Be Sg CAMBRIDGE Panos Biology for Cambridge International AS & A Level Mary Jones, Richard Fosbery, Dennis Taylor & Jennifer Gregory oryCAMBRIDGE ELEVATE BOOK CODE ‘This is your Cambridge Elevate Book Code. Please scratch the panel lightly, with a coin, to reveal the code beneath: GZSZ-NGDX-Z\_BR-QBFW How do I register and use my Book Code? 1+ Already registered? Please login at elovate.cambridge.org and then use the ‘Add books! icon in tho top right of the page to add your Book Code. Want to register? Please use your Book Code to register at elevate.cambridge.org and then use the ‘Add books’ icon to add any additional Book Codes. Terms and conditions and FAQs: ‘+ This Book Code will give you 2 years’ (24 months’) access to the Cambridge Elevate edition starting from the day you fist use the code. This code can only be used once, is personal to you, andl cannot be reused by anyone else Fall trms and conditions are available at: elevate.cambridge.org/elevate/CUPTermsOfUse.htm For Frequently Asked Questions and other help please vst the Cambridge Elevate FAQs page: clovate.cambridge.org/supportCAMBRIDGE UNIVERSITY PRESS Biology for Cambridge International AS & A Level COURSEBOOK Mary Jones, Richard Fosbery, Dennis Taylor & Jennifer GregoryGaeRrSE ‘ey intr Hous, Carre 82S ite Kingse (nei azn, 208 Flor Now York HY 10006 USA {77 winston Roa Pot Mabe, 3207 Asta 5314-321, ost 3, Slr on, aa Cts Dl 10025, a 29 too an, 06-0006, Soper 7206 Ceti et re psy at ecteuorame te ewan ins taton Cogn cRe Anco comer, SSS wc gm mat 2 cme Ome Ssetemeiayabe sarin stn Tes the a, miosieatey ee aaaanaes towne rec anilabe e ras remade peep ie ty tata ne see ecg mses BRE ‘Shorr pt cia ee i ce rotmearet cies Penns niche enal cet eee in ee est gh cy of ton (ete area at fis worn mae fe rca spot ser scan et de ean cane, bye ng ys eres gees your salen the raped ear 6 tira oad wl pores Conte Gry ean (0 Pets Tf he Cops sg ae Mars ta wick ce ar ‘Saree he prducton taht pesages wid ca Woes educa ‘Sn and eroceson fare urs sting exarnsion weston Seige eral eprint antl is putin ero unfree ‘eater ecu oper of canara serena aston Geen Aseria dan bear ogni cle ‘aamatye quate and gl sone bean tn te uh ‘Se aa i gt i aa ihe gota yw te ph of Cie Aer, anise ad ths oe gg fig ed SS eepaenemiar meget sen Econ theee rhs DEDICATED < TEACHER vw AWARDS Congratulations to our incredible winner and finalists> camomioce INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK > Contents Introduction How to use this series How to use this book 1 Cell structure 14 Callsaethe Basie units of lie 1.2 Callbiology and microscopy 4.3 Plant and animal cella en with alight microscope 1.4 Measuring size and eaeuating ‘magnification 1.5 Election microscopy 4.6 Plant and animal celia en with an cleseon mieoscone 1.7 Bacteria 1.8 Comparing prokaryote cel with eukaryote els 1.9 Views 2. Biological molecules 21 Biochemistry 2.2 Theboilding blocks of ie 2.3 Monomers polymers and rmacromolestles 2.4 Carbohydrates 25 Lipids 26 Proteins 27 Water 3. Enzymes 3.1 Whatisan enzyme? 3.2. Modeof ation of enzymes 3.3. Investigating the progress of an ‘enzyme catalysed reaction 3.4 actors that affect enzyme action 3.5 Comparing enzyme affinities 3.6 Braye inhibitors 3.7 Immobilsing enzymes vi 45 4 3 st 6 6 16 » 1 8 8s 8 4 Cell membranes and transport 41 ‘Theimportanceof membranes 98 4.2 Structure of membranes 98 4.3 Rolesof themoleeules found in membranes 101 44 Cellsignling 2 4.5 Movement of substances across embrace 108 The mitotic cell cycle 5.1 Growth nd reproduction 4 52 Chromosomes 135 53. Theadleyte 16 54 Mitosis 7 55 Theroleoftomeres im 56 Theroleof stem ex 133 57 Cancers 1 Nucleic acids and protein synthesis 641 Themokcule of Hie a 62 Thestrusureof DNA and RNA 144 63 DNArepliation| M9 64 Thegeneticcade 150 65 Protinsyathesis Ist 66 Genemutations 133 Transport in plants 7.4 The transport needs of pants 163 7.2 —Vaselar system: xylem and phlcem 163, 7.3 Seruturof stems, roots and leares and the distribution of xylem ad phloem 164 7.4 ‘The transport of water 170 7.5 ‘Transport ofasinilaus 180 Transport in mammals 8.1 Transport systems in animals 194 82 Themammalian circulatory syst 194 8.3 Blood ves Iss w >84 Tisme fuid 85 Blood 86 Theheart 9 Gas exchange 9.1 Gasctchange 92 Lames 93 Trachea, bronchi and bronchioles 94 Warming and cleaning these 95 Aveo 10 Infectious disease 401 tnfectiouscincases 102 Antibiotics 11 Immunity 11.1 Defence aginst scase 14.2 Cellsof the immune system 11.3 Activeand passive immunity P1 Practical skills for AS Level PAA Practical skis PI.2 Bxperiments PAL3 Variables and making measurements PIA Recording quantitative sus PLS Displaying data PL Makingconctsions PLT Desrbing data 1.8 Making caleultions fom data P19 Wentfyng sources of error and suggesting improvements P4410 Drawines 12 Energy and respiration 121 ‘Thenead or enc in ving orgnisns 122 Aerobie spction 123 Mitochondrial strueture and function 424 Respiration without oxyeen 125 Respiratory substrates 200 202 209 2 ns 26 ns ne 253 261 am 22 22 22 208 29 so sol so os a2 a3 a9 x0 22 13 Photosynthesis 134 132 133 135 ‘An eneray tanser process an Structure ad function ofehloropass 333 ‘Theligh-dependent photosythesis ‘The ighcindependen stage of photosynthesis Limiting factor in photosynthesis wet 14 Homeostasis, aa uz M3 ua us Homeostasis ‘Thestrueture ofthe kidney Control of water content ‘The contol of bod gloose Homeostasis in plants 15 Control and coordination 14 152 183 134 Hormonal communication [Nervous communication ‘Musee contaction Control and coordination in pants 16 Inheritance 164 162 163 164 165 166 167 168 Gametes and reproduction ‘The production of geaeti variation Genetics Monolnbrid inheritance and gente siagrams Dilybrid inbertance ‘The chi-squared (2) test Genes, proteins and phenotype Contr of gene expression 17 Selection and evolution wa 2 wa wa ws 76 wr Varition Natural selection Genetic drift and the founder fet ‘The Hardy-Weinberg principle Antti selection Bvolation entity evolutionary ationstips a oy ow 32. m 88 ww 406 ais a8 os as 407 4a 451 453 8&8 m 416 am oy $86> caManiocE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK 18 Classification, biodiversity and conservation 18a 182 103 104 18s 106 Cassitcation Biowiversity ‘Maintaining biodiversity rotting endangered spaces Control Interntinal conservation ‘organisations en species 19 Genetic technology wa 192 193 194 195. 196 197 Genetic enginesrng ‘Tools forthe gene technologist, Gene editing Separating and amplifying DNA Aang and storing ei ‘Genetic technology and medicine GGenete technology and agriculture m0 2 Practical skills for A Level P21 Practical skis se 2.2 Planing an investigation sk 2.3 Constructing hypothesis sa P24 dentyng variables 83 2.5 Desribing the seauene of steps 586 2.6 Riskasessment 86 P27 Recording and displaying results S87 P2.8 Analysis conclusions and evaluation 587 P29 Evaluating evidence oo, 2:10 Conclusions and discussion oo, Appendix 1: Amino acid R groups 60s, ‘Appendix 2: DNA and RNA wipletcodss 609 Glossary ou Index 631 Acknowledgements 643> Introduction ‘This theft edition ofthe Cambridge International AS & A Level Biology Courschook, and it provides eveything tt you ned suppor ou course Or Cambridge AS & A Level Biology (9700). 1t provides full coverage ofthe sls or ‘examinations rom 2022 onwards ‘The chapters are arrange in the sme sequence 3 the topics in the syllabus Chapters to PI cover the AS material and Chapters 12 P2 cove the mattial needed for A Level, The various features that you wil find in these chapters ae ‘explained on the next two pages. “Many questions wil esta deeper understanding ofthe facts and concepts that you ‘will lear during your course Is therefore not enough ust toler words and diagrams that you can epeat in your examinations; yo need to ensure that you really understand each concep ful. Tying to answer the questions tha you wl ind within each chapter, anda the end of each chapter, should help you to do tis Although you wil study your biology a series of diferent tpi itis very important to appreciate tat al of thes opis lnk up with each other. You ned to make links ‘between diferent areas of the syllabus to aawer some questions Fr example ou ‘might be asked a question that involves bringing together knowledge about protein synthesis infections disease and transport in mammals In particular, you wl find that ‘eta ke coneeps come up again and again These include: + Clsas units of tie + ochemical processes + DNA, the molecule of hers + Natura seletion ‘+ Organisms in thei envtonment ‘© Observation and experiment. ‘As you work through your course, make sure that you keep refstng on the work that you dd eafier and how it relates othe cureat topic that you are siding. Some of the eflestion questions tthe ends of the chapters sugges particu inks tht you ould think about. They ls ask you to think about how you lar, which my help you to mae the very best us of your time and bilities as your couse progrecs. You ‘an also use the selFevaluation checklists atthe end ofeach chapter o Jee how well You have undetstood each topic inthe sylabus, and whether or not you ae oo more work on each one. Pate sils are an important part of your biology course. You wil develop thes skills as you do experiments and other practical work related to the topics you ae studying ‘Chapters Pl (ir AS Level) and P2 for A Level explain what these skills are andl what you ned o beable to do> caMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK ‘You may ike to lok at two other books in this series the Workbook and the Practical Workbook. The Workbook provides lear guidance on many of the skills ‘tha you need to develop as you work through the course such as constructing and analysing graphs, and planing experiments with exercises For you ot. ‘The Practical Workbook is fl of detatied explanations of how to carryout al the practical required in the ylabus, and many others to, that wil help you to become ‘noe content in practical work, ‘Thissan easing ime o be staying biology, with new discoveries and tecologies constantly nding their way into the news. We very mach hope that you wll enjoy your biology couse and that his ook willhelp you not only to prepare for your ‘examinations but also to develop a life-long interest in this subject, “>| > How to use this serieseee ed ea Lom , ary i —How to use this book > How to use this book ‘Throughout this book, you wil noice lots of eiferen features that wl hep your learing, Thee ur explsna blow “This contains questions and activites on subject knowiadge you wil need before staring this chapter. SCIENCE IN ee “This feature presents reabwodlel examples and applications ofthe content in 1 chapter encouraging you to look further int topics. There are discussion {questions a the end which look at some of the