food web from the information given in the table. Animal What it was seen doing small moth feeding on nectar of a flower (morning glory) lizard feeding on insects small bird with a lizard in its beak spider feeding on insects trapped in its web small butterfly feeding on the nectar of a flower (lxora) 31 (ii) Examine the food web constructed and describe three consequences of the removal of the lizards. (iii) Describe the relationship between: (a) the moth and the morning glory; (b) the spider and the moth. (iv) Name one predator/prey relationship from the food web and describe: { (a) how the predator is adapted to catch its prey; (b) any feature used by the prey to escape the predator. 2 (i) Using named examples, describe a: (a) parasite relationship; (b) mutualistic relationship. (ii) (a) Draw a food chain with four trophic levels. (Use named organisms.) (b) Identify the producer. (c) How does the organism in the fourth trophic level obtain energy from the Sun? (d) Which organism is the primary consumer? (iii) Which organism in the food chain is a: (a) herbivore? (b) carnivore? (c) predator? (d) prey? (iv) Describe the role of the decomposers in the food chain. (v) Copy the table below and use examples from these food chains to complete it. root -+ earthworm - frog - fox pondweed - mayfly nymph -+ water beetle Stages of food chain producer primary consumer predator prey herbivore second trophic level third trophic level first trophic level 32 Two examples of organisms, one from each food chain Eicosystem, Habitat, Population, Community 0 0 0 0 0 0 understand that the Sun is the ultimate source of energy for life on Earth explain why food is the source of energy needed by living organisms understand that respiration is the process by which energy is released from food describe pyramids of energy d escribe pyramids of numbers d escribe pyramids of biomass food chain plant makes food using light energy from Sun - - - - , some energy passed on energy lost due to animal eats and obtains ~ ~espiration , in food (chemical energy) - - - - - i urine and faeces I some energy passed on J animal - - - - - - - ( ) food - source of energy for all organisms feeding pyramids: • energy • numbers • biomass I importance of photosynthesis to food chains All living organisms need energy to carry out life processes; for example your body uses energy to grow, move, inhale and eat. The energy that your body is using came from your food. U you made a food web for everything you eat, you would find that all the energy you use was trapped by plants from tbe Sun. Ultimately, all energy for life comes from the Sun. Trapping the Sun's energy Plants use the Sun's energy to make food during photosynthesis (chapter 9). During photosynthesis carbon dioxide and water are combined to make glucose and oxygen. energy from the Sun carbon dioxide + water-------+ oxygen + glucose The glucose is then used to make other carbohydrates, lipids and protein s and everything else the plant needs. These become the components of food (chapter 13) for consumers. The term 'food' can thus be used for the term 'energy', beca use energy is released from food. 33 Living Organisms in the Environment respiration > ~ IT:.Q·1 \_.)'...J Why is the Sun considered to be the ultimate source of energy for all life on Earth? So the energy in the light from the Sun is converted to chemical energy (as glucose and other chemicals) in the plant. The chemical energy (as food) then passes on to consumers as they feed on the plants (figure 4.1). Respiration releases the energy trapped in the food so that it can be used by the organism. Respiration also makes carbon dioxide and water. Food (usually glucose) is ' burnt' during respiration by plants and animals to release energy so that they can carry out all the processes necessary for life. So, not all the energy gained by a plant is passed on to an animal that eats the plant (figure 4.2). Likewise, not all the energy gained by an animal is passed on to a predator (figure 4.3) glucose+ oxygen-+ energy+ carbon dioxide+ water energy from Sun passed to Plants · (photosynthesis) make food/chemical energy l l energy from plants passed to Animals (when they feed on plants) During respiration this energy is made available to be used for everyday activities. Rgure 4. 1 Energy from the Sun is used by plants and by animals. Rest of energy stored in plant tissues. Passed on to herbivores when they feed on plant light energy energy taken in energy stored energy lost Some energy changed to heat during respiration, for life processes. Heat lost to the environment Rgure 4.2 Only some of the energy taken up by a plant can be passed on to a herbivore. Energy passed on to carnivore when it eats the COW Rgure 4.3 Only some of the energy that an animal gains through eating can be passed on to a predator. 34 How a plant gains and loses energy ~ IT:Q2 V'-' What happens to the energy that a plant gains during photosynthesis? • A plant gains energy wh en it converts light energy to chemical energy during photosynthesis. • It stores some of the energy by changing the glucose it made into other chemicals. • It uses up some of the food during respiration to release energy to grow and carry out other llie processes. Some of the energy that is released is lost as heat energy from the plant. How an animal gains and loses energy For each animal at each trophic level: • energy is gained as the organ ism feed s; • some of this energy is stored as tissue as the animal grows; • some energy is lost as faeces and urine straight out of the animal's body; • some of the stored energy is relea sed du ring respiration for the organism to stay alive and some of that energy is lost as heat to th e envirom11ent. ~ IT:Q3 V'-' What happens to the energy that an animal obtains? Movement of energy through a food chain Energy flow through a food chain or web is related to the movement of food through the chain. Figure 4.4 shows the movement of energy through a food chain. Energy lost as heat due to respiration ~l PLANT Energy stored in tissue - Energy lost as heat due to respiration Energy lost as heat due to respiration Energy lost as heat due to respiration l l l HERBIVORE or PRIMARY CONSUMER CARNIVORE or SECONDARY CONSUMER CARNIVORE or TERTIARY CONSUMER Energy stored In tis_sue - Energy stored in tissue --·---------, ! ! ! Energy lost in urine and faeces Energy lost in urine and faeces Energy lost in urine and faeces Figure 4.4 Movement of energy through a food chain. ~ IT:Q~ V'-' How is energy transferred through a food chain? ~ IT:QS V'-' What is the importance of respiration in a food chain? Figure 4.4 shows that energy is lost at every step in the food chain. This means there is less energy at each level for the animals in tha t level than in the level below. The length of a food chain is limited by the energy loss at each level. There will come a point when there is not enough energy to support another level. There are usually not more than five steps in any food chain. When the plants and animals die, the energy stored in the dead bodies is passed on to the detritivores and decomposers as they feed. They also feed on the urine and faeces made by animals. 35 Living Organisms in the Environment CHAPTER 5 l•n•1uh-S-» productivity > Unlike energy, the elemencs of which organisms are made, such as carbon and nitrogen, are recycled (chapter 5). Energy is not recycled, it moves through and out of the food chains. Energy enters a food chain as light energy from the Sun, and is lost from every trophic level as hear energy ro the environment. Its flow is non-cycl ical, which means that the energy cannot be returned to a living organism. The length of a food chain depends on the energy in the biomass availabJe at each level. Ultimately this depends on how much energy is being trapped by the producers (their productivity). If the whole ecosystem is highly productive, then the food chains will be longer because there w ill be more energy entering at the producer level of the chain. If there is on ly a small amount of energy being trapped by the producers, then they can support only a few trophic levels (figure 4.5) . Ecosystems in eq uatorial regions are generally more prod uctive tha n those in higher latitudes because they get more light (figure 4.6). fJl!I Productivity of ecosystem is high plant fJl!I Prod uctivity of ecosystem is low plant fJl!I energy loss - energy loss fJlt energy loss - ~ energy loss - Figure 4.5 The productivity of the producers in an ecosystem limits the length of food chains that can be supported (a) (b) Figure 4. 6 (al Ecosystem of high productivity. (b) Ecosystem of low product1v1ty Crop plants are mass-harvested for human consumption. If these plants are eaten directly by humans, a lot more energy can be obtained by the humans than if the plants were fed to other animals and those animals then eaten by h umans (figures 4.7 and 4.8). 36 • f/11 energy loss -" energy ~ energy loss energy loss energy energy ~ energy HUMANS Figure 4. 7 Efficient use of food chain for energy by humans. f/11 energy OTHER ANIMAL - HUMANS Figure 4.8 Inefficient use of food chain; a lot of energy is lost that could be available to humans. Pyramids of energy pyramid of energy > A pyram id of energy is a good way of showing the energy relationships between organisms in different trophic levels. Figure 4. 9 shows the pyramid of energy for a simple food chain . Each block in the pyramid shows the amount of energy available to the next trophic level. Using figure 4.9 as an example, 90 000 units of energy are available to the grasshoppers. The grasshoppers consume that energy as food and lose some of it to the environment as heat during respiration and activity, and some of it as faeces. That leaves only 15 000 units for the insect-eating birds. The birds consume that energy and lose some of it to the environment in faeces and as heat. So only 2000 units are available to the next level, the cats. The cats lose energy to the environment as faeces and as heat, leaving only 100 units of energy in their bodies. This is not enough to support another trophic level, so there are only four trophic levels in this chain. grass ---+ grasshopper ---+ insect-eating bird ---+ cat TERTIARY CONSUMER SECONDARY CONSUMER PRIMARY CONSUMER 100 units of energy 2000 units of energy 15 000 r--___.__ , _ ___ - - --- - - PRODUCER A pyramid - each block gets smaller as you go up 90000 unit s of energy Pyramid of energy Figure 4.9 A pyramid of energy shows that less and less energy is available to higher trophic levels in a food chain. Pyramids of numbers pyramid of numbers > A pyramid of n u mbers is like a pyramid of energy but shows the numbers of all the organisms at each trophic level of a food chain within a given area . Look at the pyramid in figure 4.10 (overleaf). The pyramid shows that, within the area being studied there were 80 leaves. On these leaves, 8 caterpillars were feeding. Tvvo birds were seen feeding on the caterpillars and one cat ate both birds. Ecosystems usually contain a large number of sma ll organisms and a smaller number of large animals. Predators are usually larger than their prey and must eat a number of them to stay alive. 37 Ll:ving Or-ganisms in the Environment 1O leaves grasshopper --....___ 10 leaves - - - - - - - - - - - grasshopper - - ---...,. _ __,. • bird grasshopper --------------•~ 1O leaves 10 leaves - - - - - - - - - - - • grasshopper 101eaves - - - - - - - - - - - • 10 leaves - - - - - - - - - - - • ~ ~ cat Each cat eats 2 birds a day 10 leaves - - - - - - - - - - - • 101eaves - - - - - - - - - - - • Each grasshopper eats 10 leaves each day cat bird grasshopper leaves Figure 4.10 A pyramid of numbers is obtained by counting all the individuals at each trophic level. With this type of ecological pyramid, no allowance is made for the size of the organism. Each cat and ea ch caterpillar is each counted as one. So sometimes we can see different shapes in pyramids of numbers (figure 4.11 ). One tree may be eaten by many caterpillars, though we could have counted each leaf separately to get a ' normal' pyramid shape. One dog is host to many ticks, and each tick may have several parasites, but in this case each 'predator' is actually smaller than its 'prey'. Figure 4.11 pyramid of biomass ) hawk parasites on ticks small bird ticks caterpillar dog Some pyramids of numbers are of different shapes. Pyramids of biomass Instead of estimating the numbers of organisms at each trophic level we can estimate their biomass or dry weight. From this we can construct a pyramid showing the biomass of organisms at a given time in each trophic level. The width of the boxes indicates the relative amounts of biomass present at each trophic level. At the start of the food chain in figure 4.12 is a large biomass of green leaves. The p yramid shows that a large amount of plant material supports a smaller mass of herbivores and an even smaller mass of carnivores. mass of tertiary consumers mass of secondary consumers mass of primary consumers mass of producers Rgure 4. 12 A pyramid of biomass. 38 Bioaccumulation Pesticides can spread through the environment in a food chain. Pesticides (such as fungicides, herbicides and insecticides) are chemicals that are toxic to some organisms. They work in one of two ways, on contact or once the chemical has entered the organism. A grasshopper feeding on plants sprayed with insecticide will only need to take in a small amount to kill it. But this can harm other animals in the food chain. For example, a bird feeding on the grasshoppers will accumulate in its body all the insecticide that the grasshoppers have ingested. Remember that the bird will eat a large number of grasshoppers every day. So the bird may end up with levels of insecticide high enough to poison it or harm it in some way. A hawk or other predator feeding on the small birds could end up with even higher levels of pesticide in its body, again enough to poison or harm it. This is called bioaccumulation or biological magnification. DDT (dichlorodiphenyltrichloroethane) DDT provides a well-known example of bioaccumulation (figure 4.13). It is a very effective insecticide that was used in many countries in the 1950s and 1960s to control mosquitoes, which carry malaria, and to control other insect pests. However, DDT is stored in fatty tissue so predators absorb the chemical when they eat prey that contains it. Levels of DDT that accumulate in the bodies of top predators may be enough to kill them or to harm them in other ways. In a study of ospreys (North American birds) adult birds were found to contain 8 million times more DDT than organisms at the bottom of the food chain. These high concentrations did not kill the birds, but caused the females to lay eggs with very thin shells. Many eggs broke and so numbers of these birds dropped rapidly. Since 1972 the use of DDT has been banned in many countries. DDT accumulates in the top consumers fish eats herbivore and accumulates DDT 124 ppm DDT 5 ppm DDT herbivore eats phytoplankton and accumulates DDT 1 ppm DDT Producer 0.0025 ppm DDT DDT enters phytoplankton run-off from agricultural land carries a dilute solution of pesticides, e.g. DDT Figure 4. 13 Pesticides like DDT accumulate In the tissues of each trophic level of a food chain. 39 - - Living Orgar:iisms In :the£nvir_o11rn_~~t _ r Chapter summary • Energy from the Sun is used by plants to make food during photosynthesis. • The equation for photosynthesis is: carbon dioxide + water + light energy -+ glucose (food) + oxygen • The energy that is stored in a plant is passed on to other organisms when they feed on the plant. • Respiration releases energy in plants and animals for life and growth. • The equation for respiration is: food (glucose) + oxygen -+ energy + carbon dioxide + water I • Most of the energy released in respiration is lost as heat to the environment and cannot be passed on to the next trophic level. • A pyramid of energy shows that less and less energy is passed on to the higher trophic levels of a food chain. • A pyramid of numbers shows.the number of organisms found in each trophic level of a food chain . • If the dry mass of the organisms at each tropic level of a food chain is measured, a pyramid of biomass can be produced. The energy from the Sun is used by plants or producers to make organic food that is used directly and indirectly by all animals, including humans. Withou t the Sun, plants would die so there would be no food for the animals. They would also die and life, as w e kn ow it, would cease to exist. ITQ2 A plan t stores som e of the energy in its tissues as it grows and uses som e en ergy to stay alive. Some energy is lost as heat en ergy. Som e en ergy is thus lost to the environment and some is kept in th e plant's body. ITQ3 An animal uses some of the energy from respiration to stay alive. Much of the energy is lost to the environment as heat . The animal may use up more energy than a plant sin ce it is more active. It also stores some energy as ch emical energy in its tissues as it grows. ITQ4 Energy is transferred from one trophic or feeding level to another when an organism feeds. En ergy is transferred in the form of food. Th e food is n eeded for respiration which makes energy available to the organism. So energy moves through a food ch ain when the organisms eat. ITQS Some of the ene rgy tha t is released during respiration is lost to the en vironment in the form of heat from the organism. Respiration is important in a food chain because at each level in th e food chain en ergy is lost. Only a proportion of the energy entering one trophic level is stored in the organism 's body and is thus available to the next trophic level. ITQ1 Examination-style questions grass (i) grasshopper bi re Copy the diagram above and, using arrows, annotate it to show the movement of energy into and out of each organism. (ii) What is the importance of the following in a food chain: (a) respiration? (b) photosynthesis? 40 (c} digestion? (iii} How is light energy converted to chemical energy? (iv} Most animals spend a great percentage of their day looking for food. Why must animals eat food? (v) On the TV programme Sesame Street, there is a story about a boy who ate the Sun. What do you think of this story? Give details. 2 ( Food chain A grass --+ cow --+ tick --+ egret Food chain B grass --+ grasshopper --+ izard (i} Construct possible pyramids of numbers for food chains A and B. In each case, discuss the shape of the pyramid. (ii} Construct possible pyramids of energy for the same two food chains, A and B. Discuss the shapes of the pyramids. cat bird grasshopper I leaves I (iii} Look at the pyramid of energy above. Why do leaves contain the greatest amount of energy? (iv} What happens to the energy that is not passed on to the grasshoppers? (v} What will happen to the cats if all the grasshoppers were killed by the use of insecticide? 41 0 0 0 0 0 explain the carbon cycle understand what is meant by the greenhouse effect and global warming explain the importance of nitrogen to plants and animals explain the nitrogen cycle describe the causes and effects of acid rain atoms in animals atoms in plants ,..- carbon carbon hydrogen hydrogen oxygen oxygen .-+-- nitrogen - - - - - - - - - - - nitrogen _ ......_ others others biogeochemical cycles atoms in the environment carbon hydrogen oxygen - - - - - - - - - - nitrogen _.i_ _ _ _ _ _ _ _ _., others ( greenhouse effect ) acid rain leaching global warming Biogeochemical cycles Living organisms are made u p of different kinds of atoms. The most common atoms are carbon, hydrogen and oxygen, with nitrogen following closely behind. Smaller amounts of other atoms, such as iron, calcium and sodium, are also found in living organisms. These atoms bond together to form larger structures such as protein, carbohydrates and lipids. These larger structures are then arranged in particular ways to make up all the tissues needed to build a living organism. All living organisms are, in essence, complex structures of organic molecules. If we look at a person, we see skin, hair and nails - it is difficult to imagine that basically we are just atoms of carbon, hydrogen, oxygen and nitrogen. A carbon atom that was present in Einstein's body could be present in your body right now. biogeo chemical cycles > Remember that carbon is found in carbon dioxide (C0 2) , carbohydrates, lipids and proteins, since carbon is an integral part of those compounds. As an animal grows from birth to adulthood, the growing tissues come from the food it eats. The animal increases its store of these atoms as it eats and m uscle, bone and all the tissues that make up the organism increase in mass. Then, when the organism dies, the body is broken down or decomposed, and the atoms are released back into the environment. The atoms become pan of the soil as the organism 's decomposed body becomes mixed into the soil. They may then be taken up by plants and built. into the plant's tissues as the plant absorbs them from the soil with water. These plants are then eaten by animals and the atoms thus become part of an . animal once again. The cycling processed by which these essential atoms are released and reused in nature are called biogeochemical cycles. The carbon and nitrogen cycles are examples of such cycles. The carbon cycle The carbon cycle shows how c;arbon atoms are passed from one organism to another and to their environment as they live, breathe, eat, die and decay. The numbers of the following paragraphs refer to numbers in figures 5.1 and 5.2. carbon dioxide (CO:z) in the air (0.04%) photosynthesis organic compounds in green plants respiration combustion respiration eaten by animals ------....i death and decay death and decay fossilisation organic compounds in bacteria and fungi .......... -..,;.;_~ fossilisation organic compounds in fossil fuels ~~------------' Figure 5. 1 The carbon cycle shown 1n d1agrammat1c form Equation for respiration: food (glucose) + oxygen -+ energy + carbon dioxide + water 1 .~ 2 What atoms are living organisms made up of? (ii) How do they obtain these components? (iii) What happens to these components after the organism dies? (iv) What is a biogeochemical cycle? 3 \./'-I (i) 4 5 6 The atmosphere contains about 0.04% carbon dioxide. During photosynthesis, plants use carbon dioxide from the atmosphere to make carbohydrates, proteins and lipids. This is the first source of carbon in living organisms - as a part of the plant's body. Animals then obtain their supply of carbon by eating plants or other animals that have eaten plants. As plants and animals respire, molecules of carbon dioxide are released back into the atmosphere. Waste materials from living organisms (like urine and faeces) and their dead bodies (all organisms die) , are used as food sources by decomposers. Decomposers, like bacteria and fungi, feed on dead organic matter. Carbon atoms then become incorporated into the bodies of the decomposers. Respiration of the decomposers releases carbon dioxide into the atmosphere. In waterlogged soils where oxygen is in short supply, decomposers are not able to break down tissues completely in dead bodies and the remains 43 Livir1g Organisms in lhe Environment lt•1"1§!1(!tfUflJ 7 accumulate. For example, in the Carboniferous period (about 290 million years ago) huge areas of waterlogged swamps covered many parts of the world. When the swamp plants died, partially decomposed plant material accumulated and eventually turned to coal, a solid fossil fuel. Oil and natural gas are liquid fossil fuels that formed in a similar way from the remains of plants and animals that died in oceans. Fossil fuels contain a large proportion of carbon. The burning of fossil fuels (combustion) releases carbon dioxide into the atmosphere. l~ndioxide in~the air photosynthesis Z combustion .. gas coal decomposers in the soil respiration of decomposers Figure 5.2 The carbon cycle in more detail. ~ l'.T:Q2 \..AJ (i) What is the importance of photosynthesis in the carbon cycle? (ii) What is the importance of respiration in the carbon cycle? (iii) What is combustion? (iv) What role do decomposers play in the carbon cycle? 44 And so the cycle continues, carbon dioxide in the atmosphere is taken up by plants, which are eaten by anin1als, and returned to the atmosphere through respiration, decomposition or combustion of fossi l fuels. Note the importance of plants in this cycle. Without plants, the carbon stays in the atmosphere and cannot be reused and incorporated into the bodies of animals. If there were no plants, there wou ld be no animals. The human effect on the carbon cycle Figure 5.3 shows how the level of carbon dioxide in the air has been rising. The rise in human population has been supported by an increase in manufacturing and other types of industries. Since the Industrial Revolution, humans have been burning fossil fuels to release energy for machines. This has added carbon dioxide to the air at an alarmingly fast rate. The carbon was locked away in the solid or liquid forms of fossil fu el for millions of years. Increased combustion of these fossil fuels increases the carbon dioxide concentration in the air. Increased concentration of carbon dioxide in the atmosphere is associated with the environmental problem known as global warming. - - - - - - - ----- - - 5 --The Cycling of ~utrients - The Industrial Revolution is a term used to describe the time when people started to make and use machines to do a lot of their work. It began about 200 years ago. Machines need energy to make them work, and most of this energy comes from burning fossil fuels. 7 Carbon emission from burning of fossil fuels (billion tonnes) 370 6 360 5 350 4 340 3 330 2 320 Atmospheric carbon dioxide (parts per million) 310 300 0 290 1840 1860 1880 1900 1920 1940 1960 1980 2000 '-~--'--~--'-~-'-~~'--~-'---~-'-~--'-~-----' ~840 1860 1880 1900 Year 1920 1940 1960 1980 2000 Year Figure 5.3 The levels of carbon dioxide in the atmosphere over the last 160 years. The greenhouse effect and global warming greenhouse gases > greenhouse effect > global warming > When heat from the Sun reaches the Earth's surface much of it bounces straight back into the atmosphere (figure 5.4). Within the Earth's atmosphere there are gases like carbon dioxide and methane that absorb some of the escaping heat and send it back to the Earth's surface, keeping it trapped around the Earth. They act like a greenhouse around the Earth and thus are called greenhou se gases. This is a natural process which helps keep the surface of the Earth warm. Without this natural greenhouse effect, the Earth would be too cold for most of the organisms living on it. A problem arises when the proportions of these gases in the atmosphere increase . They bounce more of the heat back to the Earth's surface. This is called the 'enhanced' greenhouse effect. As a result the temperature of the Earth increases, which is known as global warming. infrared radiation (heat) radiated back towards space absorbed by 'greenhouse gases' to space incoming solar radiation (ultraviolet, visible and infrared) reradiated into space atmosphere heated - raising Earth's temperature reflection from clouds Earth Figure 5.4 Some solar radiation that reaches the Earth is absorbed by the atmosphere rather than going back out to space. 45 Carbon dioxide concentration in the Earth's atmosphere has increased by about 20 % over the last 100 years. This effect has also been worsened by deforestation. Trees (forests) remove carbon dioxide from the atmosphere during photosynthesis, but large areas of forests are being cut down. It is not proven that higher carbon dioxide levels cause temperature increase, but scientific research suggests that the two may be associated. Some people think tha t global warming might cause the Earth's temperature to rise between 1.5 °C and 4.5 °C by the end of the 2 1st century. Possible effects of global warming • The polar ice caps may melt which could cause sea levels all over the world to rise significantly. Many millions of people now live in lowland areas and these may be flooded, driving people from their h omes. • Fertile, crop-producing land would be lost by flooding. • The distribution of organisms over the face of the Earth may change as land floods and temperature and rainfall patterns change. • Changes in the amount of land and sea could change weather patterns. This could increase rainfall in some places and increase periods of drought in others. Natural storms like hurricanes and typhoons may be more severe. • Cold countries may become more temperate and fertile. ~ IJ:Q3 \.../'-J Why are the carbon dioxide levels in the atmosphere rising? (ii) What might be some consequences of this rise? (i) We must be very careful not to say that every example of extreme weather is due to global warming. There have always been variations in climate over the years and over centuries. Also, we must be careful not to make unjustified assumptions about fu ture changes. For example, on the island of Svalbard in the Arctic Ocean, one of the glaciers is retreating, but a neighbouring glacier has advanced by more than a mile in seven years. Some sea levels are said to be lower now than in the 18th century - for example mean sea level in the Cook Islands has apparently dropped by about 20 cm in 200 years. Globally, mean sea level is rising at about 3 mm per year. So although global warming is a reality, and many experts attribute this to the enhanced greenhouse effect, we should not be too quick to predict catastrophe. The nitrogen cycle About 79 % of the air around us is nitrogen gas. This gas is very unreactive - it passes in and ou t of animal's bodies unchanged when they breathe. However, nitrogen is an essential component of biological molecules such as proteins and DNA. Muscle is composed of long strands of protein and DNA is the m olecule in each nucleus of a cell which contains the information about how to build that cell and make it work. Plants manufacture protein by absorbing nitrogen from the soil mostly as nitrate ions. These are combined with carbon, hydrogen and oxygen taken from glucose that was made during photosynthesis. The elements are then arra nged in another way as they combine with the nitrogen, to make the building blocks for proteins and DNA. Remember that glucose is made during photosynthesis and is composed of carbon, hydrogen and oxygen. Animals obtain their nitrogen from the protein in their diet, through eating plants or other animals. The protein they eat is digested, absorbed and reused as needed in the feeding animal. That is, the nitrogen obtained from the protein of a piece of plant material or meat can be used to build growing muscles, make DNA, enzym es and other proteins, and everything else requiring nitrogen. The numbers of the following paragraphs refer to numbers in figure 5.5. 46 - _ _ _ _ - - _ =- -_ 5 /ftle Cycling ~ot, Nutrients - nitrogen in the air nitrogen-fixing bacteria lightning denitrifying bacteria · animal protein plants eaten nitrogen oxide in root nodules Rhizobium and decay ammonium compounds plant protein nitrifying bacteria Nitrosomonas rain (acid rain) nitrates absorbed in soil Clostridium nitrifying bacteria Nitrobacter nitrates in the soil nitrites in soil ~1 leaching of the soil fertilisers Figure 5.5 The nitrogen cycle shown in diagrammatic form. nitrogen fixation > I 2 nitrification > 3 denitrification > 4 5 Nitrogen fixation - This occurs in nitrogen-fixing bacteria that convert nitrogen gas in the air to nitrate. Some of these bacteria, like Azotobacter and Clostridium, live in in the soil and convert the nitrogen gas found in the air in the soil to nitrate. Plants cannot absorb nitrogen gas, only substances that contain it, like nitrates. So nitrogen-fixing bacteria thus make nitrogen available to plants in a form they can absorb. Plants use the nitrogen from nitrates in the soil to make proteins and DNA. Other kinds of nitrogen-fixing bacteria, called Rhizobium, live in the roots of legumes (plants of the pea family). There, nitrogen gas is converted to nitrates and used directly inside the plant to make protein. Decay - When plants and animals die, their bodies are decomposed by decomposers to make ammonium compounds in the soil. Animal wastes, like faeces and urine, are also decomposed by bacteria living freely in the soil. Nitrification - The ammonium compounds formed during decay are converted to nitrites and then nitrates. The processes that lead to the formation of nitrates in the soil are called nitrification and are carried out by nitrifying bacteria like Nitrosomonas and Nitrobacter. Plants take up n itrate ions from the soil and make proteins. Denitrification - The nitrogen cycle is completed by denitrifying bacteria. They convert nitrates in the soil back to nitrogen gas. The activities of these bacteria reduce soil fertility, since they take nitrates out of the soil which the plants need to grow well. Lightning - This provides energy to convert a little nitrogen to nitrogen oxides which dissolve in rain to form nitrates. 47 _ 6 1@'30!.t•iJ 7 -~ ~-= - - _-= ~ =_·_ ;;_~-:_~c ~~-. - .- Living Organisms ,in the E~w!ror~!])~_ml'._ _ - - Fertilisers - To make crops grow better, we add artificial and natural fertilisers to the soil to increase the levels of nitrates. Leaching - As rain water passes through the soil on its way to the rivers, lakes or seas, it carries with it dissolved nitrates and other soil nutrients. So the nitrates can be washed out of the soil. This is called leaching (figure 5.6). ~ IJ:Q'1 L)'...I Copy and complete this table. Process in Importance Examples nitrogen cycle of bacteria involved river nitrogen fixation soil water to river takes nutrients with if decay Agure 5.6 Diagram showing how n1trates can be leached from soil. nitrification denitrification CHAPTER 3 The nitrogen cyde is thus essential to life as nitrogen is a vital component of every living organism (figure 5.7). This biogeod1emical cycle allows nitrogen to be used over and over by living organisms. Nitrogen atoms cannot be created and there is only a certain amounc on Earth. The importance of bacteria should be noted because they are an integral part of this cycle. Nitrifying bacteria can be considered 'good' bacteria, without which living organisms would slowly become extinct. The relationship be tween the plants and the nitrogen-fixing bacteria is an exampl e of mutualism (chapter 3). nitrogen in the air ~ protein 1n animals nitrogenfixing _bacteria denrtrifying bacteria lightning nitrogen fixation Rhizoblum nitrates in soil N1trobacter t nitrites in soil ammonium compounds In soil Agure 5.7 The nitrogen cycle in more detail. 48 ' 5 · The Cyclin~ of Nutri~nts Acid rain Ft;l•li:O.U Combustion of fossil fuels in industry and from motor vehicles releases acidic gases sud1 as sulfur dioxide and nitrogen dioxide. These gases dissolve in atmospheric water vapour in clouds and later fall as acid rain (figure 5.8). Sulfur dioxide dissolves in atmospheric water to give, eventually, dilute sulfuric acid. Oxides of nitrogen dissolve to form dilute nitric acid. oxides of sulfur and nitrogen from pollution dissolve in water in the cloud to make acid rain acid pollutant s from vehicles, power stations and industry pH of rain 4-5 pH of rain 5-7 Figure 5.8 The formation of acid rain. pH is a measure of how acidic or how alkaline a solution is. ApH of 7 is neutral. A solution with a pH less than this is acidic. If it has a pH above 7, it is alkaline. The acid clouds may be carried hundreds of miles away from the source of the pollution by air currents. It has been recorded that rain with a pH as low as 4 has fallen over Scandinavia, Germany and Canada. • Acid rain may kill plants and trees. Some forests, like the Black Forest in Germany, have been severely damaged (figure 5.9) . But it has been found that acid rain enhances the growth of pine forests in Scandinavia. • Acid rain also dissolves some compounds of poisonous m etals thus introducin g them into lakes and rivers. This poisons organisms living in the water. Rgure 5.9 These trees have been killed by acid About 400 lakes in Norway are rain. now rendered fishless because of acid rain. • In cities. stone (statues and carvings) and metal structures have been damaged because of erosion due to acid ra in. Governments are trying to reduce acid rain by introducing regulations th at demand th.at industries do not release atmosph eric pollutants. The design of engines for motor vehicles is also important to reduce the amount of pollutant gases that they make. 49 'Y Chapter summary • Living organisms are built up from single atoms, mostly carbon, hydrogen, oxygen, with some nitrogen, iron, calcium, sodium, sulfur and other elements. • Biogeochemical cycles show how materials are reused in nature. • The carbon cycle shows how carbon passes between the air, soil, plants and animals and back again. • The greenhouse effect is an important natural process, caused by greenhouse gases in the atmosphere that absorb heat energy from the Sun and keep the surface of the Earth warm enough for life as we know it. • Increasing levels of carbon dioxide in the air could lead to global warming which could affect sea levels and weather, with devastating consequences. • The nitrogen cycle shows how nitrogen passes between air, soil, plants and animals and back again. Bacteria are very important in this cycle. • Acid rain forms when acidic gases such as sulfur dioxide and nitrogen dioxide dissolve in atmospheric water vapour. It can be very damaging to life. (i) A Living organism is composed of different forms of proteins, carbohydrates and lipids. These are made up of atoms of carbon, hydrogen, oxygen, nitrogen and other atoms such as sodium, calcium and iron. (ii) An animal obtains these components when it feeds. Food is organic and contains carbon, hydrogen, oxygen, nitrogen, sodium, calcium and iron, etc. Food is ingested, digested, absorbed into blood and transported to all parts of the body to build tissues. Plants take in simple inorganic molecules, carbon dioxide and water from the atmosphere, and nitrates form the soil to build their tissues. (iii) The large organic molecules in dead bodies are broken down by decomposers and detritivores into their smaller components. Then the components can return to the environment and be used again by other organism s. They are recycled through living tissue in different organisms in food chains. (iv) A biogeochernical cycle is a cycling process by which an atom is released and reused in nature . ITQ2 (i) Photosynthesis is an important part of the carbon cycle because it is the only means by which carbon from the air is taken into an organism. Plants take in carbon dioxide and turn the carbon into glucose and other chemicals in the plant's tissues . When animals eat the plant, the carbon atoms can then become part of the animal's tissues. (ii) Respiration is the means by which carbon atoms get back into the air (a s carbon dioxide) from living organisms. (iii) Combustion is the burning of fu els, a process which uses oxygen. When fuels, such as wood, gas and coal, are burnt, carbon dioxide is produced, thus returning carbon atoms to the air. (iv) Dead plants and animals have carbon molecules, in carbohydrates, proteins and fats, trapped in their bodies. Decomposers feed on the dead bodies and release the carbon to the environment as carbon dioxide when they respire. ITQ3 (i) Carbon dioxide levels in the atmosphere are rising because of the vast amount of combustion of fossil fuels to release energy, especially in industry. An increase in human population leads to a greater demand for energy. Widespread deforestation adds to the problem. (ii) Global warming (or the enhanced greenhouse effect) which could lead to higher temperatures, melting of polar ice caps, flooding and changes in weather patterns. ITQ1 50 ITQ4 Process in nitrogen cycle Importance Examples of bacteria involved Nitrogen fixation Nitrogen gas is converted to nitrates in the soil and Azotobacter absorbed by plants; or to amino acids in the root Rhizobium nodules and used by the plant to make protein. Decay Tissues of plants and animals are broken down and Decay bacteria their components can be reused. They are broken down to ammonium compounds. Nitrification Ammonium compounds are converted to a more usable form, nitrates. Nitrates are absorbed by plants and used to make proteins. Nitrosomonas Nitrobacter Denitrification Nitrates are converted back to nitrogen gas in the air. Denitrifying bacteria Examination-style questions (i) Using only an annotated diagram, describe the carbon cycle. (ii) In the carbon cycle, carbon 'moves' as it becomes incorporated into the bodies of organisms or is released into the environment during various processes. Copy and complete the table below to show the movement of carbon in the processes listed. Movement of carbon Process From To respiration in an animal combustion of coal photosynthesis decomposition (iii) State three ways human activities add carbon to the atmosphere. (iv) State four possible effects of global warming. 2 (i) Copy and complete the diagram of the nitrogen cycle shown below. nitrogen in the air c ammonium compounds A nitrate In soil (ii) Describe what happens at A, B and C. (iii) How are some plants like the garden pea able to survive in soil deficient in nitrates? (iv) Describe how nitrates are leached from the soil. (v) Describe an example of symbiosis as seen in the nitrogen cycle. (vi) Nitrogen is a vital component of every living organism. Describe its importance. 51 Aopulation Grovvth, Natural Resources and their Limits 0 0 0 0 0 understand that factors affect the growth of natural populations understand why humans are not subject to the same constraints as other organisms describe various resources and their limits understand the advantage and difficulties of recycling manufactured materials consider biodegradable and non-biodegradable materials population growth ( 1 population growth of humans natural population growth I depletion of i i"' renewable resources - ( non-renewable manufactured materials - - - -· recycle r biodegradable ' non-biodegradable 11 reuse I reduce Growth of natural populations A population is composed of all the members of the same species living together in the same place. Many populations live together as a community occupying the same habitat. A population size may grow or decline depending on condjtions at the time. If food is rearuly available, or there is adequate space, then the population may grow (the number of individuals or members of the species may increase). Consider a population colonising a new habitat in which conditions are initially ideal. l At first, there are few reproducing individuals and population growth rate is slow. 2 Then, since there is an abundant food supply, no competitors, no predators or rusease, population growth rapidly reaches its maximum rate. Birth rate exceeds death rate and the population size doubles at regular intervals. This phase is called the exponential growth phase or log phase. 3 Exponential growth cannot. and does not, go on forever. Eventually the population growth slows down. This is because of various factors in the environment sud1 as lack of food or space, increase in numbers of predators, increased competition or an increase in the incidence of disease. 4 sigmoid growth curve > The population growth rate slows down and stops and the population size remains fairly constant. Figure 6. 1 shows the typical growth curve resulting from steps 1-4 above . It is called a sigmoid growth curve (or S curve). little growth rapid growth growth slows down 3 2 no growth, population size is constant --- 4 '' '' Growth parameter (e.g. number of individuals In the population) \,- - A population may decline, for example through sudden disease, a serious change in the environment or an increase in predation. (An example of this is humans over-fishing a lake.) Figure 6. 1 A typical growth curve. Factors which reduce population size carrying capacity > QSb l:t:Q-1 V'-1 What is meant by 'an environment can carry a certain number of organisms of a population?' The maximum population size that can be sustained over a period of time by the environment is called the carrying capacity of the en vironment. The environment has enough space, food and whatever is needed to sustain or 'carry' a certain number of individuals. Some individuals die from disease or predation (eaten by p redators). However, the death rate is more or less equal to the birth rate as the population stabilises. Disease and predators help to keep the population size 'in check' or constant or stable. This will continue until there is a major change in the en vironment. For example, a natural disease may develop in a popula tion that could wipe ou t or kill most of the individuals. The popula tion size would then decrease drastically (figure 6.2). population size increases plenty of suitable space few predators able to avoid predators good food supply good water supply ability to resist disease suitable abiotic conditions ~--------- (e.g. light, soil type, ideal temperature) population size poor food supply many predators present inability to avoid predators population size decreases inadequate water supply susceptible to disease unsuitable abiotic conditions (e.g. extreme temperatures, poor soil) Figure 6.2 Some of the factors affecting population size. Alterna tively, another organism may arrive in a habitat. It may be 'fitter' (more able to adapt to small environmental changes), or a better competitor for space and food, or it may reproduce at a faster rate than already existing populations. 53 Living Organisms in the Environment ~ IT:Q2 l..l'V How is it possible for the planet Earth to carry all of the different kinds of animals and plants known to exist on it? This organism could ' take over' the habitat as its population size increases causing others to decrease. Such an organism is called an invasive species. Or, a natural disaster cou ld drastically reduce population size as many individuals are killed, damaged or left homeless. For example, a fire blazing through a forest could kill many of the organ isms there. Growth of the human population Humans are subject to the same constraints as other organisms. They need space for homes and adequate food fo r th eir families . They are a lso 9 susceptible to many types of disease: 8 hereditary, deficiency, physiological and 7 Assuming an average of 6 pathogenic. Pathogenic diseases can be 2.6 children per woman 5 considered to be predators of humans. 4 At present, it is estimated that there Assuming an average of 3 2.1 children per woman are about 7.2 billion peop le on Earth. 2 The human population growth curve in 1 o ~~~~~~~~~~~~~~~~~~~ figure 6.3 shows that the population is 1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 now doubling abour every 44 years. Human population growth depends Figure 6.3 The human population growth curve 1950- 2050. on th e carrying capacity of th e Earth, or the maximum number of people that the Earth could sustain over a long time. Uni red Nation analysts predict that rhe world population may stabilise at about 12 billion in abo ut 120 years' time. Although humans are subject to the same constra ints as other populations. they have actively worked on overcoming chem. • Space - Humans have developed the equipment to move into and inhabit most places in the world. Forests are cleared, coastal ;-va ters are filled and developed for h ouses, and deseRs are made inhabitable. Some apartment blocks are over JOO storeys h igh, to increase the possible living space. Some people live permanently in boats on rivers and coasts. Humans need space for h omes and also for factories and industries to support their needs (figure 6.4). • Food - Humans practise agriculture, which is the mass production of food. Farming techniques and. more recently, developments in genetic engineering, have increased agricultural and livestock ou tputs . • Disease - Humans are constantly studying diseases, their causes, symptoms, prevention and cures. Prenatal and postnaral care, and well developed immunisation programmes, prevent the death of millions of children. Education about disease. technology to prolong life, development Agure 6.4 Humans can adapt how they of vaccina tions and gen etic engineering help preven t dea th from disease. live in order to create more space. • Predators - Humans invented gunpowder, which gave them an advantage over all other animals, even those much larger and fiercer than themselves. Humans no longer have any effective predator. 12 11 10 Population (billions) ~ IT:Q3 l..l'V The activities of humans can cause the sizes of populations of other organisms to change. Using examples of animals or plants, discuss how humans can cause these population increases and population decreases. 54 Some environmentalists believe that we need to do something now to curb our population growth because of tl1e way we are exploiting the environment. Imagine ha ving to feed 7.2 billion people every day. They say that food resources may be used up, but there is still an abundance of food in the world. However, agriculrural practices encourage pathogens, pests a nd parasites to fl ourish . Others point o ut that as a population becomes more advanced, popu lation growth slows naturall y. For the moment, disease is still the greatest controlling factor on human morta lity (death rate). Even with all our resea rch and technology, there is still a prevale nce of disease. In developing countries, such as Africa, Cen tral 6 · Population Growth, Natural Resources and their Limits ~ IT:Q~ V'-J Discuss four ways humans have 'conquered disease'. America and India, overcrowding and poor living conditions and medical care have led to prevalence of infectious diseases. In more developed countries, like USA, Canada, Japan and the UK, a far smaller percentage of people die from infectious disease. Most deaths in these areas are due to degenerative diseases (those that get worse with time) , some of which are social and self-inflicted in nature. Smoking can cause harm in a number of ways (cancer, brond1itis, asthma). Misusing drugs like alcohol and heroin may lead to the development of physical and mental disease. Eating large quantities of salty and fatty foods puts people at risk of becoming obese and then at risk of obesity-related diseases (diabetes, hypertension, heart disease). People in developed countries generally live longer than those in less-developed countries, and so there is a greater prevalence of diseases related to old age. Population growth is a function of how many individuals that are born survive to adulthood and reproduction. Birth rate and death rate are therefore important controlling factors . In natural populations, these are not usually under the control of the individual, but in humans we have a greatly reduced death rate. We can also do something that very few other species can do: control birth rate. In many developed counh·ies, birth rate has fa ll en to around the same level as the death rate because of the use of contraception, so population numbers in those countries are stabilising. In a few countries, population size is actually falling. But there are still large areas of the world where population size in increasing rapidly. Resources and their limits ~ IT:QS V'-J Name two renewable resources and two non-renewable resources. renewable resource non-renewa e resource > Figure 6.5 The solar energy panel provides a renewable electricity supply to the house. Resources are features of the environment that can be used by human society. There are many different types of resource whid1 indude: • mineral resources like bauxite and other metal ores; • soil resources for agriculture; • biotic resources, like fish and plants for food and other purposes; • water; • fuel and other energy resources, like petroleum and natural gas. Resources can also be class ified as renewable or non-renewable. A renewable resource is one which can be reused or quickly replaced. Nonrenewable resources are in limited supply and once they are used up, they are gone forever. • Mineral resources are non-renewable: once they have been removed from the ground they cannot be replaced. • Soil resources remain renewable so long as the soil is cared for properly, but if damaged by pollution or washed away by rainfall, soil is non-renewable. • Biotic resources (including for food and timber for paper) are renewable so long as they are cared for and managed properly. • Water resources are renewable so long as we prevent the water from becoming contaminated with pollution. • Fuel resources based on fossil fuels (e.g. oU, coal and natural gas) are non-renewable; others (e.g. wind, sunlight and water) are renewable (figure 6.5). Energy resources Some form of energy is used for every form of human activity. In the past, renewable energy sources like wind, water and firewood were used. Today, most energy is derived from fossil fuels, like coal, oil and natural gas. 55 - - -. - --Liv Jna:.Ol1c-1c:\r.i.i$r'llllai,i_ r:t~tt~ ~E"rn.v11JQl1~fil)lj _-~ ~ ----~~;;t__ - ~---- -- - ·= _ _ - _- -----=--_ --~=. · At present, the m ost impo rtant commercial energy resources in the Caribbean are oil and natural gas which are fou nd m a inly in and aro und Trinidad an d Tobago (figure 6.6). L liquified natural gas plant R oil refinery c cement plant . • Point Usas II oilfield oil .coal gas field • • oilfield with gas natural gas nuclear energy gas pipeline firewood and biomass energy hydroelectric, geothermal, etc. (a) (b) Figure 6.6 (a) On-shore and in-shore gas and oil fields of Trinidad; Large oil and gas fields are also found to the north-west and east of Trinidad (b) Percentage share of Trinidad and Tobago energy source. Local mineral resources Bauxite from Kwakwani is transported to Everton by barge for processing. Bauxite from ltunl is transported to Linden by rail. Bauxite and alumina from Linden and Everton are exported by ship. Baux ite is a red clay, an ore from wh ich alumin ium is obta ined. Bauxite is important in th e econ omies of Guyana and Jama ica (figure 6.7). Alumin ium and its alloys are u sed in the m anufacture of a ircra ft, trains, buses, cooking foil an d man y other item s. Ba ux ite mining uses a large area of land. In Jamaica, there are regu lation s which en sure th at: • land rema ins in agricultural use until mining begin s; • after mining, land is restored fo r oth er u ses. When land is cleared for mining, the topsoil is removed and p reserved for later use since it con tains most of the nutrients and organic m a tter. After m ining, the land is smoothed, reshaped and th e topsoil replaced. Fertilisers can be added . The reclaimed land can be used for pasture, h o using o r small-scale farming. Reducing resource consumption o processing plant bauxite bearing area .& Berbice Deepwater Facility e mining area • alumina plant (closed) - rail transport of Bauxite - water transport of Bauxite Figure 6.7 The bauxite industry of Guyana. 56 By definition, n on -ren ewable resources will eventually run o ut if w e continue to u se them . In order to preserve as much of these resources as p ossible for future gen eration s, people are being tau gh t to: • re use; • reduce; • recycle. This is particularly important in rela tion to discarded m anu factured materials such as paper, glass, metals, plastics and textiles. Human s are th e o nly species to use th ese materials. biodegradable '> These manufactured materials are used at home, school offices and factories and after a while they are discarded because they are worn out, used up or no longer needed. The average composition of domestic waste is shown in figure 6.8. When discarded into the environment, some of these materials break down naturally into simpler, usually harmless forms, by the action of microorganisms. These are called biodegradable materials, and include organic material, paper, some textiles and plastics. Non-biodegradable materials, such as metals, glass and other kinds of plastic, cannot be broken down or take a very long time to do so. As a result, these wastes accumulate in the environment, leading to all kinds of pollution of soil and water. The useful life of a fast-food package is often minutes, but it may persist in the environment for years or centuries. Reuse H•lui•M•iH Some types of waste can be reused in the same or other ways. For example, tins and jars can be reused as eontainers, soda bottles may be returned to the company for refilling and organic waste can be made into compost . Compost is used as a natural fertiliser and soil conditioner (figure 6. 9, overleaf). Reduce Table 6.1 list some manufactured materials together with their sources and uses. By simply reducing the accumulation of these manufactured materials, the amount of discarded waste will be reduced, and less pollution will take place. We can do this by buying only what is needed and choosing products that are not over-packaged. thers ~ textiles 7 .3% 5.5% Manufactured material Source Uses paper pulp from wood writing, printing, wrapping glass molten mixture of soda ash, silica.sand and lime bottles, windows, spectacles, drinking utensils, containers, ornaments metals iron, gold, tin, aluminium cars, ships, buildings, containers, electrical appliances, cables (and many others) plastics petroleum bottles, bags, containers, kitchen utensils, cases for appliances, fibres organics 26.7% paper 19.7% Table 6. 1 Some manufactured materials, their sources and uses. Figure 6.8 Pie chart showing the average composition of domestic waste. 57 Living Organisms in the Environment (a) (b) Figure 6.9 Recycling in the Caribbean. (a) Collecting glass for recycling. (bl Collecting plastic for recycling. Recycle This is the process of collecting materials from the waste stream, separating them by type, remaking them into new products, and marketing and reusing the materials as new products. Advantages of recycling • Resources will not be used up as quickly, so there will be more for later generations. • Less land is needed for disposal of waste. • Less pollution of soil and water occurs as waste decomposes. • Less toxic waste is generated. • Harm to animals is prevented (for example, plastic bags and glass are a danger to animals). • In many cases, less energy is used to recycle than to make a new product. Difficulties of recycling Collection of recyclables is rime-consuming. Each household must sort and h ave suitable containers for rubbish and recyclables. The recyclables must be further separated into glass, metal, plastic and so on, and placed in separate containers. A problem is that recycle bins or containers must be provided and placed at strategic p laces that are accessible to all. People must be educated about the importance of separating their garbage and how to separate their garbage. The recyclable materials must then be transported to recycling factories by trucks or vans. Money must be spent on vehicles, maintenance of the vehicles and gas. This uses fuel resources which must be taken into account when trying to judge whether it is worthwhile recycling a material. Tonnes of recyclables are collected weekly and there mu st be vast amounts of storage space. There must also be space for the recycling facto ries and for storage of the new product (figure 6.10) . 58 The waste for recycling is put into a box for collection or taken to a recycling depot .. - -~ !(~)' ~ J, ~ ~ ((~)' metal is compacted P.E.T. is flattened, baled l P.E.T. plastic metal for shipping to pu r chaser s at the r ec y cl i ng l l ant glass These mater i als are glass is crushed I It is separated into different materials ca ~ ~ Mater i a l s are repro c essed to make new products in factories I ...- - - - - - - - - ·...... ~ ~~ 0 11 .....- - •....._ _ _ _ _ _ ___._ ' • new bottles • fibre glass • road building materials • sewer pipes J • newsprint • boxboard • insulation • cat litter • roofing felt • egg trays REDUCE WASTE • new cans • tin plating • new Iron and steel • cars • insulation • clothing • new P.E.T. containers • other metal items SAVE OUR RESOURCES Figure 6.10 Recycling of household waste. Ideas for making less waste Shopping and the en vironment Define these terms associated with preserving and conserving the environment: (i) reuse (ii) reduce (iii) recycle. • R educe - Buy only what you need. Can you make do with what you have already? Buy long-lasting goods whenever you can afford them - you may save in the long run. Consumer magazines can h elp you make informed choices. • R ecycle - Choose containers that can be recycled (such as cans, glass and recyclable plastic) and recycle them. If you can, buy drinks in returnable bottles. • Avoid d isposables - The 'throw-away convenience' of some products may not be worth the environmental cost. Paper plates and cups, throwaway lighters and razors, and disposable diapers are handy but why not buy the sorts you can use and use again? • Avoid product s that are hazardous t o the e nvironment - Baking soda can be used to scrub out tubs and sink; warm water and vinegar can be used to dean windows; twice-weekly boiling water rinses keep drains open - and if they do clog, use a metal 'snake' or a plunger to unblock them. ~ Re ducing waste ~ l:[Q6 \./"-' l:tQ7 \./"-' What are some advantages of reusing? ~ l:tQ8 \./"-' What are the difficulties of recycling? • Save and reuse things like string, gift-wrap, shopping bags. • Give magazines and books to friends, hospitals, doctors' offices. • Help nursery schools; they love to have egg cartons, yogurt containers, toilet paper rolls, apple baskets. • Give old clothes or furniture to charitable organisations such as Goodwill, The Salvation Army, Saint Vincent de Paul. 59 • Cut down on food waste; 20% of food we buy ends up as garbage. Keep track of what you have and use groceries while they are still fresh . • Repair broken toys, appliances, fu rniture instead of bu ying new ones. • Start a compost heap with kitch en and yard waste. You can use things like banana peel, shells, coffee grou nds, leaves, grass clippings. You will reduce your garbage by a third and make a good soil conditioner for your garden . '7 Chapter summary • A population is composed of all the members of the same species living together in the same place. • The population grows if food is readily available and there is adequate space. • Many factors like disease, predation, competition, availability of food and space keep a population size constant. • A typical growth curve is sigmoid in shape (S-shaped). • The maximum population size .that can be sustained in an area is called the carrying capacity of that area. • Humans, though subject to the same constraints as other organisms, have devised many ways to overcome such constraints and, as a result, human population growth is still increasing. • Humans can make use of many natural resources such as minerals, biotic resources, water, soil and fuel. • Resources can be defined as being renewable and non-renewable. • A renewable resource can be reused. • A non-renewable resource is limited in supply and once used up is no longer available for use. • Oil and natural gas are important resources in Trinidad and Tobago. • In Guyana and Jamaica, bauxite mining is important. • Manufactured materials like paper, plastic, textures and metals are used by humans. These materials can be biodegradable or non-biodegradable. • Biodegradable materials can be broken down and recycled back into the environment. • Non-biodegradable materials accumulate in the environment. • People are being taught to reduce, reuse and recycle these materials. • There are many advantages to recycling. • There are also many difficulties involving in recycling. ITQ1 An en vironment has a certain amount of space; this will support only a specific amount of organisms, depending on how they use it. It can also provide food for a specific numbe r of organisms. Man y offspring m ay be produ ced, but some will be eaten by predators and some may die of disease. At an y time, the en vironment will make it possible for some to live a nd so the size of the population remains m ore or less constant unless there is a change to th e environment. This constant point is called the carrying capacity for the population in that environment. ITQ2 Earth h as many different environments in which a ctiversity of organism s exists. Animals and plants show adaptations for living in the differen t habitats and changing environments. Natural disasters, diseases and predators help to keep popu lation sizes under control. As long as there is physical space and food for all these organisms, they will survive on Earth. 60 ITQ3 Animals and plants that humans use for food are encouraged to grow, by creating ideal conditions in which they can live, and removing their pests and predators. Humans will cause population decreases by taking too much of a population of plant or animal for food or other purposes, such as over-fishing of whales for oil; dearance of an area of natural animal and plant populations so that the area can be used for human purposes, such as housing, industry or growing food crops; or accidentally by introducing a species from one environment to' another where it outcompetes the natural populations. ITQ4 The invention of vaccines and immunisation against deadly diseases prevents thousands from dying each year. Diseases that prevent couples from having children have been researched and studied and now many couples who would have been childless can have children of their own. Many more babies are born daily because of technology, drugs and healthcare services. The baby and mother are treated and cared for during the pregnancy, at birth and after birth. Many people live longer because of the research and technology applied to the treatment and cure of diseases like pneumonia and cancer. ITQ5 (i) Renewable resources: forest trees and fish. (You may have mentioned others.) (ii) Non-renewable resources: fossil fuels and precious metals (e.g. gold and silver). (You may have mentioned others.) ITQ6 (i) Reuse - find another use for a product which has already beed used, so that there is no waste to pollute the environment. (ii) Reduce - decrease the amount of products being used, so that there is less to pollute the environment. (iii) Recycle - utilise an already-used product in the manufacture of another product that will be used again. This reduces the amount of pollution in the environment. ITQ7 Advantages of reusing include: • less waste is generated; • there is a reduction in the rate at which the resource which makes the product is used, so the resource is not depleted as quickly; • it allows for less pollution of the environment; • fewer organisms will be affected by pollution. ITQ8 The difficulties of recycling include: • it is expensive; • the public may not cooperate, for example in separating their garbage; • waste may not be generated in large enough amounts and rates to keep the recycling plant functioning; • recycling plants cover a large area, so there is often not enough land available for the plant. 61 Examination-style questions (i) List four factors that could lead to an increase in population size. (ii) The graph below shows a typical sigmoid growth curve. Number of individuals in the population Time (a) Describe each phase of growth. (b) What factors influence the carrying capacity of the environment? (c) A disease developed that wiped out all the individuals of the population. Copy the graph above and continue the line to show how the population size is affected. Population size Time (iii) The growth curve above shows the growth of the population of humans over the last two centuries. (a) How is this curve different from the typical sigmoid growth curve of a population? (b) humans are not subject to the same constraints as other populations. Describe how humans has overcome two factors that keep other populations 'in check'. (c) What are some social and economic consequences of over-population by humans? (d) What are some implications to the environment of human over-population? 62 2 Explain the following terms giving examples of each: (a) renewable resources; (b) non-renewable resources; (c) biodegradable waste. (ii) In an effort to reduce the production of waste, people are being taught to (a) reduce, (b) reuse, and (c) recycle. Explain each of these terms using examples. 3 (i) Describe the impact of agriculture on the environment. (ii) (a) What is compost? (b) Every home should practice backyard composting. What do you think of this statement? What are some advantages to the environment of composting? (iii) Discuss some difficulties of recycling. (i) 9ihe Effects of Human Activity on the Environment 0 0 0 0 0 0 0 understand that human activities have great effects on the environment describe the origin and effects of air, soil and water pollution discuss deforestation and its consequences on the environment understand the impact of industrialisation understand the impact of human activities on marine and wetland environments discuss current and future trends regarding climate change understand how the environment can be conserved and restored human activities ') ( destruction of the environment industrialisation deforestation pollution II climate change 111 soil marine I wetland 11 water I air Humans and the environment The planet Earth is a beautiful and green place brimming with life-s usta ining water and ideal for life as we know it (figure 7.1). Millions of different species of plants and animals inhabit the Earth, living in balance w ith each other and the various reso urces that they use. One species, Homo sapiens (humans) is able ro dominate life on Earth. Humans have been able to use their intellectual abilities to 'conquer' th e Earth, to exploit all kinds of environments and harness its natural resources for their own use. Humans are very successful, as seen by their great population size; some parts of the world are very densely popu lated by humans (figure 7.2). The human environment is where humans live. Th e whole Earth can be considered as the human environment since humans can be found almost everywhere. Th e Earth itself and other living species, plants and animals, make up the Rgure 7.2 The human population is increasing. environment for humans. 63 CHAPTER 6 ~ l'.'f:Q·1 L/'--J List three reasons why it is believed that humans are 'successful'. Q9:., l'.'f:Q2 L/'--J Food, disease, predators and space are all factors that control population size and keep populations in check or at a constant number. List three practices of food production that have helped humans to feed billions of people worldwide. Humans have been able to overcome those factors which naturally keep populations in check, as we saw in the chapter 6. Each year, nearly 100 million people are added to the Earth's population. This increase in population has led to many effects on the environment. • Humans are con stantly looking for new space, and have taken over areas already inhabited by other species. They need space for homes, industries, agriculture and other activities. A5 a result, many other species are losing their living space and are becoming extinct. Changing the use of the lana for human purposes changes its suitability for other species and they die out . . • Humans are constantly producing waste from their various activities and this has led to all kinds of pollution of land, sea and air. • The great increase in human population size, together with the developmen t of global travel and communications, leads to a greater need for factories and industries. The impact of industrialisation includes the generation of more waste and increasing use of natural resources on an ever larger and more dangerous scale. • Although humans do not live in water, their activities have polluted the seas, over-fished marine life, caused oil spills and other disasters, and led to severe stress on marine environments all over the world. • More humans means more carbon dioxide in the atmosphere; many people consider this is leading to global warming. The release of other chemicals is also though t to cause depletion of the ozone layer which protects us from harmful ultraviolet radiation. • Human use and management of crops and food species changes the balance of nature. In trying to control pests, many natural populations may be destroyed. The development of genetic engineering makes these possibilities and the risks of affecting th e environment even greater. · Endangered and vulnerable organisms biodiversity > endemic species / There is an extraordinary variety of life on Earth. Biodiversity refers to this biological diversity of the millions of microorganisms, plants and animals that inhabit the Earth. Th e Caribbean islands, like most places, have a rich heritage of biodiversity. In particular, th ere are a large number of endemic species which are only found in a single geographic area, maybe just on one island. People are concerned over the rapid decline of the Earth's biodiversity. Extinction can be seen as a natural process - as environments change naturally over time, some organisms will not be as well suited to the environment and will die out. However, human activities have increased the rate of extinction to several hun dred times greater than the natural rate. For example, there are believed to be less than 1000 giant pandas in the wild in China. Since 1974, their bamboo forests h ave died out at an alarming rate. This is part of the natural life cycle of the bamboo, but increased population of the area by humans has made the possibility of the panda becoming extinct much more likely. We now classify organisms that are at risk for extinction as follows: • endangered species are species whose numbers have been reduced to the point that the survival of the species is unlikely; • vulnerable species are those that may become endangered in the near future because their populations are decreasing at alarming rates; • extinct species are no longer known to exist. Much research is being done on endangered species, to find ways to save them from extinction. The International Union for the Conservation of Nature (IUCN) regularly publishes lists of endangered organisms. 64 Reasons for increasing extinction rates The increased rate of extinction is the result of many kinds of human activity: • habitat destruction, including deforestation; • pollution; • introduction of more competitive species; • hunting or cropping more than the population can sustain. Habitat destruction The manatee is also called sea cow because it grazes on plants that grow on the sea bed. Habitat destruction is the leading cause of species extinction around the world. For example, all species of gorilla and many of the other apes are endangered because they Uve in areas where human population is increasing. Many large predators, such as tigers, and large herbivores, such as the West Indian manatee, are also enda ngered because they need space that competes with humans's need for space. Deforestation (a) Deforestation is of particular concern at present. Large areas of rainforest are being destroyed, to provide hardwood timbers and to create space for roads and mining. These forests are not only important for their contribution to carbon dioxide removal in the carbon cycle, but contain thousands of species that cou ld easily become extinct. Introducing competitive species (b) The introduction of more competitive species has a major e[fecr on endemic island species. For example rats, cats, dogs and mongoose have ca used the decline of many Caribbean species, especia lly reptiles and birds that are killed or lose their eggs through predation by the new species. Hunting (C) Hunting may directly cause the extinction of a species, for example, the Tasmanian Wolf may have been hunted to extinction in Australia by the middle of the last century, and the Dodo is a famous example of extinction through hunting which happened around 1680. The polar bear and black bear are killed for their fur and are under threat of extinction from hunters. In addition, food fish, like populations of tuna, shark and card, are over-fished and are at risk. Hunting may also indirectly affect other species. For example, drift nets are enormous nets used for commercial fishing. The nets trap and kill many creatures apart from fish, especially dolphins, porpoises, sharks and turtles. Today, many animals are at risk in the Caribbean (figure 7.3). These include many birds, like the West Indian Whistling-Duck, the West Indian Flamingo, the Barbuda Warbler and the Cayman Parrot. Of the reptiles, the Hawksbill Turtle, the Leatherback Turtle and the Loggerhead Turtle are all at risk. The American Crocodile, the Cuban Tree Boa and many iguanas are also at risk. Reducing the risk of extinction Rgure 7.3 Endangered species in the Caribbean. (a) Whistling duck (b) Leatherback turtle (c) Manatee. There are ways to reduce the risk of extinction of other species. Wildlife parks and reserves set aside land where the activities of humans are strictly controlled. This can help to increase the numbers of endangered species and prevent extinction. Zoos often specialise in looking after particular animals. However, there are many problems in the breeding of anima ls in captivity. 65 __::_Livin9 Orgenisms ir:t t~'l°' ~nvjr_~r,iu),~1J: __ _ _ _ -::-.: _ - _ _ _ 0 Although much research is being done on maimaining the Earth's biocliversity, we need to be sensitive to the needs of all the species living around us and the effect that we are having on them. Other effects of human activity Shortage of water Most living organisms must have a daily supply of water to live. Humans often use more water than is strictly necessary and the shortage of fresh water is now a worldwide problem. A number of factors working together have resulted in this water sh ortage problem. • Deforestation - This can remove large areas of densely growing trees, like rainforests. Water is transferred to the atmosphere by evaporation and transpiration by plants. This is an important part of the water cycle as it leads to the formation of rain. Rain falling into rivers, lakes and dams provide our supply of water. Removing large areas of trees can change the pattern of rainfall ail around the area and possibly beyond. • Industrialisation - Industry uses a lot of water most often simply to cool equipment. For example, water ensures the constant functioning of the iron, steel and oil industries. • Pollution - Water pollution results in less water being suitable for drinkjng. Each individual needs water for hygiene and food production. Billions of inclividuals use and waste water every day, though much of this can be recycled. • Depletion of ground water - Much water is trapped in lakes underground after it has seeped through the soil and rocks above. These lakes are known as aquifers and we get a lot of our water from these. It can take many years, even hundreds or thousands of years, for the water to seep into them, so they can be used up faster than they are replerushed by rainfall. Over 90% of the Earth's water is salt water, which we cannot drink but which could be desalted and made available for use by humans. Desalination plants convert salt water of the oceans and seas into drinkable water. However, desalination plants are costly to install. At national level, efforts co reduce pollution (especially of the rivers, lakes and seas) may result in increased water supplies, but also many simple, everyday practices could add up to conserve water and reduce shortages. These include: • turning off taps while brushing teeth; • fixing leaks in water pipes irnmeillately; • recycling-reusing water when possible; • minimising use of water in the garden; • not having over-long showers; • using a bucked instead of a hose to wash cars; • being mindful of how valuable a commodity water is. Pollution Rgure 7.4 Chemical pollution from an oil refinery. 66 Poilution is the contamination of land, water or air by the discharge of harmful substances (figure 7.4). Humans are constantly polluting the environment. Tables 7.1, 7.2 and 7.3 describe the origin of these pollutants and the effects on the environment and on humans. Pollutants Origin Control of pollutant non-biodegradable waste household and industry Harmful substances Careful removal of (e.g. mercury, lead, can accumulate on land toxic materials from plastics, cyanide) and enter air and water, waste to be disposed. where they can poison Replacement with nonliving organisms. toxic alternatives where possible. Insecticides and herbicides agriculture (e.g. DDl) Effects Accumulate in organisms through food chains, even killing top consumers. May cause mutation. May cause eutrophication in rivers and lakes. May upset the balance of food chains. Replacement with less toxic alternatives. Replacement with biological control. Table 7.1 Land pollution. biological control > Biological control is the use of living organisms to control pests, often in horticulture and agriculture. Introducing a predator or parasite of a pest can greatly reduce the popula tion size of the pest to the point where the level of damage is economically acceptable. However, great care must be taken to make sure the introduced predator or parasite does not become a pest itself by damaging populations of other organisms in that environment as happened when the cane toad was introduced to Australia. Pollutants Origin Effects oil spilled from tankers or offshore rigs Forms 'slicks' on the sea which Legislation to prevent cleaning blocks oxygen and light, killing of tankers near land, and marine life. Stops birds flying reduce the risk of loss from and feeding. Ruins beaches. Is rigs. Spills can be localised toxic to some marine life. Clogs with floating booms and respiratory systems of fish. dispersed with detergent. The dispersed material may still be harmful to marine life. hot water power stations Changes the temperature of the habitat which results in death or migration of marine life, especially death of coral. Some organisms may flourish. Cool the water before it is released into the environment. (Some of this heat can be used to heat or power local homes.) organic waste untreated sewage from housing, ships, farms Bacteria multiply and use up oxygen. Can lead to eutrophication of water. Can cause disease. Treat all sewage to remove the biological risk before release into the environment. mineral salts (e.g. phosphate, sulfate and nitrate ions) Eutrophication as increased Use detergents which contain nutrients in water encourage minimal amounts of these algal growth. Light is blocked substances. Use fertilisers in because the growth is so thick. controlled amounts, only as Algae die resulting in rapid needed, to reduce leaching into growth of anaerobic bacteria. water systems. Oxygen used up so other organisms die. detergents, fertilisers in sewage and water from housing and farms. Control of pollutant (continued) 67 Pollutants Origin toxic chemicals (e.g. organic mercury acid wastes, heavy-metal products) industrial plants May be toxic to aquatic organisms. Concentrated in organisms as they move up food chains. May change the behaviour of aquatic organisms. Effects Control of pollutant Screen all wastes from industrial processes to remove toxic materials before release to environment. Table 7.2 Water pollution. Pollutants Origin Effects carbon dioxide burning fossil Builds up in the atmosphere fuels, increased trapping heat which could lead human to global warming. population (deforestation increases problem) car exhaust Carbon monoxide combines Control CO by use of more more readily with haemoglobin efficient engines and catalytic than oxygen does. Causes converters. Use lead-free fuel. headaches, unconsciousness, death. Lead may cause mental retardation. smoke burning fossil fuels Combines with fog to form smog. Particles cause respiratory disorders, increase the risk of lung cancer. Agure 7.5 This vehicle is run on biogas. l"·@@t•W biochemical oxygen demand > 68 For energy, use renewable energy resources. For vehicles, use mass transport where possible, use biogas replacements for fossil fuel. carbon monoxide (CO), lead sulfur dioxide burning fossil fuels Biogas is a fuel made from the fermentation of waste plant products, such as sugar cane after sugar extraction. In Brazil and parts of the US, this is now being used to fuel vehicles instead of gasoline (figure 7.5). Control of pollutant Cleaning of waste gases from industrial processes can remove these and prevent their release into the environment. Dissolves in rain water forming Cleaning ('scrubbing') of waste acid rain. Affects plant growth, gases from industrial processes damages leaves, corrodes can remove sulfur dioxide and surfaces of rocks and buildings, prevent its release into the causes the death of fish and environment. plant life. Crop yields may be reduced. Aggravates asthma. Table 7.3 Air pollution. Sewage treatment Sewage consists of liquid and solid waste from urine and faeces, warer from domestic use and industrial waste. When raw sewage is discharged into rivers and sea, bacte ria in the water decompose the organic matter in the sewage. These aerobic bacteria multiply rapidly and need large amounts of oxygen dissolved in the water. This is called biochem ical oxygen dem and (BOD). The release of nutrients by the bacteria into the water encourages the rapid growth of algae. The algae add oxygen to the environment as they photosynthesise. But they are a problem because they blanket the surface of the water and restrict the entry of oxygen from the atmosphere. They also restrict the entry of light and this causes submerged plants to die thus adding to the organic matter available to the bacteria. When all this takes too much oxygen from the water, other aerobic organisms like 7 · The Effects of Human Activity on the Environment eutrophication > domestic sewage plants and fish cannot respire and so die. The decomposition of the dead material and sewage by anaerobic bacteria continues. This process, whereby large amounts of nutrients are added to a water system and lead to the death of many of the organisms living in it, is known as eutrophication. To prevent pollution of water, raw sewage must be treated to remove solid waste and other harmful substances, and decomposed aerobically before it is disposed of into the rivers and the sea. Most sewage works use a biological method of sewage treatment (figure 7.6). water drainage from streets Grit tank Large tanks where grit, stones and other heavy objects sink to the bottom. Coarse screen Has wire nets to strain out solid litter. Aeration tank Air is bubbled through the liquor to encourage growth of aerobic bacteria. These bacteria decompose organic waste into harmless substances and carbon dioxide. industrial sewage liquid sewage Primary sedimentation tank Ughter matter such as faeces settles to form sludge. Sludge digester Sludge undergoes anaerobic treatment to form methane gas (biogas) which is a good fuel. Residual matter is dried and used as a fertiliser. Biological filter The liquor is sprinkled onto large tanks from a rotating arm. The liquid sewage percolates down t hrough a bed of stones covered with a film of aerobic microbes (bacteria and protozoa) which digest the organic matter in the sewage. Effluent • Discharged Into the river and sea. • Used to water plants. • Used for flushing toilets. II Rgure 7. 6 The sewage treatment process. Deforestation Figure 7.7 Forest clearance. Every week, at least 1 million acres of forest are cleared or degraded worldwide. Although a forest is a renewable resource, removal at that rate is much greater than the rate at which the trees can be replaced. Forests are not being managed and maintained, but are being exploited in a destructive way (figure 7.7). Rainforests are being cleared for farming, timber, mining, largescale cattle ranching, housing and industry. When a small area is cleared, the forest recovers quite quickly, but when large areas are cleared, there are many consequences on the environment. • Soil erosion - Deforested slopes encourage surface run-off during rainfall. When the forest is in place, it intercepts the rain water and lets it trickle slowly to the soil. When the canopy of trees and smaller plants is removed, rain falls directly on the soil causing erosion of the topsoil as it runs off the surface of the land. The soil below is not as fertile, so will 69 - Living Orga"lsms in the E9vironrnent • • ~ ll!Q3 • V'-' (i) What is deforestation? (ii) Why do people practise deforestation? (iii) What are two consequences of deforestation? ~ • _ __ - _ not be able to sustain growth as well as the lost topsoil. The land can be permanently damaged. Soil degradation - If the land is cleared for agriculture, the soil becomes infertile due to the removal of minerals by the crops. Leaching also occurs which removes minerals that would otherwise have been taken in by the trees. Increased flooding -The increased run-off takes silt with it which blocks rivers and causes flooding in low-lying areas. Flash floods also occur because of the increased run-off. Species destruction - The plants removed may become extinct. The habitats of many organisms are destroyed, and the food chains that dependent on those plants will break down Many organisms, plants and animals, may become extinct. Destruction of natural resources - Many crop plants originated as rainforest species (cocoa, banana, rubber). Many forest plants also produce medicinal drugs. Disease-resistant varieties of plants are usually found in the wild. If we destroy these forests we may lose these resources before we have even learned about them. ll!Q~ V'-' Look back through this chapter and make a list of the results of industrialisation. ~ ll!Q5 V'-' For each item on your answer to ITQ4, give an example of how humans are attempting to reduce the impact of industrialisation on the environment. 