O X F O 2 0 1 4 R D I B D I p l O m a p R O g R a m m e E D I T I O N BI O LO G Y C O U R S E C O M PA N I O N Andrew Allott David Mindor PHOTO Tony 3 Great Clarendon Street, Oxford, OX2 6DP, United University Press is a department of the the University’s education by objective publishing of University excellence worldwide. in Oxford OLDFIELD/SCIENCE p126a: OUP; of Oxford. Oxford University Press in the UK and in OUP; Oxford University Press is research, a moral rights of the trade p144: certain other Eye been All in published rights a the prior system, permission permitted by law, reprographics the Oxford No by scope of University or of this publication transmitted, in writing licence rights or of the above at under be be or agreed reproduced, by University terms address may form Enquiries should the any Oxford organization. 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Contents 1 Cell Biology Introduction to Ultrastructure 7 cells of 1 cells 16 Membrane structure 25 Membrane transport 33 Nucleic acids (AHL) DNA structure Environmental and replication 343 Transcription and Bioformatics 591 gene expression Ecology and conser vation 355 Species origin of cells 45 Translation and communities division 603 362 Communities Cell 575 582 C The protection Medicine and 51 ecosystems 8 Impacts 2 613 Metabolism, cell Molecular Biology of humans on respiration and ecosystems Molecules to metabolism 625 photosynthesis (AHL) 61 Conservation Water 68 Metabolism 373 73 Cell 380 Population Carbohydrates and lipids respiration The Proteins 87 Enzymes 96 Photosynthesis of ecology nitrogen of DNA replication, and RNA 105 transcription 9 translation 111 cycles 649 Plant biology (AHL) Transport in the Human physiology xylem Human and 642 389 D DNA of plants nutrition 659 403 Digestion Cell respiration 122 Transport in the phloem 671 of Functions Photosynthesis 129 plants of in plants Genetics liver 678 heart 684 422 Hormones Reproduction in plants and metabolism 694 429 Transport Genes the 412 The Growth 3 635 and phosphorous Structure biodiversity of respiratory 141 gases Chromosomes 149 Meiosis 159 Inheritance 168 10 699 Genetics and evolution (AHL) Internal Assessment Meiosis 439 Inheritance 445 (with Genetic modication and his biotechnology 187 Gene pool and speciation thanks assistance Ecology Species, 11 communities and ecosystems Energy ow Carbon cycling Climate change 213 Movement 220 The this for chapter) 708 713 and 465 476 kidney and osmoregulation Sexual 5 production vaccination 229 with Headlee Animal physiology (AHL) Antibody 201 Mark 455 Index 4 to 485 reproduction 499 Evolution and biodiversity Evidence for evolution 241 A Natural selection Neurobiology and 249 behaviour Classication and Neural biodiversity development The Cladistics human brain 518 263 Perception Innate 6 513 258 and of stimuli 526 learned Human physiology behaviour Digestion The blood Defence and absorption system against Neuropharmacology 541 Ethology 548 289 infectious diseases 302 B Gas 533 279 exchange Biotechnology and 310 bioinformatics Neurones and synapses 319 Microbiology: Hormones, homeostasis organisms in and industry reproduction 557 329 Biotechnology in agriculture 565 iii Course book denition The IB Diploma resource throughout course help is Programme materials of their study students expected designed two-year in a gain from course to an books support Diploma particular the The IB Learner Prole of subject. an IB The They of aim of all a will better and what learner subject while that illustrates reect the presenting the purpose philosophy and and content in and encourage a deep aims approach of the of by providing making understanding connections opportunities for to of wider critical books mirror in the terms IB of a issues use of a wide and of Diploma of the range of resources, learner Programme knowledge, action, IB service the core prole essay, issues book materials required a variety and and and and of be so the indeed, and reading suggestions for conjunction students encouraged resources. further in to of draw the theory creativity, are given how to in with IB for each extend natural to curiosity. conduct research and actively snow enjoy independence learning and in this will be sustained throughout their love lives. that They have explore local and concepts, global ideas, signicance. doing, they acquire understanding in-depth across a knowledge broad and and balanced of disciplines. Thinkers: thinking They skills exercise critically approach complex ethical initiative and in applying creatively problems, to and recognize make decisions. other Communicators: are conclusions Suggestions their necessary IB and used below. international and (CAS). can ten the reasoned, Each the through approach; requirements, extended skills Knowledgeable: viewing whole-course develop the They learning range mindedness, described create of and thinking. philosophy They acquire develop the person to aim each In curriculum as this work The IB. and The develop world. the of subject peaceful develop who a learning. IB to attributes, inquiry They is to people Diploma They way programmes minded more programme Inquirers: Programme IB internationally Programme understanding study are students from additional ideas more of book research are and They information than one language communication. willingly in understand condently and They in work collaboration with a and and express creatively variety of effectively in modes and others. provided. Principled: In addition, and the guidance requirements They are being course on the and specic on distinctive companions course academic and provide advice assessment honesty authoritative protocol. with for a the action act sense dignity communities. own without They strong of the They and the with of integrity fairness, individual, take and justice groups responsibility consequences honesty, and for that respect and their accompany them. prescriptive. Open-minded: They understand and appreciate IB mission statement their The International inquiring, who help world Baccalaureate knowledgeable to create through a and better caring and intercultural aims more to develop young people peaceful understanding and respect. To this open of to other the governments organization and and works international challenging education with schools, organizations programmes rigorous These programmes world to their the points of to individuals of international assessment. Caring: respect They to to view, personal and seeking and become who encourage active, understand differences, can students compassionate also that be other right. across and people, They show towards have act are values histories, and communities. and evaluating willing to and are traditions They a grow are range from of the to a empathy, needs personal make and the to a feelings commitment positive the compassion and of and others. to service, to the difference and lives of environment. the lifelong with Risk-takers: They and uncertainty and have new the roles, articulate iv and perspectives, accustomed others learners cultures experience. end develop own and unfamiliar courage independence ideas, in approach with and of spirit strategies. defending their situations forethought, to They beliefs. explore are brave and Balanced: They intellectual, achieve understand physical personal and the importance emotional well-being for of ballance themselves What constitutes malpractice? to Malpractice and result others. in, is advantage in Malpractice Reective: to their able to They own assess limitations personal give learning and in thoughtful and order to their support or any one that student or more includes results in, gaining an assessment plagiarism and or may unfair component. collusion. consideration experience. understand behaviour you They are strengths their Plagiarism and learning and ideas or is work following are dened of as the another some of representation person the ways as to your of own. avoid the The plagiarism: development. ● words one’s and ideas of arguments another must be person to support acknowledged A note on academic honesty ● It is of vital importance appropriately when After that all, credit to the owners information owners of acknowledge is used ideas of in and your (intellectual property rights. To have an that enclosed work, it must be based on work. authentic your original ideas with the work verbatim quotation must marks and CD-Roms, email messages, web sites on the piece and any other electronic media must individual be and quoted property) Internet of are within acknowledged ● have passages be information of others treated in the same way as books and fully journals acknowledged. Therefore, all assignments, written ● or oral, own completed language used or for and referred assessment expression. to, whether must Where in the use sources form of the sources of all illustrations, computer or paraphrase, appropriately such sources maps, audio-visual and programs, data, graphs, are similar material must be direct acknowledged quotation photographs, your must if they are not your own work be acknowledged. ● works of theatre art, arts whether or visual music, arts lm and dance, where the How do I acknowledge the work of others? creative The way that you acknowledge that you have ideas of footnotes other and people is through the use endnotes to be from (placed (placed provided another at at the the Collusion when bottom end you document, of a quote or of a page) document) or ● summarize provided in another artist is not that is need part denitions part of the to of provide a do ‘body not a of document. need assumed footnote for knowledge’. to be allowing for footnoted include as Other is, they are that that you used in your formal list of work. forms of that accepted involves into as works to nd how the should of a compulsory art) of (e.g. or the viewer of A supporting malpractice by by to be copied another or submitted student work for and/or different diploma assessment requirements. you of malpractice an unfair another student. unauthorized include advantage or Examples material into an any action affects the include, misconduct during an examination examination and ‘Formal’ a CAS record. several you use magazines, resources, full the acknowledged. usually that books, providing Extended the This resources information. in one internet-based and reader same the categories articles, of use presentation. separating different newspaper and you forms place, the falsifying means takes includes: work assessment gives room, resources be as This your duplicating results a work information That knowledge. should a You taking Bibliographies must dened student. components do of the ● information part or are paraphrase closely a of bibliographies. another Footnotes of used original the use Cds information your work bibliography can is Essay. v Online Resources What is Kerboodle? Kerboodle is subscription to access guide a you an to online IB huge learning Biology bank through of this platform. Kerboodle resources, If your Online school Resources assessments, and has you a will be presentations able to course. What is in your Kerboodle Online Resources? There are three planning, main resources, areas and for students on the IB Biology Kerboodle: assessment. Resources There a hundreds Kerboodle develop your Watch of Online. skills videos science in Hundreds extra You and and resources can use available these knowledge animations at as of home you on or the in progress experiments, IB the Biology classroom through difcult the to course. concepts, and action. of simulations, worksheets practice – read your articles, skills, or use perform your experiments knowledge to and answer questions. Look Find at galleries out answer more of by images looking questions, or do from at the book and recommended more see sites their on details the close up. Internet, research. Planning Be prepared extra Learn Plan and about and Learn vi for resources the on the practical the to skills data and your Kerboodle that experiments analyse accurately. work Biology different prepare how IB of and you assessment with online. need your draw internal to perform an investigation. own. conclusions successfully Assessment Click on the assessment examinations. style practice Here tests: auto-marked about attempts marks how a at are you as if it each one mark. The These an of knowledge interactive marks where and these until are you to quiz you or revise quizzes for and – go your exam- can be the back to printed You after there’s condent will every markbook, for every happy, come test. how so have one you two question. you can The see year. more these will the practice for comprehension, Evaluate feedback the are need use you your in automatically may practice: worksheets get reported throughout use questions check complete examination about Assessment written your lots sub-topic. then question tests: to every auto-marked were sure see check nd these for sub-topic, progress aren’t can use quiz automatically Summative there’s to will questions. Formative feel tab you your topic. and exams Work change then any submit reported in or the as revision, through the the test questions test for markbook, a you nal so you practice. practice across out answering when and you the are performed longer examined. as a timed test. Don't forget! You can also nd extra resources on our free website www.oxfordscondry.co.uk/ib-biooy Here you can nd all of the answers and even more practice questions. vii Introduction Nature of science This book is a companion for students of Biology Here in the International Baccalaureate you can explore the methods of science and Diploma some of the knowledge issues that are associated Programme. with Biology subject is as biology the most part of should popular the lead a focus on diploma. students interconnectedness With IB choice of life to science The study appreciate within understanding of the the scientic carefully of research the endeavour. selected that led understanding of This examples, to done including paradigm the is natural shifts in using biological our world. biosphere. nature of Thory of K nowd science, level you with of of to a IB Biology scientic act on full will allow literacy issues of that local understanding you to will better and of the develop global a prepare concern, scientic `knowledge questions´. The text that follows often point details one possible answer to the knowledge question. view. The We encourage you draw on these examples of structure biology These shor t sections have headings that are equivocal of this programme headings restate book in the is the closely Subject specic based Guide. assessment on the knowledge issues in your TOK essays. Of course, much of the material elsewhere in the book , par ticularly in the Sub- statements. nature of science sections, can be used to prompt TOK discussions. Topics 1 that common 7 – is 11 – 6 explain explain to in detail both the AHL SL the and Core HL material courses. (additional higher Topics level activity material). Topics A, B, C and D cover the content A variety of shor t topics are included under this heading of the options. All topics include the following with the focus in all cases on active learning. We elements: encourage you research these topics yourself, using information available in textbooks or on the Internet. The Understanding aim is to promote an independent approach to learning. The specics of the content requirements for We believe that the optimal approach to learning is to each sub-topic are covered in detail. Concepts promote enduring are be active – the more that you do for yourself, guided by presented in ways that will your teacher, the better you will learn. understanding. Applications Data-based questions These sections help you to develop your These questions involve studying and analysing data understanding by studying a specic illustrative from biological research – this type of question appears example or learning about a signicant experiment in both Paper 2 and Paper 3 for SL and HL IB Biology. in the history of biology. Answers to these questions can be found at www.oxfordsecondary.co.uk/ib-biology Skills topics These sections encourage you to apply your End -of-Topic Questions understanding through practical activities At and analysis of results from classic the end In some cases this involves handling data from experiments and of ICT. Some experiments promoting seeing.” work valuable assessed viii Others the the skills known understanding with dene of with involve unknown problem IA (see ideas for outcomes, and opportunities in sections outcomes, through the to page 708). involve aimed “doing at and experimental where methods. build the topic you both will past IB nd a range Biology of exam you These skills and new questions. Answers can be also found use each including instructions questions for of biological questions, research. can are that a are at www.oxfordsecondary.co.uk/ib-biology 1 C E L L B I O L O G Y Introduction There cells alive is on an today. complex to all of structure is and essential have than cell but of life found multicellular specialization division chain cells Eukaryotes cell evolution cell unbroken Earth is a in from the much more prokaryotes. organisms out The allowed replacement. carried rst organisms Cell differently in prokaryotes has resulted in diversity, the there also the are uid and membranes composition and a eukaryotes. biological study of cells universal dynamic allows of While world shows features. structure them of to us For of evolution enormous that example, biological control the cells. 1.1 Ii Understanding Applications ➔ According to the cell theory, living organisms ➔ Questioning the cell theory using atypical are composed of cells. examples, including striated muscle, giant ➔ Organisms consisting of only one cell carry out algae and aseptate fungal hyphae. all functions of life in that cell. ➔ ➔ Surface area to volume ratio is impor tant in the Paramecium and one named photosynthetic limitation of cell size. ➔ Multicellular organisms have proper ties Investigation of functions of life in unicellular organism. ➔ that emerge from the interaction of their Use of stem cells to treat Stargardt ’s disease and one other named condition. cellular components. ➔ ➔ Specialized tissues can develop by cell specially created embryos, from the umbilical dierentiation in multicellular organisms. ➔ Ethics of the therapeutic use of stem cells from cord blood of a new-born baby and from an adult ’s own tissues. Dierentiation involves the expression of some genes and not others in a cell’s genome. ➔ The capacity of stem cells to divide and dierentiate along dierent pathways is necessary in embryonic development. It also makes stem cells suitable for therapeutic uses. Skills Nature of science ➔ Looking for trends and discrepancies: although ➔ are exceptions. ➔ ➔ and raises ethical issues. Drawing cell structures as seen with the light microscope. Ethical implications of research: research involving stem cells is growing in impor tance Use of a light microscope to investigate the structure of cells and tissues. most organisms conform to cell theory, there ➔ Calculation of the magnication of drawings and the actual size of structures shown in drawings or micrographs. 1 1 C E L L B I O L O G Y The cell theory Living organisms are composed of cells. The up internal from the eye organs were This are made the developed states cell. many Cells a Larger they and of nothing century animals certain are the the smallest are organisms can tissues, but seen features are the we about microscopes. were as biologists fundamental are intricate such discovered using organisms very dissected onwards basic is Organs different was features explain cells The If organisms parts. number or 17th to that living visible. of plants of individual little variation, organisms. one easily From both much was are small invented tissues. from structure very again of that until the they large – there A the cell all was theory of – consist are of tissues blocks they built and microscopes again. structure is structure Although and unicellular – see examined building multicellular and kidney theory. living of composed just of cells. vary considerably in size and shape but they share certain common features: Every ● cell Cells ● living contain needed Many ● for of So, cell’s activities. ▲ 2 can can cell’s their be the material a membrane, which separates the outside. which stores all of the instructions are chemical reactions, catalysed by enzymes cell. own thought by else activities. activities inside have cells surrounded everything genetic the Cells smaller is from these produced ● cell contents energy of as release the system smallest that living powers structures all – of the nothing survive. Figure 1 Coloured scanning electron micrograph (SEM) of a human embryo on the tip of a pin 1 . 