benefits and problems ofthese applications Bene cua “This book does not contain detailed instructions for doing particular ‘experiments, but you wl ind background information about the practical work {yl need odoin these boxes. There are ao two chapters, Pl and P2, which provide detailed information about the practical ails you need to develop ‘duing the course Questions Appearing throughout the text, questions give you a chance to check tha yo have lundrstod the topic you have jst read abou, You can find the answers to thee ‘weston nthe digital version ofthe Coursebook. “Th earatnin is secon then ry he Carre erin bus 70 or amiaton om az You shoud snay nero sprout for te yar tour aon ‘cont ne dear andr maemo the fae document ese ne Conte ‘arial ee acoder og Key vocabulary ishighlighted im the text when is firs introduced Definitions ae then ‘given inthe margin, ‘stich explain ne mmoarings of tase ‘words and phreses You wil alo fied efitions of bese ‘words inthe Glossary tthe back of ie book. ‘Command words that appear inthe slabs and might be used in exams are highlighted inthe ‘ecamstye questions nen they ao fst introduced. fe ‘margin, you wil find the Cambrdge Intemational definition. You ml ‘so find these Sofintions inthe Glossary atthe back ofthe book wth some further ‘explanation onthe ‘meaning ofthese words “>> cawBRIDGE INTERNATIONAL A & A LEVEL BIOLOGY COURSEEOOK ‘Wherever you need to know howto use a forma to catty out calculation, there are worked examples boxes to show you how to do this ‘Those actvitis ask you to look back on the topic covered inthe chapter and test how well you undeestand these topies and encourage you to react on your leaning Important equations, facts and tipsare sven in these boxes. ‘Questions at the end ofeach chapter provide more demanding xamstyle questions, some of which may rquire ‘ue of knowledge fom previous chapters Some question are taken fom pest papers Whete his ithe ee, they include references tothe ekevan past paper. All oer questions are writen by the authors Answers to tase questions ean be found in the gal version of the Coursebook. Etna ‘Theresa summary of ey points atthe ed ofeach chapter Ready to “These boxes tell you where information in Ee ">ey je 4 "eae, [eee oe a4 Saat cd a In thie chapter you willaarn how ‘+ explain that cals are the> CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK Parker nc + Maka a list of structures thet could be found ina cel + Try to write dow the functions ofthe structures you hve sted ‘+ Which stractures are found in plant cll and which are found in animal cells? + Ao thee any calls that ae not animal or plant cls? Ens Progra in scence aten depends on people thinking outside the box’ original thinkers who ae often ignored or even riled when they frst put forward their radical new ideas. One such inci, who battled constantly throughout her carer to gether ideas accopted, was the ‘American biologist Lyon Marglls (1958-2011; Figure 1.1) Her greatest achievernent was to use ‘evidence rom mirobiology to help firmly establish an idea that had been around since the mic 19th century — that new oxganisms canbe created from ombinstions of exising organs, Importantly, ‘the esting organisms are not nacestriy closely related, The exanisis form a symbiotic partnership {hoy lve together na partnership in which both partners benef, Margulis imagined that one ‘organism engulfed fate’ another. Normally the ‘engulfed orgonism would be digested and killed, but sometimes the organism engulfed may survive ‘and even be of bene tothe organism in which itfinds Rel. This ype of symbiosis nov a ‘endosymbioss end’ means inside). A completely new ype of organism is reated, representing a CAMBRIDGE INTERNATIONAL AS 8 A LEVEL ‘Organisms made of cs with membrane-bound ree are now known asco, while the simpler prokaryotes Cu’ means ve, kagon! means mucous "peo means before). Eukaryotes are thought to have volved from prokaryotes more than to bilion years ‘ago. Prokaryotes include bacteria. Eukaryots include animals plants, fungi and some other organisms. ‘eukaryote: an orgenim whose calls contain 3 hucleus and other membrane-bound organelles prokaryote: an organism whose cells do not Contain a nucleus or any ether membrane-bound organelles 1.2 Cell biology and microscopy “The study of els as given rs to an important branch of bilony known a el biology Cal blots study ‘col usng many diferent methods including the use of ‘aious types of microscope. ‘Thee are wo fundamentally diferent types of rnroscope: the ight microscope and the electron imroseope. Both use a form of radiation in order to ‘sce tho specimen being examined. The light microscope Uses light as a source of radiation, while the elect mroscope uses eletrons for reasons which ae digested ater. Units of measurement Inoder to measure objets inthe microscopic wold, weneed to use very small units of measurement, which JOLOGY: COURSEBOOK ar unfamiliar to most people. Before studyingight and ‘leciron microscopy Further, you ned to become familiar ‘vith these units Acconing to interationalagrecment, tbe International System of Units (ST unit) should be wed. In his stem, ‘he basi unit of gt isthe metre (symbol), More units are created by going thousand tines later oF soll Standard prefixes are used for the units Por ‘xampl, the petit kl! means 1000 times. TH, almetre = 1000 metes The units of lngth evant toca ties are shown in Tae I “The smalls structure visible withthe human ee is pout $0-100 pm in diameter (oughly the diameter of the sharp end ofa pin). Te eellsin your body vary in Sie from about 5 ym to 40m, It iit to imagine how smal these ells are, especially when they re clearly visible using a microscope An average bacterial ellis bout I ym across One ofthe smallest stretres you will tuy in this book isthe ribosome, which s only bout 25 am in diameter! You could lineup about 20000 ribosomes across the fll stop atthe eof this sentence, 1.3 Plant and animal cells as seen with a light microscope “Microscopes that us light as a source of raion are allah mieroseopes Figure 1.3 shows how the light microscope works Note: the structure of light microscope is ‘extension content, and is not part of the labs. one thousandth = 0.001 = 1/1000 = 10> milimet mm [ene milionty = 0000 001 = 1/1000000= 10% | micrometre bs [ane thousand milionth = 0,000 000 001 = anomete nm 471000 000 000 = 107 “able thousaneth ofa micromete nits of mossurementselevant to cll sues: | microm 3 thousandth ofa mime I aanomett 31. Callstructure basing trough the specimen NU inten ____— Eveplece lens mages and ince ‘oats theimage fom the obpctve onto the eye hgnebeam a Objective fens cote inht au site LU = Condenser lens focuses the ee at light onto the specimen hel newer between the covers and sie Hohtsouce Condenser es dphragm's osdsghty to pretice a (ativayoT) tom beam gh Figure 1.3: How the ight mizoscope was, The cover i 2 thin shoe of gas ved to cover the specimen protects pecimens om dying ou and ako prevents the objective Ian fom touching the specimen. smalsructres that Copperas edits to ently ‘pola rkochondi clsutace ‘eepy sting seared he eepy staining Figure 14: Suuctue ofa gonralsd ainalcellaretor about yn eso with avery hgh aly ight Figure 14s a draving showing the structure ofa soneralsed animal call and Figure 15 isa draing showing the stueture ofa generalised plant ce, both ‘as sen with alight microscope (A generalised el ‘Shows ll he structures that may commonly befound ina cell) Figures 1.6and 1.7 ar photomicrographs. [A phiotomerograph isa photograph ofa speci seen with ight microscope. Figure 16 shows ome human ells Fig 17 shows plant el te ro a lea Both figures show cel maghifed 400 times, which is equivalent to using the high-power objective ent on ‘light miroseope See also Figures 184 and 1.80 for Tabla drains oF these figures ‘Many of the cell contents are clauses and transparent to they ned to bestained with coloured dest be see, ‘The human callin Figure L hive bas stnec, The ehromatin in the noc particulary heavily sine, “The plant els in Figure 1-5 have not been stained becuse the chloroplasts contain the greonpigrent hlorophyll and ae easily visible without staining Question 1) Using Figures 14and 1 ‘2 animal and plant cls hae in common bb _arefound only in plant els ‘© refund only in animal ells ‘name the structures that Features that animal and plant cells have in common Cell surface membrane Alles ncding those of both eukaryotes ant prokaryotes ae surounded bya vey thin cel arface ‘membrane. This slo sometimes refered toa the plasma membrane. As mentioned befor itis purtally Permeable and contol dhe exchange of matrils between the cell and its environment Nucleus Al enkaryoticeals contain a nucleus. The meus isa rltvly large stuctore I stains intensely and ‘el surface membrane: a very thin mertrane {about 7 nm diameter) suraunding all col; tis partially permeable and control the exchango of materials betwoen the cel and its environment> CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK eae ein yer tonoplast-mambrane tral Smoundegveciie "OS cog callstace membrane plasmodesma— (pressed against ceva) Eoonetsetopinen frcghbounng cas celal loops ra jst ible rst that ‘Spying ‘rede ety snd he Golgapparatus all ametor about 0 jn) a een wth avery high qty baht microecone, Figo 1.6: Cals rm th ining of he han ches 00, gure 1.7: Cals ina reel 40, Many asec Each callshom a centrally placed nuius, which typical rele nade och cl The rane ut ila bck of aial al Tho cls are part of teu known ‘firs inside theclorepass(grars meas grins Cel wal squamous (atone) epithet, Sos deny vale arial calc1) Cellstructure is therefor very easy to sce when looking down the Imicoseope The deeply staining materi in the macus is called chromatin Cehvoms" mean clout. Chromatin isn mass of cold threads. The threads areszen to ‘collect together to form srsomes during nicest tivision (Chapter 5, Section 52, Chromosome). {Chromatin enaing DNA (deonyrihnmtie ak), he ‘molecule which contains the insractions (gone) tha, ‘contr the activites of the cell (Chapter 8). Tis the nucleus an even more deply stining area ‘evil, the acess, Thins made of loops of DNA from several ehomosomes The numberof mice is ‘arable, one to ve being common in mammals, One of {he main functions of nucleo is to make ibosomes. Cytoplasm All th ving mati inside the ell i calla proto {esa uefa to hives ter oll he vig material ide he tes scl yop, Tee “topiam + nes = protoplasm, topless an aqueous ater) materi, varying fiom aud tale consistency. Uses ht Imcroncope, any sal stusuts can be sen thin i Those have bee likened to small oganeand are {herfre Known us organi ening Te organs). [An organelle can be defined anctionsly and Structurally stint part o eal Organs ae oe, but nt alays surrounded by one or wo membranes {0 that