99:> ll!Q6 V'-' (i) What is industrialisation? (ii) Discuss one advantage and one disadvantage of industrialisation. Industrialisation Industrialisation is a sign of human success. The word industry is used to cover all forms of economic activity: primary (farming, fishing, mining and forestry); secondary (manufacturing and construction); tertiary (back-up services such as administration, retailing and transport); and quaternary (high technology and information services). Industry requires a workforce and thus provides jobs for people who can enjoy a 'good ' standard of living. It generates income for the country which can be spent on improving education, healthcare and public utilities for its people. There is, however, a price to be paid for industrialisation. If not managed properly, it can lead to serious environmental consequences (discussed above) including pollution of land, air and water, water shortages and deforestation. Industrialisation is two-sided. On one side, we see successful humans harnessing resources and living a comfortable life. On the other side, we see widespread destruction of the environment. The Earth is our only home and we should take care of it. Impact of human activities on marine and wetland environments Water is important to us. We love to go to the beach, snorkel, lie by the river, fish and do many other activities which involve wa ter. On the physiological side, over 75% of the human body is water. We cannot exist without water and die faster from dehydration than from starvation. Other living organisms depend on water as much as, or even more than, we do .. Our planet is able to sustain life because of the presence of water. Yet many human activities lead to a hotter and drier Earth, and to pollution and the destruction of aquatic environments. Belwo are examples' of the specific effects of human activity in marine environments in the Caribbean. 70 _ - .~ IJ'-.) Humans do not live in water, yet their activities and practices have affected the marine environment. Describe two effects on the marine environment that humans have had, and how they were brought about. ~ IT:Q8 IJ'-.) Why are coral reefs important to Caribbean people? ~ IT:Q9 IJ'-.) Discuss two reasons why mangrove swamps should be conserved and protected. __ 7 · The §t(ects of ir-lll!.mar'1_Activity on the.~Enviroi1rnent Some effects of human activities in the Caribbean • Destruction of mangrove swainps - Using the swamps as dumping grounds or for building rice farms or other development, leads to many problems, such as: - nursery grounds for all kinds of fish are affected; - pollution of water with toxic materials, or those wruch cause eutrophication; - pollution of water with human and animal waste can spread diseases like cholera and diarrhoea; - breeding grounds and nesting and roosting grounds for birds are reduced; - the natural habitat of many invertebrates, like oysters and crabs, is destroyed; - money generated from eco-tourism (tourists visiting the area to see the wildlife) is reduced; - money generated from fishing crabs, oysters and other local fish is reduced. • Over-fishing - In the seas of the Carinbbean this is a serious problem. Much money is spent on catching fish and too little on managing and producing them. • Destruction of coral reefs - This occurs by: - collecting coral for sale; - dynamiting for fish; pollution with raw sewage, garbage, industrial and kitchen waste; - pollution with hot water which kills the coral organisms; - pollution with insecticides and fertilisers; - smothering with silt from soil erosion; - smothering with red mud ba uxite waste, dust and cement from construction; - removal to allow the building of harbours, channels, etc.; - damage from anchors; - damage by visitors to the reef. • Damage to wetland environments - this occurs by: - allocation for rice and other farming; - fertilisers and other dangerous chemicals in the water; - n oise pollution from use of heavy rice equipment; - damage by visitors to the wetlands; - pollution from visitors; - hunting of animal s; - noise pollution from hunting; collection of animals for sale; - squatters or development of housing settlements; - over-fishing. 71 The coral reef is a natural resource important to the Caribbean islands and, as such, needs LO be conserved. Damage such as that shown in figure 7.8 is to be avoided if at all possible. Rgure 7.8 Coral reef smothered by land run-off. Impact of increase in greenhouse gases Global climate change has already had observable effects on the environment. Effects that scientists have predkted are now occurring. These changes are largely due to an increase in the levels of greenhouse gases; they include: • increase in Earth 's average temperature; • changes in the pattern and amount of rainfall; • reduction in ice and snow cover; • rise in sea level; • increase in the acidity of the oceans. Conservation and restoration of the environment conservation > sustainable > Since humans are responsible for widespread destruction of the environment on the Earth, they should take responsibility for the widespread restoration and conservation needed to 'heal' this damage to our planeL. We need to manage the environments that we live in and the resources that we use in a sustainable way. That means using them in a way that they are not damaged and depleted, so they are available for future generations . There are many ways that this can be done. Reduce pollution • Replace fossil fuels with alternative, non-polluting energy sources like solar energy, wind energy, wave energy, biogas and hydroelectricity. • Treat all sewage. • Use unleaded petrol and catalytic converters on vehicles to reduce all emissions of pollu tants in exhaust gases. • Replace harmful insecticides and herbicides with biological control or biodegradable insecticides. 72 • Use cleaners of all exhaust gases from industry. • Improve effluent release standards of industries to purify, treat and reduce effluent release. • Use recyclable materials at home and in industry; for example, paper and biodegradable plastics rather than plastics, which are not biodegradable. • Ban the disposal of garbage in rivers, swamps and seas. Conserve natural resources • • • • Recycle resources such as glass, metal and paper. Use alternative energy sources. Replace renewable resources, such as forests. Manage food species, plants and animals, in a sustainable way by imposing closed seasons and strict restrictions on how heavily populations are cropped. • Limit deforestation to a rate at which forest recovery can be maintained. Protect endangered species • Ban the killing of species in danger of extinction, such as turtles and the West Indian manatee. • Set up breeding programmes for species in danger of extinction. • Set up National Parks to provide areas for species to live and breed undisturbed by human activity. Conserve soil • Replant trees immediately after harvesting to prevent run-off when it rains. • Use crop rotation to maintain a balance of soil nutrients; different crops remove different minerals from the soil . • Use natural rather than artificial fertilisers to preserve soil structure, but only as needed so as to prevent eutrophication of nearby water sources. • Use terracing and contour ploughing around hillsides to prevent erosion by soil run-off when it rains. • Prevent over-grazing by animals like cows and sheep that remove plants and their roots which hold the soil when it rains and prevent erosion. Preserve clean water • Prevent eutrophication by treating sewage properly and using only as much fertiliser as is needed on farm land. Improve land used in mining • Replace vegetation as soon as possible after mining has finished . • Fill the mined areas with soil and use for farming, housing or industry, so that new areas do not need to be used. Eanh is home not only for humans, but for millions of species of plants and animals. The Earth can successfully 'carry' all these organisms when there is balance in population size and the natural cycles can take place efficiently. It is our responsibility to maintain that balance. 73 ITQ1 (i) They have inhabited most places on Earth and continue to colonise new areas. (ii) They have been able to overcome many natural diseases. (iii) They mass-produce food, and so do not have to search for food each day. ITQ2 (i) Agricu lture - mass cultivation of plants that can be used as food. (ii) Livestock production - mass production of animals (cows, chickens) and their prod ucts, (eggs, milk) that can be used as food. (iii) Use of tech nology to intensify production to increase the yield (e.g. the use of artificial selection) an d, in the future, possibly increasing use of genetic. engineering to speed this up. ITQ3 (i) Deforestation is the removal of a large number of trees from an area. (ii) • For quarrying - to obtain gravel, soil, sand, etc. for building. • To clear land to build homes. • To provide lumber for housing, furniture, etc. • To plant crops or for ranching. (iii) Any of the consequences mentioned on pages 69- 70 wou ld be approrpiate. ITQ4 Your list should include examples for each of the following: pollution of land, air and water, water shortages and deforestation (see tables 7. 1-7.3). ITQ5 Your answer should include examples for each of the fo llowing: control of pollution of land, air and water, water shortages and deforestation (see tables 7. 1-7.3). ITQ6 (i) Ind ustrialisation is th e spread of industries. As a coun try develops, it becomes more industrialised. (ii) As more industries develop, fewer foreign products are imported, so more money is generated by the country and more jobs are available. This is the major advantage of industrialisation. A major disadvantage is that as industrialisation increases, damage to the environment is more likely. ITQ7 (i) Hot water from power stations is poured into the sea, changing the temperature and thus the environment of marine life. Plants and animals may not be able to adapt fast enough and are killed. (ii) Oil spills from tankers form a layer of oil on the surface covering many miles of ocean. This can have disastrous effects on the marine environment as shown in table 7.2. ITQS Coral reefs have many important functions. 74 • As a to urist attraction - A lot of money is generated from to urists who wish to visit the area to see the reefs. • As a source of job opportunities in tourism and conservation . • In preserving bioctiversity - Man y different species live in the reefs. • As a spawning ground - Many species of fi sh breed in coral reef areas, including fish that w e use for food. • In protecting the coastline from erosion - The reefs absorb bursts of wave energy, especially during a storm. • As a sensitive inclicator of global environmental changes - Cora ls are very sen sitive to environrnentaJ conclitions and any change results in a chan ge in the population of corals. ITQ9 Mangrove swamps are spawning grounds for large fish and ensure the continuation of man y fish species. Mangrove swamps support bioctiversity: there are many species that live in that one ecosystem. Examination-style·questions (i) Humans are constantly looking for and occupying new space. (a) List some reasons why humans needs new space constantly. (b) Suggest three consequences of occupying new space constantly. (c) Discuss the greenhouse effect with particular reference to the over-population of humans. (ii) (a) What is a pollutant? Give some examples. (b) Account for the presence of lead as a pollutant in the atmosphere. (c) How can lead pollution be controlled? (d) Describe the causes and effects of eutrophication. (iii) (a) List four effects of sulfur dioxide pollution. (b) Account for the presence of chlorofluorocarbons in the atmosphere. (c) What are some of the effects of the build-up of these pollutants? 2 (i) What is deforestation and why is it practised? (ii) State some consequences of deforestation. (iii) State some consequences of industrialisation. (iv) Why are conservation efforts so important? 75 Section B: Life Processes and Disease 0 0 0 0 0 0 draw diagrams to show the structure of typical plant and animal c ells understand the functions of the cell wall, cell membrane, cytoplasm, mitochondrion, chloroplast, nucleus and vacuole compare plant and animal cells understand that most microbes are unicellular understand why specialisation is important in multicellular organisms understand how some substances move into and out of cells plant animal microbes - bacteria, Amoeba ) l cell - basic unit of life 1 ( microscope tissue ' organ calculating size of cells 6 image seen Is 400 times bigger than the actual specimen system --- - -- 1'5 light passes through eyepiece lens, I magnification x10 organism movement into and out of cell diffusion osmosis Why we need microscopes 4 light passes through lens, r:a.1----'~--- magnification x40 ~_....l~;;nr;::,:;;;:~;--- 3 light passes through the slide (specimen) 2 light passes through the filter and condenser l light reflects on mirror and travels up to the eyepiece Th e cell is the basic un it of life. A cell cannot be viewed by the naked eye since it is too small. It can on ly be seen w ith a mi croscope. Cells are thus described as being m icroscopic. A microscope is used to produce a magnified image of an object. There are different kinds of microscopes, for example light and e lectron. When looking through the microscope at a piece of tissue, separate cells can be distinguished which would not have been seen with the naked eye. How much you ca n see w ith a microscope depends on h ow powerful its magnification is. A light microscope typically magnifies between l 0 and 400 times real size (figu re 8.1). An electron microscope is more powerful and can magnify tens of thousands of times actual size. 8 ·Cells Calculating the size of cells ~ IT:Q·1 V'-J What is the purpose of a microscope? The actual size of an object in a photograph can easily be calculated from the image and the magnification given. If the length of the object in the ph oto is measured as Z, and the magnification is given as xlOO, that m eans the object is 100 times larger than in real life. So, the actual size of the object is Z-;-100. Plant and animal cells Syllabus reference C1.1 --<+-- Plant and animal cells have the same basic structure but each has its own characteristics that make it typically plant or typically animal. The structures found within a cell are called the cell organelles. Th ey have different functions and, as they work together, they keep the cell (and therefore the organism) alive. Figure 8.2 shows diagrams of typical plant and animal cells; figure 8.3 shows plant cell. Table 8.1 describes the functions of some cell organelles. - - nucleus contains -------\r----1 chromosomes which carry genetic Information chloroplast -""-tt-- - - mitochondrion ----l~!lii. starch grain glycogen granule Plant cell 0 Animal cell Rgure 8.2 Typical plant and animal cells. .~ Rgure 8.3 Photomicrograph of a plant cell (magnification x5000). Compare this with the plant cell drawn in figure 8.2 Organelle Function cell wall prevents bursting of a plant cell and gives it a fixed shape cell membrane Measure the width of the largest chloroplast in the cell in figure 8.3, and calculate its actual size using the magnification given. a selectively permeable barrier which controls exchange between the cell and its environment cytoplasm site of many of the chemical reactions of life nucleus controls the activities of the cell, contains chromosomes .~ vv chromosome carries genetic information in the form of DNA mitochondrion site of energy production V'-J Make a list of (i) all the organelles which are found in both plant and animal cells and (ii) organelles which are only found in plant cells. permanent vacuole important during exchange of water and minerals, and stores various substances including waste products chloroplast where photosynthesis takes place Table 8. 1 The functions of some cell organelles. (Organelles shown in green are only found in plant cells.) 79 Life Processes and Disease Table 8.2 describes differences between plant and animal cells in more detail. .~ U'-J Plant cell Animal cell Name two organelles found in a plant cell but not in an animal cell. What is the importance of these two organelles to a plant cell? Cytoplasm is surrounded by a cell membrane as Cytoplasm is surrounded by a cell membrane well as a cell wall. only. Chloroplasts are present. Chloroplasts are absent. .~ V'--1 Carbohydrates are stored as starch. Carbohydrates are stored as glycogen. A large, permanent vacuole is present in most plant cells. It has a definite, fixed shape. Many small, temporary vacuoles are present at a time. These have no fixed shape. (i) Distinguish between cell wall and cell membrane. (ii) Distinguish between mitochondrion and chloroplast. Cytoplasm is pushed to the edges of the cell by Cytoplasm is present throughout the cell. the vacuole, so it is normally confined to a thin layer. Table 8.2 The main differences between plant and animal cells. Unicellular microbes Microbes are microscopic organisms (microorganisms) that cannot be seen by the naked eye, only by using a microscope. Most, but not all, are singlecelled organisms, and are so tiny that millions could fit in the eye of a needle. Microbes are everywhere, in the air we breathe, the ground we walk on and in the food we eat. They are even inside us. They include: • viruses • bacteria • protozoa. Viruses These are very small and can only be seen with an electron microscope. They are not made of cells an d are sometimes referred to as virus particles or virions. They cannot be killed by antibiotics such as penicillin. Examples of diseases they cause include influenza, common cold, measles, mumps, german measles (Rubella), smallpox, chickenpox, HIV (can lead to AIDS) and rabies. Bacteria glycogen granules, lipid droplets mesosome· cell surface membrane ~ photosynthetic membranes' • = not pesent in all bacteria Rgure 8.4 Diagram of a bacterium. 80 ~~ small i=~ \ _ ] . .· circular DNA ribosomes Bacteria are single-celled organisms (Figure 8.4). Many of us refer to them as 'germs', but some are very useful. For example, they decompose dead organisms and digest cellulose. Examples of diseases they cause include cholera, tubercu losis, septicaemia (blood poisoning), pneumonia and gastroenteritis. S·Cells Protozoa These are generally single-celled organisms (figure 8.5). Amoeba is very common and can be found in back-yard ponds and drains. Examples of diseases they cause include malaria, sleeping sickness and dysentery peeudopodium (false foot) is sent out in the direction of the food particle the food particle is engulfed enzymes are secreted into the food vacuole and the food is digested nutrients are absorbed into the cytoplasm of the amoeba unwanted (undigested) substances are released from the amoeba into the enviroment Figure 8.5 Movement and feeding in Amoeba. Cell specialisation in multicellular organisms Organisms can be described as unicellular or multicellular. Unicellular organisms like Amoeba (animal) and Chiarella (plant) are just one cell in size. Multicellular organisms, like all the larger animals and plants are made up of many (sometimes millions) of cells. The cells of unicellular organisms (e.g. Amoeba and bacteria) are independent but are still able to carry out all characteristics of life. Multicellular organisms, however, are made up of millions of cells. These cells work together and are often dependent on each other to carry out all the characteristics of life. 81 Life Processes and Disease In multicellular organisms, each cell has the same basic structure, but there are variations in the nucleus design. Within a single organism, such as a human, there are great differences between the cells. transmits Each type of cell is specialised to, nerve pulses carry out a particular function well. For example, a muscle cell striations in cells can shorten o r lengthen is concerned with contraction of the muscle, while a nerve cell it---~ these cells is specialised to transmit nerve insulate the impulses (figure 8.6) . nerve cell In a multicellular organism, cells are arranged in groups to lt'!lflll!l""i:!P.!:i."1"(#-1 form tissues. A tissu e is a structure made up of many similar or identical cells which are adapted to perform one specific function. Skeletal muscle cells Nerve cell Muscle cells make up muscle tissue make up a muscle fibre and all these cells are concerned with the muscle function of contraction. Several different kinds of Figure 8.6 Specialised cells that are found in nerves and muscle. tissue may be grouped to form an organ . For example, intestines contain epithelial tissue and muscle tissue and a blood supply (figure 8.7). In animals, organs form parts of even larger functional units called systems. The digestive system is made up of several organs, including the stomach, intestines and liver. Epithelial cells CELLS ® (j) (ii) ~@ e l Cells mass together to form an epithelial tissue. 1.mm.1~·+1.TIJ 1 epidermal cells -TI~~ TISSUE palisade The epithelial and smooth muscle tissues combine together in the wall of an organ such as the intestine. l leaf ORGAN in an organ such as the leaf. epidermal tissue epid ermal cells TISSUE I Cellsmass together to form smooth muscle ~~ tissue. r CELLS Muscle cells Figure 8. 7 Tissues in the intestine. 82 Rgure 8.8 Grouping of cells to form tissues in the organ of a leaf. Cells in plants are also grouped into tissues, and tissues grouped into organs (figure 8.8). Table 8.3 shows examples of tissues, organs and systems that are found in plants and animals. 8 ·Cells Structure Examples in plants Examples in animals tissue palisade mesophyll (chapter 9) nerve tissue (chapter 18) phloem tissue (chapter 14) muscle tissue (chapter 17) xylem tissue (chapter 14) CHAPTERS 9, 10, 12, 14, 17, 18 organ leaf, root stomach, lung, brain , eye system (not organised into systems) digestive system (chapter 10) respiratory system (chapter 12) nervous system (chapter 18) Table 8.3 Examples of tissues, organs and s stems in plants and animals. ~ ll:Q6 V'-' Give an example of each of the following: cell, tissue, organ, system. ~ ll:Q7 V'-' Distinguish between unicellular and multicellular organisms, giving two examples of each. A healthy organism is made up of all these parts working efficiently together, enabling it to do many things at the same time, such as use its energy source and make the energy available for movement, reproduction, growth, response and excretion. A total breakdown in the normal functioning of any one of these systems can lead to the death of the organism, such as a heart attack when the circulatory system breaks down. Most animals are either predator or prey in food chains. A healthy organism has all its systems functioning efficiently and so is able to survive in the environment or wild. Unhealthy organisms may be unable to capture food or fall prey to predators more easily. Survival is for the fittest, meaning that an organism with all its systems functioning efficiently and continuously has an advantage for survival - an advantage for life. Movement of substances into and .out of cells 1@3i§U.ht1 Substances moving out of ~ the cell. (These were made , '\ by the cell and are important, ~ like hormones and enzymes.) Q All kinds of reactions take place within a cell. The organelles within a cell require many different substances to carry out these reactions. Waste products are formed during these reactions and must be removed. The substances, needed and produced, must pass into and out ·of the cell. There is thus a constant movement of substances into and out of cells. • Substances needed by the cell, like glucose and oxygen, must pass into the cell. • Substances produced by the cell must pass out of the cell. These may be waste products, like carbon dioxide and urea, or substances needed by another cell, like enzymes. This is called secretion . substances moving into cell ~ Substances can be taken in within small vesicles made from the cell membrane. Amoeba takes its food in this way. Substances can also be released from cells when vesicles containing the substance join with the cell membrane (figure 8.9). Hormones are released from cells like this. Substances may also enter and leave cells as individual molecules. They do this by various mechanisms including diffusion. Water enters and leaves cells by osmosis. Figure B. 9 Diagram showing substances moving into and out of a cell in small vesicles. 83 Life Processes and Disease Movement by diffusion l'!Dill@•hU concentration gradient > Practical activity SBA 8.1: Diffusion in a solution, page 341 permeable > Diffusion is the movement of molecules from a region of high concentration of those molecules to a region of lower concentration of those molecules. Diffusion can happen in gases and in liquids. A diffusion gradient or concentration gradient occurs when there is a difference in the number of molecules, or the concentration of molecules between the two regions. For example, when a drop of dye is added to · water, the dye molecules move around and between the water molecules and eventually are spread evenly, even when not stirred. In other words, the dye molecules move from where they are plentiful to where they are not so plentiful. We say these diffuse (figure 8.10) . Substances can also diffuse across membranes if the concentrations are different on both sides and the membrane is permeable to those molecu les (figure 8. 11 ). Figure 8.10 Over time, the dye molecules diffuse so they are evenly spread throughout the solution. • • molecules at a higher concentration e e molecules at a lower concentration - molecules at the same concentration +-+-+on both sides • • more molecules move from left to right than from right to left no net movement of molecules Figure 8. 11 Diffusion can occur across permeable cell membranes. Some examples of diffusion in the human body • After a meal, the end-products of digestion are at a high concentration in the gut. They diffuse down their concentration gradient into th e blood where they are at a lower concentration (figure 8.12). 84 8 ·Cells blood rich +-•••••m~;K~ll!l~•Klin~ZI···-- blood capillary in the endproducts of digestion ileum o f the gut end-products of digestion at a high concentration Figure 8.12 Diffusion of small food molecules from gut to blood. blood rich in oxygen (02) oxygen ata higher concentration in the alveolus / • Diffusion occurs in the lungs (figure 8.13 ). Carbon dioxide diffuses from the blood where it is at high concentration into the lungs w here its concentra tion is lower. Oxygen diffuses in the other direction because it has a higher concentration in the lungs and a lower concentration in the blood. • When the blood gets near the celJs, the oxygen concentration in the blood is higher than in the cells. The blood came from the lungs where it picked up oxygen. The oxygen concentration in the cell is low, since the o xygen that was in the cell was used for respiration. The oxygen in the blood diffuses into the cell, where it can be used for energy production during respiration .(figure 8. 14). concentration gradient - higher concentration of glucose in the gut blood capillary Figure 8. 13 Diffusion of gases between the lungs and the blood. ;;:JE.-<--- lower concentration in the blood blood capillary one cell thick many ways - more surface area, more diffusion ________., f ----lOOCly cells oxygen used up during respiration and its concentration is low Figure 8. 14 Diffusion of oxygen from blood into cells. Figure 8.15 Adaptations that help to speed up the rate of diffusion. • In the cells, carbon dioxide builds up as a waste product of respira tion. It is at a higher concentration than in the blood. Thus it diffu ses ou t of the cell and into the blood. • Other wastes made by cells, such as ammonia, are at a higher concentration in the cell than in the blood. They also diffuse out of the cell to the blood and are taken away and expelled from the body. Diffusion is a very slow process unless there is a large concentration gradient over a short distance. Tissues like the lungs and smaIJ intestine are especiaIJy adapted to maximise the rate (figure 8.15). Adaptations include: • keeping the difference between the concentration on each side as high as possible (maintaining a steep concentration gradient); 85 Life Processes and Disease • having a large surface area to volume ratio so that molecules have as Large a surface area of cells as possible to diffuse through; • being very thin and thus minimising the distance over which diffusion must take place. Movement by osmosis Practical activity SBA 8.2: Some effects of osmosis, page 342 Osmosis is a special kind of diffusion. It is the diffusion of water molecules across a selectively permeable membrane. Cell membranes are all selectively permeable membranes. ' Selectively permeable' means that water and some substances can pass through the membrane but other substances do not. Osmosis in plant cells 11"1-l(.]el!M milt-WM When a plant cell is put into a solution which has the same concentration as the cell contents (isotonic), some water molecules will move into the cell through the cell membrane and some will move out. There is no concentration gradient so the movements each way are the same and balance each other out. We say there is no net movement, or net flow, or water (figure 8.16). • ..0.. .. • concentration of solution outside isotonic with (same as) inside cell • no net flow of water •! · • outside hypotonic to (less concentrated) inside cell • net flow of water into cell • cell is turgid ·'·- ·· : ~ • outside hypertonic to (more concentrated) inside cell • net flow of water out of the cell • cell membrane pulls away from cell wall • cell is flaccid Figure 8.16 The effect of different concentrations of solution on a plant cell. liW•r•H•liiiM When a plant cell is put into a solution that is less concentrated (hypotonic) liiii•il•• hypertonic > 86 than the cell contents, there is a greater concentration of water molecules outside than inside . Some water molecules move out of the cell but more move into the cell, so there is a net flow of water into the cell . The cell becomes full of water and is described as being turgid . When a plant cell is put into a solution that is more concentrated (hypertonic) than the cell contents, there are fewer water molecules outside than inside. A few water molecules move into the cell but many more move a ·Cells 1!@13!elJ out of it, so there is a net flow of water out of the cell. The cell loses water and is described as being flaccid . Flaccid cell s are easy to distinguish un der the microscope beca use the cell membran e an d contents pull away from the cell wall. Osmosis in animal cells ~ 11!Q8 vv An animal cell placed in water will burst. Explain fully why a plant cell will not burst when placed in water. An anima l cell h as no cell wa ll like a plant cell, so hypotonic and h ypertonic solutions have different effects. In a h ypotonic (dilute) solution there is a net flow of wa ter into che cell. With no strong cell wa ll to prevent th e membrane from stretching too far, it even tually bursts. In a h ypertonic (concentra ted) solution there is a net flow of water out of the cell and the whole cell shrinks (figure 8.17) . •· ,, • cell in hypotonic solution • net flow of water into cell • no strong cell wall so cell bursts • cell in isotonic solution • no net movement of water • cell in hypertonic solution • net flow of water out of cell • cell loses water and shrinks Figure B. 17 The effect of different concentrations of solution on an animal cell . CHAPTER 16 ~ It is important for cells to be protected from large changes in con centration of the solutions aro und them . Animal bodies ha ve complex m echanisms to do this called osmoregulation and homeostasis (ch apter 16). rChapter summary • The cell is the basic unit of life. • A cell contains smaller parts called organelles. • The nucleus, cell membrane, cytoplasm and mitochondrion are some organelles found in typical plant and animal cells. • Plant cells also contain cell walls, chloroplasts and large central vacuoles. • Most microbes are unicellular. 87 Life Processes and Disease • • • • • • • • • • Cells in multicellular organisms are often specialised for a particular function. A group of specialised cells that have the same function is called a tissue. An organ is a group of different tissues that work together. Organs working together make up a system. Systems coordinate with each other and work together in a living organism. Many substances can move into and out of a cell through the cell membrane which i~ selectively permeable. Diffusion is the movement of a substance from a high concentration to a low concentration. Osmosis is the movement of water across a selectively permeable membrane from a solution where there is a high concentration of water molecules to a solution where the concentration of water molecules is lower. Diffusion and osmosis occur at many places in a living organism. Different concentrations of solution have different effects on plant and animal cells. ,. II.. ITQ1 A microscope is an instrument used to produce a magnified image of an obj ect . Organisms and objects that cannot be seen by the naked eye may be visible under a microscope. ITQ2 The measured width of the chloroplast in the photograph is 14 mm (or 14 x 10- 3 m ). The magnifica tion is x5000 . This means that the measured size is 5000 times large r than in reality. So the actual size is (14 7 5000) x 10- 3 m = 0 .0028 x 10- 3 m (or 2.8 x 10-6 m or 2 .8 µm ). ITQ3 (i) Plant a nd a nimal cells have: cell membrane, nucleus, cytoplasm, mitochondria, small vacuoles. (ii) Plant cells have a cell wall*, chloroplasts, large central vacuole. (*Fungal cells and som e bacteria also have cell walls,bu t these have a completely different structure from those in plants.) ITQ4 The plant cell wall has protective an d structural functions. It p rotects the plant by protecting each plant cell from bursting when the plant takes up w ater. It also helps to support stems and leaves of the plant when th e cells are full of wa ter, because plants have no skeleton like many animals. The chloroplast con tains the pigmen t chloroph yll which collects the light energy of the Sun. Chloroplasts are the sites of photosynthesis, so animals do n ot need them . The large plant vacuole is importan t during exchange of wa ter and minerals, and stores various substances including waste products. ITQS (i) The cell membrane is a partially permeable barrier th at controls the passage of substances into and ou t of the cell whereas the cell wall provides support and protection and allows the free passage of wa ter. (ii) Th e mitochondrion is the site of respiration during which en ergy is released from sugar. All cells have mhocd1ondria. The chloroplast is the site of ph otosynth esis where sugar is made. Chloroplasts are found only in plant cells. ITQ6 Cell: e.g. mu scle cell . Tissue: an y group of on e kind of cell w orking together e.g. muscle cells in muscle tissue. Organ: any group of tissues working together e.g. stomach , m ade up of secretory tissue, muscle tissue and other tissues; leaf, made of palisa de tissue, xylem tissue. System : any group of one kind of organs working together e.g. digestive system, made up of stomach, liver, intestines and other organs. 88 8·Cells ITQ7 A unicellular organism is an organism that h as only one cell. This small organism shows all the characteristics of We and lives an independ ent life. For exa mple, Amoeba and Chlorella . A multicellular organism is made up of man y cells. These cells work together, and the organism is able to show all the characteristics of life. For example, a human and a worm (there are many other examples you co uld have chosen ). ITQ8 A plant cell has a cellulose cell wall around the cell membrane. The wall is strong and cannot stretch. When placed in water, th e cell will take up water, but the cell membrane wilJ n ot burst because th e cellulose cell wall stops it stretching to bursting point. An animal cell does not have a cellulose cell wall and so can stretch to the point w here it bursts. Examination-style questions 1 (i) The drawing below was constructed by a biology student after viewing a slide under the microscope. The drawing made was magnified 2500 times. What is the actual size of the cell labelled A? ( C) I C) I C) J A (ii) The figure below shows how a section of a root or stem is mounted for microscopic investigation. / I Explain why it is necessary to cut a very thin section of the material which is to be observed under the microscope. (iii) (a) Name two types of microscope. (b) Why are cells described as being microscopic? 2 (i) Make labelled drawings of typical plant and animal cells. (ii) Use a table to compare typical plant and animal cells. (iii) Give one advantage of being multicellular. (iv) Name one difference between a tissue and an organ. (v) Give one named example of: (a) a tissue; (b) an organ to be found in: • • an animal; a plant. 89 Life Processes and Disease 3 The figure below shows onion rings A, B, C and D before and after immersion in water and a salt solution. onion ring A 0 onion ring before immersion in water onion ring C 0 onion ring before immersion in salt solution onion ring B onion ring D 0 onion ring after immersion in water 0 onion ring after immersion in salt solution (i) Copy and complete the table below to show the measurements of the rings. Onion ring Outer diameter Inner diameter Mean diameter A B c D (ii) (a) Using measurements.from the table, describe what happened to the onion ring placed in: • water; • salt solution. (b) Explain fully the results seen in: • water; • salt solution. (iii) (a) What process is taking place? (b) Give an example of the occurrence of this process in living organisms. (iv) Describe two examples of diffusion as it occurs in living organisms. 90 P. hotosynthesis 0 understand the difference between heterotrophic, autotrophic and saprophytic nutrition 0 0 describe photosynthesis in green plants 0 explain how environmental factors affect the rate of photosynthesis relate the structure of the leaf of a flowering plant to its function in photosynthesis photosynthesis autotrophic nutrition inorganic substances converted to organic substances ( heterotrophic nutrition - animals saprophytic nutrition leaf structures limiting factors - light, temperature, carbon dioxide; water 1 conditions adaptations for photosynthesis Plants are the food supply for animals Th e relationship between autotrophs, heterotrophs and sproph yres is sh own in figure 9. 1. AUTOTROPH HETEROTROPH 'self-feeders' e.g. plants that make their own food during photosynthesis feed on other organisms e.g. consumers that feed on plants and other animals SAPROPHYTE feed on dead organic material e.g. decomposers that feed on the dead autotrophs and heterotrophs / Figure 9.1 Relationships of autotrophs, heterotrophs and saprophytes. 91 Life Processes and Disease In the study of food chains we saw that plants are producers and are at the heterotroph > QSb start of almost all food chains. Animals are consumers and feed on the plants or on other animals. Plants do not eat, yet they are full of food. They are rich in carbohydrates, fats and proteins. This is because they are able to manufacture their own food. We call them autotrophs (self-feeders) because they are able to make organic substances (glucose) from simple inorganic substances (carbon dioxide and water). This process is called photosynthesis and requires light from the Sun to provide the energy needed to carry it out. From glucose, the plant makes all the other carbohydrates, fats and proteins it needs. . Consumers feed on the organic substances made by the plants. Consumers are h eterotrophs (other or different feeders). Heterotrophic nutrition is the intake of complex organic substances when animals feed. Autotrophic nutrition is the intake of simple inorganic substances by plants during photosynthesis and must occur before heterotrophic nutrition (figure 9.2). C02 IT:.Q-1 l./'-J Distinguish between an autotroph and a heterotroph. ~ IT:.Q2 l./'-J Why must autotrophic nutrition occur before heterotrophic nutrition? ~ IT:.Q3 l./'-J Why is saprophytic nutrition important? Autotrophic nutrition Heterotrophic nutrition ...__ _. . ~ I plants take in inorganic H20 substances and make inorganic organic substances substances animals take in organic substances when they feed ' Figure 9.2 Autotrophic nutrition must occur before heterotrophic nutrition can occur. Food chains start with plants, then animals feed on the plants. When plants and animals die, saprophytes feed on the dead bodies which are full of organic substances such as carbohydrates, fats and proteins. Saprophytes are also called decomposers and they are very important to the cycling of these materials back to the earth, from where they are then available to plants again. Photosynthesis Practical activity SBA 9.2: Is light needed for photosynthesis? page 344 Photosynthesis can be summarised in words or by the simple equation: light carbon dioxide + water _ _ _ __, glucose + oxygen chlorophyll photosynthesis equation > light 6C0 2 + 6H 2 0 C6 H 12 0 6 + 60 2 chlorophyll light-dep endent stage ) light-independent stage > Chlorophyll is a complex green pigment. At the centre of a chlorophyll molecule is a single atom of magnesium chemicaly bonded to four atom s of nitrogen. Without supplies of nitrogen, a plant cannot make chlorophyll and so cannot photosynthesise successfully. Experiments show that there are two main stages in photosynthesis (figure 9.3), namely: • the light-dependent stage • the light-independent stage Light-dependent stage Chloroplasts are organelles seen in green plants cells. They contain the green pigment chlorophyll which 'traps' the light energy from the Sun. The energy is used to 'split' water (Hp) into hydrogen and oxygen. The oxygen is a waste product and diffuses out of the leaf. 92 9 · Photosynthesis Light-independent stage The h ydrogen then combines with carbon dioxide (COJ to make glucose (C6 H 12 0 6 ). This stage of photosynthesis does not n eed light and can h appen when it is dark. ~ 3~chlorophyl , .•diffuses out of the leaf O><Jlgen / / ,/'/ water hydrogen light -dependent stage ~ / carbon dioxide diffuses into the leaf glucose light-independent stage Figure 9.3 Light-dependent and light-independent stages of photosynthesis. The organ specialised for photosynthesis is the leaf. The transverse section of a leaf reveals many cells, a rranged in a manner that is ideally suited for photosynthesis. Adaptations of the leaf for photosynthesis Practical activity SBA 9.3: Is chlorophyll needed for photosynthesis? page 345 lfU.),ifiiOJ palisade cell > Leaves a re adapted to carry out photosynth esis in a number of ways (figures 9.4 and 9.5). • They are generally broad and flat with a large surface area to a bsorb a lot of light and carbon dioxide. • They lie at 90° to the sunlight and are spaced around th e stem to ca tch as much light as possible. Rgure 9.4 How leaves catch as much • The leaves are thin to allow light sunlight as possible. and carbon dioxide to reach all cells ra pidly. • Stomata (small holes) are present in the lower epidermis to allow gases to get in and out easily. (One h ole is a stom a. Stomata is the plural. ) • Air spaces around the cells in the lower half of th e leaf allow carbon dioxide to get to the chloroplasts as quickly as possible. • Chloroplasts are most numerous in cells in the palisade layer, which is in the top part of th e leaf, closest to the sunligh t. • Xylem vessels transport wa ter to the leaf cells. • Phloem sieve tubes carry away the food made in th e leaf cells to the rest of the plant. • A waxy cuticle p revents water Joss form both surfaces of the leaf; it is transparent to le t light through . 93 Life Processes and Disease the leaf is cut at A-B and magnified B \ A veins - run throughout leaf B stoma epidermis magnification of this small section (a transverse section) upper epid ermis palisade layer air space xylem vessels vein -~:::.....~f------1._....._..... spongy layer i.,..o;r;.,,""' ~f---- p hloem tubes cell of lower epidermis - no chlorop lasts lower epid ermis guard cellthickened - - - - - - " inner wall stoma Figure 9.5 A section of a leaf. Guard cells - epidermal cell guard cell CHAPTER 14 94 A stoma is surrounded by a pair of specialised (turgid) epidermal cells called guard cells. The gua rd cells vary the size of the opening of the stoma stoma open by changing their shape, thu s the size of the stomata! pore is regulated by the guard cell. The stoma is the route by which water is lost from the plant during transpiration (chapter 14), and also by which the gaseous ___.____ guard cell exchange necessary for photosynthesis (flaccid) occurs. By controlling stomata! opening a nd closing, a plant controls the balance between stoma the need to conserve water and the need to closed exch ange gases. Stomata! opening varies as a result of ch an ges in the turgidity of the guard cells Figure 9.6 The guard cells control the (figure 9.6) opening and closing of the stomata! pore. 9 · Photosynthesis ~ IT:Q:.t \../'-.I Why do you think that the stomata of some desert plants close during the day? • when they are turgid, the stoma opens; • when they are flaccid, the stoma d oses. The following observations have been made: • most stomata open during the day and close at night; • stomata generally dose when a plant suffers water stress, or when transpiration rate exceeds the rate of water absorption by the roots; • the stomata of some desert plants close during the day and open at night. How everything gets to the chloroplast Practical activity SBA 9.4: Is carbon dioxide needed for photosynthesis? page 346 Photosynthesis takes place in the chloroplasts of specia li sed leaf cells. The following numbered paragraphs refer to Figure 9.7. light from the Sun ~ IT:QS \../'-.I Describe how carbon dioxide gas in the atmosphere gets to a photosynthesising cell inside a leaf. typical photosynthesising cell-~....... (chlorophyll is present in the chloroplasts) water travels to the v~...,..._f::;!M--f-- leaf via the xylem, from the soil surrounding the roots ti"t---i"t1r>--nt!t--- C02 used up during photosynthesis • Its concentration is thus low in the cell • carbon dioxide in the air surrounding the leaf - -+1"'.ll'tt--- • C02 in the air space. Its concentration is higher than in the cell • C02 diffuses into the cell from the air space C02 Rgure 9.8 Carbon dioxide diffuses down its concentration gradient into the leaf. Rgure 9.7 All the requirements for photosynthesis must get to all the photosynthesising cells. 1 rrr.:a_- the leaves are thin and flat and lie at right angles to the Sun's rays ~...--..--:::;;::--~ xylem vessel in ~ IT:Q6 the stem transports water \../'-.I Look at the tomato plant and describe four ways in which the plant is adapted for photosynthesis. leaves are spread around the stem 2 Ca rbon dioxide diffuses from the surrounding air into the stomata or pores on the underside of the leaf. It moves into the air space su rrounding the mesophyll cells, and then into the cells themselves. As the carbon dioxide is used up during photosynthesis, its concentration drops. There is thus a greater concentration of carbon dioxide outside the cells than inside and carbon dioxide dilfuses into them (figure 9.8). Water moves by osmosis from the soil into the roots of the plant. It then travels up the xylem vessel in the stem and into the leaves. From the 95 Life Processes and Disease 3 4 xylem in the leaf. water moves by osmosis to the palisade cells where it is used during photosynthesis. Light rays pass into the leaf from all around, especially from above. Chloroplasts are found mainly in the palisade cells where the chlorophyll can easily intercept and trap the light energy. Within the chloroplasts the light energy splits the water which then reacts with the carbon dioxide . Products of photosynthesis Practical activity SBA 9.5: Is oxygen produced during photosynthesis? page 347 .tt"t--+'ttt---;tt.~ • Oxygen is produced during photosynthesis • Its concentration is therefore high in the cell --"=t....H-- • Oxygen diffuses into the air space where its concentration is lower • Oxygen diffuses out of the cell through stomata 02 Figure 9.9 Oxygen moves out of a leaf. limiting factor > The glucose produced during photosynthesis is used in several ways. • It is broken down during respiration to release energy so the plant can carry out all the processes of life. • It is converted to starch and stored in the leaf to be used in the night when the plant is not photosynthesising. • It is converted to sucrose and transported to other parts of the plant. It can then be converted to other carbohydrates, lipids and proteins and used for growth, or it can be converted to starch and stored, as in potatoes . Oxygen is a waste product of photosynthesis. The cells in the leaf will use some for respiration, but the rest of the oxygen is not needed by the plant. Inside the leaf, photosynthesis is taking place and oxygen is being produced. It is thus at higher concentration inside the leaf than oucside. So oxygen diffu ses out of the leaf through the stomata (figure 9.9). Limiting factors in photosynthesis Photosynthesis is a chemical reaction, and the rate at which a reaction can happen depends on how fast the chemicals that are reacting can get together. In photosynthesis, a plant requires water, carbon d ioxide and light. If any one of these is in short supply, the rate of the reaction will slow down. For example, a plant may have sufficient carbon dioxide and water, but not enough light for photosynthesis to take place at its maximum rate. Light is then said to be the limiting factor, since the rate of photosynthesis is limited by the amount of light. The reaction will take place at a rate that is limited by the factor which is a t its least favourable value (light, in this example). Water, light and carbon dioxide may all be limiting factors for photosynthesis at different times. The limiting factors which affect photosynthesis are: • temperature; • light intensity; • carbon dioxide concentration; • availability of water. Temperature CHAPTER 10 96 The rate of a reaction increases as temperature increases. With heat, the molecules move about and come together faster. Photosynthesis also involves a series of enzyme-catalysed reactions. Enzymes have an optimum temperature or temperature at which they work best (chapter 10), so this w ill also affect the rate of the reaction. Temperature is often the limiting factor on the rate of photosynthesis in cool seasons in temperate regions. 9 · Photosynthesis Carbon dioxide concentration The concemrarion of carbon dioxide is re latively low in the atmosphere. So carbon dioxide is us ually the limiting fa ctor when cemperature and light levels are high. Commercial growers who grow their crops in large greenhouses often pump in extra carbon diox ide to increa se the rate of photosynthesis in the crops (figure 9.10). Light intensity The amount of light in the e nvironment varies grea tl y between night and day. Light is usually the limiting fa ctor from dusk until dawn (figu re 9.10). Rate of photosynthesis rate slows down, some ractor 1s limiting the rate 0.13% C02 at 30 °C - areater C02 concentration rate increases 0.03%'C02 at 30°C ~ co_ rate of photosynthesis slows down because of concentration - C02 is the hm1t1ng factor, not light \./'-I Which factor will most likely be limiting photosynthesis in each of these cases? (i) Middle of the day after plenty of rain in Jamaica. (ii) Cool autumn day in Britain. (iii) Dry season in Australia. +------ rate or photosynthesis increases as hyht 1ntens1ty increases - light Is the limiting factor Light intensity Rgure 9.10 How light and carbon dioxide may limit the rate of photosynthesis Availability of water The ava ilability of water varies in the environment. If the soil is dry, wa ter may be the limiring factor on photosynthesis. Etiolation mmmm.],p Cf the plant cannot get sunlight, for example it is shaded by a rock or anoth er plant, it cannot photosynthesis. Without photosynthesis it cannot make food. But this does not mean that it cannot continue to grow. For a short while, it can use some of the food stored w ithin the plant to grow and lengthen. This gives it a chance to get som e leaves into the light a nd so start to photosynth esise again. The form o f growth a plan t shows wh en it is out of light is different from n ormal. All the energy is u sed to make long thin cells, so the stem becomes e lo ngated and thin, and leaves are kept very small. Th e stems and leaves are also pale yellow as n o chJorophyll is made. This fom1 of growth is called etiolation (figure 9.11). If it does not reach light Figure 9. 11 The et1olated plants on the quickJy the plant will run o ut or rood nght have long thm, white stems and small reserves and die. yellow leaves 97 Life Processes and Disease .. _ - An autotroph is an organism that is able to make its own food (organic substances) from simple substances (inorganic substances) . A plant is an autotroph - when it photosynthesises it makes glucose from carbon dioxide and water. A heterotroph is an organism that takes in organic food when it feeds. It must have a supply of organic food since it cannot manufacture it for itself. ITQ2 Autotrophs make organic food which is eaten by heterotrophs. Autotrophic nutrition must therefore take place first so that heterotrophs can have something co eat. ITQ3 Saprophytic nutrition is important for the recycling of nutrients in the environment. Nutrients trapped in an organism are made available when that organism dies. Saprophytes can digest cellu lose and lignin and can decompose all plant remains. ITQ4 Some desert plants close their stomata during the day to p revent loss of coo much water from the leaf when it is hot. They open their stomata at night to exchange gases for photosynthesis. (They have a special mechanism which allows them to trap the energy from sunlight during the day and store it. until the stom ata open at nigh t and the energy can be used to make glucose.) ITQ5 Carbon dioxide is in the atmosphere around the leaf and gets to the photosynthesising cell by diffusion. A photosynthesising cell uses carbon dioxide, and so the ca rbon dioxide concentration decreases within the cell. Carbon dioxide diffu ses into the cell from the surrounding air space where its concentration is greater. The carbon dioxide concentration is thus lowered in the air space. Carbon dioxide _from the atmosphere can now diffuse into the air space through the stomata. ITQ6 • The leaves are spread around the stem and lie at right angles to the Sun's rays so that they can intercept as m ud1 light as possible. • Leaves are green because the cells contain chlorophyll. This captures light energy which is needed in photosynthesis. • Xylem vessels in the stem transport water to the leaf. • The leaves are thin and flat so gases can diffuse in and out as quickly as possible. ITQ7 (i) Carbon dioxide (ii) Temperature (iii) Water ITQ1 98 9 · Photosynthesis Examination-style questions The diagram below shows a transverse section of a leaf as seen under a microscope. (i) Label the parts A to F. (ii) Which cell is most actively photosynthesising? (iii) (a) Write the equation that summarises the process of photosynthesis. (b) From the equation, identity three factors/conditions necessary for photosynthesis to take place. (c) Describe how two of these factors reach a typical photosynthesising cell. (d) Describe the role of the cell labelled E. 2 (i) Define: (a) autotrophic nutrition; (b) heterotrophic nutrition. (c) saprophytic nutrition (ii) Photosynlliesis"ls summarised in one equation, but described as two stages (a) lightdependent, and (b) light-independent. Describe the two stages of photosynthesis. (iii) List five ways a plant is adapted for photosynthesis. 3 The diagram below shows a leaf in its actual size. (i) Making a drawing of the leaf. (ii) Write a heading for the drawing. (iii) Calculate the magnification of your drawing. (iv) Label the parts of the leaf. 99 ./ understand the importance of minerals in plant nutrition ./ understand the importance of a balanced diet to humans 0 describe food tests for carbohydrates, proteins and fats ./ relate a balanced diet to age, sex and activity of an individual ./ explain the meaning of the term 'malnutrition' ./ describe hypertension and diabetes ./ describe health problems associated with food additives 0 describe the role and structure of teeth f? understand the action of enzymes Z, understand how the alimentary canal of humans works ./) describe what happens to the products of digestion age minerals in plants pregnancy food additives diet balanced diet malnutrition sex alimentary system I activity ingestion physical digestion - teeth chemical digestion - enzymes } I digestion absorption villus I assimilation liver egestion constipation All organ isms, plan ts and animals, must be supplied with a source of energy fo r metabolism. This energy is used for ma intenance, growth, and repair of their bodies to sustain thei r lives. Plants (autotrophs) are able to make their own food using energy tram the Sun. They take in only very simple inorganic substances like water, carbon d ioxide and also magnesium and nitrate ions. Nitrogen and magnesium are basic components of chlorophyll. Choprophyll allows a plant to grow more rapidly and produce large amounts of succulent green leaves. These minerals also strengthen and support the roots thus enabling p lants to take in more water and nutrients from the soil. Nitrogen is 10 · Feeding and Digestion also important in the formation of proteins. Animals (heterotrophs) can only obtain energy when they feed on other living organisms made up of complex materials such as carbohydrates, proteins and lipids. Diet l!l@IJ balanced diet > IOeliM ~ IT:.Q-1 vv Define the terms 'diet' and 'balanced diet'. To maintain their bodies in good hea lth, anima ls need various materials. These include carbohydrates, proteins, lipids, vitamins and minerals. Animals eat food that contain these materials or nutrients. The term 'diet' is used to describe the quantity and quality of food eaten (i.e. which nutrients and how much of each is present in the food being eaten every day). A balanced diet is a diet which has the quality and proportions of nutrients needed to maintain good health. This includes water and fibre. Water is essential because around 70% of our body mass is water. If we do not get enough water, systems in the body soon stop functioning properly. Fibre, or roughage, is the tough fibres that come from plant material. We cannot digest and absorb them, but they an; essential to the healthy working of the gut. Without enough fibre, we soon suffer from constipation. Eventually this can lead to bowel disease. Some nutrients that are needed are organic and some are inorganic (table 10.1). Organic nutrients Inorganic nutrients Carbohydrates Minerals contain carbon (C), hydrogen (H) and oxygen (0) calcium, iron, potassium, sodium, iodine, phosphorus Proteins contain C, H, Oand also nitrogen (N) and small amounts of sulfur (S) Lipids contain C, H and 0 Vitamins contain C, H and Oand other essential elements Table 10. 1 The organic and inorganic nutrients needed by living organisms. Organic nutrients Figure 10.1 Three-dimensional ball-andstick model of a glucose molecule. monosaccharide > disaccharide > These are required in the diet in relatively large amounts (tables 10.2 and 10.3, overleaf). Carboh ydrates are compounds of carbon, hydrogen and oxygen in the radio 1 C: 2 H: 1 0. An example is glucose. Figure 10.l shows a baJJ-and-stick model of a molecule of glucose. It can also exist as a ring formed from five carbon atoms and one oxygen atom. The sixth carbon atom in a - CH 2 0H group is attached to a ring carbon. Compounds with one such ring structure are called monosaccharides . The formula can be shortened to a symbol which can be either or, for diagrams, just • . Glucose and fructose are examples of monosaccharides. Monosaccharides are often called simple sugars. Two monosaccharides can combine to form a disaccharide (figure 10.2, overleaf). This happens in a condensation reaction as a water molecule is removed. Disaccharides can be broken back down to monosaccharides by hydrolysis which is a chemical reaction involving recombination with water. 0 101 Life Processes and Disease Monosaccharides and most disaccharides reduce Benedict's solution to an orange/red compound. Sucrose is the only common disaccharide which does not react in this way. This provides a distinguishing test for sucrose. Disaccharides are called complex sugars. H O H HO H I H 20 HO OH condensation (water removed)! HO monosaccharides OH j hydrolysis (water added) H: OoO :H j H~ O\oO o001 0oO :H condensation! / dlsaccharide hydrolysis polysaccharide Figure 10.2 D1saccharide molecules are made when two monosaccharide molecules join together. Polysacchande molecules are made of many monosacchande molecules. Organic nutrient Major groups Carbohydrate Protein Structure Characteristics Importance monosaccharide (e.g. glucose, fructose) five carbon atoms and an oxygen atom form a ring called simple sugars small molecules, soluble, sweet taste major energy source disaccharide (e.g. maltose, sucrose) two rings join together called complex sugars soluble, sweet taste major energy source polysaccharide (e.g. starch, cellulose, glycogen) many rings join together long chains of simple sugar (glucose) joined together insoluble and do not have a sweet taste starch is used as the energy store in plant cells and as a food source · for animals cellulose is found in plant cell walls glycogen is used as the energy store in animals cells a difference in the order of amino acids in the chain results in different protein there are millions of proteins, some soluble e.g. haemoglobin, red pigment in blood), and some insoluble (e.g. keratin, from which hair and nails are made). used for making new cells, growth and damaged parts of the body antibodies, hormones and enzymes are also proteins insoluble in water secondary energy supply after carbohydrates have been used up important for storage (oils in seeds) also function as insulation (fat under skin) especially for animals living in cold regions foods like butter, oils and nuts are rich in lipids JlD made up of long chains of amino acids there are about 20 different amino acids they can be arranged in the protein chain in any order / ( ·-o- ~ ~ ·-~ Upids (fats and oils) four moelcules (three fatty acids and one glycerol) joined together -- [E ff glycerol fatty ac ids (continued) 102 10 · Feeding and Digestion Organic nutrient Major groups Vitamins Structure A, B, C, D, Eand K each vitmain has many funcitons Characteristics Importance small amounts needed for good health A - aids vision in dim light B- asissts in respiraiton C- keeps tiossues helathy D- aids absopriton of calcuim K- aids in blood clotting Table 10.2 The major organic nutrient groups. Vitamin Sources Functions Symptoms of deficiency A carrots, spinach, egg yolk, cod liver oil, butter keeps skin and mucous membranes healthy, aids vision in dim light dry skin, mucous membranes degenerate, poor night vision B1 liver, rice, cereals, whole wheat flour, yeast helps in respiration beriberi - muscles become weak and painful, nervous system affected B6 leafy vegetables, eggs, liver, fish, kidney helps in metabolism depression and irritability c citrus fruits, green vegetables keeps tissues healthy scurvy - guns bleed, wounds take longer to heal, heart failure D egg yolk, dairy products, cod liver oil, also made by the action of sunlight on the skin controls calcium and phosphorus absorption, important in bone and tooth formation rickets - growing bones do not calcify, results in 'bow' legs in young children, and 'knock-knee' in older children Table 10.3 Some vitamins needed by humans for healthy growth. polysaccharide > NB Both Benedict's and Fehling's solutions contain copper sulfate. Reducing sugars reduce the copper(ll) ions (CU2• ) present in the copper sulfate to insoluble red-brown copper(I) oxide which contains cu• ions and is a precipitate. Practical activity SBA 10.1: Which food groups are present in a food sample? page 348 Substance to be tested Many monosaccharides can be joined to fo rm or syn thesise a very large molecule called a p o lysacch aride. Since condensation (deh ydration) reactions are involved in the synthesis of these polymers, these reactions can be called dehydration synthesis. Starch, cellulose and glycogen are examples of polysaccharides. They can form very large molecules. Food tests Table 10.4 sh ows the standard tests which can be made on a sample of food to indicate each of the main food grou ps. Test Observations 3 Reducing sugars - all monosaccharides (e.g. glucose, fructose) and some disaccharides (e.g. maltose) (i) Benedict's test: 2 cm of the solution to be tested The initial blue colour of the mixture turns green and 3 is put into a test-tube. 2 cm of Benedict's solution is then yellow and may form a brick-red precipitate. then added. The mixture is shaken and brought gently to the boil. (ii) Fehling's test: 2 cm3 of the solution to be tested is Same as Benedict's test. put into a test-tube. 1 cm3 of Fehling's A is added. 1 cm 3 of Fehling's B is then added. The mixture is shaken and brought gently to the boil. Non-reducing sugars (e.g. sucrose) 1 cm3 of the solution is put into a test-tube and 1 cm 3 of A red-brown precipitate results as the sucrose is dilute hydrochloric acid (HCI) is also added. The mixture hydrolysed to fructose and glucose by the acid. Fructose is bolled for 1 minute. 1 cm 3 of aqueous NaOH (NaOH and glucose are reducing sugars, so Benedict's test then solution) is added, followed by 2 cm3 of Benedict's can be carried out. solution. The mixture is then shaken and boiled gently. Starch 2 cm3 of 1% starch solution is added to a test-tube. A few drops of iodine in potassium iodide (12KI) solution is added. A blue-black precipitate results. (continued) 103 Life Processes and Disease Substance to be tested Test Observations Protein Biuret test: 2 cm3 of protein solution is put into a testtube, 2 cm3 of 5% potassium hydroxide (KOH) is then added. The mixture is stirred and 2 drops of 1% copper sulfate (CuSOJ is added. A mauve or purple colour slowly develops. Fats Ethanol test: 2 cm 3 of fat solution or oil is put into a A cloudy white suspension can be seen when the water test-tube. 2 cm3-of absolute ethanol is then added. is added. The mixture is shake~ vigorously and 3 cm3 of water is added. Grease spot test: a drop of the sample is dropped onto A permanent translucent spot is seen on the paper. a piece of paper. Table 10.4 Tests for the main food groups. Inorganic nutrients trace element > ~ ll:.Q2 l../V Give three named examples of foods which can be eaten to obtain (i) organic nutrients (ii) inorganic nutrients. Minerals are inorganic nutrients that are required in small amounts for good health and development. Some are required in only trace (very small) amounts for good health and thus are called trace elements . Table 10.5 shows some mineral elements required by plants and table 10.6 shows some minerals required by humans. Element One function Deficiency effects nitrogen (N) (absorbed as necessary for proteins nitrates) small yellow leaves and poor growth magnesium (Mg) necessary for chlorophyll leaves yellow between the veins iron (Fe) necessary for chlorophyll new leaves yellow between veins calcium (Ca) necessary for cell walls poor stunted growth, leaves yellow, terminal buds die potassium (K) maintains the salt balance in cells yellow/brown edges on leaves, edges wither, plant dies early sulfur (S) makes proteins young leaves small, thin, yellow between green veins phosphorus (P) makes some proteins poor growth, small reddish-brown leaves Table 10.5 Some elements needed by plants for healthy growth. Mineral Sources Functions calcium milk, cheese formation of bones and brittle bones and teeth teeth iron red meat, green leafy vegetables formation of haemoglobin Symptoms of deficiency anaemia - tiredness, lack of energy because of a reduction in the number of red blood cells (continued) 104 Ingredients: sugar, enriched bleach flour (wheat flour, niacin, reduced iron, thiamine mononitrate, riboflavin, folate) food starch-modified, partially hydrogenated soybean and cottonseed oils, leavening (sodium bicarbonate, sodium aluminium phosphate), emulsifier (propylene glycol monoester, monoglyceride, sodium stearoyl lactylate), salt, natural and artificial flavours, citric acid, guar gum, xanthan gum, isolated soy protein, whey. Blueberries: blueberries, water. Agure 10.3 There are many additives in the ingredients of manufactured food as seen in this list of ingredients for a blueberry muffin mix. Mineral Sources iodine sea foods, iodised table formation of the salt hormone thyroxin goitre (adults) - reduced metabolic rate, swelling of the thyroid gland cretinism (children) - physical and mental retardation phosphorus meat, fish brittle bones and teeth Functions combine with calcium in the formation of bones and teeth Symptoms of deficiency Table 10.6 Some elements needed by humans for healthy growth. Food additives Many additives a re used in preparing food, for many different reasons (figure 10.3) . Food additives may be natural or artificial. Common natural additives include sugar, corn syrup and pepper. Common artificia l additives are some flavours and sweeteners. The major groups of additives include the following. Dyes and colourings These are purely cosmetic and rarely add nutritional va lu e. Tartazine is used to give a yellow colour to foods and drinks, for example, orange juice, fish fingers. It does, however, h ave some adverse effects as it is associa ted with: • h yperactivity in children; • a llergic reactions; • adverse efiects on asthmatics. Preservatives These make food less susceptible to bacterial infection, so food can be kept for longer periods of time in tins. packets, spreads and bottles without spoiling. When food is produced and packaged it may travel thousands of miles, over several months, before it is used. The health of the general population has improved because preservatives reduce the risk of bacterial poisoning. They are perhaps the most easily justified additive, but only make up l % of a ll additives used. Synthetic flavourings During preparation, food can lose some of its flavour, so these are added to improve or even ch ange the flavour. Flavour enhancers and sweeteners Saccharin is often used to sweeten prepared foods. Monosodium gl utamate (MSG, Ali-jo-moto, Vet-sin) is a commonly used flavour enhancer found in processed foods including soups, fast foods and Chinese foods. Young children and pregnant and lactating women are advised not to eat foods containing MSG as it may be related to asthma, attention deficit disorder, acute headaches, extreme mood swings, depression and paranoia. Propellants Carbon dioxide and nitrous oxide may each be used to form an aerosol, forcing food out of contain ers. 105 Life Processes and Disease Acids These are added to give a sour taste to prepared food. Firming agents Aluminium sa lts are used to retain crispness; gums increase the thickness of sauces and soups. A balanced diet 41% staples (a) cereal grains (b) starchy fruits, roots and tubers 21% legumes and nuts 11 % dark green leafy and/or yellow .. # i'if ~ vegetables 11% it/ 11 % food from f fruits animals Rgure 10.4 Pie chart showing the relative proportions of foods in a balanced diet. ~ ll!Q3 V'--J Describe a meal which includes all the nutrients necessary for good health. We ca11 group all the foods available to humans into six food groups. • Staple foods -These include cereal grain (e.g. rice), cornmeal, wheat flour, oats, sta rchy fruits, roots, tubers. • Peas and beans (legumes) - These include red beans, pigeon peas, black eyed peas, broa d beans. • Dark green, leafy vegeables and yellow vegetables - Cabbage, pak choi, lettuce, spinach are leafy examples; pumpkin and carrot are examples of yellow vegetables. • Foods from animals - Fish, poultry, meat, milk, eggs, cheese are all food s from animals. • Fruits - Citrus fruits, bananas, apples are all examples. • Fats - These include oils, butter, margarine and food with a high proportion of fat such as ca kes, biscuits. Figure 10.4 shows th e components of a balanced di et. Each block represents a food group and the size of the block indicates the proportion of the ctiet which. that food group should constitute. Balanced diet related to age, sex and activity of an individual Nutritional requirements vary with age, sex and activity. Energy requirement Energy requirements are generaJJ y greater for men (figure 10.5). They usually have more muscle, relatively less fat and weigh more than women. In women, the energy requirements are higher during the last three months of 12 000 - Energy (kcal per day) emae • mae • pregnancy. Extra energy is needed for growth of the fe tus and deposition of fat 10 000 in preparation for breast feeding. This requires extra energy because the energy 8000 needed by the baby for rapid growth in early postnatal life comes from its 6000 mother's milk. Energy requirements for a growing 4000 individual increase up to about the age of 18 years, when the energy requirements 2000 are the greatest. The requirement for energy then decreases as the person 0 1-3 I 7-10 I 15-10 I 23-26 I 31-34 I 39-42 I 47-50 I 60-64 I 75+ gets older. 4-6 11- 14 19--22 27-30 35-38 43-46 51-59 65-74 Physical activity of an individual Age (years) varies with both occupation and leisure. Rgure 10.5 Ener requirements for men and women vary as they get older Some people are mostly sedentary 1 106 10 · Feeding and Digestion (sitting for much of the time, such as in an office) and others are very active. Energy req uirements for different levels of activity can vary greatly. Protein requirement Men require more protein than wo men from around the age of 11 years onwa rds. This is when the muscle-to-fat ratio starts to differ because of the development of secondar y sexual characteristics. Women start to store fat in their hips and breasts and men develop more muscle, especia lly on their shoulders and legs. Extra protein is required by women during pregnancy and breastfeeding. Requirements of minerals and vitamins Mineral intake is especially important during pregnancy and lactation. The mother's diet must con tain sufficient iron, calcium, vitamin C, folic acid, and everything needed to make the baby's tissues inccluding blood, bone and muscle. Extra folic acid may be given to the mother to red uce the risk of spina bifida in the baby. Malnutrition malnutrition > Malnutrition means bad nutrition, and can be applied to under-eating, overea ting and bad eating habits. Malnutrition is the cause of many diseases like deficiency diseases, obesity, hea rt diseases and anorexia. Education on ba lanced di et and good health is very important in preventing the occurrence of many diseases. Under-eating Figure 10.6 A child suffering from kwash1orkor and marasmus. fht•W&WIJ Starvation is one kind of under-eating and is most often associated with developing countries. It means not eating enough food to supply the energy requirements for daily activHies. Also, not enough protein and vitamins are eaten which are necessary for growth, development, resistance to infecti on and a healthy life. Marasmus and kwashiorkor are common conditions ca used by under-eating (figure 10.6). Some signs and symptoms of marasmus and kwash.iorkor: • very underweight (less than 60 % fo r age); • thin muscles, thin a rms and legs; • redu ced growth may lead to reduced mental development; • reduced resistance to infection; • sometimes swelling of the body tissues with fluid (oedema); • shru nken features giving the face the appearance of an o ld person; • hair becomes thin, sparse and easily removed; • rough skin; • little interest in surrou ndings. Anorexia is another kind of under-eating but is associated with developed countries. It is the voluntary refu sa l to ea r and is most commonly found in teenage girls, though teenage boys can also get this illness. It is as much a psychological illness as a physical one, because the refusa l to eat is based on a poor self-image. The patient continues to think that they are fat even when they are underweight. Recovery requires treatment for the psychological condition as well as an improved diet. 107 Life Processes and Disease Obesity FMMIMJ r;rrmmm CHAPTER 13 Obesity results from over-eatin g, especially of fatty foods, a nd a lack of exercise. Excess fat accumulates in the body and body mass increases to well above norma l (figure 10.7). Obese people are predisposed to many diseases like diabetes (see below), hypertension (high blood pressure, chapter 13 ), coronary heart disease, arthritis, cancer and stroke. Over-earing can be prevented by earing sensibly, and engaging in regular aerobic exercise. Heart diseases and cardiovascular disease corona heart disease > Some diseases of the heart and cardiovascular system develop slowly after years of living on a diet of fatty foods and not much exercise. Atherosclerosis is a disease of blood vessels . It is a thickening of the inner layers of artery walls, even tu a lly the artery may become blocked. If the affected artery is the coronary artery, the heart muscle is not supplied with food and oxygen and char part of the hean dies. This could result in a heart anack (coronary heart disease). A similar blockage in a blood vessel in the brain results in a stroke. The rough surface of the thickened wall could also encourage formation of a blood clot which may block blood vessels. Diabetes Rgure 10.1 A person 1s described as 'obese· if they weigh at least 20% more than the average for someone their height. holozoic nutrition > Diabetes is a group of metabolic diseases in which a person has high blood sugar, either because rhe pancreas does not produce enough insulin, or the body cells do not respond to the insulin that is produced. Management of diabetes concentrates on keeping blood sugar levels as close to normal as possible, which can usua ll y be accomplished with diet, exercise and appropriate medication. Obesity, high blood pressure and lack of regu lar exercise accelerate the harmful effects of diabetes. Holozoic nutrition Mammals, including humans, feed by taking in or ingesting organic food. This particular type of heterotrophic nutrition is termed holozoic nutrition, and includes ingestion, digestion, absorption, assimilation and egestion. • Ingestion - The act of taking in food (into the mouth in humans). • Digestion - The process of breaking down large, complex, insoluble material into sma ll, simple, soluble molecules. The teeth physically break the food into pieces, and enzymes then chemically break down the large molecules into smaller ones. • Absorption -The diffusion of soluble fo od molecules (glucose, amino acids, fatty acids, glycerol, vitamins, minerals and water) into the bloodstream. • Assimilation - When these food molecules are taken from the blood and used by the body cells for respiration, growth and development. • Egestion - The process by w hich the undigested part of rhe good is removed from lhe body. It is also known as defecation. Digestion The physical action of teeth physical digestion > 108 Teeth h elp with the physical breakdown or mechanical breakdown of food. This is ca lled physical digestion. The structure of a typical tooth is shown in figure 10.8. 10 · Feeding and Digestion I -~---- enamel (hard material) crown ~ gum ----- root - - - - - -- pulp cavity (contains blood vessels and nerve endings) - - - - - cement (holds the tooth in the bone) - - - - - jaw bone - - - - - - - nerve Rgure 10.8 A section through a tooth showing the general structure. Mammals differ from other animals in that they have more than one type of tooth. In humans, there are four kinds and Table 10.7 summarises their structures and functions. Figure 10. 9 shows the position of the different teeth in the mouth. Type incisor canine Shape Function chisel-shaped for cutting 1 root pointed or dagger-shaped 1 root cutting food biting off bits of food grasping and tearing food (well developed in carnivores for tearing flesh) premolar flat with cusps or bumps on crush and grind food the fairly broad surface 2 pointed cusps 2 roots molar flat, with cusps on the broad surface 4 or 5 cusps 2 or 3 roots large back teeth to crush and grind food Table 10.7 The shape and function of human teeth. mJU:lrffimlJ Milk t eeth are the first set of teeth in humans. They appear singly or in pairs from the time a child is approximately 3 months old. By age 3 years, most children have about 20 teeth. These begin to fall out when a child is about 7 years old. 109 Life Processes and Disease permanent teeth > wisdom teeth > Permanent teeth are the teeth which replace the ones that have fallen out. An additional 12 new teeth also erupt which make up the complete set of permanent teeth by about age 17. Most adults have 8 incisors, 4 canines, 8 premolars and 12 molars. The 4 molars at the end of the jaw are the last set to grow through the gum and are called wisdom teeth. molars, Q:ioot-'T--1::>,._,..,r--duct from salivary gland The u se of fluorides Figure 10.9 There are four types of teeth in humans. The use of fluorides in toothpaste or in water supplies helps to prevent tooth decay in humans. Fluorides are compounds of the element fluorine which improve resistance to tooth decay by hardening the enamel. When permanent teeth are developing in children, the use of fluorides is effective in helping these 'new' teeth resist decay. Compounds of fluorine can act as serious pollutants in the environment. In the production and extraction of aluminium from bauxite, sodium aluminium fluoride (Na 3AIF 3 ) is used to lower the melting temperature of alumina from 2050 °C to 950 °C, so that less energy is used. The exhaust gases from the manufacture of aluminium then contains fluorides. Fluorides seem to affect trees, and on grass they can enter food chains. The teeth and bones of grazing animals are affected badly. Although fluoride provides resistance to tooth decay in humans, an excess in the environment can be harmful. Also fluorides can be dangerous to young children and they should never swallow fl uoridated toothpaste. The chemical action of enzymes in digestion Despite the action of teeth in breaking down food physically, food must also be chemically broken down. Chemical digestion involves enzymes . Enzymes are organic catalysts, which means they speed up chemical reactions occurring in living cells. During digestion, enzymes speed up the rate at which the large, insoluble food molecules are broken down into small, soluble food molecules. chemical digestion Practica] activity SBA 10.2: The action of an enzyme, enzymes (amylase) polysaccharides page 349 disaccharides + monosaccharides en zymes (protease) proteins amino acids enzymes (lipase) lipids------+ fatty acids +glycerol £?.Sb IT:Q4' V'--1 Define the terms 'physical digestion' and 'chemical digestion'. 110 There are thousands of enzymes bu t all have similar properties. • They are all proteins. • Each enzyme is specific for the type of chemical reaction it speeds up. • They are required in small amounts. • They are inhibited or prevented from working by poisons like cyanide and arsenic. 10 ·Feeding and Digestion • They work best at a particular temperature called the optimum temperature (Figure 10.10). • They are denatured or destroyed by high temperatures. • They work best at a particular pH, called the optimum pH (Figure 10.11 ). optimum temperature - enzyme works best at this temperature Rate of reaction rate increases as the The substance that the enzyme breaks mm;rmm down is called the substrate and the 1.u.1.rmu:tJ substances that are made are known as the products. Digestion and absorption along the alimentary canal .--<3-- - pH at which enzyme works best lower pH optimum pH for enzyme I enzyme breaks down - at higher temperature 20 30 40 50 60 Temperature ("C) Figure 10. 1O The effects of temperature on an enzyme-catalysed reaction. The activity of the enzyme is small below 20 °C, rises steadily to a maximum near 50 °C, then falls sharply. The alimentary canal (gut) is a long muscular tube, which extends from the mouth to the anus (figure 10.12). It consists of the major parts of the digestive system w here digestion and absorption of food take place. higher pH Rate of reaction gall bladder - -- - bile duct - ---=--+ optimum pH of pepsin !\ 2 4 small J duodenum intestineC leum 6 8 10 pH caecum - - - - - appendix ---.-- - - - - -- • pepsin works best at pH 2.5 • trypsin works best at pH 8.0 • most enzymes in cells work best at pH 7.2 Figure 10. 11 The effects of pH on an enzyme-catalysed reaction. The activity of the enzyme rises sharply near the optimum pH and falls just as sharply as that pH 1s exceeded. ft'tlMU salivary am lase > Figure 10.12 The human alimentary canal. The mouth Digestion begins in the mou th, after food is ingested using the hands, lips and tongue. The teeth break the food down into smaller pieces. This is done with the help of saliva, which moistens the food. Saliva is secreted from the salivary glands and is a mixture of water, mucus and salivary amylase . The water 111 Life Processes and Disease and mucus soften the food, while the enzyme salivary amylase begins to digest the starch in the food. The mucus also helps food to move easil y a long the alimentary ca nal. Salivary amylase breaks down the bonds in starch by h ydrol ysis, and so hydrolyses sta rch into smaller and sma ller cha in s, eventua lly to gl ucose molecules (fig ure l 0. J 3). glucose ••••••••••••• ! amylase starch - long chain of glucose addition of water (hydrolysis) maltase •• •t• •• •t• •t• ••• bond broken bond broken I smaller chains bond broken eventually, all the bonds will be broken ••••••••••••• "' glucose Figure 10.13 Starch is broken down to glucose by the enzyme amylase. IWlill"-IJ So both physica l digestion and chemical iligestion occur in the mouth. The tong ue churns food a nd rolls it into a bolus, or a ba ll -like structure, which is then swa llowed. The oesophagus oesophagus > G!It!IG'UW When food is swallowed it enrers rhe oesopha gus. The trachea, or windpipe, which opens to the lungs lies to the front of the oesophagus. If yo u press your hands gently on your throat, yo u can feel the rings of cartilage of the trachea . The oesophagus is directly behind this. When food is swallowed, it is prevented from going into the trachea by a small, flap-like structure ca lled the epiglottis, which covers the trachea as you swallow (figure 10.14). It is therefore impossible to swallow and inhale at the same time. 1Ty it! food bolus goes Into the oesophagus air can go .._,....,.,..____,_ into the trachea oesophagus Figure 1O. 14 The epiglottis stops food entering the trachea when you swallow 112 trachea closed 10 ·Feeding and Digestion l•MMflM!O.fJ However, if a person is eating while talking and laughing, the food can become stuck in the trachea. The Heimlich manoeuvre, which forces air rapidly out of the lungs, can be applied to remove the stuck food (figure 10.15). The oesophagus is a muscular tube and food moves down it by peristalsis. This is a wave of muscle contraction that moves downward and squeezes the food into the stomach . (b) clasp both hands around the waist (a) give five sharp slaps between the shoulder blades (c) pull sharply upwards and below the ribs Rgure 10.15 The Heimlich manoeuvre. The stomach oesophagus muscles contract, narrowing L ....