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Contents lntroduction 1 Unit 1 Characteristics and classification of living organisms 1.1 Characteristics of living organisms 1.2 Classification 1.3 Arthropods 1.4 Vertebrates 1.5 Microorganisms 1.6 Flowering plants 1.7 Use of keys Summary and exam questions Unit 2 Cells 3 2 4 6 8 10 12 14 16 24 Movement in and out of cells 26 26 3.1 Diffusion 3.2 Osmosis 3.3 Osmosis in plant and animal cells 3.4 Active transport 28 30 32 Summary and exam questions 34 Enzymes 36 Unit 4 4.1 Structure and action of enzymes 4.2 Factors affecting enzyme action 4.3 Enzymes in industry Summary and exam questions Unit 5 Nutrition 5.1 Nutrients 5.2 Chemical tests for nutrients 5.3 Sources of nutrients 5.4 Use of microorganisms in industry 5.5 Food additives 44 44 46 48 50 nutrition Photosynthesis 56 56 6.2 What is needed for photosynthesis? 5g 6.3 Products of photosynthesis 60 6.4 Rate of photosynthesis 62 Summary and exam questions 64 66 6g 70 Plant transport 8.5 Unit 88 90 92 environments 94 96 98 9 Transport in humans 100 100 102 104 (CHD) Summary and exam questions Unit 10 Respiration 10.1 Respiration 1 0.2 The gas exchange system 10.3 Gas exchange 10.4 Breathing 10.5 Rate and depth of breathing 10.6 Anaerobic respiration Summary and exam questions Unit 11 Homeostasis and excretion 11.1 Controlling conditions in the body 11.2 Controlling body temperature 11.3 Excretion 11,4 Kidney function 1.5 82 84 86 Translocation Summary and exam questions 9.1 Circulation 9.2 The heart 9.3 Blood vessels 9.4 Coronary heart disease 9.5 Blood 9.6 Blood in defence 9.7 Lymph and tissue fluid 1 72 74 76 78 80 88 8.1 Transport systems 8.2 Water uptake 8.3 Transpiration 8.4 Adaptations of plants to different 52 54 6.5 Glasshouse production 6.6 Leaves 6.7 Mineral requirement5 8 Unit 36 38 40 42 Summary and exam questions Unit 6 Plant 6.1 Summary and exam questions 18 20 22 Summary and exam questions 72 7.2 Balancing energy needs 7.3 Starvation 7.4 Digestion 7.5 Teeth 7.6 The stomach and small intestine 7.7 Absorption and assimilation 2 18 2.1 Structure of cells 2.2 Different types of cells 2.3 Levels of organisation Unit Unit 7 Animal nutrition 7 .1 A balanced diet Kidney dialysis and kidney transplants Summary and exam questions 106 108 110 112 114 116 116 118 120 122 124 126 128 130 130 132 134 136 138 140 Contents Unit 12 Coordination and response 12.1 Nervous control in humans 12.2 Neurones and reflex arcs 12.3 Reflexes and antagonistic muscles 12.4 Sense organs 12.5 The eYe 12.6 Hormones '12.7 TroPic responses SummarY and exam questions Unit 13 Drugs 13.1 Drugs and how theY work 13.2 Heroin 13.3 Alcohol 13.4 Smoking and health SummarY and exam questions Unit 14 ReProduction in Plants 14.1 Asexual and sexual reproduction 14.2 Flower structure 14.3 Pollination 14.4 Fertilisation and seed formation 14.5 Fruits and seeds 14.6 Growth and develoPment SummarY and exam questions 142 '142 '144 '146 '148 150 152 't54 156 158 158 160 162 164 166 15.3 Fertilisation and imPlantation 't5.4 Preg na ncY 15.5 Ante-natal care and birth 15.6 The menstrual cYcle 15.7 Sex hormones 15.8 Methods of birth control 15.9 Sexually transmitted diseases Summary and exam questions Unit 16 lnheritance 16.1 Chromosomes, genes and DNA 16.2 Mitosis and meiosis 16.3 Genes and chromosomes 6.4 MonohYbrid inheritance 16.5 Codominance 1 SummarY and exam questions genetic engtneering SummarY and exam questions Unit 18 Energy and nutrient transfer 18.1 Food chains and food webs 18.2 Pyramids of number and biomass 18.3 Shortening the food chain 18.4 Nutrient cYcles 18.5 The nitrogen cYcle SummarY and exam questions Unit 19 Human influences on the ecosYstem 214 214 216 218 220 222 224 224 226 228 230 232 234 SummarY and exam questions 236 236 238 240 242 244 246 248 250 252 254 Alternative to Practical PaPer 256 Revision checklist 262 192 GlossarY 270 194 196 lndex 279 Acknowledgements 284 168 168 170 172 174 176 178 180 Unit 15 Sexual reproduction in humans 182 182 15.1 The male reProductive sYstem '15.2 The female reProductive system Unit 17 Variation and selection 17.1 Variation 17.2 Mutations 17.3 Natural selection 17.4 Artificial selection and 184 186 188 190 198 200 202 202 204 206 208 210 212 19.1 PoPulattons 19.2 Human PoPulations 19.3 Resources 19.4 Pollution '19.5 The greenhouse effect 19.6 Acid rain '19.7 Water Pollution '19.8 Conservation 19.9 Sewage treatment and recycling lntrod I ction Ttris book is designed specifically for Biology TGCSE (Syllabus 0610) and is fully endórsed by Uñíversity of Cambridge tnternational Examinations (Clf). Cíf IGCSE Principal Examiners have been involved in all aspects of the book, including detailed planning to ensure that the content gives the best match possible to their syllabus. Using this book will ensure that you are well prepared for the Biology IGCSE examination and for studies beyond IGCSE level in pure sciences, in applied sciences or in science-dependent vocational courses. The features of the book outlined below are designed to make learning as interesting and effective as possible: . These are at the start of each spread and willtell you what you should be able to do at the end of the spread c .9 c a) x t¡.t . Some outcomes will only be needed if you are taking paper 3 and these are clearly labelled, as is any Supplementary content in the spread EXAMINER SAYs... thLs.provLdes a chawce To r th e. tqes E priwcL¡ aL Ç. xawLwers to ,tnare-i[,ei, expe.ñ.ewoe gf wawg Aeafs warleíwq awd tr*t^ø exawLiatLows i:X"u::^yy"riJi,H"" , i -. cowwow errors or gLve advLce ow how \t.f!L to taclzLe 1uêstLows. ÞID YOU KNOW? These are not needed in the examination but are found throughout the book to stimulate your interest in biology. PRACTICAL These show the opportunities for practical work. The results are included to help you if you do not actually tackle the experimánt or are studying at home. These summarise the most important things to learn from the spread. SUMMARY QUESTIONS Ihese questions are at the end of each spread and.allow you to test your understanding of the work covered in the spread. At the end of each unit there is a double page of examination-style questions written by the véry CIE -aiology Examiners that set the papers for the 06t 0 exams. ln most cases the questions are only set on the contents of the unit. ln the examination you will find questions that deal with the contents of iwo or more units. ln Papers 2 and 3 you may have to complete graphs by adding labels and unrts for axes, plotting points, adding bars to bar charts or joining points or giving lines of best fit. you will not have tõ draw the axes yourself. You can also expect to have photographs which are not included in these questions. At the end of the book you will also find: Alternative to practical' section - this provides guidance if you are taking Paper 6 instead of coursework or the practicaltest. A useful Revision checklist is also provided to help you prepare for the examination in paper 1,2 and 3. . List the characteristics of which are Biology is the study of living things or,livìng organisms' kingdoms: ctass¡iãd into five major groups called (bacteria) animals, plants, fungi, protoctists and prokaryotes . living organisms Describe the characteristics of living organisms These There are seven characteristics of living organisms' processes: characteristics are often described as life respiration, movement, growth, excretion' sensitivity' L ì ,-rt ìlrliiirliÍ r iíilili l{ i{r,ii/1, ), nutrition, reproduction. Nutrition and substances Nutrition is the obtaining of food to provide energy that may compounds are Nutrients ..lJà¿ for growth and iepair. or complex (like carbohydrates, proteins and vitamins) simple (like mineral ions). in which the Nutrition in green plants involves photosynthesis' dioxide carbon turn to used änd .î"tgy ttotiunlight is absorbed sugars plants simple these convert then ãnJ *.,., into siriple sugars. need They proteins' and cellulose into complex compounds", such as proteins' mineral ions from the soil to make ;i;;g. ;.i Salmon provide nutrition for bears EXAMINER SAYS... ætspLratLow Ls the reLease of ewergg front" food that ha;p1ws Lw aLL the LLvLwg oeLLs.Lwthebodg. ttLs wot breathLwg, whLch ha¡qews Lw orgaws, sttoh 'Ø# ØLtts or Lwwgs. plants, so they have to eat Animals cannot make their own food like nutrients' The process of and pìu'nit ãt ã,Áei animals to gain energy is digested, absorbed food The i;kì.é in tooa is caileJ ingästion. growth and repair' for cells by rt" af..'à blood and then aisimllated in faeces' egested is iooO *t"'l.f-, is not digested and absorbed Respiration energy' Respiration All living organisms respire because they all,,need down iÀuotu.i.ftãtlcal reactíons that occur in cells to break is nrti¡.ntt, such as glucose, to release energy Oxygen usually for nã.i.0 for respiraion to happen' This is the word equation respiration involving oxygen: glucose + water + energy released this energy for movement' growth' repair and + oxygen ---> Living things use carbon dioxide reproduction, Movement themselves into new Organisms move themselves or move parts of areas or to change Position. move down into the Plants move slowly when they grow' Their roots the light' Leaves can towards soil and their leaves and stems move up light as possible' much as move to face the Sun so they can absorb Most animals are abre move their whore bodies. They move to obtain their food or to avoid being caught by predators. some animari remain fixed to one prace throughouf their rives, but they ur"lor. to move parts. such as the tentacles on a sea anemone. Growth Growth is a permanent increase in size and the dry mass of an organism. It can involve an increase in ceil number; ceil size or both. rt arwãyiinvolves making more comprex chemicars, such as proteins, *r,"'r-.,-i, *hy the dry mass increases. prants carry on growing throughout their rives. Animals stop growing when they rea.h a certain size. Sea anemone Excretion EXAMINER SAYS... All living organisms produce toxic (poisonous) waste substances as a result of metabolism. Metaborism is ail the chemicar reactions occur in an organism. Respiration is a major part of metabolism. tÀat Excretion is the removar of these waste substances from the body. Plants store waste substances in their reaves, so the waste chemiäars are removed when the reaves fall off. Animars breathe out carboÀdioxide; other waste substances leave the body in the urine. Excre{øwktherew ,^*r^brf*;;;:;;";i:!:{ tsþodwhLchhasãsx;ea i:f th e g o ut wíth "Ø1. oeun4 dþæted.Þo o ut not oowfuse the two terA^.s. Sensitivity Living organisms are able to detect or sense changes in their environment. A change rike this is a stimurus (pru"rar: stimuri) sensitivity is the abirity to detect these stimuri and respond to them. Plants respond to movement of the sun by moving their reaves to face the light. The flowers of some prants open ¡n ihe morÃing and crose at niéHt Animals have sensory ceils.and sense organs for deteáing tigrìt, sãun¿í, touch. pressure and chemicals in the air and in food. Reproduction organisms reproduce to make new individuars. Asexuar reproduction involves one parent giving rise to offspring that are often idänticar to each other and to the parent. sexuar reproduction invorvesiwå pur.na organisms producing gametes (sex ceils) which fuse to give ,.iru to next generation. The offspring show variation. They areïot i¿enticario each other or to their parents. t" lí.1 I )i;' lÌ'1r ))r t')iirl,, The mnemonic, 'Mrs Gren, can help you remember the seven characteristics of living organisms: Movement causes an organism to change its position or place. Respiration involves chemical reactions that release energy in cells. SUMMARY QUESTIONS Sensitivity is being able to detect and respond to stimuli. 