ths activites an be separated from he Suroundingextopasn. Organising el activities in Separate conpartnen seen ora struc Complex a an anima or plant cell to work een Mitochondria (singular: mitochondrion) “The most numerous onan ee wih the ght Incrcpeae un etochn ings edn) Mion a ig \Uigattcrostope, Veco of tringce taken with he Tid of ight mone, bv shen tat itech ‘ean move about change shape and divide They are ‘specialised teary out aerobic respiration, Golgi apparatus “These of special sans containing siber resulted in the ole apparatus being discovered in 1898 by Camillo Gols. The Golgi apparatus collects and processes ‘molecules within the esl, particulaely proteins. Note: you do not need to lean this structure. tis sometimes cae the Goll body or Gol complex. chromatin: the material of which ehvomosomes are made, consisting af BNA, proains and small ‘amounts of RNA; visible a patches or fibres ‘within the nucleus when stained ‘chromosome: in the nucleus of the cals of ‘eukaryotes, «structure madi of tig called caMBnDce INTERNATIONAL AS & A LEVEL BloLOGY: COURSEBOOK structure which is outside che cl surface membrane. ‘Thowall is elaively rigid because it contains res ‘of ellos, a polysaccharide which strengthens the Wall, Tho cell Wall pve the cell definite shape. Te ‘prevents the cel fom busting when water ener by ‘osmosis allowing large pressures to develop inside the fall (Chapter 4, Section 4.5, Movement of substances ‘eros membranes). Cel wall maybe enforced with extra ellos or with ahatd material alle iin forextra strength (Chapter 7) Cll walls are feely permeable allowing free movement of molecies and {ons Unough to the call surface membrane Plant calls are lnked to neighbouring cells by means of pores contaiing fine stands of cytoplasm, “These structures are elle plasmon ngula pisses). They are ined withthe cel surface ‘membrane: Movement through the pore is thowht to ‘beconttolled by the structure of the pores Vacuoles ‘Vacuoles are suetbe structures which ae surrounded bya single membrane. Although ania elle may possess smal vacuoles such as phagocyte vacuoles {Chapter 4, Section 45, Movement of substances ‘across membranes), which are temporary seuetures, mature plant ells often possess a larg, permanent, ‘ental vacuole. The plant vacuole x surrounded by ' membrane, che tonplas, which controls exchange between the vacuole and the eytoplasm. The fluid in the vacuole isa solution of pigments enzymes, Sugars and other orpanic compounds (including some waste product), mineral salts, oxygen and carbon dioxide Inplans, vacuoles help to regulate the osmotic properties of cells (the Row of water inwards and ‘outwards as wel as having a wide range of other functions. For example, the pigments which colour the peal of certain flowers andthe parts of some ‘egeables, such asthe red pigment of beetroots, may be found in vacuoles Chloroplasts Chloroplasts are organeles specialised forthe process of photosythesis They ae ound in the green parts ‘ofthe plant, mainly inthe eaves They ae elatively Targeoranlis and soar esl sen with ait Imtoseope Its even posible to see tiny grains’ or frame (Singular: gran) inside the eloropass using ‘light microscope (Figure 1.7). These are the parts ‘of the chloroplast that contin chlorophyl the green Pigment which absorbs light during the proess of Photosynthesis. Chloroplasts are discussed thera ‘Chapter 13 (Section 13.2, Structure and function of chloroplasts). plasmodesma (plural: plasmodesms Povetike stucture found in plant cell wal; plasmodesmata of neighbouring plant col ne tip to form tbe-like pores through the cl wal, allowing the controlled passage of mater rom tne calito the other the pores contain ER nd are lined with the cal sulace membrane ‘vacuole: an organelle found in eukaryoticealls a large, permanent contal vacuole i a typical feature of plant cals, whore it has a variety of functions, including storage of biochemicals such a sls, sugars and waste products; temporary vacuoles, such as phagocysc vacuoles ko, low phage esis may frm n ‘tonoplast: the partially permeable memtyane that surounds plant vacuoles chloroplast an organelle, bounded by an envelope (two membranes in which photosyrhesis takes place in eukaryotes photosynthesis: the production of organic Substances from inorganic ones, using energy from light ‘9rana (singular: granu): stacks of membranes Inside a chloroplasteee ee a ge ee 1 Call structure You can think of plant cell as being ver similar to an anime cll but with entra structures, + Plant cells ae often larger than animales, although cll size varies enormously. + Donat confuse the cll wall with the call surface membrane, Cell walls are relatively thick and phyielly| strong, whereas cell surlace membranes are very thin. Cel walls are rely permeable whereas ell $iface membranes ae partly permeable, Alclls have a call surface membrane, but animal cls do rothave cell wall + Veeuoes are not confined to plant alls animal cells may have small vacuoles, such as phagocytic Making temporary slides ‘A common method of raining materia with alight rmirozcope ito ct thin sos ofthe material called ‘sections. The advantage of ting section is that they are thin enough to allow light to pas through the Section. The section iad (mounted) on a glass slid and covered with a covers to protoct it Light parsing though the section procices an image thi ean then be magnified using the objective ant ‘eyepiece lenses ofthe microscope, liclogica material may be examined lve or in preserved stato. Propaed sides contain material that hs been killed and preserved in Iifetike concton. ‘Temporary ses are quicker and easier to prepare and are alten used to examine Fresh material Containing ling calls In bath cases the sections {re ypicaly sained before being mounted onthe dss tide, ‘Temporary proparations of fash material are useful {or cick prelninayivestigatons. Sometimes ‘macerated (chopped up) material can be used, {when examining the structure of wood (eer) ‘Anumiber of temporary stains are commaniy used For example, iodine in potassium lode soliton is useful for plant specimens stains starch blue vacuoles although these ae not usually permanent structures, black and wil also colour nucle and call walls pale yellow. ute solution of methylene blue can bo ‘sed to stain animal cal such a cheek cell, ‘Viewing specimens youself with microscope wll help you to understand and remember structures ‘our undorstanding canbe reinfored by making a pone drawing on good quality pain paper. Remember avays to caw what you see, and not hat you think you should se, Procedure Place the biological specimen on a clean glass lide and add one or two drops of stan. Carefully ower 3 Cover over the specimen to protect the micrescope lens and to help prevent the specimen rom dying fut Adding a crop of glycerine and mixing ith, the stain can leo help prevent drying out “Suitable animal material human cheek cll ‘obtained by gently sraping tha lining ofthe ‘ook with finger nail “Suitable plant material: onion epidermal cals, lettuce epidermal cells, Chore cols, moss slip leaves (Soe Praca vestigation 1.1 in the Practical Workbook fo addtional information)> camanioce TERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK Biological drawing To reinforce your learning, you wl fd it useful to make labeled drawings of some of your temporary tnd permanent sides, s wells labelled drawings ‘ot photomicrographs Practical Activity 7.1 in Chapt ? provides goneral guidance an biological drawing, Read the relevant tloropast ran ite? callwat saving of te neighbouring anal calor Figure bbhighpower droning of wo aighbourng pant ls om Faure 17 ‘operas rout trom smalstructares (ogee) ‘blero a own) Figure 1.8: Examplas of good ceawingtachniue: a igh poner {See Practical Investigation 1.1 in the Practical Workbook for ational information) sections of Practical Activity 7.1 before answering the quostion below, which ls olevant to this chapter Figures 1.8 and b show examples of good drawing andlabeling technique based on Figures 1.6 ‘and 1.7. Note that its acceptable to draw only {2 roprocontatve portion of the call contents of Figure 1.7, but add a label explaining this. Question 2 Astudont was ake to makes high-power daing (ofthe neighbouring oi fom Figs 15, Figure L9 shows the drawing made by the student. Using Practical Activity 7.1 to help you, sgaet how] ‘the drawing ia Figure 1.9 could be improved ow ‘otopiasm Figure 1.9: studonts high-power drawing of twee neighbouring eal fom Figure 15 >1 call structure 1.4 Measuring size and calculating magnification Magicaton ithe numberof tines larger an mage of an objects than the real sizeof the objet. observed ie ofthe ings ctl see pica sn miaion {etd fe oh yan nen wn) A cal a heft caistren me. yeu kw woo a fan Aon wk culethione rca iter a Selmprun to apntip wee, oo hse se = iyo ee oa inating toto thal ‘ase finland nes Sion . cheekcesonaside —b ‘nthestage ofthe, Measuring cell size (Cells and oxzanlls canbe measured witha microscope ‘by means ofan eyepiece grate, This trnsparent scale Itusally has 100 divisions (ae Figure | 10). ‘The eyepivegraticule is placed inthe mleroscpe yep tat it can heen the sme ime the abject to be measured, as shown in Fire 1108, Figure .10b shows the sae over one of @wroap of six human cheek epithelia ells ike those show in Figure 1.6), The cell selected les between 40 ad 60 on the scale. We therefore say it measures 20 eyepin units in dlameter (the diference between 60 and 40), We will ot know the actual sie ofthe eyepace units nll he ‘eyepiece graticule is calibrated, ‘magnification: the numberof times larger an Image ofan objects than tho real sizeof te ‘object: magnification ~ image size + actual (eal Sev ofthe object {eyepiece gratcule: small scale tht i placed in a microscope eyepiece epic ‘yateuein Uheeypiee stage micrometer a Seater rmirencope Gt mand oh ‘isin Figure 1.10: Microscopical measurement. Thao fof vw sen sing high power O40] objective ee: an eyepiece gata ls; b sypormposed images ofuman chek epshalalcls andthe eyepiece gratcule sae esyptinconed images othe eyepiece gatiode scale and the stage maometer scl,> camanioce TERNATIONAL AS & A LEVEL BIOLOGY: OURSEBOOK “Tocalibrate the eyepiocegratiul a minatre Iransparent le elle stage micrometer i placed on themcroscope stages is ought into foes. Ths scale may be etcheontoa gh side or printed on a transparent Hm. commonly has subdisions of 0. dnd 101 mm. Theimages ofthe stage micrometer and the eyepiece rail en then be superimposed (peal ‘0 tp of one another) as shown in Figur 1.105 Calculating magnification Figure 1.11 shows micrographs of two sections through the same plat cell. The ference in appearance ofthe two micrographs is explained i the next section 1 we know the actual (eal length of a cll in sucha rmirograph, we can calcul its magneton, M, sing the form stage micrometer: very small acuratly dawn scale of known dimensions, engraved on & rmetoscope side ‘micrographs picture taken with the aid of a ‘microscope; a photomicrograph (or ight ‘micrograph is taken using a ight microscope; {an electron micrograph i taken using an lectron microscope Figure 1.11: Micrographs of wo sections of thesame plant cele, ae seen vith sight microscope, and bth ln electon mcoscope. Both ae shown atthe sume ‘megrieation about = 750 1 Inthe eyepiece gratcule shown in Figure 1.1, “The diameter ofthe cll shown superimposed 100 units measure 0.25 um, Hence the vale of ‘on the sce in Figre 1 8b meses 20 eepiene cach ejepisce unit i ‘nits an so ts actual diameter 6.0025 ma 20% 2.5m = 50m This diameter i greatr than that of may unan (r, converting mm om col because the ell fattened epithelia cl 0.25. 