- - - the oesophagus and pushing the bolus down bolus is pushed down and into the oesophagus The muscular wa lls of the stomach rela x and contract to churn the food as it arrives. Food is mixed with enzymes, mucus and hydrochloric acid. This mixture is called chyme. The stomach walls are dotted with pits leading to gastric juice glands that secrete gastric juice into the stomach (figure 10.17). pits in the stomach wall secrete gastric juices Figure 10.16 A bolus moves down the oesophagus to the stomach by peristalsis. part of the stomach wall magnified ~=:::::..~ ' ~ Figure 10. 17 Gastric juice pours out of pits in the stomach wall. Gastric juice consists of: • mucus; • hydrochloric acid; • pepsin. H§elelhU Digestions of proteins begins in the stomach as the long protein chains are broken down b y the enzyme pepsin into amino acids. Hydrochloric acid provides the acidk medium in which pepsin works most efficiently. It also kills any pathogens that may have entered the body with the food. The stomachs of young mammals produce the enzyme rennin. which curdles or dots the milk that they get from their mother. The milk proteins 113 Life Processes and Disease l!XEM%U are then broken down by pepsin into shorter polypeptides and then into amino acids. After one or two hours in the stomach, small amounts of chyme pass into the next region of the alimentary canal, the duodenum as the sphincter muscles at the bottom of the stomach relax and open. Peptic ulcers A peptic ulcer is a hole or 'sore' in the stomach lining. It used to be thought that excessive secretions of hydrochloric acid and pepsin damaged the stomach wall and caused these ulcers . But recent research has shown them to be caused by the presence of Helicobacter pylori, a species of bacterium that ljves in the gut. Some patients have been successfully treated with antibiotics; others have been successfully treated with a drug which suppresses the production of stomach acid. The duodenum duodenum > emulsification > pancreatic juice > ~ ll:QS V"...J Describe, giving examples, the role of enzymes in digestion. ~ ll:Q6 V"...J Copy and complete this table. Part of alimentary canal mouth stomach duodenum Importance The duodenum is the first region of the small intestine. It receives chyme from the stomach and secretions from the gall bladder and pancreas. Bile, which is produced by liver cells and stored in the gall bladder, breaks down large lumps of fat into tiny droplets. This process, called emulsification, increases the surface area of the fats making it much easier for the enzyme lipase to digest the fat. Pancreatic juice is secreted from the pancreas and contains many enzymes. • Amylase continues the digestion of starch into maltose before it can be digested into glucose. • Lipase digest fats or lipids into fatty acids and glycerol. • Trypsin is a protease (an enzyme which digests protein) that breaks down long protein d1ains into shorter ones (polypeptides) so that they can be broken down into amino acids by other proteases. These emymes work best in a neutral environment, but the chyme, which came from the stomach is aciillc because it contains hydrochloric acid. Pancreatic juice also contains sodium hydrogencarbonate which neutralises the hydrochloric acid so the pH of the mixture increases to pH 7- 8, which is optimum for pancreatic enzymes. Bile also contains bile pigments which are waste products from the liver that need to be excreted. The food is now fully broken down physically and chemically into the endproducts of digestion. The ileum llt:JilulJ The ileum is the second part of the small intestine and is the site of absorption in the alimentary canal. By the time food reaches the ile um, it has been broken down into glucose, fatty acids, glycerol, amino acids, vitamins, minerals and water. These nutrients are small enough to be absorbed and used by the body. The structure of the ileum has many adaptations which make it good for absorption. • It is about 6 metres long and has a large surface area . • There are folds and ridges that are invaginations in the intestinal walls that increase the surface area even more for efficient absorption of nutrients mlllJ (figure 10.18) . They have villi (finger-like projections) on their surfaces. They are covered with epithelial cells which themselves have microscopic ml!ijM!WfB folds on their surface, called microvilli. These further increase the surface area for absorption. 114 10 ·Feeding and Digestion 1Fmirm10 • The epithelial cells have large numbers of mitochondria, which provide the energy fo r transport of the nutrients from the ileum to the blood. • Each villus has a good blood supply in the form of a dense network of capillaries that transport those nutrients that do not diffuse across and require energy away from the ileum to the liver for processing. • Ea ch villu s contains a lacteal, or lymph capillary, whid1 absorbs fatty acids from the digestion of fat. r.-- - - - villus wall. one cell thick - diffusion of food molecules can occur readily 1a--- -T"--<-- - capillary network - food molecules are absorbed into the blood -=---1--~r-- lacteal - larger food molecules (fatty acids) are absorbed here 1----++-----+-- Small intestine large Intestine Figure 1O. 19 The arrangement of the intestines in humans. Figure 10.18 (a) The wall of the ileum is made up of villi that increase the surface area. (b) Diagrammatic section through a villus. The colon lb@t:t•» mt.htJ After most of the nutrients have been absorbed into the blood in the ileum, the remaining intestinal contents, now called faeces , continue to move slowly along the colon, or large intestine. The main fun ction of the colon is to rea bsorb water from the faeces into the bloodstream so that water loss from the body is mininlised. Th e arrangement of the small and large intestine in humans enables a very long tube to be packed into a very small space (figure 10.19). The rectum Faeces con sist of undigested cellulose and plant fibre, dead bacteria and intestinal cells scra ped off the gut walls. The faeces are stored temporarily in 115 Life Processes and Disease li4+Jil!uQ l#le!IW the rectum. As faeces accumulate, pressure increases in the rectum which results in a desire to defecate, or expel faeces through the anus . About 24 hours after earing, food has traversed the length of the alimantary canal. most of the nutrients have been absorbed, and the undigested part is ready to be expelled . Constipation constipation > ~ IJ:Q7 \..A-I Describe the route taken by a bolus from the mouth to the anus. Constipation results from poor earing habits. A diet lacking fibre can lead to a blockage of the alimentary canal. Egestion of undigested waste material cannot then occur normally. Constipation sometimes results in haemorrhoids, which are protrusions of tissues through the anus because of forced 'pushing'. Constipation also increases the chance of developing colon cancer. Dietary fibre, the undigestible pan of food from plants (mainly cellulose), aids peristalsis and prevents constipation (figure I 0.20). (a) (b) water reabsorption occurs in colon - undigested food with fibre is bulky and pushed easily along the colon I peristalsis does not take place readily - undigested food has no fibre - stored temporarily in the rectum then egested peristalsis rectum anus water reabsorption occurs ~·~1111!!!!!!1!1. . . . . .~~~~~~~~~0 faeces stays in colon and forms a hard solid mass that is difficult to move - this is constipation Figure 10.20 Dietary fibres help to prevent constipation . (a) The faeces containing fibre stay bulky and soft and are easy to egest. (b) Without fibre, the faeces become hard and solid and are difficult to get rid ot. Assimilation assimilation > Assimilation is the process of incorporating and making use of the digested food into the body. These absorbed food molecules may be sto red by the body for future use, broken down to produce energy or used for growth, repair and to maintain good health . Monosaccharides {glucose) This is taken to the liver, then to the rest of the body where: • it is used in respiration; • excess amounts are converted into glycogen in the liver, and stored in liver a nd muscle cells; • excess amounts are converted to fat and stored under the skin or around organs. Amino acids These are taken to the liver and then to the rest of the body where: • they are u sed by the body cells for growth and repair; 116 10 · Feeding and Digestion • they are used to make hormones and enzymes; • excess amounts are converted to glycogen or fat; • excess amounts are broken down, or deaminated, in the liver and converted to urea to be excreted by the kidneys. Fatty acids Fat molecules are carried by the lymph to the blood and are: • stored u nder the skin and around the organs; • used to form new membranes in cells and organelles; • used for respiration in some circumstances. Functions of the liver The liver is one of the most important organs in the body as it has many functions that are essential to keeping the body healthy. • Carbohydrate metabolism - Excess glucose is stored up as glycogen and reconverted to glucose when blood sugar levels fall. Excess carbohydrate may also be converted to fat . • Lipid meta bolism - Excess cholesterol is excreted into the bile and removed from the body. • Protein m e tabolism - Excess amino acids are broken down to form ammonia and then converted to the less toxic substance, urea. Urea is transported to the kidneys by the blood and excreted in urine. • Production of bile - Bile salts are produced and temporarily stored in the gall bladder. They then travel to the duodenum to aid in digestion. • Storage o f vitamins - A number of vitamins are stored in the liver and released if the diet is deficient in vitamins. • Storage of minerals - The liver also acts as a store for some essential minerals, such as iron and potassium. (This is why .liver is a nutritious food.) They can be released into the body if the diet lacks these minerals. • Synthesis of p lasma proteins - These important proteins are found in blood plasma. For example, prothrombin and fibrinogen are needed for blood dotting. • D e toxification - Toxic materials absorbed from the intestines are stored, broken down or removed by the liver. • Breakdown of red blood cells - Red blood cells are broken down (they live only for three months) and the iron components may be stored, reused or excreted as bile pigments. • Production of h eat - A lot of metabolic activity occurs in the liver, which requires a considerable amount of energy. Much of the energy from respiration is lost as heat, so the liver generates a lot of heat. In mamma ls (including humans) and birds, the liver also plays an important role in keeping the body at the right temperature inside. Chapter summary .. • A balanced diet is important for good health. • A balanced diet has appropriate proportions of carbohydrate, proteins, lipids, vitamins and minerals. Water and fibre are also important. • Plants need minerals for healthy growth. ~ 117 Life Processes and Disease r • Ingestion in humans is the intake of food using the mouth, hands and lips. • Physical digestion involves breakdown of food by teeth, and chemical digestion is the breakdown of food by enzymes. • In humans, there are four different kinds of teeth: incisors, canines, premolars and molars: - incisors are chisel-shaped and are used for biting food; - canines are dagger-shaped and are used to tear or rip food; - premolars and molars are used to chew food into small pieces. • Enzymes are biological catalysts: they speed up the chemical breakdown of food. • Food is broken down from insoluble to soluble substances by enzymes. • Digestion takes place in the mouth, stomach and duodenum. • Absorption is the movement of the end-products of digestion into blood. It occurs in the ileum. • The ileum has several adaptations for absorption, such as a large surface area provided by the villi. • The food is assimilated when the body cells make use of it. • The liver has many important functions relating to the assimilation of food. ITQ1 (i) Diet is the quan ti ty and quality of food eaten every day by an individual. (iii) A balanced diet has the quantity and quality of food needed to maintain good health. ITQ2 (i) Organic nutrients can be found in food such as chicken, bread, livei:. (ii) Foods which contain inorganic nutrients include: lettu ce, liver, banana. ITQ3 Your a nswer needs to includ e an example from each food group. For example: • Staple foods rice • Peas and beans red beans • Dark green leafy vegetables salad leaves, spinach • Food from animals chicken • Frui.t orange juice • Fats oil for cooking ITQ4 Physical digestion is the mechanical breakdown of food into small pieces by the teeth. Ch emical digestion is th e breakdown of food by enzymes into soluble compounds. ITQS Enzymes speed up the breakdown of food molecules into their respective end-products. Enzymes are not used up themselves. Some examples are: • am ylase, which breaks down starch eventually to glucose; • pepsin, which breaks down proteins into polypeptides; • lipase, which con verts lipids into fatty acids and glycerol. ITQ6 Part of alimentary Importance canal Mouth Food is moistened and lubricated. Physical digestion takes place. The conversion of starch to maltose (chemical digestion) begins. Stomach Acid contents kill bacteria in food. Food is churned into chyme. In babies, curdling of the milk occurs. In adults, protein digestion begins in the stomach as proteins are converted to polypeptides. (continued) 118 10 · Feeding and Digestion Part of alimentary Importance canal Duodenum Chemical digestion takes place here.The enzymes amylase, trypsin, and lipase are secreted. They break down starch to maltose, which is further broken down into glucose and fructose. Polypeptides are broken down to amino acids. Lipids are broken down to fatty acids and glycerol. ITQ7 mouth ..... oesophagus --+ stomach ..... duodenum ..... ileum ..... colon ..... rectum ..... anus Examination-style questions (i) The starch test can be summarised in a series of stages: 1 A leaf is dipped in boiling water for 10 seconds. 2 The leaf is immersed in ethanol which is placed in a water bath at 80 °c. 3 The leaf is then dipped. in tap water. 4 The leaf is tested with iodine. (a) Why was the leaf dipped in boiling water? (b) What is the role of ethanol? (c) Describe the iodine test for starch. (d) A starch test was performed on a leaf and positive results were seen. What interpretations can be suggested about activities in the leaf? (ii) Explain the meaning of the term 'destarched ' as it refers to a leaf. Give details of the process by which a leaf is destarched. (iii) Describe an investigation to show that plants need C02 for photosynthesis. 2 (i) Five main processes occur in holozoic nutrition. Define each in the order in which they occur. (ii) Give two functions of the tongue during eating. (iii) Describe how food moves down the oesophagus. {iv) Name the enzyme found in saliva and describe its action. 3 (i) List the functions of these substances in the stomach: (a) mucus {b) hydrochloric acid (c) the enzyme pepsin. (ii) A peptic ulcer is a damage to the stomach wall. It can be very painful and is easily infected. (a) How can the stomach all be damaged? Give details of how ulcers are formed. (b) Why is an ulcer painful? (c) Why is an ulcer easily infected? (iii) What are the products of digestion of: {a) starch? (b) lipids? (c) protein? 4 (i) Explain how the structure of the wall of the small intestine is adapted for its function of absorption. (ii) The table below refers to some enzymes involved in digestion of food in the digestive system. Copy and complete the table. Name of enzyme Site of production Production of reaction Fatty acids and glycerol Salivary gland Stomach wall Maltase ------- 119 Life Processes and Disease (iii) The diagrams below show different types of teeth found in a human mouth. Copy and complete the table below to show the type and function of each tooth. c B A Tooth A c B Type of tooth Function of tooth 5 (i) List the components of a balanced diet. (ii) Define (a) obesity (b) malnutrition; (c) deficiency disease (d) food additive. (iii) Vitamins and minerals are essential to a healthy life. Explain why: (a) pregnant women must include calcium and iron in their diet; (b) it is recommended that we eat an orange a day. (iv) Nutritional requirements vary with age, sex and activity. Describe the nutritional requirements of: (a) a 19-year-old male who plays competitive football; (b) a 19-year-old female who loves to read. 6 The figure below shows the graphs obtained from an investigation into an enzymecontrolled reaction. Each represents an experiment performed to study the time taken for the enzyme to break down the substance. Graph 1 shows the time taken under different temperature conditions with the reaction at a constant pH of 6.7. Graph 2 shows the time taken under different pH conditions at a c~nstant temperature of 40 °C. Graph 1 Graph 2 at a constant pH 6.7 at a constant temperature of 40°C 16 14 12 10 Time (minutes) 8 .J.....-__ -- 6 4 2 00 10 120 20 30 40 50 Temperature (°C) 60 70 2 3 4 5 Temperature {°C) 6 7 8 10 · Feeding and Digestion Study the graphs and answer the following. (i) (a) At what temperature did the reaction occur in the shortest time? (b) At what pH did the reaction occur in the shortest time? (ii) In graph 1: (a) Why did the reaction slow down at higher temperatures? (b) What effect on the reaction rates is shown by a steady increase from low to medium temperatures? 7 An experiment was carried out to investigate the effect of temperature on the rate of an enzyme-controlled reaction. The concentration of enzymes and substrate were kept constant at all the temperatures investigated. The results are shown in the table below. Temperature {°C ) Rate of reaction (mg of products per unit time) 5 0.3 10 0.5 15 0.9 20 1.4 25 2 30 2.7 35 3.3 40 3.6 45 3.6 50 2.3 55 0.9 60 0 (i) Plot the results on graph paper. (ii) Interpret and explain them as fully as you can. (iii) If the enzyme used was amylase, name the substrate used in the experiment. (iv) If the enzyme used was amylase, what effect would pH have on its activity? 8 The table below shows the activity on an enzyme in relation to pH. pH 4.5 5.5 6.5 7.5 Units of enzyme activity 3.1 9.6 14.5 10.1 (i) At which pH is most activity seen? (ii) At which pH is least activity seen? (iii) What is the optimum pHfor this enzyme? (iv) Give an example of an enzyme that might give these results. (v) Give examples of enzymes that would not be expected to give these results. 121 fl I fl describe the process of aerobic respiration 0 distinguish between aerobic and anaerobic respiration I describe the uses of anaerobic respiration to humans 0 understand simple investigations that show the products of respiration understand that respiration takes place at the level of the cell understand the function of ATP respiration aerobic anaerobic r mitochondrion humans ' bacteria yeast ADP~ATP oxygen debt alcohol production bread production yoghurt production Aerobic respiration Respiration is the process by which the energy in food is made available for a cell to do the work necessary to keep it a li ve (figure 11. 1). When oxygen is used in the reaction , we call it aerobic respiration . The process is cata lysed by enzymes and is also ca lled cell ular. internal or tissue respiration. energy for building up materials food respiration ....,... energy I energy for contraction I I I Some of the uses of the energy made by a cell. I I I I .. I I organism Is alive when all the cells are alive and working / can move can grow can reproduce Some of the activities of an organism. They all require energy. can respond Figure 11.1 An organism 1s alive when all its cells are respiring 11 · Respiration How do food and oxygen get to respiring cells? ~ IT:Q-1 V'--1 What is the purpose of respiration? ~ IT:Q2 V'--1 When do animal cells and plant cells respire? A respiring cell needs both food and oxgen (figure 11.2 ) • Food - In animals, food eaten is digested and absorbed into the bloodstream. The end-products of digestion eventually reach all the body cells. In plants, the food made in photosynthesis in the leaves travels around in phloem tubes and eventually reaches all body cells. • Oxygen - In vertebrates, oxygen comes from the air that is inhaled into the lungs. It diffuses into the bloodstream and is transported to all the bod y. cells. In plants, some of the oxygen comes from photosynthesis and some through diffusion in through the leaves and other parts of the plant. blood rich in 0 2 is taken to all body cells blood rich in glucose is taken to all body cells • body cell where respiration occurs blood rich in C02 is taken to lungs to get rid of C02 Figure 11.2 A respiring cell in a mammal is supplied with food and oxygen. Product and waste product of aerobic respiration Practical activities SBA 11 .1: Is carbon dioxide produced during respiration? page 350 SBA 11.2: Is heat produced during respiration? page 351 SBA 11.3: Is oxygen used up during respiration? page 352 In both plants and anima ls, the type of food from which energy is released is usually glucose. Energy is released when glu cose combines with oxygen (the oxidation of glucose). Carbon dioxide is a waste product of this reaction. In vertebrates, carbon dioxide diffuses back into the bloodstream , to be taken to the lungs and exhaled out of the body. In plants, it is used for photosynthesis during daylight. How does aerobic respiration occur? respiration equation > ~ IT:Q3 V'--1 What is the important product of respiration? What are the waste products of respiration? r!u:IJ Respiration or cellular respiration occurs in a series of steps, each of which is catalysed by enzymes. The overall process can be summarised in words or by the respiration equation below: glucose + oxygen -+ energy + carbon dioxide + water C6 H 12 0 6 + 60 2 -+ energy + 6C0 2 + 6H2 0 During aerobic respiration, glucose is broken down completely into carbon dioxide and water. At each step in the breakdown of glucose, energy is released. This is used to con vert a d1emi cal called ade nosine diphosphate (ADP) into adenosine triphospbate (A T P ). Ead1 molecule of ATP acts as a little 'packet' of energy. The energy can be stored and used later when needed. There are m an y advantages of storing and using energy in small packe ts like this. • The energy ca n be released from ATP wherever and whenever it is required by a cell. 123 Life Processes and Disease • The energy can be released rapidly. • Energy is not wasted. A large amount of energy is released by oxidising one glucose molecule and ma ny ATP molecules are formed. A cell may not require very much energy a t on ce. By storing the energy in small packets in ATP molecu les, the cell can use sm all amounts of energy as required (figure 11.3). • The energy can be used to drive many different chemical reactions rapidly. • Energy can be stored as ATP in one part of a cell and transpo rted and used elsewhere without causing reactions in between . adenosine ( ADP r"'"--•: energy \..+ATP c ATP ADP oxidation ,. . . . _ _ " energy ( . of ATP glucose 1""'' - - • . energy ,....,_...,. .energy high energy bond ADP I ADP (. ATP the energy from the breakdown of glucose is stored in this high energy bond ATP ATP is a packet of energy! Rgure 11.3 The oxidation of glucose results in the formation of many molecules at ATP. Ene rgy production and utilisation are very effici ently and carefully controll ed by the cell. Where does aerobic respiration occur? mitochondrion > ~ ll:Qll Respiration occurs in an organelle called the mitochondrion (figu re 11.4). Mitochondria are present in all cells, animal and plant, and are sometimes referred to as the 'power houses' of the cell. The en ergy stored in ATP (aden osine triphosphate) is released when it is converted back to ADP (adenosine diphosphate). v......i Where does respiration occur? co2 transported to lungs ~ 11:Q5 v......i Give three reasons why it is advantageous to store energy in small packets. 0 2 transported to cell --+- - energy is released during respiration in the mitochondrion _ _ _...,. energy ('' -"'-) ATP + energy used by the cell + p ADP + p + phosphate Figure 11.4 Energy can be released from ATP made during respiration in the mitochondrion. 124 11 · Respiration Anaerobic respiration anaerobic respiration > Respiration can also occur without oxygen and this type of respira tion is called anaerobic r espiration. Both anaerobic and ae robic respiration involve the breakdown of glucose (figure 11.5). However, in anaerobic respiration, it is n ot completely broken down. (a) Plant and animal cells can respire aerobically. ID1. > ~ " ' " '"""' 0 oxygen oxygen ~ Q / / glucose water I) energy • . / water oa<bon dioxide carbon dioxide (bl Animal and plant cells can respire anaerobically but do so in different ways. glucose - - -.. GJ '.:: glucose Figure 11.5 Cells can respire anaerobically and aerobically. ~ IT:Q6 l/"-.J Give two examples of organisms that respire aerobically, and two that respire anaerobically. One mole (mot) of a chemical contains 6 x 1022 molecules of that substance. Habitats such as stagnant ponds and deep underground have no oxygen. Organisms living there have adapted to survive without oxygen; the y must respire anaerobically all the time. These organisms indude some worms, some bacteria and some fungi. Parasites that live inside other organisms, such as the gut parasite tapeworm and bacteria, also live in conditions that lack oxygen. They must also respire anaerobically. Many living cells that normally respire aerobically can also respire anaerobically if oxygen is lacking. Animal and plant cells do this in different ways (table 11. 1). Aerobic respiration Anaerobic respiration uses oxygen does not use oxygen • in plants and animals: C6H1206 + 602 -+ energy + 6H20 + 6C02 water and carbon dioxide are waste products • in animal cells: C6H1206 -+ energy + 2C3H603 lactic acid is the waste product • in plant cells: C6H1206 -+ energy + 2C2H50H + 2C02 ethanol and carbon dioxide are waste products large amounts of energy produced (2880 kJ per small amounts of energy are produced (150 kJ mole for the breakdown of glucose) per mole for breakdown of glucose in animals and 21OkJ per mole in plants) glucose is broken down completely to inorganic glucose is not broken down completely molecules ethanol and lactic acid are organic molecules that still contain useful energy occurs in the mitochondria of the cell occurs in the cytoplasm of the cell Table 11.1 Differences between aerobic and anaerobic respiration. 125 Life Processes and Disease Anaerobic respiration in humans Human cells respire normally aerobically. However, during strenuous exercise, muscle ce lls need much more energy for the extra work that they are doing. The breathing rate and heart rate increase in an attempt to get more oxygen to these cells. Sweating occurs to help lose some of the extra energy as heat. With increased respiration, a lot of heat is produced which is lost from the skin (chapter 19). After a period of sustained exercise, the oxygen supply becomes inadequate, even with panting for air and the increased heart rate. The muscl~ cells then respire anaerobically. Energy is still produced when cells respire anaerobically, although it is a much sma ller amount for ead1 molecule of glucose. This means that they ca n continue to do work (contract and relax). CHAPTER 19 anaerobic respiration Figure 11.6 The build-up of lactic acid 1n muscle cells after strenuous exercise can be painful lactic acid + energy glucose in muscle cells UillU@@t•D ltfU[1!i!:il ~ IT:Q7 V'-1 Humans respire mostly aerobically. When do humans respire anaerobically? oxygen debt > Lactic acid is a waste product of this reaction. It builds up in the muscles and causes them to ache (fi gure 11.6). This is often called fatigue . After exercise, the body has to get rid of the lactic acid as quickly as possible. This is done by using oxygen to change it back to a chemical like glucose so that it can be broken down completely in aerobic respiration. When anaerobic respiration occurs in muscles it is in addition to aerobic respiration and not in place of it. A person continues to 'breathe hard ' or pant for some time after exercise as oxygen is needed to get rid of the lactic acid. The oxygen required to get rid of the lactic acid is called the oxygen debt (figure 11. 7). ~ cell during __ _. used for contraction etc. anaerobic respirat~ energy (smaller amount) - - - - - IT:Q8 V'-1 Q What is alcoholic fermentation and what are two of its uses? ~O ' Y Q O C ~lactic e.g. muscle cells, during prolonged strenuous exercise alcoholic fermentation > sugar fermentation • sugar from barley seeds • cane sugar or molasses after some time 1 ethanol + carbon dioxide fermentation fermentation t series of reactions leading to breakdown to C02 + H20 Figure 11 . 7 The oxygen debt is the oxygen needed to break down the lactic acid formed during exercise. Anaerobic respiration in yeast rum During anaerobic respiration in yeast ethanol and carbon dioxide are produced as waste products. Ethanol is an alcohol and the process is known as alcoholic fermentation . Yeast is very important in the making of alcohol and bread (figure 11.8). The ethanol can be produced in many ways to make a wide range of alcoholic drinks, including beer and wine, which are enjoyed by humans. The production of carbon dioxide is used in bread-making to make dough rise. The carbon dioxide produced by the yeast as it respires accumulates inside the dough in small pockets. The dough is seen to get bigger or rise as the gas expands with warmth. Ethanol is also produced but in small quantities - it evaporates when the bread is baking in the oven. • dough rises as bubbles of C02 get caught in the dough • baking kills the yeast and evaporates the ethanol 126 acid beer • flour and yeast dough, after kneading flour has starch which is broken down to maltose • yeast uses the maltose as a source of sugar and fermentation occurs Agure 71 .B Uses of fermentation. I 11 · Respiration ~ IT:Q9 \.../'-I Sometimes bacteria can be found in canned foods or tins, despite the fact that the cans and tins are sealed so that no air can enter. How is this possible? Anaerobic respiration in bacteria Some bacteria also respire anaerobically. Like animal cells, they make lacti c acid as a waste product. We m ake use of this in th e manufacture of yoghurt and cheese (figure 11.9). milk contains lactose ' pasteurisation heat treatment (90°C) to kill disease-causing organisms ' inoculation cooled to 40°C and a 'starter' culture of bacteria added e.g. Lactobaci//us bulgaris ' fermentation incubated in 1arge vats (40 ° C for about 5 hours)lactose converted to lactic acid producing natural yoghurt ' ' ' cool, add fruits, etc. package and distribute at 4.5 ° C the bacteria remain alive but no more fermentation occurs at this temperature store at 2 ° C Figure 11.9 The manufacture of yoghurt depends on the anaerobic respiration of Lactobacillus bacteria. I I • Anaerobic respiration releases a small amount of energy without the use of oxygen . • Humans usually respire aerobically but their muscle cells can respire anaerobically during prolonged exercise. • Lactic acid is produced during anaerobic respiration in animals and creates an oxygen debt which has to be repaid. • Anaerobic respiration in yeast produces ethanol which is used in the alcohol industry and carbon dioxide which is used in making bread. • Anaerobic respiration in bacteria is used in the making of yoghurt and cheese. 127 Life Processes and Disease Du ring respiration, the energy from the food eaten by an organism is made available. This en ergy can be used to carry o ut all the processes of life: m ovem ent, growth, reproduction, and so on . ITQ2 Animal cells respire all th e time because th e animal is in constant need of en ergy. Plane cells also respire all the time. During the day, while sunlight is available, plants also photosynthesise, but they never stop respiring. ITQ3 The important product of respiration is energy, which an organism n eeds to carry ou t th e characteristics of life. The waste products of respiration are carbon dioxide and water. ITQ4 Respiration occurs in the mitoch ondria of cells. ITQ5 Energy is released only when necessary; only as mu ch energy as is needed is used; energy is released rapidly when it is needed. ITQ6 Organism s that respire aerobically include humans and birds (there are m an y others). Organisms that respire anaerobicaIJy include yeast and tapeworms inside the intestine. Yeast can also respire aerobically if it has access to oxygen . ITQ7 Human muscle cells use anaerobic respira tion during prolonged exercise, when oxygen cannot be supplied fa st enough for sufficient aerobic respiration to take place. As a result, energy is produced to do the work n ecessar y when exercising, although less en ergy is produced from each glucose molecule than in aerobic respiration. ITQ8 Alcoholic fermentation occurs when yeast respires anaerobically to produce ethanol. This process is important in the bread, beer and win e industries. ITQ9 The bacteria tha t are fo und in cans and tins respire anaerobically. This means they do no t need oxygen to release energy for all their living processes. So the fact that there is no air in the ca n does not affect them ; th ey can live in that environm ent. ITQ1 Examination-style questions {i) Respiration is described as a characteristic of life. What is the importance of respiration to plants and animals? (ii) Although respiration occurs in a series of steps, it can be summarised in an equation. {a) Write the equation. (b) Describe how energy is made and stored. (c) Discuss three advantages of storing energy in this way. (iii) A form 2 student remarked that she had not eaten any food for breakfast or lunch and that she felt 'weak'. Explain to her why she is feeling weak and why it is important not to skip meals. 2 128 {i) Using a table, outline the differences and similarities between anaerobic and aerobic respiration. {ii) Explain the importance of anaerobic respiration in humans. {iii) Define: {a) oxygen debt; {b) alcoholic fermentation. {iv) Outline the importance of anaerobic respiration in: {a) the bread-making industry; {b) the alcohol industry. (v) Describe how yoghurt is made. 11 ·Respiration 3 Diagrams A and B below show investigations to demonstrate the products of respiration and photosynthesis. A 0 0 0 0 0 0 0 0 0 B 0 ~ (i) Copy the diagrams and, using annotated labels only, complete diagram: (a) A to show how carbon dioxide is produced during respiration; (b) B to show that oxygen is produced during photosynthesis. (ii) The diagrams below are investigations to show that oxygen is used up during respiration. (a) What is the importance of soda lime? (b) How does the investigation show that oxygen is being used up? (c) Calculate the rate at which oxygen is being used up. {d) What would you see if more organisms were put in the flask and what would this indicate about the total amount of respiration? at the start capillary oil drop tube ----------- - wiregauze after 30 minutes I" '" I"' ""'l""""'l""""'I I small animals, e.g. woodlice or millipedes 129 G aseous Exchange 0 understand the function and mechanisms of breathing and gaseous exchange in humans 0 0 0 0 understand the function and mechanisms of gaseous exchange in plants identify characteristics common to gaseous exchange surfaces discuss the effects of cigarette smoking in humans understand marijuana addiction gaseous exchange I r respiratory system ' respiratory surface rcigarette smoking inhalation exhalation lungs humans leaf plant gill fish Amoeba cell membrane characteristics thin large surface area rich blood supply constantly moving transport medium ~ lltQ·1 V'-..J (i) What is gaseous exchange? (ii) List two places where it occurs in the human body. Importance of gaseous exchange in humans Respiring cells need a continuous supply of oxygen. They must also be able to get rid of the carbon ctioxide that is being produced constantly. The blood is the means by which oxygen and carbon dioxide are transported to and from cells. At some point, blood has to pick up oxygen and give off carbon dioxide, that is, exchan ge these two gases. In humans, gaseous exchange takes place in th e lungs (figure 12. 1). 12 ·Gaseous Exchange mouth, nose air inhaled - has more oxygen than air exhaled blood rich in oxygen flows to the body cells respiring body cell uses oxygen , produces f carbon dioxide air exhaled has more carbon dioxide than the air inhaled GASEOUS EXCHANGE oxygen net diffusion } into the blood blood vessels carbon dioxide net in the lungs diffusion out of the blood ____/ ~ ._...._..._ blood rich in carbon dioxide flows towards the lungs Figure 12. 1 The role of the lungs in exchanging gases with the environment. Mechanism of gaseous exchange in humans FWl:Z•l!IJ The human respiratory system is involved in the exchange of gases in humans. The lungs are very important and are made up of many tiny air spaces or air sacs called alveoli (figure 12.2) . rib - l'---- -1----,F--- - trachea opens to mouth and nose -+--r--- larynx (voice box) ----r internal intercostal muscle -+----~ Figure 12.2 The human respiratory system. 131 Life Processes and Disease l!iB9•!¥1J Air enters the nose and/or mouth and moves down the trachea (windpipe). The trachea is supported by C-shaped rings of cartilage so that it is kept 'open' a t all times. The trachea then divides into two bronchi, the right and left. These a re also supported by rings of cartilage. Each bronchus branches into smaller and sma ller tubes called bronchioles. At the end of each bronchiole are the many tiny sacs called alveoli (figure 12.3). Gaseous exchange occurs in the alveoli. bronc hiole > leU.letijUll'-11 ring of cartilage, supports the soft tissue of the trachea and keeps the trachea 'open' so that air can pass easily bronchus branches into smaller and smaller branches ~ 1:r.Q2 V'--J What is the importance of the rings of cartilage in the wall of the trachea? ~ alveolus or air sac found at the end l:r.Q3 V'--J Describe the passage taken by an oxygen molecule from the air to a capillary in the lungs. site of gaseous exchange Figure 12.3 The route taken by air into and out of the lungs. The walls of th e alveoli are the gaseous exchange surfaces or the respiratory surfaces. The smallest blood vessels, capilJaries, are closely wrapped around each alveolus (figure 12.4). Blood is thus brought to and taken away from each alveolus. Oxygen diffuses across the walls of the alveolus into the capillary and the bl ood in the capilla ry becomes oxygenated. Carbon dioxide diffuses from the capillary into the alveolus and is exhal ed out of the body. The walls of the alveolus and capillary are very thin (onl y one cell across) so that diffusion can occu r readily (figure 12.5). capillary, transporting blood that has little oxygen (deoxygenated blood) to and from the alveolus - blood has high concentration of carbon dioxide capillary transporting oxygenated blood from lungs blood has low concentration of carbon dioxide t deoxygenatecl blood air ~--"i.--- capillary (the wall is one cell thick) alveolus (the wall is one cell thick) section of one alveolus network of capillaries surrounding alveolus - gases are exchanged here Figure 12.4 The blood supply to one alveolus. 132 flow of blood in capillary Figure 12.5 Gaseous exchange between an alveolus and the blood in a capillary. 12 ·Gaseous Exchange ~ l:fQ~ \.../'--) list the difference between the blood in the capillary coming to, and the blood leaving, the alveolus in figure 12.5. mm inspiration ) The continuous exchange of gases in the lungs is extremely important. Body cells can obtain a constant supply of oxygen for respiration and the carbon dioxide that is constantly being produced is exhaled out of the body. Gaseous exchange also occurs at the level of the cells. Here oxygen leaves the blood and diffuses into the cells. Carbon dioxide moves in the opposite direction (figure 12.1). The trachea is Lined with mucus, a slimy substance which traps and holdsr dust and microorganisms. The tra chea is also lined with microscopic hair-like extensions called cilia. These beat in a wave-like manner, moving the mucus containing dust and microorganisms upwards and out of the lungs. Pathogens can enter the lungs with air as it is breathed in. The mucus and cilia afford some protection by trapping and moving them out of the lungs. If an irritating substance like dust is breathed in, this can stimulate a sneeze during which the irritant is ejected out of the lungs. The other parts of the respiratory system, namely the ribs, intercostal musdes and diaphragm, are also involved in gaseous exchange. They help to move air in and out of the lungs. Breathing in is called inspiration and breathing out is called expiration. Table 12.1 compares the constituents of inspired and expir ed air. Table 12.2 (overleaf) compares inspiration with expiration. Constituent gases Inspired Expired air air Reason for difference oxygen 21% 16% some of the oxygen is used by the cells of the body during respiration carbon dioxide 0.04% 4% carbon dioxide is made by the cells and is transported by blood to the lungs nitrogen 78% not used 78% water content variable usually higher the alveolar surface has a thin film of moisture to aid than when gaseous exchange, and some of this evaporates inspired temperature usually higher air is warmed by the body heat while within the body than when inspired variable Table 12.1 A comparison of inspired and expired air. 133 Life Processes and Disease Inspiration Expiration • External intercostal muscles contract (internal intercostals relax) and the ribcage is raised. • The muscles of the diaphragm contract and the diaphragm moves downwards. • Internal intercostal muscles contract (external intercostals relax) and the ribcage is lowered. • The diaphragm muscles relax and the diaphragm moves upwards. air in air out ribs move up and out diaphragm contracts (moves down) vertebral diaphragm recoils upwards volume Increased volume decreased air in air out sternum moves upwards and forwards diaphragm contracts sternum moves downwards and backwards diaphragm recoils • These two movements increase the volume of the thorax. • These two movements decrease the volume of the thorax. • The pressure inside the thorax is lowered to below atmospheric pressure. This pushes air into the lungs so they expand. • The pressure inside the thorax increases which squeezed the lungs. • •Air rushes into the lungs through the mouth/nose and trachea. • Air is pushed out of the lungs. It passes out through the trachea and the mouth or nose, out of the body. Table 12.2 A comparison of inspiration and expiration. 134 12 · Gaseous Exchange Importance and mechanism of gase~us exchange in plants CHAPTERS X ~ IT:Q5 vv What is breathing and why is it important? (ii) Which muscles are involved in breathing in humans? (i) ~ The leaf is the respiratory surface or gaseous exchange surface. There are tiny pores called stomata on the underside of the leaf through which the gases pass. From the air space inside the leaf, the gases diffuse into and out of the plant cell. The gases move down their concen tration gradients (chapter 8). During the day, plants photosynthesise and need carbon dioxide. Oxygen is a waste product and must be removed. Plants respire all the time but, during the day, photosynthesis is also being carried out. More oxygen is made in photosynthesis than is used up in respiration and more carbon dioxide is used than is made. So there is a net flow of oxygen out of the leaf and a net flow of carbon dioxide into it. At night photosynthesis stops because there is no light but respiration continues. Oxygen moves into the leaf and carbon dioxide moves out figure 12.6). Day IT:Q6 Night vv Which gases leave and enter a leaf at: (i) 12 noon? (ii) 12 midnight? • respiration occurs • no light, therefore no photosynthesis 6C02 + 6H20 -+ CsH120 5 + 602 photosynthesis equation C5H120e + 602 -+ energy + 6H~ + 6C02 respiration equation Figure 12.6 The net flow of gases diffusing in and out of a leaf during the day and at night is different. Characteristics common to gaseous exchange surfaces gaseous exchange surface > Gaseous exchange or respiratory surfa ces are those surfaces where the exchange of oxygen and carbon dioxide occur. These surfaces must have certain characteristics that encourage: • a lot of gaseous exchange to take place; • gaseous exchange to take place quickly; • gaseous exchange to take place continuously. This means that organisms respiring aerobically can get a constant supply of oxygen and remove carbon dioxide. Without oxygen, ce lls die and carbon dioxide, if allowed to accumulate in cells, could poison and kill them. 135 Life Processes and Disease Adaptations for efficient gaseous exchange Large surface area For gaseous exchange to take place quickly and in large amounts, respira tory surfaces must have a large surface area or a large area over which the exchange of gases can occur (figures 12.7, 12.8 and l2.9). blood brought to the alveolus - it is low in 0 2 and high in C02 blood taken away it is rich in 0 2 and low in C02 thin wall of capillary - layer of moisture - oxygen dissolves in this moisture and there is always a high concentration of oxygen next to the capillary blood flows constantly lungs, highly folded to Increase surface area Figure 12.7 Adaptations of the lungs in humans for efficient gaseous exchange. stiff gill rakers, which filter out food particles from water as it passes over them; the food particles are then swallowed bony gill bar, supporting the gill leaf is thin and flat for large surface area I oxygen leaving leaf is 0 2 blown away, leaving a low concentration around the leaves ) wind soft, dark red gill lamellae, where gas exchange takes place - '" 7 g<eatly ""''""'"" ,,.----,.......~-,IF-~...,..-., blood capillaries - bring blood to pick up 0 2 and lose C02 , take away blood rich In 0 2 and low in C02 leaf is about 4-5 cells thick spongy mesophyll water flowing around gills Figure 12.B Adaptations of the lamellae on the gill of a fish for efficient gaseous exchange. 136 Agure 12.9 Adaptations of leaves on a plant for efficient gaseous exchange. 12 ·Gaseous Exchange - - .. .. flow of water brings more02 thin membrane small volume relative to large surface area .. flow of water takes C02 away .. movement of water Figure 12 10 The unicellular Amoeba needs no special organ for gaseous exchange. It is so small that the gases can be exchanged efficiently across its cell membrane. ~ IT:Q7 V'-...J What is the respiratory surface for each of the following organisms: a human, a fish, a plant, Amoeba? In humans, the lungs are made up of thousands of sacs called alveoli, which, if laid out side by side, would cover a tennis court. In fish, gill lamellae, which are part of the gills, form the respiratory surface. There are thousands of lamellae in each gill creating a large surface area (or exchange. In plants, the respiratory surface is the leaf. Leaves are thin and flat to create the largest area possible for gaseous exchange. On a tree, the thousands of broad flat leaves show what a large surface area is available for gaseous exchange. Protozoan s, Like Amoeba, are microscopic unicellular organisms. Their surface area to volume ratio is alreay large. Gaseous exchange occurs across the cell membrane by diffusion and, because the cell is so small, the entire body of Amoeba can be supplied with oxygen (figure 12.10). Thin surface for gaseous exchange For gaseous exchange to take place quickly, the respiratory surfaces must be thin so that diffusion of the gases can take place rapidly. In humans, the walls of the alveoli and capillaries are just one cell across. The walls of the alveoli are also moist, so that the gases dissolve in the moisture before they diffuse. In fish, the lamellae and capillaries are also one cell across and diffusion can thus readily occur across the gills. Air spaces inside leaves ensure that the gases can get dose to most of the cells into and out of which they must diffuse. The cell membranes of protozoans are very thin and diffusion readily occurs. Constantly moving transport medium For gaseous exchange to take place continuously, the medium which brings the gases to the respiratory surface must be constantly moving. This ensures that a concentration gradient is always maintained and diffusion will take place constantly. For example, in humans and in fish there is a rich blood supply constantly flowing past the respiratory surface. In humans, breathing continuously refreshes the air in the lungs; in fish, water is continuously forced across the gills. In plants, the wind blows or moves the gases away from the leaves ensuring that a concentration gradient is always maintained and that diffusion occurs readily. In unicellular protozoans, the water around the organism constantly takes away and supplies the gases which dissolve easily in water. The effects of smoking Tobacco may be the cause of over 3 million deaths a year, worldwide. Death from cigarette smoking comes mainly from lung cancer, but heart disease is also associated with smoking. The products of cigarette smoke, (whether the smoke is directly from smoking a cigarette or from inhaling another person's cigarette smoke) include nicotine, tar and (Like car exhaust fumes) carbon monoxide. Nicotine • Makes cigarettes highly addictive. • Reduces air flow in and out of the lungs. • Paralyses the cilia lining the trachea, so they cannot remove dirt and bacteria. 137 Life Processes and Disease • Raises blood pressure. • Raises heart rate. • lncreases the risk of osteoporosis. Osteoporosis is the loss of calcium carbonate from the bones which can happen in older people. It makes the bones brittle, so they break more easily and are more difficult to heal. Tar • • • • Sticks to cells in the lungs. Causes the development of cancer. Damages lung tissue. Breaks down the alveoli, thus decreasing the surface area for gaseous exchange. • Causes bronchitis or inilammation of the lining of the air passages. • Causes 'smokers cough'. Carbon monoxide • • • • • Combines irreversibly with haemoglobin in the blood. Causes less oxygen to be transported by blood. Reduces the smoker's ability to take strenuous exercise. Causes breathlessness. If a pregnant woman smokes, carbon monoxide gets into the blood of the fetus and combines with the haemoglobin. Less oxygen gets to the growing tissues, resulting in a baby with a lower birth-weight; this is associated with greater risk of health problems during and after birth. · Although studies show that there is a connection between cigarette smoking and lung cancer, m illions of people worldwide continue to smoke. A large percentage of smokers are young people who become addicted very quickly and continue to smoke throughout their lives. Statistics show that 25 % of smokers die of lung cancer. Figure I 2.11 shows the effects of smoking on human lungs. (a) (b) Figure 12.11 A normal lung (a) and a cancerous lung (b) . The cancerous lung came from a heavy smoker 138 12 · Gaseous Exchange Marijuana addiction This is a green or grey mix of dried shredded flowers and leaves of the hemp plant Cannabis sativa - also called by many, many other names including pot, herb, ganja and weed. The active ingredient is THC (tetrahydrocannabinol) which provides to the 'high' that users experience when they smoke the drug. The short-term effects of marijuana can include: • problems with memory and learning; • distorted perception; • difficulty in thinking; • difficulty in problem-solving; • loss of coordination; • increased heart rate; • anxiety; • panic attacks. Marijuana smoke is unfiltered, users inhale more deeply and hold the smoke in the lungs. The effects on the lungs are thus greater than those caused by tobacco smoke because more tar and more carbon monoxide are inhaled. 139 Life Processes and Disease ITQ1 (i) Gaseous exchange is the exchange of gases, in particular oxygen and carbon moxide. (ii) In the lungs, where gases are exchanged between the alveoli and blood. In the tissues, where gases are exchanged between the blood and cells. ITQ2 These are complete rings which keep the trachea open. They also support the trachea. ITQ3 nose -+ trachea -+ bronchus -+ bronchiole -+ alveolus -+ capillary ITQ4 Blood in the capillary approaching the alveolus contains a higher concentration of carbon moxide and lower concentration of oxygen than blood leaving the alveolus. ITQS (i) Breathing is the process whereby air is pushed into the lungs by atmosph eric pressure and expelled from the lungs by muscular contraction. It is important because it brings a supply of oxygen, wh ich is needed for respiration, and it also takes away carbon dioxide, a waste gas. (ii) The muscles involved in breathing are: the diaphragm muscles and the external and internal intercostal muscles. ITQ6 (i) At noon, oxygen is leaving the plant and carbon moxide is entering the leaf because photosynthesis is happening at a much faster rate than respiration can use the oxygen or produce carbon dioxide. (ii) At midnight, there is no light so photosynthesis cannot take place. Respiration is the only process that is occurring, so carbon moxide is leaving the plant and oxygen is being taken in. ITQ7 Human respiratory surface is the alveolus; fish - gill; plant - leaf; Amoeba - cell membrane. Examination-style questions (i) Inhalation and exhalation are movements that ventilate the lungs. The diagram below shows the ribs and diaphragm. (a) Copy the diagram and use arrows to show the movements of the diaphragm, the ribs and air during exhalation. (b) Explain fully how the volume of the thorax is increased by giving details of contraction and relaxation of muscles involved in raising of the ribs and lowering of the diaphragm. 140 12 · Gaseous Exchange (ii) List three ways inhaled air differs from exhaled air. (iii) A boa constrictor kills its prey by squeezing it to death. This is termed 'asphyxiation'. Explain how asphyxiation results in death. 2 (i) Define the following terms: (a) gaseous exchange; (b) respiratory surface. ( (ii) List three characteristics of respiratory surfaces. Describe how the lungs of humans are adapted in these three ways to increase the rate of gaseous exchange. (iii) The nicotine found in tobacco smoke can prevent the beating of cilia in the trachea. Suggest how this contributes to the development of lung diseases. (iv) List two effects of each of the following products of cigarette smoke: (a) nicotine (b) tars. (V) How are plants adapted to exchange gases efficiently by diffusion? 3 The apparatus shown in the diagram below is used to investigate the chemicals in cigarette smoke. air outlet - lighted cigarette cotton wool (i) After some time, the cotton wool turns black and appears oily. (a) What are the black particles trapped in the cotton wool? (b) What chemical causes the oily appearance? (ii) Describe and explain the colour change of the litmus paper. (iii) If a cigarette with a filter is used, what difference in the appearance of the cotton wool would you expect? (iv) One of the gases in cigarette smoke is carbon monoxide. What is the effect of carbon monoxide on the body? (v) How do chemicals in cigarette affect the cilia in the trachea? (vi) Name two respiratory diseases that may be caused by prolonged smoking. 141 liransport and Defence in Animals ./) understand why there is a need for a transport system in multicellular organisms Q) Q) Q) Q) Q) understand why certain materials must be transported in animals describe the circulatory system of humans relate the structure of the heart to its function relate the structure of blood vessels to their function describe the composition and functions of blood ./) understand how and why blood clots ./) understand blood groups and their importance in blood transfusion Q) understand the nature and danger of hypertension / describe the role of blood in defending the body against disease ./) explain how the principles of immunisation are used in the control of communicable diseases plasma haemoglobin red blood cells blood white blood cells platelets - . hypertension - transport system in humans - heart clotting action of - { heart heartbeat ( functions t take important substances to cells blood vessels ] \ t take waste products away from cells arteries veins capillaries The need for a transport system Large mu lticellul ar animals, like human s, have a large volume in re lation to Lhe ir surface area. Substances would therefore take a long time to diff use from the air into the body and would get to cells deep in the body at a much slower than th e rate at w hi ch th ey are needed by the cells. Imagine oxygen diffus ing into th e skin of an organ ism. It may not be able to get to all the cells of the skjn, far less the cells of organs inside the body. Oxygen would have to pass th rough m illions of cells to get to the liver. Also, the skin is 13 · Transport and Defence in Animals ~ IT:Q-1 V-...J A unicellular organism like Amoeba does not have a transport system and a multicellular organism like a human cannot live without one. Explain why this is so. CHAPTERS 10, 11 , 12, 16, 18 X ~ IT:Q2 V-...J Name two substances which must be transported to a cell and explain why each substance is needed. circulatory system > a to ugh waterproof layer and may also be covered with hairs, fur and feathers. It is impossible for oxygen to diffuse to cells inside the body of a m ammal or other la rge organism. In an y organism larger than a few cells, any substance needed by a cell within the bocy must be speciaDy transported to the cell. A transport system is necessary to get important and needed substances to every single cell and also to transport waste or toxic substan ces away from every cell. Just to stay alive, a m ulticellular organism requ ires a con stant supply of substances like oxygen and glucose to all its cells. When active, the~e substances are required in even greater amounts. Table 13. l shows some of the substan ces which need to be transported in animals. Substance to be transported Transported from Transported to dissolved food (chapter 1O) ileum where it is absorbed cells of the body - to be used for respiration, stored, converted to other materials, etc. nitrogenous waste (chapter 16) cells where produced kidneys to be excreted oxygen (chapter 12) lungs where it diffuses into the blood body cells to be used for respiration carbon dioxide {chapter 11) body cells where it is produced in respiration lungs to be excreted hormones (chapter 18) endocrine glands where they are produced organs where their effects are needed white blood cells including antibodies marrow of bones where they are produced where there are infections or invasions by microorganisms Table 13. 1 Some substances which are transported in animals. The circulatory system of humans Blood is the m eans by which substances travel to and from cells. These substances dissolve in blood, w hich is mainly water and diffused into th e cells where they are n eeded. The blood is transported around the body in blood vessels. The heart h elps to push blood a ro und the body.This transport system is called a circulatory system. Most substances dissolve in the plasma, but the red blood cells are specialised to transpo rt oxygen . The circula tory system is made up of three parts: • the heart, which is a pump; • th e blood, w hich is the fluid being pumped a nd contains all the ma terials to be transported around the body; • the blood vessels (like pipes) through which blood flows to get to and from the cells, these are the arteries, veins and capillaries. The structure of the heart The heart pumps blood so tha t it can get around the body. It pushes blood forcibly thus ca using it to be constantly m oving in the blood vessels. The walls of th e hea rt are made of a special type of muscle, ca lled cardiac m uscle. 143 Life Processes and Disease cardiac muscle ) fliill!ull i@nrmlm Cardiac muscle contracts and relaxes regu larly and constantly throughout life. It never grows tired. But it may stop working iI it is not supplied with the substances it needs to release energy - oxygen and glucose. These are supplied via the coronary circulation. The mammalian heart is divided into a right side and left side (figure 13. l ). Each side has two parts or chambers: • the atrium, which receives blood; • the ventricle, which pumps blood away. (a) left pulmonary artery right pulmonary ~-- veins left pulmonary (b) _ ____ left pulmonary artery r~======!= ::;;;;.---left pulmonary vein :"r-- - - left atrium 't--- - - semilunar valves ---"~-- - tricuspid valve --~~---== vena cava from - - - - - i 4 - lower part of body I - bicuspid valve -tendon, holds the valve in place left ventricle r Agure 13.1 The heart: (a) showing its blood supply and (b) in section. The action of the heart Deoxygenated blood, that is blood coming from the body cells w here some of the oxygen bas been used in respiration, flows into the right atrium through the vena cava . This blood is also rich in carbon dioxide made during respiration in the cells. The blood must now be tran sported to the lungs wh ere it can load up with more oxygen and offload the excess carbon dioxide. 144 13 ·Transport and Defence in Animals tricuspid valve } bicuspid valve } ~ l:f:Q3 \_,)'...J The heart beats continuously for years. How is heart muscle nourished and supplied with oxygen and glucose? From the right atrium, blood passes through the tricuspid valve into the right ventride. The walls of the ventricle contract and the blood is pushed into the pulmonary artery and travels to the lungs. There, gases are exchanged. Excess carbon dioxide leaves the blood and diffu ses into the lungs, and oxygen moves into the blood from the alveoli. Oxygen-rid1 blood returns from the lungs via the pulmonary veins and flows into the left atrium. It passes through the bicuspid valve and flows into the left ventricle. The thicker muscular walls of the left ventricle contract strongly and blood is pushed forcefully into the aorta and all the way around the body. Blood therefore flows through the heart twice in one circuit of the body (figure 13.2) deoxygenated blood from head deoxygenated -+-- 1 -- - - - + blood to the lungs deoxygenated blood from body J-- ,oxygenated blood to head and body oxygenated blood to the body Figure 13.2 Blood flows through the heart twice in one circulation atrioventricular valves > semi-lunar valves > Q9;, l:tQ~ \_,)'...J Describe the route taken by a red blood cell from the vena cava to the aorta. Valves prevent the back-flow of blood in the heart. The bicuspid and tricuspid valve, known as the atrioventricular valves, ensure that blood flows in one direction through the heart only. Tendons attached to the walls of the heart hold them in place. When the ventricles contract, blood pushes back on these valves, forcing them shut. So the blood can only move forward into the pulmonary arteries and aorta . Semi-lunar valves are found at the start of the pulmonary artery and aorta . They prevent the back-flow of blood into the ventricles when they relax. Heartbeat The heart 'beats' when the muscles of the heart contract and relax. The re are three phases to a heart beat. The sound s heard - 'lub dub' - are the sounds made by the valves closing and blood hitting the valves. The 'lub' sound is made during ventricular systole as blood is forced against the closed tricuspid and bicuspid valves. The 'dub' sound is made during ventricular diastole when blood impacts on the d osed semi-lunar valves in the aorta and pulmonary artery. The third stage, diastole, when blood flows into the empty atria and ventricles, makes n o sound (figure 13.3). The rate of heartbeat is controlled by the ' pacemake r', which is found in the mu scle between the ventricles. It has its own na tural rhythm of stimulating 145 Life Processes and Disease con tractions, which is usually around 70- 80 beats per minute. This can be speeded up by h ormones such as adrenalin, and by activity. from lungs atria and ventricles relax (diastole) Diastole - when all the muscles of the heart relax and blood flows into the heart atria contract (systole) Atrial systole - the muscles of the atria contract and force blood into the ventricles ~ I ventricles contract (systole) 1+I ,I ...._ Ventricular systole - the muscles of the ventricles contract and push blood out of the heart Agure 13. 3 The three phases of a heartbeat. ~ l:t!QS V'-1 List the three main stages of the heartbeat and explain the importance of each. FUC§W l!hl·lllblt'B m1eu Blood vessels Blood flows through blood vessels to get to all parts of the body from the heart and then from the body back to the heart. There are three kinds of blood vessel: • arteries (and arterioles) whlch carry blood away from the heart; • capillaries which are tiny vessels that pass close to all body cells; • veins, (and venules) which carry blood back to the heart. An artery branches into smaller and smaller vessels called arterioles. These branch into even smaller and smaller vessels, until the vessels are very small and the walls are only one cell thick. These tiny vessels are ca lled capillaries. Capillaries flow in between the cells of the organs and the exchange of substances food, oxygen, wastes, etc. takes place at this level. Capillaries then join up to form larger and larger vessels called venules, which then join to form veins which carry blood back to the heart. Fiigures 13.4 ansd 13.5 show the relationships between the three types of blood vessel. Table 13.2 compares arteries, veins and capillaries. 146 13 ·Transport and Defence in Animals arteriole from artery Rgure 13. 4 The relationship between arterioles, capillaries and venules. cells give out waste products cells take in Deoxygenated blood full of waste products goes to the heart. then to the lungs and gut to collect oxygen and food. Diffusion occurs across the capillary network. Oxygenated blood full of food and other useful substances goes to the cells. Figure 13.5 A network of capillaries surround all the cells of tissues Capillaries Arteries wall composed of a single layer of cells fibrous layer muscle and elastic layer ., smalllumen ~ Veins fibrous layer lumen and red blood cells pass in single file endothelium ___/one cell thick • thick elastic walls to withstand the hgh pressure of blood and absorb some of the energy of the pulse • walls one cell across - thin enough for diffusion to take place easily • thin elastic walls (do not have to withstand high pressure) (continued) 147 Life Processes and Disease Arteries Capillaries Veins • carry blood away from the heart • carry blood to the cells of the tissues and organs • carry blood towards the heart • blood pressure is high • blood pressure decreases along the length of the capillaries • blood at low pressure • blood flows rapidly in pulses created by • blood flow is smooth and slow contractions of the ventricles (this is the pulse you can feel most easily at your wrist) • smooth and slow flow - the large lumen offers little resistance • carry oxygenated blood, except the pulmonary artery • as it flows through a capillary network • carry deoxygenated blood, except the pulmonary vein the blood loses oxygen to body cells and gains carbon dioxide • lie deep within the body • run through the tissues • lie close to the body surface • no valves present • no valves • valves prevent the back-flow of blood because the 'push' of the heart is not felt here flow of blood l blood can flow in one direction only valve open valve closed • blood can flow in one direction only ~ ll'.Q6 \...l'-1 Describe two differences between blood leaving an arteriole and blood entering a venule, having passed across a capillary network. lfl•l•f?M G#•€•1f§kkU coronary arteries > CHAPTER 16 Table 13.2 The main differences between arteries, capillaries and veins. The circulation Blood leaves the left side of the heart at a high pressure and flows through the aorta , the largest artery, to all parts of the body. When the capillaries reach the body cells, the blood gjves up food and oxygen and picks up wastes, such as carbon dioxide and urea. Deoxygenated blood returns to the heart via the veins whid1 collect into a main vein called the vena cava. From the right side of the heart, blood flows to the lungs to be oxygenated, then back to the left side of the heart. This flow is repeated continuously. The tissues of the heart itself are supplied with oxygen by the coronary arteries . In its circulation throughout the body, blood picks up food (such as glucose and amino acids) from the gut, hormones from endocrine glands, and other vital substances. It also drops off waste products to be excreted, like urea and carbon dioxide, at sites where the body an get rid of them. that is the kidneys (chapter 16) and the lungs (figure 13.6). .~ \...l'-1 Why does the aorta have the thickest walls of all the vessels in the circulatory system? 148 ~ (1~8 (i) What is the pulse? (ii) What is the pulse rate? 13 ·Transport and Defence in Animals ---- - jugular and - ----,;-7.,._...a.. subclavian veins - carotid artery (to head) carotid and subclavian arteries head and arms subclavian artery (to arms) 1 subclavian vein pulmonary -~----,f----3it::....: vein 1 pulmonary -+-..___.,,, artery vein pulmonary artery--r--..,,, (to lungs) 1--'ilft-- hepatic portal vein (liver) . -- -----'- - -- renal artery (to kidney) hepat ic -f-~~ mesenteric ---~E=" artery (to gut) Iliac - 1---- -vein arteries vein •- - - -- -hepatic artery Iliac artery (to feet) Iliac vein deoxygenated blood pulmonary circulation - oxygenated blood - systemic circulation - ~ deoxygenated blood 11!09 oxygenated blood - l../'-J Describe the route taken by a red blood cell from the renal vein to the hepatic vein. Rgure 13.6 The circulatory system in humans. Blood l~O l../'-J Describe the differences in composition between blood: (i) in the renal artery and the renal vein (ii) in the pulmonary artery and pulmonary vein. blood plasma > red blood cells trunk and legs white blood cells > Blood is the medium by which substances or materia ls are transported. It is made up of about: • 55 % blood p lasma; • 45 % blood cells. The blood plasma is about 90% water and most of the substances which must be transported are dissolved in it. This includes dissolved food (glucose, amino acids, fatty acids and glycerol), carbon dioxide (as the bicarbonate ion), nitrogenous wastes, hormones and mineral salts (as ions such as Na+, K+, Cl+). The blood cells are of two main types, red and white. There are also fragments of cells called platelets. Table 13.3 (overleaf) summarises the structure and function of blood cells. 149 Life Processes and Disease Blood cell Function Red blood cells or erythrocytes • biconcave disc shape (squeezed in from both sides) gives large surface area for diffusion • have no nucleus so only live for 3-4 months • new cells constantly made in the bone marrow and destroyed in the liver and spleen • contain the red pigment haemoglobin which combines with and releases oxygen readily • 1 mm3 of blood contains about 5 million of these cells contains haemoglobin, a red pigment which contains iron; no nucleus transport oxygen combined with haemoglobin, from the lungs to tissues where the oxygen is given up readily t White blood cells or leucocytes • two main types: phagocytes and lymphocytes Phagocytes • move like Amoeba by pseudopodia - can move through the capillary walls to sites of infection • formed in bone marrow engulf disease-causing organisms at sites of infection Lymphocytes • produce antibodies • formed in lymph nodes and spleen produce antibodies that kill pathogens by causing them to clump together, or neutralise their toxins Platelets or thrombocytes • cell fragments • no nucleus • formed in bone marrow of lone bones help blood to clot to prevent loss ~ Table 13.3 Structure and function of blood cells ll':Q·1 1 V"-J Protection of the body is one of the functions of blood. List two components of blood concerned with protection and explain how each works. ~ ll':Q-12 V"-J Describe the process that leads to blood clotting after a cut to a blood vessel. Carriage of oxygen and carbon dioxide in the blood The respirato ry gases, oxygen and ca rbo n dioxide, are transported aroun d the body in the blood. Most of the carbon dioxide is transported in solution in blood plasma as h ydrogen carbonate ions. Oxygen is carried by the molecule haemoglobin, which is found inside red blood cells. Haemoglobin is a protein that is combined with iron - this gives it its red colour. Each m olecule of haemoglobin combines reversibly with up to four molecu les of oxygen. haemoglobin + oxygen -+ oxyhaemoglobin The oxygen is readily given up in the body tissues wh ere oxygen levels are low. The body cells can then use th e oxygen for respiration . oxyhaem oglobin -+ haemoglobin + oxygen Red blood cells are so full of haemoglobin that there is no space for a nucleus. That is why th ey only survive for 3-4 mon ths, after which th ey are cleaned out of the blood by the liver. 150 13 • Transport and Defence in Animals Blood clotting HH•M•E®U When the skin is cue and a small blood vessel is broken , a blood clot ronns haemorrhage > to prevent further blood loss (figure 13. 7). A series or reactions cake place at the site of the cut vessel which results in the formation of fibrin, an insoluble fibrous protein which traps blood cells and pl ugs the gap (figure 13.8). The dot a lso prevents the entry of disease-causing organisms. Loss of blood from a vessel is called a haemorrhage, and losing a lot of blood could result in death. In this case, a blood transfusion can be given to replace blood and save the person's life. (a) disease-causing organisms may enter no more loss of blood, pathogens have a barrier once more I ~ssofblood clot The cut is sealed with a blood clot A cut vessel (b) platelets exposed to air In damaged tissue l calcium ions vitamin K prothrombin - - - - - - - - - - - thrombin (inactive protein (active) in the blood) 1 fibrinogen ----"--+~ fibrin insoluble fibres (inactive protein that trap red blood in the blood) cells and form a clot Figure 13. 7 The formation of a blood clot. Blood groups Figure 13.8 Red blood cells trapped In fibrin. Ft.1e1.111 l(§lff i•U§ellJ During a blood transfusio n, a person is given another person's blood. Early attempts at transfusion worked in some cases, but in many they resulted in death. We now know that for a transfusion to be successful, the two sets of blood must be compatible - able to mix wirht each other without the red cells sticking together.. Th ere are four blood groups, known as A, B, AB and 0. These groups are based on proteins, ca lled antigens, that are present on the surface of red blood cells. For example if an tigen A is present on all the red blood cells of a person, that person is said to have blood group A. There are also antibodies present in the blood plasma. These are associa ted with the antigens. So a person with b lood group A, fo r example, has antigen A (A) on their red cell and and antibody anti-B (b) in their plasma (table l 3.4). During a transfusion it is important to note: • the protein (or antigen) on the red blood cell of the donor; • the type of antibody present in th e plasma of the recipient. If the antibody matches the antigen, the red blood cells stick together and transfusion will not be successfu I. 151 Life Processes and Disease Table 13.4 shows the success of transfusion for all the blood groups. A tick means that this combination of donor and recipient will make a successfu l transfusion; a cross indicates that this combination will lead to a reaction (potentially fatal) in the recipient. Donor's blood type Recipient's blood type ~ IT:.Q·1 3 v-..; State whether these transfusions are possible: • donor AB, recipient O • donor AB, recipient A • donor O, recipient A • donor B, recipient A • donor B, recipient B A B AB 0 (A) (8) (A) B none " " " " .I .I A (b) B (a) AB none .I 0 (a) (b1 " " t antibody present .I .I .I .I +- antigen present .I .I +- universal recipient: blood group AB t universal donor: blood group 0 Table 13.4 The success or failure of blood transfusions between different blood groups. Hypertension hypertension > EmlDJ ~ IT:.Q-1 4 v-..; (i) What is hypertension? (ii) What factors in a person's life may increase the chances of suffering from hypertension? 152 High blood press ure is when the pressure caused by the blood pushing against the inside walls of the main arteries is high . Persistent high blood pressure is called h yp er tension . Capillaries are tiny blood vessels, with walls that are one cell across. Blood flowing at a high pressure can cause these vessels to burst. If a vessel in the brain burst, then a portion of the brain becomes damaged from a lack of oxygen . This is called a stroke and can resu lt in paralysis or even death. Capillaries in other important organs like the kidneys may burst because of high blood pressure. This could lead to shutdown of the organ (e.g. kidney failure) and can have serious consequences on the body. Hypertension can develop without symptoms or signs and is sometimes called the 'silent killer'. It is linked with a number of factors such as: • high levels of emotional stress; • lack of exercise; • obesity; • tobacco smoking; • high alcohol intake; • high blood cholesterol levels. All these factors are influ enced by lifestyle, and can be controlled by changing lifestyle. A h ea lthy lifestyle, that includes regular exercise, no smoking, low intake of fat, salt and alcohol, can prevent the development of hypertension. 13 · Transport and Defence in Animals The role of blood in defending the body against disease physical barrier > phagocytes > Microorganism s are all around us. These microscopic o rganisms (viru ses, bacteria, etc.) are in the air we breathe, in the food we eat, on everything we tou ch and all over our bod ies. The skin is the body's first Line of defence (figure 13. 9) . It acts as a physical barrier. When there are breaks in this barrier, such as cuts or sores, the body reacts to produce blood clots and a m eshwork of fibrous scar tissue. The opening is thus blocked, which prevents pathogens (microorganisms that can cause disease) from entering the body. Sometimes the white blood cells called phagocytes move out of the blood and to the infected areas. There they engulf the invading microorganisms, killing and removing them from the body before they can cause disease. This is our second line of defence (figure 13. 10). wax in the auditory canal traps dust and other particles - - - tears contain a mild antiseptic - - - hairs in the nose trap dust and other particles trachea lined with mucus and cilia to move dust and other particles out of the lungs skin -a physical barrier stomach produces hydrochloric acid which can kill microorganisms vagina - mucus moves out constantly break in the skin - a clot forms Figure 13.9 The skin is our first line of defence. Any openings in the skin have special means of expelling dust which carries many disease-causing organisms. bacterium within the ~ phagocyte - it is killed and digested 8 G Figure 13. 10 White blood cells (phagocytes) are our second line of defence. They leave the blood and migrate to a site of infection phagocyte engulfing bacterium phagocyte moves toward site of infection blood capilliary 153 Life Processes and Disease Immune response lymphocyte > lmJOitimWJ The phagocytes can cope with any small, non-specific invasion by pathogens. U more dangerous, specific pathogens enter, then an immune response is activated. In this case, another kind of white blood cell, called lymphocytes, recognise the specific pathogen and mobilise other lymphocytes to make antibodies to attack, disarm, destroy and remove these pathogens. 1m1u.14,u Antigens and antibodies immune response > memory lymphocytes > natural immunity > Anything that is foreign or different and causes antibody formation is called an antigen. This is our third line of defence against disease. When antigens, such as the measles virus, enter the body, lymphocytes recognise them and start to produce specific antibodies on a large scale to destroy the viruses. The immune response is very specific - only the antibodies for that particular antigen are made. To defend the body against disease, antibodies act in a number of ways: • they cause the antigens to dump together resulting in their death and easy removaJ by the phagocytes; • they neutralise toxins produced by the antigens; • they prevent the antigen from entering body cells. Recognition of antigens and production of the specific antibodies against them takes time. During that time, the antigens will have produced symptoms of the disease. Once the antibodies are produced, the antigens or the toxins they produce are destroyed or neutralised and the symptoms disappear. The antibodies then gradually disappear from the blood, but they leave behind speciaJ memory lymphocytes. If the specific antigen invades a second time, the memory lymphocytes immediately recognise them, and rapidly make large amounts of the specific antibody. This time, the antigens are destroyed before symptoms develop, and the person is said to be immune to that disease. This happens naturally and is called natural immunity (figure 13.11) . Antibody concentration in the blood first infection second infection slow build-up of antibodies gives pathogens time to cause disease 0 10 20 30 large amount of antibodies made 1--- - immediately, pathogen destroyed before symptoms develop - person is said to be immune to that disease 40 50 60 70 80 90 Time in days Agure 13. 11 Immunity 1s a rapid large increase of antibodies in the blood 1?ot.s V"...J We are surrounded by pathogens. How is the body protected from infection? 154 There are two types of naturaJ immunity. • Actively acqu ired immunity - When the body has already experienced an infection by a pathogen or antigen, as described above, the lymphocytes produce large quantities of antibodies to fight the disease before symptoms develop a second time. • P assively acquired immunity - Antibodies can pass across the placenta providing a newborn baby with immunity against diseases that the mother's 13 ·Transport and Defence in Animals body is immune to. Also, antibodies present in breast milk help to protect the baby against antigens. Immunisation and the control of communicable diseases vaccination > ~ IT:Q·1 6 \....)'-/ Explain what is meant by a vaccine. artificial immunity > 1~7 \....)'-/ Copy and complete the table. Natural immunity Artificial immunity Active Passive Immunisation provides immunity to communicable diseases. This is achjeved by injecting, or administering orally, small amounts of dead or weakened (attenuated) antigens into the body. This is called vaccination . The body is stimu lated to produce antibodies. One example is the MMR vaccine given at around 2 years of age or younger to protect children against measles, mumps and rubella. DTP vaccines, administered at any age, protect against diphtheria, tetanus and pertussis (whooping cough) Smallpox has been eradjcated because of immunjsation programmes. Vaccines against tuberculosis (TB) and hepatitis B have also been developed, but there are still not vaccines against diseases such as cancers, leprosy, malaria and AIDS, despite much research. The World Health Organization (WHO) Expanded Program of Immunisation (EPI) aims to extend immurusation to children all over the world, especially in developing countries so that d1ildren can be immunised at no cost to their parents. Immunisation is known as artificial immunity. There are two types of artificia l immunity, • Actively acquired - This is by vaccination at a suitable time in the person's life, when they are not infected with the antigen. The vaccine used contains treated antigens which cannot cause the disease, but which can stinrnlate the body to make antibodies. Immunity is obta in ed because if the real antigen should enter the body, antibodies are immediately and rapidly produced to destroy il. This happens before symptoms develop and the person is said to be immune to that disease. • Passively acquired - The vaccine contains ready-made antibodies whid1 provide immediate relief by destroying the antigens. Thls is given when the person has been infected with the antigens and has no previous immunity. The importance of immunisation or vaccination is seen when children are protected from dangerous diseases like polio, measles, mumps, tetanus and whooping cough (figure 13.12). Thls is achieved in a programme of immunisation where often a second, booster injection is given. This stin1ulates a much quicker production of antibodies which is longer lasting and whlch protects the chiJd from the disease for a considerable time. ~ IT:Q·1 8 \....)'-/ Explain the meaning of the term 'immunisation' and give one advantage of immunisation. (a) (b) (C) Rgure 13. 