1 I n t r o d u c t I o n t o c e l l s Exceptions to the cell theory Looking for trends and discrepancies: although most organisms conform to cell theory, there are exceptions. An early that stage appear These trends theory make These to is a in scientic be found can way lead of are called unreliable to the Sometimes be common useful. The cell and discrepancies. is an to the Scientists theory example of of natural serious look than exceptions or The is rather development discrepancies. are theory to interpreting predictions. discrepancies investigation generally a a have then where trends to to – specic A allow trend judge make things cases. scientic Theories general enough is in theory. world. to for just are us to found. whether the predictions too discarded. scientists have looked for trends ▲ structures in and parts other Nor is living of this Elder or stems of kind So a Hooke tissue – Hooke’s living Teasels, kind of day at organisms. tree, Fearn, some with Many of in as to of kind I cork of these at only, pith Reeds lately at just discovered looked a the after cork for of have wrote pith Cany Carrets, Figure 2 Rober t Hooke’s drawing of cork cells for cork this: Aiviy the much that type of hollow Daucus, have shown one cell examining he the the etc. word upon that general tissues tissues in Fennel, have use 1665 found inner as to cells have looking and have rst this I the vegetables: many biologists did peculiar Schematisme, content looked the describing microscope other other was He After texture my any several wasn’t he of with almost Bur-docks, Hooke organisms. plants. examination such Robert of of cork. plant trend. from a huge been found Since variety to of consist ▲ of cells, so the cell theory has not been discarded. However, Figure 3 What is the unit of life: some the boy or his cells? discrepancies that do not discovered, be have consist but discarded, it been of is discovered typical cells. extremely because so – organisms More unlikely many tissues or parts discrepancies that do the cell consist of of may theory organisms These two answers represent be will the holistic and the reductionist ever approach in biology. cells. image viewed here Using light microscopes eyepiece lens Use of a light microscope to investigate the structure of cells and tissues. coarse-focusing Try to much improve as you your skill at using microscopes as knob can. ne-focusing turret knob ● ● Learn the names Understand how of parts to focus of the the microscope. microscope to objective lens get the specimen best ● possible Look after stage image. your microscope so it stays in perfect light from mirror working ● Know or light bulb order. how to troubleshoot problems. ▲ Figure 4 Compound light microscope 3 1 C E L L B I O L O G Y Focusing ● Put Types of slide the slide promising hole in on the region the stage stage, exactly that with in the the the light most middle comes The of the be slides permanent Always focus eventually at you low power need high rst even power if a magnication. long by Focus rst, with then the larger when you coarse-focusing have nearly in focus make it really got sharp ne-focusing a microscope can so slides these thin is slides slices very are slides of skilled and normally of tissues takes made are made tissue. knobs the using temporary slides is quicker and easier so the we smaller with temporary. Permanent very Making image or examine permanent time, experts. using ● we through. Making ● that can do this for ourselves. knobs. Examining and drawing plant and ● If you want to increase the magnication, animal cells move the slide so the most promising region is Almost exactly in the middle of the eld of view all cells thenaked then change to a higher magnication are too small to be seen with and eye, so a microscope is needed to lens. studythem. Looking after your microscope It ● Always focus by moving the lens and is usually plant specimen further apart, never closer to each or an Make sure before that putting the it slide on the is clean and Never your ● touch the ngers Carry hand the or under it anything to of the lenses carefully support its with sure by lens, weight when the I specimen carefully Add is easier ● Carefully try to to nd the a drop avoid Remove is in both the plant and animal on the slide in a layer not specimen if of water lower a trapping excess inside the or stain. cover a any slip uid folded air onto the drop. circle Solution: There it making and with slides when I is try so Problem: There an to a thick air you black bubble improve that are focus or stain piece of by putting paper the towel lightly on the cover and slip. is best to examine focus at Move the the slide slide to get rst the using most low promising low in the rim is up to middle there are blurred it as on your of the as air of power. eld Draw of a view few and cells, visible. their structure. slide. technique no parts well the high cover carefully lower the slip cover slip for bubbles. the image Ican. gently squeeze Solution: Either the lenses or the slide have dirt to remove ex them. Ask your teacher to clean it. uid Problem: The image is very dark. cover slip Solution: Increase through the the amount specimen by of light adjusting passing the diaphragm. slide folded Problem: The image looks rather bleached. r towel ▲ Solution: Decrease through 4 Try bubbles. slide. remember on more thick. then rst. Problem: A even a many actually positioning move Ignore from are focus. areas power is securely. power. It cell ● It the cells one pressing under cell there a slide Solution: Make types the than ● visible a though else. Troubleshooting is cell Place with to Problem: Nothing whether even stage. surfaces microscope see kingdoms. dry ● ● to animal, other. different ● easy the the the specimen amount by of light adjusting the passing diaphragm. Figure 5 Making a temporary mount so you 1 . 1 1 Moss leaf 2 Banana fruit I n t r o d u c t I o n cell 3 t o c e l l s Mammalian liver cell 10 μm 5 μm 20 µm Use a thin leaf moss in a Leaf with Mount drop methylene 4 plant leaves. of blue lower a very Scrape single water soft or drop 5 epidermis small tissue place stain. a on of amountof from a a slide. iodine Human banana Mount the Scrape and in surface a of frozen). solution. cheek cells add cell 6 from liver Smear methylene White a freshly (not previously onto blue blood cut a slide to and stain. cell 20 μm 2 μm 10 μm Peel the leaf. The lower cell epidermis drawn from Valeriana. or methylene ▲ in off here Mount in a Scrape was your water Smear blue. cells cheek from with them methylene on the a a blue inside cotton slide to A of and thin blood bud. slide add layer can and mammalian smeared stained Leishman’s stain. of be overa with stain. Figure 6 Plant and animal cell drawings Drawing cells Drawing cell structures as seen with the light microscope. Careful drawings Usually the detail than and the only a) same Use a are on use structures calculating the lines the a useful the faint way drawing shading. actually are magnication of of recording represent – Drawings the a the of drawing drawing is the structure edges of structures shows seen them explained. of cells structures. or Do using a biological show On on a page structures. unnecessary microscope magnied. Everything other not 6 drawing will the be larger method should be a sharp hard lead pencil to sharp with draw lines. b) Join to up form lines carefully continuous structures such as cells c) Draw but lines use a labelling freehand, ruler for lines. cell ▲ to magnication. single bad for shown good bad good bad cell good Figure 7 Examples of drawing styles 5 1 C E L L B I O L O G Y Calculation of magnication and actual size Calculation of the magnication of drawings and the actual size of structures shown in drawings or micrographs. When that are. we we look see The or rotating lens to three allow three the is us turret of to A microscope than magnify factors. switch typical the they magnifying to different another. levels a larger microscope microscopes two down appear structures them. from school is done one is important sure and same. by or objective has They the be thousand. millimetres ● × 40 ● × 100 (low (medium 400 we take (high a power) photo the down image bars straight a microscope, we are microscope even is called micrographs micrographs When we drawing of the wrong. by in taken draw larger drawing magnication a more. a A photo micrograph. using book, an smaller, isn’t of this taken There including electron specimen, or sometimes lines, we so nd the drawing necessarily the put need the image (in the actual size long to the of of know a a as a label length structure Determine the or things: the the or on a specimen. 30 mm size micrograph) of This formula of ×10,000 of 1 of an that the image has an of is 30 magnication = 30 × 10 3 µm = 3 × 10 m m 3 = 6 10,000 size of the 10 Or: specimen 30 mm the × × image of image and = 30,000 µm the 30,000 _ we can calculate the actual Magnication size = 3 of a specimen. = 10,000 × Data-based questions 1 a) Determine of scale b) bar magnication cells. cells represents Determine of the Thiomargarita the width in 0.2 of of gure the 8, mm the if string the [3] string [2] ▲ 6 if These that there scale mm. actual and = size size the 6 = size magnication, micrographs the was are scale a with bar a would µm. is calculation: actual know converted micrograph 3 a ___ we can by EX AMPLE: The the micrograph two drawing the magnication If be them. actual example, bar 3 the Millimetres are make same the 30 × 10 _ for or different electron magnication the For scale Magnication used (mm) be thousand. on alongside microscope. magnication we the multiplying can one Either: To by not the down microscope. can the just with represents. mm have many be must micrometres dividing or magnication a millimetres they of are can 10 magnify be formula size specimen Micrometres by drawings, bar If will the this the power) or × but for power) Scale ● of both calculation using units size ( µm) to when the could converted one magnication: that actual micrometres by microscope very make image Most specimens This It to actually Figure 8 Thiomargarita size of It represents of the 3 µm. image. to 1 . 1 2 In gure 9 the actual mitochondrion a) Determine electron b) c) is 8 the length of b) the how would on be magnication Determine long this the Determine cheek µm. of a 5 µm of scale of the [2] [2] the [1] ▲ 4 Figure 10 Human cheek cell a) Using the guide, ostrich b) width estimate egg Estimate the of (gure the the the hen’s actual egg length as of a the 11). [2] magnication of image. [2] Figure 9 Mitochondrion ▲ The magnication from is length cell. bar micrograph. mitochondrion. 3 c e l l s [2] electron width the t o this micrograph. Calculate I n t r o d u c t I o n a compound 2,000 a) of the human microscope cheek (gure cell 10) ×. Calculate how would on be long the a 20 µm scale bar image. [2] ▲ Figure 11 Ostrich egg Testing the cell theory Questioning the cell theory using atypical examples, including striated muscle, giant algae and aseptate fungal hyphae. To test the the cell structure you can, using microscope case you Three ● by or use bres, cells. and the t is change are are However are the this similar by have own worth type in division their energy muscle much own of are than of some a of for mostly of each in humans about 30 less having the as have an whereas than one sometimes the they mm, 0.03 mm nucleus many average other as in they length human length. have several of cells are Instead many, hundred. cell cells?” tissue by In as considering: tissue that our are body. muscle ways to membrane pre-existing genetic release bres larger In “Does stated position of 4. more surrounded formed They page or are at Instructions trend one the blocks on look organisms question, the of examples which their They given ask muscle They are cells. and are building should living microscope. tissue to you many consisting Striated The a use atypical we as should organism theory theory of material system. far from most typical. animal cells. ▲ Figure 12 Striated muscle bres 7 1 C E L L ● B I O L O G Y Fungi consist of called hyphae. white in They cell colour have wall. are a In divided cross walls fungi narrow These and cell there types into called are uninterrupted have a of small septa. no are and, fungi appearance. outside the cell-like septa. Each it, in by aseptate hypha structure a hyphae sections However, tube-like structures usually uffy membrane some up thread-like hyphae is with an many Figure 13 Aseptate hypha ▲ nuclei ● Algae spread are along organisms photosynthesis nuclei, and but one of these form basis They If are a mm, new It organism consist of many that to cells, to a a not algae be and chains. to a they Less much single length length one of cells. of as is much nucleus. 100 certainly just consist numbers Acetabularia having would structure oceans grow by inside vast food algae. grow only with we are the seem giant can despite discovered, still their Many marine algae as in genes in There algae most themselves their plants. cell. they known feed simpler than some yet example. 100 was are size, of that store are unicellular the larger as they microscopic common one and organization of it. mm expect it to one. Figure 14 Giant alga ▲ Unicellular organisms Organisms consisting of only one cell carry out all functions of life in that cell. The functions Some out all the organisms is – for ● Response ● Excretion ● Homeostasis an – a complex than carry out food, – chemical release the of most at to organisms cell. This this cells least the in seven provide must cell do to therefore structure stay has alive. to carry of unicellular multicellular organisms. functions energy and of the life: materials reactions – inside the cell, including cell energy. ability getting increase to rid keeping react of the to in size. changes waste conditions in the products inside the of environment. metabolism. organism within limits. unicellular in all one Because irreversible Reproduction remain 8 – to Growth tolerable that only life. obtaining ● – things of growth. Metabolism Many of organisms respiration ● are consist more Nutrition needed ● life functions Unicellular ● of organisms xed – producing organisms position or offspring also have merely a either sexually method drift in of water or asexually. movement, or air but currents. some 1 . 1 I n t r o d u c t I o n t o c e l l s Limitations on cell size Surface area to volume ratio is impor tant in the limitation of cell size. In the cytoplasm These rate reactions of these volume For metabolism move of its into the the numbers collectively (the metabolic continue, cell out The large of as chemical the rate of reactions metabolism the cell) is of take the place. cell. proportional The to cell. to the and cell. surface The of by cells, known reactions the absorbed of are and of rate cells at substances waste through which used products the in must plasma substances cross the be reactions removed. membrane this must be Substances at the membrane surface depends on area. surface area to volume ratio of a cell is therefore very important. If same cube the ratio they are is small required produced Surface too more area to then and substances waste rapidly volume than ratio will products will they be is can also not enter the accumulate cell as quickly because they as unfolded are excreted. important in relation to heat ▲ production and loss. If the ratio is too small then cells may Figure 15 Volume and surface area overheat of a cube because the metabolism produces heat faster than it is lost over the cell’ssurface. Functions of life in unicellular organisms Investigation of functions of life in Paramecium and one named photosynthetic unicellular organism. Paramecium some pond Place a Add a is a unicellular water drop cover of and use culture slip and organism a that centrifuge solution examine to can containing the slide be cultured concentrate the Paramecium with a quite easily organisms on a in in the it to microscope laboratory. see if Alternatively Paramecium is collect present. slide. microscope. The nucleus of the cell can divide to produce The contractile vacuoles at each end of the cell ll up with water and the ex tra nuclei that are needed when the cell then expel it through the plasma membrane of the cell, to keep the reproduces. Often the reproduction is asexual with cell’s water content within tolerable limits. the parent cell dividing to form two daughter cells. Food vacuoles contain smaller organisms that the Paramecium has consumed. These are gradually digested and the nutrients are absorbed into the cytoplasm where they provide energy and materials Metabolic reactions take place in the cytoplasm, including the reactions that release energy by respiration. Enzymes in the cytoplasm are the catalysts that cause these reactions to happen. needed for growth. Beating of the cilia moves the The cell membrane controls Paramecium through the water what chemicals enter and leave. and this can be controlled by the It allows the entry of oxygen for cell so that it moves in a par ticular respiration. Excretion happens direction in response to changes simply by waste products in the environment. diusing out through the membrane. ▲ Figure 16 Paramecium 9 1 C E L L B I O L O G Y Chlamydomonas research not a into true is cell plant a unicellular and and alga molecular its cell wall that lives biology. is not in soil Although made of and it is freshwater green in habitats. colour and It has been carries out used widely for photosynthesis it is cellulose. The nucleus of the cell The contractile vacuoles can divide to produce at the base of the agella genetically identical ll up with water and then nuclei for asexual expel it through the plasma reproduction. Nuclei can membrane of the cell, to keep also fuse and divide the cell’s water content within to carry out a sexual tolerable limits. form of reproduction. In this image, the nucleus is concealed by chloroplasts in the cytoplasm. Carbon dioxide can be conver ted Metabolic reactions take into the compounds needed place in the cytoplasm, for growth here, but in the dark with enzymes present to carbon compounds from other speed them up. organisms are sometimes absorbed through the cell membrane if they are available. The cell wall is freely permeable and it is the Beating of the two agella membrane inside it that moves the Chlamydomonas controls what chemicals through the water. A light- enter and leave. Oxygen sensitive “eyespot” allows is a waste product of the cell to sense where the photosynthesis and is brightest light is and respond excreted by diusing out by swimming towards it. through the membrane. ▲ Figure 1 7 Chlamydomonas Multicellular organisms Multicellular organisms have proper ties that emerge from the interaction of their cellular components. Some type a unicellular of alga protein Figure gel, 18 Figure 18 Volvox colonies shows Although single cell mass one like more cells. body is a and a common feeds on female long large very the or are are of a the are more it but reproductive to of organs. of It are cells, fused elegans. exactly such million as oak The of to inside form a adult cells. in or third of an the has cells is about might have adult elegans elegans so body This far human whales. organic C. are multicellular Caenorhabditis decomposing a a made surface. fused organisms trees hermaphrodite Almost its together, 959 cells decomposition. is to ball forming not researched multicellular million in colonies example a organism. biologists, cause anus. up most ten unseen that and mass for of attached they intensively made consists daughter single organisms lives bacteria a colonies, cells Caenorhabditis is about in with in colony identical single known and intestine not called and together Each cooperating, most number, well more colonies, so of live aureus. cells and There name pharynx, two worm even Although 500 the One millimetre seem Volvox consisting multicellular. organisms 10 with them. Organisms ▲ organisms called has matter. has both are a no It mouth, male and neurons, or 1 . 