1 A visitor from outer space lands on Earth. The first thing that it sees is a motor car passing by. Growth is a permanent increase in size and mass. a b 2 two reasons why the visitor thinks that the car is arive Give two reasons why you think that the visitor is wrong. Give Plants and animals are Reproduction results in the formation of new individuals. Excretion is the removal of two groups of living organisms. Find out and then describe how prants differ from animars in the waste chemicals made in the cells during metabolism. a feed, b Nutrition involves the use of food for energy and growth. ways in which they: move, c grory d use their senses. I ir l^)'lliìù1ll lÌÑl(i,l . j)ili.l r({'l())iùf j lÌ L',; Define the term binomial system . Describe the external features of three invertebrate PhYla: nematodes, annelids and molluscs . Describe how the animals in these phYla are adaPted to their environment grouping is the We classify organisms into groups The largest is the species. smallest the LingJor'treã previous spread) and For features' similar ïÀuîtgun¡its in a kingdom share some carry and green plants are all .*utpí., within the plãnt kingdom, known groups into is subdivrded ári ptloiot¡lnthesis. Each kinglom three with we deal spread (slnsular: phvlum)' ln this ;;;;,ii" within the animal ,rJr-rór-,vrà (nÉmato'deí annelids and molluscs) are named' organisms how But first we must explain f.i.òi"t The binomial sYstem type of mongo-ose Meerkat, suricate and Sun angel are names for a confusion tf,ui ¡u.i in the Kalahari Desert in southern Africa. To avoid system binomial àrganisms are given scientiflc names using the (binomial means'two names')' They live in the A species is a group of individuals that look alike which are fertile give offspring to together same habitat añd breed and can also breed together' f two names: the first name is for the genus applies to one species and the second name is the trivial name that be used on its own' never genus. The trivial name should Each species is given *iif.ù the but.do not A genus is a group of species that are closely related' (plural of genus) only intÉrbreed wúh each other. Some genera This may be consist of one species, as is the case with meerkats because other species in that genus are extinct' the world as it is The binomial system is used by biologists all over The table has some organisms an internationál lungrug. for naming examples. A meerkat. EXAMINER SAYS... æcvwevwber that the waywe of a speoles Ls both wînLes. tf a wavt*e has beew vtsed owoethewLt oaw be shovtewed LLÞe thís: ..........Ft sa¡Lews. L-" common name scientific name meerkat Suricata suricatta human Homo sapiens baobab tree Adansonia cholera bacterium Vibrio cholerae malarial parasite Plasmodium falciParum oyster mushroom Pleurotus ostreatus lnvertebrates column lnvertebrates are animals that do nof have a vertebral orbackbone.onthenextpageisinformationaboutthreephylaof invertebrates: nematodes, annelids and molluscs' Nematodes Nematodes or roundworms are a group of worms that have thread-rike bodies that taper at mouth and ar,rs. ihey have no obvious head and no legs. Their bodies are not made up of segments. Most are very tiny and live in soils and water. There are many tlpes of nematoder, species are parasites living inside another aïimal, the host. 1\ t\,( ár" \ Annelids Annelids are worms with soft bodies made up of segments. Some have paddle-like extensions for moving and they harie chaetae or bristles.for making contact with mud ór soir. Most species of annerids live in the sea, but some live in the soil and in fresh water frtrurrr, lakes and rivers). \ Ascaris lumbricordes, a parasitic nematode. DID YOU KNOW? Ascaris lumbricoides is a parasitic nematode that lives in the human gut. lt absorbs digested food and can grow to a length of 30cml Earthworms burrow through soil. Io help them move through the soil, earthworms have a pointed front end to their oooy unjtt àf make mucus as a lubricant. Molluscs Molluscs have soft bodies that are not segmented. They have a muscular 'foot' that they use for burrowiñg or movement. Many species of molluscs have one or two sheils for protection. the animar is able to retreat inside the sheil if a predator is ciose by, or if Ú,uv n"uJ to avoid excessive water ross. some, rike the octopus, do not havé a sheil. Other animals in this phylum are snails. slugs, clams and squids. Bearded fireworm - an annelid 1 Copy and complete the sentences using the words below: fertile genus shared trivial classification binomial breed The system of putting organlsms into groups is cared The system is used for naming organisms. Each organism has two names. The first is called the name and the second the name. A species is a very similar group of individuals -. ,1u,.:uL rogether and prodlce classify living things on the basis of their 2 3 a b a b - _ - _- Banded snaii lil r i' 2 A species is a group of individuals, living in the same habitat that breed together to produce fertile offspring. 3 lnvertebrates are animals without a vertebral column (backbone). 4 Three invertebrate phyla are nematodes, annelids and them alongside their common names. 4 ln the l Bth century, Carl Linnaeus worked out the binomial system of naming living things. Find out about his life and work and then write a brief biography in your own words. "lrìr r¡iil:,, the genus name and the trivial name. Explain the term binomialsystem. Find the scientific names of two plant species and two animal species not mentioned in this spread and write a mollusc. 1 The binomial system uses two names for each species: featurãs. State three ways in which nematodes differ from annerids. State two features that are shown by both annelids and molluscs. - molluscs. Arthropods kingdom as it Arthropods is the largest of the phyla rn the animal in this phylum contains the largest number of species' Each species and (exoskeleton) ñãr u t.g*"nteá body, an external skeleton LEARNING OUTCOMES . Describe the external features jointed legs. of arthroPods . dry land When The hard exoskeleton allows arthropods to live on and grow a new moult they they grow too bi9 for their exoskeleton, Describe the features of nsects, crustaceans, moult during the ànã. Éotu mouliall through their lives, others only early stages of their life i arachnids and mYriaPods that are used to classifY them into . classes Eachphylumisdividedintoclasses.Wewillnowconsiderfourofthe Describe how the animals in these classes are adaPted to classes in the arthroPod PhYlum: crustaceans, myriapods, insects and arachnids their environment Crustaceans (head-thorax) Crustaceans have a body divided into a cephalothorax a very provides that anJ aOdomen. Many have a chalky exoskeleton have Crustaceans predators hard and effective protection against between two pairs of antennae and compound eyes They have gills' using five and 20 pairs of legs. They breathe on land but return Nearly all crustaceans live in water' Some crabs live some land to wáterto breed. Woodllce (also known as slaters) and crabsareexceptionsastheydonotUseWaterforbreeding.Examples of crustaceans include crabs, shrimps, crayfish and lobsters' Woodlouse or slater. Notìce its antennae for detectrng stimuli Myriapods centipedes and the millipedes They have long bodies made uP of manY segments' such as the thorax Thelr bodies are not divided into separate regions each segment and abdomen. Centipedes have one pair of legs on many segments how upon depends legs of so that the total number have powerful They carnivores' fast-"moving are th.r. ur". Centipedes These are the )' D rfÉ-%,t jaws and can ParalYse therr PreY' TheV a19. Millipedes have two pairs of legs on each body segment in leaf litter you feeding them find cãn often slow-moving herbivores. , Sally lightfoot crab, Grapsus grapsus Notice its large claws for feeding and defence Millipede - with its manY legs for moving efficientlY. Centipede - a fast-moving carnivore lnsects lnsects have bodies that are divided into three parts: head, thorax and abdomen. On the thorax there are three pairs of legs and many species have two pairs of wings. They have one pair of antennae on the head and compound eyes that are made of many tiny individuat .orpoÀ.nir. Th,ey breathe.through holes in the sides of ihe thorax and abdomen called spiracles. lnsects have colonised most habitats in the worrd, arthough there are very few species that rive in the sea. Two reasons whyihey are so successful on rand is that they are covered by a waterproof cuticre that stops them losing too much watel and they can Monarch butterfly, Danaus plexippus. Notice its wings for its migration over long distances. fly! This,is th.e largest group within the arthropods. Examples include beetles, flies, locusts, cockroaches, dragonfries, butteifries, bees and wasps. rotÀr, Arachnids These arthropods have bodies divided into and abdomen. two parts, the cepharothorax Arachnids have four pairs of legs and no wings. They have no antennae but do have several pairs of simple. not compound, eyes. They paralyse their prey with poison fangs. spiders are abre to weave silken webs with their spinnerets. This ãrass of arthropod arso includes scorpions, ticks and mites. 1 a b c Name four classes of arthropod. List the key features of insects. State three ways in which arachnids look different from insects. 2 Distinguish between the foilowing on the a b Tarantula - a large spider with venom to paralyse its prey. basis of visibre features centipedes and millipedes crustaceans and arachnids. DID YOU KNOW? There are over a million known species of insects and it is estimated that there may be 30 million species altogetheç but no one knows. 3 Describe the features of insects that adapt them for living successfully on land. 4 Copy and complete the table: feature number of pairs of legs body regions number of pairs of antennae type of eyes wings myriapods crustaceans insects arachnids lirl iir' i ilt'i tlr ' , 1 Arthropods are segmented animals with jointed legs and an exoskeleton. 2 Arthropods are classified into four different classes: crustacea ns, myria pods, insects and arachnids Vertebrates LEARNING OUTCOMES . Define the term vertebrate . Describe the five main classes . are called Animals that have a veftebral column or backbone made of erther skeleton internal an have vertebrates All vertebrates. chordata which includes bone or cartilage. They all belong to the phylum the vertebrates. some invertebåtes that share common features with of vertebrates using visible, external characteristic featu res Describe how these vertebrates are adaPted to here are frve maln cl¿sses of vertebrates: fish, amphibians, reptìles, birds and mammals' their environment species' such Most fish live in water permanently, but there are some lengths varyrng for water as the mud skìpper, that can survive out of of time. swimmrng and for Typically, fish are streamllned and have fins for pressure frufun.