12 (a) Mumps and (b) chickenpox are common childhood diseases. In some children they can cause long-term damage. (c) Poliomyelitis can cause life-long damage to the body even after the infection has gone. 155 Life Processes and Disease ~ Chapter summary • Large multicellular organisms have a small surface area-to-volume ratio. This means that they need transport systems to carry substances to and from cells around the II body. • A cell needs nutrients, oxygen and other substances to stay alive. t • Waste products are produced and need to be removed from cells so they do not damage them. • The transport system of humans is composed of a pump (heart) a transport medium (blood) and vessels (blood vessels) through which blood flows. This is the circulatory system. • The structure of the heart is suited to its function as a pump. • Blood passes through the heart twice for each time it circulates the body; after one of these passes through the heart blood goes to the lungs for the exchange of gases. • There are three kinds of blood vessel: arteries, veins and capillaries. • Blood is composed of plasma, blood cells and platelets. • Plasma is mainly water with the substances being transported dissolved in it. • There are two types of blood cell; red blood cells transport oxygen and white blood cells protect the body against pathogens. • Platelets help blood to clot; this is important to prevent blood loss. • For a successful blood transfusion, the donor's and the recipient's blood groups must match because if the antigens and antibodies in their blood react together, the transfusion will not be successful. • Hypertension is persistent high blood pressure, which is dangerous to health. • White blood cells protect the body against pathogens. • Phagocytes can leave the bloodstream, gather at sites of infection and engulf and kill pathogens. • The body has three lines of defence against infection: the skin (and blood clotting), phagocytes and the immune system. • In the immune system, lymphocytes form antibodies which are specific for the pathogen. • After an infection, memory cells remain in the blood, which recognise the pathogen again quickly. A second infection does not result in symptoms of the disease because the production of antibodies is much faster and greater. • A person is immune to a disease if, on infection with the disease, no symptoms develop. - 156 13 · Transport and Defence in Animals ITQ1 In the unicellular organism, the surface area to volume ratio is large, which means that there is a lot of surface area for the volume of the organism. Diffusion can occur fast enough across the cell membrane and get to all pans of the cell for all life processes to happen effectively. In a multicellular organism, for each cell to get a supply of oxygen and everything else it needs as fast as it needs it, a transport system is necessary , because the surface area is not large enough in proportion to the volume for diffusion from the external environment to be effective. ITQ2 (i) Oxygen is used in respiration, which in tum provides the body with energy. (ii) Glucose is oxidised during respiration to provide the body w ith energy. (You may h ave chosen other substances.) ITQ3 Heart muscle has its own set of blood vessels, called the coronary arteries and coronary veins. The coronary arteries supply it with glucose and oxygen needed for respiration. ITQ4 vena cava -+ right auricle -+ right ventricle -+ pulmonary artery-+ lungs -+ pulmonary vein -+ left ventricle -+ aorta ITQS Atrial systole - pushes blood from the atria into the ventricles. Ventricular systole - pushes blood out of the heart, so that it can be pumped to the lungs through the pulmonary artery, and through the aorta to all parts of the body. Diastole - allows blood from the body to collect in the atria, before it is forced into the ventricles by contraction of the muscles around the atria. ITQ6 Blood leaving arteriole: • has a lot of oxygen in it as the arteriole carries oxygenated blood to body cells; • is rich in glucose, hormones, water, vitamins, etc. , which will be used by the cells for different purposes . Blood entering venule: • h as less oxygen, as some has been used by the cells in contact with the capillary network; • has less of other substances, as the blood has been depleted of these when passing through the capillary network • has more carbon dioxide and other waste products from cells. ITQ7 The aorta receives blood at the highest pressure from the contraction of the muscles of the left ventricle. As the blood enters the aorta, its thick muscular walls are stretched but do not burst. ITQS (i) Each heartbeat results in a surge of blood, which can be felt as the arterioles stretch to accommodate blood flowing at a high pressure. Each heartbeat results in one pulse. (ii) The pulse rate shows the rate at which the heart is beating because ead1 . heartbeat is felt as one pulse. ITQ9 renal vein -+ vena cava -+ heart -+ lungs -+ heart -+ aorta -+ hepatic artery -+ live r -+ hepatic vein l i mesenreric artery -+ gut -+ hepatic portal vein ITQ 10 (i) Renal artery Renal vein rich in oxygen little oxygen present little carbon dioxide present rich in carbon dioxide rich in glucose little glucose present 157 Life Processes and Disease (ii) Pulmonary artery Pulmonary vein rich in carbon dioxide little carbon dioxide little oxygen present rich in oxygen ITQ11 Platelets are involved in blood dotting, which prevents entry of pathogens when there is a cut on the skin. White blood cells destroy foreign bodies that might harm the organism. ITQ12 On exposure to air, platelets in the blood, in the presence of calcium ions and vitamin K, cause prothrombin, an inactive blood protein, to be converted to thrombin. The presence of thrombin causes the conversion of fibrinogen, another inactive blood protein, into fibrin. Fibrin is made up of insoluble fibres that trap red blood cells and form a clot. ITQ13 • donor AB, recipient 0: no • donor AB, recipient A: no • donor 0 , recipient A: yes • donor B, recipient A: no • donor B, recipient B: yes ITQ14 (i) Hypertension is prolonged high blood pressure. (ii) Factors that contribute to the chances of suffering from hypertension are: • a genetic predisposition (having a relative who suffers from the disease ); • smoking; • obesity; • diet that contains many fatty foods; • no exercise; • old age. ITQ15 The body ha s three lines of defence against infection: • the skin is a physical barrier and openings in the skin have special mechanisms, such as blood clotting, to keep pathogens from entering the body; • if pathogens get into the body through a wound, phagocytes migrate to this site and 'eat' the invading microorganisms; • antibodies are produced to seek out antigens (foreign invaders like bacteria) that have entered the body, and destroy them or neutralise their effects. They are completely destroyed at this point. ITQ16 A vaccine is a substance injected into the body. It contains antigens which cause the immune response, or antibodies which protect the body. ITQ17 . Natural immunity Artificial immunity Active Antigens enter the body naturally and bring about the immune response Antigens are introduced in a vaccine to the body and the immune response is generated Passive Antibodies enter the body naturally Antibodies are introduced in a and protect the body against disease vaccine to the body so the body is protected ITQ18 Immunisation is a programme of dispensing vaccines for various diseases. The act of introducing the vaccine to a person is also immunisation. One advantage is protection against disease. 158 13 • Transport and Defence in Animals Examination-style questions The functions of blood include transport of substances and protection against blood loss and infection (i) Describe the transport of a named substance from the site where it is picked up by blood to a named body cell. (ii) Describe how a blood clot forms and how the clot protects the body against blood loss and infection. 2 (i) Make a labelled drawing of a transverse section of the heart. Use arrows to show the movement of blood through the heart. (ii) Describe the role of the heart in the circulatory system. (iii) Explain why the muscles of the left ventricle are thicker than those of the right. (iv) Explain the effects on the heart if the coronary artery becomes blocked. 3 (i) Compare the structure of an artery with that of a vein. (ii) How does the structure of an artery related to its role as a blood vessel? (iii) Describe how a glucose molecule moves: (a) from the heart to a capillary next to a body cell; (b) from the capillary into the cell. (iv) Compare the composition of blood as it enters and leaves the lungs. A blood vessel in the brain may burst, resulting in a condition called a stroke. Major strokes can result in severe paralysis or even death. Minor stokes may occur without symptoms. 4 (i) Suggest a likely consequence of the bursting of a blood vessel in the brain and how this could result in paralysis or even death. (ii) Suggest reasons why some strokes occur without symptoms. 159 • 0 0 0 0 0 0 0 0 0 Plants describe the movement of substances in plants understand the structure of xylem vessels, sieve tubes and companion cells understand how the structure of xylem vessels suits them for their function describe the movement of water through a plant describe the processes involved in transpiration describe the effect of external factors on transpiration discuss adaptations in plants to conserve water understand the function of phloem in the transport of substances in plants explain how the structure of the phloem is suitable for its function transport in plants vascular bundle f \ xylem phloem I I uptake of water from soil translocation movement of food water in soil around root hairs food storage across cells of root to xylem perennating organs I movement through xylem I movement through eel lls of leaf } transpiration - potometer movement through stomata to air The importance of transport in plants There is much activity going on inside a plant, but it is difficult to imagine that j ust by looking at one. Th e main activity is photosynthesis. During daylight, 14 · Transport in Plants all the leaves of a plant are actively photosynthesising and therefore need all the substances necessary to carry out this process. Transport in plants is thus rela ted to photosynthesis as substances are transported to and away from leaves (figure 14. 1). li;il';' - - - - water may travel up to 1000 ft against gravity without a pump I root extends { further out below the soil than the branches and leaves above Rgure 14.1 Transport In plants. Photosynthesis is summarised by the equation: light carbon dioxide + water ----+ glucose + oxygen chlorophyll • The gases carbon dioxide and oxygen move between the atmosphere and the leaf. The leaves are thin, broad and flat and cover a wide surface area so that diffusion is adequate to transport these gases. • Light rays from the Sun pass into the leaf and get to all the photosynthesising cells. • Chlorophyll is p resent in the leaf cells. • Water must be transported from the soil through the roots to the leaf. Dissolved salts are present in the water. • Some of the manufactured food is transported away from the leaves to be used and/or stored in other pans of the plant. ~ l:fQ1 V'-' Use a table to show the substances that are transported in a plant. Indicate where the substance is transported from and to, and its importance to the plant. xylem vessels > phloem tubes > Transport systems of plants The transport system of plants is much simpler than that seen in animals. There is no pump (heart) or specialised transport medium (blood). Ir is made up of two types of transport vessel: • xylem vessels, which carry water and minerals; • phloem tubes, which carry food materials that the plant has made. Structure of xylem vessels llrffilhll Xylem vessels are long, very narrow, tubes formed from columns of elongated cell s that are joined end to end. The end walls of the cells have disappeared, so a long, open tube is formed . These cells are all dead and con ta in no cytoplasm or nuclei (figure 14.2). The cell walls become thickened with tough lignin . Lignin is very strong and so xylem vessels help to support the plant by keeping them upright. Wood is composed almost entirely of lignified xylem. 1.61 Life Processes and Disease space (no cytoplasm) where water passes cB thick cell wall containing lignin t gap where end walls of two cells have been lost transverse section longitudinal section Figure 14.2 Transverse and longitudinal sections through xylem tissue. Structure of phloem tubes ..1@t:llelff100 sieve tube element > companion cell > Phloem tubes are also made up of cells joined end to end. However these end walls do not break down completely, but become perforated with small holes . These perforated end walls are called sieve plates. Each cell, called a sieve tube element, contains living cytoplasm, but no nucleus. The cell wa lls do not contain lignin. Each sieve tube element has a companion cell next to it. The companion cell has a nucleus which probably controls both cells (figure 14.3). The end walls of the two cells are not completely broken down. This is called a sieve plate and has small holes. companion cell I sieve plate transverse section '-·· Companion cell containing a nucleus and cytoplasm; found next to a sieve tube element. sieve plate sieve plate ._#----l'*'i!.,...=--i.;;+-~-fl!"il!-~• ~ - section cut through phloem H+- - cytoplasm - seen as strands cell wall does not contain lignin ·-· Transverse section of these cells. Companion cells are seen when the section runs through the sieve plate. longitudinal section (a) (b) Figure 14.3 (a) Transverse and longitudinal sections of a sieve tube element and a companion cell. (b) Longitudinal section through a phloem tube and transverse section across it. 162 14 ·Transport in Plants Vascular bundles vascular bundles > Vascular bundles are made up of bundles of xylem vessels and phloem tubes close together. The arrangement of these bundles in roots and shoots is shown in figures 14.4, 14.5 and 14.6. phloem xylem xylem is made up of xylem vessels which run the length of the stem, trunk, branch, etc. a number of xylem vessels lie close together phloem is made up of phloem tubes which run the length of the stem, trunk, branch, etc. I I made up of a number of xylem vessels xylem phloem ~ vascular bundle I made up of a number of phloem vessels Agure 14.4 Transverse section of a root of a dicotyledonous plant. xylem phloem J vascular bundle Figure 14.5 Transverse section of a stem of a dicotyledonous plant. Figure 14.6 Diagram relating the transverse section to the longitudinal section of a stem. Movement of water through a plant ~ ll:Q2 V'-1 How are xylem vessels and phloem tubes arranged in a vascular bundle? (ii) Explain how the structure of the (a) xylem and (b) the phloem are suited to their function. The movement of water th rough a plant can be broken down into five stages (Figure 14.7). The numbers in the following text relate to numbers in the figure). (i) ~ ll:Q3 V'-1 (i) What are the functions of vascular bundles? (ii) Draw a sketch to show how they are arranged in the stem of a dicotyledonous plant. Figure 14.7 Diagram showing the movement or water through a plant. 163 Life Processes and Disease 1 2 3 4 Practical activity SBA 14.1: The rate of transpiration, page 353 CHAPTER9 X ~ IT:.Q~ V'-....1 Describe the route taken by a water molecule from the soil to the air as it passes through a plant. 5 Absorption of water by the root hair cells. Movement of water across the root cortex to the xylem. Movement of water up the xylem. Movement of water across the leaf cells. Movement of water from the leaves. Evaporation of water from the leaves Stomata are found on the underside of leaves (chapter 9). Just inside the stomata are the leaf cells which contain and are surrounded by water. The concentration of water molecules inside the cells is higher than in the air space, and higher there than outside the leaf. So some of the water evaporates from the cells into the air space and diffuses out of the leaf through the stomata, down the concentration gradient (figure 14.8). Figure 14.8 Diagram showing how water evaporates from cells around the air space and diffuses out of the stoma. transpiration > All the cells of the leaf obtain water by osmosiS ---+-++from the xylem. Water evaporates -~~__, from the cells around the air space. Transpiration is the loss of water by evaporation from the surface of leaves. This constant loss of water from the leaves creates a 'pull' of water through the plant. During the day, water is also constantly being taken up from the top of the xylem vessels to supply the photosynthesising cells in the leaves. This reduces the pressure at the top of the xylem vessels, and water thus flows up to the top because the pressure below is greater. This constant flow of water through the plant is known as the transpiration stream. The conversion of liquid water into watervapour as it lea ves the cells and enters the air space requires heat. Using Water moves from heat to convert water into water vapour cell to cell by osmosis. helps to cool the plant. Water moves out n.~~+:.._ of the xylem to surrounding cells. Movement of water within the leaf As water evaporates from the surfaces of cells near the air spaces, its concentration in those cells Water diffuses out (A in figure 14.9)) is lowered. Its of the plant. -+-__.,• concentration in the adjacent cells (B) is now higher than in the A cells. This Rgure 14.9 Diagram showing the movement of water from the xylem, through the cells of the resu lts in the movement of water from leaf, to the air space and then out of the leaf as water vapour. the B cells to the A cells by osmosis. 164 14 ·Transport in Plants ~ IT:QS Water is drawn through all the cells of the leaf by osmosis as it moves towards the air space and then out of the leaf. Describe how water travels from the xylem in a leaf to an air space. Movement of water up the xylem \../'-I lmlet4il•leN m.t¥UeleM ~ IT:Q6 \../'-I List the processes by which water travels up the xylem. - glass tube - water moves higher up a narrow tube Water moves up and through the xylem vessels because of three factors. • Capillarity - When a thin straw is placed in a glass of water, the water rises a little up the straw (figure 14.10). This is due to attraction between r the water molecules and the walls of the straw, which is called adhesion. Water molecules tend to stick together, which is known as cohesion. Thus; water molecules stick together and to surfaces of narrow tubes and the water rises up the tube, which is called capillarity. The narrower the straw, the higher the water will rise. Xylem vessels are extremely narrow and the attraction between the water molecules and the xylem walls is great. • Root pressure - Water constantly moves into root cells by osmosis because the presence of sugars and other dissolved substances in the root means that the water concentration can never be as high in root cells as in the soil. Water absorbed into the plant from the soil creates a pressure in the root xylem. The pressure there is greater than in the leaf xylem because water is being pulled out of the leaf xylem by transpiration. So water moves from the high pressure in the roots up the xylem vessels in the stem to the low pressure in the leaves (figure 14.11 ). • Transpiration pull - The flow in the system is mainly by cohesive forces holding water molecules together and the loss of water by evaporation in the upper areas of a plant creating a tension that 'pulls' water upwards. This is the transpiration pull. a lot of w ater coming from the roots creates a lower pressure in this region since water is lost at the top xylem, made up of narrow xylem vessels \' rf+--+--r--H----r- water molecules are attracted to ,_ the walls of the tube water Figure 14. 1O Water moves up narrow tubes. Figure 74. 11 Low pressure at the top, high pressure below and water is pushed up. Movement of water across the root cortex Water moves between the cortex cells of the roots by osmosis (figure 14.12, overleaf). As water enters the xylem, the cells next to the xylem now have a lower concentration of water. Water then moves into those cells from adjacent cells. These cells now have a lower concentration of water and water flows into them by osmosis. In this way, water moves from the root hair cells to the xylem. 165 Life Processes and Disease cortex cells xylem vessels t t 1 water moves into the xylem and is pulled up r--. ~* - ----'2 water moves from these these cells (B) have-----' more water than cells A and so water moves by osmosis to those cells cells into the xylem and so these cells have less water than the ones next to them Agure 14.12 Water moves between all the cells of the root cortex by osmosis. Absorption of water by the root hair cells ~ l:W:Q7 V'-1 Describe how water travels from the soil to the xylem vessel in the root. The soil particles are surrounded by a film of water which contains some dissolved salts. Inside the root cells, there are sugars and other dissolved substances at a much higher concentration. So water is continuously moving into the root cells by osmosis (figure 14.13). The root hair cells extend into the surrounding soil and the surface area for absorption is thus increased. soil particle cortex cells water moves from the root hair cells to the cortex cells and so water is pulled into the root hairs xylem vessels water moves across these cells to the xylem Agure 14.13 Water moves into the root hair cells. Transpiration Transpiration is the evaporation of water from a plant. It is important beause: • it pulls water up to the leaves for photosynthesis; • the moving water carries dissolved mineral salts up to the leaves; • the evaporation of water cools the plant. 166 14 ·Transport in Plants transpiration rate > • The rate at which a plant takes up water depends on the rate at which it is lost from the plant, called the transpiration rate. The faster the transpiration rate, the faster the plant takes up water. Environmental factors affect the transpiration rate. • Temperature - With high temperatures, as on a hot day, evaporation occurs rapidly. Transpiration rate increases as temperature increases. • Humidity - With high humidity, the air is almost saturated with water r vapour. So the concentration gradient of water between the air spaces and the outside air is low and the rate of evaporation of water through the stomata is slow. Transpiration decreases as humidity increa ses (figure 14. 14). • Air movement (wind) - In windy conditions, water vapour is carried rapidly away from the leaves and the rate of transpiration is fast. During still conditions, the water vapour remains around the leaves and transpiration is slow. Transpiration increases as wind speed increases (figure 14.15) . • Light intensity - During bright light, the stomata are fully opened. This may be to supply carbon dioxide for photosynthesis. With stomata fully open, the rate of transpiration can be high. With dim light, the stomata almost close and transpiration is slow. LJ HO o/ i?JwH ,O H0 H.,Q .,,,,,.---. ~ H· 0 As water molecules H,O Q < diffuse out, they are taken away by wind currents. 11 0 The concentration of water molecules outside will always be small and so there ~n ::) Agure 14.14 High humidity means that the concentration gradient of water molecules inside compared to outside the plant is low. ~ IT:Q8 l../'-1 (i) What is transpiration pull? (ii) What is the transpiration stream? (iii) What is transpiration? xerophytes > mesophytes > hydrophytes > water molecules taken away by wind currents 0 "'II be oot ootw""' d;Ho•oo. Figure 14. 15 Windy days result in more rapid transpiration. When there is very little water in the soil, the stomata almost close. This reduces the rate of transpiration to conserve water. The plant cells become flaccid and the plant wilts as the water lost in transpiration cannot be replaced. Adaptations in plants to conserve water Plants need water for their existence. Transpiration occurs constantly, so a supply of water from the environment is vital. Plants that live in places where water is in short supply are called xerophytes. They show striking adaptations which: • reduce the transpiration rate; • m aximise water uptake from the environment. Other plants are grouped into three categories. • Mesophytes are plants that live in areas where water is readily available. • Hydrophytes are plants that live in very wet, freshwater environments such as ponds, lakes and rivers. 167 Life Processes and Disease haloph es > • Halophytes are plants Lhat live in water with a high concentration of salt, such as in salt marshes, swa mps or areas close to th e sea. Xerophytes may have any of the following fea tures: • fine spine-like leaves to reduce the number of stomata and so reduce transpiration; • thickened stems or leaves capable of storing la rge amounts of water; • an extensive root system to absorb water quickJy when it rains; • a thick epiderm is covered with a thick waxy cuticle to reduce water loss and reflect light and infra -red radiation (so the plant remains cooler); • the ability to trap carbon dfoxide at n ight so that the stom ata can be closed during the da y; • other features such as sunken stomata, rolled leaves and interlocking hairs. Table 14.1 compares the adaptations of a xerophyte (e.g. cactus) and a h ydrophyte (e.g. water lily) to the environments in which th ey live. Xerophyte Hydrophyte Description of environment Very hot, sunlight intense as few or no Still, fresh water from 15 cm to 2 m clouds, no larger shade trees, soil hot deep and dry Description of leaves Small spikes, not green, usually black Broad, flat, green, lie on surface of or grey in colour water, stomata on upper surface Description of stems Thick, green, with thick cuticle Colourless, entirely under water and extending to roots in mud at bottom Table 14. 1 Comparison of a xerophyte and a hydrophyte Uptake and movement of mineral salts Mineral salts are absorbed by the root hairs as ions dissolved in soil water. They are taken up using energy because the concentra tion inside the root is much higher than outside. They are then carried throughout the plant in the xylem. Transport of manufactured food translocation > 168 The soluble product o f photosynthesis are sugars (ma inl y sucrose) and amino acids. These are transported in the phloem tubes. The transpo rt of organic food through a p lant is called translocation . This manufactured food is transported from the leaves (called the source) to wherever it is needed (called the sink) for respiration or storage. 14 ·Transport in Plants Phloem and the movement of food Plants rely on pressure gradients to move their phloem sap. The pressure- flow hypothesis, also called the mass fl ow hypothesis, was proposed by Ernst Munch in 1930 to explain h ow the phloem transports food (figure 14. 16). leaf pholem sieve tube sugar is made during elements photosynthesis ..._..;;;:_..__ _ _ _ _" _ " )- - - sugar lowers the water potential (increases the concentration) which draws in water and raises the pressure L - - - L - -- roots water sink sucrose solution transported from high to low pressure sucrose enters the roots and lowers the pressure in pholem as water is lost Figure 14. 16 The pressure-flow hypothesis. 1 IT:Q9 Sugar made during photosynthesis moves into the sieve tubes at the source (leaf) which makes it more concentrated there. 2 Water then moves into the sieve tubes since it is now more concentrated. 3 The uptake of w ater causes the pressure to build up in the sieve tubes at the source (leaf) which pushes the sap down. 4 Unloading of sugar at the sink (other parts of the plant) relieves the pressure since water is also lost at the sink. Sugar is thus translocated from the leaf to th e root and other parts of the plant that are respiring, storing and using the sugar. How are sugars transported in the phloem? Evidence that phloem translocates organic food ~ Radioisotopes V...J If a plant is supplied with carbon dioxide containing radioactive carbon it ~ V...J IT:Q·1 0 What is translocation? will make food containing radioactive carbon. If the source of radioactive carbon is removed then, after a while, the radioactivity is detected only in the phloem tubes. This means that the food which the leaves h ave made is being transported in the phloem . 169 Life Processes and Disease Ringing The phloem tu bes in a woody stem are j ust underneath the bark. If a ring of bark containing the phloem is removed, sugars accumulate above the ring, resulting in a slightly swollen appearance (figure 14.1 7). food cannot get to lower regions Figure 14. 17 Removing a nng of bark also removes the phloem. Using aphids Aphids are insects that feed on plant juices by pushing their mouth pa rts (stylets) into phloem tubes. If the mouthparts of a feeding insect are cu t off, phloem sap keeps flowing out through the stylets (figure 14. 18). The sap can be analysed and shows the presence of organic material. ~ (a) (b) l'.tQ·11 Mouthpart cut off and left In the plant. L.l'--1 Describe three ways in which the food manufactured during photosynthesis is used by a plant. stylet oozing 'food' Mouthpart (stylet) of aphid penetrates the phloem. It sucks 'food'; this is how it obtains food for energy. Aphids are parasites of plants. Figure 14. 18 If the mouthparts of (a) a feeding aphid are cut off (b) they continue to ooze sap fY - Chapter summary • • • • • • • • • • • All materials needed for photosynthesis must be transported to the leaves of a plant. Water is transported from the soil. Carbon dioxide diffuses in through the stomata. The products of photosynthesis, manufactured food and oxygen, must be transported from the leaf. Manufactured food is transported in the phloem to various sites in a plant. Oxygen diffuses out through the stomata. The structure of the xylem is suited to its transport and support functions. The structure of the phloem is suited to its transport function. Transpiration is the evaporation of water from the leaves of a plant. The rate of transpiration is influenced by many external factors. Translocation is the transport of organic food through a plant. ITQ1 Substance Taken from Transported to Importance to plant Means of transport carbon dioxide air surrounding leaves all photosynthesising cells needed for photosynthesis diffusion water soil - water forms a thin layer around soil particles needed for many purposes including photosynthesis xylem all cells (continued) 170 14 ·Transport in Plants Substance Taken from Transported to Importance to plant Means of transport minerals soil - present as soluble ions in water all cells healthy growth xylem organic food (glucose) leaf cells where it was all cells made all cells must respire to phloem have energy for giving processes oxygen leaf cells oxygen produced during diffusion photosynthesis and not needed for respiration must be removed outside the leaf ITQ2 (i) The xylem vessels are positioned together in the vascu lar bundles in a region where only xylem vessels are found. Similarly, the phloem tubes and their accompanying comparuon cells are positioned together in a part of the vascular bundle where only these structures are found. (ii) (a) Xylem vessels are elongated, tubular and made up of dead cells thus providing a water-proof vessel for the transport of water and absorbed minerals. (b) Phloem is also elongated and tubular but made up of living cells. Energy is thus available for the transport of manufactured food. ITQ3 (i) The vascular bundles consist of xylem vessels and phloem tubes. The xylem vessels transport water containing dissolved minerals from the roots to the leaves of the cell. The phloem tubes transport organic food from the leaves where it is produced to all the cells of the plant. (ii) Your sketch should look like figure 14.5. ITQ4 soil - root hair cell - root cortex cells - xylem - palisade mesophyll - air space - stoma - air ITQ5 Water travels by osmosis out of the xylem and then travels across the cells of the leaf to an air space by osmosis also. The water is moving down a concentration gradient, from a high concentration of water molecules to a lower concentration. ITQ6 Water travels up the xylem by: • root pressure; • transpiration pull; • capillarity, coh esion and adhesion. ITQ7 Water moves by osmosis into the root hair cell from the soil. The water then moves across the cells of the root cortex to the xylem. Th e water is moving along a concentration gradient. As water travels up the xylem, more water moves into the root from the soil . ITQS (i) The flow in the xylem is mainly by cohesive forces holding water molecules together and the loss of water by evaporation in the upper areas of a plant creating a tension that 'pulls' water upwards. This is the transpiration pull. (ii) The water moving up the xylem is the transpiration stream. (iii) Transpiration is the loss of water vapour from the leaves of a plant. ITQ9 Sugar is transported as sucrose which loads into the phloem from the leaf (source). This increases the concentration of the solution in the phloem, which draws in water. This increases the pressure of the solu tion. The pressure is lower at the roots and movement thus occurs from the leaf to the root. At the root (sink), the pressure is lower because the sugar moves into the roots thereby lowering the concentration of the solution, causing water to move our. ITQ10 Translocation is the movement of manufactured food from the leaves to all the cells of a plant. 171 Life Processes and Disease ITQ11 • It is stored as starch in plant cells. • It is used for respiration to release energy for use by plant cells.# • It is used for the production of fruits and seeds during reprodu ction. Examination-style questions (i) State the functions of: (a) phloem; (b) xylem. (ii) Describe how aphids can be used to investigate the function of phloem. (iii) Explain why it is necessary to water many potted plants at least once a day. 2 (i) Define transpiration. (ii) State three environmental factors that affect the rate of transpiration. (iii) Using an annotated diagram only, describe how the photometer can be used to measure the rate of transpiration. 3 (i) Suggest three ways in which transport in plants differs from transport in animals. (ii) Suggest two ways a xylem vessel is similar to an artery. (iii) A plant may be 50 metres in height and does not have a pump to push water to the leaves at the top. Describe how water travels in the xylem, from the soil to the uppermost parts of a plant. 4 Two tubes A and B were set up as shown below. Both tubes were left indoors for 50 minutes and then taken outdoors for another 50 minutes. The tubes were weighed every 1Ominutes. The table shows the results obtained. , ~· cotton wool - J..~ water Tube A Time (min.) 0 10 TubeB 20 30 40 50 60 70 80 90 100 Tube A (g) 305 294 285 272 262 250 220 206 184 150 120 Tube B (g) 280 280 280 279 279 279 278 278 278 278 278 (i) State the processes by which water was lost form (a) tube B, and (b) tube A (ii) Explain the role of the cotton wool in the investigation. (iii) Plot a graph of the results for both tubes A and B on the same page. (iv) Explain fully, the differences seen between tubes A and B. (v) Describe the differences seen for tube A between the first and second parts of the investigation. (vi) Explain fully the differences seen for tube A between the first and second parts of the investigation. 172 Storage in Plants and Animals 0 0 understand the importance of food storage in living organisms identify some products stored and the sites of storage in plants ,/) draw and annotate stages in germinating seeds ZJ describe the structure of a dicotyledonous seed Q) describe the processes taking place within a seed during germination ,/) draw buds from plant storage organs 0 identify some products stored and the sites of storage in animals food storage importance I I ( plants roots stems leaves ' animals seeds fruits liver develo~ment 1 of em~ fat deposits provide for periods of scarcity vegetative reproduction overcome the need for continuous food intake Why do organisms store food? Manufactured food (from photosynthesis using the Sun) is the source of chemical energy for aU living organisms. Glucose, which is the chem ical compound made during photosynthesis, is oxid ised to release energy. All living things depend on this energy fo r life processes to take place. Some of this food, however, is stored. Plants and animals store food in their bodies for the same reasons, some of which are listed below: • to overcome the need for contin u ous manufacture; during the night, photosynthesis stops because there is no light; • to overcome the need for continuous food intake; animals cannot eat continuou sly because other activities are also important; • to provide for periods of scarcity, like droughts and famines; • to provide for special functions (muscle cells need their own store of food); • to produce reproductive structures (fruits, seeds and embryos must store food). Food storage in plants The food made by a plant during photosynthesis may be stored temporarily as starch in the leaves. For longer periods of time, other parts of the plant are used, such as roots, stems, fruits and seeds. Table 15.l (overleaf) lists the importance of the various sites of food storage in a plant. 173 Life Processes and Disease Site of storage Importance of storage Leaves The cells of the leaf need to respire and there is a store of glucose as starch in starch grains. cabbage bokcho Sometimes underground leaves are used to store food. omon garlic leaf, swollen with food - bulbs e.g lily Stems Some stems can become swollen with stored food. Some plants can protect themselves against unfavourable conditions of weather by reserving food in underground stems which will be used to generate new plants. harsh environmental conditions -food stored in 'good' conditions plant stores food plant is still 'alive' underground good conditions again - new growth seen (continued) 174 15 · Storage in Plants and Animals Site of storage Importance of storage Underground swollen stems are sometimes used to store food. - - new shoot growing from rhizome stem tuber - the tip of an underground stem is swollen with food ~ _ y roots growing r rhizome - food stored in an underground stem from rhizome ' r-- roots stem tubers, e.g. Potatc. , - -bud - grows into new shoot corm - the base of a vertical stem becomes swollen with food rms e g eddo dasheen Above-ground swollen stems are sometimes used to store food . ...._ __,.,__ swollen stem stores food sug ne (continued) 175 Life Processes and Disease Site of storage Importance of storage Roots Underground swollen roots are sometimes used to store food. root tuber - tip of root swollen with food root tubers 1:;- 'd r - veet potato tap root - swollen main root These swollen organs (like underground stems) are called perennating organs. They are filled with food stores built up in the time of good growing conditions. They lie protected in the soil. The food store enables the plant to grow quickly when good conditions arrive again. Fruits Most fruits are adapted to protect seeds and to help their dispersal. Succulent or juicy fruits store mainly sugars to attract CHAPTER 21 animals that use the fruits as a food source. The animals help to disperse the seeds that are in the fruit (chapter 21). fleshy edible part of fruit seeds pumpKJr, seed arape Seeds Seeds contain a store of food for germination. The cotyledon(s) or endosperm of seeds store starch, protein and lipids. This store is used up during germination as the embryo develops. The seed respires, using the stores to provide energy for growth and development into a seedling. The stores are needed until the seedling develops leaves and can photosynthesise. Table 15.1 Sites of food storage 1n pants. 176 15 · Storage in Plants and Animals Germination mu1 ..111m 1m.rmm endosperm > Germination is the growth of the seed into a seedling. The seed conta ins the embryo which is made up of the plumule (grows into the shoot) and the radide (grows into the root). The parent plant sends the embryo out into the world with a store of food in the cotyledon and/or endosperm. The embryo is protected by a tough testa (figure 15.1) . ~ IT:Q2 L)'....J (i) What is a perennating organ? (ii) Distinguish between a stem tuber and a root tuber (Iii) What is the importance of the food stored in each of the following - a fruit, a seed, a leaf and an above ground stem? hilum - - --+--- micropyle (tiny hole) micropyle radicle - (a) J embryo -+-- -- plumule (b) Agure 15. 1 A seed (a) in side view, (b) in section. ~ IT:Q3 L)'....J (i) What is germination? (ii) Describe the differences between epigeal germination and hypogeal germination. In its inactive and dehydrated state, a seed can stay a seed for a long time. It is said to be dormant. When conditions are favourable, germination begins (figure 15.2). Germination requires three conditions: • water - moves rapidly into the micropyle and to all the cells. Enzymes are activated and starch is broken down to glucose for respiration; • ox ygen - needed for respiration ; • warmth - to provide the optimum temperature for enzymes. The energy demands of a germinating seed are very Wgh. Energy is released from the stored food by respiration and is used for growth of the rad icle and plumule. The radicle grows down into the soil and the plumule grows upward to develop into the shoot above ground. When the first leaves develop, the seedling begins to photosynthesise to make its own food. It continues to grow and develop more leaves and a root system until it is an adult plant ready to produce flowers. Epigeal g ermination - cotyledons brought above ground cotyledons open, are green and photosynthesise for a while food store used up as grows Hypogeal g ermination - cotyledons remain below ground leaves grow and begin to photosynthesise - leaves grow and photosynthesise _ plumule iil (a) (b) Figure 15.2 Germination. 177 Life Prq~esses a!1d .Diseas~ ~ IT:Q't V-...J Why would a human being die after 10 minutes without oxygen but could go for 5 days without food? ~ IT:QS V-...J How do humans become obese? Why are wild animals never obese? Food storage in animals Animal cells also store glucose, bur nor as search. Animals store glucose as glycogen in granules. Cells respire continuously and animals breathe continuously for their supply of oxygen bur they do not feed concinuously for their supply of glucose. Fats Triglycerides (fats) have a higher proportion of h ydrogen than either carbohydrate or protein. This means fats are a more concencrated source of energy than eicJ1er carbohydrate or prootein. One gram of fat yields twice the amount of energy that a gram of carbohydratecan yield. In mammals, excess fat is laid down for storage under the skin. When we eat excess food, we become obese, 'fat'. Animals that live in cold conditions have a thick layer of fat (blubber) under the skin which serves both as an energy store and provides insulation for the extreme cold (figure 15.3). Glycogen As blood passes through the liver, the excess glucose (from a meal) is changed to glycogen and stored. The liver is the main storage organ for glycogen. Glycogen is also stored in the muscles where it can be qu ickly accessed for muscle contraction. The liver also stores minerals (iron and potassium) and the vitamins A, D and B12 • After a meal, vitamins, minerals and other nutrients from the food pass from the intestine into the blood. This nutrient-rich blood then passes through the liver where the vitamins and minerals in excess are stored for times when they are lacking in the blood (figure 15.4). hepatic vein Rgure 15.3 Penguins and whales need extra fat stores to stay warm in polar conditions. bile duct ~ IT:Q6 hepatic portal vein from ileum Rgure 15.4 Nutrient-rich blood travels directly to the liver from the Intestine. V-...J What is the importance of food stored in: (i) a seed (ii) an egg (iii) the liver (iv) a fruit (v) a tap root? 178 Eggs Embryo birds and reptiles (snakes, turtles, alligators, etc.) develop inside a shell from cJ1e time eggs are laid until they hatch (figure 15.5). The egg white is made up of water and a protein called albumen. The yolk contains protein, far and lecithin (a natural emulsifier). 15 ·Storage in Plants and Animals yolk sac stalk amniotic cavity allantoic cavity chorionic cavity yolk sac Figure 15.5 The eggs of birds and reptiles store food for the developing embryo. ~ 'I Chapter summary • • • • • • • • • • Glucose is manufactured by plants during photosynthesis; some of it is stored Plants and animals store food in their bodies Plants store food in their leaves, stems, roots, fruits and seeds Animals store glucose as glycogen for respiration; plants store glucose as starch One gram of fat yields more energy than one gram of carbohydrate Germination is the growth of a seed into a seedling Water, oxygen and warmth are needed for germination In animals, the liver is an important storage organ Glycogen is stored in the liver and muscle of animals Birds and reptiles store food in the eggs for development of the embryo into a hatchling So that food is available when needed. To prevent shopping for every meal.. To have the choice to plan a healthy and balanced <lier. ITQ2 (i) An organ which enables plants to survive adverse conclitions, such as cold, extreme heat, lack of light or d rought. (ii) A stem tuber is an underground stem swollen with food and a root tuber is an underground swollen root. (iii) To attract agents of dispersal for the seeds. To store the energy needed for germination. To store the energy needed for the reactions that take place in the leaf cells. To help the plant survive adverse weather conclitions. ITQ3 (i) Germination is the growth of a seed into a seedli ng. (ii ) In epigeal germination, the cotyledon is brought above the ground; in hypogeal germination the cotyledon remains underground. ITQ1 179 Life Processes and D isease ITQ4 Oxygen is not stored but food is; both are needed at every moment for respiration. ITQS Humans over-eat; wild animals have no fast-food outlets or groceries. Wild animals hunt for every meal, humans may have passive lifestyles and food is readily availableITQ6 (i) Food stored in a seed is used for germination of a seed into a seedling. (ii) An egg stores food for the developing embryo. (iii) The liver stores glycogen, vitamins etc. so that when lacking in the cliet, they are still available for metabolism. (iv) Food stored in a fruit attracts animals to eat the fruit and so disperse the seed (s). (v) After adverse conditions, the tap root generates a new plant using the stored food. Examination-style questions {i) List three reasons why living organisms may need to store food. {ii) Copy and complete this table. Storage organ in plant Importance fruit seed root tuber {iii) Discuss the importance of storing glucose in plant and animal cells. 2 The weight of a germinating seedling was measured over 7 days and recorded in the table below. Day Weight in grams 1 10 2 10 3 6 4 4 5 12 6 15 7 20 {i) Plot a graph of the change in weight of the seedling over the 7 days. {ii) Describe the changes seen in the graph. {iii) Explain the changes seen in the graph. {iv) Distinguish between epigeal and hypogeal germination. 3 180 {i) Explain the importance of storage in: {a) an animal cell {b) the liver. {ii) Use a diagram to show the importance of the hepatic portal vein. {iii) What is the importance of food stored in {i) an egg and {ii) a seed? Eixcretion, Osmoregulation and Homeostasis Q) understand the importance of excretion in living organisms Q) distinguish between excretion, egestion and secretion Q) give examples of substances excreted by plants Q) give examples of substances excreted from animals Q) understand how substances are excreted from plants Q) understand how substances are excreted from animals Q) understand the structure of the excretory system Q) relate the structure of the kidney to its excretory function Q) relate the structure of the kidney to its osmoregulatory function Q) understand homeostasis Q) understand the control of blood glucose Q) understand the control of body temperature Q) understand the control of the amount of carbon dioxide in the body protein - source of urea excretion of metabolic waste (especially nitrogenous waste) f osmoregulation ( homeostasis control of • amount of water in body • blood glucose • body temperature • C02 concentration in blood ' antidiuretic hormone (ADH) ' animals plants excretory system kidney failure - dialysis I variation in concentration of urine kidneys I pressure filtration I nephrons I selective reabsorption L_ urine _ ) Metabolism The sum total of all the chemica l reactions going on in ce!Js is known as metabolism . Chemical reactions must occur in a!J li ving ce!Js, and therefore 181 Life Processes and Disease i@iji§itelelJ defecation > ~ l'.f:Q· 1 l..)'-.J all living organisms, to susta in life. These metabolic reactions produce a range of waste produces, called excretory products, which muse be eliminated from the organism. The removal of the excretory products is called excretion. Many of these excretory products are toxic and slow down metabolic reactions. If these substances were allowed to accumu late in the body, they could damage and kill body cells. They n eed to be continually removed. Excretion must not be confused with the removal of faeces (defecation.) during egestion in humans (figure 16. l ). Defecation or egestion is the removal of undigested food but excretion is the getting rid of waste products produced by cells during metabolism. Undigested food sin1ply passes through the alin1entary system and is not absorbed into the cells of the body. It passes out of the anus as faeces. Excretion must also not be confused with secretion, which is the release of a substance, such as a hormone, from cells (figure 16.1). Explain the terms 'metabolism', 'excretion', 'egestion' and 'secretion'. r ,Hf-- - -r---+-- secretion of female homlones into blood by the ovaries ~?""9---1-- excretion of urine containing metabolic waste by the urethra excretion of urine containing metabolic waste by the urethra secretion of male-;----------t~~ hormones into blood by the testes Figure 16.1 The difference between egestion, secretion and excretion. Excretory products in animals Waste products of respiration All cells respire co release energy which is used to do the work necessary to keep the cell , and therefore the organism, alive. During respiration, carbon dioxide is also produced. Carbon dioxide is dangerous to living tissue because it increases the acidity of fluids which can affect other reactions. ln humans, carbon dioxide is transported in the blood to the lungs and removed from 182 16 ·Excretion, Osmoregulation and Homeostasis CHAPTER 12 ) { CHAPTERS 10, 19 the lungs during exhalation (chapter 12). Other animals have similar ways of removing the carbon dioxide. Some of the energy produced during respiration is converted into heat energy, the accumulation of which increases the temperature of the body. At high temperatures, enzymes can be denatured (chapter 10) which means reactions will stop. Excess heat is lost through the skin (chapter 19). During exercise, when the rate of respiration is increased, the excretory ' products of respiration are being produced at a faster rate. Breathing rate increases to get rid of the excess carbon dioxide and sweating occurs to get rid . of the excess heat faster. Waste products from red blood cells A red blood cell has a short life span of about three month s. After this time, it is destroyed in the liver or spleen. The red blood cell is packed with haemoglobin, a protein pigment which transports oxygen. The excess protein portion is broken down into excess amino acids and reused by the body. The iron is extracted, stored, and may be reused later. The remainder is broken down into bile pigments and is later excreted by way of bile into the gut and out with faeces. Waste products of protein metabolism Proteins are essential in the diet. However, proteins contain nitrogen and the breakdown of protein that is not needed by the body produces nitrogenous waste which is converted to urea (figure 16.2). Urea is removed by the kidneys during the production of urine (discussed later in this chapter). Excretory products in plants Waste products of photosynthesis CHAPTER9 X Plants photosynthesise or manufacture food from inorganic compounds. This food can then be used by the plant to make energy. During photosynthesis, oxygen is produced as a waste product. It is lost from the leaves of the plant through the stomata (chapter 9). Water is also a product of photosynthesis, but this is either needed by the cells or lost from them in transpiration. liver - the amino acid groups (NH2) of the excess amino acids are converted to ammonia (NH3, highly toxic) and urea (non-toxic, soluble) absorption of amino acids into blood kidneys filter urea out of blood urine, containing urea collects in bladder Blood rich in amino acids is taken to the heart via the liver and distributed to all parts of the body. The amino acids are used during metabolism for growth and repair of body organs. Excretion of urea Figure 16.2 Ingestion of protein leads to the excretion of urea. 183 Life Processes and Disease Other plant wastes ~ IT:Q2 vv Draw up a table to show how the following excretory products are produced and where they are excreted. In animals: carbon dioxide, heat, nitrogenous compounds; in plants: oxygen. Plants al so produce some nitrogenous wastes which are converted into insoluble substances. Calcium oxalate is another insoluble waste product. These wastes are stored in leaves, bark, flowers, fruits and seeds. When the plant sheds these structures, the excretory products are removed. These products can be poisonous to the plant but may be useful to humans as dyes, oils, perfumes and for medicinal purposes. These waste products include tannins, resins, ' latexes, nicotine, caffeine, morphine and gums. Some waste products are stored permanently by the plant, such as in the old xylem (hard wood) · The human excretory system The kidney The human excretory system includes a pair of bean -shaped organs, the l3Gl114'IJ kidneys, which are positioned in the lower back region behind the intestines (figure 16.3 ). The kidneys are the major excretory and osmoregulatory organs osmoregulation > of mammals. Osmoregulation is the control of the amount of water in the blood. Since the blood is constantly in close contact with all cells of the body, this means that the kidneys control the amount of water in the body. ·' < - - ---'If - - - left kidney (slightly higher) ~l!llt---t---'----t-- renal artery takes blood with wastes to the kidney .JEL'----~--+-- renal vein takes cleansed blood away - t-,-=-=;,.,.-o---;- bladder - sac which stores urine temporarily sphincter muscle controls the release of urine ++~~+~~:.:..,ai~;_~ r~,~E;~~~~t- urethra tube leading from the bladder to the environment Figure 16.3 The excretory system of humans. The renal artery brings blood with nitrogenous and other waste products to the kidneys to be cleansed. After passing through the kidneys, this cleansed blood returns to the heart via the renal vein, while the nitrogenous and other iilileIW wastes flow down through the ureter as urine to the bladder to be stored. The Hr:DAM• bladder stores urine temporarily before it is released into the environment via lili§Jhli§M the urethra . Sphincter m uscles control the release of urine from the bladder. Sense cells in the bladder walls are stimulated when the bladder fills, triggering the desire to relax the sphincter muscles and contract the walls of the bladder. When this happens, urine flows out of the bladder through the urethra. Trying to hold back the release of urine requires conscious tightening of the sphincter muscles which can be uncomfortable. Babies are not usually ~ IT:Q3 capable of controlling this muscle before the age of 2-3 years. vv Describe the function of each of the When a person is said to be suffering from a 'weak bladder', that person following: kidney, bladder, renal vein, has to urinate frequently. In this case, it is really the sphincter muscJes that are urethra, the bladder sphincter muscle. weak and the bladder does not hold as much urine as it normally stores. 184 16 ·Excretion, Osmoregulation and Homeostasis ii1¥J•h!i•hiJ 11@00 Figure 16.4 illustrates a longitudinal section through a kidney. The three regions seen are the cortex, medulla and pelvis. Each kidney is made up of thousands of tiny structures called nephrons. Each nephron spans the cortex and medulla, the two outer regions. The pelvis, the innermost region, collects urine from the collecting ducts. The nephrons all end at collecting ducts so that urine, as it forms, flows through these collecting ducts and then out into the pelvis. The urine then flows to the bladder through the ureter. collecting duct Into which urine from a number of nephrons flow renal vein glomerulus Bowman's_. _- capsule renal artery cortex - made up of Bowman's capsules and convoluted tubules of all the nephrons _..,..___ pelvis - collects urine from all the collecting ducts medulla - contains - ......---loops of Henle and collecting ducts which open into the pelvis (a) ureter (b) Figure 16.4 (a) False-colour X-ray showing blood supply to kidney. (b) A simplified diagram of a longitudinal section through a kidney, showing the position of the nephrons. Bowman's capsule > glomerulus > The nephron and urine production Bowman's capsule arteriole from renal artery cortex venule to renal vein - J,. collecting duct The main regions of the human nephron are shown in figure 16.5. It is basically made up of a cup-shaped structure called a Bowman's capsule and a long tubule with clearly defined regions. These are called the proximal convoluted tubule, the loop of Henle, and distal convoluted tubul e and the collecting duct. Each has a very important role in the formation of urine. A mass of capillaries, called a glomerulus, is enclosed by the Bowman's capsule. The blood supply to the glomerulus comes from the renal artery which brings blood carrying nitrogenou s and other waste products to be cleansed. Figure 16.5 Detailed structure of a nephron. 185 Life Processes and Disease Pressure filtration IOifEl'fll The afferent arteriole whlch comes to the capsule has a bigger diameter than the efferent arteriole leaving it. As a result, pressure builds up in the capillaries of the glomerulus. As blood flows under this high pressure, the smaller components of the blood plasma are pushed out into the surrounding cup-like Bowman's capsule. This becomes the filtrate whlch contains water, glucose, amino acids, vitamins, hormones, salts and urea, which are some of the small compon ents of blood. Large molecules, such as plasma proteins, and blood cells (erythrocytes and leucocytes) remain in the blood. The arteriole leaving the · capsule continues to flow through a network of capillaries whlch surrounds the rest of the nephron as shown in figure 16.6. The filtrate flows into the proximal convoluted tubule (figure 16.7). High blood pressure can cause the capillaries of the glomerulus to burst thus destroying the nephron which is the basic unit of the kidney. This can lead to kidney failure. efferent arteriole has Bowman's capsule capillaries pressure builds up in the glomerulus filtrate minus glucose\ \ \ moves down to loop of Henle the~ Figure 16.6 Bowman's capsule. Rgure 16.7 The proximal convoluted tubule reabsorbs glucose from the filtrate. Selective reabsorption proximal convoluted tubule > 186 Selective reabsorption is the reabsorption of a substance in preference to others that are present. This occurs in the region of the nephron called the proximal convoluted tubule. Glucose is a small molecule, so it is a component of the filtrate as it moves through the proximal convoluted tubule. Here it is reabsorbed into the plasma of the capillaries that are wrapped around the tubules. Glucose is not a waste product - it is needed by the body because it is a source of energy. It is reabsorbed from the filtrate, which continues on into the loop of Henle. A person who has diabetes mellitus has glucose in the blood at such a high level that it exceeds that which the kidneys can reabsorb and so glucose is excreted in the urine. This condition is also known as sugar diabetes. The urine of non-illabetics does not contain glucose since all is reabsorbed back into the blood. The urine of a person with illabetes tests positively for reducing sugar (glucose). 16 · Excretion, Osmoregulation and Homeostasis Reabsorption of water loop of Henle > The filtrate now flows through the loop of Henle where water is reabsorbed into the blood capillaries. The longer the loop of Henle, the more water is reabsorbed. The filtrate continues to the distal convoluted tubule. The kangaroo rat, a rodent which lives in deserts, has a very long loop of Henle. Most of the water in the filtrate is thus reabsorbed and conserved by the anima l. It is so good at this that the rat rarely has to drink water. Selective reabsorption distal convoluted tubule collecting duct ,, CHAPTER18 X As the filtrate moves through the distal convoluted tubule and collecting duct, reabsorption of salts and water occurs (figures 16.8 and 16.9). This reabsorption, however, is controlled by h ormones and depends on the concentration of solutes in the blood (chapter 18). Urine ~ l:S:Q~ l.../'-J Describe the route taken by a red blood cell from the renal artery to the renal vein. ~ l:S:QS l.../'-J Describe the route taken by the urea molecule as it travels from the renal artery to the external environment (in urine). The filtrate is now called urine, and contains the water, salts and urea that are not needed by the body. The urine flows to the pelvis of the kidney from the thousands of collecting ducts. It then travels, via the ureter, to the bladder to be stored before urination. filtrate from filtrate with less water ""-.... r+ blood leaves with more water filtrate, water and salts reabsorbed according to the needs of the body filtrate now called urine flows to the peMs then to the bladder Figure 16.8 Water is reabsorbed from the filtrate in the loop of Henle. Figure 16.9 Reabsorption of salts and more water occurs in the distal convoluted tubule and collecting duct. Table 16. 1 compares the composition of the renal artery with the renal vein and sh ows the effect of the kidneys on 'cleansing' the blood. Renal artery Renal vein • contains more water • contains less water because some is lost with the urine • contains a high concentration • contains little or no urea because all ls filtered and lost as of urea urine • salt concentration is higher Table 16. 1 Composition of blood in the renal artery and renal vein. • salt concentration is lower • more oxygen and less carbon • more carbon dioxide and less oxygen because kidney cells dioxide respire to stay alive and do their work 187 Life Processes and Disease Describe the route taken by a glucose molecule as it travels from the renal artery to the renal vein. l.A-J Both the renal artery and the renal vein contain red blood cells and blood proteins since these are coo large to be filtered out into the Bowman's capsule. All glucose is reabsorbed apart from that used by the kidney cells for respiration. The glucose content is thus lower in the renal vein than in the renal artery. ~ Kidney failure and kidney transplants ~ IT:Q6 IT:Q7 l.A-J Explain these terms: 'pressure filtration', 'filtrate', 'selective reabsorption', 'urine'. kidney dialysis > Kidneys sometimes fail as a result of damage or infection. If one kidney is lost. . the remaining one can undertake the work necessary to remove metabolic waste and keep the body healthy. However, loss of both kidneys is fataJ if not treated. It is possible to transplant a kidney from one person (the donor) into the patient (the recipient). The tissue of both persons, the donor and recipient, must match closely since the body rejects anything that it 'perceives' to be foreign or not itself. A person suffering from kidney failure must have regular treatment on a kidney machine which carries out dialysis (figure 16.10). Dialysis must take place for many hours (up to 10 hours) every few days, to ensure the removaJ of wastes and prevent the build-up of toxic compounds that could poison and kilJ the body cells. Dialysis is a method of separating particles of different size in blood by passing the blood through a tube made from a selectively permeable membrane. This tube is surrounded by a dialysis fluid that has the same concentration as normal blood. Any substance in excess in the blood, such as urea and salts, will diffuse out. Dialysis fluid leaving the machine will therefore be rich in saJts and body wastes like urea. (b) heparin - prevents blood clotting dialysis fluid out - dialysis fluid in (a) to heart (cleansed blood) -..........~..,, cleansed blood returned to patient Figure 16.10 (a) A dialysis machine can do the job of the kidneys after kidney failure. (b) How the dialysis machine works. 188 16 ·Excretion, Osmoregulation and Homeostasis Osmoregulation osmoregulation > ~ 11~Q8 l/V (i) Define osmoregulation. (ii) Reabsorption of water occurs in the loop of Henle, and in the distal convoluted tubule and collecting duct. How is reabsorption of water different in the two areas? The kidneys have a second important function - osmoregulation . They regulate the concentration of body fluids. The amount of water and salts found in the blood is never constant. Daily activities such as sweating and eating cause the concentration to vary. The kidneys regulate the concentration of blood by controlling the amount of water and salts that are reabsorbed into the capillaries during selective reabsorption in the distal convoluted tubules and ' collecting ducts. During its normal circulation, blood passes through the hypothalamus in the brain. The h ypothalamus monitors the concentration of the blood and if the blood is too concentrated - for example, from excessive sweating, ingesting large amounts of salt or drinking too little water - the hypothalamus sends a message to the pituitary gland. The pituitary gland is situated next to the hypothalamus; when it receives the message, it secretes more antidiuretic hormone (ADH) into the blood. ADH stimulates the walls of the distal convoluted tubules and collecting ducts to reabsorb most of the water from the filtrate. As a result, small amounts of concentrated urine are produced (figure 16. 11 ). Hypothalamus detects solute concentration in blood hypothalamus If too high, sends message to pituitary to secrete more ADH If too low, sends message to pituitary to secrete less ADH ADH travels in blood to kidneys ADH travels in blood to kidneys More ADH makes distal convoluted tubules and collecting ducts more permeable to water - more water reabsorbed from filtrate Less ADH makes distal convoluted tubules and collecting ducts less permeable to water - less water reabsorbed from filtrate kidneys Small amounts of concentrated urine produced Large amounts of dilute urine produced Figure 16. 11 The concentration of urine 1s controlled by the secretion of ADH by the pituitary If the hypothalamus detects that the blood is too dilute - possibly due to drinking large volumes of water, little sweating or low salt intake - less ADH is released and little water is reabsorbed. In this case, large amounts of dilute urine are produced. Homeostasis homeostasis > Homeostasis is used to describe all the mechanisms by which a constant internal environment is ma intained. While the external environment outside the body may change, the internal environment inside the body must remain 189. Life Processes and Disease fairly constant otherwise all the reactions needed in living cells may be disrupted . The body must detect any deviation from the normal and make the necessary adjustments to return it to its normal condition as quickly as possible. The temperature within the body and the composition of tissue fluid which bathes the body cells must remain as steady as possible for the chemical reactions that occur within these cells to proceed normally (figure 16.1 2). substances to be taken away enter the capilliary b lood flows body cell blood from an arterio le Figure 16.12 Body cells surrounded by tissue fluid and capillaries. Tissue fluid must: • be within a small range of pH (acidity); • contain enough glucose for respiration and activity; • contain enough oxygen for respiration; • not contain high levels of carbon dioxide; • not contain high levels of nitrogenous wastes; • contain enough, but not too much, water; • be within a small range of temperature; • be specific in many other ways for body cells to function normally. ~ IT:Q9 vv Define homeostasis and explain why it is important. Excretion and osmoregulation are examples of homeostasis. A build-up of waste products could damage and even kill cells. Here are some examples of how. • Carbon dioxide causes the pH of the blood and tissue fluid to be lowered, which then affects the rate at which chemical reactions can occur within cells. • Nitrogenous wastes are toxic to cells so they must be cleared from the blood quickly. • Too low a temperature makes chemical reactions too slow, and too high a temperature denatures proteins, including enzymes. • In extreme amounts, water causes body cells to malfunction. Feedback The body can detect changes in these factors in the blood and has mechanisms to bring the levels back to a normal range. These mechanisms are called feedback mechanisms because a change in the internal environment causes a correction to happen which feeds back to the conditions in the internal 190 16 ·Excretion, Osmoregulation and Homeostasis negative feedback > ~ environment. Such mechanisms are used to keep the internal environment constant. ll the internal environment is disturbed, the disturbance sets in motion a sequence of events which tends to restore the system to its original state . This is called negative feedback because it removes the effect of the change. Examples of negative feedback can be seen in figures 16.1 3, 16.14, 16.15, 16. 16 and 16.17. r::= IT:Q-1 0 V'-1 In the regulation of carbon dioxide in the blood, when does an increase in carbon dioxide concentration come about, and how is the concentration brought back down to a normal level? too moch - - - - - - • corrective mechanism normal level normal level Rgure 16. 13 A typical feedback mechanism. body fluids too concentrated high levels of ADH kidneys reabsorb most water from the filtrate • excessive sweating • excessive salt intake • low water intake small amounts of concentrated urine produced correct concentration of body fluids correct concentration of body fluids • little sweating • low salt intake • large water intake large amount of dilute urine produced body fluids too dilute low levels of ADH kidneys do not reabsorb much water from the filtrate Rgure 16. 14 Osmoregulation: control of concentration or blood plasma and body fluids. too much carbon dioxide in the blood _ _ _ _ _ _ _ _ _.,. increases breathing rate - - - - - - - -...... carbon dioxide lost more rapidly from lungs e.g. exercise normal level of carbon dioxide normal level of carbon dioxide carbon dioxide lost less rapidly from lungs too little carbon dioxide in the blood breathing rate reduced Figure 16. 15 Control of the amount of carbon dioxide in the body. 191 Life Processes and Disease • skin produces sweat dilate ,__ _ _ _ _ _..,. body temperature _ _ _ _ _ _ _... •• skin hairscapillaries lie flat ~ rises above 37 °c • respiration slows • panting occurs • fever • exercise • hot environment body temperature drops normal body temperature (37 °C) normal body temperature (37 C) . ° body temperature rises • cold environment body temperature .....,,_ _ _ _ _ _..,.drops below 37 °c • no sweat produced • skin capillaries constrict • hairs become erect -------~ • shivering occurs Figure 16.16 Control of body temp~rature. ~------+ (150 high glucose level - - - - - - - -... mg/100 cm3) pancreas secretes insulin • liver converts glucose to glycogen and fat • cells absorb glucose such as after a meal correct amount of glucose in the blood (90 mg/100 cm3 correct amount of glucose in the blood (90 mg/100 cm3 • liver converts glycogen, fat and protein to glucose • cells absorb less g lucose such as fasting low glucose level _ _ _ _ _ _ _ _... (70 mg/100 cm3) pancreas secretes little insulin Rgure 16.17 Control of blood glucose. I 192 16 ·Excretion, Osmoregulation and Homeostasis • Homeostasis is the term used to describe all the mechanisms by which a constant internal environment is maintained. • Feedback mechanisms are used during homeostasis. • Feedback mechanisms are used to control blood glucose levels, water, body temperature and the amount of carbon dioxide in the blood. .... ITQ1 • Metabolism is all the activities of a cell. These require certain substrates and produce many useful products as well as some waste. The term 'metabolism' encompasses all these reactions at any given time in a cell. • Excretion is the process by which cells and the organisms get rid of metabolic waste. • Egestion is the process by which undigested food in the alimentary canal is leaves the body through the anus. • Secretion is the process by which a chemical, such as a hormone, leaves a gland; for example, the salivary gland secretes saliva into the mouth. ITQ2 How produced Where excreted carbon dioxide during respiration from the lungs heat during respiration through the skin nitrogenous compounds from breakdown of protein from the kidneys during photosynthesis through the stomata Excretory product In animals In plants oxygen The kidney is the organ of excretion of metabolic waste and excess water from th e body. • The bladder stores urine temporarily before excretion. • The renal vein takes cleansed blood away from the kidneys . • The urethra is the tube through which urine passes from the bladder to the outside environment. • The bladder sphincter muscle controls the release of urine from the body. ITQ4 renal artery -+ afferent arteriole -+ glomerulus -+ efferent arteriole -+ renal capillary -+ renal vein ITQS renal artery -+ afferent arteriole -+ glomerulus -+ Bowman's capsule -+proximal convoluted tubule -+ loop of Henle -+ distal convoluted tubule -+ collecting duct -+ pelvis -+ ureter -+ bladder -+ urethra ITQ6 renal artery -+ afferent arteriole -+ glomerulus -+ Bowman's capsule -+ proximal convoluted tubule -+ renal capillary -+ renal vein ITQ7 • Pressure filtration is the filtration of the smaller components of blood into the Bowman's capsule. It occurs because of pressure that builds up as blood flows from a wider vessel into a smaller vessel. • The filtrate consists of the smaller compon ents of blood (urea, water, salt, glucose, etc.) that are filtered into the Bowman's capsule and move along the tubes of the nephron. • Selective reabsorption is the reabsorption of a substance in preference to others that are present. Glucose is selectively reabsorbed back into the blood while other components of the filtrate continue along the nephron . • Urine is the substance that collects in the bladder. It is m ade up of water, salts and urea. ITQ3 • 193 Life Processes and Disease ITQ8 (i) Omsoregulation is the maintainance of constant osmotic conditions in the body. The regulation of the water content and solute concentration of body fluids is important for cells to work efficiently (ii) Loop of Henle Distal convoluted tubule and collecting duct re~bsorption of water is automatic reabsorption of water is controlled by antidiuretic hormone (ADH) the longer the loop of Henle, the more water is reabsorbed water reabsorbed according to needs of body Homeostasis is the maintenance of a constant internal environment. CeJls need a constant environment in which to function efficiently. Homeostasis describes all the mechanisms that come into play to keep the internal environment constant. For example, enzymes need a specific temperature and pH to function efficiently. ITQ10 During exercise, respiration increases and so does the concentration of carbon dioxide because it is a waste product of respiration. Carbon dioxide is transported to the lungs to be excreted. When there are increased amounts of carbon dioxide in the blood, the heart beats faster, allowing blood to flow faster to the lungs and therefore more carbon dioxide is excreted. The carbon dioxide concentration is thus brought back to the normal level in the blood . ITQ9 Examination-style questions (i) Define: (a) excretion (b) osmoregulation. (ii) Using an annotated diagram only, describe how urine is formed in a nephron. (iii) Describe how and why the volume and composition of urine changes: (a) after strenuous exercise; 2 (i) (b) after drinking large volumes of water. List three excretory products, besides nitrogenous waste, produced by animals. (ii) List two excretory products produced by plants. (iii) (a) Describe the production of nitrogenous waste in humans. (b) Describe the excretion of nitrogenous waste in humans. 3 (i) (a) Label the parts A, B, C, D, E, F and Gin the figure below. (b) In each case state its role in excretion. (c) List four differences between A and B. f! i------+--- A +++--- - -+-- B 1------+--- C r._- - -I + - -- 194 - - ---+- F --+- G 16 ·Excretion, Osmoregulation and Homeostasis (ii) The kidneys are very important organs involved in the removal of toxic substances which, if allowed to accumulate in the body, could be fatal. (a) The body offers some physical protection of its internal organs. How are the kidneys protected? (b) Suggest two ways the kidneys may be damaged. (iii) Describe how a dialysis machine works to cleanse blood during kidney failure. 4 (i) Define homeostasis. (ii) The figure below shows some body cells and their supply of blood. (a) List some differences between blood at A and B. (b) Name the process occurring at C. (c) Name the process occurring at D. (d) Explain fully how the cell labelled Eis supplied with oxygen. (e) Name the substance found in F. (f) State three properties of F. (g) State the importance of the properties listed in (g) above. (h) Describe the mechanism by which one of these properties is regulated. 195 ovement 0 0 0 0 0 0 0 understand the importance of movement in animals understand growth movement in plants understand how external factors affect plant movement describe the structure and function of the skeleton of humans describe the mechanism of movement in a limb of humans describe the long bones of a fore and hind limb describe the cervical, thoracic and lumbar vertebrae movement I r r plants skeleton auxin ___,__ ,, ' limbs ( I muscle - tendons ' vertebral column+ skull l joints I ( hinge ' animals ligaments ' r ' phototropism geotropism vertebrae • cervical • thoracic • lumbar ball-and-socket The importance of movement in animals Most animals have to look actively for food and, to do this, they must move from one place to another. Movement from one place to another is called locomotion and it involves the expenditure of energy. There are a number of reasons why animals move from one place to another and these include: • to find food; • to escape predators; • to find a mate; • to disperse offspring; • to reduce competition; • to avoid danger; • to avoid waste products; • to avoid extreme environmental conditions. Animals move in many ways, which include flying, swimming, walking, running and gliding. Each animal is adapted to move in its own special way. For example, humans are adapted to walk or run from place to place. 17 · Movement Movement in plants Movement in plants can be demonstrated by a germinating seedling. When a seed has germinated, it will grow into a seedling if all the conditions for germination are met. Movement is seen when it grows. The shoot grows towards a light source and the roots always grow downwards towards gravity into the soil. This is related to nutrition in the plant as plants need light and water for photosynthesis. Movement in plants is thus usually growth movement. and when we study movement in plants we look at factors that lii•l•ll•juiJ affect their growtJ1. Growth movements are called tropisms. A few plants show another kind of movement apart from growth movement. The sensitive plant (Mimosa pudica), for example, can fold its leaves when touched (figure 17. l). Some plants like the hibiscus can fold their petals at night. Insectivorous plants like the Venus flytrap can catch small insects by moving a part of its body, and the pods of pigeon pea can curl and split when dry to disperse the seeds, as a part of reproduction. Figure 17. 1 Plant movements. (a) Mimosa pudica 'wilts' when touched. (b) The trap of a Venus flytrap closes when an insect touches the sens1t1ve hairs on the surface. Growth movement in plants The most important plant movements are tropisms or growth movements. Growth in response to the stimu lus of light is called phototropism , and geotropism is growth in response to gravity. Growth in plants is controlled by l:Uf3hQ the hormone, auxin. Auxin is made in the tips of roots and shoots which are the growing parts of the plant. It diffuses to the region just behind the tip and Practical activities there it causes growth (figure 17.2). Light and gravity are examples of external factors (factors in the SBA 17.1 : Does gravity affect plant growth? page 354 environment) that affect growth in plants. The shoots of plants respond to light SBA 17.2: The growth of a radicle, by gi·owing towards it. When a shoot is Lit from one side, a uxin breaks down page 355 on the Light side and accumulates on the shaded side. This results in more SBA 17.3: Does light affect plant growth on the shaded side so the shoot bends towards the light (figure 17.3, growth? page 356 overleaf) . In a shoot whid1 is not upright, gravity causes the auxin to collect on the lower side. This has the same effect as before, rn make the shoot grow faster on that side, so it bends away from gravity. phototropism > geotropism > more auxin produced which diffuses down Rgure 17.2 A shoot grows because of the hormone auxin. 197 Life Processes and Disease more auxin accumulated on the shaded side __ growth;;~ .. •:.·/(· . ..... ' '-"'-"' ., ·") ' " ( light light less growth shoot grows towards the light shoot is horizontal less grow~;~!:)) ·~ore auxins accumulate on the lower side due to gravity growth shoot grows upwards ~ IT:Q3 Figure 17.3 Shoots always grow towards light and upwards or against gravity. Agar blocks were placed under cut tips of shoots. The blocks were then placed on growing shoots as seen. How will each shoot grow? However in roots, concentrations of auxins slow down growth. As in the shoot, auxin accumulates on the lower side because the gravity, but in a root the upper side will grow faster because it is less affected by the auxin. No matter how a root is placed in the soil, it will always grow downwards (figure 17.4). l.../'-J gravity TI I! gravity l l l agar block root placed horizontally ·.:. ·:·~ growing tip l l ~ gro~ more growth less ·:'-.., root grows downwards '(. roots always grow downwards or towards gravity Figure 17.4 Roots always grow down Simple investigations can show the effects of light and gravity on germinating seedlings as shown in figure 17.5. They use agar blocks containing auxin because the hormone can easily diffuse through the agar. :·., shoot tip cut and placed on an agar absorbs ! : ~'i -------_.theauxin ..~ shoot tip cut off cut shoots are used in investigation agar block with auxin placed on a cut shoot - shoot will grow /~ agar block with auxin placed to one side of a cut shoot agar block with no auxin results in no growth Figure 17.5 Investigations of growth in seedlings. Agar blocks which absorb auxin are used. 198 17 · Movement Uses of plant hormones · 1;rm;mmm Pesticides are poisonous chemicals which kill pests. Some plants, especially weeds, are described as being pests and herbicides are used to kill them or remove them from the environment. Synthetic plant hormones, for example auxin, can be used as a herbicide. When present in excessive amounts, much more than produced naturally, auxin can disrupt plant growth and so kill plants. 2,4-D and 2,3, 5-T are examples of selective herbicides which kill broad-leaved plants. They stimulate auxin production in the plants. The weed killer causes dicotyledons to grow so fast that they cannot sustain their own growth and they die. Some herbicides work because they are translocated throughout a plan t. They are called systemic herbicides. They are translocated from the leaves, where they were applied to the roots where they interfere with root function. Because the root is killed, the whole plant dies. The skeleton of humans endoskeleton > exoskeleton ) axial skeleton > appendicular skeleton > The skeleton of h umans is an endoskeleton , which means that it is inside the body. All vertebrates have the same arrangement of endoskeleton, with the bones inside and the muscles and other body tissues surrounding it. Some invertebrates also have an endoskeleton, such as squid and octopus, but many have an exoskeleton where the hard part is on the o utside. For example, insects have a jointed exoskeleton made of chitin, and many molluscs, like dams, have a hard calcified shell. Exoskeletons have an advantage in that they can protect the whole of the body, but they also limit the size to which the organism can grow. The body of h umans is held upright by a skeleton which is made of bones arranged as seen in figure 17.6 (overeaf). The human skeleton can be divided into two parts: the axial skeleton, which is the skull and vertebral column with the rib cage, and the appen dicula r skeleton, which includes all the other bones, the fore and hind limbs, and the pelvic and pectoral girdles. Functions of the skeleton in humans ~ l'.T:Q'4 L.-1'-I Name the bones found in the lower limb, from the pelvic girdle to the toes. ~ l'.T:Q5 L.-1'-I What is the importance of the blood vessels and the marrow in a long bone? • Protection of organs - The skull protects the brain, the vertebral column protects the spinal cord and the ribs protect the lungs, heart and much of the liver. Bones surround these delicate organs, forming cup-like structures or tube-like structures in which the organs are housed. • Support of the body - Humans are supported upright more than most mammals and can stand on two feet. The skeleton acts Like a fra me supporting the soft body parts. The limbs are separated by the width of the girdles and this helps to keep the body stable. • Movement - The skeleton is made up of a number of bones joined together. Muscles, and other tissues such as tendons, can cause movement of a single bone. The coordinated movement of many bones results in walking, running and all the movement seen in a human. • Manufactur e of red and white blood ce lls - These are made in the bone marrow of th e pelvis, ribs, sternum and leg bones. Structure of a long bone The long bones are the femur, tibia and fibula of the hind limb and the humerus, ulna and radius of the fore limb. The structure of the long bone is shown in figure 17.7 (overleaf). 199 Life Processes and Disease skull cranium - +--- shoulder girdle (pectoral girdle} ~----clavicl e thorax upper limb -+-- - - - humerus metacarpals phalanges lower limb -+-- - femur -+H--tibia r + - - - fibula the axial skeleton (skull and vertebral column) is coloured D tarsals """M'•:i:--- metatarsals phalanges Figure 17. 6 The human skeleton. The vertebral column In humans, the vertebral column extends from the neck to tailbone or coccyx ~ rf:Q6 vv Describe two functions of the vertebral column. 200 (figure 17.8). It is made up of 33 bones called vertebrae. All vertebrae have the same basic structure (figure 17.9). There are 7 neck or cervical vertebrae, the first of which are the atlas and axis. The cervical vertebrae are followed by 12 thoracic vertebrae, then 5 lumbar vertebrae. The sacrum follows the lumber vertebrae and is made of several vertebrae fused together. Finally, the tail vertebrae are fused to form the coccyx. 17 · Movement neural spine ~ ,,.,,,.... in anterior facet cervical epiphysis J....- cartilage spongy bone (contains red marrow) Structure of a typical vertebra thoracic vertebrae (12) - -compact bone marrow cavity shaft spinal cord runs through the neural canal blood vessel lumbar vertebrae (5) three vertebrae interlock to form part of the vertebral column sacral vertebrae (fused) epiphysis coccyx_o_r _'ta _i_I' - - - - - Rgure 17.8 The vertebral column in humans. Figure 17.7 The structure of a long bone. v ~C centrum transverse process ~ertebrarterial canal (two small holes in vertebra, one on either side) Cervical vertebra - has two small holes apart from the large neural canal neuraI canaI \If (}___neural spine (long) transverse process (short) - facet - - 't- neural spine (short) neural canal ~ ' facet ~ 6 centrum big and - - well developed ~ rib _/ -...- J \ .,J-~ centrum ~ Thoracic vertebra - articulate with ribs as well as other vertebrae ~ transverse process (long) ) Lumbar vertebra - has large centrum and long transverse processes Figure 17.9 The cervical, thoracic and lumbar vertebrae in humans. 201 Cervical vertebrae • • • • large neural canal because these vertebrae are closest to brain; vertebraterial canals present; shore neural spine; short transverse processes. Thoracic vertebrae • neural canal smaller than cervical because further from brain; • very long neural spine for attachment of back muscles; • short transverse processes to accommodate rib bones on either side. Lumbar vertebrae • • • • centrum big and well developed to support weight of body; neural canal small; long, wide neural spine; long transverse processes for muscle attacl1ment. Table 17. l summarises the functions of the various surfaces and projections of ead1 vertebra. Part of vertebra Function neural canal protects the spinal cord neural spine muscle attachment transverse process muscle attachment facet articulates with facets of adjacent vertebrae and allows slight movement centrum central rigid body of vertebra, discs of cartilage separate adjacent vertebrae Table 17.1 The functions of the different parts of a human vertebra. Movement in a limb of humans Practical activity SBA 17.4: Compare the movements of tour animals, page 357 spongy bone compact bone articular cartilage - functions as a Movement in a limb is brought about by many tissues, such as muscles, tendons, ligaments and bones, all working together. Bones are able to move because of the presence of joints in the skeleton. A typical joint is seen in figure 17. 10. Bones are attached to each other by ligaments. They cannot move on their own. Muscles are seen around the bones and move the bones when they shorten (contract) and lengthen (relax). This is sh own in the simplified diagram in figure 17.1 1. muscle ligament synovial membrane contract ligament synovial fluid - lubricates joint reducing friction during movement Figure 17. 1O A typical joint. 202 contract +-bone moved to the left Figure 17. 11 Bones are moved by muscles. - bone moved to the right antagonistic muscles > l(ijet•l•hll The muscles of the arm move the bones of the arm to flex or extend the arm in the same way as seen in figure 17.12. The bones are attached to each other by ligaments and attached to muscles by tendons. They have special names (triceps and biceps) and contract or relax to move the bones. All the bones of the body need muscles to help them move. Imagine the coordination of contraction and relaxation of muscles needed to cup the fingers around a , bottle, and then move the bottle to the lips to cake a drink of water. Movement is brought about by the contraction of antagonistic muscles . Antagonistic muscles are pairs of muscles that always work together: when one is contracting, the other is relaxing. They move many bones of the human skeleton . In the joint of the upper arm, the triceps and biceps are antagonistic muscles. They are attached to the bones by tendons which are non-elastic. A muscle shortens when it contracts and is lengthened when it relaxes. Movement of the bone is brought about when the muscles pull on the bones (figure 17.12). Flexing the arm Extending the arm /\~ tendons, attach r muscle to bone ~ biceps muscle (contracts) (flexor muscle) triceps muscle (contracts) (extensor muscle) triceps muscle (relaxes) ulna biceps muscle (relaxes) ,. arm bends or flexes arm extends Figure 17.12 Flexing and extending the arm. flexor muscle > extensor muscle > When the biceps contracts (and triceps relax), it pulls the bones of the lower arm upwards so the arm bends or flexes. The biceps is called a flexor muscle. When the triceps contracts (and biceps relaxes), it pulls th e bones of the lower arm so that the arm straightens or extends. The triceps is called an extensor muscle. Types of joint There a re three types of joint: • immovable joint; • partially movable joint; • movable joint. E!UliiM gliding joint > l•M•llt.lleiH Immovable joints are also called sutures. The bones are fu sed together allowing no movem ent. Examples are joints of the cranium and pelvic girdle. Partially movable joints allow some movement. Examples of joints between the tarsals (ankle) and carpals (wrist). The bon es ca n slide over each other producing the movements seen in the wrist and ankle. These are also called gliding joints. A partially movable joint also exists between the atlas and axis at the top of the neck allowing some m ovement of the head in relation to the spine (e.g. nodding or shaking). This is called a pivot joint. 