1 nerve cells. Most of these neurons are located at the front I n t r o d u c t I o n end of t o c e l l s the toK worm in a Although structure the brain environment, in this and it that in does other can C. be elegans not regarded the coordinates control multicellular as how animal’s responses individual organisms can cells be brain. to the develop. regarded as Hw a w i wh m i worm’s The cells ha ah? cooperative An emergent proper ty of a system is groups, without any cells in the group acting as a leader or supervisor. not a proper ty of any one component It is remarkable how individual cells in a group can organize themselves of the system, but it is a proper ty of and interact with each other to form a living organism with distinctive the system as a whole. Emergence overall properties. The characteristics of the whole organism, including refers to how complex systems and the fact that it is alive, are known as emergent properties. patterns arise from many small and Emergent of a complex the of properties whole an is written clay. But can structure. greater emergent text it’s carry these the than hollow that some sum was interaction of years makes things in pot of this parts. ago: the studying bigger sum its described 2,500 by the sometimes the that research from We than property more out remember arise a up A work.” are with from the in parts phrase: parts, but interactions cannot therefore necessarily predict approach known as reductionism). from Molecular biology is an example of the we we We each par t of a system separately (an philosophical biology relatively simple interactions. emergent proper ties by studying example fashioned So, component component simple Chinese “Pots result the success that a reductionist approach must between can have. Many processes occurring in living organisms have been explained components. at a molecular level. However, many argue that reductionism is less useful Cell dierentiation in multicellular organisms in the study of emergent proper ties including intelligence, consciousness Specialized tissues can develop by cell dierentiation in and other aspects of psychology. The multicellular organisms. In is multicellular sometimes or a and role. the organisms called For division example function of a the rod interconnectivity of the components different of labour. function cell cells in In of the perform a simple red retina different terms, blood of the cell eye a is is functions. function to to carry is This a job oxygen, absorb light in cases like these is at least as impor tant as the functioning of each individual component. and One approach that has been used to then transmit impulses to the brain. Often a group of cells specialize in the study interconnectivity and emergent same way to perform the same function. They are called a tissue. proper ties is computer modelling. In By becoming more the efciently ideal cells reactions in different differentiation. cell than structure, chemical of specialized, types have In if the they with the cells had to humans, been a with carry 220 tissue many enzymes associated ways in different needed the out all specic of to function. distinctively recognized, can which carry roles. carry The out their They out can all of both animal behaviour and ecology, role develop Life” has been used. It was devised the by John Conway and is available on development functions different develop is by the Internet. Test the “Game of Life” by called highly a programme known as the “Game of specialized differentiation. creating initial congurations of cells and seeing how they evolve. Research ways in which the model has been applied. Gene expression and cell dierentiation Dierentiation involves the expression of some genes and not others in a cell’s genome. There all are have have and the same able a to pigments different same activities. produce be many the set To set of its and is an that job cell of types genes. genes, take pigment do of The despite example, absorbs sensing transparent. If in multicellular cell large rod light. light. it a 220 did types differences cells in the Without A in lens cell contain it, in organism the in their retina the the of rod eye pigments, but human structure the cell eye would produces less they body light not no would 11 1 C E L L B I O L O G Y pass through developing, but these This is genes the cell and types When a in it of a not is is used cell is nose, one of Cell of the smells. in key genes This work in a or on is have in other particular happens cell a body be that gene they the are pigment, genes The with cell. on a or gene and and in human is information development expressing of most being the The in used. different control in the However, needed the the specialize genes product. because types. to 25,000 ever say genes needed switched differentiation only so how cells. makes we and involves for making expressed receptor this we gene information are Axel on just will While making cell. genes present worse. for them, sequence gene but of expression development. of and is not have cell, the different the genes rod genes protein to olfactory Richard their all the switching do be genes approximately differentiation carry These called are of would the the they are used a in cells terms, example that odorant. for the extreme smells. make expressed humans genes being involves – need, half vision contain used There simple to therefore An is In others. genes than gene expressed. they way. our types only these less and cell situation that possible genome, lens are usual instructions every the both one can in Each type cells of of distinguish Linda Buck a large family receptors in the these for skin cells inside receptor to detect so many given the genes Nobel in – the expresses between were of odorants just one type different Prize in 2004 system. Stem cells The capacity of stem cells to divide and dierentiate along dierent pathways is necessary in embryonic development. It also makes stem cells suitable for therapeutic uses. A new animal zygote. This of are tissue. different In cells stem Stem cells ● ● 12 so are the from have of cells different of At a sperm when again these dividing any of century, early to the zygote produce early stages times versatile the cell name embryo, fertilizes the many extremely into a in to stem meaning egg cell to can cell embryo, then development large that given the a cells. amounts differentiate in was all produce two embryonic found that to give four-cell produce and types an divides along particular to the tissues of zygote the them. two can key are to biology again are of not ways, properties in divide They replacement Stem divides on. research cells. when formed also 19th of cells new the Figure 19 Embryonic stem cells the areas Stem of ▲ They and active and pathways adult is capable animal. the starts embryo sixteen cells life embryo two-cell eight, the An and therefore cells fully that that and have again different the lost They cell them one of the most today. produce for been differentiated. produce to useful have made medicine or of quantities tissues damaged. can types. copious growth differentiate in or 1 . 1 Embryonic be used have to stem suffered such as cells produce type burns. 1 are called health There are is to for use also human is the might – stem stage The whether to cell in including the may of still same cells means cell in for useful. skin for of type the They people healing has to therapies for could who lost grow These c e l l s diseases been future example. allow to way of cells as They skin one to limited a or is whole types of diseases repair into cells, brain, use or give and a to a cell Eventually type. cells Once will cells. and some be cattle. which they human The meat, therefore cell stem many repair. at these however, or versatile. another. of possibility themselves specic all kidney may points or One bres, slaughter most longer in They and the of but and commit one no present liver. – are cells cells. muscle future rear series are stem and that divide, regeneration the to pathway they are of the stem striated need develop and of burgers the able remain marrow, embryonic involves along be body. powers for stem This develop adult bone considerable only very as provide development committed the numbers tissues embryo becomes beef without embryonic decides a large cells, differentiation. in they uses of present a used quantities produce pattern Small be to during differentiate provide particular kidneys, because consumption. committed, or such non-therapeutic from early cell a even hearts Gradually each could where potentially tissue, t o problems. them produced It They organs therapeutic, other therefore They diabetes malfunctioning. replacement are regenerated I n t r o d u c t I o n human stem cells heart are still tissues, for tissues in other example. Therapeutic uses of stem cells Use of stem cells to treat Stargardt’s disease and one other named condition. There are diseases, many of few and a cells are current huge which examples stem a are one range being given and uses here: using of of stem cells possible actively one treat future uses, researched. involving adult to stem Two embryonic Researchers embryonic This were a cells. was stem done then developed cells similar cells were with into to methods develop initially injected condition injected have the into not retina mouse eyes of Stargardt’s rejected, for cells. cells, which mice that disease. did not making had The develop Stargardt’s disease into The full name of this disease is Stargardt’s It is a genetic disease that moved children between the ages of six and cases are due to a recessive mutation gene called protein used ABCA4. for malfunction. As This active a causes transport consequence, a in in the detect retina light, degenerate. so vision an retina cells got in 50s her The person loss to of be These becomes vision can registered be as retina where they The attached and remained. improvement Very in the encouragingly, vision of the they mice. 2010, approval researchers for trials in in the United humans. with Stargardt’s disease was A woman treated by photoreceptive are the 50,000 retina cells derived from embryonic cells cells injected into her eyes. Again the cells progressively severe enough to the retina and remained there during for the the the to attached worse. to November States stem that problems. membrane having cells other of In a any twelve. caused Most cause develops themselves in or macular cells dystrophy. tumours four-month trial. There was an improvement blind. in her vision, and no harmful side effects. 13 1 C E L L Further are we B I O L O G Y trials needed, can be larger after optimistic treatments stem with but for numbers these initial about Stargardt’s the of at using be done chemicals least, development disease can patients trials is of embryonic known healthy able cells. to to by in needle the cells by and blood that present, The patient blood cells procedure can be needed produce they following remain must cells but to are killed procedure is is inserted pelvis, and into uid is a large bone, removed from marrow. cells stored ▲ be with The However, the white Stem must bone Stem patient cells. used: large the term the disease. usually ● long chemotherapy. A the dividing chemotherapy. the cells therefore ● as treating kill produce ght blood by that are extracted freezing only from them. have the this They uid are potential and adult for are stem producing cells. Figure 20 Stargardt’s disease ● A high dose of chemotherapy drugs is given lkmia to This disease when is a type mutations division. For a of occur cancer cancer. in to All genes cancers that develop, start control several the cell must occur in these genes in patient, bone ability is one very unlikely numbers of to cells happen, in the but body, as there the The stem of a becomes million year globally from the Once form with of a or leukemia. bone it are More are over than a blood cells marrow in loses of into when leukemia. In most tumour White a such 200,000 cells are body. then They returned re-establish to the themselves are the bone red marrow, and multiply white blood and start to cells. each In many cases this procedure cures the leukemia completely. deaths the blood, normal large this both in numbers adult in the are the femur. white of cancer not cells happen produced hollow They are normal are involves numbers does cells tissue the repeatedly, Leukemia cancers, but have divides cells. blood soft as excessive A more abnormally marrow, bones and in centre then conditions produced blood cell with count is 3 between person 4,000 with and 11,000 leukemia this per mm number of blood. rises In higher a and 3 higher. a Counts person may above have 30,000 per leukemia. If mm there suggest are that more 3 than has To 100,000 acute cure 14 mm white it is likely that the person leukemia. leukemia, marrow of per that are blood the cancer producing cells must cells in excessive be its cells. quarter diagnosed mutations grows and cells. lump released there cell, more blood large and a production white the and larger. leukemia cancer-inducing in producing the of bone cancer disease. the occurred much cases The the overall produce chance produce all cell. in huge kill marrow. to patient’s This to specic ● mutations the the bone numbers destroyed. This ▲ Figure 2 1 Removal of stem cells from bone marrow 1 . 1 I n t r o d u c t I o n t o c e l l s The ethics of stem cell research Ethical implications of research: research involving stem cells is growing in impor tance and raises ethical issues. Stem cell Many research ethical Scientists has should always implications of Some research past of the would today, not such patients been objections as their be that the was out ethically research in out the stem it. the acceptable carried informed of ethical doing carried Decisions about acceptable raised. before considered their controversial. been consider research medical without very have of of consent. science cell whether be the stem cells possible research research based involved. research misunderstanding three on must as on a Some the being sources involving but different used. of In stem them ethically understanding people unethical, of is clear the next and all shows possible cells are dismiss this a sources section, the ethics discussed. Sources of stem cells and the ethics of using them Ethics of the therapeutic use of stem cells from specially created embryos, from the umbilical cord blood of a new-born baby and from an adult’s own tissues. Stem ● cells can Embryos obtained can fertilizing the be be egg resulting from a deliberately cells with zygote to variety of created sperm and develop for sources. and by a few it has between four and sixteen cells. the cells are embryonic stem Stem Blood can be extracted from the of a new-born baby and stem from it. The cells can be emyi m Almost unlimited growth potential. ● Can dierentiate into any type in cells types below give the Easily obtained and stored. ● Commercial collection and as be obtained bone from some adult marrow. of stem their cell vary potential in for their properties therapeutic use. and The gives some properties of the three types, scientic basis for an ethical assessment. A m ● Dicult to obtain as there are very few of them and they are buried deep in tissues. storage services already available. ● Less growth potential than embryonic stem cells. ● including teratomas that contain Fully compatible with the tissues of the adult that grows from the baby, dierent tissue types. ● in ● More risk of becoming tumour cells than with adult stem cells, can such c m the body. ● the frozen to ● in cells table obtained later umbilical therefore cord use cells. These ● possible All tissues of for days ● until stored baby’slife. allowing ● so no rejection problems occur. Less chance of malignant tumours developing than from Less chance of genetic damage embryonic stem cells. ● Limited capacity to dierentiate due to the accumulation of into dierent cell types – only ● Limited capacity to dierentiate mutations than with adult into dierent cell types. naturally develop into blood stem cells. cells, but research may lead to ● ● Likely to be genetically dierent Fully compatible with the adult’s production of other types. tissues, so rejection problems do from an adult patient receiving ● Limited quantities of stem cells not occur. the tissue. from one baby’s cord. ● ● Removal of stem cells does not Removal of cells from the ● The umbilical cord is discarded kill the adult from which the cells whether or not stem cells are are taken. embryo kills it, unless only one or two cells are taken. taken from it. 15 1 C E L L Stem cell Many are the research ethical most cells, B I O L O G Y objections because death taken. stage of The been to current the is undoubtedly the when is a which raised. usually the stem whether human case stem involve cells an are early individual killing the as lived However, There embryonic techniques much in of have controversial. been use question as baby, very have embryo main embryo new-born is has objections a embryo to create has a human obtaining stem cells. of well invasive of as an eggs from supplying denied lives treatment its the of solely Also, women, eggs exploitation unethical. been counterargument IVF If that the vulnerable unethical purpose procedure could living. is are lead groups of hormone associated women this of it involves some surgical ovary. for for IVF with chance is risk, as forremoval paid to such for the as college students. When views does on sperm say developed of so stem begins brain that Some that they when Some capable There that human stage be is a embryos thought that of stages take has surviving in as is developed groups truly tissue a that into the yet suffer life after view outside not cannot bone a or few it fetus scientists argue that if embryos by in vitro fertilization (IVF) cells. the stem cells, no human that would the They potential to allow of treatment methods diseases disabilities they and that are incurable, could greatly specially in order the suffering ▲ Figure 22 Har vesting umbilical to of obtain of have reduce created forget embryonic currently uterus. are of stem for is not arguments favour use so Some must ethical simply place Another We begun. have human or different the has and a are when life heartbeat, embryo of a suggest These the begin? characteristics development. when is egg, early there life consider should cells. of the human activity. weeks only human fertilizes Others pain, a this. some individuals. cord blood otherwise 1.2 ua Understanding Applications ➔ Prokaryotes have a simple cell structure ➔ The structure and function of organelles within without compar tments. exocrine gland cells of the pancreas. ➔ Eukaryotes have a compar tmentalized cell ➔ The structure and function of organelles within structure. palisade mesophyll cells of the leaf. ➔ Prokaryotes divide by binary ssion. ➔ Electron microscopes have a much higher resolution than light microscopes. Skills Nature of science ➔ Developments in scientic research follow ➔ based on electron micrographs. improvements in apparatus: the invention of electron microscopes led to greater Drawing the ultrastructure of prokaryotic cells ➔ understanding of cell structure. Drawing the ultrastructure of eukaryotic cells based on electron micrographs. ➔ Interpretation of electron micrographs to identify organelles and deduce the function of specialized cells. 16 1 . 2 u lt r A s t r u c t u r e o f c e l l s th ivi h mip Developments in scientic research follow improvements in apparatus: the invention of electron microscopes led to greater understanding of cell structure. Much years of the has progress followed microscopes. improved of In light bacteria and Chromosomes processes were many had the other were structures of the the the 19th the rst time William such discovered 0.001 of found had to as be to the Harvey chloroplasts and be was made than a limit though. explained cannot a later was the other tiny clear images structures of are membranes microscope cells than are until invented – For 0.01 a that lysosomes is It electron of is microscopes were developed these in the and the 1930s and came into use microscope. in in in the 1940s and 50s. electron the and The ideas green the electron of in the interpreted attened located under microscope shown microscope mitochondria spheres was light areas and stacks cells biologists were 1890s chlorophyll internal in appear the as light revealed membrane of in there be A the are them structure. electron what cells, reticulum 1950s, but for example, as were all example. signicant improvements microscopes allows is including Ribosomes, structures discovered, recent of features. improvement made. revealed endoplasmic named that to design new continue discoveries described in to sub- Germany 8.2, is electron tomography – a method of research producing laboratories or light most grana fact Whereas unknown still each topic during the ultrastructure and unlikely as be Electron in as with than darker the rods in small eukaryotic called microscopes the discovered thick. type called previously smaller example, μm the are with intricate electron now biological different the The are microscopes structures Many grana structureless an were chlorophyll. sacs, of previous revealed membranes. have many as than intricate example, They that things could micrometre this. about hampered was of (A millimetre.) smaller in was a (μm). light and had of smaller structure more For of membrane times The far microscope, that reasons sub-topic, be wrong. showed of cells. discoveries technical this micrometres thousandth Progress the For in produce 0.2 to to droplets to There produced 200 expected be as embryos. kidney – chloroplast. and fusion of be microscope formation the the within and to μm microscopes. century reproduction, development organs images 150 discovery gamete sexual seen last design organisms. and eluded mitochondria, were of the of was in allowed for basis subsequent and half meiosis The biologists, complexity over unicellular seen previously and revealed second mitosis, other gametes biology microscopes discovered. which The of in improvements They 3-D images by electron microscopy. allowed The resolution of electron microscopes Electron microscopes have a much higher resolution than light microscopes. If we we look cannot with a within things size the at a see of tree the 0.1 leaf with a cells mm we size with within as need of become individually Making the unaided its separate to down use to visible separate eyes parts a leaves. light they of an can The objects, about – we but see its unaided no 0.2 μm be object as eye smaller. microscope. can individual This can To see see allows separate leaves, objects, things the us to so but cells see cells can distinguished. distinguishable by eye is called resolution. The maximum nanometres are, the resolution (nm). resolution of However cannot a light microscope powerful be higher the than is lenses this 0.2 of a μm, light because it is which is 200 microscope limited by the ▲ wavelength of light (400–700 nm). If we try to resolve smaller objects Figure 1 An electron microscope by in use 17 1 C E L L B I O L O G Y making focus lenses them with magnication Beams of have much a microscopes is could size not of be It 1 a blurred microscopes a much μm or times the 1 nm. structure explains why until electron that × is of so but electron with microscopes a to maximum microscopes therefore This is have why microscopes were needed diameter had impossible the electron microscopes. microscopes is electron modern microscopes light it why 400. wavelength, cells, viruses nd This usually resolution than light but is Electron of we image. shorter The greater micrometre, seen magnication, get resolution. 