é. They have eyes and a lateral line for detecting lÀrng.t ìn water. Thãy breathe dissolved oxygen from the waler ,rtg-tt.r"it gills. Their tt in it covered with scales Examples include tuna, herring, shark, catfish and cod' I Fish for detecting Unlike fish, the other classes of vertebrates have ears soundandfourlimbs,althoughsomehaveevolvedintoleglessforms This dace has fins, tail and a streamlined shape adaPlations for swimming' like snakes and some llzards. Amphibians most These vertebrates have smooth, moist skin Although Fertilisation uÅpÁiuiun, Iive on land, they return to water to breed. is external because inrii" rp"rt uni eggs are released into the water (not eggs u female body). Development is external: the fertilrsed breathing' hatch into swimming tadpoles whìch have gìlls for but when On land, the adult amphibians breathe usrng lungs' Examples of tt.ì.y urà'in wateç they can breathe through iheir skin ,rþhìbiunt include frogs, toads and salamanders' Reptiles The bright red eyes of this tree frog are thought to startle predators, givìng time for the frog to escaPe loss They can lrve in Reptiles have dry, scaly skin to cut down water to breed' water to return to Ji¡l iléi".t as they dó not have Howeveç Fertrlisation takes place insìde the female's body waterproof development is external as they lay eggs with leathery' to breathe lungs have iÀells which stop them from diying óut Reptiles reptiles' all are air. Crocodiles, lizards, snakes, turtles and tortoises Birds as wings lVìost Birds have feathers and their front limbs are modified cannot ostriches' and penguins are able to fly but some, like ãi deal to adapted beaks have Birds have no teeth but different rp..i"t ifl.t with different American crocodile, Crocodylus acutus' tYPes of food. Fertilisation is internarand deveropment is externaras the femares ray eggs which are protected by hard shells. Birds are homeothermic (warm-brooded). This means that they are able to regulate their body temperature. they can keep it .onrtant even though the outside temperature changes. Examples include hawks, eagles, sparrows, parrots and starlings of birds Mammals Mammals are the vertebrates that have hair or fur. Fertirisation is internal and so is development. The young develop in a womb and they are born already well developui. ru.ñulu mammals suckle their young on milk from mammary glands. All mammals, even aquatil ones like whales and dolphins, use lungs for breathing Grey Heron, Ardea cinerea a bird with a long beak for catching fish. Like birds, mammals are arso homeothermic, maintaining a constant internal temperature. Leopards, bats, dolphins, bears, leñrurs and wolves are all mammals. EXAMINER SAYS... ::.yr,^, ã rw Le tabLe to heg gout e at .th fe u r es u ytve cLasses. >o this"¡itn Lw the sawc.wag as showw t e w nuestt ow + ow >,u a nL,,a irirîi åir,,Ír" , * nrî gou L¿qTwthLstopLc. ÞtÐ Y'ou KNOW? A chimpa nzee has hands and feet adapted to living in trees 'l Copy and complete these sentences using the words below: development five wings scaly moist land water classes breed fly fish fur fãathers are There different groups or sharks belong to the class called _ of vertebrate. and spend ail their time Amphibians have skin and return to water Reptiles have skin and lay their eggs on Birds have front limbs that are modifiãd to foiri They also have and most are able to Mammals or hair and give birth to their young in an advanced state of in to -. 2 a b c _ _- have _ .- -. State the features that are shown by all vertebrates. Name the five classes of vertebrates. 1 Vertebrates are animals that have a vertebral column or backbone. Give an example of each of class. 3To which class of vertebrates does each of the following belong turtle, bbat, cwhale, dsalamandel esnake, Í hawk, g shark? a Many amphibian species are threatened with extinction. Some rare Panamanian golden frogs were filmed for Sir David Attenborough's BBC W series life in Cold Blood. After the filming the frogs were removed to a zoo to protect them from disease, habitat loss and pollution. 2 The vertebrates are divided into five classes: fish, amphibians, reptiles, birds and mammals. Microorganlsms or Bacteria, viruses and fungi are all microorganisms (see page 2)' Viruses are kingdoms in-separate are fungr Bacteria and so they are Ãåì-firi"g organiims like the others we have considered microbes' LEARNING OUTCOMES . State the main features of bacteria, fungi and viruses . Describe the adaPtations classified in a different waY. dead and decaying Many species of bacteria arrcì furrgi break down (see page 230) Some matérial and these are called decòmposers food' for our making in used spà.ie, of bacteria and fungi are use of made have We wine .*rÀpf . yoghurt, bread, ch-eese and cause that Microbes (see page 22'l) iígãnetic engineerìng of each grouP to their environment ;i;;tJt disease are called Bacteria EXAMINER SAYS... :Èactewa you can see in the diagram' Bacterìa have a simple cell structure that in are spherical and some are rod-shaped Many exist length in short chains of cells. Most bacteria are a few micrometres (One microscopes electron and light with and can only be seen mrcrometreis one-thousandth of a millimetre ) iåÀe Ou.t"ria awd,fingL reprodvtceto gLvehwge o{ LwdLvLdwak. Mawt¿ do wot swwLve as theg do natf,wd a s,,útabLe þ o d s ovwce. e,qro dwctLo w wwvwb ers to gLve tnrge wwvwbers owe adaytaú,owtotheLr waA of LLfe. Bacterialcellsaresurroundedbycellwalls.Thecellsofsomebacterlal species are surrounded by slime capsules' the cytoplasm Bacteria There is no nucleus, just a loop of DNA within c.alled often have addition;l loops of DNA inside their cytoplasm Ls pluifnia, stored cell wall food ;t),.:- re5efve a o a a membrane ..: o es loop of p lasmid DNA Figure (see page 221).Thestructure of bacteria differs from animal mitochondria. some ãnJôf un* cells as ihey do not have chloroplasts or (singular flagellum) for moving bacteria have extensions called flagella through water or other fluids' -ÞEE" flagellum Pathogens' 1.5.1 A tYPical bacterium water and in the soìl' Bacteria are found everywhere- rn the atr' in 20 minutes' so it every divide may gooO conditions, bacteria UnJ.r of bacteria that you does nõt take long to have a very large number just one cell' from starts colony can see on agar as a colony. fach food source The food Bacteria feed by secreting enzymes onto their are absorbed. L broken down and simfile mtlecules such as sugars such as heat' cold and Bacteria which can survive harsh conditions' have a protective These cells their drought, produce spores within .ou"ñng so they can survive for a long time When suitable .ánJ¡tiãnt retuin, the spores germinate and divide agarn' Fungi are also vrsible Fungi are visrble under a light microscope.' Many yeasts are although multicellular are fuÃ9i Most to tñe naked eye. out ,i.öi...rr.J. Each cell has ã nucleus and cellwallwhich is made and chlorophyll of Ër,itin, not cellulose as rn plants. They do not have cannot carry out PhotosYnthesis' Staphylococcus, a type of bacterium' The main fungus body is called the mycelium. lt consists of a a. branching network of threads or hypñae which grow over the surface of its food source, releasing enzymes which digest the food ortriiå the fungus. The digesred food ilthen absorbed by the hyphae. Fungi reproduce by making spores that can be carried by the wind. Most fungi are saprotrophs, which means they feed oÁ O.u¿ o,. decaying matter, but some are parasites. Viruses Viruses are extremery smail; far smailer than bacteria and fungi. For example, the virus that causes infruenza is about 120 nanometres in ?. Bread mould, Rhizopus nigricans. The black structu res contain spores. size. (one nanometre is one-thousandth of a micrometre.) Viruses are only visible under an electron microscope. Viruses are not cells. They are parlicres made up of genetic materiar (DNA or RNA) surrounded by,a protein coat. The genetic irateriar ¡t lãÀpàrø of a few genes that code for the proteins thãt form ;;tl. the coat ..d other proteins that herp it reproduce. Viruses are parasites that enter the cells of ano-ther organism (the host) in order to murtipry. Viruses take over the host cell and direct it to make new viruses. rial protein coat ce proteins lf you breathe in the viruses that cause cords or infruenza, they enter the cells of your nose and throat. Here they reproduce and make lots of new viruses. These are abre even more viruses. to invade more ceils to make Figure 1.5.2 Structure of a human vlrus Viruses can be very harmfu.l because they can reproduce so quickly and do not respond to antibiotics. They ãre constantry changing iÁto new strains. KEY POINTS 1 Copy and complete the sentences using the words below: nucleus decay inside parasites hyphae protein antibiotics reproduce colony genes Viruses are not cells but are made up of a few surrounded by a coat. Viruses are that can only reproduce healthy cells. Bacteria are cells with no very quickly to form a bacterial _ are cells but have no nucleus. Ihey can be seen under a light microscope. 2 Bacteria inside the human body can be killed by chemicals called Fungi are made up of a networkof threads . Fungi act as saprotrophs when they cause dead materials to _. 3 a e cholera, b typhoid, athlete's foot, f c tuberculosis (TB), candidiasis. d syphilis, Viruses can only be seen under an electron microscope. They are not cells but a few genes inside a protein coat. 4 Viruses are parasites that invade healthy cells, 2 Each of the following diseases is caused by a bacterium or fungus. ln each case, state whether the páthogen (disease_ causing organism) is a bacterium or a fungus and then find out how the disease is spread: ln favourable conditions. bacterial cells can divide quickly to form a colony. _ - _. called. 1 Bacteria reproducing to produce many new virus particles. 