1000 ae (a RT RCTS RS »)>Ens Step 2 Suppove we want to know the magnification ofthe plant call labeled Pin Figure -11h The real length oF th cel 80 gm, Use the equation to calculate the magnification. image sie, magnification, 3a Calculate the magnification ofthe drawing of the animal alin Figure 1 z ‘3. Figure 12 shows a lymphocyte with a sale bur. Wecan use this seal ar to calculate the magnification, Step? step3 ‘Stop 1 Measure tho lng in mm of th cll in the cw 4 rnjeropraph using rule, You should ind that ti about SO mm, Step2 Convert mm tom. (It ease if west. conver all measurements othe same ‘nite in thi cae miromnetes, “The multiplication sgn (in font ofthe number (25 means ‘times, Wey tha the magnification So: {m= 1000 fetimes 625 ‘nm = 50% 1000 jm 50000 un Question bb Caleulatethe atl (el) mgt ofthe ‘hlroplast belied X in Figure 1234 ‘Measure the sae ar, Her it 36 mm, 36 mm = 36 1000 ym = 36000 ym “The seal bar epresens 6 jm, This he ctl size, 4. Use the equation to calelte the smagniication image size. ~aetualsize _360004m «6000 agniistion,> camanoce TERNATIONAL AS 8 A LEVEL BIOLOGY: COURSEBOOK Calculating the real size of an object from its magnification ‘To caleulate the rea or ata se of an object, we ean tse the sume magnieation equation. Figure 1.20 shows parts of thee plant cells ‘magnified *5600, Suppose we want to know the actual length af the labeled ehloropast inthis Sectron mirograph, Stop 1 Measure the observed length ofthe image of the ehiroplst (in mm, ‘ing a ruler. The maximum lth is 2s, (Convert mm to 5 > 1000 pm = 25000 jm Step2 25mm Use the equation to cculat the cual length steps image size icon, 25000 um 5000 =45 um (0 one cima place) cual ies, A= 1.5 Electron microscopy ‘Before studying what el look ike with a eletron microscope, you need to understand the difleence between maghifistion and solution, Magnification and resolution ‘Look agin at Figute 1.11, Figure 11a slight micrograph. Figure .11bisan electron micrograph, Both micrographs at of the same cells and both have {he sime magnification. However, you cn se that Figure 1.115 the electron mirograh, is much caret ‘Thisis because it has preater resolution Resolution ‘an be define asthe abiiy to dsingish between two sepate points. If the to pots cannot bere, they wll be seen as one point. In practic, escation is ‘he amount of deal tat canbe sen the gree the resolution, the greater the deta “The maximum resolution ofa ight miroscope i200 nm, ‘The reason for thsi explined in the next secton, "The clecromagnete spectrum’, A resolution of 200 nm means that, if two points or objects are closer togethe- thas 210, they cannot be distinguished a separ. ‘You might imagine that you could see mote det in Figure 11a by magniying i simply makingit lrg) In practice you would beable o sce what iabeady ‘there more ei, bu you would ot se any more etal. The image would just get more and more blurred as mogsfication increased. The resolution Would not bo greater, The electromagnetic spectrum How is resolution link withthe nature of igh? One ofthe properties of light ith ves in waves The Jeng ofthe waves af vse ight vay, angina from bout 00m to abot 700 nm, The human eye ean Aistinguish between these diferent wavelength, and inthe bran the dierones are converted 1 cour dferences Waves that are 400m in ength a sce as ‘ile. Waves that are 70am in length ae son sre Visible ight is form of electromagnetic raison. ‘Therange of diferent wavelengths of elctroragnetic radiation is aed the eletromagneti spectrum. Visible light is only ene part of thi petra. Figure 1-13 shows some ofthe parts ofthe elteomagnete spectrum. The longer the waves, the lover ther Frequency, (Al the waves rave a the same sped, so imagine them passing a post: shorter waves pss at higher frequency) In theory, there is no limit how shor or how long the waves an be Wavclengh changes ‘with energy: th peter the ener, the shorter the wavelength resolution: the ability to cstinguish between ‘wo objects ver close together: the higher the resolution ofan image, the greater the deal that ‘canbe soen1 Callstrcture 000m 500nm ——eodnm 7000 violet “gyn” range ea Figure 1. Diagram ofthe alecromagnaticspactur. The numbers indicat the wavelengths ofthe ifort ypecot Slecromasneti cation Note the waves vas fe very short to verylong, Visible ight is prt tha spectrum. Thedouble tana tochondon ‘nerves wth hgh waves MA UAE Figure 1.14: rstochonion and sme bosoms ia the path ofigh waves of 00 rn ang, [Now look at Figure 1.1. It shows. mitochondrion ‘nd some very smal cll organelles ealled ribosomes. alo shows some wary blue lines that represent ight ‘of 400 am waelength. This isthe shortest visible ‘raveength, The mitochondrion i large enough to Interfere with the light waves However the ribosomes are far oo smal o ave any effet on te light waves. ‘The general rule when viewing specimens is that the limit of resolution is bout one half the wavelength of the radiation used to view the specimen. Inher ‘words, iP an objects any smaller than half the teaelength of the radiation used Lo view i iteannot teseensepartely from nearby objets. This means tha the best resolution that ean be obtained wing a Imiroscope that uses visible light (alight microscope) {2200 nm snc the shortest waelength of visble hight {400 am (volt light) Ribosomes are approximately 25 nm in diameter and ean therefore never been Using a ight microscope 1am objec transparent, wllallw ight wanes pas through it and therefore wil sil no be vise This Fe wty many biological stuctures have to be stined bre they ean be een. Question 4 Explain why ribosomes are not visible usin alight smiroseope The electron microscope So how can we look at things smaller han 200 i? The only solution o this problem isto we maton of shorter wavelength than Vibe ight I youstady Figure 113, you wl se that ltl ight or X-rays Took like possbl candidates. A much titer slution, though, ito ueelectrons Eetons ae negatively ‘charged partes which oi the macys of a om ‘When a metal becomes ery ho, some of i elestons >> _camartoce INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK tin so much energy that they escape fom thei orbits, similar oa rocket escaping from Ears gravity. Fee ‘dzcroas behave like electromagnetic ration, They he avery short wavelength: the greater the ene theshorte the wavelength, Electrons area very stable fou of ration for mirosopy for two major reason. rst, their wavelengths extemal short at est a short at hat of Xray), Second, unlike Xray they ae ‘negatively charged, ey cam be focused easly using clectromagness a magnet can be made tater the pth of the beam, the equivalent of gs lens bending ih) Using an electron microscope, resoation of 05m ean ‘be obtained, 400 mes beer than alight microscope Transmission and scanning electron microscopes ‘Two types of eleciron mieoscope are now in common use. The transmission eletton microscope (TEND wat te ype orginally developed, The beam of electrons x pased through the specimen before being viewed. Only those lectrons that ae transmitted (pass through the ‘spetmen) are see, This allows wo se thin sections of ‘Specimens andl thus to seeinsie cll In the seaming ‘lecton mieoseope (SEND, the elect beam i used uctres and only the reflected An example of a scaning electron micrograph is shown in Figure 1.15. The advantage of this micrssope ith sure structures eam be see, Because mich of the ‘specimen isin fous athe same time, a threedimensional ‘appearance is achieved. A disadvantage of the SEM is ‘att cannot achive the sume resolution as TEM, ‘Using an SEM, resolution i between 3am a 20m, Figure 1.15: Scaning elation micrograph SEMI of» tardrade.Teegrades or water bea ate about 5mm long. ith four pas of logs. They ae corron nso and an sunive extreme ecnmontl conan 88, > Viewing specimens with the electron microscope Figure 1.16 shows how a TEM works and Fig 1.17 shows onc in us slectron gun and anode produces beamafelectons ‘econ beam (atinay oleae E =} condenser slectronognetic L lene~dectethe ton bean ‘ont the specimen specimen placodona or objective tectromagnetic Tens = produces an mage projector electompnetic enses focus the nognied Image cntotheseran — ||. seren or photogephic fim senor shows eine Figure 1.16: How 2 TEM wok, Note: the structure of an electron microscope ‘oxtorsion contont, and is not part of the aylabus, isnot posible to sean elecron beam, soto make the image visible the eleetuon beam as tobe projected ‘onto Muoresent serezn. The areas it by eletrons1 call structure shine bright, giving veal aback and white picture “The stains used to improve the contas of biological spscmens fr electron microscopy contain heavy metal atoms, which stop the passge of electrons. The resling Picture slike an X-ray photograph, with the more ‘Sensoly stained parts ofthe specimen appeaing blacker Fals-colour images can be created by colouring the standard black and white image using a computer. Question The clectron beam, and therefore the specimen and ‘he Muorescent sree, must bein a vac. If the ‘lectrons collided with tr molecules they would cttt, ‘making imposible to achieve a sharp picture Also. ‘rater boils at room temperature ina vactum,s all Specimens must he dedrated before being peed in {Me micranpe, Tht meane that oy send meri or non-living eat be examined. Great effris are tere ‘made to try to preserve material in aifeike sate when preparing ifr electron microscopy. 