200 reveal ultrastructure. a have 0.001 is and light higher that microscopes with with electrons resolution greater properly been of to 0.1 a light reveal see the bacteria micrometres invented. ri Miim Mim nam (mm) (µm) (m) Unaided eyes 0.1 Light microscopes Electron microscopes 100 100,000 0.0002 0.2 200 0.000001 0.001 1 Aiviy cmm a i Prokaryotic cell structure While still a young student in Berlin in the late 1920s Ernst Ruska developed magnetic Prokaryotes have a simple cell structure without compar tments coils that could focus beams All organisms can be divided into two groups according to their cell of electrons. He worked on the structure. Eukaryotes have a compartment within the cell that contains idea of using these lenses to the chromosomes. It is called the nucleus and is bounded by a nuclear obtain an image as in a light envelope consisting of a double layer of membrane. Prokaryotes do not microscope, but with electron have a nucleus. beams instead of light. During the 1930s he developed and Prokaryotes rened this technology. By have 1939 Ruska had designed are the rst commercial electron intestines the were the simplest found almost and rst cell organisms structure. everywhere even in pools – of to They in soil, hot evolve are on mostly in water, water in Earth small on and in our volcanic they size skin, still and in our areas. microscope. In 1986 he was All cells have a cell membrane, but some cells, including prokaryotes, awarded the Nobel Prize in also have a cell wall outside the cell membrane. This is a much Physics for this pioneering thicker and stronger structure than the membrane. It protects the cell, work. Ruska worked with the maintains its shape and prevents it from bursting. In prokaryotes as being the cell German rm Siemens. Other wall contains peptidoglycan. It is often referred to extracellular. companies in Britain, Canada and the United States also developed and manufactured electron microscopes. As no with nucleus membranes simpler ● is cytoplasm. – than it in present The is in a prokaryotic cytoplasm one is not uninterrupted eukaryotic cells, cell divided its chamber. though we interior into The must is entirely compartments structure remember is lled by therefore that it is still Scientists in dierent very complex in terms of the biochemicals present in the cytoplasm that are present, including countries usually many enzymes. cooperate with each other but commercial Organelles companies do not. What analogous are the reasons for this distinct dierence? cytoplasmic the organs structures Svedberg 18 are to with organelles units (S) is of specialized apart 70S, of multi-cellular from which eukaryotic organisms functions. ribosomes. is smaller cells in that Prokaryotes Their than size, those of that are they do not are have measured in eukaryotes. 1 . 2 Part of the cytoplasm micrographs. one circular explains that DNA the contain nucleoid – This appears region molecule. lighter lighter contains The appearance enzymes meaning and than the DNA is ribosomes. as the in many cell, other lighter contains area DNA with parts of but in the form proteins, of the is o f c e l l s electron usually associated with This it rest of not compared nucleus-like the DNA u lt r A s t r u c t u r e the cell not a of which cytoplasm is called true the nucleus. Cell division in prokaryotes Prokaryotes divide by binary ssion. All living division binary organisms of ssion chromosome to opposite follows. so they need pre-existing and is are is used replicated ends Each it to of of the the produce cells. Cell for and cell. genetically asexual the two Division daughter new division cells cells. in They can prokaryotic reproduction. copies of the of the The one do is copy of single the of the this by called circular chromosome cytoplasm contains only cells cell move quickly chromosome identical. dawig pkayi Draw the ultrastructure of prokaryotic cells based on electron micrographs. Because cannot prokaryotes be seen magnication using in are a Aiviy mostly light electron very small, microscope. micrographs It their is that internal only we with can see structure much the higher details oh am pkay of Biologists sometimes use the structure, called the ultrastructure. Drawings of the ultrastructure the term “bacteria” instead of prokaryotes are therefore based on electron micrographs. of “prokaryote”. This may Shown E.coli, and below a shows also you the learn the found internal technique shown. can on bacterium different is and By next in our and shows to The the the identify are two intestines. structure. comparing how page One other external drawings structures electron has of micrographs them been structure. with within the is a thin prepared A electron prokaryotic section by drawing of a of not always be appropriate because the term prokaryote encompasses each micrographs cells. a larger group of organisms than true bacteria (Eubacteria). It also includes organisms in another group Electron micrograph of Escherichia coli (1–2μm in length) called the Archaea. There is a group of photosynthetic organisms that used to be called blue-green algae, but their cell structure is prokaryotic and algae are eukaryotic. This problem has been Drawing to help interpret the electron micrograph solved by renaming them as nucleoid (region Cyanobacteria. containing naked DNA) ribosomes cell wall plasma membrane cytoplasm ● What problems are caused by scientists using dierent words for things than non- scientists? 19 1 C E L L B I O L O G Y Electron micrograph of Escherichia coli showing surface features pili agellum Shown below practice can and your also try many copies another at other drawing indicate and nd is skill of their annotate electron these. a micrograph drawing appearance your of a is no need structure, in drawing one to prokaryote. ultrastructure micrographs There particular the such small say of to of can prokaryotic cells a as ribosomes. the long they are time part found use of it cells. on spend representative that You prokaryotic the to You internet drawing You the can cytoplasm elsewhere. Aiviy Gai a mpa maizai Garlic cells store a harmless sulphur-containing compound called alliin in their vacuoles. They store an enzyme called alliinase in other parts of the cell. Alliinase converts alliin into a compound called allicin, which has a very strong smell and avour and is toxic to some herbivores. ▲ Figure 2 Brucella abor tus (Bang’s bacillus), 2 μm in length This reaction occurs when herbivores bite into garlic and damage cells, mixing the Eukaryotic cell structure enzyme and its substrate. Perhaps surprisingly, many Eukaryotes have a compar tmentalized cell structure. humans like the avour, but to Eukaryotic cells have a much more complicated internal structure than get it garlic must be crushed prokaryotic cells. Whereas the cytoplasm of a prokaryotic cell is one or cut, not used whole. undivided ● You can test this by that smelling a whole garlic are they space, are single or eukaryotic divided double up by cells are compartmentalized. partitions into compartments. This The means partitions membranes. bulb, then cutting or The most important of these compartments is the nucleus. It contains crushing it and smelling the cell’s chromosomes. The compartments in the cytoplasm are known it again. as 20 organelles. Just as each organ in an animal’s body is specialized 1 . 2 to perform distinctive There ● are a particular structure several Enzymes ● ● that membrane of a could lysosome the particular other if such Organelles in with being a cause digest as organelle in a eukaryotic cell has c e l l s a spread damage For and compartmentalized: particular were organelle. process, processes in for they could an lysosome Conditions ● substrates than Substances inside each o f function. advantages and concentrated role, and u lt r A s t r u c t u r e kill process to the example, a cell, can throughout if cell the they be much the can be kept digestive were more cytoplasm. inside enzymes not safely the of stored membrane. pH can which a be maintained may be at different an to ideal the level levels for a needed for cell. their contents can be moved around within thecell. dawig kayi Draw the ultrastructure of eukaryotic cells based on electron micrographs. The ultrastructure complex of a the cell. and it Your structure, structure of is of eukaryotic often drawing so the you best is an need organelles n to cells draw is very only part interpretation to understand that might be of the present. The of table each with a of below the drawing recognition organelle contains of the features are an commonly electron occurring structure. and the micrograph organelles, Brief function notes of on each included. The nuclear membrane is double and has pores through it. The nucleus contains the chromosomes, double nuclear membrane consisting of DNA associated with histone proteins. nuclear pores Uncoiled chromosomes are spread through the nucleus and are called chromatin. There are often densely staining areas of chromatin around the edge of the nucleus. The nucleus is where DNA is replicated and transcribed to form mRNA , which is expor ted via dense chromatin the nuclear pores to the cytoplasm. chromatin rgh pami The rER consists of attened membrane sacs, called im cisternae. Attached to the outside of these cisternae are ribosomes. They are larger than in prokaryotes and ribosomes are classied as 80S. The main function of the rER is to synthesize protein for secretion from the cell. Protein synthesized by the ribosomes of the rER passes into its cisternae and is then carried by vesicles, which bud o and are moved to the Golgi apparatus. cisterna 21 1 C E L L B I O L O G Y Ggi appaa This organelle consists of attened membrane sacs called cisternae, like rER. However the cisternae are cisterna not as long, are often curved, do not have attached ribosomes and have many vesicles nearby. The Golgi apparatus processes proteins brought in vesicles from the rER. Most of these proteins are then carried in vesicles vesicles to the plasma membrane for secretion. These are approximately spherical with a single lym digestive enzymes membrane. They are formed from Golgi vesicles. They contain high concentrations of protein, which makes them densely staining in electron micrographs. They contain digestive enzymes, which can be used to break down ingested food in vesicles or break down organelles in the cell or even the whole cell. lysosome membrane Mihi inner outer membrane membrane A double membrane surrounds mitochondria, with the inner of these membranes invaginated to form structures called cristae. The uid inside is called the matrix. The shape of mitochondria is variable but is usually spherical or ovoid. They produce ATP for the cell by aerobic cell respiration. Fat is digested here if it is being used as an energy source in the cell. matrix crista f im These appear as dark granules in the cytoplasm and are not surrounded by a membrane. They have the same size as ribosomes attached to the rER – about 20nm in diameter, and known as 80S. Free ribosomes synthesize protein, releasing it to work in the cytoplasm, as enzymes or in other ways. Ribosomes are constructed in a region of the nucleus called the nucleolus. A double membrane surrounds the chloroplast. Inside chpa are stacks of thylakoids, which are attened sacs of starch grain membrane. The shape of chloroplasts is variable but stroma is usually spherical or ovoid. They produce glucose and a wide variety of other organic compounds by double membrane thylakoid photosynthesis. Starch grains may be present inside chloroplasts if they have been photosynthesizing rapidly. Va a These are organelles that consist simply of a single vi membrane with uid inside. Many plant cells have vacuole containing food large vacuoles that occupy more than half of the cell volume. Some animals absorb foods from outside and digest them inside vacuoles. Some unicellular organisms use vacuoles to expel excess water. large vacuole Vesicles are very small vacuoles used to transpor t vesicles materials inside the cell. 22 1 . 2 u lt r A s t r u c t u r e o f c e l l s Mi a In the cytoplasm of cells there are small cylindrical i bres called microtubules that have a variety of roles, including moving chromosomes during cell division. triple Animal cells have structures called centrioles, which consist of two groups of nine triple microtubules. Centrioles form an anchor point for microtubules during cell division and also for microtubules inside cilia and agella. These are whip-like structures projecting from the ciia a aga cell surface. They contain a ring of nine double microtubules plus two central ones. Flagella are larger and usually only one is present, as in a sperm. Cilia are smaller and many are present. Cilia and agella can be used for locomotion. Cilia can be also be used to create a current in the uid next to the cell. microtubule membrane The electron with are labels micrograph to identify below some of shows the a liver organelles cell that ● Using draw your the understanding whole cell to of show these its organelles, ultrastructure. present. free mitochondrion rough endoplasmic reticulum ▲ nucleus ribosomes Golgi lysosome apparatus Figure 3 Electron micrograph of par t of a liver cell 23 1 C E L L B I O L O G Y Exocrine gland cells of the pancreas The structure and function of organelles within exocrine gland cells of the pancreas. Gland cells through types cells of digestive small Enzymes have in cells gland ready intestine are micrograph plasma in proteins, and on the a the to right secrete carries digest them them. cells them the The plasma electron organelles: apparatus mitochondrion vesicles nucleus lysosomes rough to proteins to these Golgi gland make them shows membrane to them foods. synthesize release them two Endocrine exocrine transport are bloodstream. that they release There pancreas process the the duct so needed then they pancreas. into where secretion, membrane the into quantities, for in cells enzymes – membrane. hormones organelles large substances plasma gland secrete Exocrine the secrete their ▲ ER Figure 4 Electron micrograph of pancreas cell Paia mphy The structure and function of organelles within palisade mesophyll cells of the leaf. The function producing dioxide using out and light most of other cylindrical. Like surrounded membrane the simple The shape all by inside right mesophyll cell is a of in type the these – carbon compounds, that carries leaf is palisade cells is roughly plant wall, The the from inorganic living cell it. shows cell photosynthesis cell photosynthesis The on leaf compounds energy. mesophyll. is the organic cells with electron organelles a the cell plasma micrograph that a palisade contains: wall plasma membrane chloroplasts mitochondrion vacuole ▲ nucleus 24 Figure 5 Electron micrograph of palisade mesophyll cell 1 . 3 M e M b r A n e s t r u c t u r e Ipig h kayi Interpret electron micrographs to identify organelles and deduce the function of specialized cells. If the organelles identied possible ● and to Study in deduce the and 8. and try eukaryotic function the electron Identify to a their the deduce is overall cell function micrographs organelles the can known, in that function of be it of is often the gures are cell. 6, 7 present each cell. ▲ ▲ Figure 7 Figure 6 ▲ Figure 8 1.3 Mma Understanding Applications ➔ Phospholipids form bilayers in water due to the ➔ Cholesterol in mammalian membranes reduces amphipathic properties of phospholipid molecules. membrane uidity and permeability to some ➔ Membrane proteins are diverse in terms of solutes. structure, position in the membrane and function. ➔ Cholesterol is a component of animal cell membranes. Skills Nature of science ➔ Using models as representations of the real world: there are alternative models of ➔ Drawing the uid mosaic model. ➔ Analysis of evidence from electron microscopy that membrane structure. ➔ Falsication of theories with one theory being superseded by another: evidence falsied the led to the proposal of the Davson–Danielli model. ➔ Analysis of the falsication of the Davson–Danielli model that led to the Singer–Nicolson model Davson–Danielli model. 25 1 C E L L B I O L O G Y OH Phospholipid bilayers hydrophilic O O P phosphate Phospholipids form bilayers in water due to the O head H C H H H amphipathic proper ties of phospholipid molecules. C C Some O substances are attracted to water – they are hydrophilic O H C O C O C H C H C H C H Other substances Phospholipids hydrophilic C H C H C H C H C H C H described The H C H C H C H hydrophilic structure C H H C H C H H C H of not attracted unusual part is to because water part hydrophobic. of – a they are hydrophobic. phospholipid Substances with molecule this property is are amphipathic. hydrophobic C are and as are part part of a phospholipid consists of phospholipids two is is the phosphate hydrocarbon shown in gure chains. group. The The chemical 1. hydrophobic hydrocarbon The structure can be represented simply using a circle for the phosphate tails C H C H H C H C H H C H C H C H C H C H C H C H C H C H C H group ▲ and two two parts hydrocarbon H hydrocarbon chains. of the tails. molecule When are often phospholipids called are phosphate mixed with heads water and the heads are attracted to the water but the hydrocarbon H tails ▲ the H C phosphate H for Figure 2 Simplied diagram of a phospholipid molecule The C lines are attracted Figure 1 The molecular structure phospholipids of a phospholipid. hydrocarbon The phosphate often has other hydrophilic groups heads facing to each become tails the but arranged facing water other, into inwards on not either to water. double towards side. layers, each These Because with other double of the and this the layers the hydrophobic hydrophilic are called attached to it, but these are not phospholipid bilayers. They are stable structures and they form the basis shown in this diagram of all cell membranes. hydrophilic phosphate hydrophobic head hydrocarbon tails phospholipid bilayer ▲ Figure 3 Simplied diagram of a phospholipid bilayer M mma Using models as representations of the real world: there are alternative models of membrane structure. In the 1920s, Gor te r phospholipids of red area 26 blood that fro m cells the a nd the a nd Gr e nde l pla s ma ca lcul ate d pho s p ho l ip id s e x t ra c t e d me mbr an e that occupi ed arranged the area the in of a mono l a ye r plasma the that w h en phospholipids. wa s twice me mb ra ne . membran e co ntai ne d The r e w er e as The y a la rg e bilayer s e ve ra l as d ed u c ed er r or s of in 1 . 