5 Fungi are made up of threads called hyphae. These grow over the food supply, digest it externally and then absorb it. Flowering Plants Features of flowering Plants LEARNING OUTCOMES . Describe the main features of flowering Plants . State the differences between dicotYledons and Like all plants, colour flowering plants are multicellu.lar' They are green in chloroplasts many of their ãells contain chloroplasts. These for light absorbs which .oÀiu,n the gieen pigment chlorophyll, cellulose' of made wall cell a by pÀoiotyntf'.r"tis. Each"cell is surrc'urrclecl n.iurrå They have transport Flowerrng plants have stems, roots and leaves ;";tisting of tiny tubes These a.re called xylem vessels' ;Áì;h .rr.ty wateiand m¡neral salts, and phloem tubes' which monocotYledons ;yti;;; transport dissolved food. which make seeds' Flowering plants reproduce by means of flowers flower' the within ovary the rÁe seedi are produced inside apical bud Shoots and roots ground The shoot is made The shoot is the part of the plant above rs ,p J u-rt". bearing leaves, buds and flowers The apical budthe supports stem iÅ" purt where the stem grows new leaves The leaf de buds stem so that they can root main root food r00t Figure 1.6.1 structures of the shoot, u-nd tpu..t out the leaves ;;..ir; adequare light and air (see page 66.) tr holds the flowers in a position which enables pollination to take place' soil up to the leaves and The stem allows transport of water from the the roots' from the leaves to other parts of the plant' such as Structure of a tYPical dicotyledonous Plant below ground' The roots are the parts of flowering plants found Roots chlorophyll contain noãt, ur" usually white since they do not being from it prevent uÃihot the plani firmly in the ground and and mineral ions blown ou"r by the wind. Roots also absorb water from the soil (see Page 90) Dicotyledonous and monocotyledonous plants EXAMINER SAYS... groups: Flowering plants can be divided into two main lwthe exat4,L dicotyledons and monocotYledons etw w.fLow uou vway be a sk ed ab o,,+t"dLfþ,e,í" r, erLwg ¡ La ra,ts awd awL,rwaLs. Note awd Learw the dLfferewces t w ceLL structwre awd, rqrodutotLowthat aye b ee desorLbed here. " ,gÈ-j. Magnolia is a dicotYledon lrlaize, Zea mays, is a monocotyledon Dicotyledons look like the plant at the top of the opposite page. Their leaves are often broad with a network of branching veins. The parts of the flowet for example the male parts known aí stamens, are in multiples of four or five in each frower. Dicotyredons have two cotyledons (seed leaves) in a seed. Grasses and cereals, like monocotyledons. EXAMINER SAYS... Both these grouLps ju:ow a Lot of varLatLow, ¡or exan*pLe wot aLL the maize plant opposite, are wow,ocot!)Ledows The leaves of most monocotyredons have parailer veins. Grasses and cereals have long, narrow leaves. other monocotyledons have leaves with a variety of shapes, such as those of parm trees. The parts of the flower are in multiples of three. Monocotyredons have one cotyredán inside each seed. p-ara,LLeL veLws. sqecLes used have ,4wg Lwthe exawLwatLow wLLL have ,,- cne teatLtres gLvew here. t PRACTICAL Comparing dicotyledons and monocotyledons Obtain two plants, one a dicotyledon and the other monocotyledon. leaf of dicotyledon clusters of fl a leaf of monocotyledon Compare the shape of their leaves and look carefully at the leaf pattern of their veins. How do they differ? Figure 1.6.2 ln what other ways do the two plants differ? Structure of a typical monocotyledon plant Make labelled drawings to illustrate your answers. SUMMARY QUESTTONS 1 Copy and complete the sentences using the words below: KËY POINTS I parallel two narrow flowering broad network one Monocotyledons with are plants that often have veins. They have cotyledon tnside _ the seed. Dicotyledons often have leaves with a of veins. They have cotyledons inside each seed. leaves 2 Find the names of five dicotyledonous plants and five monocotyledonous plants that grow where you live. 3Fi nd out and list the functions (jobs) of each of the followi ng a leaves, b stems, c roots, d flowers. Flowering plants are multicellular - each cell is surrounded by a cellulose cell wall and those in leaves and some stems contain chloroplasts. 2 Monocotyledons have one cotyledon in their seeds and leaves 3 with parallel veins. Dicotyledons have two cotyledons and broad leaves with a network of branching veins. Sorting things out . Toidentifythenameofaplantoranimalyoucouldlookthroughthe Use simple dichotomous keYs to identify Plants and animals pi.trr", would iÁ a book until you found the right one. However, that take a lot of time and effort' . ldentify external features of animals and Plants that are useful for making a keY start n0 yes ln this section, we have used has it got a shell? external features to identifY and classify organisms. Cladistics is the method used bY scientists to classify organisms using other features to show how they evolved. TheY use manY techniques including comParing earthworm has it got 6 legs? I spr0er I 2 pairs of the DNA of different sPecies to see how closelY related theY are. housefly Figure 1.7.1 A branching d ichotomous keY. dichotomous keys to identify living things' Dichotomous means dividing into two' Scientists use key A key has a number of steps - you can see them in the branched branching in the and the numbered key on this page At each step and fuy Vo, find a question or statemènt' Start at the beginning un,*.,,yes,or,no,to the first question or Statement. This takes you to anothlr question or to an identifrcation. Use the branching above to identify the animals to the left' key Usethenumberedkeybelowtoidentifythesameanimals.ltisset way' Start àut differently from the first key, but it works in the same stage' each at questions the at the beginning and answer legs Has no legs 2 Has 6 legs Has 8 legs 1 Has Go to 2 Go to 4 Go to 3 SPider 3 Has 1 pair of wings HouseflY Has 2 pairs of wings WasP 4 Has a shell 1,,7,2 : Five invertebrates' Has no shell Snail Earthworm PRACTICAL Making a leaf key Now try making a key of your own. EXAMINER SAYS... different leaves and label them A to F. Put the six leaves out in front of you. Think of a question that will divide them into two groups. Take six Write down the question. Now think up questions to divide each group into two. Write these down. ylt:waFzLq a þnu. ::Lze'ßasyj ? sooa{iature , LLví.vtøthLi,As ::e uoy so wqchL*sLzí. Ll* t Carry on until you come to the last pair of leaves. Write out your key as a branching key or a numbered key. EXAMINER SAYS... Pond animals key ,::,:,^ wtLL : ua wivwtLo w owLA Now try making a key of these pond animals below !As, haveb damsel fly larva I ** water Y4t Lt usuaLLg wuwbered r<eUs yath er th freshwater shrrmp Ao vLse ,fo"wíLL a w b ra n¿h ed wothaveb aevLse owe gourseLf. beetle water 1 scorpion pond snail sna il Figure 1.7.3 Pond animals Dichotomous keys are used to identify organisms, such plants and animals. 2 A dichotomous key includes a series of paired statements or questions which lead to an identification. Dichotomous means dividing into two. SUMMARY QUESTIONS 1 when a scientist visited an isrand she discovered some insects. She made some drawings and brought them back to the laboratory. Her drawings are shown on the right. a b Give each insect a suitable name. Make a dichotomous key to identify them. present your key either as a branching key or as a numbered key. 2 write down the features that wourd enabre you to crassify a fish, an amphibian. a reptile, a bird and a mammal. (you can üse the photos on pages B and 9 to help you.) Now make a key that you could use to identify each of these vertebrate groups. as lf .r.Hz.. ^aå EXAM-STYLE QUESTIONS SUMMARY QUESTIONS 1 Write definitions of the following terms: excretion, growth, movement, nutrition, reproduction, respiration, sensitivity' 2 The binomial system is used to give scientific names to organisms. State what the two words in a binomial, such as Homo saplens' stand for. 3 Write out the full scientific names of the following: meerkat malarial Parasite American crocodile maize Monarch butterflY. 4 List the external features used to identify the following PhYla of animals: annelids, arthropods, molluscs, nematodes' 5 List the external features used to identify the following classes of the arthropod phylum: arachnids, crustaceans, insects, myriapods' 6 Vertebrates are divided into five classes' Name these classes and state three external features shown by the animals in each class' 7 State the differences between monocotyledons and dicotyledons that are used to classify these two groups of flowering Plants. 8 State what is meant by dichotomous when used in the term dichotomous keY' 9 List the main features used to classify the following groups of microorganisms: 1 Which process is carried out by all the orgattisttts tlrat live in a forcst? A moulting B photosYnthesis C pollination D respiration (Paper 1) tll 2 What are characteristics of all organisms? A excretion and resPiration B Ingestion and growth C photosYnthesis and egestion D respiration and PhotosYnthesis (Paper 1) tll 3 Which group of animals includes those with a segmenled body, an exoskeleton and jointed limbs? A annelids B arthroPods C molluscs D vertebrates (Paper 1) tll class of vertebrate includes those with dry scaly skin and four legs? 4 Which A amphiblans B fish C mammals D reptiles (Paper 1) tl 5 The drawings show five animals, A to E' They are not drawn to scale' viruses, bacteria. fungi' 10 Explain how viruses, bacteria and fungi are adapted to s urvive in their environments. c D E l (a) Name (i) the phylum, and (ii) the class into which each of these animals, A to E, is classified. (a) rcl (b) Give three reasons for the choice of phylum, and one reason for each choice of class that you made in part (a). til (Paper 2) 6 (i) ldentify the group of flowering plants to which each species belongs. (ii) State the features that you used to make your t5l (b) List five features shown by the leaves identifications. that would be useful in devising a dichotomous key to identify species of flowering Draw and complete the table using ticks and to indicate whether the four phyla show the features or not. crosses feature UI o ttt p a) c 16 E o r! o o. o a) c r^ t^ J =o E ro til 9 The drawing shows a giant pangolin, Smutsia gigantea. Pangolins are mammals with bodies covered in plates made of the protein keratin, which is also found in skin, hair. claws and nails. The body covering makes pangolins look t^ E plants. (Paper 2) similar to reptiles. E segmented bod v lointed limbs exoskeleton (a) Explain what the giant pangolin's scientific name tells us about how this animal is internal or classified. external shell (Paper 2) t4l 7 (a) Define the term vertebrate. tl l There are five classes within the vertebrate group. (b) List three external features shared by the following classes of vertebrates: amphibians. reptiles, birds and mammals. t3l (c) State two external features of mammals that are not seen in reptiles. t2l (d) State two external features shared by amphibians and fish. t2l (Paper 2) covering. Bl (c) Explain why pangolins are classified as mammals and nof as reptiles. t3l (d) Ihe table shows the features shown by some microorganisms. Copy and complete the table using ticks and crosses. feature vrruses bacteria leaves from three species of flowering plant, A to C. They are not drawn can make ca psu les produce have hyphae scale. t4l (e) Explain how: (i) a fungus, such as Rhizopus nigricans shown on page 1 1, is adapted to feed and disperse from one source of food to another; (ii¡ (iii) A fungi have nuclei spores 8 The drawings show to pl (b) State two external features that pangolins share with reptiles otherthan the body B c ßl bacteria survive adverse conditions; 12/ viruses increase in t3l (Paper 3) number. Cells . . Describe the structures of plant and animal cells as seen under a light microscoPe Describe the differences in structure between Plant and animal cells .Re ate the structures seen under the light microscoPe in the plant cell and in the animal cell to their functions Cellsarethesmallbuildingblocksthatmakeupalllivingorganisms