1.6 Plant and animal cells as seen with an electron microscope ‘Thefine (Getaled) structure of acl as revealed by the CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK Question 7 Compare Figue 121 with Figure 1.5. Name the structures ina plant ell hat can be sen with the electron ‘mroscope but not With the ght microscope ‘al wal of nighbourng cs tonopast celsap we stein = cal face menbrane (essed apant cel wal bosoms ces} yorain ear emetape ‘twomembanes) roughER —icoubule Figure 1.21: Urasrcture of typical plant calla saan with he lecton microscope, The daing based on nay ‘uae stron nveny bu ts mer oes shaw ee enone ny aabe me seas ce sac enone oes Cell surface membrane cet nenbone eps ‘The cell surface membrane is extremely thin (about (ahead wifoapete heater Tom). However, at very high magnifications ican be seen to have thee layers —tvo dark (heal stained) layers surrounding a narrow pale interior (Figure 1.2), “The membrane is partially permeable and controls xchange between the cell and its envzonment “Membrane strtare is icussed Further in Chapter 4 Figure 1.22 Cel sufsee mamibrane 25000) A the rmazrication the marae appenrs two dk nes at {he edge oth caMicrovilli crv (single: coils) ae fingrsikeextensions ofthe cell surface membrane. They are ypc oferta ‘imal el, such as epithelial cells Epithelial ols cover the surfaces of strueturs. The nero prety increase th surface ea othe cell susfae membrane shown 0 Figure 119. This uefl for example fr rebsonpion inthe proximal convoluted tubules ofthe kxiney atid for heorpion of digested food into cls ning the et. ‘microvilli (gngular: mierovillus: smal, ngarike ‘extensions ofa cel which increase the surface tara ofthe call for more efficient absorption frsecretion Question 8 Using the magnification given, determine the actual maximum diameter of the maleus shown in Figure 123, b Thediameteryou have clelated forthe nucleus shown in Figure 1.23 st scesaty the maximum diameter ofthis maleus Explain ‘wy thsi the ease. Use madeling clay to make aspherical shape (eal ikea nucleus. Tr cuting into two at different places and ooking atthe sizes of te cut ‘surfaces. Ths ropresonte the process of sectoning ‘materal for examination using a miroscope Nucleus: ‘Thenucleus (Figure 123) the largest cell org, Figure 1.28: Transmison electron micrograph (TEM) fancies. This the sues of elo the pancas of bat (61000) The cel deus surownded by a deube layered nuclear envelope containing neat pore. Thenadeolsie ‘mote dy tained, Rough Es vse inthe reunding cope,CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY COURSEBOOK The nuclear envelope “The mcs ir sounded by two membranes foming Ate ehelope The omer membrae of tenor Ernlpe ir contnaous with the enoplsaeeicuam (Gignes 119 and 12, “The mica envelope has many small pores called ler pores These allow and control exchange between th auleus and the etoplasm. Examples of substances Jeavng the icles through the pores are mesenger RNA (mRNA), uansfer RNA (RNA) and ribosomes for protein synthesis Examples of substances entering ‘through the miler pores are proteins (to help make ribosomes), aeleotides, ATP (adenosine wiphosphate) ‘and some hormones such as thyroid hormone T3. Chromosomes and chromatin “Thenucleus contains the chromosomes. Chromosomes, ‘entain DNA, the gene material. DNA is organised into functional units called yes. Genes con the ‘tvs of th el ad inheritance; thus the nucleus onto the eas activin ‘The DNA molecu ares long (a human ell eontins shout two metres of DNA) tht they have tobe folded ‘up intoa more compact shape to prevent the strands ‘becoming tangled. This is achieved by combining with reins, partially wth proteins known as histones. ‘The combination of DNA and protein is known as chromatin, Chromatin also contin some RNA. Thus, chromosomes are made of chromatin (Chapter 5, ‘Section 82, Chromosomes). When el isabout to dvd the cs vides isso tha ‘ech new cl wile its ow niles (Chapter Sand 16) Also within the nutes structure called the nucleolus, Nucleolus ‘Thenucleolus appears. darkly stained, rounded structure in the nels (Figure 1.23). As mentioned Earlier one or more maybe present, although ones most, common Its funetion isto make ribosomes ising the information nits on DNA. contains a core of DNA from one or more chromosomes which contain the genes {hat code for ribosomal RNA (FRNA), the form of RNA. ‘wed in the manufacture of ribosomes Tt ao contains ‘ene for making RNA. Around the core ar ess dense ‘egions where the slbosomal subunits are assembled, ‘combining the rRNA with ribosomal proteins imported fiom the eytoplasm, The more ribosomes a ell makes, the lager its mucous ‘The diferent pars ofthe auleolus only come together bring the manufactur of ribosomes: They separate when, a during nuclear division, sbosome synthesis ‘ceases The miclolusas a structure then dssppsars Endoplasmic reticulum ‘When cls wr fir sen with the clton moses Soloists were sme toe so mth dtl rere “Thecus of much of hs ad not bon upte ‘This atl he posi (Ci) gues 123, 2¢and 12), The maeaes of the ER orm Matec compartments called as oF Figure 1.24: TEN of ugh ER covered with bso (Bic dos (17 050, Some fee ibesomas cana be seen nthe cropasm on thot. nuclear envelope: the two membranes, stuated dose together, tha surround the nucleus the ‘envelope is perforated with nuclear pores nuclear pores: pores found inthe nuclear envelope ‘which contol the exchange of materials eg. ‘mRNA, between the nucleus and the etoplasm endoplasmic reticulum (ER): a networkof flattened sacs runing though the eytglasm of ‘eukaryotic cell; molecules, particularly proteins, can bo transportod through the cel inside the acs Separate fom the rest of the cytoplasm: ER Fecontinuous wth the auter membrane of the nuclear envelope 2)1 Coll structure ‘dxtorac. Processes can take place inside the cisternae “epaated fom the cytoplasm. Molecules, particularly prolens cam be tansported through the ER separate From the rest ofthe etoplasm, The ER i continuous with the outer membrane ofthe nuclear envelope (Figures 1.49 and 1.20, Rough endoplasmic reticulum “There are two pet of ER: rough ER (RER) and smooth ER (SER). RER is socalled because its covered with many tiny ongunels called ribosomes {described late), These ar jas visible as black dots in Figures 128 and 1.24 Ribosomes ae the sites of protein sythesis (Chapter 6). They canbe found fre in the eytoplasm as well aon the RER. ‘Smooth endoplasmic reticulum SER has a smooth apearance because it ick ribosomes I his completely dierent unetion to RRER Ita lipds and steroids such as cholesterol and the reproductive hormones oestrogen ad testosterone. SER also a major storage ste fr caleium ions This explains wy cis abundantin muscle cel, re calcium fons are volved in must contraction {Chapter 15, Section 153, Mute coneation). In the liver SER is involved in drug metabolism. Ribosomes ‘bosoms are ery small and are not visible with 2 light microscope. At very high magnifications using tncectron microscope they ean be seen to consis, fortwo subunits a large ad smal abut. The Sines of structures this smal ar often quoted in S ‘nis (Svedberg units). S units area measure of how rapidly substances sediment na high speed centage (an ulvacentige). The faster they sediment, the higher the Sumber. Eukaryotic ribosomes are 808 ribosomes, The rbosomes of prokaryotes are 708 "ibosomes so ate slightly smaller. Mitochondria and ¢hloroplasis contain 708 ribosomes revealing their prokaryotic ongins (ee the sections on mitochondria and chloroplast), ‘Ribosomes are made of roughly equal amounts by ‘mass of ribosomal RNA (¢RNA) and protein, Thi {hroe-imensional structure has now been worked ‘ut (Figure 1.25) Ribosomes allow al the interacting ‘moleules involved in poten synthesis such as mRNA, RNA, amino acids and regulatory pros, ‘o gather together in one place (Chaper 6, Section 65, Protein symtbess) Figure 1.25: Stroctre ofthe human 05 oso Golgi apparatus ‘The Gol apparatus ita stack of tend sts cae sSslerna (Figure 26). More than one Gol apparatus ‘may be present ina cl, The sac constantly being formed at ne end from vesicles which bud of om. the ER, and are broken down again atthe oherend to form Golg shes, The stack of ses together with the sssocited veils referrd 0 asthe Goel apparatus or Golgi complex ribosome tiny organelle found in large rhumbes in all els; prokaryotic ribosomes fare about 20: in diameter while oukaryose ‘ibosomes are about 251m in clameter Golgi apparatus (Golgi body, Golgi complex} {an organelle found in ukaryotc calls; the Golgi “pparatus consist af a stack of fattoned sas, Constantly forming atone end and breaking Up Into Golgi vesicles atthe other end Golgi vesicles: eany their contents to other parts ‘ofthe cel often to the ell surface membrane for secretion; the Gola apporatus chemicly ‘modifies the molecules anspor, ©. segars ‘maybe added to protons to make glycoproteins) cammtoce INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK “The Gol apparatus collet and processes molecules particularly proteins rom the RER. Itcontains Jnundred of enzymes for this purpose. ter processing, the moleeles can be transported in Goi vesicles to ‘othe parts of thecell or out of the ell Releasing ‘moletls from the call cll scretion and the pathway followed by the molecules is called the seretory pathway. These are some examples of the functions of the Gols apparatus Figure 1.26 TEM of Gola apparatus A conta tack saucerhaped sac canbe sean budding of sme Gogh ‘se (yee) Tho ma fom zecretoy vals hace ‘tents canbe elened ot the call anf enceytons (Chapters + Gols vesiies are used to make ysosomes + Sugrs are added to proteins to make molecules known as gycoprteins ‘+ Sugrs are added o lipids to make sjcolipids Giyeoprotcns and ebysoipds ae important ‘samponents of membranes (Chapter 4, Section 442, Steucture of membranes) and are important ‘molecules in cel signaling (Chapter 4, Section 4.4, (Cat signatng). * During plant el division, Gols enzymes are involved inthe synthesis of ew ell wall, + Inthe gut nd the gas exchange sytem, cells. called goblet el release a sbtance called cin fiom the Golgi apparatus (Chapter, Section 9.4, Warming and cleaning the ai) Mucins one of the ‘main components of mucus Lysosomes [soso ae simple ses, surrounded by sng ‘membrane In animal cells hey are usually 01-05 um in meter (Figure 1.27-In plan call the lenge central ‘vacuole may set as a isosome although sesomes similar o these in animal cells ae also see inthe ytoplasm. lysosome: spherical organelle Found in eukaryotic cel contains digestive (hydro) ferzymos and has a variety of destructive {unetions, such as removal of old cll organelles Figure 1.27: Lysosomes orange in mouse tidy cal (5000, They contain cll race inthe process of gestion. Gpoplsm is eoloured buehor. Lysosomes contain digestive enzymes, The enymes elle hydrolases beens they cary ont yobs reaetons. These enzymes mist be kept spare fom the rest ofthe cell to prevent damage: Lysosomes are responsible forthe breakdown digestion) of anwanted futstanoes and sructres such as old orgneles of ‘even whole cel, Hydrolysis works fastest in acid ‘environmen so the contents of ysosomes ar acidic, pI4- compared with 65-7.0in the surounting Eytoplasm. Among the 60+ enzymes contain in Tysosomes are proteases, lipases ad nocleass which breakdown