3 their methods other for out cell and but l uck il y the r e membrane s is the s e now b e i ng canc e l le d ve ry s tr ong ba s ed on ea c h e vid en c e p ho sp h ol ipi d Membranes also and Grendel’s this is to the proposed because very some the 1950s, of – protein on this and appear dark phospholipids appearance thought barrier High to the would very showed dark a railroad lines with a the tted the in electron appear light, Davson-Danielli proteins the membrane. the inner cases tiles move. track of occupy a protruding free to bilayer, the The Integral out from move the in model its are in the are this attached are some bilayer likened to phospholipid each proteins In positions proteins bilayer, proteins Because the of proteins phospholipid was Nicolson. variety surface. sides. gives structure and Peripheral mosaic. are the This mosaic lighter parts a Singer outer the both in molecules layers in or or in with one membrane by to the of of 1966 in on are electron made in embedded explain thin, movement were of sandwich magnication membranes two it model sides model proposed adjacent this being Another Gorter where and both proposed despite which appearance of and explain Davson bilayer, they substances. micrographs 1930s They effective not layers membranes, protein did the phospholipid model a In membrane. how contain model located. the between.Proteins micrographs so s t r u c t u r e model. bilayers. Danielli band M e M b r A n e of are name the also – two able the to uid model. Pm wih h dav–daii m Falsication of theories with one theory being superseded by another: evidence falsied the Davson–Danielli model. The Davson–Danielli structure for about tted and In the was 30 the 1950s accumulated Danielli ● years. model electron including of membrane most of cell biologists many X-ray experiments diffraction studies microscopy. and 60s that some did not experimental t with the evidence Davson– model: This technique cells and then occurs along centre of scattered electron involves through of Structure them. of The fracture the structures freeze-etched were of including Globular membranes images of interpreted as proteins. membrane Improvements freezing weakness, membranes. centre allowed of micrographs. rapid fracturing lines transmembrane ● by Results Freeze-etched the model accepted in proteins proteins. biochemical to be techniques extracted ▲ from Figure 4 Freeze-etched electron micrograph of nuclear membranes, with nuclear pores visible and vesicles in the membranes. They were found to be very surrounding cytoplasm. The diagram on page 28 shows the line varied in size and globular in shape so of fracture through the centre of the inner and outer nuclear were unlike the type of structural protein membranes. Transmembrane proteins are visible in both of the that would form continuous layers on the membranes 27 1 C E L L B I O L O G Y periphery were of the membrane. hydrophobic surface so they on at would tails centre membrane. the of be hydrocarbon of Also least the the part of attracted proteins to the the phospholipids in replacement and their the it Fluorescent green uorescent antibodies The antibody that tagged with with green together. green markers bind membrane to red of markers Within 40 were and The other cells mixed were the leading be model unwise superseded. uid to There of An maxim in important that science dogma fused mosaic for over assume are tted widely the model. fty that already evidence accepted it was It has years but will some never the suggested model. you happen and for might scientists be because instead search is “Think mistaken.” scientists it Advances reject continually for better understanding. and throughout modications possible were cells red the would that became to proteins. cells needed that or attached some minutes were Red membrane proteins markers. markers tagging. was model Singer–Nicolson been be ● the the cytoplasm membrane of membrane proteins the membrane peripheral Taken the the are rather cell. This free to than showed move being that within xed in a layer. together, falsied fused this experimental Davson–Danielli evidence model. nucleus A inner membrane outer membrane Evidence for and against the Davson–Danielli model of membrane structure Analysis of evidence from electron microscopy that led to the proposal of the Davson–Danielli model. Figure blood edge 1. 5 shows cell of and the the plasma some of the membrane cytoplasm of a near red the cell. Describe the appearance of the plasma membrane. 2. Explain how membrane with 3. of 4. the of the are two sets used to on for of on either the dark red 10 that types the of the that side. [2] appearance cell. the [2] electron thickness nanometres. of questions data that the phospholipid grainy Davson–Danielli structure. of blood magnication is suggested region the data-based the falsify membrane 28 of central assuming membrane based appearance protein reasons micrograph The a cytoplasm Calculate the this had layers Suggest [2] of [3] that follow were model of ▲ Figure 5 TEM of plasma membrane of a red blood cell 1 . 3 M e M b r A n e s t r u c t u r e daa-a qi: Membranes in Diusion of proteins in membranes freeze-etched electron micrographs Frye to Figure 6 shows a freeze-etched and Edidin obtain image of part of a cell. It by Professor Horst Robenek uid technique nature They attached of uorescent markers membrane proteins – green markers to mouse of cells Münster elegant the was to prepared an for electron membranes. micrograph used evidence and red markers to human cells. In both University. cases, spherical were used. were then had but one the green were minutes completely cell membrane. not prevent processes tim a mixing in the culture human the one fusion, merged, of cells one, the red until the ATP (ATP cells fused red throughout Blocking this rst, following mixed tissue and and gradually did active At hemisphere markers in mouse together. the for growing marked fused green over and cells The they whole of production supplies energy cell). c wih mak y mix/% i / r r r r 1 2 3 4 5 0 0 – – 10 3 0 – – 25 40 54 – – 40 87 88 93 100 120 100 – – – Ma mi ▲ 1 Figure 6 In all of the fractured micrograph small membranes granules are in the visible. 1 a) State what b) Explain these granules are. Calculate markers [2] the fully mean percentage mixed for each of cells time with after fusion. the granules in membrane signicance the of investigation 2 of structure. Plot bars [3] in 2 One the of the membranes nucleus is micrograph. visible Deduce that on the a graph for the or outer left whether nuclear results. it of is and lowest your reasons membrane. when Identify the three asked describing 4 Explain that its mitochondria this their the either to cell visible using was from join these labels the in or 4 Explain at this with with plot will a the lie micrograph proteins the you a range variation plot small ruled mean on trend whether Davson–Danielli Singer–Nicolson 5 the bar highest and line. You the result range with a bar. [4] Explain the shown the results model model benet by of or the t graph. in [1] the the more closely. plotting range [2] bars ongraphs. [2] [2] 6 questions also Describe by cytoplasm. Extension results bars This 3 [2] processing do was deduce positions. evidence To including there (Always [2] micrograph, results, the something.) 3 the where the cross. give of times surround should inner [4] these on this topic can be found www.oxfordsecondary.co.uk/ib-biology During this incubated experiment at researchers 37 °C. the Suggest choosing this cells a were reason for temperature. the [1] 29 1 C E L L 7 B I O L O G Y The experiment the trends temperatures 8 Explain the When the ATP trends of the 15 15 the in results. graph 35 the for °C. [2] graph for °C. was red in different the and shown below at shows shown synthesis mixing 7 between temperatures 9 repeated [2] blocked and srekram htiw sllec fo % Explain was Figure green in the cells, markers setunim 04 retfa dexim ylluf temperatures. 1 100 1 1 1 1 50 still 1 1 1 1 occurred. drawn Explain from what conclusion can be 0 this. Predict, with 15 reasons, the results of 25 35 incubation temperature (°C) [1] ▲ 10 5 Figure 7 Eect of temperature on the the rate of diusion of uorescent markers experiment if it was repeated using cells in membranes from or arctic sh rather than from mice humans. [1] Membrane proteins Membrane proteins are diverse in terms of structure, position in the membrane and function. Cell is to membranes form cannot all a barrier easily other have examples are wide through pass. functions a This are listed in is range which carried carried table of ions out out functions. and by by The primary hydrophilic the molecules phospholipid proteins in the function bilayer. membrane. Almost Six 1. fi mma pi Hormone binding sites (also called hormone receptors), for example the insulin receptor. Figure 8 shows an example. Immobilized enzymes with the active site on the outside, for example in the small intestine. Cell adhesion to form tight junctions between groups of cells in tissues and organs. Cell-to-cell communication, for example receptors for neurotransmitters at synapses. Channels for passive transpor t to allow hydrophilic par ticles across by facilitated diusion. Pumps for active transpor t which use ATP to move par ticles across the membrane. ▲ T able 1 Because in ▲ Figure 8 Hormone receptor (purple) of these structure into two and varied in their functions, position membrane in the proteins membrane. are They very can diverse be divided groups. embedded in phospholipid bilayer (grey). ● Integral proteins are hydrophobic on at least part of their surface and The hormone (blue/red) is thyroid they are therefore embedded in the hydrocarbon chains in the centre stimulating hormone. G-protein (brown) of the membrane. Many integral proteins are transmembrane – conveys the hormone's message to the interior of the cell extend across through 30 the the membrane, regions of with phosphate hydrophilic heads on parts either projecting side. they 1 . 3 ● Peripheral proteins embedded in of a integral single the Figure the proteins includes all orientated example, plants are pump The protein of have pump them membranes just as The cell content about 50%. chloroplasts respiration. that the of and and of face most have which is the of membrane up face out to surface have into surface. membrane function membranes potassium the Some protein. and their not inserted membrane outer carry are reversible. to plasma pick so attached often them an can is surface, are s t r u c t u r e of ions root from correctly. cells the in soil cell. is very active in the a a protein sheath content contents which because membrane, membranes protein protein variable, myelin plasma mitochondria, These and the more highest to types they they have their them protein membranes The The attached in root of attachment both that Membranes insulators protein is so varies. content. inner so on Most the of proteins into content protein act an orientated and chain examples proteins For this anchoring Membranes are hydrophilic and hydrocarbon membrane, 9 are membrane. M e M b r A n e are contents of only on in about higher around are active of the the in the function is nerve its bres 18 %. outside the of the membranes photosynthesis of and 75 % dawig mma Draw the uid mosaic model of membrane structure. The for but structure us to we can symbols A in to diagram gure of show membranes all show of it our represent of in full is far too detail in understanding the membrane molecules structure complicated a of drawing, it The diagram shows these components of a membrane: using ● phospholipids; ● integral ● peripheral ● cholesterol. present. is shown proteins; 9. ▲ proteins; Figure 9 Membrane structure 31 1 C E L L Identify Using B I O L O G Y which similar each symbols components draw according the these to proteins: pumps for receptors It worth is of you membrane interpret in a science merely on visual with are A we diagram which is but is a a a book and draw. to to their are and as it all For paper based example, the cells we usually author, for printing. still the needed biologists skills. of software, perhaps drawing our not theory. by is and group suitable ability show are a and used membranes, computer artistic drawing, improve They cell paper make are process scientic use paper No the been model simplify plasma on or or tissue the enzymes have They theories. drawingon up you mosaic Drawings or contains diffusion, neurotransmitters. uid animal drawing possible pencil to scientic and in or structure represent our as an that immobilized Drawings like. diagramis. membrane, facilitated process. hypotheses a model, explanations. a the the of what the or looks tidied now way it to basing out of show lines starts It what models, when about draw structure. understanding for hormones structure as mosaic transport, for in represent structure channels thinking when to the uid active and doing component can Of best for develop course some ▲ biologists Some produce examples particularly are shown in good gure Figure 10 Anatomical drawings by Leonardo da Vinci drawings. 10. Cholesterol in membranes Cholesterol is a component of animal cell membranes. The two main proteins. Cholesterol CH CH 3 CH 2 CH CH is a cell type of cell membranes of lipid, but membranes also it is contain not a fat are phospholipids and cholesterol. or oil. Instead it belongs CH 2 3 to cholesterol components Animal a group of substances called steroids. Most of a cholesterol molecule CH 2 is hydrophobic so it is attracted to the hydrophobic hydrocarbon CH 3 CH tails in the centre of the membrane, but one end of the cholesterol 3 molecule has a hydroxyl ( OH) group which is hydrophilic. This is CH 3 attracted to Cholesterol in the the phosphate molecules are heads on therefore the periphery positioned of the between membrane. phospholipids membrane. HO The hydrophilic amount membranes ▲ of cholesterol in animal cell membranes of vesicles that hold neurotransmitters Figure 11 The structure of cholesterol of 32 varies. In the hydrophobic 30% of the lipid in the membrane is cholesterol. at synapses as much 1 . 4 M e M b r A n e t r A n s P o r t The role of cholesterol in membranes Cholesterol in mammalian membranes reduces membrane uidity and permeability to some solutes. Cell of membranes matter. liquid, but Overall free The to The the the of If of is exactly hydrocarbon phosphate uid as to any tails heads of the usually act components as a permeability hydrogen curve vesicles the to into a during uid and the so Ho wev er of hyd r o p hi l ic to i ts conca v e but r eg ul a r ui di ty Due they if needs more of the pa c ki n g it a ls o s ha pe s ha pe , it three behave like a states as a solid. membrane are of whi c h he l ps able to uid be hydr oc ar bon al s o ca n h e lp the t a i ls and m o t io n re duc e s s odi u m the restricted. m ol e c ul a r in control enough c r ys t a ll iz in g It as ch ol e st e r ol not t he r es t r ic t s such carefully less would them me m br a ne . p ar ti cle s be be were within p re ven t s the to would they substances mo l e cule s , soli d . ions. membranes too through, cell disrupts therefore cell were pass the phospholipid behaving to animal they substances Cholesterol and correspond hydrophilic membrane uidity movement of not move. controlled. what do hydrophobic io ns the and m e m bra n e s f or m a t i on of end o cy tos is . 1.4 Mma ap Understanding Applications ➔ Par ticles move across membranes by simple ➔ Structure and function of sodium–potassium diusion, facilitated diusion, osmosis and pumps for active transpor t and potassium active transpor t. channels for facilitated diusion in axons. ➔ The uidity of membranes allows materials to ➔ Tissues or organs to be used in medical be taken into cells by endocytosis or released procedures must be bathed in a solution with by exocytosis. the same osmolarity as the cytoplasm to ➔ Vesicles move materials within cells. prevent osmosis. Nature of science ➔ Experimental design: accurate quantitative measurements in osmosis experiments Skills ➔ Estimation of osmolarity in tissues by bathing samples in hypotonic and hyper tonic solutions. are essential. 33 1 C E L L B I O L O G Y Endocytosis outside of cell endocytosis The uidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. cell interior A vesicle Vesicles They are around of a a small To very and this a Vesicles method Figure of 1 Vesicles outside the be of It a cell from in of uid inside. eukaryotic are happen cells. constructed, because surrounded by a of moved the uidity membrane to by is into a ls o p as s are is the off the in pulled from the membrane rest carry out a small on was cell. piece the outside It is of inside the called the of plasma the cell, so plasma this is a endocytosis. occurs. e ndo cy tos i s the y membrane Proteins formed that process large a off. pinching p l a ce nta , in of ATP . material ca nno t take droplet They can structures vesicle the antibod i e s , cells a present cells. This region by The but the of pinched materials in that in including is energy how cell feature small and contains taken with normally allows formed taking the are move. cells. shows example, Some and using can membrane. by which vesicle, membrane membrane deconstructed. membrane process, of and dynamic then shape form the sac spherical membranes, change of is are co nta i n ofte n a cr os s the p ro te ins wat e r c on t a i n p la sm a fr om a bs or be d i nt o undi g es ted the the foo d and la r g er so lu t e s m e m bra n e . mot h er ’s fetus f ro m m ol e c ul e s by pa rti c l es n e ed ed For bl ood , e nd oc yt os is . by e ndo c yt os is . Th is vesicle happens Some and ▲ in unicel l ul a r types of viruses whi te by o rg a ni sms b l oo d ce l ls end o cy tos i s a nd i ncl u di ng ta ke in then Amoeba pa t h og e n s kil l them, as and Paramecium . in c l u din g p ar t of ba c t e r ia the b ody’s Figure 1 Endocytosis response to infect i o n. Vesicle movement in cells Vesicles move materials within cells. Vesicles can be cases it is the cases it is proteins vesicle An The vesicles a into Golgi protein In of is the the a nd bud its off the materials vesicle around that membrane the ve s icl e the na l by of need the inside to be vesicle r ER the a nd a nd Gol g i f o r m. cells. In moved. that insi de carr y to this th e occ u r s on th e has the r E R. th e m ap pa r at u s , W he n mo ve c ont e n t s ri bo s om e s a ccumul ate s wi th apparatus are some In the other reason for to p la sm a s ec r e t or y e n dop la s m i c Ves i c le s t he wh i c h bee n in r oug h Golg i c o nt a i ni n g a pp ar a t u s. p ro ces s es don e , t he ves i c le s m em bra n e , bu d where off th e secreted . growing proteins off of the synthe s ize d fuse cell, Phospholipids into in move mo v i ng is (rER) proteins protein the contents Protein reticulum the to movement. example cells. 34 used rER are area and of the synthesized membrane. which rER the also to next to Ribosomes become move plasma the plasma the on inserted membrane rER the into and rER the needs become synthesize membrane. membrane. They to increase. inserted membrane Vesicles fuse with it, bud each 1 . 