203 synovial joint > Moveable joints are also called synovialjoints. Synovial fluid in these joints reduces friction allowing free movement of the bones. There are two types of synovial joint (figure 17.13). • Hinge joint - Allows movement in one plane; for example, elbow, knee and finger joints. Bones of a hinge joint are capable of carrying heavy loads. • Ball-and-socket joint - Allows movement in all planes; for example, the shoulder and hip joints. Hinge joint Ball-and-socket Joint one plane - - s o cket • movement is restricted to one p lane • may be dislocated • e.g. elbow, knee, fingers • movement is allowed in three planes • easily dislocated • e.g. pelvic girdle (hip), shoulder Figure 17. 13 The hinge and ball-and-socket joints. ~ ~ l:F:Q1' l:F:Q9 (i) What is a joint? (ii) What is the importance of joints? Put these in the order they occur when extending the arm: (a) the arm is pulled down. (b) biceps muscle relax. (c) ligaments stretch arm. (d) muscles pull on radius and ulna. (e) triceps muscle contract. \../'-I ~ l:F:Q8 \../'-I Name the structures found around a typical joint, giving a reason why each is important. \../'-I ~ l:F:Q·1 0 \../'-I (i) What kind of joints are seen in the fingers? (ii) What is the advantage of each finger having a number of hinge joints, rather than one hinge joint? 204 17 · Movement fl' - Chapter summary • Movement is a characteristic of life. • There are a number of reasons why animals move. • Some plants can move some of their parts, but all plants show growth movement or tropisms. • During growth, plants respond to light (phototropism) and gravity (geotropism). • The tips of the growing parts of a plant produce auxin, the hormone responsible for growth in plants. • The skeleton of humans has many functions, one of which is movement. • The skeleton forms a framework inside the body of humans and is made up of the axial and appendicular skeletons. • The axial skeleton consists of the cranium and the vertebral column. • The vertebral column is made up of many bones called vertebrae and includes the cervical, thoracic and lumbar vertebrae. • The appendicular skeleton consists of the limbs and rib cage. • The skeleton is made up of many bones joined together; movement is seen at these joints. • Movement is brought about by muscles, tendons and ligaments at these joints. • There are many kinds of joint: immovable, partially movable and movable joints. Any two of the examples from the bullet list on page 000 is suitable. A plant has to move (grow) towards the ligh t because light is necessary for photosynthesis. Some plants are able to close special leaves that trap small insects. These plants need to acquire their protein from insects, because they live in nitratedeficient soil. ITQ1 ITQ2 ITQ3 Pelvic girdle, femur, tibia and fibula, tarsals, metatarsals, phalanges. The blood vessels bring nutrients and oxygen to the bone, since it is alive and must respire. Also, these vessels take away waste produced by the bone. The marrow cavity is important for the production of red blood cells. Red blood cells are constantly produced in the bone marrow. ITQ6 The vertebral column holds the body upright and protects the spinal cord. ITQ7 (i) A joint is where two bones m eet. It is lubricated to reduce friction when the two bones move. (ii) Joints are important for movement. All movement takes place because muscles contract and move the appropriate bones. The bones move from where they are joined to another bone. Without joints, no movem ent would not be possible (not movement of the entire body, nor movement of a part of the body). ITQ4 ITQS 205 ~;.; :.- .... L~f~! ~.recesses and DiseC!_se · · .. .. ITQ8 Structure Importance ligament joins bone to bone, and can stretch as the bones move away from and towards each other during movement muscle can contract or lengthen - because it is attached to bone, it can pull on (extend) the bone, so muscles bring about movement ( tendon joins muscle to bone, is non-elastic, so the effect of the muscle contraction or· relaxation can be applied to the bone synovial fluid fluid found in the joint which helps to reduce friction when bones move with respect to one another. ITQ9 1 - b and e (antagonistic muscles); 2 - d; 3 - c; 4 - a ITQ10 (i) The fingers have hinge joints. (ii) Having a number of hinge joints allows fingers to be curled around an object. Examination-style questions (i) List the main functions of a vertebrate skeleton. (ii) Make a labelled drawing of: (a) a typical vertebra; (b) a vertical section of a typical long bone. (iii) The human skeleton, as is typical of mammalian skeletons, can be divided into two components or parts. Name these parts and the bones included. 206 2 (i) Suggest some differences between movement in plants and animals. (ii) Define: (a) phototropism; (b) geotropism. (iii) Explain fully how plants respond to light. (iv) How do plants growth substances differ from animal hormones? (V) (a) Since the late 1980s, scientists have been conducting experiments on the effects of space travel on seed germination. Why do you think there is an interest in such studies? (b) Experiments conducted on seeds in space yielded growing plants, but these 'extra-terrestrial' plants did not grow straight, they grew in all directions. Explain what might have caused this to happen. (c) Suggest ways of producing 'straight plants in space. 3 (i) Make a labelled drawing of a typical joint. (ii) The exoskeleton of an insect lies outside the muscles that are attached to it. Like the joints of the endoskeleton, the joints of an exoskeleton, provide an excellent means of locomotion. The diagrams I and II below show joints seen in an insect and humans. I - insect's limb extensor muscle II-human limb A E c (a) (b) (c) (d) Name the parts A, B, C, D, Eand F. Using a diagram, show how the insect can flex or bend its leg. Using a diagram, show how the human can bend the arm. What name is given to muscles that work together to move a limb? Give examples of these muscles as seen in the insect's limb and human's limb. (iii) Describe the state of these muscles when: (a) the insect's limb is extended or straightened. (b) the human's limb is extended or straightened. 207 l·nritabi Iity, Sensitivity and Coordination 0 0 0 0 0 0 0 0 0 0 define the terms 'stimulus' and 'response' describe responses of green plant and invertebrates to stimuli understand why responses to stimuli are important for survival of organisms define the terms 'receptor' and 'effector' identify the main sense organs and the stimuli to which they respond describe the main sense organs describe the nervous system describe the endocrine system explain a simple reflex action distinguish between a cranial and spinal reflex 0 describe the functions of the main regions of the brain 0 discuss the physiological, social and economic effects of drug abuse sense organs eye ear nose tongue skin receptor stimulus survival of organism ' nervous(system spinal(chord response ' brain effector motor sensory relay synapse neurone movement towards or away : Irritability, Sensitivity and Coordination Irritability CHAPTER 1 1n chapter 1, we found that irritability is one of the seven d1aracteristics of living things. It means that living organisms can respond to changes in their internal environment and the world around them. These responses usually increase their chances of survival. Animals and plants react to changes in the environment, not only drastic climate changes, but also simple everyday changes. For example, a snake looking for food will move toward the scent of a rat, and the shoots of a seedling will grow towards Ugbt. Stimulus Eihuii!ilO-fl li%l•r•lli'--J#I A stimulus is a change in the environment that an organism reacts or responds to. It could be light, temperature, a texture, a chemical in the air or moisture, a response is the d1ange in the organism brought about by the stimulus (figures 18.1 and 18.2). The response to stirnuU is important for the survival of organi sms. Response of animals Stimulus Figure 18.2 This male moth has large antennae that can sense just a few molecules of a chemical attractant that a female several miles away has released. Q5b IT:Q·1 l...A.J (i) Define irritability. (ii) Why is it important for the survival of an animal? Molecules from the rat are in the air. The snake detects these as it 'tastes' the air with Its forked tongue. Response The snake moves towards the rat. It is delicious food and important to the survival of the snake. Figure 18.1 A snake responds to the stimulus of food. Table 18.1 shows some examples of stirn ulL the responses and the importance to the organism of responding in this way. Stimulus Possible response Importance to organism of response chemical from an organism move towards organism organism may be a potential mate or potential prey moisture in soil move towards moist areas prevent desiccation or dying, especially for organisms without a waterproof outer covering light move from light to darker areas escape from predators since it is harder to be seen in darker areas cold temperatures move away from cold temperature organism cannot survive In cold temperatures, body not adapted Table 18.1 Responses to some stimuli and the importance of those responses. 209 --- . Life Processes and Disease Response of green plants CHAPTER 17 In chapter 17, we saw that seedlings respond to unilateral (one-directional) stimuli of light and gravity. The roots grew in the direction of gravity and the shoots grew towards light. Plants need water and minerals from the soil, so the roots must grow down into the soil to reach them. Green plants, including seedlings, also need light for photosynthesis. It is therefore important for the survival of green plants to grow towards light (figure 18.3). A plant in a room will grow towards the window where there is sunlight. A seed may be taken into a cave by a bird or bat. It may germinate and then the seedling will grow towards light and out of the ca ve's entrance or any other opening. Otherwise, the plant will die for lack of food in the darkness. Invertebrates, like millipedes, earthworms and wood li ce, need certain conditions to survive. They respond to variations in light intensity, temperature and moisture. The investigation illustrated in figure 18.4 shows that these invertebrates respond by moving towards a cooler temperature, moist soil and away from bright light. These responses ensure that they do not dehydrate and are hidden from predators, that is, the responses help to ensure their survival. It germinates and begins to grow towards the light at the cave's entrance. It could die in the darkness. seed taken into a cave by a bird or bat It reaches the entrance where there is light. It can now photosynthesise efficiently and will survive. Figure 18.3 A plant responds to the stimulus of light. Ilght dry soil 10 organisms, e.g. woodlice, are placed in the apparatus After a while they all move towards the dark, moist areas. Figure 18.4 Many small invertebrates respond to the stimuli of light and moisture. ~ ll'!Q2 V-...J The senses of some animals are said to be better developed than in a human. Give two examples of animals like this, and explain the importance of the sense to the animal. sense organs > 210 Unlike most humans, anima ls in the wild have to find food every day and maybe avoid being food for another organism. They have to be very aware of stimuli coming from their environment and be able to make the appropriate response. More often than not, these everyday changes in the environment are a matter of life or death. The sense organs of humans Humans have five senses: hearing, sight, smeU, ta ste and tou ch. In humans, the main sense organs are the eyes, ears, nose, tongue and skin. A group of sen se cells and other tissues fo rm a sense organ. • Eye - At the back of the eye is the retina which is a layer of sensory cells that respond to light. Impulses are sent from these ceUs to the brain by the optic nerve so that d1anges in shape, colour, brightness and distance are detected. : Figure 18.5 Taste buds on a human tongue. Irritability, Sensitivity and Coordination • Ears - Sensitive hairs in the inner ear respond to vibrations in the air (sound waves). Impulses are sem from these hairs to the brain by the auditory nerve so that changes in the quality, tone, pitch and loudness are detected. • Nose - As air flows into the nose during breathing, chemica l molecules in it touch sensitive hairs. These send messages to the brain so that changes in scent are detected. • Tongu e - Groups of receptor cells, called taste buds, respond to chemicals in the food (figure 18.5 ). Different parts of the tongue are sensitive to different flavours like salt, sweet, bitter and sour. These send m essages to the brain so that changes in flavour of the food are detected. • Skin - This is the largest organ of the body. Nerves ending as sensory cells are scattered throughout the skin. These are sensitive to pain, touch, change in temperature, light pressure and heavy pressure. They send in1pulses to the brain so that it can detect what has been touched. The nervous system 1.r411g.ur41 Practical atctivity SBA 18.1 : Touch receptors in skin, page 359 The ne rvous system is made up of neurones or nerve cells. Neurones transmit electrical impulses to and from the brain. The nervous system is made up of: • the central nervous system (CNS) whkh consists of the brain and spinal cord; • the peripheral nervous system (PNS) whid1 consists of all the nerves outside the central nervous system (figure 18.6). central nervous system (CNS) cranial nerves (from brain) peripheral nervous system (PNS) ~r++- spinal nerves (from spinal cord) Rgure 18. 6 The nervous system. sensory neurone > motor neurone > relay neurone > The peripheral nervous system forms a vast communication network linking the reception of the stimuli to a response. Receptors receive stimuli from the environment and responses are brought about by effectors. Sensory neurones conduct impulses from receptors to the central n ervous system. Motor neurones conduct in1pulses from the centra l. nervous system to the effectors. Intermediate or relay neurones link sen sory and motor neurones. They are found in the central nervous system (figure 18.7, overleaf). 211 Life Processes and Disease dendron - carries impulses towards the cell body intermediate or relay neurone motor neurone sensory neurone node of Ranvier Figure 18. 7 Motor, relay and sensory neurones. .,____ ----- stimulus sensory neurone I receptor IITT-O~L relay neurone / - motor neurone effector brings about response Figure 18.8 The structures of the sensory, relay and motor neurones can be related to this typical nervous pathway. ~ IT:Q3 V'-1 Describe the nervous system of humans. (ii) How do you respond to a stimulus? (i) 212 Figure 18.8 is a typical pathway, from the s~ulu s touching the receptor to the effector bringing about a response. The numbers in the following paragraphs refer to figure 18.9. 1 The stimulus is, say, a hot object touching a pain receptor in the skin of the hand. 2 A signal travels along the sensory neurone to the central nervous system (CNS). 3 In the CNS, a relay neurone carries the signal through the brain. 4 The rela y neurone passes the signal to the motor neurone. 5 The signal travels along the motor neurone to the effector (biceps muscle) which responds (contracts). 6 The hand is moved away from the hot object. . 18 ·Irritability, Sensitivity and Coordination contraction of the biceps muscle moves hand away from hot object axon dendron - CNS spinal cord to brain stimulus e.g. hot object motor neurone conducts nervous impulses from CNS to the effector sensory neurone conducts nervous impulses from receptor to CNS Rgure 78.9 A typical pathway of receptor to effector. ~ l'.fQ~ V'-' Describe a typical nervous pathway. The nervous system is adapted to carry messages quickly between specific locations in the body, so that quick responses can be made. Sometimes the effector may be a gland. Endocrine glands are found throughout the body and they regulate a wide range of activities, including heart rate, metabolism and reproduction. Together, the nervous system and endocrine system co-ordinate all of the body's activities. The synapse E'AhM"1¥il Signals travel along neurones as electrical impulses, which are very fast. However, there are millions of neurones in your body, and where the ends of two neurones meet there is a small gap called a synapse (Figure 18.10). Electrical impulses cannot cross th ese gaps, so they are converted to a chemical signal in order to cross the synapse. As they reach the other neurone, they are converted back into electrical impulses so that they can con tinue quickly on their way. A sensory neurone impulse arrives in sensory neurone cell body mltochondrlon sensory A~neurone synapse Figure 18.10 A synapse. - - next nerve cell message is transferred to another nerve cell B 213 Life Processes and Disease ~ Table 18.2 describes some receptors, effectors and responses in humans. V'-1 Stimulus l:T:QS What is the receptor, the effector and response of an animal when it sees and moves towards a mate? Receptor Effector Response object moving towards retina of the eye the face receives and sends a message to the brain muscles of the neck head turns away so the object cannot hit the face very hot object which is nerve endings in about to be picked up the skin sensitive to temperature send a message to the brain muscles of the arm hand pulls away from. the hot object chemicals from food (smell) reach the nose chemoreceptors in the salivary gland nose send a message to the brain saliva secreted and body prepares to digest food Table 18.2 Receptors, effectors and their responses in humans. ~ l:T:Q6 V'-1 (i) What is a synapse? All activity involves the coordination of the brain, spinal cord, sensory and motor neurones. Stimuli are constantly being received, sent to the brain where they are analysed and appropriate responses sent back (figure 18. 11). (ii) Describe what happens at a synapse. 1 Receptors in the skin (and face) receive information and messages are sent to the brain. @ Brain receives and interprets '-._. ' / message: appropriate response determined. / ·! / -1 I\ Examples 3 Messages are sent from the brain to the appropriate effector. Jl Touched on shoulder nervous Person turns around Receptors in skin of shoulder ~ system ~ Effectors are muscles needed to turn the body Your name is called Receptors in ears nervous Sees a friend Receptors in eyes nervous system ~ ~ system Person stands up Effectors are muscles needed to stand up (legs) Person walks towards friend Effectors are muscles needed to walk Rgure 18. 11 Every day, millions of messages are received by the brain and appropriate responses made. This Involves the coordination of sensory neurones, CNS and motor neurones. 214 ~~~.l!!'itabil.!_ty, Sensitivity and Coordination Reflex actions reflex action > Practical activity SBA 18.2: Two reflex actions, page 360 ~ IT:Q7 V-...J What is the reflex action? A reflex action is a rapid and automatic response to a stimulus. It does not require conscious control (you do not think about doing it). Examples of reflex actions are the knee jerk, sneezing, the pupil reflex and blinking. The pathway between the receptor and effector is called the reflex arc. There are two kinds of reflex: 1 • spinal reflexes are nerve impulses that pass through the spinal cord and do not go to the brain (e.g. the knee jerk response, figures 18. 12 and 18.13 ); • cranial reflexes are reflexes in the head region (e.g. blinking and the response of the pupil in the eye to light, figure 18.12). (a) Simple (flow) diagram of the knee jerk reflex (spinal) (b) Simple (flow) diagram of the pupil reflex (cranial) bright light stimulus stimulus received by pressure receptors at base of knee .....I sensory nerve from receptors in eye sensory nerve to spinal cord ---~ r----~ motor nerve to leg muscles (effector) pupil gets smaller in response to bright light to protect the retina motor nerve to muscles in iris Rgure 18. 12 Simple diagrams of a spinal reflex and a cranial reflex. 2 stretch receptors detect impulse causes the leg muscles to contract. pulling the foot forwards the pressure on the tendons ::::~~~===f=.==~ 9 sensory neurone 4 Impulse comes to the CNS but does not go to the b rain knee cap femur 1 st imulus - pressure on tendons ---i- ---r- tibia 7 foot pulled forwards - res ponse Figure 18.13 Detailed description of the knee jerk spinal reflex. 215 Life Processes and Disease The brain ~ IT:QS \./'-I A person who suffered brain damage is now unable to see. Explain how this could happen. (ii} What consequences would result from damage to the cerebellum of the brain? (i} The brain is the most important part of the nervous system. It enables humans to 'think' or 'reason', a skill which is supposedly lacking in most animals. The brain has grey maner on the outside and white matter on the inside. It is surrounded by tough membranes, called meninges, and cerebrospinal fluid which cushion it from knocks. It is also surrounded by the bones of the skull. Your brain is very well protected (figure 18.14) . Humans can perform compl ex mental and physical activities co-ordinated by different areas of the brain (figure 18.15). They receive stimuli from the environment and the brain brings about the appropriate response. (a) (b) meninges - the membranes covering the brain and spinal cord ~-- left cerebral hemisphere bone cerebrospinal LM-....._,,....,__~ fluid h<=;;;:;;;;;:;;:~~~~;:;;:::,~~c_~%-~'7'--fr hypothalamus - -11-.<--..,....::.+ - cerebellum medulla oblong ata dorsal root} sp inal cord ganglio n ventral root . 1 sp1na nerve Figure 18. 14 The brain (a) Section through the head. (b) External view of human brain. motor areas toot cerebrum leg trunk skin and muscle sensory areas receive impulses from receptors via sensory neurones hypothalamus controls the - - -- .::...- - - body's internal environment - homeostasis pituitary gland - ----'=tendocrine gland, secretes several hormones cerebellum controls balance by coordinating muscular activity -~--- m edulla oblongata controls involuntary muscular actions, e.g. heartbeat, breathing, swallowing , peristalsis, blood pressure Agure 18. 15 Functions of the various parts of the brain. 216 '°1.:;l 18 ·Ir r it a bility, Sensitivity and Coordination The spinal cord is also composed of grey and white matter, but here the white matter is on the outside and the grey matter on the inside (figure 18.16 ) back of body ventral root front of body Figure 18.16 Cross-section of the spinal cord. Autonomic nervous system autonomic nervous system > CHAPTER 16 ~ IT:Q9 vv Name six activities that occur in the body while a person is sleeping. (ii) How is it possible for these activities to take place? (i) The autonomic nervous system is the n ame given to all the nerves which automatically control the normal functioning of internal organs like the heart without conscious control. For example, your heart keeps beating, peristalsis occurs, breathing occurs, pupils dilate and blood vessels constrict, without you having to think about any of these responses - they occur even when you sleep. The internal environment of the body must be kept stable (chapter 16). Homeostasis, the maintenance of a constant internal environment, depends on the autonomic nervous system. All cells, and th erefore tissues and organs, function efficiently in certain conditions of temperature, pH and wate r. Any change in these conditions must be remedied: for example, if there is a lack of water, cells become dehydrated, so th e body responds to increase the amount of water available. Animals and plants respond to internal changes in ways that lead to stabilising the internal environment. The endocrine system In humans, the endocrine system consists of a number of glands called endocrine gland > endocrine glands. The endocrine system controls growth and developmen t. A gland is a structure which secretes a specific chemical substance. In humans, there are two types of gland: exocrine glands and endocrine glands (figure 18. 17). exocrine gland endocr ine gland (gland w ith a duct) (ductless gland) blood with no secretion secretions arrive at target area duct through which secretions pass blood with the secretion flows to the target organ Figure 18. 17 Exocrine and endocrine glands. 217 Life Processes and Disease exocrine gland > ~ IT:Q-1 0 V"--1 Draw up a table to show the differences between endocrine and exocrine glands. Describe how they work and give examples of the substances that they secrete. Exocrine glands transport their secretions by ducts to other parts of the body. For example, salivary glands in the mouth secrete saliva via ducts into the mouth; tea r glands by the eye secrete fluid which passes through ducts onto the eye's surface. Endocrine glands secrete chemicals called hormones directly into the bloodstream . These glands have a rich blood supply to collect the hormone and transport it to its target organ. The pancreas is an organ of the digestive system. It contains rwo types of secretory cell. One type produces enzymes that make up pancreatic juice which is secreted through a duct to the duodenum. Tbe type produces the hormone insulin that diffuses into blood vessels which pass through the pancreas. The pancreas is therefore a structure that is made up of both exocrine and endocrine glands (figure 18. 18). pancreas - some cells make enzymes, some make insulin blood with no hormone (insulin) flows to pancreas enzymes in the gut - blood rich in insulin leaves the pancreas Figure 18. 18 The pancreas contains both endocrine and exocrine glands. Hormones help to control and coordinate many body activities, including growth and development. They are produced by endocrine glands positioned in specific areas of the body (figure 18.19). - --+-- hypothalamus (manager) pituitary (master gland) ovary (female) 1-- r.,.-- - tt-+- (progesterone, oestrogen) ---.,,c-- testis (male) (testosterone) Rgure 18. 19 The endocrine system in humans Hormones are produced in very small amounts and travel through the body in the bloodstream to target organs. Hormones influence the activities of these target organs . 218 · 18 ·Irritability, Sensitivity and Coordination The pituitary and the hypothalamus hypothalamus > ~ IT:Q-11 V'-1 (i) What are hormones? (ii) Name four different hormones produced in humans. Most, but not all, endocrine glands work under the influence of a single master gland - the pitu itary, which is situated beneath the brain. The hypoth a lamu s is situated close to the pituitary. While the h ypothalamus is not an endocrine gland, it regulates the secretion of some of the pituitary gland hormones. If the pituitary is thought of as the master gland of the endocrine system, then the hypothalamus can be tho ught of as the manager. The hormones produced by the pituitary and their effects are shown in Table 18.3. Hormone Functions pituitary growth hormone stimulates growth of the entire body: too much causes gigantism; too little causes dwarfism antidiuretic hormone (ADH) stimulates the kidneys to reabsorb more water from filtrate when the blood plasma becomes too concentrated other hormones: e.g. follicle stimulating stimulate other glands such as the hormone (FSH), luteinising hormone (LH), thyroid ovaries,thyroid, and testes into activity stimulating hormone (TSH) Table 18 3 Functions of the hormones produced by the pituitary. Drugs and the effects of drug abuse li!il[eiJ A drug is any substance or chemical which alters the body's action, or interferes with some aspect of the body's metabolism. It affects chemical reactions in the body and ultimately, has effects on the brain. A drug can be administered to the body in many ways: • by injection; • orally; • applied to the skin; • inhaled. Medicinal use of drugs (prescription drugs) Doctors assess the need for these drugs very carefully, since many have side-effects. However, some people abuse steroids, diet pills, tranquillisers and antibiotics for personal 'miracles', ignoring and sometimes ignorant of the harmful effects. You should take care to read all instructions on any medicines that you use, or are prescribed by your doctor to make sure you are aware of the risks and side-effects (figure 18.20). J • f f.dl.t-J d P ror" ""'*<# de Whar shou/d I avoid . t.ld··• /uru: can mcrea I /Wee while increase rhe lrl..e~~h r It: "lllounr of Ml OOd rhar YOU will What arr th . • SI ' Poss1b/, sldr tHttts owed hearrb (b • Stomach Problear radycardi~ o d' h ems such as Ou nut d ,,,, ,~ 81dpi::tru11"'' " ' ' rarr ea nausea vomiting stomach are C b 111d1ges11on a a dominaf) • fec/rng tired and • skin problems suc~eak as redness ~ Tell Your docto b ' ' r a out an 'd ,_: nor go away. Th y sr e effect th · . ese are not II h ' o'..v Fo r more informati a t e POSSib ~ on ask your doctor or r (~~ :.?,~r _doctor for medir:ol , .,,.: Figure 18.20 The side-effects of one medicinal drug. 219 Life Processes and Disease therapeutic drugs > Medicinal drugs are widely u sed to diagnose, prevent and treat disease. These include painkillers, antibiotics and vitamins which are described as being t h e ra p e u tic d rugs. Penicilljn is a common antibiotic, which is used for the treatment of many bacteria l infections. Antibiotics save millions of lives each year, but are sometimes used unnecessa rily and ineffectively to treat viral diseases. This misuse can increase the risk of resistant strains of bacteria deve loping and eventually serious bacterial diseases may become untrea ta ble. Painkillers (analgesics) are very u seful but can be abused. Aspi rin is a common painkiller which a lso reduces fever and inflammation. It works by blocking the transmjssion of pain signals from the receptors to the spinal cord and brain. However, it can cause irritation to the stomach waJls and is n ot recommended fo r ch ildren as it may cause fata l brain and Uver damage. We often resort to painkillers too easily, unmindfu l o{ the side-effects. Many people drink coffee every morning, and some continue to consume coffee all day. Caffeine is the drug found in coffee and is also added to some soft drinks, incl uding many colas. It is a stimulant, making the user fee l more alert and en ergetic. However; it is addictive and interferes with the proper functioning of the central ne"rvous system. Caffeine also prevems ca lcium absorption and can thus lead to weak bon es and teeth in the o lder years. The use of diet pills, laxatives and diuretics is an unh ealth y and potentially very dangerous way to lose weight. Some diet pills contain ephedrine w h ich increases metabolism and makes the hea rt beat faster. This can lead to heart palpitations, cardiac arrest, stroke, and death, even in an oth erwise healthy person. Steroids, which work similarly to some hormones, are used in the treatment of asthma . However, th ey are sometimes abused by athletes and body-builders to build up muscle, thus increasing strength and speed. The associated risks · include aggression, reduced sex drive and masculinisation of women. Tranquilisers are sedatives that depress the nervous system , and are used in the treatment of anxiety and stress. They are valuable drugs but over-u se ca n make a person unmotivated and unable to cope with daily activities. Abuse of drugs psychoactive drugs '> drug addiction ! CHAPTER 12 withdrawal symptoms \ Drug abuse refers to use of substances which may cause a person to become dependent. These range from mild stimu lants like caffeine to powerful chemica ls like narcotic drugs that can a lter mood and behaviour. Drugs that interfere with the nervous system and cause change in menta l sta te and behaviour are called psych oactive drugs . These include LSD, alcohol, coca ine, nicotine and heroin. Use of these can lead to drug addiction, which is the state of psychologica l dependence on the drug. Marijuana addiction is discussed in chapter 12. Physical dependence occurs when the body adapts to a drug and increases its tolerance to the drug's effects. This leads to using larger doses of drug to achieve the origina l effect. Severe physica l withd rawa l symptoms occur if the drug is not taken. Alcohol Euip'J;ml!+j Alcohol is found in intoxicating beverages and is a depressant of the central nervous system. In small amounts, its effect is to make the drinker more sociable, more self-confident and to give a sense of weU-being and release from anxiety. However, people abuse alcohol by repeatedl y drinking it in excessive amounts. People who must drink alcohol every day to cope with life are alcoholics: this dependence is classed as a disease ca ll ed alcoholism. 220 - - -- - -- - - - - -- - - -- - - - 18 ·Irritability, Sensitivity and Coordination Short-term effects of a lcohol abuse: • slurred speech; • impaired menta l function; • loss of muscular coordination; • increased excretion leading to dehydration; • na usea and vomiting; • possibl y vio lent or agg ressive behaviour; • possibl e loss of conscio usness. Lo ng-term effects of a lcohol abuse: • physical and psychological dependence; • severe physica l w ithdrawa l symptoms that in clude nausea, vomiti ng, shaking, abdo minal cramps and pain, e n larged blood vesse ls in the face; • sudde n discontinuation can lead to severe sbak.ing, hallucinations a nd sometimes fatal convu lsions; • malnutrition and risk of deficiency diseases; • cirrhosis of the liver (wh en dead cells in the liver are replaced with fibrous tissue); • liver ca nce r; • stomach ulcers as alcohol irritates the stomach lining ca using it to produce excess gastric juice; • corona ry heart disease and rugh blood press ure; • a range of social, persona l and occupa tio nal problems. Drinking during pregnancy can cause low birth weigh t, poor physical and mental development in the fetu s, even fatal abnormalities; it can also lead to miscarriage. Cocaine Cocaine has long been used by doctors as a local anaesthetic. However, it is abu sed as a drug for the sense of euphoria or ' h igh ' it produces. It is a stimulant, w hich helps in socia l situations. Tt can be very addictive, especia lly as ' crack'. Symptoms of cocaine a buse include: • strange and violent behaviou r; • hallucinations leading to schizophrenia, menta l illness and sometimes death; • increased blood pressure and heartbea t; • lung and nasa l damage; • red uced need for sleep. Coca ine addiction is a worldwide problem. Many governments try to ed ucate their people about th e dangers associated with cocaine, includ ing the murder and corrup tio n wh ich ofte n follow its production and sa le. Ao addict's famil y suffe rs emotiona lly, financially and socially. But a lot of mone y is involved in th e illega l dru g trade a nd trafficking and the problem of addiction persists in many parts of the world . Social and economic implications of drug abuse • loss o f working time which red uces th e productivity of the econom y and causes loss o[ earn ings for th e country and reduced standard of li ving for its people. • loss of U(e due to overdose. 221 Life Processes and Disease • Increased demands on hea lth services [or rreatment and sornerimes pro longed and expensive care. Research for cures is a lso very expen sive. • Increa sed crime and social unrest. • Fam il y and personal neglect. • A stimulus is a change in the environment that an organism reacts to. • A response is the change in the organism brought about by the stimulus. • Responding to stimuli is important for the survival of animals; responses may help to find food, to escape predators and to find a mate. • Green plants respond to the stimulus of light by growing towards it. • Sense organs are organs that receive stimuli. In humans, the sense organs are the eyes, ears, nose, tongue and skin. The eye responds to light; the ears respond to sound; the nose and tongue respond to chemicals; the skin responds to pressure and temperature. • The nervous system is responsible for receiving stimuli and coordinating a response. • The nervous system is made up of the central and peripheral nervous systems. • The central nervous system is composed of the brain and spinal cord. • The peripheral nervous system is composed of all the other nerves. • Sensory nerves carry impulses towards the central nervous system. • Motor nerves carry impulses away from the central nervous system. • The junction between two neurones is called a synapse. • Receptors receive stimuli from the environment. • An effector brings about a response to a stimulus. It is often a muscle. • A reflex is an automatic response to a stimulus and does not require conscious control. • The brain enables humans to perform complex mental and physical activities. • The autonomic nervous system controls those responses that do not require conscious control. • Any substance which changes a body's action is a drug. • Prescription drugs and drugs used for medicinal purposes can also be abused . • Some drugs such as alcohol, cocaine and marijuana can lead to addiction or a state of physiological dependence on the drug. • Drug abuse has many social and economic implications for the family, community and country. 222 ··S:,,:_ . _. ~ ·.1~ ..· l~rjt?bility, Sensitivity and Coordination ITQ1 (i) I rrita bility is th e ability of livi ng o rga nism s to respond the stimuH co m in g from the enviro nment. (ii) lrrira bility is importa nt because stimuli from the en vironm ent ca rry informa tio n abo ut food, predators, co mpeti tors a nd so on. An o rga nism ma y die q u ickly i[ it cann o t respond to this informa tio n . ITQ2 Dogs have a very keen sen se o f sme ll w hich they use to hunr fo r l'ood.( A rabbit has eyes at the sid es o [ its head, w h.ich give the ra bbit a bigger fi e ld o ( view to see preda tors. Yo u may have tho ught of o the r examples - the re are ma n y. ITQ3 (i) The nervo us system o f h uma ns co nsists of the brain, spina l co rd and a n umbe r of ne rves that extend th ro ugho u t the bod y. (ti) Senso ry ne rves d ecec1 stim u li from th e e nvi ro rune nt a nd m essages are sent to the brain, which whe n processes a nd sto res che informatio n . Messages are sent back to certai n o rgans in respon se to the stimuli . ITQ4 stimulus - recep to r - sensory ne u ro ne - cen tra l ne rvous system mo ror ne uro ne - effector - respon se ITQ5 Receptor Effector Response eyes see the potential mate muscles animal moves towards the mate, showing courtship behaviour, etc. ITQ6 (i) A sy napse is the j unction between rwo ne rve cells. (ii) Messages in the fo rm o f e lecrr ica l im pu lses a rrive at the e nd o f o ne nerve cell. Thi s ca uses a che mical to cross th e junction be tween the two nerve cel ls. On arrivaJ o f rhe ch emi ca l ar th e oth er n erve cell, electrica l imp ulses are gene rated the re and the m essage is senr o n . ITQ7 A re fl ex actio n is a respo nse to a stimu lus w itho u t conscio us knowledge. ITQ8 (i) The person m ust have received da mage co the regio n of the brain respo nsible [or receiving a nd p rocessing info rmation comi ng from tbe eyes. Even tho ugh the eyes may function perfectly, tbe bra in can no t receive o r process signals from ch em so there is n o perceptio n o f seeing. (i i) The cere be llu m is responsible for bala nce and coordina tio n o f muscle activity. If rh e cerebeLlu m is dam aged, the person will not be able to sta nd, wa lk, eat o r perfo rm activities chat involve the mu scle coordination . ITQ9 (i) Respiratio n in a ll ce lls; bearing o r th e heart; brea th ing movements; m ovem ent of food a long che aLim eora ry ca nal; movem e nt o f blood through o ut the body; prod uctio n o[ urine by th e kidneys. (ii) The a u tonom ic n ervous system is respo nsible fo r a ll these activi ties. Messages a re sent to va rio us orga ns consta ntl y, ensurin g tha t they continu e to do their j obs, e ve n during sleep . ITQ10 Endocrine Exocrine gland lies next to a blood capillary gland has a tube that connects to its site of action hormone diffuses across membranes to the blood and is transported by the blood to the site of action (e.g. insulin and adrenalin) chemical passes through the duct to the site of action (e.g digestive juices and saliva) ITQ11 (i) A h o rmo ne is a cl1e1nical messe nge r. II travels in the blood and has its e ffect at a rarget site w here th e chem ica l brings abo u t a reaction. (ii) lns u li n, ad re na li n, resterone, oestroge n 223 Life Processes and Disease Examination-style questions (i) Explain the meaning of the terms: (a) stimulus; {b) response. (ii) Describe fully a named response and explain why it may be important to the survival of the organism . ·~ (iii) Copy and complete the table below. Sense organ Stimulus to which An example of its importance (describe an everyday it responds activity that uses the sense organ and explain how it is used) eye ear nose tongue skin {iv) A person deficie.nt in one sense organ is said to develop another sense to a greater extent than normal. For example, a blind man is said to have a better sense of hearing. {a) Suggest an explanation for this phenomenon in nature. (b) Suggest two ways a person who has lost his/her sense of sight may be affected. 2 {i) The nervous system is made up of two parts. Name the parts and give a description of each part. (ii) Make a labelled drawing of a typical motor neurone. (iii) List some differences between a motor neurone and a sensory neurone. (iv) A child touches something hot, and pulls away her hand from the hot object. Describe the pathway of this response through her nervous system , from the time the hot object touches the receptors in her skin to the contraction of muscles as she pulls her hand away. 3 (i) Copy the figure below which shows a section of the human brain. Name the parts labelled A, B, C, D and E. (ii) All the activities of the body are controlled by the brain. Annotate your copy of the figure to show the sites of control of these functions: (a) intelligence (b) hearing (c) sight (d) coordination of muscular activity. 224 9ihe Eye, the Ear and the Skin 0 0 0 0 0 0 0 0 relate the structure of the human eye to its function as a sense organ 0 discuss skin care understand sight d efects and their correction relate the structure of the ear in humans to its function as a sense organ understand how we hear understand how the ear is used for balance explain the terms poikilotherm and homeotherm understand why temperature regulation is an example of ho meostasis relate the structure of the human skin to its function in temperature regulation and prot ection sense organs light r I tongue eye I sight defects I sound nose ' pupil - light intensity retina _ ' l outer ear distance homeotherm middle ear J l behaviour . skin ear accommodation lens - poikilotherm J conserve heat lose heat inner ear r optic nerve to brain r ear sac balance I \ semicircular canals skin care ' hearing I cochlea Our s urviva l, ind eed o ur very existen ce, dep end s o n o ur reactio ns to stim ul i co rning from th e en vironmen t. We feel, bea r, see, taste and sm e ll o ur su rro un dings every Uving m o ment. The ma in sense o rga ns in hu mans a re tJ1 e skin , ea rs, eyes, ton g ue a nd nose (table 19. l ). Sense organ Stimulus to which it responds tongue Taste buds on the tongue are composed of sensory cells. Chemicals dissolved in moisture in the mouth are detected by these cells. The taste buds on the tongue are sensitive to four different tastes - sweet, sour, salt and bitter. Messages are sent to the brain to determine the taste. nose Sensory cells line the nasal passage. These cells detect chemicals in the air entering the nose. Messages are sent to the brain to determine the smell. (continued) 225 Life Processes and Disease Sense organ Stimulus to which it responds skin There are many different nerve endings in the skin. It is thus very sensitive to many different stimuli - pain, touch, temperature change and pressure. The skin 'touches' the environment. The receptors in the skin send messages to the brain to determine what we have touched. The skin is also a protective barrier against the environment. The internal organs are protected from the dangers of the t physical environment, such as UV rays and microorganisms (pathogens). ear The ear collects and directs sound waves (pressure changes) to the eardrum. Vibrations of the eardrum eventually cause movement of the sensory hairs in the cochlea. This causes nerve impulses in the auditory nerve which are interpreted by the brain as sounds. eye Sensitive cells on the retina of the eye detect light reflected from objects. An image is formed in the brain when we see. Table 19. 1 The main sense organs in humans and the stimuli to which they respond. The eye Structure of the human eye The eye is a ligh t-sen sitive orga n that enab les us to see small va riations of colo ur, sh ape, size, brightness and dista nce. Light rays from objects are co nve ned to nerve impulses w hich are sent Lo the brain. Th e braio, not the eye, is w here the actual process of seeing is p er formed. The eyebas a num ber o r re lated strucwres (figure 19 .l}: • eyebro w directs sweat mov ing down the [orehead away fro m the eye; • eyelids close to protect the eye against dust and bright Light; • tear gland prod uces tears wh ich wash away d ust particles and conta in the enzyme lysozyme which ki ll s bacteria; • • eyelas hes keep the front. o f the eye free from dust a nd dirt; pupil is the bo le w hich a llows light to em er the eyeba ll; • iris gives colo ur t0 the eye and con trols the size of the pu pil . • scle ra is the white fibrous coa t w hicb protects the eyeba ll. .~ V'--J Where are the eyes positioned in the human body and how is this different from a herbivore such as a zebra? (ii) Give an explanation for the difference in the position of the eyes between a carnivore and a herbivore. (i) ~;;::.:___ upper eyelid and lashes !--..IJ~-- lower eyelid .;_...__ protect the eye _ duct draining tears to nose ~ Figure 19. 1 The eye and associated structures. V'--J The eyeballs are ba ll- li ke structure situated in cavities in the sku ll ca lled orbits. Figure L9.2 shows a sectio n th ro ugh the human eye and figure 19.3 describes the functions of vario us parts of the eye. IT:Q2 List three reasons why eyes are important to a human. 226 19 ·The Eye, the Ear and the Skin ,, eye lid " ,f./ /.< 'iY.:V,All'~-Y:~ eyelash ~~ ciliary body ---h~• iris - -----,7'7"--.• I aqueous humour - --r-.-+cornea --~ lens - -+---+--- -; su spenso ry --~ ligament Figure 19.2 A section through the human eye. conjunctiva - thin transparent skin continuous with lining of eyelids: pro tects cornea iris - coloured disc composed o f muscle; controls amount of light entering eye ~ aqueous humour - colourless fluid . sclera - tough, white fibrous coat; protects eyeball ciliary body c horoid - contains blood vessels to supply retina with food and oxygen; black pigment to prevent reflection of light insid e the eye 1' / / 1 .:- / ...411 ~ ~'/ /,/. '""~--- re tina - contains light- cornea - transparent front part of sclera; refracts (bends) light -~~• rays to a focus on the retina pupil - hole In centre of iris; allows light to enter eyeball sensitive cells: rods and cones fo vea - contains cones only; most sensitive part of retina; most light rays are focused here blind sp ot - point where op tic nerve leaves eye; no light-sensitive cells lens - transparent, elastic, biconvex / structure; makes fine adjustments to focus light on retina optic nerve - carries impulses from retina to b rain susp ensory ligament - attaches lens to ciliary body ciliary muscle - circular ring of muscle fibres; alters lens shape during accommodation Figure 19.3 Functions of the various parts of the human eye. How we see rnhieijH Light rays from the o bject travel in a straigh t lin e to th e eyeba lls. They pass thro ugh th e stru ctures a t the fro nt o f the e ye ba ll , th ro ugh the p upil and a re focu se d on the retina (fig ure l 9.4, overlea f). Th e ligh t stimula tes ligb.rse nsitive cell s of. the retin a w hich send impu lses a long t he op tic nerve to the bra in. The brai n the n fo rms a n image o f size, shape. colo u r and di stan ce away fro m the o bject. 227 Life Processes and Disease l'Alt:fffll The cornea ben ds (o r refracts) the light LOwards the retina. The lens, however, can vary tJ1e amo unt of bending or refraction and thus ensures the accurate focusin g of th e image on the retina (figure 19.5). The iris is composed of circular a nd radial muscles and con trols the size of the p upil which then va ri es the amo un t of light that enters the eye. The iris closes down in brigh t light to protect the cells in the retina. Th e len s is transparent an d bi convex in shape. The amo unt o ( refraction~ of the ligh t passing thro ugh it depends o n its shape. It can be flattened (less convex) or made m ore ro unded (more convex). Th is adjustmem is needed fo.r focusing on objects that are different distances away (figure 19.6). lens - varies the amount of refraction so as to focus the light rays into a sharp image on the retina light rays light rays ;~\ lens to brain Figure 19.4 Light rays pass through the cornea. pupil, lens and humours and are focused on the retina. (a) Flattened lens, less refraction of light light rays from a distant object (b) Rounded lens, more refraction of light cornea - refracts \ the light \ to brain " Figure 19.5 Light refracts as it passes through the cornea and lens. Detail of ciliary muscle, ligaments and lens less refraction '/ / light rays light rays from a near object bulged lens shape more refraction The ciliary muscle Is ring-shaped ; on contraction the ring gets smaller. This causes the suspensory ligaments to slacken and the lens becomes a more b ulged shape. Figure 19.6 The lens in the eye changes its shape to ensure that the rays focus on the retina. 228 19 ·The Eye, the Ear and the Skin Accommodation accommodation > ~ IT:Q3 V'-' Name in order the parts of the eye through which a light ray passes on its way from the conjunctiva to the retina. The adj ustm ent of the lens fo r focusing on near and distant objects is called accommodation. The len s is connected by ligam ents to the ring-shaped ciliary muscle. Contraction and relaxation of the ci liary muscle affects the tension in the ligam ents which cbanges the shape o f the lens. Wh en focusing on a distant object, the ciliary muscles relax. This pulls the suspensory liga ments tight which m akes the lens flatten ed (less con vex). Thi~ shape refracts the light less a nd the image is focused sh a rpl y on the retina (figure 19.7). When focusing on a nea r object, 1..he ciliary muscles contract. This reduces the tension on the suspensory ligam ents an d they slacken. The ligaments pull less on the lens and it becomes more rounded (more convex). A very curved shape refracts the light m ore. Th e image is again sha rp on the retin a (figure 19.8). / lens flattened less refraction light rays from distant object light rays from near object to brain Figure 19.8 Focusing on a near object. Figure 19.7 Focusing on a distant object. The effect of pupil size QSb IT:Q'I V'-' What is meant by the term 'accommodation'? If you wear glasses, try making an artificially small pupil with the tips of three fingers and look through it (without your glasses on) at something which looks blurred (figure 19.10). Because of the increased depth of focus, you should see it more clearly. When the p upil is wide open, more light enters the eye than w hen the pupil is sm all. In bright light the pupil contracts to protect th e eye from excess ligh t. ln dim light th e p up il expands to tak e advan tage of as much ligh t as possible (fig ure 19.9). To expa nd the pupil the circu lar muscles in the iris re lax and the radia l muscles contract, pulling th e iris back an d so op ening the pupil . To m ake th e pupil smaller th e radial muscles re lax and the circular mu scles contract. Figure 19.9 Changing pupil size in different light conditions. Figure 19. 1O An artificial pupil. depth of focus > Depth of focus Wh en th e pupil is sm all (in bright Ligh t) the eye has a grea te r depth of focus . The sh a pe of the lens does not n eed to chan ge quite so much to sw itch from viewing a distant obj ect to viewing a n ea re r o ne. In dim light w hen the pupil is wide, the depth of focus is less and the lens m ust change m ore. 229 Life Processes and Disease This is sometimes noticed if a person is slightly Jong-sighted or slightl y short-sighted. ln bright Light the y will see objects clearly which in dim ligh t appear a little blurred. Also, as a person ages, their power of accommodation gets less and the range of distances over wbich they can see sharp images is reduced. This is much more noticeable in dim light than in bright light. The retina The retina is a photosensitive layer at the back of the eye. It is made up or two mm H·leI:tJI types of phororeceptor ca lled rods and cones (figure 19.11) . The rods are l(.l@fil sensitive to light and dark onJy; the y do not react to colour. They function best in low light intensities such as when it is getting dark. This is why we see on ly in black and whjte at night. The rods are located around the sides or the retina away from the fovea . Rods are desensitised by bright light, whid1 explains why yo u cannot see clearJ y if yo u move from a bright area to a dim or dark o ne. After a few minutes though , the rods recover th eiT sensitivity and yo u can see more dearly aga in. retina B - -+-- ID-CC~ - -fovea (cones only) retina magnified A blind spot -~~~ optic nerve - messages from all the photoreceptors go to the brain Figure 19.11 The retina is made up of rods and cones (light-sensitive cells). Light falling on the cells causes nerve impulses which travel to the brain via the optic nerve. ~ IT:QS V'-1 Describe how we see. liJnml#l•i•iH The cones are sensitive to colour and function best in high light intensities. They are located mostly around the centre of the retina. Tbe fovea is composed entirely of cones and is at the centre of the retina. Light focused on the fovea produce a clear well -defined image in tbe brightest colour. Th e point of exit o[ the optic nerve from th e eye is called the blind spot because it lacks photoreceptors and is in sensitive to light. Light fa lling on thls spot does not ca use a response in the nerve, so you are 'bli nd' at th.is point. Sight defects and their corrections A sight defect is caused by any condition that prevents proper focu sing of Light on the retina . A faulty focusing mechanism may be ca used by a number of fa ctors, such as th e shape of the eyeba ll or hard ening of the lens. Some common sight defects a re lo ng-sightedness, near-sightedness, cata ract and glaucoma. 230 19 · The Eye , the Ear and the Skin Long-sightedness hypermetro ia > Long-sightedness, o r hypermetropia , is ca used by the eyeba ll being too short from rront to back, or the lens being too fla t. As a resu lt, li gh t from distant objects can focus on the retina, but light from nea r objects is focused behind the retina. So disra11 t objecrs are seen m ore clearl y than near ones. The condition can be corrected by wear ing con vex o r con ve rging lens (fi gure l 9. 12). light rays from near object - - - -tt:JCTb~::::=:::'.~ focus of light rays from near object before correction - behind retina converging lens bends light rays inwards before entering the eye Figure 19.12 Long-sightedness and its correction. Near-sightedness ~ Nea r-sighted ness (or sl1o n -sigbted11ess), or myopia , is ca used by the eyeball being too long from front to back, or the le ns being too cu rved. As a res ult, lig ht rays fro m a distant o bj ect a re bent m ore tha n necessary a nd focus in frolll o f th e retina. However, light rays from near o bjects focus 0~1 the re tina . So near objects are seen more cl ea rl y than d istant o nes. Wea ring concave o r diverging · len s h e lps the person to see far objects clearly (figure L9.l3). IT:Q6 V'-' What kind of lens is needed to correct (i) long-sightedness (ii) nearsightedness? focus of light rays from distant object after correction - on retina light rays from distant object diverging lens bends light rays outwards before entering the eye '-1 focus of light rays fro m distant object before correction - in front of retina ~ "\.. ' \ Figure 19.13 Near-sightedness and its correction. Astigmatism This is ca used by the surface o f Lhe lens or corn ea being curved irreg ula rly. Specia ll y shaped lenses, whid1 balance o ut these irreg ula rid es, need to be worn to provide a clear image o n tbe re tina . Cataract Figure 19. 74 A cataract reduces the light entering the eye. This occu rs when the Lens becomes opaqu e a nd light cannot pass th ro ug h, so the person is una bl e to see (figure 19.14) . The le ns ca n be removed during surgery. Adjustments t:O vision ca n be made with approp ri ate specrad es or conta ct lenses, so that the person ca n see clearly again. Alternatively, tbe lens ca n be replaced w ith an intra ocu lar le n s. 231 Life Processes and Disease Glaucoma W-, IT:Q7 V'-' (i) What are defects of the eye? (ii) Name two defects of the eye and explain what causes them. This occu rs w he n there is a build-u p o f pressure in Lhe aqueous h umou r. This increased pressure inside Lhe eyebaU ca n da mage the optic ne rve. The sufferer expe ri e nces pa in ful and infla m ed e yes, and a ha lo is seen a ro und objects. Visio n is p oor, and the su ffe re r may experie nce sightless a reas io the fiel d of visio n. It is associa ted w itb an increase in age bu t may develop a t a n y time fro m in [an cy on . t The ris k factors for gla ucoma a re age, h ered ity, myopia, and general diseas.e such as a su o ke . In its earl y stages, glau coma can be effecti vely treated with m edicatio n, li ke e ye drops a nd o ral m edi catio n . Tf left un treated, it ca n cause vision loss o r blindness. ln its late r stages, su rge ry ma y be necessary to ease the pressure in the eyeba lls. Gla uco ma is the most common ca use o f bli ndness. Damage to th e optic ne rve is irreve rsible . The ear Structure of the human ear The ma mma lian ear per[orms two fu nctions: • hea ring; • ba la nce. It is d ivided into three regio ns: the o u te r ear, the m iddle ear a nd the in ne r ear. Figure 19. l 5 sho ws tbe str uctu re o f the hum a n ear. pinna bones of skull semicircular canals vestibular apparatus stapes ossicles [ incus --~ malleus tympanum (eardrum) outer ear middle ear Figure 19. 15 Structure of the human ear. 232 inner ear 19 ·The Eye, the Ear and the Skin How we hear A n o ise is se t o f vibrari ons o r so und waves in th e a ir. Th e so und wa ves reach l•liehfiH th e ea r a nd rh e pinna (tbe o u te r ear ) directs the m into the a ud itory ca na l. Th e l•1'i'·U'9!4'1J 13-13E@IJ la@l+@QIJ so un d waves travel down th e ear ca nal to the ea rdrum. The ea rdrum vib ra tes w h e n hi t by the so und waves. This ca uses rhe ea r ossicles, o r ear bo n es, in the middle ea r w vibra te. Th e inne r ea r is filled w ith flu id . The vibra tio ns a t th e , ova l w indow start up press ure waves i11 the flui d o r th e coch lea (fi gures 19. 16 a nd 19 .17 ). The iJ1ne r ear is made up o f two pa ns, th e cochlea a nd th e vestibu la r a ppa ra tus. Th e cochlea is a lo ng, coiled, three-cha mbe red tu be w hi ch is res pon sible [o r o ur sen se oJ h earing. The i11ne r ea r is fill ed w ith fluid. Th e vibra tion s at rh e ova l window start up press u re waves in th e fluid o f th e cochlea. Th e cochlea conrains receptor s ca lled hair cells which vibra te in respo nse to the press ure waves in the cochl ea r fl u id. Nerve impul ses a re gen e ra red which pass a lon g th e aucfaor y n erve to th e brain and we h ea r. Th e vib ra tio ns th e n pa ss a way lO the roun d wi ndow and we are read y to h ea r aga in. middle ear outer ear vibration is amplified - - inner ear (fluid-filled) membrane covering oval window sensory cell stimulated impulse sent to the brain -------~~---- impulse taken to the brain -+ - j~ sound wave membrane covering round window (absorbs the waves and prepares the fluid to detect new waves) cochlea Figure 19. 16 Sound waves are vibrations that travel through air to the outer ear. They are amplified as they pass through ossicles of the middle ear and then converted to pressure waves in the cochlea. Figure 19. 17 The three bones (ossicles) of the middle ear. m anic membrane > The eardrum tympanic membrane or eardrum kept taut by equal pressure on both sides inner ear outer ear pressure fluid air \ ressure ~ \ \ Eustachian tube from the throat controls the pressure of the air in the middle ear 1 The ea rdrum is a thin membran e which is puU ed ta ut a nd separa tes th e o u te r a nd middle pa rt o[ the ear (fi gure 19. 18). lt is a lso called th e tympanic membrane. Th e vi bra ti o ns in the sound waves a re con ve rted to m ovem ent w h e n th ey ' hit' th e eardrum a nd are amplifi e d as they pass thro ugh the tb ree ea r bo n es. Pressure o n both sides o f th e ty rnpan ic me mbra n e must be eq ua l so tha t it stays stra ight and ra ut, and sound m essages ca n be passed o n effi cie n tly. We som etimes feel o ur ea rs 'pop', such as w he n fl yin g in an ae ropla n e. This ha ppens as rhe rympa ni c m e m bra n e m oves back ifl to positio n w hen th e press ure o n both sides equa li ses (Figure 19.1 9, overl ea f). ~ IT:Q8 V'--J When we hear, what is the role of (i) the pinna (ii) the ear bones (iii) the cochlea? Rgure 19. 18 The eardrum separates two air-filled regions of the ear. 233 Life Processes and Disease m iddle ear Equal pressure on the eardrum whilst airplane on the ground. sound waves As the airplane g oes up, the atmospheric pressure is lower. The pressure in the middle ear is now greater and the eardrum 'bends'. Hearing is distorted. The p ressure may equalise (naturally, or by chewing gum) and the eardrum returns to the normal position. It 'pops' as it does so. Agure 19. 19 The eardrum can 'bend' if the pressures on either side are unequal. Balance vest ibular apparatu s > sem icirc ular canals ) The vestibu lar apparatus is responsible for o ur sense of ba lance and in formation about the position and movement o f our body. Th e vestibu lar apparatu s is made up of: • th e semicircu lar canals w hich detect movement o f th e head; mmam ..1uaa11m • the utricle and saccu le (ea r sac) wh ich detect the position of th e head . Elule!iilrn Receptors inside these stru ctu res are the ha ir cells tha r deflect o n mo vement. This causes a n impu lse co be sent to the brain. The semicircuJar ca na ls are at right-an gles co each other, in th e three pla nes, so that any movement of the head, and th erefore the body, is detecteo. At the base of each sem ici rcular cana l is a sweUing ca lled a n ampu lla . Figure 19.20 sh o ws how the am.p ulla works. movement of the body / cupula displaced by _ __ movement of endolymph Figure 19.20 Movement of the body moves fluid in the ampullae in the opposite direction. The brain gets impulses from all three ampullae and interprets the messages as movement. 234 vestibular nerve to the brain, which interprets the message - -- relative movement of endolymph because of movement of the body 19 ·The Eye, the Ear and the Skin ~ l'.'f:Q9 \.../"-' Even with the eyes closed, the brain can detect movement of the body, that is, the direction and the relative speed of the movement. How is this possible? Tbe ea r sac is posirio n ed below the sem i-circu la r ca na ls. lnfo rmation a bo m tbe position of rh e h ead and therefo re the body is de tected by receptor cells a nd impulses are sent to th e bra in. Th e utricle responds Lo verrica l movemems o f the bead and th e saccul e responds LO la tera l o r sid eways m ovem e m of rhe head. Fig ures 19.2 1 a nd 19.22 illustrate h ow they wo rk. lean forward ball pulls on sensory hairs Figure 19.21 Movement of the head vertically, pulls on sensory hairs in the utricle. Impulses are sent to the brain which are interpreted as movement of the head. Rgure 19.22 The saccule responds to lateral or sideways movement of the head. The skin World te mpera LU re varies fro m -58 °c in th e col d polar regio ns LO around 30 °C in tropica l ra info rest a nd over 60 °C in h o t deserts. Some a nim als are adapted to live in extrem ely cold enviro n m e nts w hile others ex ist whe re e n vironme nta l te mpe ra tu res can exceed 60 °C. Despite the te m perature o f th e e n vironme nt, th e bod y te mpera ture o f a huma n is a lways abo ut 37 °C (fig ure 19.23). Figure 19.23 The body temperature of both boys is about 37 °C, even though one lives in an extremely hot environment and the other in an extremely cold environment Temperature control homeotherm > oikilotherm > In the an imal kingdo m , birds and mamma ls a re a ble to mai nta in a fa irly constam body te m perarnre. They are described as being homeotherm ic (or, less co rrectl y, as warm -b looded). Th is fa irly constan t body temperature is ma i;1rained using ph ysiologica l m echanisms o r processes w hich occur wit hin th e body, fo r exa mple respiratio n w hi ch gen e rates heat, a nd consrrictio n o f blood vessels which reduces b lood flow to the skin a nd the re fore h ea t loss. All invertebra tes, fish, amp h ibia ns a nd repti les are unable to regula te the ir body Le mperarure by ph ysio logica l means. They are described as poi kilothermic (or, less correctl y, as cold-blooded) . They re ly o n heat derived from th e e nvi ro nm e nt ro kee p the body warm. Conrrol o[ bod y te mpera ture 235 Life Processes and Disease is ach ie ved by beha vio ura l mecharusms, fo r example moving ro a cool place under a rock a nd basking in sunsh ioe. The body tempera ture or poiki lo t11erms usuall y depe nds on their e nvironment (figure 19.24). ~ l:tQil 0 Noon - lizard hides from the Sun Morning - lizard warms up l/'-) Define (i) homeothermy (ii) poikilothermy, giving examples of each. Its body temperature was low from the night. so It basks in the Sun to increase its body temperature. Its body temperature could rise too high if exposed to the Sun so it hides under a rock. Rgure 19.24 The body temperature of a lizard (poikilotherm) varies with the environment. ~ l:tQ· 11 l/'-) Why are humans able to live in extremely hot and extremely cold environmental conditions, unlike some animals? Th e gra ph Lo figure I 9.25 compares the body te mpera tures of a hu man and a lizard for 24 hours of a day. The change in body tempe rature of the liza rd may be m o re than 10 °C, while th e change in body tempe rature o r a human is less than 2 °C. The bo dy temperature o r the lizard may drop Lo abo ut 5 °C a t n igh t when the re is no solar heat, and be raised to a bout 20 °C in the hea t of the day. liemperat ure 1 50 air temperature varies from morning to noon to evening -·· ·-- -·i----······ ····· -· · ·--:r-· '°C) 40 ····- -· - --~-··-·-·--·-· ~-------- ------- · - -· - · 1 - -- - - - · - ----·--1 so ----~ i I 20 ----1--7''-----=4--=:--- t - -Y-"' - 12 noon human temperature -------1- - stays about the same 18 I lizard comes out of hiding to bask or move around looking for food lizard in a cool place - its body temperature is lower than air temperature 24 midnight Rgure 19.25 How the body temperature of a lizard and a human. and the air temperature may vary in one day. CHAPTER 16 236 ~ A body te mpe rature o f about 37 °C is idea l fo r chemi ca l reactions to ra ke place as maoy en zymatic reactions have an optim um temperature o f aro und 37 °C. These reactions are impo rtant Lo sustain life; they occu r continuo usly in eve ry cell. The regu la tio n a nd maioteoan ce o f cons taot condition s wi th in an o rganism is called ho meostasis (chapter 16). Therefore, keeping the te mperatu re of tlle tissue fluid surround ing cells fairl y constant is an example of ho meostasis. The temperat ure r ange o n Earth is ve ry w ide and va ries with lalitude (from the poles ro the equator) : con ditions range from extrem e cold in the po lar regio ns to extreme beat in the tropics (figure 19.26). Mosq u itoes and fli es {invertebrates) are poikilo the rmic and infest the tropics w he re the e n vironmental temperature (28-3 1 °C) is idea l fo r them to live a nd nourish. M a n y are vectors o f disease, and so tb e tropics team w ith disease-ca rrying and disease-ca using organ.ism s. Diseases li ke ch o le ra, malaria, de ngue fever a nd yello w fe ver are m onitored con sta ntly in order to try to keep them unde r 19 ·The Eye, the Ear and the Skin ~ ll!Q-1 2 V'-1 Why are people who live on and around the equator more likely to suffer from certain diseases, such as malaria and dengue fever? control. Poikilo therms a re restricted polar N to ce rtain a reas in th e wo rld because th ey beco me sluggish a nd e ven rorally inactive in low temperatures. Low te mpera tures slow down e n zymatic reactions. Mamma ls a re able to ma intain th eir bod y tempe rature close to o p tim um despite changes in th e environm e nt. They ca n re main acti ve da y a n d night, summ e r a nd winter, a nd can inhabit or li ve in a ny part of the wo rld . Howeve r, the y req uire more food . Mainta ining s region a bod y te mperature diffe rent from the environme n t requires a lot oJ e ne rgy. A Figure 19.26 The surface temperature of m o use, ror example, eats about its own the Earth varies with latitude. bod y mass of food per day w h ereas a cockroach can go for days without a mea l. All a nimals wi ll die in te mpe rature extrem es. Temperature regulation in humans Practical activity SBA 19.1: Heat flow from a warm object, page 361 Meta bo lic reactions (especia lly in 1he Uver ) ge ne rate h eat and this h eat is transported by b lood thro u gh o ut the body to keep it warm at 37 °C. Som e heat is lost to the environmenr through the skin . The loss o f this gene ra ted hea t is regu lated a nd controll ed; for example, in a cold e n vironme nt, less is lost and mo re is conserved. Regu la tion of body temperature is contro lled by the h ypotha lam us of th e brain. The organ wh ich brings abo u t the changes if n ecessa ry, to conserve or lose h eat, is the skin (fi gure 19.27). Temperature receptors in th e skin receive the stim u lus o f ch a nging external te mpe rature (fig ure 19.28, overlea f) . T hey send impulses to the hypotha lam us, which mon ito rs these stim uli as well as interna l body temperature. If body temperature is chan ging, the hypotha la mus responds by sending impul ses to effectors in the skin to bring a bo ut the responses sh own in table 19.2 (overleaf) . sweat pore epidermis[ cornified layer (old skin cells) ~I · I- ~ Malp ighian layer (pigmented} - j p igment protects tower layers from damage by ultraviolet rays in sunlight - - .F------19- ~~- dermis hair erector muscle sebaceous gland produces oil that coats and protects hair capillary network -+-- hair follicle ·'----"-...n..:'"'._..__...,,,. _ fatty layer below skin i.,;.---1-- .__-...~_.__.,., sweat g land Figure 19.27 A section of human skin. 237 Life Processes and Disease Heat gain Sun Heat toss convection of heat by wind - - • • • atmosphere warmed evaporation of water from body surface ,__,_____ __ reflected sunlight / ~ ~"'of"" to cooler parts of the environment radiation of heat from warmer parts of the environment heat lost in urine and faeces soil conduction lo the cooler ground close to water conduction from the warmer ground heated by the Sun Figure 19.28 The skin of a mammal is important tor temperature regulation. To conserve heat To lose heat • Sweating increases evaporation of the sweat removes heat from the body • Vasodilation occurs - capillaries in the dermis dilate so blood flow through skin increases, heat is lost from the blood • Hair erector muscles relax hairs lie flat so moving air can get closer to skin and remove heat sweat heat is carried away ./" as sweat evaporates • Sweating decreases less blood now close to the skin sweat gland \ t I a lot of b lood flow close to the skin heat is lost from the blood • Vasoconstriction occurs capillaries of the dermis constrict so blood flow to skin decreases, heat is retained in blood vessels deeper in the body • Hair erector muscle contract hairs stand up trapping a layer of warm air next to the skin (insulation) layer o f warm air trapped which keeps body warm hair erector muscles contract --.~_..,___ arterioles dilate heat can be easily lost from the skin hair erector muscles relax Table 19.2 Responses in the skin of a mammal that help it to conserve or lose heat. 238 19 ·The Eye, the Ear and the Skin Name the main organ of temperature regulation in humans. Describe two ways it is adapted to perform this function. Humans can gene rate an excessive amo unt o r hea t du ri ng exercise o r increased activi ty. To maimain a consrant temperature we have 10 lose th is excess heat. Temperawre reg ul ation is physio logica l in huma ns si nce we are a mamma l. However, we may cha nge our behaviour to h elp the process. If yo u are is hot because o f stre nuo us exerci se, yo u co u ld: • re move some clothing; ~ IT:Q-1 4 • • bave a co ld dr ink; move to a coo le r place; • stop activity. ~ IT:Q-1 3 \J'-1 \J'-1 What changes occur to control body temperature in the body of a human who is running a race? Humans do n ot have a Ll1ick laye r o[ hair an d, if the e nvirornn ent is very cold, th ey d o not ha ve effective insu latio n . Heat is genera ted by th e live r, bur this may not be e no ugh to kee p body temperatu re at the ri ght level. M uscles sta rt LO shiver involu ntarily, to genera te more heat. Huma ns get 'goose b u mps' as the ha ir erector muscles contract. However, we are conside red Lo be 'na ked ' o r hai rless and can on ly tra p a thin laye r of warm air arou nd the skin . We can b e lp by: • putting on thick cl o thing; • having hot d rinks; • moving to a warmer place; • m oving a ro und ro generate more heat. Temperature regulation in birds The e ffect o[ e rector muscles is m ost marked in birds. In cold weather, the mu scles contact, as in hum ans, and th e birds' feathe rs sta nd o ut fro m U1e skin . (fig u re 19.29). This tra ps a great deal of air next to th e skin. wh ich acts as a good ins ula ro r. Tt a lso srops air fl ow over th e skin, vvhi ch redu ces loss o [ beat by convecti on . Skin care O ne o f tb e most imponam way tO take ca re o f the skin is to protect it from the Sun. Ultravio let rays o f the Sun ca n ca use w rin kles, age spots and increase rbe risk o [ cance r. To protect skin fro m th e Su n : • use sunscree n; • seek sh ade; • wear protective cloth ing. Figure 19.29 A bird can insulate itself from the worst of the cold by fluffing up its feathers. Smokin g m ay damage co llage n and e lasrin, the fi bres tha t give skin it"s e lasticit:y and stren gth. So, a good skin ca re regim e incl udes no t smoking. Daily cl eansing a nd shaving can ta ke a tall on th e skin so strong soaps shou ld be avoided and a moi sturiser used. A healthy diet and ma naged stress p ro m ote yo unger loo king and hea lthy skin . 239 Life Processes and D isease r Chapter summary • • • • • • • • • • • • • The main sense organs in humans are the tongue, nose, skin, ear and eye. The eye enables us to see variations in colour, shape, size, brightness and distance. We see when light enters the eye. Light is refracted as it passes through the cornea and lens. The iris controls the amount of light entering the eye. The lens controls refraction of light for near and far objects - this is called accommodation. Anything that prevents proper focusing of light on the retina is a sight defect. Astigmatism occurs when the surface of the lens or cornea is irregular. A cataract occurs when the lens become opaque and light cannot pass through. A build-up of pressure in the aqueous humour results in glaucoma. The ear is a sense organ that enables us to hear sounds from the environment. The ear detects sound waves from the environment. The ear is made up of three parts: the outer ear, middle ear and inner ear. • • • • • • Sound waves reach the cochlea from which impulses are sent to the brain. The ear is also involved with balance. The semicircular canals detect movement. The utricle and saccule in the ear sac detect the position of the head. Surface temperatures on the Earth vary greatly. Animals can be grouped as poikilotherms and homeotherms depending on their ability to control body temperature. • In humans, the skin is an organ of temperature regulation, meaning that skin care is important. ITQ1 (i) Ln humans, the eyes are posirioned o n the uppe r front side of the face. The human skull bas a pair of bo les ca lled eye sockets wh ich 'cradl e' th e eyes. In this position, th e eyes obta in som e protection and the optic n e rve can easily connect w ith the b rain . Human eyes a re used mainJ y fo r mo vem e nt and to focus o n the task at ha nd . A zeb ra's eyes are positioned on eithe r side of its head wh ich greatly increases the a nimal's field o( visio n so it ca n spot predators easi ly. H uman s do no t need to be on th e con stant lookout for predato rs. (ii) A zebra is a la rge h erbi vo re and is prey to many la rge cats sucb as lio ns and cheeta hs. Having eyes o n the sides o f its head allow it to h ave an a lmost comple te view of its surro u ndings at any time, even while it is grazing and feeding. The e nables the anima l to be on th e lookou t for preda tors and aware of any m ovem e nt in its surroundings. Carn ivores, on the o the r hand , need to focus o n their p rey. Th e ir eyes are p ositio ned in front o [ their faces. This makes it possible for them to judge the distance between the m selves and their prey. ITQ2 To aid in movement (avoid obstacles, note di stances. etc.); to aid eatiJ1 g (finding food, ingestion, etc.); to focus o n an y task (reading. cookin g). Other a nswe rs are possible. ITQ3 Conj un cti va -+cornea -+ [pupil] -+aqueous hum o u r-+ lens-+ vi treous hu mo ur -+ retina ITQ4 Accommodation descri bes the adjustm em or th e pupil a nd the le ns to allow a person to see objects at diffe rent distances. ITQ5 Light rays from an object ente r the eye. a nd a message is sent to the brain, which interprets tl1 e message. The light rays pass th rough maJl y structures 240 f · 19 ·The Eye, the Ear and the Skin in the eye, each performing an importanr function. The lighL rays from an object mu st focus or meet at a point on tbe retina, from w here the opti c nerve sends a message to the brain. The cornea, aqueous humour and lens are important because they bend the ligh Lrays to focus on the retina. The cornea and aqueous hu mour bend ligh t automatica ll y, but the Lens can control the degree of ben ding. The pupils a re ' holes' in the eyes, the size of which ca n be adjusted to aJJow controlled amo u nts o f ligh t to e nter the eye. The deg ree of refraction is adjusted by the lens and th e rays focus on the retina . At the retina, ligh t-sensi ti ve cells { send messages to the brain, which interprets rhe message as sigh t. ITQ6 (i) Converging or convex len s. (ii) Diverging or concave lens. ITQ7 (i) A de fect oJ the eye is th e malfunction ing of a n y o n e part of the eye so thaL good vision is preve nted. (ii) A cataract occurs when the lens becom e L1a rd e ned a nd ca nnot adjust to focus light ra ys from o bjects ar varying distances. Astigmatism is a defect which occurs when tb.e cornea does not have a smooth curve; the rays are not refracted evenly as they enter the e ye. There are othe r de fects. ITQ8 (i) The pitrna traps the so und waves and directs them into the auditory ca n.al. (ii) The ear bones ampli fy the sou n d waves afrer they have passed th rough the ou te r ea r on their way LO the inner ear. (ii i) The sound waves ca use pressure waves in the .flu id of Lhe coch lea. Depend ing o n the pressu re of the wave, specific hair cells in the cochlea are stim ulated a nd specific messages are sent to th e brain. The brain interprets these m essages as sounds th at we hear. Th e coch lea is responsi ble for o ur sense of hearing. ITQ9 The ears are a lso concerned w ith ba lance, so any m ovement of the body can be de tected by the ears. The sem i-circular ca nals in the ear are filled · w ith fluid . Any m ovement is detected b y this Ouid. At the base o f tbe semicircular ca nal are s tructures called ampullae. The fluid in the ampu llae moves in the opposite direction to the bod y's movement, pulling on sensory ha ir cells as it does so. Messages are sent to the brain from the sensory cells and are iJJterpreted as movement. ITQ10 (i) Hom eotherm y is the abili ty of an orga n ism LO comrol its body te m pera tu re and keep it at a ce rtain val ue; for example, h um ans ma intain their body tempera ture at aro und 37 °C (birds ha ve a slightly higher body tempe ra ture around 39 °C). (ii) Poikilotbermy describes the inability of an organism to co ntrol its bod y temperature. Th e o rga nism 's body temperature varies w ith the e n vironmenra l te mperature; for exa mple, the body tempera tures o f repLiles and fish vary with the ir e nvironmenta l temperature. ITQ11 Humans can live in extremely hot a nd extremely cold e n viro nments because th ey be lp mainta in their bod y tempera ture ar a constanL va lue by some beh.avio LLral processes. For examp le, they can wear clothes to su it the ir needs, live in buildings which protect them and whi ch may be cooled or heated . Al so, huma ns do not ha ve to go in sea rch of food every day in extreme te rn pera w res. ITQ12 Organisms lik e bacteria and viruses that cause disease can su rvive in any tempe ra ture, but the vectors that carry the pa thogen from host ro host are usua ll y insects (like mosq uiros and flies) wh ich a re poikilotherm ic. These no u rish in the stea dy wa rm temperawres around the equator. ITQ13 The skin is th e major o rgan of tempe ra ture regula tion . l Lis adapted to sui t thi s fu n ction in several ways: • it co nta ins a layer o f [at, which acts as ins ulalio n; • it can co ntrol the fl ow o f blood into the many capillary networks close to the skin; 241 Life Processes and Disease • it has hai rs wh ich can be ra ised o r lowered to increase o r reduce air now next to the skin; • it conta ins sweat glands which produce swea t tha t evaporates to cool the sur[ace o( the body. (Any two o[ tha above) ITQ14• Sweat is produced by the sweat glands. • Erector muscles rela x, causing the hai rs to li e fl at againsLthe ski n . • Hea r is lost from the body as the water prod uced in sweat uses the h eat from the body to evapo ra te. • B lood vessels n ea r the skin open wider, allowing blood LO fl ow through the many capillaries close to Lhe skin. As a result, hea t is brough t close to th e surface o f the body, and ca n be lost by radiation, conductio n, or eva poration of swear. Examination-style questions (i) Make a diagram of the eye as seen in a vertical section. Label these parts in each case stating its function: (e) retina (a) iris cornea (n sclera (g) choroid pupil lens What is the shape of the lens when the eye is focused on a near object? Describe fully the mechanism that changes the shape of the lens when focusing on a near object. (iii) (a) Which structure controls the size of the pupil? (b) Using annotated diagrams only, explain how the size of the pupil is controlled. (iv) Suggest why, on first entering a dimly lit room , it is difficult to see objects clearly, but that they gradually become more clearly visible. (b) (c) (d) (ii) (a) (b) 242 - - - ---- · 2 (i) A sight defect is caused by any condition that prevents proper focusing of light on the retina. Describe fully these common sight defects: (a) long-sightedness; (b) short-sightedness; (c) glaucoma. (ii) Using annotated diagrams only, describe how these eye defects are corrected: (a) short-sightedness; (b) long-sightedness. 3 (i) The diagram below shows the structure of the human ear. Copy the diagram and label the parts listed below and in each case state its function. 19 ·The Eye, the Ear and the Skin (a) pinna (b) tympani um (c) ear ossicles (d) vestibular apparatus (e) cochlea (n auditory nerve (ii) Describe how the ear functions as an organ of balance when (a) the position of the head changes; (b) the body moves. 4 (i) Explain the meaning of the following terms: (a) homeotherm ; (b) poikilotherm. (ii) The graph below shows the variations in temperature during the course of one day for a human, a lizard and the air. Copy the graph and label, appropriately, the three lines in the graph. · 50 40 - -- --------- - -..:::::::.::.: :.:~~·:,._____ __ _ ··.. . :· 30 . ..... Temperature (OC) .. .. . 20 10 .· .· 6 12 noon 18 24 midnight (iii) Explain fully, the changes seen in the body temperature of the human. (iv) Explain the changes seen in the air temperature. (v) Suggest what the lizard might be doing and where it might be found during these times: (a) 6.00 a.m. (b) 12.00 noon (c) 6.00 p.m. (d) 12.00 midnight 5 (i) Draw a diagram of a section of human skin and include the following labels: (a) epidermis (b) dermis (c) receptor (d) capillary network (e) sweat gland (n sweat pore (g) hair follicle (h) hair erector muscle (ii) Describe fully the possible behavioural activities and physiological mechanisms that enable the human body to lose excess heat and maintain a fairly constant temperature. 243 -- --- - - -- - - --- - - - - - - • 0 0 0 0 0 0 0 0 0 0 distinguish between sexual and asexual reproduction describe the structure and function of the human male reproductive system describe the structure and function of the human female reproductive system describe the structure and function of the ovum and spermatozoon understand the menstrual cycle understand fertilisation understand the development of the embryo in humans understand the role and methods of contraception discuss the advangates and disadvantages of contraception discuss the transmission and control of AIDS and gonorrhoea reproduction I t ""sexual asexual advantages and disadvantages reproduction in humans contraception Reproduction I Reprod uctio n is a characteris tic o f We. Every living thing mu st di e and, a ltho ugh ind ividua ls die, a s pecies w ill continu e as lo n g as its me mbe rs a re able to live lo ng eno ugh l"O reprodu ce. n the m embers o f a species die be l'ore the y ca n reprod u ce the n tha t species is in danger o f becoming extinct. Reprodu ctio n is th e re fo re im porta nt fo r a species to conrinu e ro exist, to be ab le to colon ise new ha bi ta ts and r.o s m vive ch a nging e n viro nrne llla l conditio ns. Th er-e a re two ma in types o [ reprod u ction : • asexual; • sexual. Asexual reproduction (one parent) Asex ua l rep rodu cti o n hap pe n s w he n o n e indi vidua l p rodu ces o Hspri ng w itho u t ferti lisatio n . Th.is invo lves cell division by m itos is o nl y (cha pter 23). Th ese o ffs p rin g a re geneticall y ide mica l to each oth e r a nd tO th e ir parent. ft is described as bei ng con se rvative a nd, in esse nce, clon es a re p roduced. Advantages of asexual reproduction • No time o r e n e rgy is wasted seeking a mare. • Large numbers o f o ffspring ca n be prod u ced . 20 · Reproduction in Animals • Offspring ca n be prod u ced continu ously and therefore q u ickly. • O([spring can make good use of fa vo urab le e n vironrnem al co nd irions. • lf the pare nt is of 's uperior' quality, all th e offspring wi ll also be of ' superior' q ua lity. Disadvantages of asexual reproduction Figure 20. 