trih ut bacteria are made of only one cell' ù"rv iÀrf l living things one knows An insect such as a fly may contain millions of cells' No for certain how many celli there are in a human being - estimates vary between 10 x 1012 and 50 x 1012' Plant cells Animal cells loroplasts cell cell wa nucl cytop lasm cell membrane I A cheek cell (stained with a blue dye). A palisade mesoPhYll cell from a leaf. Differences between plant and an¡mal cells Liver cells magnified bY x300 EXAMINER SAYS... Whew Uonhaveto state dLfþreloes betweew pLawt awd awLn*ak ceLk, nt"aÞe svLre uow w r t te s o,rwethLwg ib o,,ct looth tgpes of oeLL. summarised in The differences between plant and animal cells are this table. feature plant cell animal cell cellulose cell wall present absent sha pe permanent shaPe determined bY the cell wall; shapes can be nearlY spherical, box-like or shapes vary as there is no cellwall cylindrical chloroplasts present in some cells absent vacuole large permanent vacuole containing cell saP small vacuoles, do not contain cell saP nucleus present (often at the side of the cell close to the cell wall) present (found anywhere within the cell) Functions of cell structures cell structure functions cell membrane . forms a barrier between . . . . EXAMINER SAYS... cell, e.g. oxygen, carbon dioxide and water controls movement of other substances into and out of cell, e.g. glucose often described as partially permeable of awd paú.sade wesophgLL ceLLs, LabeL the struott{res awd, uwd,erweath eaoh , LabeL wntethefuwotiows. þu yovtr dLagrawb :o-: "r, neup gonr revLsLow. . controls all activities in the cell . controls how cells deve lop cytoplasm . chloroplast . photosynthesis . stores starch . stops cells from bursting when they fill with water . gives shape to cells . allows water and dissolved substances to pass cellwall t surrou ndings keeps contents of cell inside allows simple substances to enter and leave the (see page 28) nucleus d.rawLwgs I?-,"t tver oeLLs the cell and its place where many chemical reactions take place, e.g. respiration and makin g proteins for the cell -= through freely (often described as freely or fully permeable) sap vacuole . . full of water to maintain shape and ,firmness, of cell stores salts and sugars Cells of onion epidermis magnified by x250 SUMMARY QUESTIONS 1 Copy and complete this table by using ticks and crosses to indicate if the structures are present or not. cell cheek cell structures (animal) onion cell (plant) leaf cell (plant) nucleus cellwall large vacuole 1 A cell membrane. cytoplasm and a nucleus are found in both plant and animal cells. cytoplasm 2 All plant chloroplasts c o a) x t¡J 2 State the functions of the following parts: a chloroplast, b cell membrane, c cell wall, d nucleus cells have a cellulose cell wall; some have chloroplasts and a vacuole containing cell sap. Animal cells do not have these parts. Different tYPes of cell cells To function efficiently, many-celled organisms have LEARNING OUTCOMES . ldentify different . tYPes of cell from diagrams and photograPhs Relate the features of these cells to their functions . Calculate magnification and actual size of biological specimens using millrmetres as units ciliated cells cilia move mucus alonq these cells make Specialised cells (trachea and Ciliated cells are found in the air passages in the lungs bronchi)andintheoviductsinthefemalereproductivesystem.These to create cells have cilia on their surfaces. cilia beat back and forth current in the fluid next to the cell surfaces' a pathogens ln the airways, cìlia move the mucus that traps dust and egg from the move cilia oviducts, ,p to tt',. nóse and throat' ln the the ovary to the uterus. \-J C 0 C surface Root hair cells have long extensions that give them a large area to absorb water and ions from the soil' xylem vessels root hair cells Figure 2.2.1 that are that the functions specialised to carry out certain functions. This means cells' of groups different of the body are divided between produced. These ãrguÀiffi ievelops from a fertilìsed egg, new cells are functions. ln certain for specialised i"í, gro* and change to become cells' specialised of examples this ipread we look ãt tom" Ciliated cells line the airways. c o0 o o a l^t EXAMINER SAYS.., Whew expLaLwLwg how a ceLLLs adaptedto Lts fwwctLows ttralze sure gow gLv e the stntctt LraL featwres awd sat¿ how each owe hel¡s the caryr¿ ottt Lts ceLL fwwctLow. Þ,-¿ o co Figure 2.2.2 Root haìr cells are long and thìn to absorb water from the soil. Figure 2.2.3 Xylem vessels are small tubes that carry water up the stem. Xylem vessels are cylindrical and empty' They are arranged into .ãlrÀn, like pipes. T-he cell walls are thickened wrth bands or spirals allow of cellulose and a waterproof material called lì9nin. These cells plant They the of rest the to roots water and ions to move from the leaves' also help to support the stem and Some Muscle cells make u p frbres that are able to shorlen or contract contract they move muscles are attached to the skeleton; when they the heart bones at joints. Muscle cells are also in the gut and in Red blood cells contain the protein haemoglobin red blood cells (_, that carries oxygen. TheY are shaped lrke flattened discs. muscle cells Figure 2.2.4 These muscle cells contract to move bones. This shape Provides a large sudace area comPared with their volume whlch makes for efficient absorPtìon of oxYgen Figure 2.2.4 Red blood cells have a substance called haemoglobin that carries oxygen. Size of cells and specimens r! a 0 Look at the photograph of some human cheek cells. t The cells are 1000 times larger than in real life. l This means that they have been magnified 1000 times. a 1 I To work out the actual size of a cell measure the length of one magnified cell in millimetres. Let,s say that it measures 13 mm. t i; Now we can use this formula to work out actual size: So the actual size of our..¡¡ ì.Ë-' Human cheek cells. image size actual size = magnification : --13 : 000 0.013 mm 1 There are 1000 micrometres (!m) in a millimetre. we can convert the answer to micrometres by multiplying by .1000 to give 13gm. we can use a similar technique when the image size has been reduced, as in this photograph of a goldfish. This time ìhere has been a reduction of actual size in the photograph. lf you calculate the fish,s actualsize using the sameformula you willfind it is 90mm long. To calculate the magnification of an image we reorganise the formula: - magnificat'on The image of this goldfish is one third (x0.33) actual size. ilmage slze actual size EXAMINER SAYS... Vlhew,vweasnrLwg o r,o Lo 1 Draw a table matching the type of cell in the first column with ciliated cells long banded threads wea Function keep the air passages free from dust muscle cells xylem vessels long and thin have cilia that move contract (shorten) to move muscles transport oxygen absorb water from the soil b¡rk KEY PO¡NTS 1 During development, cell, b nerve cell, c white blood cell, human egg cell, e palisade mesophyll cell. often their shape. 2 onpageslBandl9. Specialised cells have a structure that enables them to carry out a particular function, e.g. ciliated cells have cilia sperm 3 calculate the actual sizes of the liver cells and the onion cells cells change their structure and 2 Here are some other specialised cells. use this book to find out the functions of these cells and how they are adapted to carry out their functions. a d sure Lw wLLLl,vuetres, wever Lw cewtLvuetres. transport water and ions root hair cells flat discs L specLvwews specLwews, aLways its correct shape and function: Type of cell Shape red blood cells hollow tube gL c a orphotographs of to move mucus along the windpipe. 3 We can calculate both the magnification and actual sizes of images of biological specimens. isation ll jr :t^ i ,ìr.!litiì1lii . . i|)llll i¡ i, r Tissues and organs lrilr i ' A group of similar cells is called a tissue. All the cells in a tissue look thã ,ur. and they work together to carry out a shared function. Muscle tissue is made up of identical muscle cells. These cells work together and so the muscle tissue contracts' Define the terms tissue, organ and organ sYstem Describe examples of the above that occur in Plants and animals cells: the building blocks organ: similar cells working together in the same waY groups of tlssues working together a group of organs working together your heaft is made of muscle and other tissues. lt Pumps blood around your bodY vour heart and blood vessels 'make up your circulatorY sYstem which carries blood around your body = Æ æ= muscle cells contract and relax the human circulatory sYstem. EXAMINER SAYS... L¿a rw these def,wLtLon s of orøaw awd orgaw sgstent". MaÞe a List of Ë,LssrLe, AanLpLes of awLwaL awd, plar,r,t tíssø es, orgaws awd, a w sgsten+s fron," lûook. -----tri<: cardiac muscle tissue is made of muscle cells that contract and relax together Levels of organìsation in ?rØ system: tissue: th"s An organ is made up of a group of different tissues that work together to perform specific functions. The heart is an example of an organ. lt is made up of different tissues such as cardiac muscle, nervous tissue, fibrous tissue and blood that work together to pump blood around the body' The stomach, lungs, brain and kidneys are all organs' Different organs work together as part of an organ system' Organ systems .on"ritt of a group of organs with related functions, working tågether to perform body functions F91 example, the heart and blõod vessels work together as part of the circulatory system. Here are some other organ systems: . The digestive . . . system is made up of the gullet, stomach, pancreas. liver and intestines. The excretory system is made up of the kidneys, ureters and bladder' The nervous system is made up of the brain, spinal cord and nerves The reproductive system in females is the ovaries, oviducts, uterus and vagina; in males it is the testes, sperm ducts, prostate gland and penis. All the different organ systems make up a living organism' Plant tissues and organs The diagrams show the tissues in a leaf. The tissue that carries out photosynthesis in leaves is called mesophyll. The cells making up the upper layer of the mesophyll are called palisade cells. These cells are closely packed and full of chloroplasts so that they are well adapted to absorb lots of light. The palisade cells make up the palisade mesophyll tissue. All the cells making up this tissue look alike and do the same function - they absorb light for photosynthesis. DI.D YOU KNOW? The word 'palisade' is used because the cells are close together líke the wooden stakes used to make walls known as palisades. A leaf is an organ. other plant organs are roots and stems. other structures, such as flowers and fruits, are modified leaves. cells; the building blocks organ: groups of tissues leaf palisade tissue: similar cells working cells absorb light together in the same way \ working together the leaf makes food and allows for gas exchange / palisade mesophyll cells u pper \| epidermis photosynthesis takes place in the mesophyll tlssue cells organism: the milkweed plant spongy mesophyll cells is made up of 0rga n5 lower epidermis cells Figure 2.3,2 Levels of organisation in a flowering plant. EXAMINER SAYS... 1 Copy and complete the sentences using the words below: organ system cells tissues Mal"e suLre function wesophgLL A tissue is made up of that carry out the same An organ is formed from a group working together An ----.