4 increasing This the method area can of also the be plasma used to membrane increase by the a very size of small M e M b r A n e t r A n s P o r t outside of cell amount. organelles in the exocytosis cytoplasm such as lysosomes and mitochondria. Vesicles bud o from Proteins are synthesized Vesicles bud o from The Golgi the Golgi apparatus by ribosomes and then enter the rER and carry the apparatus and carry the modied the rough endoplasmic proteins to the Golgi modies the proteins to the plasma reticulum apparatus proteins membrane vesicle ENDOCYTOSIS EXOCYTOSIS Part of the plasma Vesicles fuse membrane is pulled inwards with the plasma A droplet of uid becomes membrane enclosed when a vesicle is The contents of pinched o the vesicle are expelled Vesicles can then move through the cytoplasm The membrane carrying their contents then attens out again ▲ Figure 2 Exocytosis The uidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. Vesicles the can plasma be used outside Digestive enzymes polypeptides Golgi in the In this the cell. are the materials contents This and case then the from are from are process released enzymes apparatus exocytosis. release membrane, therefore the to then is gland release is to a vesicle the by by to with membrane exocytosis. the rER, membrane referred fuses and exocytosis. cells the If outside called synthesized carried cells. as The processed in vesicles secretion, in for because cell interior a ▲ useful substance Exocytosis materials. unicellular called a can An is being also used example organisms. contractile membrane be for released, is to the The expel by is which a waste waste removal water vacuole, expulsion not of is then exocytosis. products excess loaded into or water a can unwanted from vesicle, moved This Figure 3 Exocytosis product. to be the the cells of sometimes plasma seen quite easily in contractile Paramecium, showing a using a microscope. contractile vesicle at Figure each 4 end shows of the a drawing of Paramecium vesicle cell. Simple diusion mouth Par ticles move across membranes by simple diusion, facilitated diusion, osmosis and active transpor t. Simple across diffusion is one of the four methods of moving endoplastule particles membranes. endoplast Diffusion happens is the spreading because the out particles of particles are in in liquids continuous and gases random that motion. contractile vesicle More area particles of There lower is move from an concentration therefore concentration – a a net area than of move movement movement higher down in from the concentration the the opposite higher to concentration to an direction. the lower gradient. Living ▲ Figure 4 Drawing of Paramecium 35 1 C E L L B I O L O G Y organisms do not have to use energy to make diffusion occur so it is a toK passive process. ca h am aa jiy Simple may xiv between i? if the diffusion the across phospholipid particles membranes phospholipids such as bilayer oxygen in is can the involves particles membrane. permeable diffuse to It the through can passing only particles. easily. If happen Non-polar the oxygen In an experiment to test concentration inside a cell is reduced due to aerobic respiration and whether NaCl can diuse the concentration outside is higher, oxygen will pass into the cell through dialysis tubing, a through the plasma membrane by passive diffusion. An example is 1% solution of NaCl was shown in gure 6. placed inside a dialysis tube and the tube was clamped shut. The tube containing the solution was immersed in a beaker containing water. A conductivity meter was inser ted into the water surrounding the tubing. If the Figure 5 Model of diusion with dots representing par ticles ▲ conductivity of the solution increases, then the NaCl is The centre of membranes is hydrophobic, so ions with positive or negative diusing out of the tubing. charges cannot positive tim / ± 1 and easily negative pass through. charges over Polar their molecules, surface, can which have diffuse at partial low rates particles such civiy between 1 the phospholipids of the membrane. Small polar as ± 10 mg urea 0 81.442 30 84.803 60 88.681 90 95.403 120 99.799 or ethanol pass through more easily than largeparticles. the cornea has no blood supply so its cells obtain oxygen by simple diusion from the air high concentration of oxygen in the air air high concentration uid (tears) of oxygen in the tears Noting the uncer tainty of the cell on outer that coat the cornea conductivity probe, discuss surface of the cornea whether the data suppor ts the conclusion that NaCl is diusing out of the dialysis oxygen passes through tubing. lower concentration the plasma membrane by of oxygen in the cornea simple diusion cells due to aerobic respiration Figure 6 Passive diusion ▲ daa-a qi: Diusion of oxygen in the cornea Oxygen cornea concentrations of anesthetized were 1 measured rabbits at in different the outer surface. These the thickness into the aqueous the The rabbit’s cornea is 400 a) behind μm) thick. The graph Describe the trend to the of eye The 20 36 structure oxygen You may before 7) shows look answering concentration kilopascals to (20kPa). in in the oxygen cornea from the surface. [2] micrometres (gure need in inner Suggest reasons the normal at a is in the trend in oxygen thecornea. [2] diagram questions. air for the concentration measurements. in the b) (400 cornea were outer cornea. rabbit distances measurements humor the [1] concentrations continued of millimetres. 2 from Calculate 3 a) Compare the the aqueous oxygen concentrations humorwith concentrations in the in the cornea. [2] 1 . 4 b) Using the whether cornea Using as a the to a) Predict lenses the b) the data method graph, deduce the 20 humor. graph, moving effect of oxygen [2] evaluate substances diffusion in large [2] wearing contact concentrations in cornea. Suggest [1] how this effect could t r A n s P o r t the organisms. the on the diffusesfrom aqueous in of multicellular 5 in aPk/negyxo fo noitartnecnoC 4 data oxygen M e M b r A n e be 15 10 5 minimized. 6 The range how bars much the [1] for each data point measurements indicate varied. 0 Explain the reason for showing range 0 barson the graph. 100 200 300 400 [2] distance from outer surface of cornea/µm ▲ Figure 7 Facilitated diusion Par ticles move across membranes by simple diusion, facilitated diusion, osmosis and active transpor t. Facilitated across Ions can the and pass other into plasma diameter. and diffusion walls passes both. Because a are of these higher the four cannot if channels methods of the for and of moving channel a Cells in are to can the for particles phospholipids them with protein. ensure lower that ions, pass a only or control in and one the type ions, process of and (a) of membrane, the types membrane diffuse narrow diameter potassium through which through very The concentration, plasma substances holes of sodium particles to between channels consist example help placed which diffuse are channels channel diffusion. control there These the concentration facilitated can of that cells through, synthesized they of properties but not out membrane. particle called one particles or The chemical from is membranes. is channel in this way out. (b) Figure 8 viewed shows from the the structure side and of from a channel the for outside of magnesium the ions, membrane. The Membrane structure of magnesium the protein ions are making able to up pass the channel through the ensures hole in that the only centre. Cytoplasm Osmosis Par ticles move across membranes by simple diusion, facilitated diusion, osmosis and active transpor t. Osmosis is one membranes. of the four methods of moving particles across ▲ Figure 8 Magnesium channel 37 1 C E L L B I O L O G Y Water is able Sometimes in and but at out is other direction Osmosis or is dissolve Figure 9 water of the water therefore than is a to have regions net because with no Osmosis can cells increase reabsorb its a of have water in all cells hair the which regions of pass to cells channel therefore an pass in is of with movement free of to this it is passive occur. despite which are only greatly the cells that soil. slightly le. being bilayer. kidney from single move there concentration phospholipid water aquaporin through the molecules, Examples absorb osmosis. concentration make the one is Substances bonds solute aquaporins, water. that in water movement, in movement to freely. moving concentration Because lower though called the restrict This cells net molecules directly because to no move (solutes). solute water most movement in bonds higher of expended channels root point, a concentration. enough is intermolecular concentration. from be net water These with permeability and molecules, to there This in of molecules molecules differences forming solute solute water membrane to out water and other. molecules. water small the and of more dissolved by in same concentration has happen are the times Regions lower higher narrowest water lower energy hydrophilic, At a with movement regions Some molecules. move number due substances ▲ to the wider Positive than charges + at this point in the channel prevent protons (H ) from passing through. Active transport Par ticles move across membranes by simple diusion, facilitated diusion, osmosis and active transpor t. Active transport is one of the four methods of moving particles across membranes. Cells sometimes higher against pump the type needed transport process. Active of to uses 10 enters the The though Less The commonly, there is already is called produces is carried its out proteins. proteins membranes therefore ATP own by as allowing not is cells a already is a absorbed sometimes larger the cell ATP proteins to of and transport. energy of membranes the diffusion active supply globular The is called supply by in cell energy Most for this respiration. contain the many content of illustrates pump After this, pump and how protein change the the protein ion a pump and to or pump shown can the protein reach protein molecule protein far takes can as The a place pass returns transports works. as to to its Vitamin molecule central using the its B intoE. ion chamber. energy opposite original or A from side of the conformation. coli is active membranes, cells control 12 38 there substance precisely. membrane Figure 10 Action of a pump protein even outside. though across It substance pump conformational ▲ than gradient. even out. cell pump Figure ATP . it a Every cytoplasm out, movement carry called different substances, inside outside. transport usually in concentration substances concentration This take concentration 1 . 4 M e M b r A n e t r A n s P o r t o x yg nig Phpha /% /% api/μm daa-a qi: Phosphate absorption in barley roots Roots were cut off from barley plants and were used to investigate 1 g phosphate air was in each in the absorption. bubbled case, air 1 but Table Describe on the the rate the Explain 21.0to effect the 0.1 of the on of of phosphate concentration and solutions was nitrogen phosphate the was the oxygen in was the roots.Youshould In 0.07 99.7 0.15 0.9 99.1 0.27 2.1 97.1 0.32 21.0 79.0 0.33 only use T able 1 ▲ 0.4 [3] oxygen absorption. 99.9 0.3 below21.0 % youranswer. reducing phosphate by 0.1 same varied absorption concentration percentage your 1 h and results. absorption table in oxygen rate reducing phosphate effect of The the placed phosphate percentage shows from were The through. 1 of information 2 through. bubbled measured. Roots 0.3 from answer you Phosphate 0.2 shoulduse as much biological understanding as possible absorption of 1 /µmol g howcells absorb mineral ions. 1 0.1 h [3] 0 An experiment was done to test which method of membrane 0 2 4 6 8 10 3 transport placed in the bubbling DNP was were added. with Discuss DNP the thegraph theroots 11 a phosphateby 4 the roots blocks shows reason, to absorb as phosphate. before, the the with of a production results of the the transport. that can method of be roots 21.0 % ATP DNP concentration / mmol dm were oxygen by Figure 11 Eect of DNP concentration ▲ on phosphate absorption called aerobic cell experiment. whether active Roots substance of or conclusions the absorb concentrations diffusion about to solution Varying Figure Deduce, by phosphate through. respiration. 3 used absorbed drawn membrane the [2] from the transport data in used by phosphate. [2] Active transport of sodium and potassium in axons Structure and function of sodium–potassium pumps for active transpor t. An axon consists inside. in is of part a Axons diameter, function part of called is the a of a neuron tubular can but to be as nerve as long convey body to (nerve membrane narrow as one in as one micrometre from electrical one form nerve sodium and involves then rapid potassium These movements being through ions movements across occur by the sodium and The axon. They occur by between The active because the inside concentration transport, potassium of pumped it in the in. axon Each uses follows three one and time ATP . a repeating sodium two the The ions potassium pump cycle goes consists steps: interior the pump axon pump of carried and of the three attach pump is sodium to their open ions to the enter binding inside the sites. ATP transfers the and out pump; a phosphate this causes group the from pump to itself change concentration outside gradients protein. axon; potassium shape gradients out cycle pump result facilitated to channels. this these of of 2 diffusion that pumped round of steps impulse. impulse membrane. of being 1 A sodium–potassium cycle ions Their rapidly an The and cytoplasm metre. messages another cell) with by are a of built and the interior is then closed. the up sodium– 3 The interior outside ions are of of the the pump axon and opens the to three the sodium released. 39 1 C E L L 4 Two B I O L O G Y potassium enter and ions attach to from their outside binding can then 6 The sites. of interior the axon released; 5 Binding of potassium causes release of change open group; shape to the this again inside causes so of that the it the is pump again the pump the sodium two ions opens to the potassium can then inside ions enter are and bind the to phosphate of and the pump again (stage 1). to only axon. 1 2 3 p p ATP ADP 4 5 6 p p Figure 12 Active transpor t in axons ▲ Facilitated diusion of potassium in axons Structure and function of sodium–potassium pumps for active transpor t and potassium channels for facilitated diusion in axons. A nerve sodium impulse and membrane. diffusion Each as a subunits allows The 40 special with a is 0.3 example narrow ions nm and channels channel potassium pore sodium of wide of axon facilitated be of described in diffusion. four protein them either that direction. narrowest. Potassium but to a too potassium will between its the by facilitated pass at across occur consists pore to movements ions movements Potassium potassium rapid potassium These through channels. here involves then when shell large through, ion and ions they of to water pass the the ar e thr o ug h bonds the and a ion ion has form seri e s part passed of of the tha t po re . the wa te r a mino thi s 0. 3 To them p a ss p ot a ss i um mo l ec ul e s acid s After pa r t nm, bo n de d m a ke s te mpor a ri ly p or e . thr o ug h th a n be come the b e twe en surro und i ng and s mal le r the y mo l e cule s bond s broken narrowest s l i g htly dis s o l v e in the of a re b e t wee n the pota s si u m t he por e , 1 . 4 it can again become a s s ocia te d wi th a sh e l l of positive M e M b r A n e charges channels watermolecules. impulse Other positively charged ions that we might pass through the pore are either too there large to This or are acids in too small the narrowest to form bonds part of with the cannot shed explains their the shell specicity of of water the Voltages imbalance the channels across of in axons membranes positive membrane. If an and are are has a positive nerve charges causes potassium ions to channels diffuse to open, through. to the be channel due to rapidly an extra closes again. globular This protein molecules. voltage due negative axon more or ball, attached by a exible chain of pump. amino Potassium potassium during so subunit This inside, stage the pore, seems they than one relatively potassium However, amino are At t allowing through outside closed. expect inside. to are t r A n s P o r t to gated. an pore charges relatively pore, across more acids. which The it opening. ball does The channel state. is t within ball potassium This can in the open milliseconds remains returns shown inside to gure in its of place the until original the closed 13. net negative charge 1 channel closed + + + 2 + + + + channel briey open - + - - - - - - - outside + + + + + + + + + + + + + ++ - - - + - - - - - inside of axon - chain net negative charge inside + K ball net positive ions the axon and net positive charge charge outside 3 channel closed by ‘ball and chain’ + + + + + + + ▲ + hydrophobic core hydrophilic outer of the membrane parts of the membrane Figure 13 eimai maiy Estimation of osmolarity in tissues by bathing samples in hypotonic and hyper tonic solutions. Osmosis water. is Glucose, ions due These are to sodium all solutes solutes are ions, that form potassium osmotically bonds osmotically active ions and with and chloride solutions units is about are often used in osmosis experiments. many different osmotically active The 300 isotonic a tissue. osmolarity concentration of of a solution osmotically is the osmolarity. total active are osmoles osmolarity or of milliosmoles human tissue mOsm. solution A has hypertonic the same solution osmolarity has a higher solutes. osmolarity The it normal Cells as contain measuring of An them for (mOsm). active. solutes. The in and If hypertonic a hypotonic samples and of a solution tissue hypotonic are has a lower bathed solutions, and 41 1 C E L L B I O L O G Y measurements water enters deduce are or what taken leaves to the nd out tissue, concentration of it whether is isotonic possible solution to would be tissue. the results 4 daa-a qi: Osmosis in plant tissues If samples of plant tissue are bathed in salt and the therefore The from Explain nd data-based the an out the experiment reasons mass change rather mass change in for of using than grams osmolarity questions in the below this type. percentage actual this type of or experiment. sugar or solutions decrease in for a mass short is time, due any almost of give [2] increase entirely to 40 water entering or leaving the cells by osmosis. + + + + + Figure14 shows the percentage mass change + + + 30 + PINE of four tissues, when they were bathed in salt KERNEL solutions of different 20 concentrations. Sodium chloride 1 a) State whether water moved into or out 10 concentration 3 of the tissues at 0.0 mol dm sodium % 3 / mol dm 0 chloride solution. 0.1 Mass [1] 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 change BUTTERNUT 10 b) State whether water moved into or out SQUASH 3 of the tissues at 1.0 mol dm sodium 20 chloride solution. SWEET [2] POTATO 30 2 Deduce which concentration how you tissue in its reached had the lowest cytoplasm. your solute Include conclusion 40 in CACTUS 50 your 3 answer. Suggest [2] reasons concentration The be experiment repeated plant tissue from homogeneous without in using for the between the tubers, around tough the in solute tissues. data-based potato and differences the question or world enough [3] any be Figure 14 Mass changes in plant tissues bathed in salt solutions 5 can not is the the so mass, handled tissue to get long such a in that as the solutions signicant another mass factor for affects with a following Dilute a solution on 2 the Obtain are partner or group how you could do You in might your gives things: 1 mol to dm obtain choose to be experimental one idea turgidity of could used. for plant more inventive approach. measuring tissue, but Figure changes other sodium the chloride concentrations be samples similar of a enough plant to tissue each shown that other to ° give angle gives results. measure plant tissue of turgidity Ensure dry and that when end the surface nding of the their of the mass, tissue both samples at the is start experiment. weight 4 Ensure apart from bathing 42 that all salt variables are kept concentration solution. of constant, the ▲ Figure 15 Method of assessing turgidity of plant tissue 15 to the methods graph. comparable 3 but the decomposition! 3 1 long change, disintegrating. 6 Discuss Leave enough other that to ▲ 1 . 4 M e M b r A n e t r A n s P o r t expima ig Experimental design: accurate quantitative measurements in osmosis experiments are essential. An ideal experiment interpretation. doubts and can or or be This ● uncertainties. uncertainties, a can be if than used have drawn only from experiments design should Repeats needed, are best of an one the there then provides reasonable results are experiment is without some rigorous, strong any doubts these evidence for All might that with and all be taken only as quantitative accurate meters other affect the experiment: as these possible, other give stronger using of under remaining the most apparatus. accurately samples results factors factors as or however biological the an results. because are factors be designing quality measurements controlled, when possible and vary most the that be experiment appropriate to can descriptive Measurements ● In if The should evidence ● results hypothesis. checklist Results ● but minimized. against gives Conclusions are the quantitative variable. experiment investigation must being be allowed ▲ constant. Figure 16 Replicates are needed for each treatment in a rigorous experiment After doing checklist. that If you can The would tissue an were made done bathed evaluate solution, evaluation have have are experiment and its an in probably osmosis If lead can to experiment of you were in which for similar to using to the this design rigorous. solute repeats very evaluated improvements varying did be more experiment solutions results design might the design. the the samples of plant concentration, each each you concentration other, your of results reliable. Designing osmosis experiments Rigorous experimental design is needed to produce reliable results: how can accurate quantitative measurements be obtained in osmosis experiments? The osmolarity Figure 17 sodium of shows chloride observe the 1 Peel off 2 Cut 3 Mount slide, tissues red solution. a The the with of sample a of epidermis sample cover it, in can onion consequences some out plant some a slip. be cells investigated that following osmosis from about drop the 5 of × in had method red scale can onion of a in been red many placed be ways. in used a to cells. onion bulb. 5mm. distilled water on a microscope ▲ Figure 1 7 Micrograph of red onion cells placed in salt solution 43 1 C E L L B I O L O G Y 4 Observe inside 5 using the Mount cell a microscope. wall, another with sample the of The cytoplasm plasma should membrane epidermis in ll the pushed sodium space up chloride against it. solutions 3 with by concentration osmosis membrane Plant are This cells with method can of be used be to can try 0.5mol volume away their onion cytoplasm can the pulls plasmolysed osmolarity the and of and to cell process help or be seen. that 3%. pulled is The water leaves reduced, as shown away the in from the cells plasma Figure17. their cell walls plasmolysis. cells the If is wall, design other ensure or cytoplasm the membranes cells easily of from the used to dm an in experiment which checklist design is the in to area the nd out occupied previous the by section rigorous. Preventing osmosis in excised tissues and organs Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis. Animal Figure cells 18 can be shows damaged blood cells by that osmosis. bathed have (b) been in solutions higher with osmolarity (a) and the (c) same lower osmolarity, osmolarity. a) ▲ In a Figure 18 Blood cells bathed in solutions of dierent solute concentration solution solution), their with water cytoplasm higher leaves osmolarity the shrinks in cells by (a hypertonic osmosis volume. The so used, which osmolarity plasma membrane does not change, so indentations, which are sometimes (hypotonic), and swell ruptured Both In a the up. solution cells They plasma hypertonic take may with in water eventually membranes and lower by hypotonic osmolarity saline red human osmolarity enter and remain any an the leave healthy. human isotonic Usually 44 as an cells, but cells the It tissues solution at the therefore and solution isotonic a (isotonic), cells is in organs during sodium same be medical chloride an used in many medical It can be: to intravenous a patient’s blood system drip. ● used to rinse ● used to keep areas skin grafts. wounds and skin abrasions. of damaged skin moistened therefore to same ● used ● frozen as the basis for eye drops. molecules rate important to has ghosts. with water is introduced an prior damage It (milliOsmoles). leaving cell solutions safely via osmosis burst, called saline. mOsm called ● crenellations. normal 300 it procedures. develops called about area Normal of is of so they for bathed hearts, in procedures. solution is have the to the consistency kidneys to be and other transported transplant to operation of slush donor the is to for packing organs hospital be that where done. 1 . 