1 An aphid producing live young • Uthe e nvironme nt is cha ng ing, the offspring may fi nd it d ifficu lt LO surviv e. • If th e parenr is o f ' poor' q ua li ty, th e offspring w il l also be o nl y o f that ' poo r.' quality. • Over-crowding a n d competition rnay occu r as o ffs pri ng colo nise th e same a rea as tbe pare nt. CHAPTER 23 There a re severa l rypes of asex u a l reproduction : • vegetative propaga ti on (ch apte r 2 3); CHAPTER 23 • cl on ing (chapte r 2 3) (figure 20. l ); • binary fissio n see n in unice llular orga nisms like bacteria and protozoans such as Amoeba (Figure 20.2) . C!J- 0 one parent identical offspring Figure 20.2 Asexual reproduction in Amoeba. Sexual reproduction (two parents) CHAPTER 24 Sexua l reproductio n involves two pare nrs prod ucing specia l re prod ucti ve cells o r ga metes. This happens as a result o f meiosis (chapte r 24). fusion of rh e gametes produ ces o ffspri ng tha t are di[(e renL fro m ea ch o ther and from both parents. Advantages of sexual reproduction • Generic va riabi lity o f the species is increased . • The species is thus m o re li kely to be able ro adapt to a ch ang iJ1g e ovironme nc. • The species ma y be a ble to colo n ise new a reas successfull y. • lI the pa rents are bo th of poor qu a lity, the o [fsp ring may be o f be tter quali ty. ~ IT:Q-1 \../'-' Draw up a table to show the differences between asexual and sexual reproduction. Disadvantages of sexual reproduction • A lo t o ( lime a nd e n ergy is spent se eki ng a mate. • O ffspring a re no t produ ced continuously a n d therefore not very q uickly. ~ • Few o ffs pri ng may be p roduced (as in hu m a n s). \..)'V • Even if th e pare nts a re o f good qua lit y, rhe o[(sp ring can be o f poo r q ua liry. IT:Q2 What is the importance of reproduction? 245 - - --- - - - Life Processes and Disease , -- • • CHAPTER 24 Practical activity SBA 20.1 : Observing the reproductive cells of a mammal, page 362 ..,,.,..., spermatozoon > _ -· Reproduction in humans ln humans there are two sexes: ma le (ma n) and female (woma n ). Each sex produces gametes o r reprodu ctive cells, by meiosis (chapter 24) . In ma les the gam etes are ca lled spermatozoa, and in females, ova. The sing ular or spermatozoa is spermatozoon , and the singular of ova is ov u m (figu re 20.3). ~ Testes make spermatozoa Ovaries make eggs ~ IT:Q3 /I ovary \/"-/ What type of reproduction do humans show? (ii) Describe two advantages of this type of reproduction. (i) primary follicle, secretes /~-- -:~r~:~s~:elops ( ~-@;, . ', . ~ - + ' . ----@ \ \f ]J "'" .,_ - - -· - - ~ ~~orpus V '- ...... ~ v-v- ~:::::- luteum - k ,.:::;--seminiferous tubule p rogesterone mature ovar~:~! "\. Graafian follicle ~ · • • • • • • - - tail for swimming • spermatozoon • one produced per month • millions produced continuously • live for about 3 - 4 days after release from the ovary (ovulation) • live for about 2 to 3 days in the body of the female after release (ejaculation) • moved along the oviduct by the beating of cilia; cannot move on its own • can swim actively using its tail, secretions from the seminal vesicles and prostate gland help its movement Figure 20.3 Details of the ovum and spermatozoon. The male reproductive system ltffiHFll The plural of testis is testes. l@11M•*I 246 The visible parts of the ma le reproductive syste m are the penis and scrotum (figure 20.4) . The scrorw11 con tains a pa ir o f testes. Each testis is composed or coiled tubes ca ll ed semini(erous tubules, inside of which spe rmatozoa (or sperms) are fo rmed. After fo rm atio n, th e sperms are stored in the epidid ymis. During sex ual inte rco urse, the sperms are moved o ut o f the epididym is and pass thro ugh th e vas deferens on the wa y to the penis. Fluid is made in the prostate gland a nd semina l vesicles which mixes with the sperms to make semen . This se me n, conta ining 200-500 mi llio n sperms, is ejaculated o r released from the erect penis during mati11g or cop ula tion. · 20 · Reproduction in Animals (a) ureter sperm duct spermatic cord _ (sperm duct and blood vessels) _ seminal vesicle _,______._ ·~ prostate gland (b) erectile tissue: blood sinuses that can fill with blood from the artery at the base or the penis urethra ~-- testis foreskin glans----"'--""~ ~---:;;£..--- scrotum Figure 20.4 The human male reproductive system (a) in section, (b) seen from the front (front section). ~ IT:Q'4 V'-1 Describe the route taken by a spermatozoon from its site of production to ejaculation. me ns truation > ~ The female reproductive system The fema le reprodu cti ve system is positioned in the pelvic region (figure 20.5). The re are two ovaries, each usua ll y releasing a single ov um (or egg) every otber monch into the fuDJlel o f the oviduct. Th e ovu m is moved along rhe oviduct, or Fa llopia n tube, by the beating o f ci lia w hich line the rube. ff sperms a re not p resent, tbe o the ov u m moves down the u terus and out of the body during menstruation . Each month the wa ll o r lining o f the ute ru s is b uilt up in prepa ration for a fertilised ovum. The lining is shed if fe rti lisatio n does no t take place. IT:QS V'-1 How does an ovum travel along the oviduct? (a) Figure 20.5 The human female reproductive system (a) in section, (b) seen from the front (front section) 247 Life Processes and Disease·;; : - . _ - _· Hormones of the gonads l'itl'!il'ftim seconda sexual c ha racteristics ) Th e gonads, testes in males and ovaries in fema les, also secrete hormones that influence growth a nd deve lopme nt. Even before birth, while still in the ute rus, rhe testes of a boy produce the hormooe testosterone w hid1 in fluen ces sex ua l development and causes th e ma le sex organs to deve lop. At puberty, the ovaries in girls secrete the hormone oestrogen. Boys, ·~ at this time, make larger amounts of testosterone from the testes. These ho rmones are secreted in respon se to signa ls from the pituita ry which is able. to determin e that further develo pment into a man or a woman must begin. Th is sta rts between the ages of 10 and 14, as boys and gi rls begin to develop the ph ysica l features that distinguish male from fema le. These district physica l and emotiona l features, or chara cteristics, are called secon da r y sexu a l c h a r acteristics (table 20. l ). Males Females • enlargement of reproductive orgars. e.g. penis, testes, etc. • enlargement of reproductive organs and breasts • ejaculation is possible • menstruation starts • increased muscle development • broadening of the hips for child-bearing • growth of pubic and underarm hair • growth of pubic and underarm hair • extra growth of hair on face and chest • deepening of the voice Table 20.1 ~ IT:Q6 V"-J What are the secondary sex characteristics? (ii) When do they arise? (iii) Why are they important? ~ IT:Q7 V"-J How many ova are produced by a normal adult female in a year? (ii) How many spermatozoa are produced by a normal adult male in a year? (i) ~ IT:Q8 V"-J When in the menstrual cycle is the likelihood of fertilisation of an ovum at its lowest? ~ IT:Q9 V"-J Why is the uterine lining built up every month, only to be shed during each monthly period? Secondary sexual characteristics of males and females. These be havio ura l and physica l changes are associa ted with co urtship, mating a nd parenta l concerns. More importantly, these ho rmones also resu lt in the release of the gam e tes. At puberty, gi rls begin ro menstruate, a sign that th e menstrual cycle has begun . Female ga metes or ova are released and can be ferti lised by spermatozoa as boys also begi n to ejacu late o r release ma le ga metes in lO the environment. A d1 il d grows and develops into a sexua l indi vidu al with easi ly recognisa bl e (ea tures tha t are a ttractive lO a potentia l partner, th us ensu ring reproduction a nd co ntinuatio n o r the species (figure 20.6) . Prod uction o f yo ung is a natura l d1a racte ri stic of li fe a nd th ese ho rmo nes produced by the gonads a re impo rtant, no t o nl y for growth and development of an organism into a sexual being, but a lso fo r th ose attractive forces n ecessary fo r the contin uation of Rgure 20.6 Typical physical characteristics of adult the species. human female and male. 248 - - - - - - - - - - - -- -- - - - -- - -- - -- - - - - - -- - - - - - - - 20 · Reproduction in Animals The menstrual cycle On reaching puberty (around L2 years o ld ), a human fema le w ill Sta n to re lease ova from he r ovaries: this is known as ovulation. Ovulation is one part o[ her monrhly menstrual cycle, which sLarts at p ube rt y and continues un Lil menopause (around the age o [ 45- 50 yea rs). Each cycle laSLS for approx ima tely 28 days. The events o f the cycle a re controll ed by ho rmo n es which e n sure that, if the ovum is fe rtilised, the ute ru s is rea dy LO receive it. ~ Th e cycl e starts w ith m e nstrua tion (Lhe sh edding of t he uterus lin in g) whid~ lasts for abo ut 5 da ys (fig ure 20.7). After a few days th e uterus lining starts LO build back up agam - by day 14 o f r..he cycle it has th ickened considera bl y and has a n increa sed blood suppl y. This is ca ll ed the follic ul a r pha se and is control led by the h ormone oestrogen . The events a re syn chronised so that on e ov um is n ow fu ll y developed in a Graafi a n fo llicle in the ova ry and o vulation takes place (the ovu lato ry phase) . The peak lr1 oestrogen le ve l ca uses ovu lation. After ovu lation, th e Graa£i an follicle develops into th e corpus lute um . The hormone progestero ne is secreted by the corpu s lute um and is responsible for ma intaining th e built-up u teru s lining. This is the lucea l phase of the cycle. U rhe o vum is no t fe rti lised by a sperm, it passes th roug h the uterus and vagina during menstruatio n . The co rpus lute um degenerates and th e le vel of progesterone dec reases. This ca uses the built-up uterus lining to start to disintegrate and peel away fro m the ute rus wal l. It passes ou t o f the vagina in menstruation or the m o nthl y period. And Lhe cycle stares aga in . me ns trua l c c le > me no pa use > l~O V'-1 When does ovulation occur in the menstrual cycle, and which hormone is responsible for ovulation? ~ IT:Q-1 1 V'-1 What is the importance of the corpus luteum? (ii) Why is progesterone called the pregnancy hormone? (i) Figure 20.7 The human menstrual cycle Events in the ovary during a cycle ovulation ovarian follicle growing @ '~JJ· ~ ~,-- ® no fertilisation corpus lu teum secretes oeslrogen ~ degenerates produces progesterone • release of ovum (ovulalion) Hormone levels during a cycle a peak in oestrogen - results in ovulation progesterone level rises. stays high if fertilisation occurs J• • • • • •• • • • .... .. ,.·· .·.. ........ .. ....···•··•••••••·•·••·••·····•···· ....... ' ... ·· Events in the uterus during a c ycle menstruation shedding of lhe uterine walls walls built up as oestrogen level rises -+ start or another cycle I no fertilisation w alls shed fertilisation - walls stay built up 2 3 4 5 6 7 8 g 10 11 12 13 14 15 16 17 18 1g 20 21 22 23 24 25 26 27 28 Days 249 Life Processes and Disease Ferti Iisation pregnancy > gestation period > co ulation > fertilisation > ~ l:tQ12 vv What do you understand by the terms (i) courtship behaviour (ii) copulation? ~ l:tQ-1 3 vv (i) What is fertilisation and where does it occur? (ii) Describe the route taken by a sperm after ejaculation in the vagina until it fertilises an ovum. implantation > Tf fe rrilisa tio n takes place and the zygoce successfull y implants itse lf inLO th e bu ilt -up uterus li ning the fe male is sa id to be pregnant. The ute ru s lining musr now sta y bui lt-up LO nouris h th e embryo, so the re is no mo re m e nstrua tion (' pe riods'). This lasts for rhe e n tire pregnancy (o r gestation period ) w hich is usually 9 months in humans. Th is m ea ns that the wo mar 's p roges tero ne level must remain high w ma inta in the bu il t- up ute ru s lining. Also oesrroge n leve ls must remain low so that no more ovulat ion can ta ke place. Tb.e pregnan t woman may experience ' morn ing sic kn ess' (nausea) for the first rbree months o r so as she gets used to th e high le vel o f progesterone and its effects on he r body. Mating, for huma ns (and other mamma ls) , is us ua lly preceded by courtship behaviour. Co urtship establishes a bond betwee n rhe pa rt:ners tha t may keep the m LOgethe r while the young are bro ught up . A m ale and fema le are attracted LO each ocher a nd a s uccessfu l courtship leads to copulation a nd fertilisation . The act o [ copu latio n , o r mating, b ri ngs the gam e tes close LOgether. The penis becomes erect during sex ual aro usa l as the erecti le tissu e fill s w ith b lood. In the fe male, sexua l aro usal res ul ts in the lubrication o f the vagina . The pen is is then inserted into the vagina, bringing the ga m etes close r togethe r. The spe rms a re usua ll y eja cu lated just below the ce rvix, a nd the n 'swim ' across the u te r us and up the ovidu ct. Close LO 500 million spe rms are re leased, bu t only o n e w ill fuse with the ovum. This is fertili sation. Development of the embryo, fetus and placenta Tbe nucle i o f the spe rm a nd fe rti li sed egg fu se ro form 1be zygote (figure 20 .8). Th e zygo te di vides as it m oves slowly to th e ute rus. After seve ral h ours, it is a ba ll of cells ca lle d a n embryo, a11d on reaching the uterus, it sinks into the th ick spon gy lin ing (fig ure 20.9). This is ca lled implantation . He re it obta ins protectio n and nutri ern s unri l th e pla cen ta develo ps. more mi tosis -"--------'~ oviduct occurs stage stage fertilisation (fusion of the nuclei of ovum and spermatozoon) uterus implantation - ball of cells becomes attached to the uterine wall Figure 20.8 A human sperm fertilising an ovum. ( ~--ovary Rgure 20.9 Events that occur in the oviduct leading to implantation. 250 20 · Reproduction in Animals •m••~'*' F1€iB§eiFH ~ The e mbryo deve lo ps tissues and organs and by 8 weeks it is clearly human. It is now a fet u s (figure 20 .10). As the embryo grows, it develops a p lacenta whid1 con nects i1 very closely w ith the wall o ( cbe uterus (figu re 20.1 1). IT:Q·1 4 vv Describe implantation and explain its importance. Figure 20. 1O The embryo develops into a fetus and lives for nine months in the uterus. motlier's blood] diffusion occurs sending nutrients to fetus' blood and waste products to lhe mother's blood fetus' blood ! l to fetus mother's blood from fetus uterus wall space filled with mother's blood vessels umbilical cord ! l Figure 20. 11 Structure of the placenta. 251 Life Processes and Disease The structure of the placenta is shown in figure 20. l I . Th e placenta ha s various [un ctio ns w hi ch include the fo ll owing. • Il al lows exchange of materials between the mother and the fetu s, by bringin g tbeir blood sys te ms very close togetJ1er w ithout the two bloods mixing. Oxygen , water, amino acids, glu cose and essential minera ls diffu se thro ugh the placenta to the blood of the fetus. Carbon diox id e, urea and other wastes diffu se from the fetus into the mo ther's blood. ~ • It protects the embryo by pre venting many pathogens and chemicals from crossing the placenta. Howeve r, there are some exceptio ns, lik e the German measles virus, the HIV virus, nicotine, alcohol and heroin , wh ich are all able to cross the placenta. • It protects th e fems and the mother since it a llows their two blood systems to ope rate at different pressures (the m othe r's body needs a highe r pressure to get blood round a larger syste m) . • lt produces the hormones iJnportant for a successful pregnancy. Effects of drug abuse in pregnancy Nutrients diffuse from the m o ther's blood to the placenta, and the n trave l to tbe fetu s during gestation . Harmful substances ma y also diHu se across to th e fetus if they are present in th e m othe r's bloodstream . • Carbon monoxide and nicotine from cigarette smoke - Problems associated w ith ciga rette smoking incl ude prematu re birtl1, red uced birth weight and the risk of mi scarriage . • AJcohol - There a re seri o us conseq ue nces of alcohol abuse during pregnancy. Alcoho l crosses tl1e placenta easil y and ca uses symptoms in the baby includi ng poor m enta l dvelopm ent, small h ead and brain size, h yperactivity, poor concentra tion and reduced growth ra te. 1~5 \....)'-./ The placenta is described as the lungs, kidneys and alimentary canal of the embryo. Why is it so described? • Drugs like heroin and cocaine - Babies may become addi cted to these drugs whi le inside the m other's wom b. • Pharmaceutical products -These a re carefu ll y tested for harmful e ffects, but it is a wise preca uti on not to use any drugs (even for headach es or nausea) d uring pregn an cy unless prescribed by a doctor. Birth amnioti c fluid > l•J#limiOt•hi 1m;1m1 lftl•I•liill £6b IT:Q·1 6 \....)'-./ Give a brief explanation of (i) gestation (ii) parturition (iii) prenatal care (iv) postnatal care. 252 The fetus is surro unded by a stron g m embrane called the a mnio n . Insid e is a liquid called amniotic fluid wrucb helps to keep a consrant environment aro und the [ems. The amniotic fluid a lso helps to sup port and protect the fetus from ba rm. A[ter 40 weeks in the m other's ute rus (a lso ca ll ed th e womb), the baby is sent o ur .into tbe world . Parturition is the act o f giving birth and is controlled by hormones. The hormone oxytocin ca uses contractio ns of th e ute rus w hich ca n be very pa inful. This is known as 'labour' o r ' labo ur pa ins'. During th ese powerful contractio ns, tb e amn iotic sac bu rsts. The amn io tic fluid po urs o ur o f the uterus and the baby is the n pushed o ur. The umbi lica l cord is cut, sepa ra ting the baby from its mother. After a few minutes, the placenta sepa rates fro m the uterus wall a nd passes out of the body. Th is is sometim es ca lle d th e a fte r-birth. Prenatal (a ntenata l) ca re ensures good .hea lth of the baby a nd m m her during the pregnancy. The m other should, for example, eat a balanced d iet, should not smoke o r drink a lco hol a nd should avo id dru gs. Postna ta l ca re describes care of tbe child Cro m birth to teens. fr in volves the physica l, e motio na l and me ntal ca re essential for hea lthy growth and deve lopme nt. 20 · Reproduction in Animals Breast-feeding l•li•IF:tiJIGI limGmiiiluU Mamma ls suckle their yo ung. After birth of a baby, milk is produced by th e breasts o r mam mary glands as a result of th e effects of m a n y horm o nes, in particu lar, prolactin. The firs t secretio n of th e breast is called colostrum. It is rich in antibod ies and protects th e n ew-born from som e pathogens it may e11counte r on th e first days of its life o ut of the ute rus. Hum an breast milk conta ins the appropriate prop ortio ns of sugar, fat and { protein sui table for a yo ung human ba by. If she is breastfeedjn g, the mother's . ilie t sho uld be rich in foods that w ill provide th e e nergy, p ro te ins, vitarruns and min erals n ecessa ry for hea lth y growth and develop me nt of t he infa nt. 'Formula' milk, w hich is ofte n bottle-fed co infams, at.tem pts to recreate Lhis balan ce. It consists o f dri ed m ilk made to a special fo rmula and is mixed w ith water and fed to the baby in a bo ttle. The role of contraception The wo rl d's popula tion is do ubli ng every 44 yea rs or so. It may soon be di tficult to su ppl y all the needs of a ll of its people. A solution to t he ove r-popula tion pro blem lies in contracep tio n (a lso known as birth control). Table 20.2 summa rises some commo n methods o f contraception and figure 20.12 (overlea f) shows the si.tes of action of some contracep tive methods. Method How it works Effectiveness Advantages Disadvantages sterilisation male (vasectomy) - the vas deferens are cut and tied off 100% no drugs or artificial device used, irreversible no further costs 100% very reliable if taken as prescribed possible nausea, breast tenderness, and water retention leading to an increase in weight; may increase risk of cervical cancer, but decreases risk of breast cancer female (tubal ligation) - the oviducts are cut and tied off contraceptive pill contains progesterone which prevents fertilisation, some also contain oestrogen which prevents ovulation intra-uterine device (IUD) (loop, coil) device inserted into the womb by a 99-100% doctor - prevents implantation reliable possible menstrual discomfort spermicide cream, jelly or foam inserted in vagina before copulation not reliable alone simple to use may reduce the sensitivity of the penis mechanical barriers male (condom) - sheath of latex unrolled onto the erect penis reliable especially available for use by all men and may reduce the sensitivity of the when used with women, and the condom gives penis spermicide some protection against sexually transmitted diseases female (diaphragm, cap) - domeshaped sheet of thin rubber inserted over the cervix before copulation rhythm method refraining from sexual intercourse during those times in menstrual cycle when fertilisation is likely not very reliable no devices or drugs used not really reliable because women can have irregular menstrual cycles (continued) 253 Life Processes and Disease Method How it works Effectiveness Advantages Disadvantages injectable hormone prevents release of ova and thickens the mucus in a woman's cervix very reliable no need to remember medication, no device used injection must be repeated by a doctor every 13 weeks abstinence no traditional sexual intercourse (i.e. almost 100% penis I sperm entering vagina) protects against sexually transmitted diseases if there is no transfer of fluids Table 20.2 Some methods of contraception, their effectiveness, advantages and disadvantaqes. 1?at.7 In the female \...)'..J Match these forms of contraceptive with mode of action A or B: • contraceptive pill • IUD • spermicide • condom • rhythm method • tubal ligation • vasectomy Mode of action: A prevents implantation B prevents fertilisation. Intra-uterine device (IUD) injection/implant (contraceptive pill) barrier techniques - --\--1 In the male • diaphragm (cap) • contraceptive sponge • spermicides • female condom Agure 20. 12 The sites of action of different contraception methods. HIV/AIDS and other STDs liJlB opportunistic infections > 254 STDs are sexua lly rransmitted diseases; th is mea ns they a re diseases th at are transferred fro m o ne person to a nother during sex ua l inte rcourse. AIDS (acqu ired immune defi cie ncy syndrome) is tho ught to have origi nated in Central Africa and bas a lrea dy killed over 3 mi lli on people worldwide. AIDS is ca used by the human immunodeficiency virus (HIV ), wh ich can onJ y survive in body flu ids. HIV can be transferred in other ways as well as by sexual intercou rse beca use is transmi tted wben t be blood or semen of a n infected person m ixes with th e body fluids of another person . This can ha ppen during sexua l interco urse, blood transfusion or when sha ring a hypodermic needle. An infected pregnant woman can also pass HJV to h er ba by through the p lacenta or by la ter breast-feeding. Close contact between people with ope n wounds has also been known to pass on the viru s. Infection w ith HIV weakens the body's natura l defence syste m (th e immune system) because the virus attacks particular white blood cells, ca lled T-Lymphocytes (figure 20 .13). This means t he body is vulnerable to other infection s (known as opp o r tunistic infectio n s) like common viral, bacterial and [un gal infections. Table 20.3 compa res two STDs: HIV/AID S a nd gono rrhoea . 20 · Reproduction in Animals Figure 20. 13 False-colour scanning electron micrograph of a T lymphocyte white blood cell infected with HIV Disease Causative agent Symptoms Control AIDS (acquired immune deficiency syndrome) Virus (HIV) • Persistent cough, fever. Skin rashes, swollen lymph glands, diarrhoea, wasting away of body, weakness. • Secondary (opportunistic) infections - pneumonia, tuberculosis (TB), candidiasis (fungal), cancers. • Keep to one sexual partner (or to partners who have been safely screened for STDs) • Do not inject drugs • Use condom during sex • Education about the spread I prevention of disease • A vaccine is being sought Gonorrhoea Bacterium • Yellowish discharge from urethra, • Keep to one sexual partner pain when urinating. Often (or to partners who have been not noticed in females. If left safely screened for STDs) untreated, causes inflammation • Treatment by anti-biotics, e.g. of Fallopian tubes and sperm penicillin, streptomycin ducts leading to sterility. • No known vaccine • Arthritis, weakened heart, blindness. Table 20.3 Information on AIDS and gonorrhoea. ~ IT:Q-1 8 V"-J What kind of disease is an STD and why is it so called? Prevalence (%) by WHO region 0 Western pacilic: 0.1 (0.1-0.11 0 Eastern Meditteranean: [0.1-0.31 0 South-East Asia: 0.3 (0.2-0.41 Europe: 0.4 (0.4-0.51 • Americas: 0.5 (0.4-0.61 • Africa: 4.6 [4.4-4.81 ' 0 ) Global prevalence: 0.8% [0.7-0.8] Figure 20. 14 Estimate of the numbers of people (15-49 years) living with HIV (2011) . Social and economic implications of STDs especially HIV/AIDS • Th e cosLo f rrea ri n g and carin g for chose a fl'ecLed is h igh , especia ll y in co un tries whe re a high perce nrage o ( Lhe pop u la tion is infected . • Th ere is a reduCLio n in the wor kfo rce a n d loss o f va lua ble working h ours. • The family o f a n in fected person suffers e m otio n a lly a nd fin an cia lly. • M illi on s o f do llars a re s pe n t w o rldwide o n resea rch for a possible cure fo r HJ V infection . • People w ith AIDS .(in cl udi ng childre n ) ma y be scorned and a lie nated fro m so cie ty. • STDs a re easily s pread by sexu a l inte rco u rse. • M illio n s o f child re n worldw id e are living w ith the e ffecLs o f HIV /AID S; man y a re orph a n s. 255 Life Processes and D isease r Chapter summary • Reproduction is necessary for the propagation of life on Earth. • Asexual reproduction involves only one parent and no fertilisation. The offspring are genetically identical to the parent and each other. • Sexual reproduction involves two parents and fertilisation. The offspring are differen\ from each other and their parents. • Variation in offspring resulting from sexual reproduction is important when there are changes in the environment. • In humans there are two sexes: female and male. • The female gamete is the ovum and the male gamete is the spermatozoon. • The menstrual cycle starts at puberty and is usually a 28-day cycle in human females. • Ovulation, the build-up of the uterine walls and menstruation are processes which are part of the menstrual cycle. They are controlled by the hormones oestrogen and progesterone. • If fertilisation of the female gamete by the male gamete occurs in the oviduct, a zygote is formed. • The zygote implants itself in the wall of the uterus. • The developing embryo is protected by the amniotic fluid and is nourished by the developing placenta. • Drug and alcohol abuse are very harmful to a developing fetus. • Contraception methods prevent pregnancy from occurring. ITQ1 Asexual reproduction Sexual reproduction single parent involved two parents involved offspring identical to parent offspring different from parents offspring identical to each other O.e. no variation offspring different from each other (i.e. variation between individuals) is seen) less likely to survive a changing environment (none may be able to survive because no variation in offspring) more likely to survive a changing environment (some offspring may be able to survive as a result of variation in offspring) evolution of the species less likely (only through evolution of the species can occur more readily mutation because of variation type of cell division is only mitosis type of cell division involves meiosis ITQ2 Reproduction is the prod uction of offspring and it ensures the continu atio n of the species. lf m ost individuals in a po pula tio n die be fore th ey reprodu ce, the n that popu la tion cou ld beco me extin ct. ITQ3 (i) Sexua l reproduction. (ii) Any of th e adva ntages mentioned on page 000 could be me ntion ed. ITQ4 testes - epididymis - sperm du ct - ureth ra ITQS An o vum is pushed a long the oviduct o n release fro m the ovary. Tt is 's ucked ' in ro the oviduct and is pushed along by a curre nt produced by the 256 20 · Reproduction in Animals beating o f the cilia that Line the ovid uct. Also, contractions of the oviduct walls he lp to move the ov um aJong. ITQ6 (i) Secondary sexual characteristics are those special [eatures that make a male orga n ism look different Erom a fema le organism (e.g. broad hips, deep voice). (ii) Th ey start a t pu be rty. (iii) Th ey are im porta nt for a ttraction to the opposite sex and courtship. ITQ7 (i) A femaJe usuaJ ly produ ces o ne ovum a month, that is a to ta l of ~ twelve ova in a year. . (ii} A male ca n produce over 1 mrnio n spermatozoa in one ejaculation. There is no set rate at w hich he ejacu la tes, as it depends on how often he h as sex ual intercourse or e ngages in some so rt of sexua l activity. A m a le can produce bi1lions o f spermatozoa in a yea r. ITQ8 An average menstr ual cycle is take n to be abou t 28 days. During the first 10 days, no ovum is presen t to be fertilised. Spermarozoa can live inside the fema le for 2- 3 days after ejacu lation, so inte rcourse 2- 3 days before ovulation may res ul t in fertilisation. The ovum may live for 3-4 days, so sexual intercou rse up to 5 days a fter ovulation may result in fertil isation. Ovulation usua lly occurs around day 14. So, in an average cycle, intercourse is least likely to resu lt in fertilisation during days 1-10, and 20- 28. ITQ9 Every m onth , ovulation occurs, so that fertilisation can occur. Thus, every mon th, the ute ru s has to be prepa red for implantation. If implantatio n does n ot occu r, that m onth's lining is shed . ITQ10 Ovu lation occurs in the m id dJe of the cycle, around day 14 in a 28 -day cycle. Oestrogen is the hormone responsible for ovulation. 1t is secreted by the Graa fi an fo ll icle as it develops in th e ovary. When the oestrogen concentration in rhe blood reach es a certain level, ovula tion occurs. ITQ11 (i) The co rp us lu te u m produces the hormone progesterone, whid1 ma in ta ins the lini ng of the uterus fo r a few days a fter ovu latio n . This prepares the body for imp lanta tion, if fertilisation occurs. (ii) Progesterone is ca lled the pregnancy hormone because its level stays h igh during pregnancy. This h ormone causes the uterine lining co stay thick and rich w ith blood vessels, so that the developing offspring can obtain the nutrients it needs. ITQ12 (i) Courtship behavio u r is used to attract a mate and, hopefu ll y, results in m a ting and p roduction of offspring. Tc includes special body movemem s, ca lls a nd da n ces. (ii) Copulation is th e sex act, th e insertio n o f the pen is into the vagi na. O n ejacula tion, sperma tozoa are r eleased at the base o f the cervix . Copu lation res ults in th e transfe r o f m ale gametes to the female w here fertilisation with the fem ale gam ete is possible. ITQ13 (i) Fertilisatio n is th e fu sion of the ma le nucle us, carried by the sp e rmatozoo n, w ith the female n ucleus that is in the ovum. l r occurs in tbe ovid u ct or Fallopian tube. (ii) vagina-+ cervix ...... u teru s ...... ovid uct ...... ovum ITQ14 The zygote or fertilised egg travels down the oviduct to the uterus. Ir implants itself in the wa ll of the tJ1ickened uterus. A placenta then develops from the emb ryo a nd bei ngs to obtain nutrients and oxygen from the mother's blood. ITQ15 The placenta is th e site o f exchan ge of materials berween mother and fe tus. By diffusion across the p lacenta, the fetus obta ins oxygen and nutrients an d gets rid of its waste products. These are the fu nctions that the lungs, kidneys and a lin1entary canal w ill ca rry ou t after birth. ITQ16 (i) Gestation is the pe riod o f develop ment from impla nta tion to binh. In hu mans it is a bo ut nin e m o nths. (ii) Partu ritio n is birth . I t is the expulsion of the baby from the uterus. 257 Life Processes and Disease (iii) Prenata l care describes rhe care of pregnant woman takes during pregnancy to ensure the birth of a h ea lr11y baby. It includes a proper diet and abstinence from drugs and alcohol. (i v) The newly born baby is tora ll y helpless and dependent on irs mother to sa tisfy all its needs. Postnatal care is care of the baby after it is born. ITQ17 An l.UD has mode of acrion A; al l the other forms of contraception have mode of action B. ITQ 18 An STD is a sexuall y rransmined disease. Tb is means it can be passed on by sexual Lnrercourse. Examination-style questions (i) Make a labelled drawing of the human female reproductive system. (ii) Indicate on your drawing with: (a) an X, where fertilisation normally occurs; (b) a Y, where spermatozoa are deposited during copulation; (c) a Z, where implantation can occur. (iii) List three advantages of sexual reproduction. (iv) Is it possible for a woman to have 30 children? Explain fully. (v) Suggest reasons why you think it is disadvantageous to have many children. (vi) List four methods of contraception. 2 (i) Define the following terms: (a) implantation; (b) fertilisation; (c) gestation period; (d) contraception; (e) asexual reproduction. (ii) Illustrate, using large, clearly labelled diagrams, to show the differences in size, shape and activity of male and female gametes. (iii) Give full and accurate accounts of how: (a) the zygote develops and moves to be implanted, from the time right after fertilisation to implantation; (b) the embryo is nourished and protected as it develops in the uterus: (c) the baby is nourished and protected right after birth. 3 The events of the menstrual cycle are divided into three phases: the follicular, ovulatory and the luteal. (i) Copy and complete the table below to show the activities in the uterus and ovary during these phases. Events that occur in the ovary Events that occur in the uterus Follicular phase Ovulatory phase Luteal phase (ii) In human females, the menstrual cycle lasts approximately 28 days. What significant events happen during these parts of the cycle? (a) days 0- 5 (b) days 5-1 O (c) days 13- 15 (d) days 15-25 (iii) Describe and explain the changes that take place in the menstrual cycle after fertilisation. 258 Reproduction Plants 0 0 0 • understand the life cycle of a plant describe the structure of a flower and relate the structures to their functions understand the differences between wind-pollinatd and insect-pollinated flowers 0 understand fertilisation in a flowering plant and the development of fruit and seed 0 0 describe the structure of a fr.uit and adaptations for dispersal understand why dispersal is necessary and how it can be brought about plant I flower pollen grain male gamete ovule - female gamete ~,~~~~~~~~~--...--------------------' cross self }- pollination fertilisation development of seed/fruit wind water dispersal animal germination exploding new plant Life cycle of a plant Reprod uction is important for the conlinuatio n o f life. Tr is the process by wh id1 new orga nism s are produced. Flowering plants reproduce sexua ll y (fusion of m a le and fema le ga m etes). Sexual reproduction in hu mans in volves two sexes: the mal e produces the ma le ga mete, a nd rbe fema le prod uces 259 Life Processes and Disease the female gamete. However, in plants, the reproductive organ, which is the flower, usuall y produces both male and female gametes (figure 21.1). Sexual reproduction in animals involves two sexes: male female reproductive organ produces the male gamete reproductive organ produces the female gamete Sexual reproduction in flowering plants usually involves one flower that produces both male and female gametes. Figure 21.1 Parents in sexual reproduction of animals and plants. The life cycle of a typical flowering plant is seen in figure 21.2. ~ IT:Q-1 v'-' Why is the flower described as a reproductive organ? pollination followed by fertilisation occurs ~ fruit containing seed ............... seeds are ~ • dispersed IT:Q2 V'-' .\ ••• Put these in the correct sequence of the plant life cycle, starting with (a): (a) development of flowers (b) germination (c) fertilisation (d) dispersal of seeds (e) pollination (f) formation of seeds (g) growth of plant ,, Figure 21.2 Life cycle of a typical flowering plant. The plant grows until it is mature and produces flowers. These flowers are I elelllijfilitelelJ the organs of reproduction. After pollination (bringing the gametes closer together) and fertilisation (fusion of the gametes), fruits are formed which contain seeds. The seed conta ins the embryos or developing plants which are usua lly dispersed. Dispersal ta.ke them to new places where the seeds germinate, if possible, into seed li ngs or young plants . The seedling then grows and mature into ao adult plant and the cyde repeats itself. 260 21 · Reproduction in Plants Structure of a flower pollen grain > Flowers are the reproductive organs of a plant. This m eans tha t the fl owers, regardless of the colour, size or sbape, produce and contain the ga me tes or sex cells. The fema le game te is the ovule and the ma le gamete is the pollen grain. A flowe r is structured to protect, house and bring togethe r the ma le and female gametes. , A typica l flower has fi ve main parts. Th e n umbers in the paragraphs below refer to figure 21. 3 stigma I' 1 Gynaecium -+ carpels (pistils) -+ style \, ovary -+ ovu le (female gamete); ./' 2 3 4 5 filamen t Androecium -+ stamens ..,.. a nther -+ pollen grains (male gametes); Corolla --+ petals; Calyx -+ sepals; Receptacle . e - petals form the corolla - -- - - - - often brightly coloured and scented gynaec ium is composed of: ca~el androecium is composed of: anther l sti: : : _ __ L - - - filament ovary - -- J stamen the anther c ontains pollen grains (male gametes) (several carpels fused together are called a pistil) sepal - part of the calyx which protects the flower in the bud stage nectary contains nectar rec eptacle flower stalk Rgure 21 .3 Parts of a flower. ~ IT:Q3 Ta ble 2 1. 1 sh ows th e importance of th efive ma in fl ower pa rts. Label the parts of the flower below. Part of flower Importance of function V'-1 A B c gynaecium produces and contains the female gamete androecium produces and contains the male gamete corolla attracts pollinators, such as insects, to the flower calyx protects the flower in the bud stage receptacle holdings the flower and then the fruit/seed Table 21.1 The roles of different parts of a flower. 261 Life Processes and Disease Pollination self-pollination > cross-pollination > Pol lination is tbe transfer of the pollen gra in from the amher to the stig ma or othe r flowe rs o f the sa me species (figure 21.4). Self-pollination is th e trans fe r of po llen to the sa me flower o r flowers on the sa me plant. Cross-pollination is the transfer of poll en to flowers on another plant of tbe sa m e species. Most plants undergo cross- polli nati o n, w h ich increases the va riety in the o ffspring \ p rodu ced. Seli-po!Jination gene ra ll y happe ns w he n cross-polli natio n cam1ot be ach ieved . flower cross-pollination ----- - plants of the same species - - Agure 21.4 Self-pollination and cross-pollination. Figure 21.5 Flowers are pollinated by different agents, such as insects and birds. ~ IT:.Q~ \./'-' (i) What is pollination? (ii) Why are agents of pollination necessary? (iii) Name three agents of pollination. ~ IT:.QS In plants, tb e mal e and fema le ga me tes (po llen gra ins a nd ovules) are bro ught cl oser togethe r usuall y by w ind o r by a nima ls, most co mmonl y insecrs and birds. Tbe planr is dependent on these agents to help bring their ga m etes toge ther. Plowers o f these plants ha ve evolved over mill io ns o r years into orga n s that are high ly specialised to tl1e type of po llin atin g agenr (figure 21.5). For example, if insects are to transfer pollen, then they musr be suffici e n tly attracted tO the flowe rs to approach them . This is achieved by insect-po lJ inared flowers h aving nectar, a sugary liquid which is a food so urce fo r insects. Tl1e insects mu st go tbe flowe rs fo r food. Flowers a lso attract insects with brig l1L colo u rs and strong scents. And so, a n in sect visiting fl ower afte r flo we r as it feeds, picks up the pollen gra ins (male gam etes) from o ne fl ower and tra nsfers them to the fem a le gam et e of other flowers . A wind -pollinated fl ower h as a diffe re nt type o f fl ower. These fl owers ca n be inconspicuous and sm alJ beca use they do n o t need w a m act insecrs o r birds. They a re specia Lised i_n a way that allows rh eir pollen to be p icked up by wind curre nrs. Insect-po linated fl owers an d wind-pollinared fl owe rs are compared in fi g ure 21.6 and ta ble 2 1.2. colourful petal \./'-' Define (i) cross-pollination (ii) selfpollination. r-~~1--- stamen inside flower stamen hangs out of flower Figure 21.6 Flowers are adapted for either insect-pollination or wind-pollination. 262 Reproduction in Plants Q6t., Insect-pollinated flower Wind-pollinated flower Examples Pride of Barbados, pea (Crotalaria) corn (Zea mays), grass, sugar cane Flower large and brightly coloured small and inconspicuous Petal large, brightly coloured scented nectaries small, green or brown in colour, no scent at the base of petal and no nectaries Stamen short, with anthers firmly attached inside long filaments, with anthers that hang the flower outside the flower Stigma sticky and situated inside the flower large, branched and feathery Pollen grain large, sticky or spiky- small quantities produced small, smooth and light - large quantities are produced ITQ6 \..?V How is the flower below pollinated? Give reasons to support your answer. ' ~ ITQ7 v'-.J Describe what happens in the flower after pollination, leading to successful fertilisation. Table 21.2 Comparison of insect-pollinated and wind-pollinated flowers. fiower Fertilisation and development of seed After fertilisation, the ovules develop into seeds and the ovary into a fruit. -+--~-- style - 2 pollen tube grows down t11e style to the ovary ! The fruit grows more as the petals begin to drop off. pollen tube enters micropyle to reach female nucleus Figure 21.7 The male nucleus is brought close to the female nucleus for their fusion (fertilisation). The fruit containing the seeds ~ continues to mature. Figure 21 .8 Development of a fruit. Afrer fertilisa tion, the ovu le d evelops into a seed contain in g th e em bryo. The ova ry grows into th e frui t as the pe ta ls shrivel a nd drop o ff. Th e stigma, style and stame rts a lso d rop off. Th e sepa ls may rema in (figure 21.8). 263 - - - - - -- - - Life Processes and Disease The structure of the fru it and seed of a dicory ledonous plant are related to rbe structure of the fl ower. A fruit, whici1. contains one or mo re seeds, deve lops from the ovary. Its shape and the position of the seeds in it relate directly to the shape of the ovary and the posi tion of the ovu les imide (table 21.3 ). Ovary with ovule(s) Fruit with seed(s) long ovary containing four ovules in a row long pod-like fruit containing four seeds in a row ovary containing one ovule oval-shaped fruit containing one seed round ovary with rows of ovules a 'i' round-shaped fruit containing rows of seeds. Table 21.3 After fertilisation, a fruit develops which relates to the shape of the ovary and the number and position of the ovules. Dispersal Practical activity SBA 21.1: Dispersal of fruits, page 363 Practical activity SBA 21.2: Seeds and food storage, page 364 The fruits conta ining the seeds a re 6rmly attached to Lhe pla nt as the y develop, grow and mature. When mature, o r ripe, they a re dispersed o r sent away from the parent plant. Most plants depend on the he lp of agents Uke w ind, water and anima ls to di sperse their seeds. Each fruit is th us highly specia lised in structure, size, shape and compositio n fo r its type of dispersa l. Spreading th e seeds away from the parent p lant is im porranr ro: • pre ve nt overcrowding and th e refore competition for light, space, water and mine rals; • a ll ow colonisa tio n of new areas o r habitats. Dispersal by animals ~ IT:Q8 V"-' Why does a fruit have two scars? The wa ll o.f the fruit is ca ll ed the perica rp and may be composed of three layers - the epica rp, mesocarp and endocarp. In some fruits, these layers are fl esh y and succulent and a nimals are attracted to th em for food (fig ure 2 J .9). - colourful scented fruit 7--- endocarp sweet, soft (succulent) succulent/fleshy inside Rgure 21.9 A succulent fruit, like a passion fruit or orange, is colourful and scented. 264 ~ production in Plants hooksonthefruit Fruits li ke .mangoes, romaroes, oranges, and wate rm e lons conta in srored food, a nd a re colo urful and seemed to attract animals. The fruir. may be green, unscen ted and in conspicuous w hen young but, as it ripens and is read y for dispersa l, it develops bright colo urs li ke red and orange, and becomes scented, so that animals a re attracted LO the plant for food. As they eat the fru its, they may move away and so disperse the seeds. If the seeds are large, they a re spa t out or discarded in a new place away f rom the parent plant. 1f the seeds are , small, th ey may be swa llowed and then egested (figure 21.10). Some, like to mato seeds, ca n pass tbrougb the dlgestive system u n harmed. b ird then flies away seeds in the faeces of the bird fall far away from the parent plant fruit hooks onto animal's fur or clothing as they pass through bird eats fruit swallowing the seed Figure 21.10 Berries are succulent fruits. They can be taken far away from the parent plant by birds. Figure 21.11 Some fruits have hook-like structures. Fru its ca n also be dispersed by animals in a different way. These ki11ds of fruit do nor. anract a n ima ls for food because they a re dry. They have hooks or hairs or spikes, and become attached to the an ima l instead (figu re 2 1. 11 ). When the an imal is wa lking tl1ro ugh the env ironment, these fruits, li ke sweetheart and burr grass, stick or book on to the anima l's legs or body and ge l dispe rsed as the animal moves away from the parent plant. Dispersal by water Fruits d ispersed by water rnusr be buoyant so that they can fl oa t away, for examp le, coconu t trees a re usua ll y found on coastlines. Cocon u ts can be taken by ocean currents to otl1er coasts, islands or countries. The ep icarp is waterproof and the mesocarp fibrous and ligh t - adaptations fo r dispersa l by water (figure 2 1.1 2). the mesocarp is fibrous and traps air which makes the large fruit buoyant coconut oats on water and is taken away from the parent plant coconut sprouting on a new beach Figure 21.12 Some fruits such as coconuts are dispersed by water. Dispersal by wind Some fruits a re ca rried by the gentlest of w ind currents a nd so mu st be li ght and particu lar adaptations (fig u re 2 1.1 3, overleaf). Dan delion and silk corron 265 Life Processes and Disease ~ seeds ha ve radiaring rhrea ds that form a parac.hure; mahogany seeds h ave w ing- li ke stru clllres w hich a llo w them to be carried away fro m the ir pa re nt. IT:Q9 V'-1 wing-like structure What is dispersal? The fruit spins in the wind and can be taken far away 1--- - parachute shape can take fruit far away Figure 21. 13 Some fruits are adapted to 'fly' in wind currents. Dispersal by explosive devices W h en expl osive fr uits dry, th ey split and curl su ddenly to nick o ul Lhe seeds (fi gure 2 l.1.4). These are fr u its with pods like ga rden pea (Crotalaria), thorn apple and Pride o f Barbados. This is al so ca lled se lf-di spersa l o r m ech an ical dispe rsa l. ln th is case, the h e lp o f som e oth e r agen t is n ot needed - th e drying out o f the pod ca uses it to spl it a lo n g its line o r wea kness a lo ng th e side. ~ IT:Q·10 V'-1 Draw a table with named examples of plants which show each of the following methods of dispersal: animals, water, wind, self-explosive. Describe how their seeds are adapted for dispersal in this way and make a simple sketch in each case. 266 Figure 27.14 Some fruits such as thorn apple (Datura stramonium) 'explode' and release their seeds The pod splits when the walls curl back as they dry out. The seeds are flicked out. 21 · Reproduction in Plants lf the seeds eventuall y I.and o n fertile soil, away from the parent, the y have a good chance o f germina ting into a seed ling wh ich can then grow into new plant. Life continues and the cycle continues. ' ITQ1 Tbe fl ower produces the rep rod u ctive cells or ga meces which, on fu sion, prod uce oCfspring. ITQ2 a, e, c, f, d, b, g ITQ3 A petal Banther ~~~.........,..~~- C ovule ITQ4 (i) Po lli nation is the transfer of polle n grains from th e a nthe r to a stigma o f a flower o f the same s pecies. (ii) Po lle n gra ins cannot move by themselves. They requ ire agents to move them from th e anther to th e stigma. (iii) Insects (e.g. bee); birds (e.g. hummingbird) ; wind. ITQS (i) Cross-pollination is the transfer o[ pollen grains from the anther o f o ne pla nt to the stigma o f another plant o r the sa m e speci es. (ii ) SeH-pollinatio n is the tra nsfe r o f pollen g rains from the anther o [ one fl ower to the stigm a o f the sa m e flo wer, or to OLher flowers on the same p lan t. 267 Life Processes and Disease ITQ6 Th is flower is insect-po ll inated because: • it is brightly colo ured; • th e stig ma is inside the fl ower; • it has large peta ls; • the anthe rs a re [ound inside the fl ower. ITQ7 During pollina tion, th e pollen gra ins land on tJ1e stigm a or a fl owe r. U th e polle n a nd th e stigma a re o f th e same species, th e pollen grain th en , germin ates and develops a lo ng polle n tube w hich grows down in side the style. The pollen tube conta ins two m ale nuclei an d it contin ues to grow un til it reach es the ova ry and th en the ovules. It grows th roug h the micropyle an d e nters the ov ule. A male n ucle us in rh e pollen tu be the n fuses w ith the [ema le n ucl eu s in tJ1e ovul e. This is fe rtilisation ITQS Whe n a frui t develo ps from an ova ry, it has a sca r wher e it was atta d 1ed to the rece ptacle or stem a nd a scar wh ich used to be the style. ITQ9 Dispersal is the p rocess which describes how the offspring of a pla n t m ove away from the parent plant. Neither the fru its containing the o ffspri ng n or the seed (offspring) ca n m ove from place to place, so they depend o n age nts of dispersa l li ke water, w ind and animals. ITQ10 Fruit Agent of dispersal Adaptations for dispersal in this way Cherry Animals The fruit is brightly coloured and juicy. Animals are attracted to it for food, and they disperse the seeds when they move away from the parent plant with the fruit. Coconut Water The fruit is dull and very large; it is also buoyant and light. It can stay afloat for long periods of time. Purple petria Wind Wing-like structures are present. Seeds are light and small and can be picked up and carried by wind currents for miles. Thorn apple Self-explosive It is dull-coloured and has four parts. They lose water and become harder and harder, placing strain where they join together. Eventually the parts 'burst' and scatter the seeds which were Inside the fruit. 268 -- --~-- - - - - -- - 21 · Reproduction in Plants Examination-style questions (i) Define: (c) germination (a) pollination (d) dispersal (b) fertilisation (ii) Examine the diagrams of the two fruits I and II below and describe fully how dispersal occurs in each. (iii) List two advantages of dispersal. (iv) List three conditions necessary for germination. 2 (i) Name the parts of the flower in the diagrams I and II below. H 269 Life Processes and Disease (ii) State some differences between the stamens of the wind-pollinated flower and insect-pollinated flower. (iii) List two characteristics of the pollen grains of insect-pollinated plants. (iv) What is the main advantage of cross-pollination? (v) Pollination can be described as an example of symbiosis. Describe fully the relationship between bees and flowers. 3 (i) Copy and complete the diagram below which shows the reproductive cycle of a flowering plant. adult plant with flowers ( I I ..•. ·- fertilisation dispersal (fusion of gametes) t.____ _ __ -! (ii) Name A, B, C, D, E, F and G in the diagram below. :L=-- GI - - A l-+--8 c F E (iii) Distinguish between pollination and fertilisation. (iv) Pollen grains from many different species may land on a stigma. However, the seeds produced belong only to the same species as the flower. Explain why this happens. 270 ~D) isease and Humans 0 underst and what is meant by pathogenic, deficiency, hereditary and physiological diseases 0 distinguish among the methods used to treat and control the four main groups of diseases 0 0 understand the role of vectors in the transmission of disease 0 understand the importance of knowing the life history of a vector in relstion to control understand the social and economic implications of disease in plants and animals disease r deficiency pathogenic r I vector I } MOS control of disease hereditary ' role of blood immunity physiological ' social and economic implications drugs • alcohol • caffeine • cocaine • heroin life cycle ' ( natural artificial vaccination Health and disease Hea lth h as been de fined a s 'co mplete ph ysica l, m e nta l a nd social we ll -being'. l t is m ore t han just rhe absence of disea se; it incl udes th e me nra l a nd socia l d imension s o [ li fe. A disease is a condiri.0n in w hic h th e h ea lth o f an o rgan ism is impaired. Note that a proper diet a nd adequate exercise a re im po rta nt to good hea lth. Th ey h elp to preve m the onse t of, a nd even he lp to treat, diseases. Eati ng foods Lh.a t make up a ba lanced diet increases the body's resista n ce to in fection. A p rog ramme o f exercise stre n gthens a ll the o rga n systems and leads to overa ll good hea lth - physical, me nta l and socia l. Types and control of disease Diseases can be divided imo fo ur main types - pathogenic, deficiency, h e redhary and physio logica l. 271 Life Processes and Disease Table 22. L distingu ish es between th ese types of disease, describes one exa mple of each type and discusses the m ethods used to treat and control these Lypes of diseases. Type of disease Named example cause Symptoms Pathogenic Caused by parasitic organisms (pathogens) like viruses, bacteria, fungi, protozoa and worms. Examples: malaria, TB, cholera, influenza Influenza Virus (pathogen) invades Headache, sore throat, the body by contact muscular pains, fever with infected person. It is airborne or dropletborne. Deficiency Caused by a shortage of a nutrient (e.g. vitamin, mineral) in diet. Examples: kwashiorkor, night-blindness, irondeficiency anaemia Iron-deficiency Deficiency of iron Weakness, fatigue, anaemia causes a reduction in shortness of breath, the number of red blood increased heartbeat, cells which reduces pale appearance the oxygen-carrying capacity of the blood. This is because iron is an integral part of the structure of haemoglobin in red blood cells. Hereditary Caused by genes passed on from one generation to the next. Examples: haemophilia, cystic fibrosis, sickle cell anaemia Sickle cell anaemia Gene for the disease is passed to the offspring. The gene causes the red blood cells to be sickle shaped which reduces oxygencarrying ability. Physiological Caused by a malfunction of body's organ. Examples: asthma, hypertension, diabetes, glaucoma, stroke Diabetes Inability of the islet of Tiredness, continual Langerhans to produce thirst, weight loss, insulin. Body cells are increased urination, unable to absorb glucose coma which stays in the blood. Weakness, tiredness, weight loss, May lead to kidney failure, heart failure Treatment Control Rest and treatment for Prevent overthe symptoms. Vaccine crowding and for specific strains of exposure to the the virus. virus. Prevent droplet infection through coughs, sneezes, etc. Eat iron-rich foods (e.g. red meat, green leafy vegetables). Take iron tablets. Education about a balanced diet, food groups, etc. Avoid situations where Genetic counselling oxygen supply is reduced. No treatment or cure available. Insulin injection/tablet Low carbohydrate diet, exercise. Education on the importance of diet and exercise. Table 22.1 Some diseases in humans. CHAPTER 13 ~ IT:Q·1 V'-.1 What do you understand by the terms: (i) pathogenic disease (ii) hereditary disease (iii) physiological disease (iv) deficiency disease? 272 Som e djseases are more common ly found in certain pa n s of the wo rld than in oth e rs. For example, in developing countries a grea ter proportion of dea Lbs occur as a result of infectio us diseases, like den gue fever, ch ole ra a nd tube rculosis. In developed co um ries, a smaller proportion of people die from infect ious ruseases. and more death s are d ue to p hysiologica l diseases like ca nce r and hea n disease. These kjnds o f disease are infl uenced by facto rs such as diet, life style, genetic prerusposition and exposure to ha rmful cond itions. For example, hypertension (chapter L3) results from a stressful li fe, filled wi th worry, a nger, nervo us fatigue, n o rest or relaxation, and u nh ea lth y ea ti ng habits (e.g. too mu ch fatty, sa lty fast-food) . Hyperte n sion can to some extent be controlle d by good diet and exercise. This difference in distributio n is refe rred to as th e globa l distributi on of disease. It often reflects th e wea lth and sta ndards ol medica l care in the diffe rent coun tries. Th us, the occu rren ce o f disease in deve loping countries is often iofl uenced by facto rs such as overcrowrung, lack of clea n water, lack of preventative medkin es and lack of proper nutrition. 22 · Disease and Humans Pathogenic diseases and vectors l•fi\hr•lo!4•*J A pathogen , or disease -causing organism, Lives on or inside an organism, the host, causing it to be diseased o r sick. Pathogens ca n move from one host to a nother, or inrect another organ ism in a number of wa ys including by: • water; • food ; • airbo rne droplets; • direct contact; • du st pa rticles; • contact w ith fa eces; • anima ls (ma inly insects), ca lJ ed vectors. Vectors l@AMIJ Vectors spread disease- by carryi ng the pathogen from host to host. Examples o f vectors in cl ude fl ies, mosqu itoes a nd rats (figu res 22. 1,22. 2 and 22.3). Table 22 .2 gives sosme examples .. Vector Examples of disease(s) spread mosquitoes yellow fever, malaria, dengue fever, flies gastroenteritis rat flea plague rat leptospirosis Table 22.2 Some vectors and the disease they spread. vector 'bites' infected host and picks up the pathogen vector with the pathogen l -- - ~~ ~ " / -- vector 'bites' new host, transferring the pathogen infected host Figure 22.1 new host. infected by a vector Mosquitoes are vectors for malaria and many other diseases in humans. ~ l:F:Q2 V'-1 Figure 22.2 Flies feed on the food we then eat and so spread disease. (i) What is a vector? (ii) Discuss why a fly can be considered to be a vector. 273 Life Processes and Disease Controlling mosquitoes If the vector can be controlled, Lheo th e spread o f tile d isease will also be comrolled, since Lhe chance o[ being in contact wiLh Lhe vector and so getting Lhe infeaio n w ill be red uced. Th us, it is important to study th e venor's life cycle ro find ou t how to prevent them laying eggs, or how to prevent their development into adulrs, or how to destroy the adults. A good example of this is the atLempt to control the mosq uitoes rhar act as vectors (o r malaria (figure 22.3). t spiracles for breathing / larva lives in water ~ egg laid on water pupa lives in water / Agure 22.3 The life cycle of a mosquito. Tbe erad ica tion o ( a d isease sprea d by m osquitoes wo u ld be poss ible if a concened effort were made by the genera l public in the following areas. • Drai n stagnan t w ater around t h e ho m e a nd workplaces - Th is wou ld drastica ll y reduce th e number o( places for female mosqu itoes to la y eggs as well as reduce the numbe r o( eggs and pupae s urviving to deveJop into adu lts . • Spread a thi n layer of oil ove r w ater which must be ke pt - This would preveoc larvae a nd pupae in th e water from breathing and so kill th em . • Kill t he adu lts with insecticide. • Use mosqui t o nets - TIJ.js would reduce the possibility of being bine n when mosquitoes are a round . • Keep the area a round the l1o use clear of bush where adu lt mosquitoes rest. In tile sa me way, knowing where flies lay their eggs, how they develop a nd whar Lhey feed o n, can help to reduce the number of flies and thus reduce the incidence of diseases spread by flies . Pathogens ~111fll 274 Pathogens are usua ll y m icroscopic organisms (li ke viruses, bacteria and protozoans) that Live in Lhe blood and tissues of their host. Some are larger, li ke fungi and worms, which are easie r to get rid of and control. Some pathogens spread by direct comact o r dose in teraction between Lhe infected host and a new hosr. These include the sex ually trans mitted diseases (STDs) like herpes, AIDS, gonorrhoea and syphilis. AJDS is of most impo rtance beca use it has reached epidemic statu s in the world and can lead co 22 · Disease and Humans dea th because it compromises the body's immune system leaving the pa tient defenceless against secondary opportunistic infections. Expensive drug regimes can prolo ng rhe life of someone li ving w ith HIV, but there is no means of elimating the virus from th e body and no cu re for AIDS. Herpes is also incurable but not fa tal. The other STDs can be trea ted and conrrolled if diagnosed ea rly. Social and economic implications of disease The loss of life and loss of wo rking hours to disease a re important socia l and eco nomic fa ctors. Trearmems for pathogenic diseases sud1 a s AlDS a nd degenerative disea ses su ch as cancer place increasin g demand s on health services. Lifestyl e diseases related to smoking, lack of exercise and over-eating are increasingly important economica lly in develo ped countries, again beca use of the cost of treatment and their effects o n social and econo mic life. Implications for humans of disease in plants and animals Human s a re also a ffected eco no mically by the hea lth o f the crops and animal stocks grown for food. Loss of li vestock (cows, pigs, chi cke ns, e tc. ) and agricultural crops (rice, wheat, porntoes, etc.) due to disease can have se rio u s economic impli cation s. A disease can grea tly reduce o r w ipe o ut the livestock o r food crop oJ any area in a short space o f time; [or exa mple, m ea ly bu g in festation in the Caribbean, and foot-and-mo uth disease in Europe. This results in loss of income for the farmers and reduction in food ava ilability. Food, in the form of livestock and ag ricultural prod uce, moves a ll over the world io ships a nd a irpla nes o n a daily basis. Disease control is therdore ve ry difficult. Quarantine procedures at porrs and ai rports help but do n ot prevent the sp read of diseases. Many pathogen s a re microorga ni sms so are not seen; man y can ex ist as spores for long periods of time. Chapter summary • A healthy person is physically, socially and mentally well. • A disease impairs good health. • There are four main classes of disease: pathogenic, deficiency, hereditary and physiological diseases. • A pathogenic disease is caused by parasitic (and often microscopic) organisms like viruses, bacteria, fungi , protozoans and worms. • A deficiency disease results when there is a deficiency of a nutrient in the diet. • A hereditary disease is passed on by genes from a person to their offspring . • A physiological disease is caused by a malfunction of an organ in the body. , II • A vector transports pathogens from one host to another. • Vectors are usually insects, such as mosquitoes and flies. • Understanding the life cycle of a vector can help to control or eradicate a disease spread by that vector. • The social , environmental and economic implications of disease include loss of life, loss of working hours, loss of money. Disease in crops and livestock can lead to famine. Research into cures for disease is expensive. _,.... 275 Life Processes and Disease ITQ1 (i) Pathogen ic disease - symptoms of disease a re seen because of the presen ce of another organ ism (a pathogen ) in th e body. (i i) Hereditar y disease - sym ptoms of di sease seen beca use of the presence of a 'disease-carrying' gene which was passed to an o rga nism from its pare nts. (iii) Physiologica l di sease - symptom s o f disease seen because an orga n o r part of the body is not working. (iv) Deficiency disease - sympto ms of disease seen w he n a nutrient o r nutrients are la cking in the dlet of the orga nism. ITQ2 (i) A vector ca rries a pa thogen from host to bost. It is able to pi ck l:IP the pathogen in or on its body w hen it feeds and then transfe rs the pathogen when it m oves to another host. (ii) Flies pick up microorganisms wben they feed. They feed o n any orga nic matter, especially dead a nd rotting o rganic ma trer. The ir bod ies are hairy a nd can easil y ca rry pa thoge ns. They a lso regurgitate or vomit previous food whe n they eat. If they land to Jeed o n any substance th at is go ing to be food or drink to another anima l, they can pass th e pathogen to a new host. Flies are thus con sidered to be vectors. Examination-style questions (i) Explain what is meant by the following types of disease and give one example of each: (a) hereditary; (c) deficiency; (b) physiological; (d) infectious. (ii) Describe the causes and symptoms of: (a) gonorrhoea (b) diabetes. (iii) Explain how diseases like malaria and sickle-cell anaemia are spread and describe the importance of these diseases worldwide. (iv) Describe the social and economic implications of AIDS. List some ways the spread of AIDS can be prevented and controlled. (v) Describe and compare the global pattern of distribution of yellow fever and coronary heart disease. 2 (i) Describe how phagocytes protect the body against infection. {ii) List four ways the skin and openings on the skin are adapted to control the entry of pathogens into the bo"dy. (iii) (a) Distinguish between active natural immunity and active artificial immunity. (b) Give one example of artificial passive immunity and one example of natural passive immunity. (iv) It is estimated that a human can synthesise 1Omillion different types of antibodies. Describe three ways antibodies defend the body against disease. (v) Copy and complete the table. Drug Two effects on the body Social or economic implications Alcohol Cocaine Caffeine 3 276 (i) Explain the meaning of the term 'drug'. Using named examples discuss the use and abuse of drugs. (ii) Describe the immediate and long-term consequences of alcohol consumption. (iii) Discuss the social consequences of excessive alcohol use with particular reference to drink driving, aggressive behaviour, family breakdown and petty crime. Section C: Continuity and Variation 0 0 0 0 0 understand the importance of maintaining species chromosome number describe the process of mitosis understand the role of mitosis in growth explain the role of mitosis in asexual reproduction explain why asexual reproduction gives rise to genetically identical offspring cell cell division ( meiosis '\ mitosis ( prophase metaphase anaphase telophase '\ cloning of animals tissue culture in plants asexual reproduction growth Dolly Chromosome number ,. chromosome number > Ch ro mosomes a re presen t in th e nudei of ce lls. They com a in geneti c info rmacion in the form o f genes. Each species bas a speci fi c nu mber of chro m osomes in its body cell - this is call ed th e chromosome number for th a t species (fi gure 23 .J a n d table 23. J ). ~ ll:Qjl ~ (i) What is meant by the 'chromosome _number' of an organism? What is the chromosome number for (a) humans and (b) an onion? Figure 23. 1 Each species has its own chromosome number. 23 ·Mitosis Species Chromosome number onion 16 tomato 24 locust 24 corn 40 mouse 40 human 46 potato 48 Th e ch ro m osom e n umbe r for hu mans is 4 6. This mea ns rha t in every bod y cell o [ every hu man rh e re a re 46 ch rom o somes. A chromosom e is m ade up o f gen es. Wh ile th e ch rom osom e o u m be r is th e same fo r all h uma ns, the combina tion of genes is diffe re nt (figure 2 3.2 ). The 46 ch ro m osomes a re diffe re nL fo r e ver y hu m a n except id e n tical twin s. Table 23. 1 Chromosome numbers for seven different species ~ IT:Q2 \./'-I (i) List three differences between the people in figure 23.2. (ii) List three similarities. (iii) Why can these differences be seen? There are 46 chromosomes in each of his She also has 46 chromosomes in each of her body cells, but the combination of genes 1s cells but with her own combination of genes on special to this individual. This produces outward the 46 chromosomes. Each individual is unique characteristics that are special to this individual. and special. Figure 23.2 Members of the same species have the same chromosome number, but the combination of genes is different for each. The eel I cycle RRl!ii1fft:IJ [jjlU.~·U•'IJ IGl@•hfiM:tJ The cell cycle is the sequ e n ce o f e ve nts rha r occurs be tween the s1a n of o ne cell d ivisio n (mitosis) a nd th e Starr o r th e n ext (fi gure 23. 3) . Th e lo ngesr e ve nt in rh e cell cycle is ca ll ed interphase du ring which the cell grovvs a nd carries o u t its fu n ctions. A L the e nd of inte rphase ce ll division begins. M itosis is di vided into fo u r stages: prophase, m e rap hase, a naph ase and relo phase. At th e end o f telo phase, l\<\' O nuclei ha ve been fo rmed but th e cytop las m is n ot fu lly d ivided be twee n two cell s. Th is happe ns n ext a nd th e process is called cyto ke n isis (figu re 23 .4) . interphase Figure 23.3 The cell cycle. Figure 23.4 Mitosis has four stages and is a part of the cell cycle. 279 Continuity and Variation - - 1----- nuclear envelope centrioles The processes of mitosis and cytokinesis are shown in figure 23.5 . The numbers in the text on page 281 relate to figure23.5. i;•~-f-- nucleolus chromosome Y. r:-1 chromatids ~ centromere prophas ,, 0 metaphase E anaphase 4 telophase 10 OI IO 10 cleavage Figure 23.5 Mitosis and cytokinesis. 280 01 identical cells 23 · Mitosis lnterphase before mitosis • The cell is prepared for ctivision. • The chromosomes become shorter and fatter (and are easily seen). • Each chromosome makes an exact copy of itself, forming two chromatids joined at a centromere. Prophase (1) • • • • • Chromosomes (made of two chromatids) are visible. The nucleolus shrinks and disappears. The centrioles move to opposite sides of the cell. The spindle fibres form. The nuclear envelope breaks down. The centrioles play an important part in cell ctivision: the spindle fibres originate from them. The spindle fibres attach to chromosomes and pull them to either side of the cell. Metaphase (2) • The chromosomes line up along the 'equator' of the cell. • NB Each chromosome is still made up of two chromatids joined at the centromere. Anaphase (3) • The ch romatids separate and move to opposite sid es of the cell. • The chromatids reach opposite sides of the cell. • Exact copies of chromosomes a re at both sides of the cell. Telophase (4) • The ch romosomes lengthen as they umavel. • Th e nuclear envelope forms around each group of chromosomes to make two nuclei. • New nucleoLi form in each nucleus. • Two identica l nuclei a re formed. Cytokinesis (5) ~ • The cell membrane develops down the middle of the cell to djvide it into two (cleavage). • Two identical cells are produced. IT:.Q3 V"-J (i) What is mitosis? (ii) Why does mitosis occur? ~ IT:.Q~ V"-J Why is it important to maintain the species chromosome number? Importance of maintaining species chromosome number As you know, each species has its chromosome number and its own set of characteristics that make it unique a nd set it apart from other species. Rapid and repeated cell division must occur after fertilisation so that an organism can grow and develop from one cell (the zygote). It is important that after cell ctivision, the chromosome number remains the same and all the cells in a multicellular organism retain the correct number of chromosomes and the chara cteristics of the species. 281 Continuity and Variation The process of mitosis CHAPTER20 ~ The only variation that can happen in cells produced by mitosis is mutation, when a gene is copied incorrectly. Even minor faults in copying can result in major changes. An example occurs in sickle cell anaemia where a major change in the structure of haemoglobin arises from just a single fault in copying of the gene at some time in the past (chapter 26). Every cell of an organism has, locked within the nucleus, the 'blueprint' or complete set of instructions needed for that organism to develop. Remember that after the male gamete fuses with the female gamete at fertilisation, a single cell is formed which contains the complete set of information needed for development of the organism. Mitosis then occurs over and over, producing thousands of identical cells that differentiate to perform different functions. This leads to the formation of a multicellular organism in which every cell has maintained the chromosome number of the species with its unique combination of genes. CHAPTER 26 ~ IT:QS L/V Put these in order as they would occur during mitosis. A B Mitosis is cell division that occurs in all body cells except in gamete formation. It results in the formation of two genetically identical cells, each containing the same number of chromosomes and the same combination of genes. A cell is described as being diploid or 2n when it has the full chromosome number. Mitosis is essential for cell repair and for growth from the zygote to the multicellular organism as described in chapter 20. It is important that all body cells have the full chromosome number and thus carry all the genetic information to allow that cell to develop its role within the body. Mitosis is also the method by which organisms reproduce asexually forming offspring identical to the parent. It ensures that: • the species chromosome number is maintained; • each daughter cell receives an identical combination of genes. c Figure 23.6 Replication of a DNA molecule results in two identical copies. Replication of chromosomes Replication is the process during interphase by which a chromosome is able to copy itself exactly. A chromosome carries genetic material in the form of deoxyribonucleic acid (DNA). Watson and Crick published the first description of DNA in 1953. The structure is a double helix, made of two chains. By the process of replication, a cell is able to produce two identical cells when it divides by mitosis (figure 23.6). DNA made up of two chains The chains unwind from one another (DNA 'unzips') Each chain makes an exact copy of itself Two exact copies of DNA at the end of the replication Mitosis and asexual reproduction Asexual reproduction requires only a single parent. In essence, the parent divides into two, or a pan of the parent separates and then develops into a new individual. It is important to note that the offspring are genetically identical to the parent. This means that the physical and behavioural characteristics are also identical to the parent except for variation due to the environment. 282 23 ·Mitosis Binary fission, vegetative propagation and cloning in animals are examples of asexual reproduction. Mitosis results in the formation of identica l cells. When organisms divide asexually, they divide by mitosis. Binary fission binary fission > ~ This occurs in simple, unicellular (one-cell ed ) organisms, like bacteria and protozoans such as Amoeba (figure 23.7). The organism divides into two part , each of which develops into a new organism. This is known as binary fission . In Amoeba/ protozoa the chromosomes replicate first, then the nucleus divides · into two, followed by the cytoplasm . Two identical organisms are formed. ll:Q6 \../'J An Amoeba seen today is identical to one that existed 100 years ago. How can this be so? Figure 23. 7 Binary fission in Amoeba. the cytoplasm begins the nucleus begins to divide into two activities stop as the Amoeba prepares for division two identical Amoeba move (J tod©- ~ ·:c~JM' nuclear division is complete cytokinesis continues ~ Vegetative propagation vegetative propagation > CHAPTER 15 X ljihUI§il 11mi.u11 Vegetative reproduction or vegetative propagation is a common form of asexual reproduction in plants. In some plants, a bud grows and develops into a new plant, and then becomes detached from th e parent plant. Bulbs, corms, rhizomes, tubers, tap roots (chapter 15), runners, stolons and tillers can all give rise to new plants by vegetative reproduction. In a runner, such as those on a strawberry plant, a number of stem s grow out from the parent plant. The runner touches the ground, adventitious roots develop and a new plant forms. The runner connecting it to the parent plant decays and the new plant becomes established (figure 23.8 (a)). A stolon is simply a runner formed underground. This method of reproduction can be very effective; nut grass, for example, is very difficult to eradicate once it is established. A B1yophyllum leaf ('leaf of life' ) will generate n ew plants around its edges. After a while these plamlets become detached from th e parent leaf (figure 23.8 (b)). (b) (a) side branch/ 'runner' adventitious roots new plants Figure 23.8 (a) New plants are established from a side branch or runner. (b) Many new plants can be propagated from a single Bryophyflum leaf. 283 Continuity and Variation Artificial propagation Horticulturists and agriculturists have extended asexual propagation to include cuttings, budding, layering and grafting. This is termed artificial propagation . These techniques are commonly used in gardening and the commercial growing of plants. artificial propagation > new plant (fl cut stem is placed in a suitable medium for growth lb) Cuttings A stem is cut near a node and pushed into the soil (figure 23.9 (a)). New roots grow ou t from the submerging part of the stem, Particularly if treated with a plant growth substa nce (e.g. rooting powder). Examp les includ e sugar cane, geranium, African violet. chrysanthemum. adventitious roots new plant •tockroot'~ ~ Grafting with a system A cutting, called the scion, which is co be propagated is inserted into a slit in the stem of another plant (the stock), and the joint is bound up to seat it. The stock a lready has a root system so the scion is able to grow into a new plant (figure 23.9 (b)). scion cutting of plant to be propagated Figure 23.9 Art1fic1al propagation of plants by (a) cutting, and (b) gnft11g Tissue culture tissue culture > Tissue culture is a form of vegetative propagation used to make large numbers of identical plants (figure 23.10). Like binary fi ssion, it also results from mitosis. Using tissue culture propagation or cloning, whole plants can be made from very sma ll pieces cut from the parent plant. This depends on the fact that the majority of plant cells have the potential to form a whole plant. A very small piece of tissue is taken from this plant. The tissue is cultured on a sterile nutrient medium. The piece of tissue is made up of a number of identical cells. nutrient medium / The cells divide by mitosis to form a callus - a ball of cells. Rgure 23. 1O Tissue culture in plants. 284 The callus is stimulated to develop into a plantlet. Plantlet transferred to soil. This is genetically identical (clone) to the original plant. Many clones can be made from one plant. 23 ·Mitosis Advantages of tissue culture ~ IT:Q7 V'-1 (i) Define the term 'tissue culture'? (ii) Describe how tissue culture is used to generate many identical plants. • Large numbers of identical plants can be produced relatively quickly from 'superior' individuals. This can make them much cheaper. • Tissue culture can be used to propagate plant species which do not develop naturally through sexual reproduction easily, such as orchids. The propagation of orchids for sale on a massive scale is now possible. Disadvantage of tissue culture • Variety within a plant species is being replaced with similarity because it is cheaper. This is risky because if that one kind becomes susceptible to a particular disease or pest, the whole crop may be lost. Cloning of animals identical twins > ~ IT:Q8 V'-1 (i) Explain what is meant by 'cloning'? (ii) Describe a natural occurrence of cloning? A clone is an exact copy of an organism. Identical twins are, in essence, clones, since after the first cell division of the zygote, two identica l cells are formed. These two identical cells somehow separate from each other and then grow and develop into separate beings that are identical to each other (figure 23. 11 ). The environment confers subtle differences as they grow and develop. one organism ~ --+ w zygote divides into two ~ ---+ two-cell stage w separation of the two cells occurs resulting in two identical cells each divides and develops separately • another organism ~ ·twin') they develop in their mother's womb and identical twins are born Figure 23. 11 The development of identical twins. CHAPTER 26 Scientists can now easily separate the first four cells of a zygote and use these to create clones of the organism (figure 23.12, overleaf). This is practised mainly in the livestock and dairy industries. It is financia ll y advantageous to make clones of a 'superio r' animal, such as one which produces large amounts of a high-quality milk or high -protein mea t. It is also used to 'copy' individuals which have been genetically engineered (chapter 26). An example here would be Hvestock with genes to produce human hormones in the animal's milk. Cloning may be used to produce an animal with some specia l characteristic (such as speed in a racehorse) as that could be financially beneficial. Clones need a surrogate mother in which to develop. This is a female who is not the genetic mother but in whose womb the fertilised ovum is implanted so that it can develop as a fetus until birth. 285 Continuity and Variation - - - - - - - - - - - - - - - - - - organism growth and development in mother's womb zygote 2-cell stage 4-cell stage _ __. organism • 2-cell stage 4-cell stage each of the four ' cells are separated ~ clones (exact copies) .. ~0 zygote of a 'superior' organism Clones would all have the same 'superior' characteristics. _ __,. organism _ __,. organism (!) - - - organism Each cell then continues to grow and develop into an organism. They are exact copies of each other. Each can be implanted in a female's womb (surrogate mother). Rgure 23. 12 Cloning of fertilised eggs. ~ ll'!Q9 \...l'-1 Describe one way that scientists can make copies or clones of a 'superior' animal? A second way to create a clone is to ta ke the nucleus of a body cell from the 'superior' individual and use it to replace the nucleus of an unfertilised ovum. The cell can be made to divide as it would have done if it was a fertilised ovum and implanted in the womb of a surrogate mother, but all the cells it makes now have the chromosomes from the 'superior' animal. The first example of this kind of cloning was the sheep called Dolly(figure 23.13). normal development how Dolly was cloned (9\ unfertilised ~ egg unfertilised egg / 1 ~ 1 ~~om 00 . (!) egg fertilised byE f sperm forms M a zygote II" • 1 starts to divide II' 1 @ @ 1 l / The nucleus is removed and replaces the nucleus of the ovum. Development continues in the surrogate mother. The dividing nucleus contains Dolly's chromosomes. A surrogate mother is one in which the embryo is implanted and she •oam~· • b•by th•t ;, oot "'" Surrogate mother gives birth to Dolly who is genetically identical (a clone) with the original sheep. ~ ll'!Q·1 0 \...l'-1 How was Dolly cloned? Rgure 23. 13 How Dolly the sheep was cloned. 286 a sheep 23 ·Mitosis Advantages of animal cloning CHAPTER24 ~ • Superior traits can be passed on to offspring without the risk of losing them through genetic exchange during meiosis (chapter 24). • The use of surrogate m others means that more 'superior' offspring can be created than could be carried by just the genetic mother. Disadvantages of animal cloning • The effects of using a body cell, as in crea ting Dolly, are still being studied: It is possible that using what is in effect an 'old ' nucle us may cause problems . in the cloned individual. • The technique used to crea te Dolly could be used to clone humans. Many countries now have legislation to prevent this because it is considered unethical. For example, it might be done for purely selfish reasons. Chapter summary • Each species has its own chromosome number, that is the number of chromosomes found in each nucleus in the cells of the individual. • The chromosome number of humans is 46. This means that there are 46 chromosomes in every nucleus in every body cell of a human. • Although each individual of a species has the same chromosome number, the combination of genes in the chromosomes varies and so members of a species differ. • Cells divide by mitosis to produce two genetically identical cells. • Mitosis is important for growth, repair and asexual reproduction . • Mitosis is divided into four stages: prophase, metaphase, anaphase and telophase. • During replication each chromosome makes an exact copy of itself. This occurs in interphase, just before prophase. · • These two copies of a chromosome are called chromatids - they lie side by side and are joined at the centromere. • During prophase, the chromosomes become shorter and fatter and are easily stained and seen. • During metaphase, the chromosomes line up along the middle of the cell. • During anaphase, the chromatids are pulled apart to opposite sides of the cell. • During telophase, two identical nuclei are formed. • In cytokinesis, a new cell membrane develops to divide the cell in two identical cells. • Binary fission in Amoeba is an example of cloning. • Cloning is the production of identical copies of an individual. • Animals and plants can be cloned using several techniques. • Tissue culture is one way of cloning plants. The chromosome number is the number of chromosomes found in a typical cell of an individual of the species. It is a fixed and specific number to each species. ITQ1 (i) (ii) (a) 46 (b) 16 ITQ2 (i) The eyebrows are shaped differently and of different thickness. The size and shape of their lips are different . The shapes of their faces are dillerent. (There are other differences that you may have seen.) 287 on 1nu1ty and Variation (ii) Both individuals have two eyes. In both individuals, the nose is in the middle of the face. The position of both their lips is the sa me. (There may be other similarities that yo u have mentioned, relating to characteristics that are general to being of the same species.) (iii) Differences can be seen because, altho ugh they both have 46 chromosomes in each cell, the composition of the chromosomes is different. Their genes code for different characteristics. • ITQ3 (i) Mitosis is cell division that res ults in the formation of two identiq1J daughter cells. (ii) Mitosis is important for growth and repair. ITQ4 A species has special characteristics that separate it from other species. The number of chromosomes is very important. A change in chromosome number may change the species-specific characteristics. ITQS 1 C, 2 B, 3 A. ITQ6 Amoeba divides by mitosis producing gen etically identical offspring. Over the years, when it divided, identical offspring were produced, so that one seen today wou ld be genetica lJy iden tica l to one which existed 100 years ago. ITQ7 (i) Tissue culture uses a piece of tissue from a 'parent' plant to make many plants that are identical to the parent plant. (ii) A piece of tissue is taken from a parent plant. It is placed in a medium conta ining nutrients and growth hormones . It is kept under sterile conditions to prevent microorganisms from entering the medium. In the nutrient medium, the piece of tissue divides rapidly by mitosis, forming a structure called a callus, which is a ball of cells. The callus may be divided and placed in many jars containing the nutrient medium. Each piece develops into a plantlet which is cared for carefully. The many plantlets are all identical to the parent plant. ITQ8 (i) Cloning means making exact copie.s. An exact copy of an individual is m ade when it is cloned. (ii) Cloning may occur naturally in the formation of identical twins. After the zygote is formed it divides into two cells. Usually the two cells stay stuck together and continue to divide to make one individual. In identical twins, these first two cells separate and develop into individual organisms. They are genetically identical. ITQ9 Scientists allow a zygote of a 'superior' animal to divide naturally twice, producing four identical nuclei. These are then separated and implanted in the uterus of other animals (surrogate mothers) and allowed to develop . Four clones of the superior animal are thus made. ITQ10 Dolly was cloned by extracting the nucleus from one of the cells of a ewe. This nucleus contained all the information needed for the forma tion of Dolly. The nucleus of an ovum was also removed and replaced with Dolly's nucleus. The ovum containing Dolly's nucleus was made to implant in a surrogate mother and it developed into an individual which was Dolly. Examination-style questions (i) List the stages of mitosis. (ii) Explain fully the importance of interphase just before mitosis begins. (iii) Explain the meaning of the term 'diploid'. (iv) (a) Label the parts A to Gin the diagram on the next page. (b) Identify each stage. (c) Describe what happens in each stage of mitosis. 