protcns, pis and mucec acids respectively ‘Theenzymes are synthesied on RER a delivered to 'ysosomes via the Gol apparatus “>‘The actives of lysosomes cam be split into the four citeories discussed below. Getting rid of unwanted cell components Lysosomes can engulf and destroy unvanted cll components, such as molecle or organelles, that are Toca inside the cel, Endocytosis Endocytosis is described in more det in (Chapter 4 (Seton 4.5, Movement of substances across ‘membranes). Material maybe taken into the cel by erndeytosy, for example when white blood ells gl Tmaetria.L3sosomes may Tse with the endocytic. ‘vacuoles formed and release their enzymes to digest the contents Exocytosis “Lysosomal enzymes may be reased fromthe el for tracellular digestion, An examples the replacement of catlge by bone daring development The heuds of sperms contain special sosome he aerosome for digesting a path through the layers of els surrounding the eg jut befor fertlsation, Self-digestion The contents of lysosomes are sometimes released into the etoplsm, This ests inthe whole cell being Aigesed (proces called autolysis). This may be part ‘of normal development, s when a tadpole tail is reabsorbed during metamorptosi or when ers is restored tits norma size ae pregnancy Te also curs fer the death ofan individual as membranes lose thie arial permeability Mitochondria Structure The structure ofthe mitochondrion (pra: mitochondria) as een with the electon microscope is ‘xl in Figures [18,128 and 1210, Mitochondria ae usualy about um in dameter and ean be various shapes, offen sausage-shaped asin Figure 1.28. They ae surrounded by two membranes (an exvelop) ‘The inner membrane fe folded to form finger-like cyst Singular: erst which project int the interior ofthe mitochondrion which ie called the matrix. ‘Thespace between the two membranes called the intermembrane space 1 Call etructure Figure 1.28 Miochorion ange with is doutle membrane fnvlope: th inner ambrane is fla to feem rate 12000) Micchondia a the sit cf eric «eal rogpration, Note aso the RE “The number of mitochondria ina eli ery variable. As they ate responsible for aerobic respiration, it ot “surprising that cls with high demand for ene, suchas lverand muscle ol, contain large numbers of mitochondria. Alive ell may contain as many as 2000 If you exer regularly, your meses wll Functions of mitochondria and the role of ATP ‘Te main function of mitochondria cary cut aerobic respiration, although they do have ther Funetions, such asthe synthesis o ips, During expiration, a sere of reactions takes place in which nergy is eeased from eneaysich molecules suchas ‘Sipars and fats Most of the energy is tanserel 10 roleules of ATP (adenosine trihospate), This the nergy-carying molecule found in al ving el. eis known as the universal enegy crc. cristae (Gingular: rst): folds of the inner ‘membrane ofthe mitochondal envelope on vihich ae found stalked particles of ATP sypthase and electron transport chains associated with aerobic rspiration ATP (aceonosin tiphosphatok the molecule ‘thats the universal energy cuency inal ving calls the purpose of respiration is to make ATP> camaRince TERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK “The retetions of respiration take pice in solution in the mati and in the inner membrane (rise. The matrix onlains enzymes in solution, including thos of the Krebs ele Flecton caries are found in the esta, For more det soe Chapter 12 (Section 12.2). ‘Once made, ATP ewes the mitochondrion and, as itisa small, soluble molecule it can spread rapily toall parts ofthe cll where energy is psd. Ns neg i released by breaking the molenle down {© ADP (adenosine diphosphate). This sa hydrolysis reaction, The ADP then be rcyled in 8 rilochondrion for comersion back o ATP during serobie respiration, ‘The endosymbiont theory tendosymbiont theory is extension content, and is not part bus. Inthe 1960 it was discovered that mitochondria and hogopasts contain ribosomes which te hts ‘than those in the eytoplasm and are the same size as those found in bacteria. Cytoplasmic ribosomes are 80S, while those of acters, mitochondria and chloroplasts fate 70S was also discovered inthe 160s that ‘itochondia and chloroplasts contain smal crcular DNA molecules, also ike those found in bacteria. It was later proved that mitochondria and chops ae in ffs, ancient bacteria which now ie inside the larger tls of animals and plants Ge "Thinking outside the ‘bos atthe begining ofthis chapter), This known asthe endosymbiont theory. Endo” means side’ and 4 symbionts anorzanism which ies in a mutually ‘beneficial lationship with anther organism. The DNA and ribosomes of mitchoodria ad chloroplasts ae sill ‘civ and responsible forthe eoding and synthesis of ‘rian vita proteins, but mitechondsia and ehloroplsts ‘anno long live independeny. Mitochondrial ‘bosomes ae just vsble sty dark orange dot inthe ‘mitochondrial matrix ia Figure 28, Microtubules and microtubule organising centres (MTOCs) Microtabules re ong gi, hollow tubes found in ‘he eytoplasm. They are very smal, about 25 nmin siamete. Together with atin filaments and intermeite laments (not discussed his book), they make up the ‘ytosteeton, am essential strvetural component of els hich helps to determine cell shape ‘Microtubules are made of a protein called tun, “Tubulin has two forms, ectubulin alpha-tubui) and B-tubulin beta-tubaln). c- and -cbulin mokeules combine to frm dimes (double molecules). These imers are then joined end to end to form lone ‘protofilaments. This isan example of polymerisation, the proces by which giant molecules are mace by joining together many identical subunits. Thee rotoflaments ne up alongside each other na ring to forma extnde with a hollow centre This ylnder the microtubule: Figure 29a shows the heed pattern Formod by neighbouring cand tubulin mobeules. Apert fiom theit mechanical function of support, ‘microtubules havea numberof other funetions. + Secretory veses and other organelles ad ell components an be moved slong the outside furftces ofthe microtubules, forming an intracellular transport system, as inthe movement (of Golg veils during exocytosis + Dring nckear division (Chapter 5), a sine ‘made of microtubules i sed forthe separation of ‘chromatids or ebomosores + Microtobuss form par of the structure of centrioles ‘+ Microtubules form sn essential part of he ‘mechanism involved inthe beating movements of cis and lage “The asembly of microtubules rom ubulin mobos is controled by special locations in al called miotuble ‘npanising cents (MTOCS), These are deus further in the flowing setion on centrioles Bocuse of ter imple ‘onstruction, microtubules canbe formed and token down, ‘ery enya the MTOCS, according toned. ADP {acionosine diphosphate: the molecule ‘thats converted to.ATP by addition of [Bhosphate (a eaction known as phospheyation) ‘uring cal respiration; the enzyme responsible is [ATP synthase; the reaction requires enorey ‘microtubules: ny tubes made ofa protein nerscanrevesbly Sita oa mero = “Teds fom 1 peotoflament ound aheliow coe ‘hediers havea fale arangemnt Figure 1.292 The structure ofa microtubule arb the srangemant of miceubules in two call. The mctubules ae Centrioles and centrosomes Note: Centrosomes ae extension content, an are not part ofthe syllabus, The extra resolution of the election microscope reveals ‘hat just ouside the nucleus of animal ell there are ‘eily tv centrioles and not one a it appears under the light microscope (compare Figures 14 and 1.1). tuple of microtbutsone omplete micrtubute ond ‘wort micwte) ees Figure 1.30: The suc ofa cnt. conse af rine gous of mrotubules. Each group is mede up ofee rcotbuls, tuple, They lie close together and aright ange to each oer ina region known asthe cntonone. Centrolesand the ‘etonomte are absent from most plant cell ‘centile is hollow cinder about 501 ons, formed fhoma ringf shor microtubules Fach entolecontains ine tps of microtubules (Figures 30 and 131, Ut cently it was belived that centrioles act as [MTOCS forthe assembly ofthe microtubules tht make up the spindle daring nuclear division (Chapter). 105 now known that this is done bythe centrosome but dass not involve the centrioles However, centrioles are nse for the production of ea. Centrioles are foundat the bse of ea and gel, where they are knows basa bodies The centrioles at ns MTOCs. The microtubules tha extnd from the basal bodies nt the cin ad Magen are eset for the beating movernents ofthese oman. controle: one of two small, cynical stctres, ‘made from microtubules, found just outside the nucleus in animal coll, in a region known a5 the ‘centrosome; they ae also found atthe bates of lia and Nagel centrosome: the main microtubule organising entre (TOC) in animal calls> CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK Figure 1.31: Contos in ranoveree and anginal ston (TS and (5) x8600 The one onthe ltr aon ‘Sand deal shows the ine pat of miotubules which ‘maka up the stucure. cilia 6ingular: lium) whip structures projecting from the surface of many animal celle and the cells of many urea erganisms; thoy ‘beat, causing locomotion or the movement of ‘id aroee the call surface flagella (singular flagellum): whip-ke structures projecting fom the surface of some animal calls fd the cells of many urieolular organisms; thoy ‘beat, causing locomotion or the movement of ‘id arose the call aurface; they are ietial in structure to cil, but longer "Note: the structure of fagelais extension content, and not par of the sylabus. celsutace membrane Cilia and flagella Cin (sng: lian) and ages singular yl) have Mental structures They ae whips, beating ‘extesion of many eukaryote ells Each is srroundet tyyan extension ofthe el surface membrane, They were given diferent names before their structs were discovered: Hagel ae long and found wsuallyone oF two per cll, wera lia are short and olen wumerous Structure Cia and flagella are extremely complicate succes, ‘composed of over 60 different polypeptides his ‘complet results in very ine contol of how they beat The structure ofa clu is shown in Figure 1.32, Cilia have two central microtubules and ring of mine microtubule doublets (MTDs) around the ouside ‘This refered to as a°9 +2” structure: Each ITD contains an A and a microtubule (Figure 1.8). ‘The all of the A microtubule complete rng of 15 protoflaments and the B mirotubuleatached isan incomplete ring with only 10 protailameats (see Figure 1.32). Figure 1.3 shows that each A ‘microtubule has ona and outer arms, These a6 made of the protein dyncia. They conacet with the B Imirotubules of neighbouring MTDs during beating. You imagine the micotubale in three dimensions thes !e wo rows of several hundred dyin arms slong the Outside ofeach A microtubule The whole eyladical fHructure inside the el surface membrane cle