5 ▲ t H e o r I G I n o f c e l l s Figure 19 Donor liver packed in an isotonic medium, surrounded by isotonic slush. There is a worldwide shor tage of donor organs – in most countries it is possible to register as a possible future donor 1.5 th igi Understanding Applications ➔ Cells can only be formed by division of Evidence from Pasteur ’s experiments that ➔ pre-existing cells. spontaneous generation of cells and organisms ➔ The rst cells must have arisen from does not now occur on Ear th. non-living material. ➔ The origin of eukaryotic cells can be explained Nature of science by the endosymbiotic theory. Testing the general principles that underlie the ➔ natural world: the principle that cells only come from pre-existing cells needs to be veried. Cell division and the origin of cells Cells can only be formed by division of pre-existing cells. Since the produced is very The 1880s by there division strong and implications trillions of cells is of in has of a been discussed the our a theory pre-existing in the hypothesis bodies, each in cell. biology The nature are of that science remarkable. one was cells evidence panel If formed for we can this only below. consider when be hypothesis a the previously 45 1 C E L L B I O L O G Y existing cell divided in two. Before that all of the genetic material in toK the nucleus nucleus was with a copied full so that both complement of cells formed genes. We by can cell trace division the had origin of a cells Wha w gai, a wha w , in the body back to the rst cell – the zygote that was the start of our wh w am mhig? lives, produced by the fusion of a sperm and an egg. When Dr Craig Venter ’s team Sperm and egg cells were produced by cell division in our parents. We announced that they had succeeded can trace the origins of all cells in our parents’ bodies back to the zygote in transplanting the synthetic genome from which they developed, and then continue this process over the from one bacterium into another generations of our human ancestors. If we accept that humans evolved bacterium in the journal Science some from pre-existing ancestral species, we can trace the origins of cells back ethicists responded by questioning through hundreds of millions of years to the earliest cells on Earth. the language of calling it the creation There is therefore a continuity of life from its origins on Earth to the cells of a “synthetic cell”: in our bodies In 2010 today. The science is ying 30,000 feet over the public’s understanding ... Scientists can be their own worst enemy by using words like “clone” or “synthetic life”. cell, of but a there this were cell bacterium few deliberate of different reports was not (Mycoplasma changes. that biologists entirely new. mycoides) This DNA was was had The created base the sequence synthesized transferred to rst of articial the articially, DNA with pre-existing a cells G Mg, Amia a type of bacterium ( Mycoplasma capricolum), which was Ja bihi effectively Frankly, he’s describing it in a way that’s drumming up controversy more an converted extreme new cells form of remains into Mycoplasma genetic an mycoides. modication insuperable and challenge This the at process creation the was of therefore entirely moment. than characterising it accurately. His claim that we’ve got the rst self- replicating life form whose parent is a Aiviy computer, that’s just silly. th siphim It misuses the word “parent”. The The Greek coin in gure 2 depicts a Silphium plant, which grew in a small par t advance here needs to be described of what is now Libya and was highly prized for its medicinal uses, especially in sane and accurate ways. What as a bir th control agent. It seems to have been so widely collected that within a he's managed to do is synthesise a few hundred years of the ancient Greeks colonizing Nor th Africa it had become genome much larger than any genome extinct. Rather than arising again spontaneously, Silphium has remained extinct that’s been synthesised from scratch and we cannot now test its contraceptive proper ties scientically. How can we before. prevent the loss of other plants that could be of use to us? Ggy Kaik , Haig Ii rah sha ▲ ▲ Figure 1 Synthetic Mycoplasma bacteria 46 Figure 2 An ancient Greek coin, showing Silphium 1 . 5 t H e o r I G I n o f c e l l s Spontaneous generation and the origin of cells Verifying the general principles that underlie the natural world: the principle that cells only come from pre-existing cells needs to be veried. Spontaneous organisms philosopher that a plant where this it as an the dew faeces Swiss not of had In and the or 16th astrologer living was reported up and from soil described formed the hair, century the Paracelsus Some biologists spontaneous by access esh or German- of spontaneous and eels from water, air or of is easy to see generation how could ideas have of decaying had been when the and cells discovered biologists come from of sexual the 17th reproduction century was onwards not experiments arise from showed meat if to test non-living that ies maggots were the only allowed that come it. Lazzaro Spallanzani A cell No could is a highly others then open containers to left sealed the air. open four of Organisms but not in tissue rotting in and grew the se c t i on of from there the are experiments other reasons accepting that cells only cells: complex has structure been and suggested no for from simpler subunits. of is known cells without in a cell of increases population, division in the organism or occurring. contact soup them cells example Viruses left in are produced from simpler subunits eight but containers, evidence others, mechanism number Redi in into boiled Pa ste u r ’s ne xt the ● with o ccur. the carried life Francesco developed to in understood. biologists theory matter. s pont a n e ou s no w d e s cr i b e d e xp er i me n t s e s t a bli sh e d and and ● out tha t not universally producing From whi ch d o ub t does pre-existing natural nature are d es i gned a s k s , t h er e re s pon d ed matter. spontaneous persisted not from Pasteur ● microorganisms life Pa s te ur if mice, for It ca r e ful l y reasonabl e of L oui s th a t occur quoted generation of frogs a i r. convinced coul d sub-topic. Apart observations out experiments this the swan-necked generation from rema i ned gene r a ti o n to carrying with beyond generation. being from of Greek sprung present insects leaves The Theophrastus spontaneous about on formation matter. Silphium animals. botanist the previously example falling of botanist called wrote is non-living and was Aristotle generation from they do not consist of cells, and they can the only be produced they have inside the host cells that the infected. others. Spontaneous generation and Pasteur ’s experiments Evidence from Pasteur ’s experiments that spontaneous generation of cells and organisms does not now occur on Ear th. Louis Pasteur made a water containing if broth was kept unchanged, and no this nutrient yeast and in a broth sugar. sealed by He boiling showed ask, it that then a melted variety or other He then passed air then though a pad wool in a tube, to lter out from the air, including bacteria and of placed in fungi. If broth in the pad of cotton wool sealed ask, to kill were large number of as broth and mould grew within 36 its any most involved samples famous the of of Pasteur’s use of swan-necked in asks with it into in some of the present Fungi and but other left others organisms the unboiled even after asks long but periods not of in time. broth it in had the asks been was in suggested contact was with needed air, for in generation, yet no spontaneous surface. some experiments broth broth organisms in ones, generation The bent 3. hours, microorganisms over the controls. spontaneous the boiled appeared boiled which there and gure was The a necks in the the spores the microscopic soon particles of shown of unboiled cotton glass organisms asks appeared. the shapes, remained Pasteur fungi of asks. long He necks placed and of occurred. the Organisms asks were decomposed the to Pasteur leave soon a snapped shorter apparent in the necks vertical these of neck. asks and broth. 47 1 C E L L Pasteur B I O L O G Y published subsequently including urine concluded his results repeated that and the them milk, swan in 1860 with with necks and other the from liquids same and results. prevented He the that air getting no experiments organisms time of into organisms convinced publication the broth appeared and or other liquids spontaneously. most biologists, since then. both at His the Origin of the rst cells The rst cells must have arisen from non-living material. If we trace eventually living else all for have It the is a over to long they been there periods of is cells it how argued time. could that this cells as must the rst somewhere hardest material. question complex as the of cell material? structures can may from non-living the structure complex we were happen have cannot in a evolved arise series over of by stages hundreds Figure 3 Drawings of Pasteur ’s of swan-necked asks millions stages of could years. have There Miller through a ammonia. The representative Earth. and mixture carbon of of They the Urey was discharges compounds passed that needed thought were of to life simulate and were A possible other produced. site compounds cracks early to acids and be the used amino for steam hydrogen atmosphere found for in gushing the hot chemicals represent source of is for Earth’s water such as readily energy compounds the around into (NH iron for the ) electrode 4 (H ) 2 condenser cold water in cooled water containing organic compounds ▲ sample taken for chemical analysis Figure 4 Miller and Urey’s apparatus Figure 5 Deep sea vents the of the rst vents. main carbon These characterized reduced of are by inorganic These supplies assembly polymers. ) of sulphide. accessible hydrogen ▲ some deep-sea carrying 3 methane (CH origin surface, ammonia water vapour how polymers methane, mixture Electrical lightning. Harold hypotheses 2. Assembly of carbon compounds into sugars and amino acids Stanley are occurred. 1. Production of carbon compounds such as 48 from perhaps a years, These Earth non-living that Living on arisen gives of existed. arrived from evidence billions have have but means over to cells must answer: natural of cells Unless conclusion, sometimes but earliest Earth. biologists by ancestry the universe, evolution, ▲ on logical arisen has the reach things in This back of chemicals energy, these a carbon 1 . 5 3. Formation of membranes If phospholipids compounds were compounds, into plasma the would the form membrane different of a to carbon shown cell. This chemistry Living assembled that resembling small o f c e l l s inheritance carbon naturally have vesicles internal surroundings rst have o r I G I n 4. Development of a mechanism for amphipathic Experiments readily allowed other among they bilayers. bilayers or t H e these the and DNA and enzymes would from organisms DNA have that be of use be able are made, develop. evolution It can DNA act but as a ar e may when store to as pass need e d . genes conundrum cur r e ntly enzy me s is ne e d ed . ha v e R NA both g ene s be en wa s ge n es on Ho we ve r, informa ti o n it ha ve ca tal ys ts . an the in to for The To sol ut ion ea r l ie r sa m e s e l f- r ep li ca ting of o f fsp ri n g, e n z ym e s g e ne tic the ma de r ep li c a t e to to t hi s p ha s e in m at e r ia l . wa y an d as can i tse l f catalyst. Figure 6 Liposomes ▲ Endosymbiosis and eukaryotic cells The origin of eukaryotic cells can be explained by the endosymbiotic theory. The theory eukaryotic of endosymbiosis cells. It states prokaryotic organisms respiration. Larger helps that that to explain mitochondria had developed prokaryotes that could the evolution were the once process only of respire of free-living aerobic cell anaerobically Aiviy took them smaller in by endocytosis. prokaryotes cytoplasm. As long they as Instead allowed the smaller of them killing to and digesting continue prokaryotes grew to live and the in Wh i i gi? their divided as fast Erasmus Darwin was as the larger ones, they could persist indenitely inside the larger cells. Charles Darwin’s According to the theory of endosymbiosis they have persisted over grandfather. In a poem hundreds of millions of years of evolution to become the mitochondria entitled The Temple of inside eukaryotic cells today. Nature, published in 1803, The larger in symbiotic a known as supplied carried cell. prokaryotes a relationship mutualistic with out and food aerobic Natural by in smaller which the larger therefore The one. to aerobically both relationship. respiration selection endosymbiotic the The supply of them smaller favoured cells ones beneted. cell smaller energy respiring would cell that This had is have would efciently were been have to the he believed life to have originated: Organic Life began larger developed he tells us how and where this relationship. beneath the waves ... Hence without parent by spontaneous bir th Rise the rst specks of The endosymbiotic theory also explains the origin of chloroplasts. animated ear th If a a prokaryote larger have cell that and developed Again, both of had was into the developed allowed the to photosynthesis survive, chloroplasts organisms in the of grow and was divide, photosynthetic endosymbiotic taken it in by could eukaryotes. relationship would Has Erasmus Darwin’s hypothesis that life began in the sea been falsied? havebeneted. 49 1 C E L L B I O L O G Y original ancestral prokaryote Aiviy evolution of the nucleus Bangiomorpha a h igi x . evolution of The rst known eukaryote evolution of photosynthesis evolution of and rst known linear chromosomes, multicellular organism is mitosis and meiosis Bangiomorpha pubescens. Fossils of this red alga were discovered in 1,200 million year old rocks from nor thern Canada. It is the rst organism known mitochondria to produce two dierent endocytosis types of gamete –a larger to produce sessile female gamete chloroplasts and a smaller motile male gamete. Bangiomorpha is therefore the rst organism known to reproduce sexually. It seems unlikely evolution of evolution of plant cells animal cells that eukaryote cell structure, multicellularity and sexual reproduction evolved simultaneously. What is the most likely sequence for these landmarks in evolution? plant cell animal cell (eukaryotic) ▲ (eukaryotic) Figure 7 Endosymbiosis Although and no independent ● longer mitochondria They capable both of have living independently, features that suggest chloroplasts they evolved from prokaryotes: have their own genes, own 70S on a circular DNA molecule like that of prokaryotes. ● They some ● They their ● They and 50 have their ribosomes of a size and shape typical of prokaryotes. transcribe own can their DNA and use the mRNA to synthesize some of proteins. only be chloroplasts. produced by division of pre-existing mitochondria 1 . 6 c e l l d I V I s I o n 1.6 c i vii Understanding Applications ➔ Mitosis is division of the nucleus into two The correlation between smoking and incidence ➔ genetically identical daughter nuclei. of cancers. ➔ Chromosomes condense by supercoiling during mitosis. ➔ Skills Cytokinesis occurs after mitosis and is dierent in plant and animal cells. ➔ Identication of phases of mitosis in cells ➔ viewed with a microscope. Interphase is a very active phase of the cell cycle with many processes occurring in the Determination of a mitotic index from a ➔ nucleus and cytoplasm. ➔ micrograph. Cyclins are involved in the control of the cell cycle. ➔ Nature of science Mutagens, oncogenes and metastasis are involved in the development of primary and Serendipity and scientic discoveries: the ➔ secondary tumours. discovery of cyclins was accidental. The role of mitosis Mitosis is division of the nucleus into two genetically identical daughter nuclei. The nucleus identical divide two genetically eukaryotic by a can This DNA chromatids Mitosis is required repair and Although events is to mitosis four The events that this sub-topic. divide to mitosis. each with form Mitosis one of two genetically allows the the nuclei cell and to therefore other. all of the during each can called converted DNA a the cells nucleus the single chromatids. daughter during in interphase, from called whenever eukaryotes: asexual into the molecules, passes cell cells, occur, involved in to happens chromosome identical process daughter identical mitosis replicated. Each a nuclei into Before of period DNA must be before molecule During mitosis, mitosis. into one two of these nucleus. with genetically embryonic identical development, nuclei growth, are tissue reproduction. is a continuous phases: occur in process, prophase, these cytologists metaphase, phases are have anaphase described in a divided and later the telophase. section of ▲ Figure 1 Hydra viridissima with a small new polyp attached, produced by asexual reproduction involving mitosis 51 1 C E L L B I O L O G Y Interphase Aiviy Interphase is a very active phase of the cell cycle with There is a limit to how many times many processes occurring in the nucleus and cytoplasm. most cells in an organism can undergo mitosis. Cells taken from a human The cell cycle is the sequence and the next. It has two of events between one cell division embryo will only divide between main phases: interphase and cell division. 40 and 60 times, but given that Interphase is a very active phase in the life of a cell when many the number of cells doubles with metabolic reactions o c c u r. Some of these, such as the reactions of each division, it is easily enough to cell respiration, also occur during cell division, but DNA replication produce an adult human body. There in the nucleus and protein synthesis in the cytoplasm only happen are exceptions where much greater during interphase. numbers of divisions can occur, such During interphase the numbers of mitochondria in the cytoplasm increase. as the germinal epithelium in the This is due to the growth and division of mitochondria. In plant cells and testes. This is a layer of cells that algae the numbers of chloroplasts increase in the same way. They also divides to provide cells used in sperm synthesize cellulose and use vesicles three phases, to add it to their cell walls. production. Discuss how many times the cells in this layer might need to Interphase consists of the G the genetic phase, S phase and G 1 divide during a man's life. In the that do S phase after not the mitosis progress cell both replicates the beyond new G , all cells have because they phase. 2 a material complete are never in set its of going nucleus, genes. to divide so Some so do 1 not need to prepare for mitosis. They enter a phase called G which may 0 be temporary or permanent. Supercoiling of chromosomes G2 Mitosis Chromosomes condense by supercoiling during mitosis. y C to in k e is s mitosis, the two chromatids that make up each chromosome must N During R S P H Each of the be separated and moved to opposite poles of the cell. The DNA molecules A SE G1 chromosomes in these chromosomes are immensely long. Human nuclei are on average Cellular contents, is duplicated apart from the less than 5 µm in diameter but DNA molecules in them are more than chromosomes are duplicated. 