-- is a group of organs working together to perform several body functions. - -. correct system from those listed on the right. oaw ceLL Ls adapted to carrytt out p.hotosAwthesLibu of 2 Copy out the organs listed on the left. Match HouL expLaLw how'a paLLsade Lt st.Ln,g ttne ft atuft.s a wd %pLar.wLng how each owe ncLÞs. each with the : I Organs System lungs and trachea heart and blood vessels digestive brain and spinal cord ovaries, oviducts and uterus gullet, stomach and intestínes kidneys and bladder gas exchange .,-:{u NETVOUS I function are grouped together to form tissues. excretory reproductive circulatory 3 Arrange the following words into the correct sequence, starting with the smallest and ending with the largest: organ organ system tissue organism Cells that have the same cell 2 Different tíssues make up organs which work together to do a particular function. 3 Different organs work together as organ systems. SUMMARY QUESTIONS EXAM-SWLE QUEST¡ONS I 1 Which structure State three structures that are present in both plant and animal cells. 2 State three structures present in plant cells that are never found in animal cells. 3 Match the cell types with their functions: cell type function red blood cells root hair cells movement of mucus contraction and movement absorption of water and ions muscle cells xylem vessels ciliated cells transport of oxYgen conduction of water and ions 4 Write definitions of the following (a) tissue (b) organ (c) organ system. 5 (a) Name three animal tissues. (b) Name three Plant tissues' .9 o x t¡J 6 The following structures are present in both plant and animal cells: cell membrane, cytoplasm and nucleus. State the functions of each of these structures. 7 All plant cells have cell walls; some plant cells have chloroplasts and large vacuoles. State the function of each of these structures. is found only in plant cells? A cell membrane B chloroplast C cytoplasm D nucleus (Paper 1) l tl 2 Which of the following structures is nof found ìn animal cells? A cell membrane B cell wall C cytoplasm D nucleus (Paper 1) tt l tt l is the correct sequence, starting with the smallest and ending with the largest? A tissue, organ system, organ, cell 3 Which B cell, tissue, organ system, organ C tissue, cell, organ, organ sYstem D cell, tissue, organ, organ sYstem (Paper 1) made a drawing of a biological specimen. The length of the specimen in the drawing is 140 mm. The magnification rs x40. What is the actual size of the specimen? 4 A student A 5600mm C 35mm (Paper 1) B D 56mm 3.5mm tl l 5 The palisade mesophyll cell is a type of plant cell. A liver cell is a type of animal cell. Copy and complete the table to compare these two cells. Copy the table and put a tick (/) if you think the structure is present and a cross (X) if you think it is absent. cell structure palisade liver cell mesophyllcell cellwall cell membrane cytoplasm nucleus chloroplast large vacuole t6l (Paper 2) 6 The diagram shows three animal cells. 8 (a) Name: (¡) an animal cell which does not have a nucleus; tl l (ii) a plant cell that does not have nucleus; (iii) the organ a mammals; A (iv) the plant tissue that transports c B sugars. (a) ldentify the cells A, B and C. t3l (b) State the functions of the three cells. t3l (c) State where in the body these cells are found. t3l (d) Ihe magnification of cell A is x 1000, Calculate its actual size. t2l (Paper 2) tl l system for transport in tll tl l (b) Distinguish between the following pairs of terms. (i) tissues. (íi) Cytoplasm and nucleus. (iii) Cell membrane and cell wall. (iv) Organ system and organism Organs and t2l t2l t2l t2l (Paper 2) 7 The diagram shows three plant o a cells, 9 (a) Match each cell structure on the left with its function on the right. o nucleus .aj oo D E controls the entry and exit of materials from the cell cell full of cell sap as a store of membrane water and ions cell wall contains chlorophyll and carries out photosynthesis large vacuole F (a) ldentify the cells D. E and F. t3l (b) State the functions of the three cells. t3l (c) For each cell, D, E and F, state a plant organ where it is found. ln each case give a different organ. t3l (d) The actual length of cell D is 0.05 mm. Calculate the magnification of the drawing. t2l (Paper 2) place where most chemical reactions in the cell take place chloroplast contains the instructions for the cell cytoplasm made of cellulose to withstand pressure of water inside the cell t6l (b) A student looked at a cell under a light microscope. She made a drawing of the cell and showed the diameter of the nucleus in her drawing as 70 mm. She calculated the magnification of her drawing as x 1 0 000. What is the actual size of the nucleus? t2l (Paper 3) i l; Trtllri iii ilti r¡ I Ír)1 Lllr iì Ìrr) ùrliì Molecules in gases move about in a random way. They bump into one another and spread out to fill up all the space available. Molecules in a liquid do this as well, although it takes longer for them to fill the space. Movement in a gas is faster as the molecules are more spread out. The difference in speed between movement in gases and liquids is rl' i . Define the term diffusion . Describe the importance of . diffusion of gases and solutes Describe the importance of water as a solvent important for organisms. This movement of molecules ìs called diffusion. water molecules ooo oo -Oo ^oo o o o o oo o at^a .i' o o before o o o o o oa ôo o o o o o o o a a o Õ diffusion o o o o¡ o Whew gor,twrLte alOovtt ttt"oLeonLes that are dLffusLwg tronL owe¡Laoeb awothev aLwags swrethat uon sagtheg,^ou, fo** the oowoewtratLow gradLewt. A oowoewtrated soLvttLow has a Large @ %%.. @@ @@@ @ @ o@ o .i@ o "o @ substance soluble in water molecules of solute dispersed through water after diffusion before diffusion Diffusion in a liquid. after diffusion EXAMINER SAYS... @ @ @ 9oo @ o Diffusìon in a gas. Molecuìes @ @ @o Õ of a coloured gas sPread out through the container. nLaþ,e @ o -o o au o a o o When molecules diffuse they spread out from where there are lots of them in a given volume (a high concentration) to where there are not as many of them (a low concentration). The difference between the concentration of molecules in two places is a concentration gradient. Molecules carry on diffusing until they are spread out ãvenly. When this happens the molecules keep moving, but there is no longer a difference in concentrations so diffusion has stopped' Diffusion is the net movement of molecules from a region of high concentration to a region of lower concentration down a concentration gradient. Cells gain some of the substances they need by diffusion from their surroúndings. They also lose some of their waste substances to their surroundings by diffusion. These substances have to cross cell membranes they allow the movement of small moleculés such as oxygen, carbon dioxide and water to pass through easily, but not larger molecules. The movement of molecules by diffusion across cell membranes is passive movement as cells do not need to use that are partiaily permeable as wass of soLute energy to move the molecules. dLssoLved Lw a gLvew voLnnt"e ùf the soLvewt. Factors that affect diffusion A These factors influence the efficiency of diffusion. dLLvtte soLv*Lowhas a sntaLL nt"ass of soLv*e ,,dLssoLved L* a gLve* YoLun+e of the soLvewt. . The distance molecules have to travel - note that cell membranes are very thin. . The concentration gradient - cells use the substances that diffuse in as quickly as possible, so they keep a low concentration inside the cytoplasm. This means that molecules keep diffusing into the cell because the cell is maintaining a steep concentration gradient' . The surface area . The temperature - some cells have cell membranes that are folded to give a large surface to allow many molecules to cross by diffusion. - molecules move faster and colìide more often as the is faster at warmer temperatures. temperature increases. Diffusion . The size of molecule - small molecules diffuse faster than large ones. Gas versus liquid Animals and plants exchange the gases oxygen and carbon dioxide with their surroundings at gas exchange surfaces. ln mammals, the gas exchange surface is formed of the alveoli in the lungs (see page 'l 21). Blood transports these two gases between the lungs and all the cells in the body. ln the alveoli, oxygen diffuses across a very thin layer of cells into the blood. Carbon dioxide diffuses in the opposite direction. Breathing constantly refreshes the air in the alveoli and blood constantly removes oxygen and brings carbon dioxide, so the concentration gradients are always steep. There are many alveoli to There is a short distance between the red blood cells and the air in the alveoli Magnification x 1500. give a very large surface area for gas exchange. ln plants, gas exchange occurs inside the leaves. The spongy mesophyll cells provide a large surface area for exchange of gases. There are air spaces between the cells in a plant and each cell exchanges gases with this air (see page 66). Thìs is efficient because diffusion through the air is EXAMINER SAYS... 300 000 times faster than through water. ALwags reþrb o o w c e wtr ate d s o L utLo ws awd dLLwte soLvctions, weverto,stronq, awd ' weaÞ' soLutLows. tw thLs Water as a solvent A solution is made up of two parts, the solute and the solvent. The solute dissolves in the solvent. lf you dissolve sugar in wateryou make a sugar solution. The sugar is the solute and the water is the solvent. The solute is not always a solid like sugar. Liquids and gases can be solutes as they can dissoìve in solvents too. Something which dissolves in a solvent is described as being soluble. Water is sometimes called the universal solvent. About 75o/o of cytoplasm is water and it is the main component of transport fluids like blood, and xylem sap and phloem sap in plants. Everything transported in plants and animals has to dissolve in water and most of the chemical reactions that occur in cells happen in water. SUMMARY QUESTIONS 1 Copy and complete the sentences using the words below liquid random diffusion low gas : gradient, e temperature. 3 What do the terms so/ufion and concentration gradient mean? 4 aussoLved Lw a l¿woww of soLvewt. voLnvwe tr.l \Í 1 Diffusion is the net movement of molecules from a region of high concentration to a region of low concentration down a concentration g radient. 