288 23 ·Mitosis 2 (i) Explain the following terms: (a) asexual reproduction ; (b) binary fission. (ii) List two advantages of asexual reproduction. (iii) One major disadvantage of asexual reproduction is that the offspring vary only rarely. Many species use only asexual reproduction but their offspring are not all clones. Suggest how variation comes about in these asexually reproducing species. (iv) What is a clone? (v) Suggest an argument: (a) for animal cloning; (b) against human cloning. (vi) Give a brief description of tissue culture. Discuss some advantages and disadvantages of the use of tissue culture in agriculture. 289 / understand the importance of halving of the chromosome number in the formation of gametes 0 0 describe the process of meiosis f7 understand the role of meiosis in the transmission of inheritable genetic characteristics distinguish between mitosis and meiosis cell I division ( mitosis ' meiosis r meiosis I and II ' variation evolution The importance of meiosis Body cells divide for growth and repair, and it is important that the new cells are identical to the existing o nes. This is the significance of mitosis. However, cells of th e reprod uctive o rgans must also divide, but in this case, to form the gametes or reprod uctive cells. Two gametes, one from the ma le and one from the female, fuse to form the zygote which develops into the new organ ism. These gametes must therefore concain half the chromosome number of d1romosomes. If they did not, the new organism would have twice the species chromosome number. Meiosis is the cell division which occurs only in the reproductive organs during gamete formation, and results in the formation of cells containing half the number of chromosomes as the parent cell. Half the number of chromosomes is the haploid o r n n umber. For example, a h uman body cell has 46 chromosomes. When body cells divide by mitosis for growth and repair, cells containing 46 chromosomes (d iplo id or 2n number) are always produced. However, cells of the reproductive organs must divide by meiosis to make gametes. The gametes must contain 23 chromosomes (haploid or n number) so that, after fu sio n with another gamete, the original number of 46 d1romosomes is restored (figure 24. l ). 24 · Meiosis diploid (2n) ~ l:T:.Q·1 l../V mitosis diploid (2n) _ _.,. diploid (2n) Where does meiosis occur (i) in females (ii) in males? ~ l:T:.Q2 l../V list the differences between a diploid cell and a haploid cell. Give an example of where each can be found in the human body. ~ reproductive cell diploid (2n) ( . : \ reproductive cell ~ of female ~ meiosy / \' haploid (n) @ @ haploid (n) ~ GAMETES meiosis fertilisation Figure 24.1 The importance of meiosis in maintaining the chromosome number. haplok:t (n) ~ ~ ~ 0 0 diploid (2n) /I \"'eiosis of male GAMETES fertilisation or fusion of gametes to form a diploid zygote diploid v~ I (2n) + The process of meiosis develops into an organism with 46 chromosomes like its parents Meiosis ensures that: • each da ughter cell has the haploid number of chrom osomes so that the diploid number can be restored after fertilisation; • each daughter cell has a different combination of genes which leads to variation among th e offspring. homologous pair > A human cell has 46 chromosomes: 23 came from the m other and 23 came from th e father. Each chrom osome from the set from the mother pairs up with a corresponding chromosome from the fa ther. These are called homologous pairs. The ch romosome in hom ologous pairs in humans are the same size an d shape apart from the sex chrom osome (figure 24.2). nuclear membrane a homologous pair centrioles Figure 24.2 The homologous pairs of chromosomes in a cell with four chromosomes two chromosomes of maternal origin homologous chromosomes (a homologous pair) similar chromosomes, one from the mother, one from the father 291 Continuity and Variation ~ crossing over > IT:Q3 V'-J Why is meiosis important in gamete cells? ~ IT:Q'I V'-J Explain the terms (i) homologous pairs (ii) chromatid. At the beginning of meiosis, each chromosome forms two chroma tids joined by a centromere, as in mitosis. The homologous chromosomes then come together, so there are now four chromatids dose together. Genetic information is exchanged randomly between the chromatids. This is known as crossing over. In metaphase I, the homologous chromosomes align randomly across the equator of the cell, and then the members of homologous pairs separate and move to opposite sides of the cell. The cell then splits to form two cells. The · division repeats with the chromosomes again lining up randomly along the equator of the cell, only the second time around the chromatids separate, resulting in four daughter cells, each with different genetic information (figure 24.3 and table 24.1). Prophase II • centrioles migrate to opposite sides of the cells lnterphase • replication of all four chromosomes occurs • cell with diploid number l Prophase I • homologous chromosomes come together (bivalent) • pieces of chromatlds are exchanged (crossing over) .~X~ . ~ :~ bivalent Met aphase II • chromosomes line up along the equator Met aphase I • bivalents line up along the equator CHROMATIDS SEPARATE! Anaphase I • bivalents separate • chromosomes move to opposite sides CHROMOSOMES SEPARATE! Telophase II • nuclear membranes form around each set of chromosomes Telophase I • two cells are formed each with the haploid number . • Figure 24.3 Meiosis of a cell with four chromosomes. 292 Anaphase II • chromatids move away from each other Four cells formed, each with the haploid number of chromosomes, and are different from each other. 24 · Meiosis Mitosis Meiosis occurs in body cells or somatic cells either occurs in reproductive cells only or occurs in formation of gametes only number of chromosomes remains the same in the daughter cells number of chromosomes is halved in the daughter cells daughter cells are identical to parent cells and each other daughter cells are genetically different to parent cell and each other two daughter cells are formed four daughter cells are formed homologous chromosomes do not come together homologous chromosomes come together no exchange of genetic material between chromosomes exchange of genetic material between chromosomes Table 24. 1 The differences between m1tos1s and me1os1s Variation of gametes A single human male can prod uce over 100 million spermatozoa or male gametes in one ejaculation. These gametes are all different. This variation of the gametes comes about when the cell divides by meiosis. Variation results from the following processes. • Crossing over between homologous pairs of chromosomes in the early stages of meiosis is random. There are no limits to how this happens. Every homologous pair of ch romosomes exchanges genetic material differently. Imagine the various ways a cell yvith 23 homologous pairs can exchange genetic material. • During metaphase I. the pairs of chromosomes align themselves long the equator of the cell randomly. Imagine the various ways 23 pairs of chromosomes can be aligned along the equator. The pattern of alignment determines which chromosomes are grouped together. • During metaph ase II, the chromosomes (now formed of two chromatids) align randomly along the equator of the cell. This also determines how the chromosomes are grouped in the gamete. Significance of meiosis Figure 24.4 These people all belong to the same family and so share some of the same genes. At the en d of meiosis, four genetica ll y different cells are produced from each original cell. This means that the gametes from each individual are all different. When these fuse with gametes from another individual, there will be even more variation in the genetic information of the offspring (figure 24.4). The gametes carry genetic information from the parents . When they fuse to form an offspring, genetic information is transmitted from the parents to the offspring. The offspring are all differenr from each o ther, since the gametes are all different. They are also different from their parents, though some characteristics will clearly come from the mother and some from the father. Some features may appear that are unlike either parent. 293 Continuity and Variation ~ IT:Q5 \.,..)'....J The daughter cells of meiosis are all different from each other. List three ways in which this variation is brought about. Conditions in the environment are not constant. They may change, sometimes abruptly. The survival of a species depends on the ability of the individuals in that species to adapt to changes in the environment. When there is variation among offspring, some will be able to withstand the changes of the environment and survive to reproduce. The surviva l of the species is thus ensured. Darwin's theory of evolution Darwin's theory of evolution > ~ IT:Q6 \.,..)'....J Variation obtained from meiosis ensures that the gametes are all different. Give one advantage and one disadvantage of this variation. Darwin's theory of evolution through natural selection is based on the fact that among the variety of offspring produced, some will be better able to withstand changes in living conditions than others. That is, some are better adapted or 'fitter' to survive in the struggle for existence. These offspring will then produce offspring that are similar (not identical ) to themselves, passing on the advantageou s characteristics. Through these gradual changes, over many generations, the evolution of new species is possible. • During meiosis, homologous chromosomes come together and crossing over occurs, whereby genetic information is exchanged. • Each gamete of the millions produced is unique and so each organism produced by their fusion is unique. • Inheritable genetic characteristics are transmitted from the parents to the offspring by the gametes. • The resulting offspring are all different to or vary from each other and to their parents. • This variation can be important if the environment changed, as those organism better adapted will survive. • This variation can lead to evolution. 294 24 ·Meiosis ITQ1 (i) In females, meiosis occurs in the ovaries. (ii) In males, meiosis occurs in the testes. ITQ2 Haploid cell Diploid cell half the number of chromosomes in the nucleus the full number of chromosomes in the nucleus found only as gametes in the reproductive organs - ovaries and testes found all over the body occur as individual cells as gametes, some are able to move (e.g. sperm) most are fixed and occur together, forming tissues ITQ3 Meiosis is important for the formation of haploid gametes so that, when two gametes fu se during fertilisation, a diploid zygote with the original number of chromosomes is obtained. ITQ4 (i) The 46 chromosomes of a human cell are made up of 23 homologous, or corresponding, pairs. One chromosome of each homologous pair came from the father and one from the mother. (ii) In the early stages of cell division each chromosome replicates to form two identical copies of itself that are joined by a centromere. Each copy is called a chromatid. ITQ5 • Crossing over - the exchange of genetic information between chromosomes. • Random alignment of the homologous pairs of chromosomes along the equator before separation of the chromosomes. • Random alignment of the chromosomes along the equator before separation of the chromatids. ITQ6 One advantage is that all the offspring have different characteristics, so some may be able to survive a change in an environmental condition. The propagation of the species is more likely to be ensured. One disadvantage is that all the organisms may be different from the parents and not as adapted to the environment as the parents. All the offspring may die easily. Examination-style questions 2 (i) Explain these terms and state and importance of each: (a) mitosis; (b) meiosis. (ii) List four differences between mitosis and meiosis. (iii) Explain the following terms, giving an example of each: (a) diploid number; (b) chromosome number. (iv) Explain the importance of crossing over which occurs during meiosis. Explain the importance of meiosis in making evolution possible. 295 0 understand the terms gene, allele, dominant, recessive, genotype and phenotype 0 0 0 explain the meaning of the terms codominance, homozygous and heterozygous 0 predict the results of crosses involving one pair of alleles use a genetic diagram to explain the inheritance of a single pair of characters explain the inheritance of traits using sickle cell anaemia and albinism /) understand the inheritance of sex in humans 0 understand crosses involving sex-linked characters variation continuous discontinuous l ) genes on chromosomes/DNA I phenotype - genotype - alleles ~ dominant recessive back cross incomplete dominance co-dominance inheritance of characters blood groups pedigree charts sickle cell anaemia sex determination - sex-linked characters The Earth is h om e to billions of organ ism s, eve ry on e of w hich is un iq ue. Millio ns of species can be found on the land, and in the wa te r and air of the Earth 's surface. Different species m ay differ greatly from each other and may be easy to distinguish . For example, birds differ grea tly from fish . However, the membe rs of rhe sa me species ma y differ in only sm all ways . Th ese dilferen ces a re the result of the genotype a nd the enviro nment. The gen otype of organism is its generic m ake-up. Th e envi ron m ent is the 25 · Heredity and Genetics su rrounding of the organism. Identical twins have the same genetic make-up but their environments are different (such as the food they eat, th eir activities, relationships and experiences) and so subtle differences develop between them (figure 25. 1). Genes Figure 25. 7 The differences between identical twins are due to the environment. as they have the same genes homologous Generic information is passed o n chromosomes from parents to offspring in the / chromosomes. Chromosomes occur in pa irs in body cells. In a human body cell, there are 23 pairs of chromosomes: 23 individual chromosomes are paternal (from the father) and 23 are maternal (from the mother). Pairs are caUed homologous chromosomes (figure 25.2 ). Each chromosome is made up of genes, or units of inherita nce. These control specifi c characteristics in the homologous organism. Each chromosome of a chromosomes homologo us pair carries the same set of genes, therefore each body cell has two Figure 25.2 A diploid cell h:t.. chromosomes has two pairs of homologous copies o f each gene. However a gene that are the same as each other, or two chromosomes. alleles for a gene that are different. If the alleles of a gene are the same, we say the organism is homozygous for that gene o r character. If the alleles are different, the o rgan isms is sa id to be heterozygous for that gene o r character (figure 25.3 ). uu homozygous > heterozygous > gene for eye colour gene for hair colour gene for hair texture Chromosomes exist in homologous pairs the genes are the same but the form the gene can take may be different. These are called alleles. gene for shape of nose brown gene for size of lip gene for length of finger gene for length of arm gene for eye colour gene for hair colour gene for hair texture A chromosome is made up of genes. This is a very simplified diagram of a chromosome. In the gene for hair colour, there are many alleles for hair colour, producing many different hair colours. In this case the two alleles are for red and brown. The alleles present determine what the individual will look like: the outward charactenstics. Alleles exist for every feature of every organism and each organism has its own combination of alleles which make it unique. Figure 25.3 Homologous chromosomes. 297 Continuity and Variation Dominance dominant allele > recessive allele > If the alleles are different, one may mask the expression of the other. The one that is expressed (visible in the organism) is called the dominant allele, and the one that is masked is the recessive a llele . We use capital and lowercase letters to represent the different alleles. For example, in the gene for hair colour, B represent the allele for black hair, and b represents the allele for red hair. Black hair, B is dominant to red hair, b; and red hair, b, is recessive to black hair, B. The dominant allele is expressed in the homozygous (BB ) or heterozygous (Bb) genotype, whereas the recessive allele is expressed only in the homozygous (bb) genotype (figure 25 .4). homologous chromosomes '"" foe Mic "'""" l allele for black hair symbol B (dominant) genotype is the genetic make-up, the alleles allele for red hair symbol b (recessive) B and b phenotype is the outward characteristic - - - black hair homozygous genotype has same alleles, e.g. BB bb heterozygous g enotype has different alleles, e.g. Bb Figure 25.4 The allele for black hair, B, will mask the expression of the allele for red hair, b. The heterozygous individual will have black hair phenotype ) £19.., The composition of genes, or genetic make-up, within the cells of an organism is its genotype. The phenotyp e is the observable characteristics of the organism. These observable characteristics are the result of the genotype and the environment interacting (table 25.1). genotype phenotype BB (homozygous) black hair Bb (heterozygous) black hair: B is dominant to b bb (homozygous) red hair Table 25.1 Phenotype 1s determined by the genotype. 11'.Q-1 \../'-' Define the following: (i) chromosome (ii) gene (iii) allele. ~ l'.fQ2 \../'-' Define the following: (i) genotype (ii) phenotype. 298 Genetic diagrams A genetic diagram shows the cross between two genotypes. It shows the phenotypes and genotypes of the parents and the possible genotypes and phenotypes of the offspring. For example, a cross between a homozygous dominant genotype (BB) and homozygous recessive genotype (bb) is shown in figure 22.5. 25 · Heredity and Genetics phenotype of parents black hair x red hair genotype BB x bb I I 0 gametes offspring genotype ~ Bb / offspring phenotype black hair segregation 8 All offspring heterozygous with black hair. Probability of a red-haired offspring is 0% Ratio 4 black hair : 0 red hair Figure 25.5 A genetic cross of a homozygous black-haired parent and a red-haired parent. Note in the diagrams that the offspring from a single cross are ca lled the F 1 (which means first filial) generation. We then use the term 'F2 generation' to refer to offspring of a cross between individuals of the F 1 generation. If both parents are heterozygous, the cross is as shown in figure 25.6. phenotype of parents black hair genotype Bb x black hair Bb gametes segregation offspring genotype offspring phenotype BB Bb Bb bb black black red black hair hair hair hair (homozygous) (heterozygous) (heterozygous) (homozygous) Ratio of 1 red hair : 3 black hair ~ 25% probability of an offspring having red hair IT:Q3 lJ'-1 Albinism (absence of pigmentation) in humans is caused by a recessive gene which is transmitted in a normal fashion. A phenotypically normal (nonalbino) couple have four children: the first three are normal and the fourth is albino. (i) What can you say about the genotype of the parents? (ii) What is the possibility that their next child will be albino? (iii) One of the normal children eventually marries a normal woman. What predictions can be made of their first child? (iv) The albino child eventually marries a normal woman. What predictions can be made of their first child? Where there are several possibilities, state them all. Figure 25.6 A genetic cross showing how two black-haired parents can have a red-haired child. A cross can also be represented in another way. A cross between a heterozygous parent and a homozygous recessive parent can be drawn as in figure 25.7. x phenotype of parents black hair genotype Bb bb ~ ~ gametes 0 8 red hair 8 8 gametes Bb Bb ® B black hair black hair ---- ----··- -------·- ·-- ---- bb red hair ... bb red hair Ratio 1 black hair : 1 red hair 1, 2 offspring are heterozygous with black hair 1t2 offsprlng are homozygous with red hair Chances of an offspring having red hair is 50% Figure 25.7 A genetic cross using a table. 299 Continuity and Variation Test cross or back cross Homozygous dominant and heterozygous individuals have the same phenotype - you cannot teU which is which just by looking at them . A test cross (back cross) is used to determine the genotype of individuals which have the same phenotype. In a test cross, the individual is crossed with a homozygous recessive and the offspring examined, as shown in figure 25 .8. ~ l:F:Q'I \./'-I A breed of dogs has long hair dominant over short hair. A long-haired bitch was first mated with a short-haired dog and produced three long-haired and three short-haired puppies. Her second mating, with a long-haired dog, produced a litter with all the puppies long-haired. Use the symbol L to represent the allele for long hair and I to represent the allele for short hair. (i) What was the genotype of the long-haired bitch? (ii) How could it be determined which of the long-haired puppies of the second mating were homozygous? phenotype of Individual - - - - + black hair possible genotypes - - - - - BB and Bb Individual is crossed with bb and offspring examined. gametes 0 0 ® Bb Bb ·0 -- gametes ® Bb '0 Bb - 0 I 0 Bb Bb bb bb 1- If there are red-haired individuals in the offspring, then the genotype is Bb. If all the offspring are black-haired, then the genotype is BB. Rgure 25.B A test cross. Incomplete dominance incomplete dominance > QSb l:F:QS \./'-I What offspring will you expect, and in what proportions, if two pink-flowered plants are crossed? Flower colour in some plants, such as Impatiens, shows incomplete dominance of the alleles. This means that there is a blending or combination of expression of both alleles in the h eterozygous condition. If allele CR produces red flowers {genotype CRR) and the allele cw produces white flowers (genotype cww), then the genotype CRW produces pink flowers (figure 25.9). A blending of red and white will produce pink. 99:, l:F:Q6 \./'-I The figure shows the result from a cross between a red-flowered plant and a white-flowered plant, and what happens when the offspring produced are crossed with red-flowered plants. • A x B x • • ' D 300 white red c RR x cWW I offspring genotype 0 a11 c Rw offspring phenotype F Using the alleles CR and CW, give the genotypes of the plants labelled A-F. (ii) If plant D had been white, what would the result of the cross between C and D have been? (i) genotype gametes l E phenotype of parents Figure 25.9 Incomplete dominance as seen in Impatiens. all pink 25 · Heredity and Genetics Co-dominance co-dominance > In co-dominance, there is expression of both alleles in the heterozygous genotype. In this case, the gen otype cRw produces fl owers that have patches of red and white colour. There is n o blending, each allele is expressed as shown in figure 25. 10. phenotype of parents red white cRR genotype c ww x I I 0 gametes 0 au c Rw offspring genotype offspring phenotype all red and white Figure 25.1O Co-dominance in Impatiens. Genotype Phenotype IAA blood group A !AO blood group A !BB blood group B IBO blood group B IAB blood group AB Worked example 100 blood group 0 1 Table 25.2 Genotypes and phenotypes of blood group in humans. ~ Another example of co -dominance is found in ABO blood groups in humans. Your blood group is controlled by three different alleles: JA, 18 and 1°. IA and 18 are equally or co-dominant to each other and both are dominant to 1°. Only two alleles can be present in any cell, one on each homologous chromosom e that carries the gen e for blood group. This gives four possible phenotypes for blood group (table 25.2). What are the possible blood groups of children whose parents are blood group A (h eterozygou s) and B (h omozygous)? The h eterozygo us gen otype fo r blood group A is JA0 . The h om ozygou s gen otype for blood group B is 18 8 • l:tQ7 genotype of parents What offspring will you expect, and in what proportion, if two Ft generation plants from figure 25.10 were crossed? gametes V"-1 ~ l:tQS V"-1 A baby has blood type B, his mother had blood type A. His paternal grandfather has blood type A and his paternal grandmother has blood type B. Determine {i) the genotype of the baby, and {ii) the possible genotypes of the baby's father. offspring genotypes ! AO ~~ 1AB 1BB x 1AB 100 JBO Possible blood groups of children are AB and B. 301 Continuity and Variation Worked example 2 What if both parents had heterozygous genotypes? The heterozygous genotype for blood group A is JA 0 . The heterozygous genotype for blood group B is 18°. X genotype of parents JAO gametes gametes ® @ ® JAB 1BO @ 1AO ·-- 100 Possible blood groups of children are A, B, AB and 0. Examples of genetic effects Sex determination Practical activity SBA 25.1: How the sex of an offspring is determined, page 365 Of the 23 pairs of chromosomes in any human cell, one pair determines the sex of the organism. There are two sex chromosomes, X and Y. The genotype XX is female and the genotype XY is male in humans (figure 25.11). ® ® human cell I All the cells of a female have two X-shaped chromosomes nucleus has 23 pairs of homologous chromosomes one pair determines the sex of the individual Figure 25. 11 All the cells of a male have one X-shaped chromosome and one Y-shaped chromosome. The Y chromosome is an X chromosome with a missing piece. How sex is determined in humans. Figure 25.12 sh ows the inheritance of sex in humans. Each time a couple has a child, there is a 50% possibility it could be a boy and a 50% possibility it could be a girl. x male phenotype of parents female genotype gametes offspring genotype offspring phenotype female female male Ratio 1 male : 1 female Figure 25. 12 How sex is inherited in humans. 302 male 25 · Heredity and Genetics Sex-linked characteristics The sex chromosomes also carry genes other than those which determine sex. The characteristic of those genes are said to be sex-linked, and they are carried on the X chromosome. Haemophilia or bleeder's disease sex-linked characteristics haemophilia > Sex-linked characteristics include haemophilia and colour-blindness. Table 25.3 shows sex-linkage in haemophilia. Genotype Phenotype XHXH female, normal clotting of blood female, normal clotting of blood; she is a carrier since she carries the recessive allele but it is not expressed. XhXh female, a haemophiliac XHY male, normal clotting of blood Table 25.3 The genotypes and phenotypes in haemophilia. The dominant allele, H , causes blood to clot normally. The recessive allele, h , causes haemophilia, a condition in which blood does not clot and any small cut will bleed for a long time. The inheritance of haemophilia is shown in figure 25.13. ~ IT:Q9 V'-J (i) What is mean by the term 'sex linkage'? (ii) A normal man marred a normal woman and all the female offspring were normal, but half of the male offspring were colourblind and the other half were normal. How do you account for this? Worked example 3 A carrier female marred a normal male. What is the possibility of their having a haemophiliac child? carrier female normal female normal male x normal male normal female (carrier) haemophiliac male Figure 25. 13 Haemophilia inheritance The mother transfers the haemophiliac gene to her son. There is a 25 % possibility of having a haemophiliac son . Other genetic disorders Sickle cell anaemia sickle cell anaemia > CHAPTER 26 In sickle cell anaemia (chapter 26), the red blood cell can take a sickle shape instead of the normal biconcave shape. Allele HbNproduces normal red blood cells and the allele Hb5 produces sickle-shaped red blood cells; the possible genotypes and phenotypes are shown in table 25.4 (overleaf). The inheritance of sickle cell anaemia is shown in figure 25 .14 (overleaf). 303 Continuity and Variation Genotype Phenotype HbNN all red blood cells are normal, the person is normal Hb55 all red blood cells take the sickle shape, the person has sickle cell anaemia HbNs 30-40% of the red blood cells are sickle shaped, the person has sickle cell trait Table 25.4 Genotypes and phenotypes in sickle cell anaemia. Worked example 4 If two people with the sickle cell trait were to marry, what are the possible genotypes and phenotypes of their offspring? parental phenotypes x trait trait parental genotypes gametes offspring genotype offspring photype normal trait trait sickle cell anaemia Figure 25.14 Sickle cell anaemia inheritance. The possibility of having a child who suffers sickle cell anaemia is 25%. The possibility of having a normal child is 25%. Ratio is 1 normal : 2 rraH : I anaemia . Pedigree charts A pedigree chart shows the occurrence of a particular characteristic in a family tree (figure 2 5. l 5). The chart can be used to show the possible genotypes of individuals in the chart, which can be important in genetic counselling. 304 25 · Heredity and Genetics 2 • female with black hair II male with black hair female with red hair 3 4 5 6 7 8 9 10 12 13 14 15 16 17 18 II male with red hair II 11 The allele for black hair B is dominant to the allele for red hair b. What are the genotypes of all the individuals? The males and females with red hair would have to be bb. I ( bb 3 B? 4 B? 6 bb 1 ( ~b r ~? bb 3 ( I bb l= I 1 I I To have a bb offspring, individual 2 would have to be Bb. All their black-haired children are Bb. B? 9 bb 7 Bb 2 Bb 6 I I µ-; :·r~ 8 bb bb Bb To have a bb offspring, individual 5 would have to be Bb. bb Figure 25. 15 A pedigree chart showing the inheritance of hair colour in members of a family. ~ l~Q·10 L-"-1 The family tree below shows how coat colour in mice is passed on from generation to generation. both parents are homozygous for coat colour p F, 5 11 e D Q brown coat colour white coat colour 305 Continuity and Variation (i) Explain the term 'homozygous'. (ii) What do the symbols P, F1 and F2 stand for? (iii) Which generation of mice is heterozygous for coat colour? (iv) What is the percentage of brown and white mice in the F2 generation? (v) Which allele for coat colour is recessive? (vi) What might be the percentage of white coat mice if breeding pairs were set up between: (a) 1 and 4 (b) 1 and 5? , Chapter summary • • • • • II • • • • • • • • • • ~ Each chromosome is made up of genes, or units of inheritance. An allele is the form of gene taken. The genetic make-up of an organism is its genotype. The observable characteristics of an organism make up its phenotype. If the alleles of a gene are the same on the homologous chromosomes, the genotype is described as being homozygous. If the alleles of the gene are different, the genotype is described as being heterozygous. In a heterozygous individual, the allele which is expressed in the phenotype is described as being dominant. Recessive alleles are only expressed in the phenotype if present in the homozygous form. Their effect is masked by the presence of a dominant allele. A test cross is used to determine the genotype of an individual. A genetic diagram shows the cross between two organisms for a characteristic. Incomplete dominance occurs when no one allele is completely dominant over the other. As a result, the expressions of the alleles blend. Equally dominant alleles are described as being codominant. Both alleles are expressed in the phenotype. The sex of an organism is determined by the sex chromosomes. In humans XX codes for female and XY codes for male. Characteristics carried on the X chromosome are said to be sex-linked. Examples are haemophilia and colour-blindness in humans. A pedigree chart shows the occurrence of particular characteristics in a family tree. ~ ~ ITQ1 (i) Ch romosome - In humans there are 46 chrom osomes in sid e the nucleus of each cell . Each chromosom e is a separa te stru cture which came from a parent and is made up of a stand of DNA or deoxyribonucleic acid. Each chromosome has its homologous partne r which came from the other parent . (ii) A gen e is a sm all pa rt of a chromosome . It has the code to make a specific protein which may lead to a specific ph ysical characteristic. (iii) An allele is the form a gene can tak e. It is the actual code of the gene. ITQ2 (i) The genotype of an organism is th e total com bina tion of all th e alleles that make up tha t organism . (ii) Th e phenotype describes the specific physical characteristics that can be seen and result from the genotype and the effect of the environment. ITQ3 Using N for the dominant allele of normal skin colouring, and n for the recessive allele of albino colouring. Parents a re n ormal; children are 3 normal : l albino. 306 25 · Heredity and Genetics (i) The albino child's genotype is nn. The parents' genotypes can only be Nn and Nn (heterozygous) since they are both normal and the albino child must get a n allele from each parent. N n N NN N Nn Nn nn (ii) The probability of the next child, or any child of these parents, being albino is 1 in 4 or 25%. Whenever this couple have a child, the probability of having an albino child will be 25 % . It would be quite possible for them to have 4 albino children and no normal children. (iii) The no rmal child can have either of two genotypes, Nn or NN. The normal woman that he marries could also have either of the same two genotypes. There are therefore three possible crosses: • NN x NN offspring all normal • NN x Nn offspring all normal • Nn x Nn offspring 3 norma l : 1 albino First child has a 75% to 100% of being normal. (iv) The albino child (nn) marries a normal woman (Nn or NN). Two possible crosses are: • nn x NN offspring are all normal • nn x Nn offspring 1 normal : 1 albino Their first child has a 50% to 100% chance of being normal. ITQ4 (i) To produce short-haired puppies, the long-haired bitch must have the genotype LI. The short-haired puppies, being 11. got one of the I alleles from their mother. (ii) The long-haired puppies from the second mating can have two possible genotypes, LI (heterozygous) or U (homozygous). To determine which is homozygous, the breeder must do a test cross, that is cross each puppy (when mature) with a short-haired dog and examine the offspring of each mating. If there is at least one sh ort-haired puppy in the litter, then the genotype is LI. If all the o ffspring are long-haired, then the genotype is LL. ITQS Crossing two pink- fl owered plants (CRw) would give the following result: offspring 1 CRR (red ) : 2 cRw (pink) : 1 cww (white) CR ITQ6 (i) cw A: CRR, B: cww, C: cRw, D: CRR, E: cRw, F: CRR (ii) Genotypes of offspring: CRW and CWW. Phenotypes of offspring: pink and white. ITQ7 The F 1 generation have the genotype cRw. If two of these are crossed, the offspring woul d be produced as follows: CR cw This would give a proportion of phenotypes of I red (CRR) : 2 red and white (CRw) : 1 white (cww). 307 Continuity and Variation ITQ8 ~ grandparents ~ \/ m":" \/ / ~ parents d" A B rath" babyB Mother has blood group A, possible genotypes are JAA or JA 0 . The baby has blood group B, possible genotypes are 18 8 or 180 . The baby must get one allele from the mother, but has no JA allele. So the mother's genotype must be JA0 and the baby's genotype must be 18°. (ii) The father must have given the baby the other allele, 18. The father's mother had blood group B and so had genotype 188 or 180, and the father's father had blood group A and so had genotype JAA or JA0 . The father got the 18 allele from his mother and could have inherited either the JA or the 1° allele from his father. The possible genotypes for the baby's father are JAB or 180 . ITQ9 (i) Characteristics that are carried on the X sex chromosome are described as being sex-linked. (i) normal man x normal female xNy parents gametes / y offspring X"Y normal female normal female female offspring all normal normal male colour-blind . male male offspring about half normal and the other half colour-blind The gene for colour-blindness is recessive and sex-linked. The normal female parent is heterozygous XNX" and passes the recessive allele to some of her sons. ITQ10 (i) Homozygous describes the genotype with two similar alleles, such as BB or bb. (ii) P stands for parents (genotypes and phenotypes). F 1 is the first (filial) generation, and F2 is the second (filial) generation. (iii) The F 1 generation. (iv) 75 % are brown and 25% are white. (v) The allele for white coat colour is recessive. (vi) (a) Probability of cross Bb x Bb producing white mice is 25%. (b) Probability of cross Bb x bb producing white mice is 50%. (ii) 308 25 · Heredity and Genetics Examination-style questions (i) 2 3 4 Define the following: (a) homozygous; (b) heterozygous; (c) dominant; (d) recessive; (e) allele. (ii) Distinguish between genotype and phenotype. (iii) Explain how mutation contributes to variation. (iv) Cystic fibrosis is an inherited condition caused by a single recessive allele. The normal gene is dominant and masks the recessive allele. What is the probability of two healthy people being parents to a child born with cystic fibrosis? Show all the working and use a genetic diagram. (v) (a) Explain what is meant when a person is said to be a 'carrier' for cystic fibrosis. (b) What is the probability of two healthy people (where one is a 'carrier') being parents to a child born with cystic fibrosis? (vi) Why are most lethal genes (genes which cause mortality) recessive? (i) Distinguish between continuous and discontinuous variation. (ii) List all the possible genotypes of a person belonging to blood group B. (iii) A woman with blood group A has a child who is also of blood group A. What are all the possible genotypes of the father? Explain fully, using genetic diagrams. (i) Explain, using genetic diagrams, how sex is determined in humans. (ii) Relating to the probability of having a boy or girl in part (i), suggest why: (a) at birth there are about 106 boy babies for every 100 girl babies; (b) at puberty the proportions of males and females are about equal; (c) In old age, females outnumber males. (iv) Define sex linkage and describe how haemophilia is inherited. (v) What is the probability of a haemophilic father and a mother carrying the allele for haemophilia having a haemophilic daughter? (i) In a test cross, the genotype of an organism showing the dominant characteristic (which can be homozygous or heterozygous) is determined. Using the symbols T for tall plant and t for short plant, show the results of a test cross on a tall plant which turned out to be homozygous for height. Draw a genetic diagram to illustrate your answer. (ii) Construct a pedigree chart of the following information. Female Male parents brown hair red hair children one - red hair two - both brown hair grandchildren (from (:laughter who married brown-haired man) one - red hair one - brown hair (iii) Explain the following using an example for each: (a) co-dominance; (b) incomplete dominance. 309 0 0 0 0 0 distinguish between genetic and environmental variation understand why genetic variation is important distinguish between continuous and discontinuous variation define a species describe how new spec ies are formed 0 understand the process of natural selection in evolution 0 0 0 0 distinguish between natural and artificial selection understand the causes and effects of mutation understand what is meant by genetic engineering and how it can be used discuss the advantages and disadvantages of genetic engineeering discontinuous variation } genotype environment l.._____......_____J continuous variation ( phenotype ( variation in phenotype I artificial selection ( selective breeding mutation ' natural selection ' genetic engineering ( sickle cell anaemia ' Down's syndrome selection pressure evolution species Genetic variation Ead1 organism is unique. This uniqueness is a result of genetic differences and influences of the environment, and is expressed in the phen otype. Each organism is born with its own genetic make-up inhe rited from its parents. The genetic make-up of every organism is different except for clones. Genetic variation is inherited and the differences may be small or large (fi gure 26. l). ~ IT:Q·1 l....l'V What is genetic variation? 26 · Variation and Evolution Figure 26 1 Variation is seen among and between species. Variation due to the environment environmental variation > The environment also plays a very important role in determining the phenotype of an organism. The variation seen because of the influence of tbe enviromnent is not inherited but occurs because of differences in the surroundings of the organism. For example, ten genetically identical plants grown from cuttings taken from a single parent should be identical in appearance since the genes for all the characteristics are identical. Suppose these plants are divided into two groups of five, and each group is grown in rwo very different environments: • good soil, watered regularly; • poor soil, not watered, After a while, the phenotypes of the two groups will vary greatly. Variation in appearance will be seen be tween plants th at have the same genetic make-up and therefore should look the same (figure 26.2). cutting grown in rich soil, watered regularly ~ genetically identical plants in different environments (soil and water) ~ IT:Q2 \.../'-' . cutting from the same plant grown In poor soil, watered little 1 (i) What is the phenotype of an organism? (ii) How is the phenotype determined? ~ IT:Q3 \.../'-' List three differences which may be seen in the phenotypes of identical twins even though they have identical genotypes. Figure 26.2 The environment plays a very important role in determining the phenotype of an organism Genetically identical plans are very different if grown in different environments. Genetically identical twins, as they grow and develop, acqu ire subtle differences. These differences occur becau se their e nvironments are different, even if they live in the same house . They eat different foods at different times and in different amounts. Their da ily activities and inte rests are different, and their intera ctions with people, even their parents, are different. The d ifferences in their 'en vironments' may be subtle, but enough to produce differences in their physical appearance. Identical twins also have different fingerprints. 311 Continuity and Variation Importance of genetic variation Genetic variation among a species ensures survival of that species if the environment changed drastically. This can be seen in the following example. A population of wolves living the wild vary with respect to body hair length. A few have very long hair (5-6 cm) and a few have very short body hair (1-2 cm) . Most have medium hair length (3-4 cm), which is well suited to the temperature of the environment (figure 26. 3). Practical activity SBA 26.1 : Continuous variation, page 366 _ _____.,__ most individuals in the population of wolves will have body hair length 3-4 cm Number of individuals in the population of wolves I I 2 3 4 5 6 7 8 Body hair length (cm) Figure 26.3 Graph showing how boay hair length varies in a population of wolves. ~ IT:Q't 1.../'--1 What do you think would happen to the population of wolves shown in figure 26.3 if the environmental temperature got warmer? Suppose the temperature changed drastically, say it got much colder, then the wolves with short hair would be more likely to die, but those with long hair would be more likely to live. Because of the variation which existed naturally, the wolves with very long body hair would be able to survive the cold temperatures better than those with short body hair. Those with long body hair, therefore, would be more likely to reproduce. Surviva l of the species is thus ensured because of natural variation. Figure 26.4 shows what would happen to wolf body hair length in such circumstances. -+-- -- Number of individuals in the population of wolves Figure 26.4 Graph showing a change in the occurrence of body hair length as the environment changed. continuous variation > discontinuous variation > 2 3 4 5 6 most individuals now have body hair length 5-6 cm to survive the colder environment 7 8 Body hair length (cm) Variation is thus the result of the genetic make-up and the influence of the environment. There are two types of variation: • continuous variation; • discontinuou s variation. In continu ous variation, the differences are slight and merge or grade into each other to produce a smooth bell-shaped curve (Figure 26.5): for example, height in humans, human foot length, human skin colour, leaf size and pod size in legumes, and body hair length in wolves. Number of 15-yr olds in class Figure 26.5 The height of a class of 15 year-olds shows contiuous variation. 312 - 145 150 most individuals in the population -\--- - are between 160 and 170 cm 155 160 165 170 175 Height of individuals In cm 180 185 26 · Variation and Evolution In discontinuous variation, the differences are separate and clear cut; they do not merge or grade into each other (figure 26.6). Examples are tongue-rolling in humans, blood groups in humans and horns in cattle. Number of individuals Figure 26.6 Graph showing discontinuous variation in human blood groups. t A B AB 0 Blood groups DNA testing and forensic science Agure 26. 7 Every individual has a unique DNA pattern. DNA testing or 'genetic fingerprinting' is a technique pioneered by Dr. Alec Jeffreys. He found short DNA sequences from the non -coding part of the DNA that were repeated several times and were uruque to each individual. Dr. Jeffreys developed a genetic probe to look for these sequences and was able to use electrophoresis and autoradiography to produce a DNA image (figure 26. 7). Each dark band in the autoradiograph shows as area w here the DNA probe attached to a similar sequence in the subject's genome. Each person's genetic fingerprint is unique - this means that each individual can be identified by their DNA, perhaps from a strand of hair or a scrape of skin. This application can be used in pa ternity and maternity tests and in as forensic evidence in rape and murder trials. Natural selection natural selection > Practical activity SBA 26.2: Natural selection. page 367 Charles Darwin, an English naturalist, first spoke about natural selection. He observed organisms that lived on the Ga lapagos Islands in the Pacific Ocean. From his observations, Darwin concluded that within a population, although many offspring are produced, m any individuals do not survive becuase they: • compete for limited food and resources; • try to avoid predators; • struggle to avoid disease; • try to tolerate changes in the environment. There is a constant struggle for existence, and those individuals that are best adapted to their environment have an advantage. That is, th ey are more likely to survive and produce offspring. Their offspring will inherit the advantageous characteristics and the population will remain well adapted to its habitat. Selection by the environment is known as natural selection. It favours those that have the best adaptations for the.environment in w hich they live (figure 26 .8). These organisms Nature 'selected ' birds with strong beaks. Birds with pointed beaks were able are said to have a selective advantage. They were able to crack the hard shell to feed on flying insects. Nature also Sometimes we describe these individuals of nuts and feed on the nuts. 'selected' these birds because of as being the fittest for the environment. They thus obtained food and lived to the shape of their beaks. reproduce; produce offspring with strong b eaks. Because of this, natural selection has become known as 'survival of the fittest'. Figure 26.B Some individuals are better adapted to the environment. selective advantage > 313 Continuity and Variation Natural selection and evolution Natural section provides the mechanism for one species co change into another. The change is very slow and is called evolution as one species evolves into another. Long necks of giraffes Figure 26.9 Long necks are an advantage when feeding from tall trees. antibiotic resistance > insecticide resistance > ~ IT:Q5 V'-J How do bacteria evolve to acquire resistance to antibiotics? The long n eck of the giraffe is thoug ht to have evolved when food was in short supply and only rhe tallest inc:Uviduals co uld reach en o ugh food to survive. The 'tallness' genes were passed on ro the n ext generation so they were, on average, tal ler than their parent genera tion . As selection for lon g necks continued, the gira ffes which produced most offspring were the ta llest inc:Uviduals. After many gen erations of selection, the long-necked species of giraffe have evolved (figure 26.9). Antibiotic resistance in bacteria Antibiotic resistance of bacteria is a serious problem . When antibiotics are used o n a p opulation of bacteria, any bacteria with genes to resist the drug will s urvive and most of the rest will be killed. The resistant bacteria then multiply, prod ucing populations of antibiotic-resistant bacte ria. Because of the w idespread use of antibiotics like penicillin, many kinds of bacteria a re n ow resistant to these drugs. Insects that are resistant to insecticides have evolved in much the same way as antibiotic-resista nt bacteria, due to the w idespread use of insecticides (fig ure 26.10). For exa mple, many populations of mosq uitoes are now resistant to DDT which was widely used last centu ry to attempt to co ntrol them and the spread o f ma laria. R original gene pool A selection +-pressure All the genes present in this population of mosquitoes make up the gene pool. The resistance gene R is also present. There are some individuals with resistance to insecticide. The application of insecticide to the population of mosquitoes puts a pressure on the gene pool (selection pressure). Those individuals with the resistance gene are seen to be fitter, i.e. able to survive. Most of the others die. (Some may survive because they avoided the insecticide.) The mosquitoes with the resistance gene live to reproduce, passing the resistance gene to their offspring. gene pool after the use of insecticide Most individuals are now resistant to the insecticide. The population is said to have developed resistance to the insecticide. A stronger dose or a new insecticide must now be used. Figure 26. 10 New populations evolve under pressure Dark form of the peppered moth camouflage > 314 The peppered moth (Biston betularia) is found in many parts of England (figure 26. 11). Ir was origina lly found as a pale fo rm, well con cea led by camouflage on the lichen-covered trees on which they rested. Predators fo und the moth difficult to spot. Then in the ea rl y 19th to mid -20th century, pollution in indu strial a reas, blackened the trunks of the trees witb soot. The 26 · Variation and Evolution pale m oths were n ow easily seen by predators, but the rare black form was better camouflaged. So the frequency (numbers) of the dark form increased as they were better suited to the environment. ln the unpolluted areas, the pale form still predominated. Today, as pollution from industry gets less, the pale form is again becoming more common than the dark form. (a) (b) dark form p redominates light form predominates selection pressure Ondustrialisation) Rgure 26. 11 (a) Pale and dark forms of Biston betularia moth. (b) Populations change with a change in the environment. Geographical isolation and speciation ~ IT:Q6 V'-J Describe briefly the following terms: (i) natural selection (ii) selective advantage (iii) survival of the fittest (iv) evolution. A popu lation that is geographically isolated from another may experience different environmental conditions and so evolve differently due Lo natural selection. Over time, the isolated population would become more and more different from the origina l popu lation to fill a new and different ecological niche. During his visit to the Galapagos Islands, Darwin observed several different species of finch (now called Darwin's finch es). This group of islands is in the Pacific Ocean, about 600 miles from the South American mainland. Darwin concluded that the islands must have been colonised by a few individuals from a species of finch found on the mainland. These individuals then evolved independently to fill the different ecological niches on each island. Today 14 different species o f finch are found on the Galapagos Islands, differing greatly in size and other features, including beak size and shape (figure 26. 12). warbler finch beak long and thin. feeds on insects vegetarian tree finch feeds on buds, leaves and fruit Galapagos Islands Rgure 26. 12 Four of the 14 species of finches that Darwin observed on the Galapagos Islands. probable common ancestor. likely to have been a seed-and insect-feeder woodpecker finch often holds a small twig and uses it asa tool cactus finch beak long and slightly curved Mainland 315 Continuity and Variation The islan ds of the Caribbean are a group of volcanic islands in the Atlantic Ocean. This arc of islands sweeps north and west from t he South American mainland and is ca lled the West Indies. It h as been suggested that the Anolis lizards of the West Indies have evolved in much the same way as Darwin's find1es. A few individuals may have drifted (for example on a log) along a water current from South America and reached the banks of Grenada (th e most likely arrival point for a rafting colonist). The original species may still exist in Guyana, Venezuela or north-western Brazil. The colonisa tion of other close islands followed, such as the islands of the southe rn Lesser Antilles, including St Vincent, St Lucia, Martiniqu e, Barbados, and La Blanquilla and Bonaire far to the west of Lhe main chain. Each population would have been subjected to dillerent environmental conditions. The vegetation, in sect population, air te mperature and weather patterns all diifer from island to island. By natural selection, each p opulation would have evolved inde pendently adapting to each new ecological niche (figure 26.13). Over time, the popu la tions would have become different from each other, evolving into nine different species (table 26 .1 and figure 26.14). Locality Species Martinique A. roquet Barbados A. extremis Grenada A. aeneus A. richardii St Vincent A. trinitatus A. griseus St Lucia A. luciae La Blanquilla A. blanqillenus Bonaire A. bonairensis Martinique St Lucia (, St Vincent Barbados La Blanquilla Bonaore Naturally occurring current which brought the Anolos lizard to Grenada . Table 26. 1 Species of Ano/is lizards in the Lesser Antilles. South American Ma i nland G U YAN A Rgure 26. 13 Possible colonisation sequence of the Ano/is lizards of the southern part of the Lesser Antilles. (a) (b) (C) Figure 26 14 Ano/is lizards of the Lesser Antilles. (a) Ano/is roquet, (b) Ano/is trmitatis, (c) Ano/is mtens tandae- a rare species found in Peru. It is also suggested that two independent landings on St. Vincent separated by sufficient time could have resu lted in a second colonisation. Two reproductively isolated species are found there, the giant Ano/is griseus and the smaller A. trinitatus. 316 26 · Variation and Evolution Ecological speciation and behavioural speciation predators present no predator ~on I '' ' ''' ' fish here do not interbreed with fish from region A some interbreeding may occur between fish from region A and fish from region B Figure 26. 15 Ecological spec1at1on backyard feeding in the UK means food Is readily available for birds in winter Ecological speciation is the evolution of barriers to gene flow resu lting from ecologically based rnvergent selection. For example, there are two populations of the Bahamas mosquitofish (Gambusia hubbsi), one has larger and more powerful caudal (tail) region than the other. The fish with the larger tail regions are in environments where there are predatory fish that will feed on the mosquitofish. The mosquito fish with the smaller tail regions live in areas without predators. Modern research suggests that the more powerful tail regions are more powerful swinuners than the mosquito fish with the sma ller tail regions. The bigger fish can therefore escape from their predators more easily. Speciation is resulting because each fish chooses the same type to mate with (figure 26.15). Behavioral speciation is seen when species engage in distinct courtship and mating rituals. For example, the birds called blackcaps from Germany. These birds generally fl y to Spain or north Africa to overwinter but some have adapted to 'backyard bird feeding' areas in the UK where there is a ready supply of food waiting for them. The change in migration behaviour has led to a shift in mate availability and populations are becoming increasingly reproductively isolated as they choose birds from the sa me population to mate with (figure 26.16). Artificial selection Rgure 26.16 Behavioural spec1ation. artificial selection > Artificial selection is the process by which plants and anima ls used by humans in agriculture, horticulture, transport, companionship and leisure have been obtained from wild organisms. In natural selection, nature selects the fittest individuals but, in artificial selection, humans select individuals with characteristics they see as useful. Only those individuals selected by humans are allowed to produce offspring. 317 Continuity and Variation selective breeding > Due to the constant removal of those with unwanted features and breeding of only chosen individuals, the genetic composition of the population changes. This is called selective breeding and continues today by a combination of inbreeding (between closely related individuals) and outbreeding (between geneticall y distinct individuals). The aim of artificial selection is to produce animals and plants with characteristics humans find desirable. These include: • high yield; • improved quality; • reduced production costs; • faster growth rates; • greater resistance to disease . Drugs like growth hormones and steroids are sometimes used LO enhance or quicken growth and development in animals that are used for food, such as poultry. These can have negative effects on humans and increase the risk of populations of antibiotic-resistant bacteria evolving. A comparison of natural and artificial selection is made in figure 26. 17. NATURAL SELECTION ARTIFICIAL SELECTION gene pool of a population selection pressure selection pressure The environment may change, e.g. get hotter, colder, drier, etc. Those that can survive in the 'new' environment live to reproduce, passing on those genes. Humans allow some individuals to live to reproduce, passing on those genes advantageous. e.g. greater yield, speed (horses), size, etc. New population New population • able to survive in the wild • is a natural part of the environment • may not be advantageous to humans • retains most genes • may not be able to survive in the wild • Is advantageous to humans • may have lost other advantageous genes Rgure 26. 17 Similarities and differences between natural and artificial selection. Examples of artificial selection in the Caribbean Very productive (meat and milk) breeds of cattle have been developed in temperate countries, such as the UK and the US. Beef cattle, like Hereford and Angus, and dairy cattle, like Friesian and Jersey, do not thrive well in tropical conditions because: • they suffer from heat stress; • tropical grasses are generally less nutritious than temperate species; • diseases like tick fever, foot rot and mastitis are serious problems that these breeds suffer from. 318 26 · Variation and Evolution Thus, cattle fa rmers in the Caribbean have developed new breeds. • In Jamaica, cross-breeding Indian and European breeds with local Creole cattle has led to beef and dairy herds such as the Jamaica Red Poll and the Jamaica Hope. These can cope with heat stress and poor pasture, and are disease- resistant, while producing much more milk and mea t than traditional Caribbean breeds. • In Trinidad, a new breed, the Buffalypso, has been selectively bred from the water buffalo brought from India in 1903 to pull cars and help in ploughing. The matu re animal produces high grade meat, which is marketed as beef. The ca lves are sold for breeding to va rio us countries, including Guyana, Cuba and other Latin American countries, and the US . Captive breeding Plants and anima ls are kept b y scientists in order to introduce particular genes into the population. The genome is improved by manipulated crossing of parent organisms or breeding. For example, corn origina.lly grown from wild seeds would gradually change as breeding introduced into the population genes for resistance to disease, large cobs and gra ins rich in nutrients. Similarly, animals can be kept in breeding programmes to maintain and improve the genome. Captive breeding programmes a re important for p reventing extinction and for improving on the diversity of the population of the organism concerned. Mutation lu!mmt.leU A mutation is a change in the amount or number of chromosomes, or a change in the structure of the ch romosome or DNA of an organism . It results in a change in the genotype of an organism. An example of a gene mutation is sickle cell anaemia, and an example of a chromosome mutation which d1anges the number of chromosomes is Down's syndrome. Mutation occurs randomly - you ca nnot predict exactly where or w hen a change will happen. The ca uses of mutation are: • exposu re to high-energy electromagnetic radiation like X-rays, ultraviolet light and gamma (g) rays; • exposure to certain chemicals like m ustard gas, caffeine, formaldeh yde, colchicine, tar in tobacco, a n increasing number of drugs, food preserva tives and pesticides. mutagenic > Any substance or process that increases the frequency of mu tation is described as mutagenic. If a mutation happens in a body cell, it w ill not be inherited or passed on to offspring and is lost when the organism dies. However, if it occurs in a gam ete cell, it can be inherited. This ca n add variation to the population. The offspring of sexual reproduction show variation naturally, because of crossing over and random alignm ent of the chromosomes on the equator of the cell, before anaphase. A muta tion which can be inhe rited, can add new variation. The change in the chromosome because of the mutation is n ew information. It may resu lt in an advantageous or disadvantageous chara cteristic in th e organism. Most major mutations a re disadvantageous. 319 Continuity and Variation Sickle cell anaemia Figure 26. 18 Sickle and normal red blood cells. sickle cell disease > sickle cell trait > Sickle cell anaemia is a good example of how a mutation of a part of a chromosome can have drastic effects. It also shows the role o f natural selection in control lin g the occurrence of mutated genes. ln sickle cell anaemia, the gene or part of the chromosome that determines the shape of the haemoglobin in red blood celJs has mutated or changed. This new form of a llele of this gene causes the red blood cell to take a sickle shape instead of the n orma l biconcave disc shape (figure 26. 18). The sickle-shaped red blood cell cannot transport oxygen efficiently which makes it a disadvantageous characteristic. However, the presence of sickle-shaped red blood cells in the body makes the person far less susceptible to infection by the malarial parasite than a person withou t sickle-sh aped red blood cells. Thi s is an advantageous characteristic since malaria is a leading cause of death in areas where it occurs. Since every person carries two alleles for th is gene, one on each homologous chromosome, there a re three possible genotypes: • homozygous for normal haemoglobin; • heterozygo us with one allele for normal a nd one allele for sickle cell haemoglobin; • homozygous for sickle cell haemoglobin. Those people who are homozygous for sickle cell have sickle cell disease. They experience severe pain in the joints, anaemia, kidney failure, poor growth and development, are prone to infections and a re likely to die young. In those who are heterozygous, only about half the red blood cells change to sickle shape. These people are unaffected by the condition except at low oxygen concentrations, such as when flying in an ai rplane or goi ng to high a ltitudes. This conditions is known as sick le cell trait. The sickle cell gene was selected for in those regions of the world where malaria is seen (parts of Africa, the Middle East, Tndia and sou thern Europe). People h ere who are heterozygous for the gene are at a selective advantage, as they are less likely to die from malaria tha n those who do not have the sickle cell allele, and less likely to die than those who have two sickle cell alleles. By natu ral selection, the gene continues to be passed on to offspring, since these people survive malaria. However, the sickle cell alle le is at a selective disadvantage in areas where rhere is no malaria. People who originally came from malarial areas. such as Africa, bur now live in areas where there is n o malaria , such as America, still carry the allele. Abou t l in 400 black people in America have sickle cell anaemia. and the disease causes about 100 000 deaths per year worldwide. Down's syndrome Down's syndrome is a change in the number of chromosomes in a cell. It occurs in all races and a correlation wi th the age of the mother is seen. Inciden ce of th e disease rises with the mother's age, especia lly after 40 yea rs. Th.is may be due to the fact that a woman is born with all her eggs and they age with he r. Men, on the other hand, constantly produce new sperms. The cells of a person with Down 's syndrome a ll have 47 ch romosomes instead of 46. People with the cond ition show typical facial features (fl at and rounded). Other symptoms include: • learning difficulties; • • • • 320 sh ort stature; heart defects; increased risk of infection; intestinal problems. 26 · Variation and Evolution People with Down's syndrome are generally very friendly and cheerful, and greatly enjoy music. Genetic engineering genetic engineering > ~ rr.01 \J'V Describe brieflythe following terms: (i) genetic engineering (ii) a transgenic organism. Biotechnology is the science which involves the harnessing and exploitation of biological processes, systems and organisms (particularly microorganisms) iJ;l manufacturing industries. The most powerful tool available to biotechnologists is genetic engineering. The benefits of genetic engineering include the development of high-performance food crops that grow quickly with less use of fertiliser. This could ease the pressure on food supplies from the growing human population. Another important area of development is diseaseresistance in crop plants, which would reduce the need for use of pesticides. An organism that has genes added to it from another species by genetic engineering is known as a transgenic organism. Some examples of genetic engineering in food production include: • resistance to pathogenic fungi in maize and potato; • resistance to insect pests in many crop plants; • increased growth rates in salmon and chicken; • production of meat with less fat in pork and beef animals; bact~mjO ~J pl~d I"'°"'" y DNA found in bacteria) plasmid cut using enzymes @~ @""~"""' v."'P./ /@ human DNA (insulin gene) ~ ~ DNA extracted from • production of higher quality dairy products (e.g. milk with more protein); • • human pancreatic cells human DNA inserted into bacterial plasmid and joined back up again bacterial DNA l recombinant DNA - DNA from two different species • plasmid (recombinant DNA) introduced into a bacterium As bacteria multiply, the genes are expressed to make their different parts. The insulin gene which was inserted will also be expressed. • The plasmids are mass produced as the bacteria multiply. The insulin gene is also being mass produced and insulin is produced when the gene is expressed. human insulin is separated and purified • • • increase in the proportion of protein in seeds such as soya; long shelf-life of fruits such as tomato and bananas; tastier and more nutritious foods like tomato; increase in size, and therefore in yield, of many crop plants and cattle and dairy animals; production and subtropical crops so they are able to grow in temperate climates (e.g. sugar cane and millet); production of cows and sheep from temperate areas so that they can grow well in tropica I regions; grain crops that can fix atmospheric nitrogen (e.g. wheat and maize). Human insulin is now manufactured in bacteria as a result of genetic engineering (figure 26.19). Insulin was previously obtained from cows or pigs and caused many side-effects in people with diabetes who needed it. It is now produced by inserting the human gene that codes for insulin into bacteria and allowing them to Agure 26.19 Using genetic engineering to make insulin from bacteria. 321 Continuity and Variation grow and multiply. As they do so, they produce insulin. The insulin is then separated, purified and packaged. Production of human insulin rhis way is now a large-scale enterprise and rhe product is used by thousands of people w ith diabetes. Genetic engineering is also being used to help treat some hereditary diseases in humans. Cystic fibrosis is a disease which affects around one in every 2500 babies. It is caused by a recessive allele which makes the mucus in the lungs thick and sticky. Bacteria get trapped in the mucus and cause infections whlch can lead to early death. Traditionally, the on ly treatment fo r cystic fibrosis is daily physiotherapy to clear the mucus in the lungs. Current research is studying trearment using a viral vector to transmit the normal a llele inro the lungs. ti the vector is taken up by the cells, they wou ld than be able to make normal mucus. Treatment wo uld have to be continuous because the ce lls lining the lungs a re shed frequenrly and replaced with new ones. Implications of genetic engineering Are there risks to human health? Some people argue thar there may be long-term risks from genetic engineering. There is much discussion on the effects of genetically modified organisms (GMOs) used in food production. An example is bovine somarotrophln (BST). This hormone is produced artificially by bacteria and injected into cows to stimulate growth and increase milk production. The hea lth o f humans drinking the milk or eating the meat appears to be unaffected by the hormone. But are there long-term effects on human health? As yet, we do not know. Should genetically mod ified food be labelled as such ? What would you p refer? Feeding the world Many crop plants are modified for disease resistance and increased yield. Plants can be engin eered to incorporate the characters of a number of different species (e.g. starchy potatoes with bera-caroteoe from green vegetables and vitamins from citrus fruirs). Millions of people are starving in the world - why not use such foods to ease the problem of starvation? Scientists have a lso been able to insert two genes from daffodil and one gene from a bacterium into rice so thar it can now contain vitamin A and its precursor beta-carotene. This gives the rice a yellow colour - hence it is w idely known as golden rice. It is hoped that it will help to combat malnutrition in less developed nations, especially those where a lack of beta-carotene in the diet leads to blindness. Economic and diversity problems Figure 26.20 Genetically modified soya bean could replace conventional crops. 322 There is also fear that small farmers would no longer find it economical to culti va te loca l varieties of crop plants when they have to compete w irh imported, economicall y superior varieties (figure 26.20). Cou ld this lead co a serious loss of genetic diversity among cultivated crop plants? This would make the dwindling genetic diversity problem worse. Are there dangers in relying on just a few varieties of crop plants? A new strain of disease could then wipe out a major crop. Gene banks o f many varieties of seeds and plants have been set up in many countries to conserve diversity, for example cocoa seeds and planes are stored in Trinidad . Some people fear that the genetically engineered trait cou ld get transferred into wild relatives of A engineered crop plant (it has been shown that pollen from crops such as o il-seed rape can spread for at least I 00 m from the GM plants). Might this produce pest species w hich cou ld spread uncontrollably 26 · Variation and Evolution and eliminate other plants, upsetting th e ecological balance? What are the implications of genetically engineered tra its transferring into other species? Treating disease Advances in genetic engineering will undo ubtedly eventually lead to the control of genetic diseases, su ch as cystic fibrosis, by replacing defective gen es with healthy ones. This could be wonderful for those livin g with theg'e conditions. There are many advantages of this kind of technology. Might this be taken further? Wou ld genes for low intelligence by replaced by those for · high er intelligence? Would this be good or bad? Are some human characters superior to others? Who would decide? ~ r:roa l/'V Describe two benefits and two hazards of genetic engineering. The future Should humans be allowed to genetically manipulate animals and plants to serve the needs of humans rath er than the environment as a whole? Is exploitation of living organisms, whether for commercial gain or to reduce suffering, the height of misuse of the environment, or is it another example of human s's triumph over adversity? • The theory of natural selection is based on genetic variation among a population. It is selection of the fittest organisms by nature. • In artificial selection, humans select individuals that are allowed to reproduce and produce offspring. We select characteristics advantageous to us like high yield and reduced production costs. • Mutation can occur that change the genotype of an organism . • A mutation may be a change in the structure of the chromosome, such as sickle cell anaemia. • A mutation may change the number of chromosomes in a cell, as in Down's syndrome. • Genetic engineering is the deliberate changing of the genotype of an organism by humans. • The production of human insulin by bacteria is an example of genetic engineering; • There is much discussion around the possible advantages and disadvantages of genetic engineering. 323 Continuity and Variation Each organism has its own genotype which is different from every other genotype (except for identical twins and individuals produced by asexual reproduction). Genetic variation is variation in the genotype that helps to determine differences in the phenotype. Genetic variation explains wh y every organism is unique. ITQ2 (i) The phen otype is the physical appearance of an organism. It describes all its physical characteristics. (ii) An organism develops its physical characteristics from a combination of its genotype and its e nvironment. The genotype confers on the organ ism the possibility of developing certain characteristics. The environ ment guides the development of these characteristics. ITQ3 Height - one may be taller; complexion - one may be darker; body size - one may be fa tter (there are many other examples). ITQ4 If the en vi ronmental temperature got warmer, all might survive, but the ones with the shorter hair length would be at an advantage. The wolves with long hair stand a chance of over-heating because of the insulation provided by the thick coat of hair. They are at a disadvantage. The wolves with the advantage for that new environment would be selected by nature (i.e. they would be more able to Live and reproduce). Eventually a population of shorthaired wolves would be seen . ITQ5 The use of an antibiotic on a population of bacteria results in an increase in occurrence or frequency of those with the gene that gives resistance to that antibiotic. Over time, and with constant use of many different antibiotics, a population of bacteria could evolve that is resistant to many different antibiotics. ITQ6 (i) Natural selection is a theory first put forward by Charles Darwin. He explained how the environment could select for characteristics in a population showing variation. He concluded that new species could come into being by slow and gradual changes, called evolution, as a result of the process of natural selection. (ii) A characteristic that suits an organism to its environment has selective advantage because organism with that characteristic stands a better drnnce of surviving and reproducing than those which do not have it. (iii) The process of natural selection is also known as 'survival of the fittest' because nature selects those individuals best 'fitted ' (adapted) to the environment. (iv) Evolution describes the change which takes place in a species over time and which leads to the formation of a new species. ITQ7 (i) Genetic engineering is the technology in which genes from o ne organism are transferred to another organism, often a different species. (ii) A transgenic organism is one which has had gene (s) transferred to it from another species. The transgenic organism s can live and reproduce normally although it has been changed. ITQ8 Any of the benefits and hazards mentioned in the text could be mentioned, or you might have researched some more. This new area of knowledge is constantly changing and new developments are frequently reported in the media. ·ITQ1 324 26 · Variation and Evolution Examination-style questions 1 (i) Explain these terms: (a) evolution; (b) mutation; (c) artificial selection; (d) selection pressure. (ii) Explain what is meant by 'selective advantage; using antibiotic resistance as an example. (iii) Describe, using an example, how the environment may affect the phenotype. (iv) Explain, using the sickle cell gene, how mutation may affect the phenotype. 2 (i) Describe four examples of artificial selection and the characteristics that are being selected for by humans. · (ii) Explain, using examples, how environmental factors like temperature, act as forces of natural selection. (iii) Using a table, list five differences between natural and artificial selection. (iv) If two offspring (not identical) are brought up in different environments, suggest why there may be difference in the development of the following characteristics: (a) body weight; (b) intelligence. Compare this with two identical offspring, brought up in the same environment. 3 (i) The aim of artificial selection is to produce animals and plants with characteristics desirable to humans. Suggest four characteristics of animals and plants that may be chosen. (ii) The peppered moth exists as two main types, a pale form and a dark form. (a) What is the importance of the colour of the moth? (b) What effect did industrialisation and the production of pollution have on both forms? (c) Why do you think heavy-metal tolerant plants are rare in unpolluted areas? 4 (i) Outline the general process of genetic engineering. (ii) Give two uses of genetic engineering in (a) agriculture, and (b) medicine. (iii) Discuss the possible risks of genetic engineering. How can these risks be reduced? (iv) Many people are against the practice of genetic engineering. Suggest some reasons for this. 325 Section D: School-Based Assessment Practical work in Biology The present CSEC Biology syllabu s (201 3) makes clear that assessed practical work - the School-Based Assessment (SBA) - is an integral part of a student's studies. This aspect of the course gives the chance to personalise the curriculum to meet students' particular needs and assess the development of h is or her skills. Specified topics In biology, assessment in at least 18 exercises (spread across 7 specified topics) is needed to satisfy the CXC requirements. The specified topics are: 1. Ecological study 2. Movement at molecular level (diffusion, osmosis) 3. Photosynthesis/respira tion 4. Food tests 5. Germination 6. Nutrition and diseases 7. Genetics This chapter indudes outlines of 31 activities (in addition to those mentioned in the syllabus itself), which are suitable, after proper development, for use in SBA practical investigations. There are both qualitative and quantitative investigations. The chapter comains at least one practical exercise associated with each of the specified content areas, as well as other topics encountered in this course. Sufficient detail is given to make possible the practical conduct of each experiment, and each one can be developed to illu strate material in the text. Each gives students the opportunity to develop their experimental and reasoning skills and also their ability to present results in the clear, appropriate way detailed in the syllabus. Assessment of skills If you are doing an experiment in class as part of your week's work, your teacher may have done som e or all of the planning for you, collected alJ the ma terials that you need, and give you instructions how to do the work, or even a written worksheet to fo llow. But you still have to show that you can follow the instructions, do the experiment and present your resu lts well. The skills which will be tested are: Experimental skills (XIS) • • • • Manipulation and measurement (M/M) Observation, recording and reporting (O/R/R) Planning and designing (P/D) Drawing (D) 27 • School-Based Assessment • Use of knowledge (UK) • Analysis and interpretation (A/I) A three-step approach in preparing for your SBA When planning and presenting your project, your SBA has three parts: l . Planning and designing the experiment 2. Doing the laboratory work 3. Presenting a lab report 1 Planning and designing the experiment In any experiment, you are trying to find an answer: it might be a relationship or a value. You will need to devise and follow a logical series of steps to find out that information. Therefore, whatever your hypothesis, you must have a plan. In some cases, the proposed activities already in this section contain an outline plan. However, you would still need to design your experiment bearing in mind the equipment and facilities ava ilable in your lab. In other activities, you are given a problem to solve, and here you would have to Plan and Design your investigation from the beginning. In this latter case that your work would most likely be assessed under Planning and Designing [PD] . Part of your planning is specifying, in detail, how to carry out your experiment. You need to plan the experiment in such specific detail that someon e else reading your design would be able to do exactly the san1e as you did and get the same results. Think about: • What apparatus will you need? (e.g. 'a 250 cm 3 beaker' - n ot just 'a beaker') • What ch emicals will you need? (e.g. '3 or 4 potassium manganate(VII) crystals abou t 2 mm long' ) • What will you do? (e.g. 'stir the mixture gently with a sturdy plastic drinking straw just before taking each temperature' - not just 'stir the mixture and take the temperature') • What could go wrong? • What are some possible hazards? What safety precautions should be taken? You will n eed to put your plan in writing. It is always a good thing to have your teacher, as well as colleagues, check your plan before attempting to carry ou t your investigation. Often, no matter how carefully you have planned an experiment, it doesn't go as you thought it would . However, it has still told you something - an experiment never 'fails'. If it didn't produce the effect you n eeded, find out why. If the experiment 'worked' but didn't give the result you expected, then you've found ou t som ething new. 2 Doing the laboratory work Here you carry out your plan. Always consult with your teacher if you are not sure exactly how to use the equipment, and how to use it safely. CSEC expects you to have practised using equipment before being formally assessed in its use. 3 Presenting a lab report Labs should be written up using the following format. The questions included in each activity are a guide to the content of the discussion . 329 School-Based Assessment Writing in the correct tense Remember that your research is already finished. Use the past tense when talking about the experiment: 'The objective of the experiment was ...' or 'The mixture was added to the beaker.' Your report, the theory you are testing and your equipment still exist; therefore, these get the present tense: 'The purpose of this report is .. .' Date and title The title should be brief and describe the main point of the experiment or investigation. Aim Keeping it simple and achievable, describe the purpose of the experiment. Discussion Background information to relate the experiment to something you have learnt or seen, or to a problem you have faced. Hypothesis Should be clear and be in the form of a question that you want to find the answer to, for example: 'Does vitamin C in orange juice oxidise over time when exposed to the air?' (From the data you obtain from your experiment you should be able to say if the hypothesis has been either supported or not in your conclusion.) Procedure Use the past tense (see box above). In a bulleted list or in separate paragraphs, state, in order, what you did. Include clear, quantifiable detail (e.g. quantities stated and apparatus specified). Your teacher will suggest that you use one of these two forms of words: 'I washed a 250 cmJ beaker.' or 'A 250 cmJ beaker was washed.' if you have written a good account then someone else, having read it, should be able to repeat the experiment exactly as you did it without any other help. Diagram Draw the apparatus as neatly as you can. Results • Table - title stated, neatly drawn with accurate data (times, volumes, masses, colours .. .) and proper units for quantities. • Graph (if necessary) - title stated, axes labelled with proper units, points accurately plotted. Use a line or a bar graph as required. Remember that you should choose the correct type ofgraph for the data you are presenting. • Include any calculations you used. Explain the results in detail, using values found in your results. Answer the questions given in paragraph style. Limitations Explain any condition or factor that is out ofyour control and affects the results obtained. Conclusion One short paragraph to summarise results. Make it related to the aim. Review your data and state your opinions and arguments of what the results show, for example, 'as graph 3 shows, there is a marked difference between group A and group B which allows the conclusion that .. . ' . 330 27 · School-Based Assessment State ifyour hypothesis has been supported or not. If the data you have obtained is not sufficient to support or reject the hypothesis, state why and say what further work could be done that would allow you to draw a stronger conclusion. If you are undertaking a complete project (which will be the case in the second year when you carry out your investigation) then more will be expected of you, and you can see from page 45 of the syllabus how marks for the project will be awarded. Your report will need to be more comprehensive than for a class experiment. It will be assessed for Planning and Design and for Analysis and Interpretation. Planning and Design has twice the marks of Analysis and · Interpretation. Safety first There are several sources of danger that you need to address as you develop your SBA activities. There are dangers to yourself, your colleagues, the equipment and even the school building itself. Here are a few safety symbols concerning situations you should bear in mind. Electrical hazard Hot surface Laser light No food and drink allowed Biohazard Wear safety goggles Radioactive No pointed objects allowed Corrosive substance Flammable materials Toxic materials • 331 School-Based Assessment School-Based Assessment contents 332 Photocopiable 1.1 To observe visible characteristics of plants and animals 333 2.1 A simple ecological study 334 2.2 To compare the water-holding capacity of three types of soil 338 2.3 To estimate the percentage of water in a soil sample 339 2.4 To estimate the percentage of air in a soil sample 340 8.1 To observe diffusion in a solution 34~ 8.2 To observe some effects of osmosis 342 9.1 To investigate the presence of starch in a green leaf 9.2 To see if light is needed for photosynthesis 343 344 9.3 To see if chlorophyll is needed for photosynthesis 345 9.4 To see if carbon dioxide is needed for photosynthesis 346 9.5 To see whether oxygen is produced during photosynthesis 347 10.1 To investigate the action of an enzyme 348 10.2 To investigate which food groups are present in a food sample 349 11 .1 To discover whether carbon dioxide is produced during respiration 350 11.2 To observe whether heat is produced during respiration 351 11.3 To discover whether oxygen is used up during respiration 352 14.1 To investigate the rate of transpiration using a photometer 353 17.1 To discover how gravity can affect plant growth 354 17.2 To investigate the growth of a radicle 355 17.3 To discover how light can affect plant growth 356 17.4 To compare the movement of four animals 357 18.1 To find whether the skin of the back of the hand, the palm or the back of the neck contains the most touch receptors 359 18.2 To investigate two reflex reactions 360 19.1 To investigate heat flow from a warm object 361 20.1 Observing the reproductive cells of a mammal 362 21 .1 Dispersal of fruits 363 21 .2 Seeds and food storage 364 25.1 To investigate how the sex of an offspring is determined 365 26.1 To investigate continuous variation 366 26.2 To investigate natural selection 367 © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment 1.1 To observe visible characteristics of animals and plants Chapter 1 The Variety of Living Organisms ' ) ( Syllabus skills: O/R/R Procedure: animals 1. Visit a backyard garden, a nearby cocoa estate, a nature centre, foothills of forest (anywhere a range of organisms can be seen). 