the OQ» 2 singlet microtubules evi ae ee £75 owe uv Figure 1.32: The structure of cum, a Actum saan in TS. Note the 9 +7 arangemant of microtubules DA clun, TS ofthe cium +2 and bel body tpt ate ls show, | TT I RT A RTT 2)At the base ofeach cium and dagllum isa structure called the basal body which sient in structure to the entriole We now know that controls repiate themeelves to produce these basal bodies, and that iia. ‘and lagela grow fom basal bodies. Figure 1.33 is 8 Scanning electron mierograph of ela in the respiratory Figure 1.33: Scaming alecron micrograph of lan the repeat wae Beating mechanism ‘The beating motion of cia and Hag is caused by the Ayuein (protein arms making contact wit, and moving slong neighbouring microtubules. This produce the {ones eeded fr cilia to beat. As neighbouring MTD slide past each other, the sliding motion x converted into bending by other parts of the ium, Functions 16 the eis tached to something so that it cannot ‘ove, ui will move past the eal I the calls not tached the cll il win through the fd. Single- Called organisms can therfore use the ation of eia and fags for locomotion. You wiles be able find videos of such motion on the internet a vertebates, beating iia are found on some epithelial ces, suchas ‘hose lning the srways (Chapter 9) Here more than {Omilion ela may be found per mm. They maintain ‘low of mucus which moves dabis such as dust and Teta from the respiratory tact Question 9 Invertebrates beating iia ae aso found en the epithelia alo the oviduct (the fube connecting the ory to the ters), Suggest what uncon lia have in the oviduct Chloroplasts The struetue ofthe chloroplast as sen wth theetetron tmiroscope is shown in Figures 120,121 and 134 You ea also se higheresoltion micrographin Figure 13.4. Chloroplasts tend to have an elongted shape anda diameter of about 3-10 um fompre | ym ameter for mitochonda). Like mitochondria they ate surrounded by two membranes, which form he ‘horoplast envelope. The main fnetion of eloroplasts isto carryout ‘photosynthesis During the fst sage of photomathesis (Ghelight-dependen stage, light nergy is sored by Photosynthetic pigments paticalarychloroptl. The ements are found onthe membranes of the ch oroplast ‘Themembrane system consists of Hide sacs called tla, which spread out ke sheets in thee > camBRo0cE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK ‘Groular DNA. In eetron micrographs, the sibosomes ‘can jst be sen as smal lack dots in the stroma (gure 1.4). ‘As with mitochondiaithas been shown that Chloroplasts ovginated as endorymbote bacteria, fn this case photosynthetic ble-preen bacteria, The endosymbiont theory is dscussed in more detail inthe tarher ston on mitochondria Cell walls Structure The fist walls formed by plan calls ae known primary walls Tey are relatively igi. Te primary wall ‘onsets of paral! bres ofthe poysacharie close ‘running trough a mati of other polysaccharides ‘Sich ss potins and hemicluioses Cellulose fibres are Inlasticand hav high esl strength, meaning they are df to break by pling on each end, This makes itdificult to setch the wall, or example when water centr the cell by osmosis "The structure of ceulose is ‘escribed in Chapter 2 {in most alls extra layers of ellulse are added tothe frst ayer of the primary wal, forming a seconds vel, In given lier te cellos besa paral, but {he fibres of eifornt layers ran in diferent directions forming a erossply structure which s stronger asa result Ge Figure 210), Figure 1.3: Tro clorplets (x6 00, yaoi lon run through the stems dak re) end ae stacked in places to form cana Back ceae among th thylakoid re line rope See als Figures 13.35nd 138. CHoroplst X isvfered tain Quertion So, ‘Some cell alls become een stronger and mor rigid by theaddition of lignin. Xylem veel elements and scleenchyma ae examples (Chapter ) Lignin adds ‘compressional strength to tensile strength (it revens ‘uekling). Is what gives wood (secondary x3lem) strength ands needed for suppor in shrubs and ces. Functions ‘Some ofthe main functions of call walls are sumarised bone + Mechanical strength and support fr ingvidual ‘lls and the plant asa whole Ligation x one means of support. Turd tues are anoher means ‘of support that dependent on srong cl wall + Callas prevent cx from bursting by osmosis iTeallsare surrounded by a solution witha higher water potential (Chapter 2) + Dilferent orientations of the yer of eet ulose ‘bres help determine the shapes of ella they rom ‘+The stem of interconnected el wall ina plant isealled the apoplast. Ie isa major transport route {or water, inorganic ions and other mateals| (Chapter ‘+ Living connections through neighbouring ell wal, the plasmodesmata, help form another trnsport pathway Urough the plant known as the symplast (Chapter. ‘+The cell alls af the wot endoderm are impregnated with suberin, «waterproof substance that forms a arse othe movement of wate, thus helping in the contol of water and nea on uptake by the plant (Chapter 7. + Bpidermal ells often have a waterproof hye of way eatin the ction dei outer wal. This helps reduce water lose by eraporation, Vacuoles ‘As we have seen, animal cell vacuo are relat small nd include phagocytic vacuoles, food vacuoles and sutophagie Yacoles ‘lke anima els plant calls typically have alange central vacuole (Figure 1.20) Some examples of the fonctions ofthe large cena vacuole of pant are Histed ‘below Ieisuseful to uy to remember ne o 00 oF these cxamples »)>1 Coll structure Support ‘The solution in the vacuole relatively concetrte. Water therefore enters the vacuole by osmosis inating the vacuole and causing a build-up of pressure. A ally insted cel described ws turgid. Turi sues help to suppor the stems of plants that lack wood (wing ‘demoasttates the importance of this). Lysosomal activity Plan vacuoles may contain hydrolases and act ax lysosomes Secondary metabolites Plans contain wide rane of chemicals known as secondary metabolites wish although no exential for growth and deselopmea, coatibue to survival in various ways These ar ofien stored in vacoles. Examples oftheir fetons ae + Anthocyanins are pigments that are sponsible or mos ofthe ed, purple pink and blue colours of fers anal ruts They ata polinators and sod disperser. Eien nan + Certain alkaloids and tannins deter herbivrs fom cating the plat. + Latex, milly fd can acumulate in vacuo, for examplein ubber trex The le of the opium poppy contains alkaloids such as moxphinefrom ‘which opium and heroin are obtained Food reserves ood reserves such as eros sugar beet, oF mineral salts, maybe stored in the vacuole Protin-storng ‘actos are common in sod Waste products ‘Waste products, suchas estas of ealium oxalts may bestored in vacuoles. Growth in size ‘Osmotic uptake of water into the vacuoles responsible for most af the inreaseinYolume of plant esldring growth. The vacuole occupies upto thd ofthe foal fell volume ‘Werk in groups often. Each group should make one copy ofthe following table on sti card START Photosynthess occusin this organalla Chloroplast ‘Nucleus Ribosomes eval Nucleolie Chromosomes are found in this structure in eukaryotic alle These are found on ough endoplasmic reticulum (RER) This structure contains cellulose ae a strengthening material Makes ribosomes Sito of ATP symhesisin aerobic respiration ‘Mitochondion | Makes lysoromes Golglapparatus [Has a9 +2 arrangement of mconubues [churn Mainly contains digestive nays ysosome END CCutup the cad o that each piace of card has one tm andl ane desctiption (one row of the table). These are therefore tn card ‘Shuffle the cards and take one each, The student with the START card ead out the description and the student who has the cortct matching trm reads out THE correct term from their card. They then read cut the ‘esctption onthe card. This continves unt reaches the END card Your teachor will help fyou get stick. ‘The cards canbe reshufled and the activity repeated to 90 ifyou can doit aster the second tine,) cam@rioce INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK 1.7 Bacteria ‘You wil eal that ther re two Fundamental types fel: prokaryotes and eukaryotes The plant and “imal els you have studied so fa are eukaryotic els Bacteria are prokaryotes and their ess are mac simpler than thse of eukaryotes Prokaryoti els re generally bout 1000 times sale in volume an lak a nucleus that is surrounded by a double membrane. Prokaryotes fate thought o ave boen the first ving organisms Earth. The carlist known fss prokaryotes are about 4. bilion year old (dhe Earth was formed about 43 billion years ago). Most biologists belive that eukaryotes evolved from prokaryotes about Zillion ‘years ago. There are two groups of prokaryotes, known ‘as acteria and Archaea (The cassifeation of ving ‘uganismssdscused in Chapter 18) We consider only actri in this book. calla eptidoyan| cellautace ‘ola ‘ee Sraleileof ON Severna bepresent Structure of bacteria ne 1.38 shows the structure of a typical cron (plural acter) The et side of thedgram shows the sSrctures that are always present. The right sie of the caMmtoGe INTERNATIONAL AS & LEVEL BIOLOGY: COURSEBOOK 1.8 Comparing prokaryotic cells with eukaryotic cells ‘Tble 1.3 compares prokaryotic ell with eukaryote cll Prokarytes are thought to have evolved | Eukaryotes are thought to have evolved about 1.5 lio about 35 billion years ago. yeas ago. Thee sypical clameteris 1-5 ym Calls re up to 40 ym diameter and up ta 1000 times the volume of prokarytie cll. DNAs creulr and fee inthe etoplast [DNA snot circular and is contained ina nudeus, The nadous i isnot surtounded by a double membrane, | surounded by a double membrane (the nuclear envelope. 