2 Factors that affect diffusion are: size of a - diffusion into cells: factors affect 2 State how the following a distance, b size of molecule, c surface area, concentration ?o:: to the oowoewtratLo*lf the soLute - the wass high or a is the net movement of molecules of a concentration as from an area of to an area of result of the movement of molecules. - d Aon are yeferyLwg Explain why water is an important solvent for animals and plants. i'{o)lllill L!,r molecule, distance, surface area, temperature and the steepness of the concentration grad ient. I f f . Define the term osrnosr . Describe the effect of osmosis on plant and animal tissues . c o c(¡,, x trl Each cell is surrounded by a cell membrane. lt separates the contents of the cell from the outside. The cell membrane has tiny holes in it which allows small molecules to pass through but not large ones. The cell membrane is described as being partially permeable. Explain the movement is a special kind of diffusion involving water molecules. lt occurs when two solutions are separated by a partially permeable of water into and out of membrane. cells using the term water Osmosis is the diffusion of water from a dilute solution into a more concentrated solution through a partially permeable membrane. potential Osmosis The tiny holes in the membrane allow small water molecules to pass through, but the large solute molecules are solute molecu tf asked to defi,we oswosLs orwrLte about tt, yuake sure tt:at l4otL Lt Ls the o¡ water vwoLecuLes. i *n- sau aiffusLi, a is many diffusing from a place where there is a dilute solution with a high EXAMINER SAYS... o water. I I I a ar a o a a o tl. o.o i> oo ala a o a -i> a +o o water molecules a I dilute solution is a concentrated solution with a low concentration of a + o o molecu les concentration of water to a place where there o rO + o o a a aa Oa a too big to pass through the partially permeable membrane. Water a Water molecules diffuse from a high water concentration to a lower water concentration concentrated solution partially permeable membrane Figure 3.2"1 ' osmosis. Water potential ìs a way of thinking about the ability of water by osmosis. This is influenced by how much water is avail¿ble, but also by other factors such as the pressure exerted on water in plant cells by the cell wall. lt is more accurate to say that a dilute solution (containing a lot of water molecules) has a high to move water potential. A concentrated solution (containing fewer water molecules) has a low water potential. ln the diagram above, there is a water potential gradient between the two sides of the membrane. The water molecules diffuse dor¡zn this water potential gradient, from a region of high water potential to a region of lower water potential. A model cell Dialysis tubing (Visking tubing) is partially permeable. We can use to represent the cell membrane and the sugar solution dialysis tubing to represent the cytoplasm. m x + o 9. o :t PRACTICAL Cut two pieces of dialysis tubing, each 12cm long. Tie one end of each with water diffuses into 'cell' sugêr solution cotton. Fill one model cellwith a dilute sugar solution (cell A). Fill the other model cell with water (cell B). Tie the other end of both model cells and weigh them on a balance. Put dialysis tubing (partially permeable membrane) 'cell A water diffuses out of'cell' EXAMINER SAYS... 'cell A into a beaker of water and put 'cell B' into a beaker containing a concentrated solution of sugar. After 30 minutes take out the model cells and weigh them again. 'Cell A yt( tA,LaAbe gLvewthe r¿sa[ts of apraotLcaL ewo t t stratío w tf o sw o sis a,wd t^e expectedto uptaLw the resvù3. Mal¿e stLre uov d, dialysis tubing (partially sugaf solution permeable membrane) rew¿wb er efi,vwtíoi awd appLg Lt to.the resuLts goi Lo^,ee. 'cell B' tt increases in mass because water has diffused rnto the 'cell' by osmosis. 'Cell B'decreases in mass because water has diffused out of capillary tube level of tVte d oswosLs ALwaAs Q<?laLwthatthe results are dwetowater sugar solution wol¿cuLcs wovL^î¿b¡ the cell by osmosis. OSt'uOsî.5. An osmometer You can see the effects of osmosis if you set up this apparatus. Fill diaìysis tubing conta in i ng wateÍ concentrated sugar solution l *Þ the partially permeable membrane with a very concentrated solution of sugar. Tie it to a capillary tube and stand it in water. Very quickly you will see the liquid moving up the tube. You can measure how fast it is moving using a ruler and a stopwatch. Use your ideas about osmosis to explain why the liquid rises in the tube 1 SUMMARY QUESTIONS 1 Define the following terms: diffusion osmosis partially permeable membrane 2 Describe how you can find out how fast water diffuses by osmosis into a sugar solution. Remember to include all practical details. c o c u x t¡J 3 Explain in terms of water potential, how water passes into plant cells placed in distilled water. Osmosis is the diffusion of water molecules from a region of their higher concentration (dilute solution) to a region of their lower concentration (concentrated solution) through a partially permeable membrane. 2 A partially permeable membrane allows small molecules such as water to pass through but not large solute molecules. Osmosis in plant and animal cells LEARNING OUTCOMES PRACTICAL . Osmosis in potato cells Describe how water can enter and leave plant cells by osmosis . Describe how osmosis can affect animalcells Cut nine cores from a potato so that they are exactly the same length. Record this length. Feel the cores to see how firm and 'bendy' they are. Set up the following test-tubes - distilled water B - dilute sugar A test-tube A EXAMINER SAYS.., Whew descrLbLwa the wevubrawe ai ceLL :: g;! t' i ii,l:?å ::, wot ^sevwt pervuealoLe, " I membrane (partia lly permeable) cytoplasm measure their lengths. Calculate the average length of the cores in each test-tube. sol ution A - lwall (freely permeable) the solution outside the cell is less concentraled than in the vacuole Figure 3.3.1 Osmosis in a plant cell EXAMINER SAYS c .9 6 o # x t¡J lwPaper s Aor{ wa?t be expectedío u-setñe teynL, w ater potewtLalJ w n"tr.nq ab o ut Lw ostn*osLs awdplawt or anívuaL ceL.s awdtLssues. þu caw a"so reter 'water potewtLaL .yo Øra dLev*s' to Upt_aLw water tn*ovewe,wtLwto awd out of oeLk awdtíssx¿s. Cores will be longer and feel firmer than at the start. C - up no change c suga r B 0sm0srs tissue swells Remove the cores and passes into the vacuole by suga r test-tube C - concentrated sugar solution. of potato into each test-tube and leave them for 60 minutes. \1æe dilute water sol ution Place three cores _ perweabLe. water test-tube solution B |TrrrfrT-rrrrrfrrrrrfrr 10r234s6789r0 tissue shrunken and flaccid Cores will be about the same length and firmness as at the starl. Cores will be shorter and feel much softer and 'bendier' than at the start. These results are explained in the text. Turgidity The cell membrane of the plant cell is partially permeable and the cell sap inside the vacuole is a solution of salts and sugars. When plant cells are placed in water, the water enters the cells. This is because there is a water concentration gradient so that water molecules diffuse into the cells by osmosis. As water enters it makes the cell swell up. The water pushes against the cell wall. Eventually the cell contains as much water as it can hold. lt's like a blown-up balloon. The strong cell wall stops the cell bursting. We say that the cell is turgid. This is what has happened to the cells in the potato cores in tube A. The cells have absorbed water, swollen and caused the core to get slightly longer. Turgid cells give the plant support. They keep the stems of many plants upright. However, when these cells lose water, they are no longer firm and turgid. Plant stems and leaves that have lost water wilt. Plasmolysis When plant cells are placed into a concentrated sugar or salt solution water passes out of the cells by osmosis. As water passes out, the sap vacuole starts to shrink. These cells are no longer firm, and become limp. We say that they are flaccid. As more water leaves the cells the cytoplasm starts to move away from the cell wall. These cells are now plasmolysed. This is what has happened to the cells in the potato cores in C. The cells have decreased in volume so the whole core is shorter than at the start. The cores in B did not change in length very much because the water concentration of the sugar solution was about the same as the water concentration of the cell sap in the potato cells. There has been no overall diffusion of water into or out of the cells so they the solution outside the cell is more concentrated than in the vacuole water passes oul of the cell by osmosis pulled cell the va wall, the cell becomes shrinks Figure 3.3.2 plasmolysed Water passes out of a plant cell by osmosis. have stayed about the same length. Osmosis in animal cells This diagram shows what happens to red blood cells when they are placed in different concentrations of a salt solutlon. Remember that the cell membrane is partially permeable. The red blood cells in the picture have been placed into different liquids. Their cytoplasm is a concentrated solution of proteins, salts and sugars. The cells in D were in distilled water. Water passes rnto the cells by osmosis. However, animal cells have no cell wall to stop them swelling so they burst, When red blood cells are put into a concentrated salt solution (F), they shrink as water passes out of the cells by osmosis. The ceils in E have not changed in size as they are in a solution which has the same water concentration as the cells. This is how they are in the blood when surrounded by blood plasma. öQ€ftP Figure 3.3.3 tø This shows what happens when red blood cells are put into distilled water (D) and a concentrated solution of salt (F). E shows red blood cells as they appear when suspended in blood plasma, These epidermal cells from a red onion are (a) turgid and (b) plasmolysed. 1 Water passes into plant cells by osmosis. A plant cell that SUMMARY QUESTTONS 1 Explain what is meant by each of the follow terms: turgid flaccid plasmolysis is 2 .9 c a) x t¿¡ 3 Explain, using the Íerm water potential, what happens to cores of potato when they are placed into distilled water for 60 minutes. su ga r a solution, water passes out by osmosis. These cell are no longer firm, they are flaccid. As the vacuole The mass of the potato cores had stayed unchanged. a What does this tell you about the concentration of the sugar solution? Explain your answer to part a in terms of osmosis. is turgid. lf plant cells are placed into concentrated 2 Some potato cores were weighed and then placed into a dilute sugar solution. After 2 hours, they were taken out of the solution, dried on a paper towel and weighed again. b full of water Turgid cells provide support for leaves and young stems. shrinla, the cell membrane moves away from the cell wall - the cell is now plasmolysed. 3 Animal cells burst if they are placed into water as they have no cell wall to resist the increase in size. Active transport . Define the term active transporf . Explain the importance of active transport as an energy- Cells take up molecules and ions and keep them in high concentrations. Look at the concentration of magnesium ions in the root hair cell and the concentration of magnesium ions in the soil solution: consuming process . Describe the active transport . of ions in plant roots Describe the active uptake of glucose by epithelial cells in villi vacuole of root hair cell W. a soil solution a Key: a: t0ns Root hair cells absorb ions by active transport. The concentration of magnesium ions is far greater inside the vacuole of the root hair cell than it is in the water in the soil. We might expect magnesium ions to diffuse out of the root hair cell into the soil water down a diffusion gradient. The magnesium ions are maintained at a high concentration inside the root hair cell by a process called active EXAMINER SAYS... NotLoethe use of the terw ,cowoewtratLow gradLewt,Lwthe deft wLtLow of Active transport is the movement of ions or molecules in or out of a cell through the cell membrane against a concentration gradient, using energy released during respiration. aotLve trawsport,. AgaLwst a oo woewtr atL o w g r a dLewt, vweÌws a Low fron* oowoewtratLowto a hLgh ,. 