2. Copy the table below into your lab book and observe five animals (include three insects). Describe what each animal was seen doing e.g. sucking nectar from a flower, sitting on the bark of a plant. Make a simple drawing of each animal. Animal 3. 4. 5. 6. What it was seen doing Simple drawing For the three insects, list visible characteristics that they share. Name the phylum and class they belong to. List two ways one insect is different to the other two. Draw a simple classification table to include the five animals. Procedure: plants 1. Visit a backyard garden, a nearby cocoa estate, a nature centre, foothills of forest (anywhere a range of organisms can be seen). 2. Copy the table below into your lab book and observe five plants. Make a simple drawing of a leaf from each plant. Plant Drawing of a leaf (show parallel or branched veins) 3. List all the dicotyledonous and monocotyledonous leaves. 4. Choose two leaves and list three differences you observe. 5. Choose three leaves and list similarities you observe. © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable 333 School-Based Assessment 2.1 A simple ecological study Chapter 2 Ecology and the Impact of Abiotic Factors on Living Organisms Syllabus skills: O/R/R; M/M The area to be studied should be small, such as a tree, a small pond, a small area in the foothills, a small area in a cocoa estate or a small garden. The aim is to study the biotic and abiotic factors of the area. The area being studied can be marked by funning string and the area calculated. The biotic factors A list of all the animals and plants seen in the area should be made. This can be done by walking quietly and slowly through the area {if it is on land) A representative sample of any study area and observing the organisms. Organisms may be found in and on the soil, can be taken . under leaf litter and stones, on the stems and leaves of small plants, flying in the area, on and under the bark of a tree, on the branches of a tree or just visiting the area for a short time. Food chains and a simple food web can then be constructed using the organisms (plants and animals) on the list. Interrelationships between the organisms may be noted as examples of the parasitism , commensalism and mutualism. Other interrelationships like competition (for light, space, etc.), camouflage, pollination and protection should also be noted. A reader of the study should have a good idea of the organisms seen there and what they are doing. An ecological study may also involve collecting data about the abundance and distribution of organisms. The population size of an organism in the area may be difficult to obtain since it means counting every individual in the area. However, the population density may be calculated from a smaller area, as the number of organisms present per square meter (m 3) . Then the population size of the whole area can be calcu lated if the area is known. To do this, representative samples of the area must be taken. These are usually chosen at random to avoid bias. Sampling methods include line transects, belt transects and the use of quadrats and sweeping nets. The most appropriate sampling method for a particular study depends on the area being studied. Sampling methods Quad rats These can be used if the area is fairly uniform and flat. A quad rat is a square frame (meal, plastic or wooden) of a know n area, usually 0.25 m2 or 1 m 2 . It is placed randomly at several places within the study area and the number of individuals counted. This method is suitable for plants and slow-moving animals like millipedes and some insets. The results can be tabulated as shown . Quad rat Number of individuals* 7 2 14 3 3 4 23 5 5 *number of individuals of one population e.g. millipedes or nutgrass. The mean number of individuals per quadrat is then calculated and used to find the population density or population size of the species counted in the whole study area. 334 Photocopiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment For example: 7 + 14 + 3 + 23 + 5 - 52 = 10 4 5 - 5 . There are on average 10.4 individuals in every quadrat. If the 1 m 2 quadrat was used then: population density = 10.4 individuals/m2 If the size of the area being studied is known, for example 25.6 m 2 , then the popu lation size can be calculated: If in 1 m 2 there are 10.4 individuals, then in 25.6 m 2 there are: 10.4 x 25.6 =266.24 individuals So the population size for the area studied is 266 individuals (m illipedes or nutgrass or whatever was being estimated). Line transects A line transect is a better sampling method if one type of habitat changes into another or the area is sloping, such as a rocky or swampy shore. A string is pulled in a straight line across the area being studied . All the animals (slow-moving) and plants actually touching the line are considered to be a representative sample of the animals and plants there. Measuring the height of the line at regular points can describe the slope of t he area. A B c D E A transect line Position along line Distance between soil and string Description of soil (water present) Plant and animals observed A B c D E Worksheet for the transect line Transect line across the edge of a pond, and a recording sheet. © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. Photocopiable 335 School-Based Assessment Sweep nets These are used for sampling insects, especially flying insects. At randomly set places within the area a net is swept through the plants (like grass) a fixed number of times and the individuals caught are counted. The mean represents a sample of the insects found t here. Sweep nets can be used with quadrats or line transects. The abiotic factors The distribution and abundance of organisms relate to abiotic factors. Commonly measured and described factors are temperature, pH, light intensity and wind. The soil is a very important abiotic factor since it directly influences the distribution of plants and therefore the animals that feed on them. Temperature Temperature can be measured using a thermometer. The temperature range over a period of time like a day may be more important than a reading at any particular moment. Standard maxim um/ minimum thermometers can be used. pH pH is a measure of the alkalinity or acidity. To determine the pH of the soil, about 1 cm 3 of soil can be missed with 10 cm3 of distilled water. After shaking, the mixture is allowed to settle and the pH determined with the use of universal indicator or pH paper. Using various sampling techniques in an ecological study. (a) Pond dipping. (b) Collet1ng insects in a net. 14 13 12 pH strip 11 10 This one is pH 6 9 8 7 A pH strip placed into the solution being tested, then compared to these standards 1n order to determine the pH of the solution. Light intensity Light can be measured at any time using light meters (like those used by photographers). However, it is the light received over a long period of time that affects plant growth. (a) card ,.......,1-- pin upon which vane 1s pivoted tunnel 336 Photocopiable card vane wooden arm Wind Wind speed and direction affect those animals and plants exposed to the elements of nature. Wind speed is ~-+-- scale - supporting pole upon which wooden arm pivots I \ ~ wind direction Two simple wind gauges. © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment measured by an instrument called an anemometer and a simple wind vane can measure the direction. Simple, but effective gauges can be improvised which may not give the exact speed values but give comparative readings . Water flow Water speed can be determined by measuring the time taken by a floating object to travel a measured distance of the stream or river. The speed per hour can then be determined. '- Soil Factors of the soil which affect plant growth include the pH, water content, air content, humus content, water-holding capacity and soil type (composition and distribution of inorganic soil particles). Investigations to measure the water content, air content and water-holding capacity follow. Humus content A sample of soil is heated at 100 °C (to remove all the water) and weighed to give weight X. The dry sample is then heated again until red hot; this mean that the humus is burnt off. It is then reweighed to give weight Y. The percentage of humus in the soil = xx =100% Y Soil type The distribution and composition of the rock particles can be determined using the sedimentation test. A sample of the soil is taken and mixed with excess water in a measuring cylinder. The mixture is shaken vigorously and left to settle. The largest and heaviest particles will settle first, the smallest last, the particles will settle in layers. The thickness of each layer can be recorded to indicate soil type. :S:::~~~~--- bits of twigs, leaves, etc. ·: · ·· .: : : : ·: : ..·: / .: :-..·:-.+-- -- very small particles (clay) . ·:.:· ~ :' ·~ ·:..::. ·: ·.: .~.=:::-. ~·:.:·: ~: :':::. :.: ·..:...:-:· .··.... ....·::.·:... . . . ·. ·.· ·.·. ·: ... .·... .:..·. .·.·..:... • · • .+-- - - small particles (silt) • • : ••• : •: •• : • •- 1 - -- - large particles (sand) ....... ·......· =+--- - - stones and gravel Results of a sedimentation test. © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 2014. Photocopiable 337 School-Based Assessment 2.2 To compare the water-holding capacity of three types of SOil Chapter 2 Ecology and the Impact of Abiotic Factors on Living Organisms X: Syllabus skills: O/R/R; M/M Procedure You need samples of a sandy soi l, a clay soil and a loamy soil. measuring cylinder 1. Set up three sets of apparatus as shown in the diagram. Use 100 g samples of soils A, B and C. 2. Draw up a table like the one shown below. 3. Pour 100 cm3 of tap water through each sample. 4. Wait until no more water is passing through the samples. (This may take some time!) Record the volume of water which has passed through each. Soil sample A Soil sample B Soil sample C Amount of water drained through (cm~ Amount of water retained in soil (cm~ Questions 1. Through w hich soil did the water flow (i) most quickly (ii) most slowly? 2. Which soil retained (i) least water (ii) most water? 3. From this data, which do you think is the sandy soi l? Explain your reasoning. 4. From this data, which do you think is the clay soil? Explain your reasoning. 338 Photocopiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment 2.3 To estimate the percentage of water in a soil sample Chapter 2 Ecology and the Impact of Abiotic Factors on Living Organisms } ( Syllabus skills: M/M Share the samples A, Band C from investigation 2.2 among class members. Procedure 1. Weigh a suitable sized sample of soil. 2. Heat the sample of soil in a dish until it seems dry. Do not heat the soil strongly enough to decompose organic matter - a temperature of about 90 °C is ideal. 3. Let the soil cool and reweigh it. 4. Reheat the soil for several minutes. 5. Repeat steps 3 and 4 until there is no further loss of weight. 6. Calculate the percentage of water in the soil from the formula: % = mass of wet soil - m ass _of dry soil x 100 mass of wet soil Questions 1. Which type of soil contained the highest percentage of water? (Your answer may be different from season to season!) 2. Explain the necessity for step 3 in the experiment. © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable 339 School-Based Assessment 2.4 To estimate the percentage of air in .a soil sample Chapter 2 Ecology and the Impact of Abiotic Factors on Living Organisms X Syllabus skills: O/R/R; M/M Procedure 1. Choose a small tin with a volume of about 200 cm 3 • Punch several holes in the base. 2. Press the tin down into the soil which you are going to test. (Take care! Some tins have very sharp edges.) A tin ,,---., tin of soil collected, the holes at the bottom are plugged with plasticine tin pressed into the soil 3. 4. 5. 6. Plug the holes in the base of the tin with plasticine. Pull out the tin without losing any of the soil inside it. Add 300 cm 3 of water to a large (1000 cm3 or larger) measuring cylinder. Pour the soil from the tin into the water in the cylinder, swirl or stir the mixture and allow it to settle. Note the new volume. Call this X cm3 . B 15001400 1300 1200 1100 1000 900 eoo 700 volume of soil 3 and 300 cm y of water and tin full of water { : 400 : J J 100 volume of the tin { volume of soil X and 300 cm3 of water 7. Fill the tin with water to the brim and pour the water into the cylinder. Again note the new volume. Call this Y cm3 . Calculation Volume of tin = Y - X cm 3• This is the volume of (soil + air). X = 300 +total volume of the tin - volume of air in the soil (the air is lost as bubbles) X = 300 + (Y - X) - volume of air. Therefore volume of air = 300 + Y - 2X. % of air = 300 +CY - 2 Xl x 100 (Y - X) Questions What is the importance of air in the soil? 340 Photocopiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 201 4. 27 • School-Based Assessment 8 . 1 To observe diffusion in a solution Chapter 8 Cells Syllabus skills: O/R/R ; M/M Data Potassium manganite(Vll) is soluble in water giving an intensely purple solution. Procedure 1. On a sheet of white paper draw five circles all with the same centre. Make their radii 1, 2, 3, 4 and 5 cm. 2. Place a large beaker over the circles and fill it to three-quarters with water. Put the beaker aside, out of direct sunlight, for five minutes so that the water can become quite still. 3. Choose a single crystal of potassium manganite(Vll) (potassium permanganate) and drop it through the water so that it lands near the centre of the rings you have drawn. crystals placed 4 . Time how long it takes for the pool of dark purple solution to spread out through each of the rings. Put your results in a table. Questions 1. Why was it important to keep the beaker of water out of the sunlight? 2. Why did the colour move through the water? 3. What is t he mean speed of diffusion of the purple coloration through the water? 4. In a vacuum the coloured particles would move very quickly. Why did they move so much more slowly in your solution? Extension It is not easy to get the potassium manganite(Vll) crystal to fall where you want it. Can you devise a better way of placing it in the water in the beaker? Remember that the water must remain still. © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable 341 School-Based Assessment 8.2 To observe some effects of osmosis Chapter 8 Cells X Syllabus skills: A/I; O/R/R; M/M Procedure 1. Cut two potato strips roughly 1 cm square and 3 cm long. 2. Measure the length of each as accurately as you can. 3. Rub the potato strips between your fingers to assess their texture. 4. Put each potato strip into a petri dish. Cover one with clean water and the other with a strong solution of sodium chloride (common salt). t t _........__ ___,,....___ _ _.....__, wat~r petn dish potato strip 5. 6. 7. 8. Leave the potato strips in their dishes for 15 minutes. Remove the potato strips, dry them, and measure the length of each as accurately as you can. Note the texture of the potato strips. Record your observations in a table like the one below. First texture Final texture First length Final length Change in length %± water salt solution Questions 1. In terms of the cells forming the potato strips, why have the lengths of the strips changed in the way they have? 2. Do the changes in texture of the strips fit in with your explanation? Explain. 3. The cells of the potato contained water to start with . Why did more water move one way than the other across each cell wall? Extension Design an experiment to investigate the effect of using different concentrations of sodium chloride to surround the potato strips. What result would you expect to find in your experiment? 342 Photocopiable © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 2014. 27 • School-Based Assessment 9.1 To investigate the presence of starch in a green leaf Chapter 9 Photosynthesis Syllabus skills: M/M Caution: ethanol is flammable. Do not heat the tube directly with a Bunsen flame Data Starch reacts with iodine to give a blue-black coloration. Procedure 1. Take a small fresh green leaf from a suitable dicotyledonous plant. 2. Dip the leaf into boiling water for about 10 seconds. 3. Put the leaf into a test-tube no more than one-third full of ethanol (alcohol). 4. Place the test-tube into the beaker of boiling water. 5 . When the leaf appears colourless, remove the leaf and rinse it in water. 6. Lay the leaf in a petri dish and pour a little iodine solution over it. Leave the leaf for several minutes. 7 . Pour the iodine solution back into the beaker provided. 8. Rinse t he leaf in water. Observe t he colour of t he leaf. Questions 1. What effect did the boiling water have on the leaf? 2. What happened when the leaf was boiled in alcohol? What did the alcohol remove from the leaf? 3. Why was the leaf then rinsed in water? 4. What was the colour of the leaf at the end of the experiment? 5. What do you conclude about the original green leaf? The leaf is dipped in bolling water for about 10 seconds l beaker The leaf is placed in a test tube of alcohol that is in boiling water. NB alcohol is very inflammable and must not be heated directly over a bunsen flame. test tube alcohol leaf boiling water l The leaf is dipped in water The leaf is placed in a petri dish and covered with iodine solution. Iodine turns blueblack in the presence of starch. @ © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable ~ 343 School-Based Assessment 9.2 To see if light is needed for photosynthesis Chapter 9 Photosynthesis Syllabus skills: A/I; O/R/R; M/M Procedure 1. Choose a small potted plant (such as Impatiens or a geranium). De-starch the whole plant by putting it in darkness for at least 24 hours. 2. Cover a part of one leaf on the plant with foi l or black polythene held in place with paper-clips. (Leave the leaf on the plant.) 3. Put the plant in the sunshine for at least 3 hours. 4. Remove the test leaf, remove the covering and at once test the leaf for starch. 5. Make a drawing to show your results. Questions 1. Why was the plant de-starched? 2. What was used as a control in the experiment? 3. Which part of the leaf contained starch before the foil cover was added? 4. Which part of the leaf contained starch at the end of the experiment? 5. What do you conclude from your results? Explain fully why you reach this conclusion . 344 Photocopiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment 9.3 To see if chlorophyll is needed for photosynthesis Chapter 9 Photosynthesis Syllabus skills: A/I; O/R/R; M/M Procedure 1. Choose a small potted plant with strongly variegated leaves. Some portions of the leaves should be as nearly white as possible. 2. De-starch the whole plant but putting it in darkness for at least 24 hours. variegated leaf chlorophyll - - + -absent chlorophyll present 3. 4. 5. 6. Choose a boldly marked leaf and make a careful drawing of it to show the green and white areas. Place the plant in the sunshine for at least three hours. Carry out a starch test on the leaf that you sketched. Make a drawing of the leaf showing the brown and the blue-black areas. Questions 1. Why is a variegated leaf used for this experiment? 2. Why was a drawing of the leaf made before the experiment began? 3. What do the results of the starch test show? 4. Is there anything in common between the blue-black areas of the starch test and the green areas of t he original leaf? 5 . What conclusions can you draw from your experiment? © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable 345 School-Based Assessment 9.4 To see if carbon dioxide is needed for photosynthesis Chapter 9 Photosynthesis X Syllabus skills: A/I ; O/R/R ; M/M 1 - -- - bell jar - -----< KOH - distilled water potassium r:-;::::-!?.9-----+-- hydroxide ..__....:a__ solution glass sheets smeared / with Vaseline Data Potassium hydroxide, sodium hydroxide and soda-lime all combine with carbon dioxide. Procedure 1. Set up the apparatus shown in the diagram. If potassium hydroxide is not available, sodium hydroxide or soda-lime can be used. Leave the apparatus for some hours. 2. Place a thoroughly de-starched plant under each bell jar. Do this quickly so that the bell jar is not removed from the glass sheet for any length of time. 3. Leave the plants for two days. 4. Test one leaf from each plant for starch. Questions 1. 2. 3. 4. 5. 6. 7. 346 What does t he potassi um hydroxide do in this experiment? What is another name for potassium hydroxide? Which bell jar contains the control plant? Why were the glass sheets smeared with Vaseline? Which plant contained starch at t he end of the experiment? How could you test the air in the bell jars for carbon dioxide? Why would it be better to test more than one leaf from each plant? Photocopiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment 9.5 To discover whether oxygen is produced during photosynthesis Chapter 9 Photosynthesis Syllabus skills: A/I; O/R/R; M/M Procedure 1. Obtain a fresh sample of a water plant such as Elodea or Ceratorphyllum. 2. Set up the apparatus shown in t he diagram, making sure that the test-tube is full of water to begin with. 3. Leave the apparatus in sunlight until the tube is nearly full of gas. This may take hours or several days depending on the conditions. 4. Light a wooden splint then blow out the flame. The tip should continue to glow. 5. Remove the test-tube from the apparatus and put the glowing splint half-way into the tube. 6. Record what happens. gas 0 0 0 beaker filled with water glowing splint ,,__--+- inverted funnel llll'iii~l,---1- water plant photosynthesising test tube Questions 1. What happened to the glowing splint? 2. What gas was present in the test-tube? 3. How do you know that the gas in the test-tube was not just ordinary air? 4. Where did the plant obtain the carbon dioxide needed for photosynthesis? 5. What can you deduce from this experiment? © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. Photocopiable 347 School-Based Assessment 10.1 To investigate which food groups are present in a food Sample Chapter 10 Feeding and Digestion Syllabus skills: M/M Procedure 1. A potato is peeled and a small piece (about 1 cm 3) is crushed and placed in a test-tube. 2. The test-tube is half-filled with water. 3. 2 cm 3 samples are removed from the test-tube and tested for the presence of reducing sugar, nonreducing sugar, starch, protein and fat. 4. Use a table like the one below to show the tests, the results of the tests and deductions. 5. The albumen (white) of an egg is collected in a test-tube. 6. Repeat steps 3 and 4. Food tested Details of test carried out Results or observations Deduction (presence or absence of food group) potato Questions 1. 2. 3. 4. 5. 6. 348 Which food groups are present in the potato? Which food groups are present in the egg albumen? Why was the potato crushed before being tested? Describe another method for testing for a reducing sugar. What is the importance of protein in egg albumen? Why is potato rich in starch? Photocopiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment 10.2 To investigate the action of an enzyme Chapter 10 Feeding and Digestion "1( Syllabus skills: A/I Data Catalase is an enzyme which catalyses the breakdown of hydrogen peroxide (the substrate) into water and oxygen gas (the products). Hydrogen peroxide is available as a dilute solution in water. Procedure 1. Cut four pieces of fresh liver, each roughly 1 cm2 square. 2. Draw up a table like the following and record your observations as you go along. Effect of whole tissue Effect of boiled tissue Effect of crushed tissue Effect of whole tissue with acid liver potato Set up four test-tubes each containing about 2 cm 3 of hydrogen peroxide solution. Put one piece of liver into the first tube. Boil one piece of liver in water for 2 minutes, cool the liver and add it to the second tube. Crush one piece of liver and add it to the t hird tube. Put a glowing splint into the mouth of this test-tube. Put 2 cm3 of hydrogen peroxide solution and 1 cm3 of concentrated hydrochloric acid into a test-tube. Add one piece of liver. 9. Repeat steps 3-8 using 1 cm3 pieces of potato. 3. 4. 5. 6. 7. 8. Questions 1. 2. 3. 4. 5. 6. Which gas was produced in the reaction? How do you know? Which tissue, liver or potato, showed more reaction? Suggest why. Why was the result using boiled tissue different from that using whole tissue? Why was the result using crushed tissue different from that using whole tissue? Why was the result of using whole tissue and acid different from that using whole tissue? What general statement about the conditions necessary for enzyme-catalysed reactions could you write as a result of these experiments? Extension The conditions used in some of these experiments were extreme (boiling; concentrated acid). 1. Devise experiments to investigate the activity of a state enzyme in conditions that vary less sharply. 2. Find out the optimum conditions for the action of a named enzyme. © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. Photocopiable 349 School-Based Assessment 11.1 To discover whether carbon dioxide is produced during respiration Chapter 11 Respiration X Syllabus skills: All; O/R/R filter pump air drawn out air in t 1 0 0 0 0 0 0 A potasium hydroxide solution (removes carbon dioxide from the air by absorbing it) 0 0 B limewateror hydrogencarbonate indicator (tests for the presence of carbon dioxide) c respiring mouse (produces carbon dioxide) limewater or hydrogencarbonate indicator (tests for the presence of carbon dioxide) Procedure 1. You need a healthy live mouse! (Do not try to use any wild rodent.) 2. Set up the apparatus as shown in the diagram. A, B and C can be flasks instead of jars. Put the mouse gently into the other jar. 3. At once turn on the pump to draw air through the apparatus at a rate of about one or two bubbles per second. 4. Wait until there is a definite change in the liquid in jar C. 5. Note the appearance of the liquid in jar C. 6. Release t he mouse gently back into its usual living space. Questions 1. What is the function of flask A? 2. What did you observe happening in flask B? (For a good answer you must say what the liquid was like at the start as well as what it was like at the end.) 3. What does this change tell you about the air going into the jar containing the mouse? 4. What can you deduce from the change you saw happening in jar C? 5. What can you deduce from this experiment? 6. Why might it have been better to have a second flask containing limewater between flask B and the jar containing the mouse? 350 Photocopiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 · School- Based Assessment 11 .2 To observe whether heat is produced during respiration Chapter 11 Respiration Syllabus skills: A/I; M/M vacuum flask (e.g. a Thermos) 11--- dead peas washed in disinfectant -1t-- - germinating peas washed in disinfectant cotton wool 1-1--- A - thermometer B Procedure 1. Soak some pea seeds for 24 hours. Divide the seeds into two sets of roughly equal number. 2. Kill one set by putting the seeds in boiling water for 5 minutes. Rinse the peas with a mild disinfectant solution. 3. Rinse the live peas with the same disinfectant. 4. Put the two sets of peas into separate 'Thermos' (or simi lar) flasks. Wedge a thermometer into each flask with cotton wool and then carefully invert the flasks, as in'the diagram. 5. Arrange the thermometers so that you can read the temperature on each. 6. Leave the flasks side-by-side for three days. 7. Read the two thermometers at the end of this time. Questions 1. What was the purpose of the disinfectant solution? 2. Has the temperature indicated by the thermometer in the dead seeds changed? Account for this. 3. Has the temperature of the live seeds gone up or down? Account for this change. 4. Would you expect to find a difference between the reading shown by either thermometer in the morning and in the evening? Why? 5. Suggest one way in which you could make the experiment more reliable. © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable 351 School-Based Assessment 11.3 To discover whether oxygen is used up during respiration Chapter 11 Respiration Syllabus skills: A/I; O/R/R Procedure 1. Set up the two sets of apparatus shown in the diagram. The capillary tubes must be gas-tight in the bungs, which must be gas-tight in the flasks. 2. Once the apparatus is gas-tight you can adjust the position of the oil drop by very gently pressing the bung into the flask or releasing it very slig htly. 3. Note the position of the right-hand edge of each oil drop. The drops should be near zero to start the experiment. Put the flasks out of direct sunlight so that their temperatures do not change. 4. Draw a table recording the positions of the oil drops every 5 minutes. 5. Stop the experiment when you have enough readings to see the pattern of the results. A good method is to draw a graph of position {y-axis) against time (x-axis) as you go along . 6. Release the animals gently back to where you found them. capillary tube 3 2 1 oil drop O wire gauze soda lime (absorbs carbon dioxide) A bl111~1IIIii 1 1I1 1 I 11 'l' 11I11 I11 1~ 111 l 0 ~=-+-- small animals, e.g.woodlice or millipedes soda lime (absorbs carbon dioxide) B Questions 1. Why was it important to keep the flasks at a constant temperature? 2. Why did the oil drop in A move in the way it did, quickly at first and then hardly at all? What was the purpose of this part of the experiment? 3. What happened to the oil drop in B? How was it different from the behaviour of the oil drop in A? 4. Why did the oil drop in B behave in this different way? Explain what the experiment tells us about the necessity for oxygen in respiration. 352 Photocopiable © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 201 4. 27 · School-Based Assessment 14.1 To investigate the rate of transpiration using a photometer Chapter 14 Transport in Plants Syllabus skills: All ; O/R/R; M/M plant stem, e.g. geranium Achillea or Impatiens water containing a few drops of ink zero point clip 10 9 8 7 6 5 4 3 2 1 I 0 meniscus Procedure 1. Select a plant with stems which will fit into the rubber tubing on your potometer. 2. Put the stem under water (keep the leaves out if you can) and cut the stem with a sharp knife. Leave the stem under water to stop air getting into the xylem vessels. 3. Still under water, attach the stem into the photometer which has been filled with coloured water. (Coloured water is easier to see in the capillary tube.) 4. Take the apparatus to your bench. Open the clip slowly until the meniscus moves to a point near to zero. Start timing form this point. 5. Record the position of the meniscus every two minutes until it reaches the end of the graduations. 6. Repeat steps 4 and 5 but: 7. (i) with a fan blowing air across the stem 8. (ii) with the lab closed up and lights out. Questions 1. Draw three graphs (on the same set of axes) showing photometer reading (vertically) against time (horizontally). Which conditions produced the highest transpiration rate? Which conditions produced the lowest transpiration rate. 2. How do you deduce these answers from the graphs? 3. Why did the fan cause the transpiration rate to change as it did? 4. Why was the transpiration rate in the closed, darkened room different from that in the open, sunny lab? © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable 353 School-Based Assessment 17 .1 To discover how gravity can affect plant growth Chapter 17 Movement Syllabus skill s: A/I; O/R/R (See also Investigation 17.2.) Procedure 1. Place three kidney beans or red beans on some tissue paper soaked in water. Leave them for a day. 2. Place several layers of tissue paper along the inside of a glass and soak the tissue with water. The wet tissue will stick to the glass. 3. Gently place the germinating beans between the glass and the tissue in the position shown in the 4. 5. 6. 7. diagram. Leave the beans there for one day. Make sure t hat -the tissue is always moist. At the end of one day make drawings of the seedlings. Record your observations of the growth of the seedlings, particularly the growth of the radicle. Turn the glass upside down and leave it for another day. Make further drawings of the seedlings. layers of moist tissue paper against the g lass germinating seedling placed between the tisue paper and the glass glass turned upside down seedling, note in particular the growth of the radicle Questions 1. Why is the tissue paper always kept moist? 2. Why did the radicle and the shoot now grow in the same direction? 3. From the point of view of the seedling, what effect does turning the glass upside down have? 4. What was the effect on the growth of the shoot and the growth of the radicle of turning the glass upside down? 5. Why is this response important to a plant? 6. Suggest two ways in which the experiment might be improved. 354 Photocopiable © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limit ed 2014. 27 · School-Based Assessment 17 .2 To investigate the growth of a radicle Chapter 17 Movement Syllabus skills: D Procedure 1. Soak three bean seeds in water for 24 hours. 2. Line the wall of a gas-jar or tall beaker with a piece of thick, wet blotting paper or several layers of wet tissue paper. 3. Place the seeds between the blotting paper and the wall of the gas-jar. ~beaker wet tissue I, -1-- ---tt- bean seed I + - - - --++- marked ( \ I ,, ..-Y - ~- -- radicle water 4. Put about 1 cm depth of water in the gas-jar to keep the paper moist. 5. When the radicles have reached a length of about 1 cm remove the seeds carefully and make marks along each radicle at roughly 2 mm intervals using a fine cotton thread soaked in Indian or other waterproof ink. 6. Return the seeds to the gas-jar making sure that the weight of the seedling is supported by the testa and not the radicle. 7. For the next six days, make a sketch of each bean seedling showing how the ink marks have separated. Make measurements of the gaps between the marked lines if you can do so. Arrange your sketches in a table like the one below. Questions 1. Why did you use more than one seed? 2. Did all three seeds behave in the same way? 3. Did the radicles grow uniformly, mostly at their base, or mostly at their tip? 4. What would be the effect on growth if the extreme tip of the radicle were cut off after three days? 5. What happens at the tip of the radicle to cause the effect you have observed? 6. Suggest why flowering plants continue to flower if dead flowers are removed. 0 2 3 4 5 6 seed 1 seed 2 seed 3 A possible way of arranging your sketches (after King, Soper and Tyrell Smith: Macmillan, 211d ed 1991 page 213). © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable 355 School-Based Assessment 17 .3 To discover how light can affect plant growth Chapter 17 Movement Syllabus skills: All; O/R/R Procedure "1. Place three kidney beans or red beans in a small container lined with wet tissue paper. Leave them for one day. 2. Cut a small hole in the short side of a box such as a shoe box. 3. Put the terminating beans, in their container, in the box as far away from the hole as possible. Keep the tissue paper wet. Leave the experiment for two days in sunlight. 4. After this time make drawings of the seedlings and measure the length of each. 5. Replace the box lid and leave the seedlings for a further two days. Again , keep the tissue paper moist. 6. Draw up a table showing the lengths of the seedlings and their mean lengths after two days and after four days. 7. Write a general statement describing the appearance of the seedlings at each stage. seedlings shoe box length of seedling - hole Questions Why is it important that the tissue paper is kept moist? Did the seedlings grow more in the first two days or the second two days? Why? What external factor made the seedlings grow in the way they have? What part does the plant hormone auxin play in this growth? Explain carefully how the effect is important to the plant. 5. What is etiolation? "1. 2. 3. 4. Extension Use six beans. Allow the shoots (coleoptiles) to reach a length of about 2 cm . Cover the tips of two shoots with a small piece of aluminium foil. Cut off the top of two of the shoots. Do nothing to the remaining two shoots. Place all six beans in the growth box, making sure that the tissue is damp. After two days, examine the shoots and explain why they are different from each other. 356 Photocopiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Lim ited 2014. 27 · School-Based Assessment 17.4 To compare the movements of four animals Chapter 17 Movement ~ Syllabus skills: O/R/R In this investigation you will observe the movements of an earthworm, a fish , a frog and a human. Record your observations in your notebook as you work. Where explanations are asked for, write them afterwards, giving as much detail as you can. (You may have to look up material in your library.) Finally, answer the questions set at the end of this set of experiments. Procedure: earthworm 1. Place the earthworm (alive) on a sheet of white tile. Use your index finger to touch the outside of the earthworm's body. 2. Is the skin hard or soft? The skin should feel moist. How does this moisture on the skin of the worm help it to move? 3. Is the body of the worm segmented or unsegmented? 4. Does the external structure of the worm suit its ability to burrow in the soil? Explain your answer. 5. Allow the earthworm to crawl on the sheet of paper. Listen carefully as it moves. Do you hear a scratching noise? What causes it? 6. Turn over the earthworm and, with the aid of a hand lens, observe each segment. What do you observe? What are these stiff bristles used for? 7. Describe the movement of the earthworm over the paper. Explain how the earthworm bring about the changes in its shape in order to move. 8. Place the earthworm on a white tile. Does the earthworm move as quickly on the tile as it did on the paper? Explain your answer. Procedure: fish 1. 2. 3. 4. 5. Watch a fish swim in an aquarium . Describe the motion of the body, fins and tail as the fish moves from one place to the next. Which structure moves the fish in a forward motion? Explain how this occurs. How does a fish turn around in the water to change direction of motion, whether to the left or right? Did you notice the fish stopping in the water (not swimming around)? Explain how the fish is able to do this. 6 . Use your hand to disturb the water by swaying it side to side. Did the fish sway with the water currents created? If not, explain how it was able to remain steady in the water. 7. Observe the shape of the fish's body. Explain how the shape of the fish is suited for its movement in the water. Procedure: frog 1. Hold the frog firmly in your hand and observe the length of the front and back legs. Which set of legs are longer and more muscular? 2. Place the frog in a cardboard box (keep the top open) and watch how it moves. 3. Describe the hopping or jumping motion of the frog . 4. Which set of legs (front or hind) played the more important role in its hopping movement? Explain your answer. 5. Observe the structure of the feet of the frog . 6. Put the frog in a tank of water and observe it swimming. How did the frog move its legs in order to obtain a forward motion? 7. Explain how the structure of the feet enables the frog to swim in water. © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. Photocopiable 357 School-Based Assessment Procedure: human For this experiment you will work with a partner. Your teacher will put on display in the front of the class a human skeleton like the one shown here. 1. With you and your partner taking turns, walk up and down a short distance around your work area. 2. Describe the motion of your partner while walking. 3. Did your partner walk upright on two legs? 4. Look at the skeleton and identify the structure that is responsible for supporting the body in the upright posture. 5. How did your partner move their legs while walking? Did they bend the legs or keep them straight? 6. Look at the skeleton and identify the structures used in the motion of the legs which you have described. Make a list of the structures, stating the function of each. 7. Did your partner move their hands while walking? Can you give a reason why? 8. Are bones able to move on their own? If not, state the structures that are responsible for moving bones. 9. Explain how the muscles move the legs while walking. Questions 1. How are the movements of the earthworm different from those of the frog and the fish? 2. How is this difference related to the fact that a frog has a bony skeleton while an earthworm does not? 3. Why can a human perform a wider range of movements than a frog , but cannot jump or swim so well? 358 Photocopiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment 18.1 To find whether the skin of the back of the hand, the palm or the back of the neck contains the most touch receptors Chapter 18 Irritability, Sensitivity and Coordination Syllabus skills: A/I; O/R/R Procedure 1. Attach two pins to a ruler, 2 cm apart, as shown I the diagram. 2. Draw up a table like that shown for your results. 3. Make sure that your partner understands what is going to happen in the experiment. He or she then closes their eyes. 4. Touch your partner gently on the back of the hand with one or both pins on the ru ler. 5. Ask how many pins they think are touching their hand. Record a tick if they are right and a cross if they are wrong. 6. Repeat step 4 nine more times making ten in all. 7. Adjust the pins to be 1 cm apart and repeat steps 3, 4 and 5. 8. Adjust the pins to be 0.05 cm apart and repeat steps 3, 4 and 5. 9. Adjust the pins to be 0.2 cm apart and repeat steps 3, 4 and 5. 10. Present your results as a histogram like the one shown below. Number correct back palm neck 10 Number of correct responses • 9 back of hand D palm of hand D back of neck 8 7 6 5 4 3 2 0 2cm 1 cm 0 .5cm 0. 1 cm Distance apart of pins Questions 1. 2. 3. 4. Which of the three parts tested do you think has the most receptors? Give reasons. Why do you think that this part of the body needs to be so sensitive? Why is it important to have touch receptors in the skin all over the body? What are some sources of error in the experiment? How can the experiment be improved? © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable 359 School-Based Assessment 18.2 To investigate two reflex actions Chapter 18 Irritability, Sensitivity and Coordination Syllabus skills: O/R/R Procedure: effects of light on the pupil of the eye Prop up a small mirror in front of your face. Look into the mirror and draw a diagram of one of your eyes. Label the pupil and the iris. 2. Look again into the mirror. Close both your eyes and cover them with the palms of your hands. After 20 seconds remove one hand and at the same moment open that eye. What happens to the pupil immediately after you uncover your eye? How long is it before there is no further change? 3. Look into the mirror once more. Shine a small torchlight into one eye and observe what happens. 4. Draw diagrams showing the appearance of your eye (a) in dim light, and (b) in bright light. 1. Questions 1. Explain what caused the pupil of your eye to change size in 2 and 3. Draw a diagram to show the changes. 2. Did your pupil change size quickly or very slowly? Suggest why this is important to your body. Procedure: the knee-jerk reflex 1. Sit on the edge of a table with both feet hanging loosely. 2. Use your fingertips to locate the base of one knee-cap. 3. Tap the front of your leg firmly, just underneath your knee-cap, with the side of your hand or the edge of a ruler. 4. Describe what happens when you do so. Questions 1. How is this reflex different from the reflex change in pupil size which you studied? 2. Draw diagrams to illustrate this difference. thigh knee-cap hand tapping leg 360 Photocopiable © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment 19.1 To investigate heat flow from a warm object Chapter 19The Eye, the Ear and the Skin ) ( Syllabus skills: A/I; O/R/R; M/M Procedure 1. Set up three thin plastic cups as shown in the diagram. • A is wrapped in several layers of tissue paper held in place with elastic bands . The paper is soaked in cold water. • Bis not wrapped . • C is wrapped with corrugated cardboard (from an old box) held in place with elastic bands. 2. Draw up a table with four columns and 18 rows for the measurements. 3. Heat a supply of water in a beaker or a kettle until it is hotter than 70 °C. 4. Half-fill each cup with the hot water. (Take care!) 5. At once take the temperature of the water in each cup. 6. Take the temperature of the water in each cup every 30 seconds for the next 8 minutes. Record your results in the table. thermometer Results 1. On the same axes, plot three graphs (one for each cup) of temperature against time. Plot temperature vertically and time horizontally. 2. Complete the graphs by drawing smooth curves through the points. 3. Use the graphs to explain which cup lost heat most quickly and which cooled most slowly. elastic band Questions 1. Why did wrapping the cups with the wet tissue and the cardboard have these effects? 2. Why is it helpful to humans to sweat in hot weather and put on more clothes when the weather turns colder? c © Linda Atwaroo-Ali 2014. Design and illustration © Mac millan Publishers Limited 201 4. Photocopiable 361 School-Based Assessment 20.1 Observing the reproductive cells of a mammal Chapter 20 Reproduction in Animals ~ Syllabus skills: O/R/R; D Procedure: observing the reproductive cells of a mammal 1. Your teacher will provide you with pre-prepared slides of mature ova and of the sperm of a mammal. 2. Observe the slide of the male gamete under the microscope, first under low power and then high power. Make a note of the magnification at each power. 3. What structure is contained in the head of the sperm? 4. In your laboratory report book make an accurately labelled diagram of the sperm. 5. Write a description of the sperm. 6. Then remove the slide and replace it with the slide of the ova. 7. Which are the mature ova? How can you tell? 8. Locate the cell membrane with a jelly coat, nucleus containing chromosomes and cytoplasm. 9. Make an accurately labelled drawing of one mature ovum. 10. Write a description of the mature ovum in your laboratory report book. Questions 1. Which are larger, sperm of ova? Make an estimate of their relative sizes. 2. Sate one advantage of sexual reproduction over asexual reproduction. Procedure: observing the budding of yeast 1. 2. 3. 4. 5. 6. 7. 8. Make a mixture of yeast, water and a little glucose. Place a drop of the yeast mixture on a slide and stain it with methylene blue. Cover with a cover slip. Observe the slide under a microscope, first at low power then at high power. Make a sketch in your notebook of a yeast cell. How many budding cells can you see? How long does it take for a bud to form and separate from its parent? Make sketches to illustrate the stages in budding in yeast. Questions 1. Each new cell must contain a nucleus. What must happen in the parent cell before the bud finally detaches from it. 2. The family of yeasts are the saccharomycetes - meaning the 'sugar fungi '. How does this relate to one important use of yeast? 362 Photoc opiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 • School-Based Assessment 21 .1 Dispersal of fruits Chapter 21 Reproduction in Plants ~ Syllabus skills: O/R/R; D Procedure 1. Collect examples of fruit whose seeds are dispersed: (i) by animals eating the fruit, (ii) by animals passing by the plant, (iii) by mechanical means, (iv) by water, (v) by the wind. Example 2. (i) Tomato (ii) Sweetheart (iii) Pride of Barbados ~v) Coconut (v) Dandelion Make a sketch of each and, by each sketch, state wh ich features of the seed are important for that method of dispersal. Questions 1. Most plants, in the course of their evolution, have developed an efficient method of seed dispersal. What would be the consequences for a plant which had no dispersal mechanism? Explain your reasoning 2. Oranges are brightly coloured and have an attractive scent. How do these factors help dispersal of the seeds? 3. List four ways in which animals (including humans) help in the dispersal of fruits and seeds. © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. Photocopiable 363 School-Based Assessment 21.2 Seeds and food storage Chapter 21 Reproduction in Plants Syllabus skills: O/R/R; M/M ; D Procedure 1. 2. 3. 4. Remove the seeds from an orange. Peel the seeds and crush them. Collect some juice from the fleshy part of the orange. Test the crushed seeds and the orange juice for sugars, starch, protein and lip (fat) using the tests given in Chapter 10. Questions 1. What food groups are stored in the fruit? 2. Why do fruits store these food groups? 3. What food groups are stored in the seeds? 4. Why do seeds store these food groups? 364 Photocopiable © Linda Atwaroo-Ali 2014. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment 25.1 To investigate how the sex of an offspring is determined Chapter 25 Heredity and Genetics Syllabus skills: All ; O/R/R Number of individuals Procedure 1. Fifty black beads are placed in a container. In another container, 25 black beads and 25 white beads are mixed thoroughly together. The beakers are placed side by side with two empty beakers clearly labelled A and B. 2. Close your eyes. Pick one bead from each of the first two beakers. If both beads are black , put them into beaker A. If one is black and the other white, put them into beaker B. Record the result in a table like the one shown, but putting a tick to show the combination of beads produced each time. Selection number Both black Height (cm) (in 2 cm g roups) Black and white 2 3 4 5 6 7 8 9 10 3. Do this nine more times, making ten in al l. Questions 1. 2. 3. 4. 5. What does each black bead represent? What does each white bead represent? What does the beaker represent? Why did you have to close your eyes when taking beads? Use a genetic diagram to predict the expected ratio of male to female offspring in humans. How does this relate to the experiment you have just done? 6. How many pairs of black beads did you select? 7. How many pairs contai ning both black and white beads did you select? 8. What ratio of 'boys' to 'girls' did you find in the ten offspring of th is experiment? 9. Relate your obtained ratio to the prediction you made in 5. 10. In what ways does the experiment differ from what really happens? © Linda Atwaroo-Ali 2014. Design and .illustration © Macmillan Publishers Limited 2014. Photocopiable 365 School-Based Assessment 26.1 To investigate continuous variation Chapter 26 Variation and Evolution Syllabus skills: A/I; O/R/R Procedure 1. Measure the height of each member of your class. 2. From the list, draw up a frequency table like that shown in the diagram. Make sure that you have enough groups to take in all the measurements. (It is quite possible that there are may be a group with no individual results in it.) Height group (cm) No. of individuals 150- 152 153-1 55 156- 158 159-161 etc. 3. Use the frequency table to draw a histogram showing how height varies among your classmates . • () A B Questions 1. What is the height range (i.e. shortest to tallest) in your class? 2. Describe.the overall shape of your histogram? 3. Imagine that you had measured the height of a very large number of people, but grouped those heights in 0.5 cm groups. Make a sketch of what you think that the histogram would look like. 4 . What kind of variation is.seen in the height of humans? 5. State three other examples of this type of variation in humans. 6. Name, and give one example of, a different type of variation . 366 Photocopiable © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 2014. 27 · School-Based Assessment 26.2 To investigate natural selection Chapter 26 Variation and Evolution Syllabus skills: A/I ; M/M Procedure 1. You need 240 matchsticks (or- toothpicks) and some coloured marker pens. 2. Colour 60 matchsticks blue, 60 brown, 60 yellow and 60 green. 3. Scatter a mixture of 30 matchsticks of each colour onto a large surface such as the floor, a lab table or a law n. These are the prey. 4. One student, the predator, has 10 seconds to 'catch ' as many prey as possible by picking up one matchstick at a time and putting it into a beaker. The remaining matchsticks are the 'survivors' . The number of survivors of each colour is counted. 5. Each survivor is given one offspring of the same colour. 6. Repeat steps 4 and 5. 7. Record the results in a table like the one below. Prey population Number of prey caught Number of survivors New prey population (after each survivor is given one offspring) 30 blue 15 15 30 30 brown 5 25 50 30 yellow 20 10 20 29 58 30 green 30 blue 20 10 20 50 brown 7 43 86 20 yellow 15 5 10 58 green 0 58 116 Sample results from a background of lawn grass. Questions 1. 2. 3. 4. 5. 6. 7. 8. 9. What does each matchstick represent? What does each colour represent? How did the number of sticks of each colour change over time? Which colour survived best? Why? Which colour survived worst? Why? How do these results relate to the process of natural selection? Explain what is meant by camouflage. .r In this experiment, which characteristic is being pressured and selected? Predict what would have happened in your experiment if the survivors had been given two offspring instead of one. 10. Describe some s.ources of error in the experiment. © Linda Atwaroo-Ali 201 4. Design and illustration © Macmillan Publishers Limited 201 4. Photocopiable 367 Index ca ffeine 220 calcium 104 calyx 261 camou fla ge 3 l4 canine tee th 109 Cannabis saliva 139, 22 1 capilla ri es 146, 147- 8 bursting of 152 gaseou s excha nge 132 ca pillariLy 165 car exhau st 68 carbohydra tes IO 1-2 metabo lism I 17 storage 80 see also glucose; sta rch carbo n cycle 43-4 human effect on 44-5 ca rbon d ioxide atmosph eric 4 3, 44, 45- 6. 133 in the body 191 diffusion 85 from fermentation 126 in phoiosymhesis 92- 3, 95, 343 concen tration 97 pollution from 68 from respira tion 123, 182. 347 tra n spon in the body l43. 150- 1 see a lso gaseous exchange carbon monoxide 68, 138, 252 ca rdiac muscle 144 ca rd iovascular d isease I 08, 137 Ca ribbean Anolis lizard s 315 a n ificia l selenio n in the 3 18- 19 endangered species 65 human activity effecLs on 71-2 carnivores 25, 26, 35 ca rrying capaci ty 53 cata lase 345 cata lysts I I O cataracts 23 1 caule fa rming 3 18-19 cell cycle 279-80 cell membran e 79, 80 permeability 84. 86 cell wall 79 cel ls capillaries su rround ing 147 gaseous exchange 133 homeosLasis I 90, 2 17 muvemem in and out of 83 respiration 123 size 78, 79 specia lisa ti on 8 1- 3 see a lso an ima l cells; human cells; pla m cells cellu lose I 02 cen tra l nervous sysLem (CNS) 211 response LO stimuli 2 14 centrioles 28 1 cemru m 202 cereb rospinal fluid 216 cerebrum 2 16 cervi ca l venebrae 200-2 ch emica l d igestion I I O copper 20-1 chemical energy 34 c_o ppenulfate I 03 chlorophyll 92, I 00, 342 · ··•... ;_ - coral reefs destructio n 7 1, 72 .. wrms 175 · ch lo roplasts 5, 79, 80. 92 . · co'rnea 227 · in the pa lisade layer 93 in photosyn thesis 95- 6 coro lla 26 1 . . ··. '. . coro·naryaneries 148 ch o rdates 8- 9 choroid 227 corpus lu teum 249 cortex (kidney) 185 chroma tids 28 1. 292 chromosome nu m ber 278-9. 28 1, cortex ( root) 165-6 282 cotyledons 176, 177 and meiosis 290- 1 cou rtship 250 chromosomes 79 cows 29 Down's syndrome 320 cran ia l re fl exes 215 homologous pairs 29 1- 2, 293, cretinism J 05 297 crop pla m s in mitosis 281 diseases in 275 m uta tio n 3 19 genetica lly e ngin eered 32 1. repl ication 282 322 see a lso game tes green h ouse 97 ch yme 113, 114 cross-po llination 262 cilia 133 crossing o ver 292, 293 ci liary mu scle 227, 228. 229 crustaceans 8 circu lat0ry system, humans 143, cu ticle 93, 94 149 cu n ings 284 ci r rhos is of the li ver 221 cystic fibros is 322, 323 class 11 , 12 cyto kinesis 279-8 1 classifica tion cy1oplasm 79, 80 artificial and natural 9 binomial system I 0-12 Darwin, Charles 313, 315 dichotomous keys IO Darwin's fin ches 3 l5 organisms 2 Darwin's theory of evo lution 294 cloning 245 daughter ce lls 29 1, 292 of ani mals 285- 7 DDT 38-9, 3 14 cnidaria 8 death rates 55 co-dominance 30 1- 2 decomposers 24-5, 28-9. 35 cocaine 22 1, 252 in Lhe ca rbon cycle 43-4 coccyx 200, 201 in the nitrogen cycle 4 8 cochlea 233 defecation 182 coconu ts 265 deficiency d iseases 272 cohesion 165 d efores tation 46, 65, 69- 70 collecting du ct 185. 187 and water shortage 66 colo n 11 5 degenerative diseases 55 colo n cancer 116 denitrifica tio n 47 colon isatio n 3 15- 16 deoxygen ated blood 132, 145, 149 colostrum 253 depth o f focus 229 commensalism 29- 30 desalination pla111s 66 commun icable diseases 155 detergents 67 com munity 16 detox ification I 17 com pan ion ce lls 162 detrilivores 28-9, 35 com petitive species 65 diabetes I08, 186, 272 compost 57, 59 dia lysis 188 concentra tion g radient 84, 85, 137 diaphragm (contraception ) 253, condoms 253. 254 254 cones 230 diaphragm (t horax) 134 conjunctiva 227 diastole 145-6 conserva tion dichotomous keys I 0 environmental 72 dicotyledons 7 reso u rces 72-3 diet 10 1- 6 soi l 73 ba lanced IOI . 106- 7, 27 1 wa ter in plants 167-8 sec also food ; nutrition constipation 11 6 diet pills 220 consu mers 24-5. 26, 35. 92 diffusion 84-6 co min uous variation 312, 363 gaseous exchange 137 co mracept ion 253-4 oxygen 85, 142- 3 contraceptive pi ll 253, 254 in the placema 2 5 1- 2 converging le ns 231 in a solu tion 338 digestion along the alimentary cana l 111-16 definition LOS enzymes in 11 0-1 1 teeth and I 08- 1O diploid numbe r 282. 291 , 297 disaccha rides 10 1- 2, 103, 110- 1 1 discontinuous variation 312·~ diseases blood 's role defending against 153-5 communicable I 55 he red itary 272. 303-4 pathogenic 272, 273 in plams and an ima ls 27 5 and population g rowth 54, 55 from prot0zoa 81 social and economic implications 275 types and control of 2 7 1- 2 vecto rs 236 from vi ruses and baderia 80, 272 dispersa l 260, 264 by animals 264-5 by explosive devices 266 by fru it 264-6, 360 by water 265 by wind 266 distal convoluted wbu le 185, 187 diverging lens 231 DNA and evolution I 0 function of 46 replica tion 282 Dolly th e sh eep 286- 7 domestic sewage treatment 69 domesti c waste 57 cont rol o f 67 recycl ing 58 domina nt alle le 298 donors 151-2, 188 Down's synd rome 319, 320 drug abuse 220- 2 and HJ V/AJDS 254 in pregnancy 252 drugs definition 2 19 p rescripti on 2 19-20. 252 DTP vaccine 155 duodenum I 14 dyes 84, l 05 ear sac 234-5 eardrum 233-4 ears 21 I hearing 233 role in balance 234-5 a nd ~ Li mu l i response 226 structure 232 eanhworms 354 ecology 15- 16, 2 3 definition 15 speciation 3 17 study of 331-4 econom ic implica tions diseases 275 369 Index drug abu se 222 1-lfV/AfDS 255 ecosyste m s 16- 17 p roducti vit y 36 e cto pa rasites 30 eda phic factors 16 e ffe ct o rs 2 11 -1 3. 2 14 egesti o n I 08, 182 eggs 178 egre ts 29 e lect rica l im pu lses 2 13 e lectron m icroscopes 78 e mbryos 2 50- 1 emu lsification 1 14 e n dangered species 64, 65 protectio n 73 e n demic species 64 , 65 e n docrine gla nds 213. 2 17- 19 e nd ocrine syste m 2 17- 19 e nd opa rasi tes 30 e nd oske lc to n 199 e ndosperm 176. 177 e n e rgy gain a n d loss in a·ni m a ls 34-5 ga in a n d loss in p lan ts 34, 35 n utritio na l re quire m e n ts 106 pyra mid s of 36- 7 reso urces 5 6 fro m resp irati o n 123-4 so la r 33-4 e n vironme n t a da pta tion to 3 13 ca rryin g ca pacity 53 co nservation a n d reswra tion 7 2 a nd gene tic va ria tio n 3 1 L a nd gen o type 296- 7 a nd hu m a n s 63-4 m a rin e a nd wetland 70, 7 1 a nd sh opp ing 59 was te prod u cts a nd 57- 9, 64, 67 environ m e nt a l !"acto rs 15-1 6, 17 e nzymes act ion o r 34 5 in d igestio n I J O- I I opti m u m te mpe rature 236 in p ho wsynth esis 96 in the sm a ll in testin e 1 14 e pigea l germi na tio n 177 e piglottis I 12 Eryngi11111 foe1idu111 I I Esclteric/1ia coli 4 e than o l test I 04 e ti ola tion 97 e u kar yotes 3 e u trophicat io n 67, 69 e va pora tio n 164 evolutio n Da rw in 's th eory of 294 a n d DNA LO a n d n a tura l se lect.ion 313- 17 excretio n 3, 182 e xcretory prod ucts in a nimals 182- 3 in plan ts 183-4 excretor y syste m , h u m a n 184-8 e xercise a n d h ea lt h 27 1 370 and hea t ge n e ra tion 2 39 and respira t.ion 12 5-6. 183 exocrine glands 2 17- 18 exoske le to n 199 expira tion 133, 134 expo ne mia l growth ph ase 52 exte n sor mu scles 20 3 extinc tio n of species 64-6 a nd dt:foresta tio 11 70 eyes 2 1O a nd stim u li response 22 6 Stru cture 226- 7 e yesig h t 227- 8 acco m m oda tio n 228- 9 defects and correctio ns 230- 2 a nd pupi l size 22 9- 30. 357 face t 202 faeces 11 5-16, 182 Fa llopia n tubes (ovid u cts) 2 47, 250 fa m ily (cl assifi ca tio n ) l 1, 12 fa mi ly tree.s 30 5 fa ts 10 6 as food sto re 178 see a lso lipids fa u y acids I 0 2, I I 0- 1 I assim ilat ion I 17 feed back m echan isms 190- 2 Fe h ling·s solut.ion 103 fema le n ut ri tio n a l req u ire m e n ts 10 6-7 re p rod u ctive syste m 247 fe rme nta tion J 26, 127 fe rt ilisa tion in hu mans 25 0 in pla n t.s 260 , 263-4 fe rtil isers 4 8, 67 fe tu s 25 1- 2 fib re 10 1. 1 16 fi brin 15 1 fi rmi ng agents I 0 6 fi sh 9 a daptat.ion to wate r 18 gaseou s excha nge in 136. L37 m ove men t 354 fi shi ng 65, 71 Oaccid cel ls 86, 87, 94-5 fl avo u rings 10 5 Oexor muscles 203 fli es 273 fl ooding 70 Oowe rs colou r 300, 30 I ga metes in 260 , 26 1, 263 pollina tion 262- 3 stru ct.u re 26 1 Ouo rides I I 0 focu sing 227- 9, 23 1 food a bsorplion I 08, I I 1- 16 a dd itives 10 5- 6 from a ni ma ls I 06 di ffusion in the bod y 85 fruit as 264-5 gene tic engineering 32 1 pla nts as 9 1-2 in respi rin g cells 123 as stimu lu s 209 tests I 03-4, 346 t.ranspo n in th e bo d y 143, 148 transpo rt t.h roug h p la nts 168-70 see a lso d ie t; nutrit.io n food cha ins 2 4. 25- 6 bioaccumu lati o n 38- 9 energ \' m ove m e nt th ro ug h 35- 6 p redator/ prey re la tio nshi ps 27 pyra mids o f e n e rgy 37 pyra m ids o f n um bers 37- 8 food storage in an imals 178 carbo h yd ra tes 80 in fru its 176, 36 1 m ine ra ls a nd vit a m ins I 17, 178 in pla nts 173- 8 food webs 27. 3 1 form ula mi lk 253 fossi l fuels 56 a nd a cid ra i_n 4 9 combustio n 4 3, 44-5, 68 fovea 227, 230 fre sh wa te r 17- 18 fni its 106 developm e nt 263-4 d ispe rsa l 264-6. 36 0 rood storage 176, 36 1 forma tio n 2 60 fungi 3, 5- 6 in the ca r bo n cycle 43 in decompositio n 28 Ga la pa gos Isla nd s 3 I 3. 3 15 G11111b11sia hubbsi 3 17 ga m e tes 245, 246, 248. 302- 3 in fl owers 260, 26 1, 263 for111a 1io n 290- 1 va ria tio n of 293 see a lso ovum; spe rma tozoa gaseous exchan ge adapta tion s fo r 136- 7 in t.he hea rt 145 in h u ma n s 130-4 in pla n ts 135, 136, 137 su rraces 13 5-6 gast ric ju ice I 13 gene bank s 322 gene po ol 3 14 genes 2 79, 297 see a lso a lleles genet ic d iagra ms 298- 9 genetic d isorders 303- 4 gen et ic e n gineering 28 5. 32 1- 2 implica tio n s o f 3 22- 3 genet ic varia tio n 3 10 a nd th e enviro n ment 31 1 importance of 3 1 1- 12 loss o f 322 a n d mu tation 3 19 in o ffspri n g 293-4 ge ne tically m o difi e d organ isms (GMOs) 322 genotype. 296- 7, 298- 9 co-d o m inan ce 30 I haem ophilia 303 in com ple te dom in a n ce 300 sickle cell an aemia 304 test cross 300 gen us I I , 12 geogra phi ca l isola tion 3 15 geotro pism 197-8. 35 1 germ ina t.io n 177 gesta tio n p e ri od 2 50 giraffes 3 13 gla u com a 232 glid ing jo int s 20 3 glo ba l dis1ribu tio n o f d ise ase 272 distribu tion of HIV/ A I DS 255 tem pe ra w re ra nge 235. 236. 237 glo ba l wa rm ing 45-6 glo m e r ulu s 185- 6 glu cose 3 4, 46 in aerobic respira tion 123-4 in a naerobic respira tio n 125. 126 assimi lation 116 ba ll -a nd -stick m ode l IO I blood glucose le ve ls 19 2 fro m h ydro lysis I 12 m a nu facture in plants 92- 3. 96 selective. re absorptio n 186 tests I 03 glycerol 10 2. 1 10-1 1 glyco gen I 02, 178 goit re 105 gold e n rice 322 go nads see ova ri es; testes gonorrh oea 255 Graa fi a n fo ll icle 249 grafti ng 284 gravity see geotropism gre ase spo t test. I 04 green house e ffect 4 5- 6 greenho u se gases 45, 72 see also carbon diox ide greenho use pla m s 97 grey ma u e r 2 16 ground wa te r, de pletion o f 66 growth 3 horm o nes 219, 3 18 move m en ts L97- 8 see also populati o n growt h g ua rd cells 94 Guya na, ba u xite in dustr\' 56 gynaeciu m 26 1 ha bita1 destru ct.ion 65 see a lso defo resta tion habitats 16 ha e moglobi n I 50- 1, 183, 3 19- 20 ha e m o p h il ia 3 03 hae m o rrhage I 5 I ha em o rrho ids I 16 ha ir cells 233, 234 ha ir co lo ur 297- 9. 305 ha ir e rector m uscles 238, 239 ha loph ytes 168 hap lo id n umbe r 290- 1 h ealt h 27 1 ris ks to 322 Index healthy lifestyle 152, 271 hearing 2 33 heart act ion o f the 144-6 blood supply 144 section th rough 144 stru cture o f 143-4 heart d isease J 08 and smoki n g 137 h ea rtbeat 14 5-6 h ea t conservat ion a n d loss 238 fl ow from a warm object 358 p ro du ction 117, 183. 239, 348 see a lso tem pera ture h eavy meta ls 20- 1, 68 Heimlich ma noeu vre 1 13 He/icobacler pylori I 14 herbicides 199 herbivores 2 5, 26, 35 h ered itary diseases 272, 30 3-4 h eroin 252 heterotrophs 9 l. 9 2 h eterozygou s 297-9 co-dom inance 301 - 2 inco mplete do mina n ee 300 for sickle cell a nae mia 320 h inge joi n ts 204 HI V/AIDS 254-5 pa thogens and 2 74-5 holozoic nu tri tion 108 homeostasis 189-90, 2 17, 236 h o111eot herm ic a ni ma ls 20, 235 Homo s pecies 12 ho m ologous pairs 29 1-2. 293, 297 ho m ozygo us 297-9 fo r sickle ce ll anaem ia 320 hormon es amid iure tic 189, 219 gonads 24 8 growt h 2 19, 318 injecta ble 254 duri n g m e nstrual cycl e 249 pla n t 199 secretio n J 82. 2 18, 219 tra nspon 14 3, 148 hoSLS 30, 273. 274 human activiti es and th e ca rbon cycle 44-5 effects in the Ca ribbean 7 1- 2 and marine/wet land e nviron m e n ts 70, 7 1 a nd resou rce consumpti on 57- 9 and species ext inct ion 64-6, 70 a nd water sh o rt age 66 see also deforesta tio n : in d u stria li sa tion ; pollutants; po lluti o n human cells 2 9 J, 297, 302 humans al i111en tary cana l I I I , l 15 anaerobic respira tio n 125-6 body tem pe ra tu re 23 5, 2 36, 237-9 c hromosom e number 279 circ ulatory system 14 3. 14 9 class ifi catio n 11-1 2 diffusion in 84-6 ears 2 32- 5 efficienC)I Of J'o od Chai n s 36 e ndocrine syste m 2 17- 19 and th e enviro nme nt 63-4· e xc re tory sysrem 184-8 eyes/eyesig ht 226-32 fe rt ilisa tion 250 gaseous exchange 130-4 gaseous excha nge in lungs 136- 7 min era ls needed by I 04-5 movement in 355 n ervous system 2 J 1- 17 nutritio na l require111e11ts I 06-7 a nd pla nt /anima l d iseases 275 pop ulat io n growth 54-5, 64 reprod uction in 246 respi ratory syste m 13 1 sense o rga ns 2 10- 1 I skele ton 199-204 skin section 237 teet h 109 vitam in s needed by I 03 h umid ity, and tra nspira ti on rate 167 hum us 28, 337 hunting 65 h yd rochloric acid 113, I 14 h yd rogen pe ro xide 345 h ydrophyres J 67, 168 hyperm et ro pia 23 1 h ypertension I 08, I 52, 272 h yperto n ic sol ut io n 86, 87 h yphae 5 h ypogeal germ ina tion 177 hypotha la mus 189, 2 16, 219, 237 h ypoto ni c solu tio n 86, 87 ide ntica l twi ns 279, 285 differences be tween 297 variation 3 1 1 ileu m 1 14-15 im m o va ble joints 203 immune response 154 immune syste m 2 54 immu nisation 15 5 lmpnriens 300, 30 I im pla ntatio n 250 inbreedin g 3 18 incisors I 09 incom plete domin a n ce 300 ind ividua ls adaptation to the e nvironme nt 313 in a popu la tion 33 1- 2 Indust rial Revol u tio n 45 industria l sewage trea tment 69 indu strialisa tion 64. 70 an d pollu tio n 68 and wa te r s hortage 66 infectious diseases 55 infl uenza 272 ingestio n I 08 in ne r ear 232-3 inorganic n ut rients IOI , 104-5 in sect icides, resistance to 314 in sects 8 aph ids 170 pollinatio n 262-3 in spira tio n 133. 134 in suli n 2 18, 321 intercosta l muscl es I 34 Lnte rnationa l Un io n for the Con serva tion of Nat u re (I UCN) 64 im e rphase 2 79- 81 , 2 92 intestine see la rge intestin e; small int estin e in t ra- ute rine device 253, 2 54 invasive s pecies 53 inve rt e bra tes respo nse to sti m uli 210 see also insect s iodine I 05 iris (eye ) 226. 227- 8 iron L04. 150, 183 de fi ciency 272 irr itability 3, 209 isoton ic solutio n 86 Jamaica, min e ral resources 56 Jamaica Hope 3 19 Jama ica Red Poll 319 joints 202 types of 203-4 kidneys 184-8 fa ilure 188 lon gi wdinal sectio n 185 osmoregu la t.ion 184, 189 press ure filtrat ion 186 se lective rcabso rp tio n 186 transplan rs 188 kingdoms 3-4, I L J 2 knee jerk reflex 215, 357 kwash iorkor 107 lab w rit e- up 328- 9 labo u r 252 lactati o n 106-7 lact ea l capil lary 1 15 lactic acid 126 lamellae 136, 137 land po ll ution 67 large intesti n e 11 5 lcacl1in g 4 8, 70 lead 20- 1 leaves adaptations fo r photosynthesis 93-5 cells and tissu es 82 chloroplasts in p h otosyn thesis 95-6 evapora tion o f water from 164 food storage 174 gaseous exchange 135, 136. 137 m ovement of wa te r withi n 164 sect ion o f a 94 starch in 340 legumes I 06 legu m inous p la nts 29. 4 7 lens 227- 8 accommoda tion 22 8- 9 converging 23 1 diverging 231 Lesser Antilles 3 15- 16 life, characteristics o f 2. 3 lifestyle, a nd h ypert ension 152, 272 liga m e n ts 202-3 light a biot ic facto r 333 in photosynthesis 92-3, 96. 97, 34 1 phototrupism 197- 8, 2 J 0, 353 and species d is t ribu Lion 20 and tra n spiratio n ra te 167 ligh t mic roscopes 78 light rays, focusing 227- 9, 231 lig htni ng 47 ligni n 16 1 limbs, 111ovem ent 202-3 limiting factors 96-7 li ne transects 332 Li nna eus, Carl I 0-1 I lipase 11 4 lipids 101, 102 digestion I J 0- 1 1, 11 4, I 15 metabol ism I 17 tests I 04 see also fats liver cirrhosis 221 food storage 178 fu nctions of 1 17 living organ isms binomia l system I 0- 12 ce ll special isation 81-3 classifica tio n of 2 d ecom position 28- 9 ecology and environment 1516, 23, 331 -4 major groups 3-9 o rga nic compo unds in 42- 3 respira tio n 122 transgenic 32 1 va rie ty of 2-14 visible characterist ics 9-1 0, 330 see also animals; pla nts liza rds 236 lucom ot ion 196 lo ng bone 199, 20 I long-sigh tedness 23 1 loop o f Henle 185, 186, 187 lumbar vertebrae 200- 2 lu ng ca nce r 137, 138 lu ngs d iffu sio n in 85 gaseous exch a nge 13 1-3. L36 lymphocy tes 150. 154. 254, 255 m agnesi um 92, I 00, I 04 magn ification 78, 79 ma laria 5, 30, 273-4 su sceptibil ity to 320 m a le nutritio nal requiremen ts 106- 7 re producti ve syste m 246-7 371 Index ma lnutrition 107 ma lpighian layer 23 7 m a mmals charac1eris1ics 9 reproductive cells 359 respi ri ng cells 123 tempera tu re reg ula ti on 238 ma ngroves 6 des1ructio n of7 1 zones of vegetation 19 marasmus l07 marijuana 139, 220 mecha nica l dispersa l 266 medulla 185 medulla oblongata 216 meiosis 245, 246 im porta nce of 290- 1 process of 291 -2 significance of 293-4 vs mi1osis 292 memory lym phocytes 154 meninges 2 16 menopause 249 menstrual cycle 249 menstrua tion 247, 248 mercu ry 20- 1 mesoph yll cells 94, 95 mesophytes l67 metabolism 117, 181 - 2 proteins 117, 183 metaphase 279- 8 1 metaphase I/II 292, 293 m ice, coat colo ur 305 microhabitat s 16 micronutrients 20 microorga nisms 80 see also bacteria; viruses m icroscopes 7 8 microvilli 114 m iddle ea r 232-3 migra tio n 317 milk teeth J 09 mined areas 73 minerals (dieta ry) IO I, 104-5 requirements I 07 storage I 17, 178 minerals (resources) 56 minerals (soil) 168 miiochondria 7 9. 124 mi1osis 244, 27 9-8 1 and asex ua l reproductio n 282-8 process o f 282 vs meiosis 292 MMR vaccine 155 molars 109 mollu scs 8 monocotyledons 7 monosaccharides IO1-2. I 03, 110- 11 monosod ium glutama te I 05 mosqui1oes 273 cont rolling 274 DDT- resistant 3 14 mosquitofi sh 3 17 · m otor ne uro nes 211-1 3 response IO stimuli 214 372 mo uth I 11-12 movement 3 in a nimals 196, 354-5 and ba lance 234-5 by diffu sion 84-6 energy through rood chains 35-6 joints 204 limbs 202-3 mine ral sahs in plan1s 168 by osm osis 86- 7 in plants 163-6, 197-9 skel et0n a nd 199 substances in cells 8 3 wa ter 1hrough a pla nt J 63- 6 see a lso tra nspon system muscle cells 82 m uscles movement 202- 3 see a lso individual muscles mushrooms 6 mutage ns 319 muta tion 282, 3 19- 20 muLUalism 29, 47 m yopia 231 naw ral cla ssifica1ion 9 natura l imm unity l 54 nawra l select.ion 294, 313 an d evolu1io n 3 13- 17 investigating 364 vs artificia l selec1io n 3 18 near-sightedness 231 nectar 262 nega tive feedba ck 19 1- 2 nematodes 8 nephrons 185- 6 nervou s pathway 2 12, 213 nervo us system 2 1 1-17 neural canal 202 neura l spine 202 neurones 82, 2 1 L- 13 niches 16 nicotine 137-8, 252 nit.ra tes 47, 48 ni trification 48 nitrogen 47. 92. 100-1 , 104 cycle 46-8 fixation 47-8 ni1rogen oxides 47, 49 nitrogeno us was1e 143, 183, 184 in Lhe kidneys 184 non-biodegradable ma te rials 57, 67 non- re newable resources 55 1iose 211 , 225 nucleus 79 in cloni ng 286 fo rma tion 281 numbe rs. pyramids o f 37- 8 nutritio n 3 holozoic I 08 human requ'iremen ts I 06-7 ma lnutrition l 07 see a lso diet; rood obesi1y 55, 108, 178 ocelot 12 oesophagus 1 12-1 3 oestrogen 248, 249, 250. 253 offspring genotype and phenotype 299, 300 sex determ inatio n 302, 362 varia tio n among 293-4 o il po ll ut ion 67 o m ni vores 25 o pportu nistic infections 254. 255 o ptic nerve 227 da mage IO 232 order I I, 12 orga nell es 79 organ ic nu1rients 10 1-4 orga ns 82- 3 protection or 199 se nse o rgans 210- 1 I. 225-6 osmorcgu la1 ion 184, 189 nega1 ive feedback 191 osmosis 86~7. 95-6. 164, 165-6 effects of 339 ossicles 23 3 osteoporosis 138 ou tbreed ing 3 18 ou te r ear 232-3 oval window 233 ovaries 246. 24 7 ho rmones 248 in plants 264 over-fish ing 65, 7 1 ovulat io n 249 o vu les 26 1, 262. 264 ovum 246, 247, 359 cloning of fertilised 286 feni lisa tion 250 release o[ 248, 249 oxygen in air I 33 biochemica l demand 68 d iffusion 85, 142-3 from pho tosynthesis 92- 3. 96, 344 in respiration 123, 349 1ra nspo n in blood 150-1 1ranspo n in th e body L43, 148, 150 see also gaseous excha nge oxygen de bt 126 oxygenated blood 132, 145 , 149 oxyhaemoglobin 151 oxytocin 252 'pacemaker' 146 pa inkillers 220 pa li sade layer 93, 94 pancreas 2 18 pa ncreaticju ice 114, 218 parasitism 30 pa nially movable joims 203 pa nu ri tio n 252 passively acqu ired immu nity 154, 155 pa1 hoge nic diseases 272, 273 pathogens 153-4, 272, 273, 274-5 pedigree charts 304-5 pelvis 185 pen ici ll in 6, 220, 313 pen is 246, 250 peppered moth 3 14 pepsin 113 peptic ulce rs 114 perennat ing o rga ns 176 pe ricarp 264 peripheral nervous system (PNS) 2 11 { peristalsis I 13 permanent 1eeth I IO permanent vacuole 79, 80 permeable membrane 84 pesticides 199 bioaccumu lation 38 DDT 38- 9, 3 14 effects a nd control o r 67 pe1als 26 1. 262, 263 pH 49. 333 o p1imum I l L phagocytes 150, 153 phenotype 298-9 co-dominance 30 l amt the environ mem 3 11 haemophilia 303 incom plete dom ina nce 300 sickle cell anaem ia 304 1es1 cross 300 ph loem 93, 94 and move me nt of food 169- 70 s1rucw re o f 162 in vascular bund les 163 phosph o rus 104, J 05 pho1o meter 350 pho1osy111hesis 24, 161 and carbon d ioxide 92- 3, 95, 97, 343 and chloroph yll 342 chloroplas1 in volvemen1 in 95-6 equa1ion 33, 92 lea f adaptations for 93-5 and light 92- 3, 96, 97, 34J lim iLing factors in 96-7 oxygen from 92- 3, 96, 344 waste products 183 photo1 ropism 197-8, 2 10. 353 ph ylum 7-8. I I. 12 physica l d igestio n I 08 ph ysiological diseases 272 ph ytoplan kton 24 pinna 233 pilllil ary gla nd 189, 2 16, 2 19 pituita ry growth hormone 219 pivot joint.s 203 placenta 2 5 1-2 plan t cells 79-80 os mosis in 86- 7 in respiration 125 plan1 growth and gra vit}' 351 and light 353 plant horm o nes 199 plants 3, 6-7 and acid rain 49 ada pta1ion LO ligh1 20 adap1atio11 10 water 18- 19, 167-8 Index in the carbon cycle 43. 44 excretory produ cts 183-4 fertilisation in 260, 263-4 food ma nufacture 91 - 2, I 00 food sto rage in 173- 8 ga in and loss o f energy 34, 35 gaseous exchange 135, 136, 137 heavy metal tolerance 21 legu mino us 29, 47 life cycle 259- 60 minerals and 104, 168 movement .in 163-6, 197-9 in the nitrogen cycle 46- 7 photosy mhesis see photosynt.hesis as producers 24-5, 26 respo nse to stimul i 21 O selective breeding 3 18 tissues, organs and systems 83 transpo rt system 161-3 t ra nspon th rough 160-1 , 168- 70 variation 3 11 see also crop pla n ts; flowers; leaves; living o rga nisms; roots; stems plasma proteins I 17 platelets 149, 150 plat yhelmimhes 8 plumules 177 poi kilothermic an imals 20, 235- 7 pollen gra ins 26 1. 262, 263 pollination 260, 262-3 pollu ta nt s acid ra in 49 fl uorides as I 1 o heavy metals 20 origin, effects and control 67- 8 pol lution 66- 9 fro m human activiti es 20, 64 mangrove swamps 7 1 red uction of 72 a nd water sho n age 66 polysaccha rides 102. 103, 11 0-11 pond ecosystem 16-17 population 16 geographica l isolation 3 15 in na t ural a nd artificia l select ion 3 18 size 33 1- 2 po pulation growth 52-3 facto rs red ucing 53-4 human 54-5, 64 post na ta l care 252 potassium I 04 potassium manganite 338 predawrs 26-7 and populatio n growth 54 pregnancy 250 alcohol during 221, 252 drug a buse in 252 fetus 25 1-2 and HJ V/AIDS 254 m11ritional requiremen ts I 06-7 pn:mola rs I 09 prena tal ca re 252 prescription drugs 219-20, 252 preservatives I 05 pressure fi lt ra tion 186 pressure- flow hypothesis 169 prey 26- 7 primary consu me rs 26. 35 producers 24-5, 26, 35-6. 92 prod uct ivity 35-6 prod ucts (in digestion ) 111 progesterone 249. 250. 253 proka ryotes 3, 4-5 see a lso bacteria prolact in 253 propagatio n see vegetative propagat ion propellants I 05 prophase 279-8 1 prophase I/I I 292 prote ins 101 . 102 a nima l and plam 46-7 digestion 11 0-11 . 113, 114 metabo lism I 17. 183 requ irement s I 07 tests I 04 see also enzymes protoctists 3, 5 prowzoa 5. 81 see also a moeba proxima l convolut ed tubule 185, 186 psychoactive drugs 220 pubert y 248 pulmonary circu lation 149 pupil (eye) 226, 227- 8 effect of size 229- 30, 357 refle x215 pyramids biomass 38 energy 36-7 numbers 37-8 quadrat s 334-5 radicles 177, 352 ra dioisotopes 169 reabsorption 186, 187 receptacles 261 receptors 2 11- 13, 2 14 touch 356 recessive a llele 298 recipients 151-2, 188 rectum 1 15- 16 recycling 58, 59 red blood cells 149-50 amigens 15 1-2 breakdown I 17 manufa cture of 199 oxygen tra nsport 15 1 sickle shaped 3 19-20 waste prod ucts from 183 reduction of waste 57. 59 reflex act io ns 2 15, 357 re flex arc 2 15 refraction 227-8 relay neu rones 2 12 renal artery 184, 187-8 rena l ve in L84, 187-8 renewable resources 55, 56 ren nin 113 replica tion 282 reproduction 3. 244 in humans 246 see also asex ual reprod uction; sexual reproductio n reproduct.ive cells 290- 1, 359 reproductive system female 247 ma le 246-7 reptiles 9 resources conserva tion of 72-3 destru ction of 70 ene rgy 56 limi ts of 55 minera l 56 reducing consumption 56-9 respira tion 3. 34 aerobic 122-4, 12 5 ana ero bi c 125- 7 ca rbo n dioxide from 123, 182, 347 equa ti on 43 gases involved in 85 heat production from 348 oxygen in 123. 349 waste product.s 123, 182- 3 respiratory system, human 131 response to stimu li 209- 10, 2 14 in sense o rgan s 225- 6 retina 2 10. 227-8, 230 reuse of waste 57 Rhizobiu111 29, 47 rh izomes 175 rh ythm method 253 ribs 134 rickets L03 ringing 170 rods 230 root ha ir cells 166 root pressure 165 root lllbers 176 roots development I 77 food storage 176 movement of wa ter across 165-6 tropism 198 vascular bu nd les 163 runners 283 sedime matio n test 334 seedlings 177 growth in 198 movemem in 197 seeds 176-7. 260 deve lopmen t 263-4 dispersal 264-5 see also frui ts selection pressu re 31 4, 318 selective advantage 313 selecrive breeding 3 18 selecti ve reabsorption 186, 187 selecti vely permeable m embrane 86, 188 sel f-dispersa l 266 self-po llinatio n 262 semen 246 semi-l unar valves 145 semici rcular canals 234 seminife rous tubu les 246 sense o rgans 210-1 1 stimuli respondi ng LO 225- 6 sensory neu rones 2 I 1-1 3 response to SLimuli 214 sepa ls 261 sewage 67 treatment 68- 9 sex d1romosomes see gametes sex determination 302, 362 sex -linked cha rac1eristics 303 sex ual intercou rse 246, 250 sex ua l reproduction 245 in plants 259-60 shoots see stems shopping, environment and 59 sickle cell anaemia 272, 282. 303-4 and mu tation 3 19- 20 sickle cell disease 320 sickle cell tra it 320 side effects 2 19 sieve tubes 162, 169 sight see eyesigh t sigmoid growth curve 53 skeleton I 99- 204 functions of 199 skin 21 1,235 ca re of 239 physica l barri er 153 section th rou gh 237 and stimuli response 226 temperatu re control in animals 235- 7 temperature control in birds 239 sa ccu le 234, 235 sacrum 200, 201 temperature control in humans saliva 112 237-9 sa liva ry glands 217 touch receptors 356 sa lt wa te r 17- 18, 66 small int estine 114-1 5 sa mpling methods 33 1-3 cells and tiss ues 82 saprophytes 29, 9 1, 92 smoke 68 scle ra 226, 227 smoking 55. 137-8 scurvy 103 in pregnancy 252 sea levels 46 and skin damage 239 sebaceous glands 237 social implications diseases 275 secondary consumers 26, 35 drug abuse 222 secondary sex ual d 1aracterisrics 248 secre tion 83, 182, 218, 2 19 HIV/AIDS 255 373 - - Index soil abiotic factor 334 conse rvatio n 73 degrada tio n 70 erosio n 69- 70 mo isture in 209 percentage o r a ir in 337 pe rccn Lage of wa ter in 336 a nd species d ist ribution 2 1 water- ho lding capacity 335 sola r e nergy 33--4 so und waves 23 3-4 species I I , 12 Ano lis lizards 3 16 chromosome n um be r 278, 279, 28 1 Darwin's fi nches 3 15 d istri butio n o r 17-2 1 a nd eco logy 3 17 e ndangered and vu lnerable 64. 65, 73 extincLion 64-6, 70 ge ne tic va riatio n 3 10, 3 11 geno type 296 invasive 53 surviva l o r 294, 3 11 spermatozoa 246, 248. 359 release of 250 spermi cide 253, 254 sphincter mu scles 184 spinal cu rd 2 16. 217 spinal reflexes 21 5 spo res 6 sta mens 26 1. 262, 263 staple foocls I 06 sta rch 96, I 02 hyd rolysis 11 2 in a leaf 340 sto rage in pla nts 174 tests I 03 sta rvat io n l07, 32 1 STDs (sexua lly transmi tted diseases) 254-5 pa th ogens and 274-5 protection aga inst 253 stems develop me m 177 food sto rage 174-5 photot.ro pism 197- 8 vascular bund les 163 ste rilisaLio n 253 steroids 220, 3 18 stigm a 26 1. 262, 263 stimulus 209- 10 in the ne rvo us pathwa y 2 12. 213 recep to rs, e ffecto rs a nd respo nse 2 14 i reflex actio ns 2 15 respo nse to sense o rga ns 225-6 sto lo ns 283 stomach I I 3-14 stoma ta 93, 94-5, 135 in evapora tio n 164 374 SLro ke I 08, I 52 su b-phylu m I I , 12 su bstra te I 11 sucrose 96, I 0 2 Lests I 03 transport 169 sulfur I 04 su lfur diox ide 49, 68 surrogaLe mo th er 285-7 survival of a species 294. 3 11 s11spenso ry liga men ts 227. 228, 22 9 sustainabili ty 72 su Lures 203 swea ting 238 sweep nets 333 sweeteners I 0 5 symbiosis 29-30 synapse 2 13 synovia l jo ints 204 systemic ci rculation L49 system ic herbicides 199 sysLems 82-3 systo le 145-6 tra nq uillise rs 220 transgenic orga nisms 32 1 tra nslocatio n 168- 70. 199 t ranspira tion 164. 166-7, 350 pull 165 rate 167 transport syste m in a nimals 142- 3 food t hrough pla nts 168- 70 in pla nts 161 - 3 sce also blood; hea rt ; move me nt tra nsvcrse process 202 trees, commensa lism 29 tri cuspid valve 1.45 Trin idad a nd Tobago, e nergy resources 56 Lrophic levels 26 bioaccumu latio n 39 pyramids of e nergy 37 pyra mids o r numbers 37, 38 tropisms 197-8 trypsi n I 14 tuba l liga tion 253, 254 tu bers 175, 176 turgid cell s 86, 94-5 tympani c mem bra ne 233--4 T-lymphocytes 254, 255 tap roo ts 176 ta r 138 tanrazine I 05 unde r-ea ting 107 taste buds 2 1 I, 225 unde rground stems 174-5 tear glands 2 17. 226 unicellu lar o rganisms 80- 1 teeth I 08- 10 urea 183 te lophase 279- 8 1 u re ter 185 te lo phase I/II 292 ureth ra 1.84 te mpera wre urine 184, 187 concent ra ti o n 189 a biotic factor 333 and enzyme cat alysis I I I production 185 glo bal range 235. 236, 237 ute rus 247 globa l wa rming 45-6 fe ta l developm ent 251 and ph o tosynthesis 96 lining 249, 250 a nd species distributio n 20 uLricl e 234, 235 a nd tra nspiratio n rate 167 see also bod y tem pe ra ture; hea t vacci natio n 155 vagi na 250 te ndo ns 203 te rrestria l food diai ns 26 vascular bund les 163 Lerrcstria l rood webs 27, 3 1 vasecto my 253, 254 vasoconst riclio n 238 te rtia ry consumers 26, 35 test cross 30 0 vasud ila tio n 238 testa 177 vectors 236, 273--4, 322 testes 246 vege tables I 06 ho rm o nes 248 vegetative propagat io n 245, 283 testoster~.~Sf.4~· -·· ~·' · · '-'"'' _ ,, _.., . ·. :/r~'.fi~i~ l 284-5 thoracic vC!nc5fAe- WO~ .: · , •.. .ve111s .1'4'6'; -14'.7-,8 t ho rai 1 3~(<-:U ;4 ~ :\ • '1~ · _. 1 . ·.;::,'.~xi~~a -~iivC:l."4.8 ~ tissue cul tnf~ 'Z8~i ,.. • ; ~- ve.ilfril:lei t.f44f6 tissue fl u~ -~-90 [_ · 1 , , '. ' 1 ..."_~ -~.~· vcfitne!>i.146,).47 concehrrat10H·· U.91 , . . . ,,. . " ·. ' vette htai,:":2'0~2 tissues 82-3 · - ·" verlcbra·l- c~1w:ii111 200-2 tongue 21 1. 225 vert ebra tes 8-9 to uch rece pt ors 356 vesicles 83 • vestibu lar appa ra tus 233, 234 toxic che mica ls 20. 67. 68 villi I 14- 15 waste produas 182 trace eleme nts I 04 viruses 4. 80, 272 trachea 11 2. 132, 133 vectors 322 .".i: ·;::.- '. visibl e characteristi cs 9- 10, 330 vita mins IOI , 103 req uirem ent s I 07 slOrage I 17. 178 vuln erable species 64 waste products build-up o r 190 cell ular 83. 148 e nvironmental 57-9, 64, 67 or pho tosyn thesis 183 respi ratio n 123, 182- 3 see also excretory products; nit rogeno us waste water conserva tio n in pla nts 167- 8 in the d iet IO I a nd disease 274 d ispe rsal by 265 flo w 334 movement th ro ugh a pla nt 163-6 in photosynt hesis 92-3. 95-6, 97 rea bsorptio n 187 shortage o r 66 in soil 335-6 and species distribu tion 17-1 9 wat er poll mio n 67- 8 mangrove swamps 7 1 white blood cells 143, 149-50 defence against d isease 153, 154 manu fa ct ure of 199 whi te ma iler 2 16 WH O Expa nclcd Program of Immunisa tion 155 wind d ispe rsa l 266 po ll ination 262- 3 speed 333--4 a nd transpi ratio n ra te J 67 w isdo m teeth I IO withdrawal sympt oms 220, 221 wolves, body hair 3 I I xeroph ytes 18. 167, 168 xylem 93. 94, 95 structure or 161 - 2 in vascula r bundles 163 in wa le r m oveme nt 164, 165 yeast 6 anaerobic respiratio n 126 budding 359 yoghurt manu fact.ure 127 zones or vegetatio n 19 zygote 250 d ivisio n 285, 286 Biology for CSEce Examinations is part of a well-established series of books aimed at students preparing for their CSEC Science studies. Rejuvenated In a third edition, Biology for CSEC- Examinations featul9 comprehensive, systematic coverage of the latest CSEC syllabus (2013). Written by an expert team of science educators, this revised edition benefits from a new, clear and accessible design and the most up to date aclentiftc Information. Key features of the CSEC Science series: • Intuitive and easy-to-follow format makes It simple to study a whole topic, or to find answers to specific problems • Regular consolidation (In-text questions and exam preparation) checks understanding and reinforces learning • New group-work feature tests students' Investigative and problemsolvlng skllla and demor.sbates real-wor1d applications of key syllabus points • Practical activities aid experiments throughout the text encourage hands-on learning • Dedicated School-Based Assessment section gives step-by4pp tips to maximise success in the CSEC coursework. ~ CSBC• is a registered trade mark of the c:arlbbean 'Ruminations Council (CXC). BiOioqy for CSBC- Bzaminations is an lnd.epCodcnt pubUcadon and bas not bcc:ii authorized. spomored. or otherwise approved by cxc. ISB N 9 78 ·0·230·43883·5 ,II'~IJllJll~JIJIJIl,~l l

Biology for CSEC 3rd Edition

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