708 ribosomes are present (smaller than [60S ribosomes are present (larger than those of prokaryotes) those of eukaryotes ery few types of ell organele are Many per of cal organele are present. Peseclcc ae brecenr eben |. Some organelles ae surounded by a single membrane {@.. lysosomes, Golgi apparatus, vacuoles, E. + Some are surrounded by an envelope of two membranes (eg. nucleus, mitochandvion, chloroplast ‘+ Some have no membrane (6.9. ribosomes, centols, microtubules The call wall contains peptidoglycan a | A call walls sometimes present (e.g in plans and fang) t polysaccharide combined with amino | contains cellulose or hgnin in plant, and chitin fa itrogan- beds) containing polysaccharide sma to clllae) in ug Fiagoll ae simple and ack microtubules; | Flagella(and cla) are complox with a9 +2" thoy project outside the cel surface arrangement of microtubules; thoy are surrounded by the. membrane so they ae extracellular Surface membrane so they are intracellular side the cll (outside th cap. Cell dvison occurs by nay fesion (the | Collision takes place by mitosis or meiosis and involos@| callsplits into wo) itdoes not involve a | spindle (see Chapter 6). spindle 600 Chapter 8) Some cary out rivogen fixation None cares out nitrogen tration ‘Table 1.2: Comparing prokaryotic cleaned eukaryote i tiny ‘pasties which are much smaller than bacteria and Question freon the boundary between what we think fa ving 10 Lise thestructurl features that prokaryotic and and non-iving. Unite prokaryotes and eukaryotes, ‘ckaryotceall hae in common Bely explain why vues do not hae a eel structure Tn other word, they each ofthe traces you hae listed is sential, 1.9 Viruses In 1882, Russian sions sovered that esti diseases could be transite by agents hat, uke bacteria, could passthrough very fine filters This Was the frat evidence for the existence of viruses, Vises re virus: a very small 20-300 nn infectious particle ‘which ean replicate only inside living cell Consists of a molorule of DNA or RNA (he {genome surounded by a protein coat; an outer lipid envelope may also be present “>1) Callstructure are not surounded by a pat pormeable membrane Containing cytoplasm with ribosomes. They are much ‘Smpler in structure. They consist only of the fellow + asetfrepiatiag molecule of DNA or RNA (the enone or complete genetic instructions) + protective coat of poten molecules calle capsid + ome vies on) a memibrancike outer layer, called te envelope, thats made of poss. (The structure of phospholipids is deseribed in (Chapter 2) Proteins may project om the envelope Figure 1.36shows the stractre ofa virus with an envelope Viruses typialy have a ery symmetrcl shape “Tepe coat (reaps is made up of separate rosin molecules each of which called eapsomere . b © exetpe peoin Semele ‘Phospholipid a lipid to which phosphate added! the molecule is made up of ayceral ‘molecule, two fatty acids and a phosphate ‘group a double layer (a layer of phospholipids {rm the Basie structure ofl call omrnnee ‘Viruses rang in size from about 20 nm o 300 om (about 50 times smaller on average than bacteria) All vines ae parasite because they can only reproduce ‘yinfeting an taking over ving cls The vis DNA or [INA takes over the protein synthessng machinery ofthe host el which then eps to make new is paris. « Zia is Figure 1.36: Tho structure of vue wth an envelope b made of Za vu. The vs fan RNA virus ts capsidhar ‘mover envelope electron micrograph of cal fected by Zits vis. The viru parle are the daly tamed rosshy i ‘shefcl structures Each vis prt Think about everything you know about calls. What answors would you glve tothe following questions? © Whatisa cal? “Why areal ving things made of col? Look back atthe differences between eukaryotic and prokaryotic calls © Write down a ist of eiteria to compare the _ecess of prokaryotic and eukaryotic calls Suggest why tying to compare the success ‘of prokaryotic and eukaryotic calls may be 2 meaningless exerse. Tip: think about the ‘eoning ofthe word success) Personal reflection questions Changing from studying at GCSE to studying at ‘AS Love's big jump. Has anything surprised you about the change? Are you canfidert about min acter beng able to adapt the way you work? Hfnot what particular concems do you have? You have stood cells in Chapter 1 and lear lot about their structure and function. The Rlletion fctivty gives you a chance to use this information to think again about celle from a slightly cifferert pont of view. How dl he Reflection actity prove your Understanding of what you have tuled in Chaptr 1? Final reflection Discuss with a fend which, any, pats of Chapter you need to: + read through again 0 make sure you really tnderstand + seekmore guidance on, even ater going over it again,> camamoc€ wTERNATIONALAS & A LEVEL BIOLOGY: COURSEBOOK “The basic unit of lie isthe cel, The simplest calls are prokaryote cell, which ae thought to have evo ‘before and given rst, the much more complex and much lager eukaryotic el, ‘Callscan be seen cary only with the ad of mieoscopes. The light microscope uses ight ara suse of radiation, whereas the electron microscope uses electrons. Te electron mzroscope has pester reson (allows more detail o be seen) than the ight microscope because electrons havea shorter wavelength than ght formula A = the actual sizeof an object (4) or ts magnification (§M) can be ound if its observed mags) size (is meatred and A or Ma appropri, known, ‘Allcallsare surrounded by a patally permeable cell surface membrane that contol exchange bev the all and its environment, Allclls contain genetic material in the form of DNA, and sibosomes for protein shat ‘All eukaryotic ells possess a mucleus containing DNA. The DNA i inca (ot crcl) and bound to protean fand RIA to form chromatin, “The cytoplasm of eukaryote cls contains many ovganelles, some of which are surrounded by one oF membranes Organs of eukaryotic call include endoplasmic reticulum (ER), SIS ribosomes, Goel apparatus, lysosomes and mitochondria, Animal calls also contin a entrsoine an centiles and may contain ci. Plant ells have a el wall containing cellulose. They may contain chloroplasts and often have & large central acuole, rokaryotc cls lack e tue nucleus and have smaller (WS) ribosomes than eukaryote celle They also ek membrane-bound organeles Their DNA is iteular and es fren the eytoplas, ‘Viruses d nor ave a alr set. They ae extreely smal and simple. They canst of molecule of DNA or RNA. protein oa a sometimes an outer evelpe | Exe 11 Which one ofthe following ell structures can be sen with ight microscope? ‘A mitochondrion © rough ER B tibosome smooth ER m 2 What property of electrons allows high resolution tobe achieved by olecton microscopes? ‘2 Electrons are negatively charged. bb letrons canbe focused using eletromagnats. Electrons havea very short wavelength 4 List tenstuctures you could find in an eletron micrograph of an 6 Lise imal ell which would be absent from the eel of Bacau 10) '5 Distinguish between the follwing pairs of terms: ‘2 magnification and resolution 8 blight microscope and electron microscope (a ‘© nucleus and mcleols oT . camantoce INTERNATIONAL AS & ALEVE IOLOGY: COURSEBOOK nm {8 The transmission electron misograph shows parts of two palisade cells fiom leCony the table, [dent the labeled struturesA-J and writ brie shout thee funtions A 1 8 3) c a > ia e fo F 3 6 fo] 4 ea ra J ca otal 25)> CAMBRIDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK CONTINUED 9 The electron micrograph shows part ofa seretory cl from the pancreas You treo expected to hae een a micrograph ofthis type of cel before. The cel “contains many secretory vesicles, These ate Goi vescles. They appear as small, ‘oughly cteuarsiretars with black eeular contents. The magnification s >, 28 Copy the table. Calulate the actual sizes ofthe structures listed inthe table. Usea ruler with mm divisions o help you. Show your measurements and calculations, When you have your answer, complete the table with the required information. Give your answers in micrometres, maximum dameter of a Golgi vesicle maximum diameter of clus ‘maximum length ofthe labelled ritochonde| 1 1b Male fly labeled drawing of representative parts of the el. You do not have to draw overything. but enough to show the structs of the main ongunlles Use afl page of plain paper anda sharp pei: Use Figures 1-18 and 119 inthis book andthe simplified diagram ad below to hop you identi dhe structures. 14) © Themitochondi in panreatic ells are mostly sawsage-shaped in three dimension. Sogyest why sme ofthe mitochondria nthe eleston Imirograph here appenr rover. m Caleulate: wok out from given fats, igus ‘orinoratio, Give: produeean answer rom a given ‘source orrecallmemony. Svagest: app snowledge and tinderstancing to Situations bere tere is range ofl responses nee to ‘make proposals / put {ovat considerations i Use modeling cay tomakea sumge shape to repreent ‘2 mitochondion or se areal sausage), Ty euting the sausage with abe at fferent anges. This represents the process of sectioning material for examination using { mieroscope. The cat surfaces wil veal he vatiaton you an expect 10500 in sections1 callstructure nm ‘d_Thofigure ia diagram based on an eletron micrograph ofa secretory cell from the paneeas. This typeof ell i specialised for secreting (exporting) proteins Some of the proteins ar digestive enzymes ofthe pancreatic juice. ‘The cells very activ, requiring alot of eneray- The arrows A,B, Cand D show the route taken bythe protein molecules. [Note that arrow Ais shown magnified in separate diagram, magni 1 Dosribetriely whats happening at cach ofthe stages A, B Cand [8] Arrow B shows the path of «molecule o strut leaving the nucleus tvough the meu envelope: Name one molecule or structure which leaves the niceus by route E. 1 Ii The moleule o structure you named ini pases through the milear envelope. Name the strutrein the miler envelope Uvoush whi th Imoleule or structure passes i jv Name the molecule which leaves the mitochondrion in onde to provide energy for the eal. oT Total: 35) 10. One technique used to investigate the ativity of cell nals scaled sliferential entiation. In this technique a tsue is homogenised (around in «bender, paced in abes an spn ina centige, This makes ‘organelles sediment etl) othe bottom ofthe tubes The a ‘gael, the faster they sediment. By repeating the proces a faster sped the organelles ean be separated from each other according to size Some liver tise was treated inthis way to separate ribosomes, noel ‘nd mitochondsi. The centefuge was spun a 100, 10600 0 100000 (eis gravitational force). 2 State in which ofthe thre sediments (1000 g, 1000 or 100000) you ‘would expt to nd the Following "ibosomes Describe: state the W nuclei Ponts af atopic / give salochoudea tn | Sharacteeticsand bb Livertisue contains many lysosomes. Suggest why this makes it imeutt | 2" Features to study mitochondria using the diferent ceatsfugation technique. [4] | Stato: exprossin clear otat: 5) | terms> caMBtuDGE INTERNATIONAL AS & A LEVEL BIOLOGY: COURSEBOOK LUATION Ci ‘expla that ells are the base units oie ‘we the units of measurement relevant 10 mmiroscony "evognise the common structures found in cal ‘sen with ight microscope and outline hair “Sruetures an unetions ‘compare the key structural atures oF animal ‘an plan cll ‘we a ight miroscope and make temporary reparations to observe cll ‘ecognise draw and measure cll structure from temporary preparations and micrographs ‘aeulate magnifications of images and acta sizes of specimens using drawings or micrographs “expla the uso of the electron mroseope to study ells with erence to the inreased ‘solation of eletton microscopes "ecognise the common structures found in call ‘seen with an electron microscope and utne their structures and functions ‘ullinebity the oie of ATP in els “esse te sirwstre of bacteria and compare the structure of prokaryotic eal with eukaryotic calls ‘describe the sructure of viruses