'igoowoewtrûtLow. ç transport. 4000 o P @ o o 3000 I inside cell l--l in water outside E c o 'F 2000 g C a c 1 000 o 0 Nat sodium K+ N/g2+ potassium magnesium ca2+ cl- calcium chloride The bar chart shows the concentrations of some ions inside the cells of a freshwater plant and in the water in which it lives. These ions cannot have been taken into the plant by diffusion. They are taken in against a concentration gradient by active transport. Active transport needs energy The cell membrane contains carrier proteins. These carrier proteins span the cell membrane and provide means by which ions and molecules can enter or leave a cell by active transport. First the molecule or ion combines wìth a carrier protein. Energyfrom respiration enables the carrier protein to change its shape to carry the ion or molecule to the inside of the membrane. The molecule or ion is released to the inside of the membrane and the carrier protein reverts to its original shape. t0ns o outside cell outside cell cell membrane cell membrane energy carrier protein Figure 3.4.3 inside cell O oo o O inside cell o Carrier proteins ìn membranes carry out active transport. Epithelial cells lining the villi in the small intestine absorb glucose by active transport (see page 84). These cells have high rates of respiration to provìde energy for this active transport. Active transport relies upon respiration to take up ions or molecules against a concentration gradient. Any factor that affects the rate of respiration will also affect the rate of active transport. So a lack of oxygen would reduce respiration rate and active transport. An ìncrease in temperature would increase the rate of respiration, up to a point, so would also have the same effect on active transport. The presence of poisons such as cyanide can stop respiration, so active transport would stop altogether. EXAMINER SAYS... æoothaLr ceL]'s awd qLtheLLaL ceLLs of vLLLL are adapted aotLve for trawnort bg haví.ng wawA cawLerproteLwsLw theLr ceLL,*e^bra*es a wd a hLgh rate ùf respLratLow , toTrovLde e^ergy,. *. SUMMARY QUESTIONS 1 a b Explain what is meant by active transport. Describe the role of carrier proteins and respiration in active transport. c Give two examples of active transport taking place. 2 Make a table to compare diffusion with active transport. Make sure that you have three columns headed 'features', 'diffusion' and 'active transport'. For features you can include 'needs energy from the cell', 'concentration gradient'. You may be able to think of some other features to use in your table. 3 State what effect each of the following would have on active transport, in each case give reasons for your answer: a a lack of oxygen b c an increase in temperature the presence of a poison, such as cyanide. KEY POINTS 1 Actíve transport the movement of ions or molecules across the cell membrane. against a concentration gradient, using is energy from respiration. 2 Active transport enables root hair cells to take up ions, and epithelial cells of the villi to take up glucose. SUMMARY QUESTIONS EXAM-STYLE QUESTTONS 1 Define the terms solvent, so/ufe and soluble. 1 Which of the following 2 Explain why diffusion occurs faster in a gas than in a liquid. A B C D 3 Name the process by which each of the following occur: (a) molecules of oxygen move from the air spaces in the alveoli in the lungs into the blood (b) molecules of carbon dioxide move from respiring cells into the blood (c) water molecules move into root hair cells. 1) l tl is the besf definition of diffusion? movement of molecules down concentration g rad ient 4 Define the following terms: B (a) concentration grad ient (b) diffusion movement of molecules up concentration g radient C movement of solvent molecules through a partially permeable membrane down a concentration D g a a radient random movement of molecules in a gas or a liquid (Paper 1) 3 Which of the following l tl is the besf definition of osmosis? 6 Describe what happens to animal and plant A diffusion of molecules through a partially permeable membrane from a dilute solution to a concentrated solution B diffusion of molecules through a partially permeable membrane from a high concentration to a low concentration Use the Term water potentialto explain why plant cells increase in size when placed in water and decrease in size when placed in very concentrated solutions of salt or sugar. C diffusion of water molecules from a region with a dilute solution to a region with a concentrated solution through a partially 9 Some resources required by cells, such as molecules and ions, are often in very low concentrations in their surroundlngs. Describe how root hair cells and epithelial cells from the gut obtain resources from their D cells when they are placed in (a) water, and (b) concentrated solutions of salt. 7 Explain your answers to question 6 (a) and (b) using the terms partially permeable membrane and osrnosls. x dialysis tubing A 5 Water forms about 75% of the cytoplasm of cells and a higher proportion of body fluids such as blood. Explain the importance of water as a solvent in the body. a) cellwall 2 Which of the following (d) osmosis. ul noi partially cell membrane of palisade mesophyll cell cell membrane of red blood cell (Paper (c) partially permeable membrane .9 is permeable? 8 surroundings under these circumstances. 10 Explain why root hair cells have to provide energy for the absorption of ions from the soil. 11 Explain what is meant by the term concentration gradient and explain how the term is used when describing the movement of molecules across cell membranes. permeable membrane diffusion of water molecules through partially permeable membrane (Paper 4 a 1) l tl Some fresh plant tissue was put into a concentrated salt solution for 60 minutes. Which best explains why the tissue became softer? A B C D The cells became turgid. to their surroundings. Water diffused from a dilute solution in the cells to a more concentrated solution The cells lost water outside the cells. Water diffused by osmosis from the cell sap in the vacuoles into the more concentrated solution outside the cells. (Paper 1) tl l 5 (a) State three factors that increase the rate of diffusion. t3l ln the lungs, oxygen and carbon dioxide are exchanged between the blood and the air in the alveoli by diffusion. move up the (b) State three ways in which the alveoli in the lungs are adapted for efficient gas exchange. (Paper 2) as shown in the diagram below. tube with scale marked in mm 15 tube. t4l (Paper 2) t3l 6 A student set up some apparatus (c) Calculate the rate of movement in millimetres per minute of the meniscus over the B minutes. t2l (d) Explain what caused the sugar solution to meniscus of the sugar solutìon in tube 7 An experiment was set up to investigate the factors influencing the uptake of ions by plant roots. Some roots were cut from a plant, washed and placed in three solutions, A, B and C, containing potassium ions. A mixture of gases was bubbled through each of the solutions. A gas mixture rich in oxygen was bubbled through solution A; solution B received a gas mixture with a very low concentration of oxygen; solution C received no oxygen in the gas mixture. The roots were left for 24hours and then the rate of uptake of potassium ions was determined. The rate of uptake of potassium ions was highest in solution A and lowest in solution C. dialysìs concentrated sugar solution tu bi ng The student measured the level of the meniscus in the glass tube every minute and the results are shown in the table. time (minutes) 0 position of the meniscus in the tube (mm) (a) Explain how the supply of oxygen to roots influences their uptake of potassium ions. The experiment was repeated with solutions containing roots kept at different temperatures. They were all provided with the gas mixture that had been given to solution A. The results are shown in the table. temperature fc) U 1 24 2 52 3 73 4 102 5 127 6 138 7 180 B 190 (a) Draw a graph of the results. t6l (b) Describe the results shown by your graph. t2l 13/ rate of uptake of potassium ions (arbitrary units) 5 3 '10 5 20 10 30 20 40 15 (b) Draw a graph of the results. t6l (c) Describe the results shown in your graph. t4l (d) Explain the effect of temperature on the uptake of potassium ions by the roots. t3l (Paper 3) ct¡on of . Define the term catalyst as a substance that speeds up a chemical reaction and is not changed by the reaction . Define enzymes as proteins that act as biological catalysts to speed up the rate of chemical reactions a .9 c o P x uJ ain how an enzyme works using the 'lock and key' model A catalyst speeds up a chemical reaction and remains unchanged at the end of the reaction. Enzymes are proteìns, produced by organisms, that speed up chemical reactions. They are known as biological catalysts. How enzymes work Many chemical reactions take place in organisms. These reactions happen too slowly to keep organisms alive unless they are speeded up by enzymes. There are many different types of enzyme as each one catalyses a different reaction. Most enzymes work inside cells, but many of those that we will discuss here work outslde cells, for example in the gut (see pages 7B and B2). The reactions that enzymes catalyse can be divided into three types. 'l Breaking large molecules into small ones This is important in nutrition when large food molecules are broken down into small ones so that they can be absorbed and then used. Bacteria and fungi release enzymes to break down their food and we release enzymes into the gut for the same reason. 2 Building up large molecules from small ones Small molecules, such as glucose, are joined together to make Iarge molecules. These enzymes work inside cells to speed up the formation of storage molecules, such as starch, and structural molecules such as cellulose for cell walls of plants. 3 Converting one small molecule into another This computer-generated image of an enzyme (on the right) shows its 3D shape. Many of the chemìcal reactions that occur inside cells involve small to molecules, such as adding or removing atoms or groups of atoms. For example, there are enzymes that remove hydrogen from compounds during respiration. changes Figure 4.1.1 shows the way ìn which an enzyme catalyses the breakdown of a molecule. EXAMINER SAYS... WhewwrLtLwg abowt ewzAwes aLwaus sag s at a s e ^= a l.l!!.: u reActL)ws. ^e i i hr¡Þ enzyme substrate L subslrate in active sile enzyme products released Figure 4.1.1 Figure 4.'1.2 shows how an enzyme is involved in building a molecule from two smaller molecules.