50,000 much µm long. shorter It is therefore structures. chromosomes and it This occurs essential process during is the to package known rst as stage chromosomes condensation of into of mitosis. G0 Condensation make the Proteins ▲ by chromosome called chromosomes Figure 2 The cell cycle occurs shorter histones help means that with repeatedly and are wider. associated supercoiling and coiling This the DNA process with DNA enzymes is in are molecule called to supercoiling. eukaryote also involved. Phases of mitosis Identication of phases of mitosis in cells viewed with a microscope. There tips are of large growing chemically can be make mitosis 52 allow squashed microscope to to numbers roots. slide. the can to If the a be tips to are be single that chromosomes then dividing cells form Stains of root bind in separated, to of it a they cells DNA and using To the treated layer visible observed cells are stages on a used of microscope. be is in able to identify necessary them. section cells After you using assign to a them the studying should be one of the able microscope to four understand or the stages what is of mitosis, happening information to observe in a in this dividing micrograph phases. and 1 . 6 c e l l d I V I s I o n Prophase The chromosomes become shor ter and fatter by coiling. To become shor t enough they have to coil repeatedly. This is called supercoiling. The nucleolus breaks down. Microtubules grow from structures called microtubule organizing centres (MTOC) to form ▲ Interphase – chromosomes are ▲ a spindle-shaped array that links visible inside the nuclear membrane Prophase – nucleoli visible in the nucleus but no the poles of the cell. At the end of individual chromosomes prophase the nuclear membrane centromere MTOC breaks down microtubules nuclear envelope disintegrates chromosome spindle consisting of two microtubules sister chromatids ▲ Early prophase ▲ Late prophase Metaphase Microtubules continue to grow and attach to the centromeres Metaphase on each chromosome. The two plate equator attachment points on opposite sides of each centromere allow the chromatids of a chromosome to mitotic spindle attach to microtubules from dierent poles. The microtubules are all put under tension to test whether the ▲ Metaphase – chromosomes ▲ Metaphase attachment is correct. This happens aligned on the equator and not by shortening of the microtubules at inside a nuclear membrane the centromere. If the attachment is correct, the chromosomes remain on the equator of the cell. Anaphase At the star t of anaphase, each centromere divides, allowing the pairs of sister chromatids to separate. The spindle microtubules pull them rapidly towards the poles of the cell. Mitosis produces two genetically identical nuclei Daughter because sister chromatids are chromosomes pulled to opposite poles. This separate is ensured by the way that the ▲ Anaphase – two groups of V-shaped ▲ spindle microtubules were Anaphase chromatids pointing to the two poles attached in metaphase. 53 1 C E L L B I O L O G Y Telophase The chromatids have reached the poles and are now called chromosomes. At each pole the chromosomes are pulled into a tight group near the MTOC and a nuclear membrane reforms around them. The chromosomes uncoil and a nucleolus is formed. ▲ Telophase – tight groups of ▲ Interphase – nucleoli visible By this stage of mitosis the cell is chromosomes at each pole, new inside the nuclear membranes cell wall forming at the equator but not individual chromosomes usually already dividing and the two daughter cells enter interphase again. Cleavage furrow Nuclear envelope forming ▲ Telophase daa-a qi: Centromeres and telomeres Figure cells 3 and centromeres ends have 1 of the been have the cell has State b) Explain In with stage a) c) been In of gure stained a with there are green mitosis on 3, the preceeding DNA has a uorescent red structures uorescent that the been pages stained called dye. show blue. At The the telomeres. These dye. cell was in, giving reasons answer. an how having ▲ micrographs chromosomes your The other mitosis. stained Deduce for 2 the undergoing the even number many the an [3] chromosomes. chromosomes reason even of for body number micrograph of a of cell there cells in are in plants this and cell. [1] animals chromosomes. in interphase, [2] the centromeres Figure 3 Cell in mitosis d) are on the other An one is produce cycle a 54 in the only or nucleus repeating in the When cells, the of the for germ of the is telomeres the shorter. telomeres, sequences cells that telomere Predict shortening on [2] replicated the are this. lengthens base DNA end becomes animal and reasons telomerase active gametes. body the Suggest short telomere plant of called many enzyme so side. enzyme adding side of of are DNA. used during the to the cannot by This be cell replicated, consequences telomeres. for [2] 1 . 6 c e l l d I V I s I o n The mitotic index Determination of a mitotic index from a micrograph. The mitotic in tissue a using this index and is the the total ratio between number of the number observed cells. of cells in mitosis It can be calculated that has developed equation: number of cells in mitosis ___ Mitotic index = total Figure from be 4 a is a micrograph Leydig calculated and To also nd the the in the the total number mitotic proliferating ● cell if a of testis. cells the of these prepared andexamine number cells The in of from number index rapidly, Obtain of cells a tumour mitotic of cells the for this tumour micrograph is can counted meiosis. the part of a instructions slide index in of an meristematic root can onion region, tip be or i.e. where garlic a cells are used: root region of tip. Find rapid celldivision. Figure 4 Cells undergoing mitosis in a Leydig ● ● Create a region as Use tally this chart. being data Classify either to in each of interphase calculate the about or mitotic in a hundred any of the cells in stages this of cell tumour mitosis. index. Cytokinesis Cytokinesis occurs after mitosis and is dierent in plant and animal cells. Cells can present usually divide in a In different animal equator ring at the of these the The centre, cells of the of next cell it This of by builds in are and forms own is to for the middle cells adjacent wall to to the and to the that are the similar they of fuse more to cells. to form vesicles membrane across membranes plasma using furrow daughter of the the membranes at cytoplasm. substances between will link cellulose middle the of existing other bring the adjacent happens membrane cleavage two plasma of lamella and fusion exocytosis then it around plasma the layers the division by and are It accomplished where the two into pectins deposited into equator form the When apart is the myosin With develop inwards This inside and the connected daughter cell to nuclei cytokinesis. completed pulled muscle. equator. completing exocytosis its moved the actin in identical called been furrow. pinched merge plants the are is which and cell, vesicles Both deposit cells the membranes. walls. are structures stage in cell is cleavage is cells. immediately proteins across actually animal contraction equator, daughter sides a genetically division membrane form the two cell has and protein vesicles structures brought plasma The of mitosis plant to cause tubular whole two that the plant tubular the cell equator. reaches In the in when process before contractile proteins mitosis The way cells of after cell. begins in a a to lamella. equator. to be the two the new the As a new cell equator result, and each ▲ Figure 5 Cytokinesis in (a) fer tilized sea urchin egg (b) cell from shoot tip of Coleus plant 55 1 C E L L B I O L O G Y Cyclins and the control of the cell cycle Cyclins are involved in the control of the cell cycle. Each of the phases group of at correct the the cycle Cyclins then cell. bind The There are four cycle. that and the of called involves used cell to only many ensure moves important that on tasks of cyclin-dependent phosphate phosphate types levels specic of cyclin these tasks to the tasks. are A performed next cell but one in the not the of stage at not cell fall. of The cycle other of to and to the graph the cycle. gure6 cyclins next ensure in become cell in these the kinases proteins proteins Unless progress These other phases cells. and to other the human rise does control needed, to kinases. groups triggers cyclins the therefore are is attach concentration, cells cycle appropriate. out Cyclins new cell cyclins enzymes main the threshold when is active carry how the and attachment and shows cell to it of called time when become active a proteins stage that cells reach of the divide times. noitartnecnoc G phase S phase G 1 phase mitosis 2 Cyclin D triggers cells to move from G to G 0 and from G 1 into S phase. 1 Cyclin E prepares the cell for DNA replication in S phase. Cyclin A activates DNA replication inside the nucleus in S phase. Cyclin B promotes the assembly of the mitotic spindle and other tasks in the cytoplasm to prepare for mitosis. ▲ Figure 6 Discovery of cyclins Serendipity and scientic discoveries: the discovery of cyclins was accidental. During in sea that research urchin increased decreased which in soon over after experiments repeated that 56 to a period was being with Hunt of The the of ten named 30 was minutes being and Further went through concentration the cell minutes the then proteins down. in synthesis protein fertilization other protein phases a protein about broken about protein after unlike decreases the occurred mitosis. that and of discovered increase. showed coincided of control Hunt concentration increases breakdown start in the Tim concentration, continued synthesized then into eggs, protein cycle. after The the cyclin. Further research conrmed stage of Prize in be In – the that cell for the what cyclins cycle. downloaded it he how discovery is in an the the cell factor was 2001 to His he cycle of discovery is in the honour Nobel internet had and from awarded importance example unexpected key cyclins. because the a cyclins suspected Hunt from mentions times discover and of other had are Tim Physiology discovery several revealed Hunt not work can viewed. serendipity set out serendipity by Nobel his controlled. made early control a Lecture and of an – to This a happy accident. 1 . 6 c e l l d I V I s I o n tm mai a a Aiviy Mutagens, oncogenes and metastasis are involved in the ca ah development of primary and secondary tumours. Tumours can form in any tissue at any Tumours any do part not are of abnormal the invade tumours In other in the are body. body malignant In nearby unlikely tumours and and groups the some tissues to develop are or very that the move much can into cells cases cause cells of cells to become to be at adhere other harm and are stage each of the body. move These of other classied and tumours. any to parts detached secondary likely develop as life in and (bowel), breast and prostate gland are These par ticularly vulnerable. Cancer is a benign. major cause of death in most human elsewhere tumours age, but the skin, lung, large intestine populations so there is a pressing are need to nd methods of prevention life-threatening. and treatment. This involves basic research into the control of the cell Diseases due to malignant tumours are commonly known as cancer cycle. Great progress has been made and have diverse causes. Chemicals and agents that cause cancer are but more is needed. known There as are various mutagens energy are do become normal are not division. cell division are so on. and are malignant including chemical that changes cancer is a some mutagens short-wave cause gene of tumour occur cells from the in cells is is a in tumours. viruses. and also ultraviolet mutations light. and Who should pay for research into All cancer? high This is mutations in in is a primary of genes. genes that Most can are known as oncogenes. control of the them can same cell result for extremely the form called few the body, signicant. to sequence The cell in In cycle a and uncontrolled formation. the happening of base mutating mutations lifetime of the mutate. involved repeatedly cells parts this to they after why numbers group of if are must of divides This other both X-rays therefore during movement in This and vast it carcinogens agents random chance formation formed are cause mutations The there as oncogenes cell cell. such cancer-causing cell Several of carcinomas cancer. Mutations genes types mutagens cause because carcinogenic, radiation because can carcinogens, the then primary tumour to total When two, it small, a four, chance then set up a tumour because tumour tumour. to become but of cell tumour has eight Metastasis secondary been cells is and the tumours body. Smoking and cancer The correlation between smoking and incidence of cancers. A correlation factors. of a The in correlation. correlation, they also factor one decrease is death rate 1 There when increases There table science a is relationship due shows to the are relationship two factor together. the positive a between other results of increases a and two cancer correlation. the other negative variable is an With one a also correlation, example positive increases; when one decreases. correlation cancer. types With between smoking This of between has one of been the cigarette shown largest smoking repeatedly surveys, and in and the surveys. the longest 57 1 C E L L B I O L O G Y continuous day, the death The rate is of rate due bladder, table 1 in of smoking is not than cancer contains have been other that body, and there cancers cervix. of one is the cigarettes They time but also larynx into a the in smokers the and per higher death lung. This with each correlation rate likely a stopped. stomach, death timesmore had and positive smoked show contact esophagus, in also increases comes Although different are at huge cigarettes but more pharynx, several kidney, due to other non-smokers, to die from all non-smokers. in the science that there not in animals in is are humans. is a to cause There of causes a is are correlation between cancer. established. substances. smoke cause between correlation smoking well chemical cigarette ca ah w 1951 positive experiments or smoking distinguish a that links different shown to prove causal chemicals doubt from and show mouth, the cancer. smoked also the to smokers many laboratory of that due signicantly does case shows rate who survey the pancreas Finding this those smoke important cause. and as shows cancers is the data death cancers parts between It of to expected these The the among results cancers one. higher tumours evidence of in that carcinogenic. a However, Cigarette Twenty and smoking smoke these the at lungs least This of forty leaves little cancer. M aiy a p 10 0,0 0 0 m/ya a 20 01 (samp iz: 34,439 ma lig fm -mk iga c mk (iga/ay) 1–14 i biai) All cancers Lung cancer 15–24 ≥25 mk 360 466 588 747 1,061 17 68 131 233 417 9 26 36 47 106 334 372 421 467 538 Cancer of mouth, pharynx, larynx and esophagus All other cancers ▲ 58 T able 1 from British Medical Journal 328(7455) June 24 2004 1 . 6 c e l l d I V I s I o n daa-a qi: The eect of smoking on health One of the smoking doctors. they largest on ever health Information smoked from studies involved was 1951 of the 34,439 collected to 2001 effect male on and how the of death British much cause was during of of the recorded this period. results. deaths per The for each of The table below gures hundred the given thousand are men doctors shows the who number per died some of year. 1–14 15–24 iga iga p ay p ay 107 237 310 471 1,037 1,447 1,671 1,938 >25 iga typ ia n-mk p ay Respiratory (diseases of the lungs and airways) Circulatory (diseases of the hear t and blood vessels) 1 Stomach and duodenal ulcers 8 11 33 34 Cirrhosis of the liver 6 13 22 68 Parkinson’s disease 20 22 6 18 Deduce whether between due 2 to Using threat all the to there smoking types data of in health respiratory or and a positive correlation mortality the table, 4 rate disease. from with is the discuss circulatory is whether greater diseases. the with [4] Discuss whether the data suggests that small number of cigarettes is safe. a the cause data of proves cirrhosis of that the 5 The [3] table cancer. of does The cancer not include survey are cancers linked that deaths showed with you that due seven smoking. would to types Suggest expect smoking smoking a is liver. three 3 whether smoking [2] smoking Discuss to cause. [3] [3] 59 1 C E L L B I O L O G Y Questions 1 Figure 7 represents a cell from a c) multicellular Explain and organism. d) Using the 3 In the chloride the with a reason, whether the cell of health (i) prokaryotic (ii) part (iii) in a of a or root phase of eukaryotic; tip or a mitosis in cells. The magnication of the Calculate the actual tip; a) [1] interphase. drawing size positively The and Calculate how long a 5 State (i) [1] the should be if it was is 2,500 of the cell. placed hour. what μm added in a happen concentrated Include reasons salt for to to the b) if it for shows the area of move Explain by chloride move the cells associated the positively processes charged that: ions out of cells [1] chloride ions out of the cells. [1] membranes water out of the secretory cells. [1] in why cystic the uid brosis is secreted thick and by people viscous. [4] [3] The amount a cells of was DNA present measured taken from two in a in each large different cell number cultures of rat human liver the ions one answer. of 2 of secretory move nucleus Table from was 4 2 moves the cell solution your with are secreted. brosis, secreted lung passively also few the scale [1] would of [2] with Predict in ions been too liquid two × drawing. c) and [3] [2] follow has viscous, names move (iii) bar identify charged cystic inner cells. Water that the example ions channels. secretory (ii) for of problems. (ii) (i) liver chloride liquid area membranes. table, of cells, disease thick the b) in [1] nger or the malfunction the becomes is the genetic channels Identify, and into out a) out, the cells in secretory through In Figure 7 data activities pancreas, pumped ▲ difference mitochondrial the main human and the outer bone marrow (gure 8). cell. a) For each label (I, II and III) in the Sample B 2 Mma mp Aa (μm ) graph, Plasma membrane the 1,780 b) Rough endoplasmic reticulum cells Estimate Mitochondrial outer membrane 7,470 Mitochondrial inner membrane 39,600 Lysosomes 100 Other components 18,500 T able 2 liver b) the total area of membranes in cell. Calculate the [2] the area of percentage in 60 the cell. of the Show plasma total your in; i.e. of G1, approximate the G2 membrane area of working. that would cell or amount human cell S. of cycle [3] DNA at prophase (ii) bone marrow at telophase. (non-dividing cell culture) 2 1 10 DNA/pg per nucleus membranes ▲ Figure 8 15 in the types: marrow as [3] expected bone Sample A 3 be (i) 5 a be phase )sdnasuoht ni( sllec fo rebmuN 280 Calculate the nucleus following )sdnasuoht ni( sllec fo rebmuN Nucleus a) could which 30,400 per ▲ deduce [2] Sample B 3 (rapidly dividing cell culture) I 2 III 1 II 5 10 DNA/pg per nucleus 15 2 M o l e c u l a r B I o l o G Y Intdtin Water is control of the chemical medium. sunlight for life when medium their reactions is life. supply cell by that Photosynthesis to and it for composition the occur uses organisms complex within the chemical respiration needed. Living a of this energy energy releases Compounds web this in hydrogen store control have a the oxygen Many Genetic energy be range information accurately proteins are copied needed by used proteins metabolism diverse needed carbon, and energy. of is of the cell in supply as biological stored and the to act and enzymes and to others functions. DNA translated to and can make the cell. 2.1 M mm undstnding appitins ➔ Molecular biology explains living processes in ➔ Urea as an example of a compound that is terms of the chemical substances involved. produced by living organisms but can also be ➔ Carbon atoms can form four bonds allowing a ar ticially synthesized. diversity of compounds to exist. ➔ Life is based on carbon compounds Skis including carbohydrates, lipids, proteins and nucleic acids. ➔ Drawing molecular diagrams of glucose, ribose, a saturated fatty acid and a generalized amino acid. Metabolism is the web of all the enzyme catalysed reactions in a cell or organism. ➔ ➔ ➔ Identication of biochemicals such as carbohydrate, lipid or protein from Anabolism is the synthesis of complex molecular diagrams. molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions. Nt f sin ➔ Catabolism is the breakdown of complex ➔ Falsication of theories: the ar ticial synthesis molecules into simpler molecules including the of urea helped to falsify vitalism. hydrolysis of macromolecules into monomers. 61 2 M O L E C U L A R B I O L O G Y M bigy Molecular biology explains living processes in terms of the chemical substances involved. The discovery biology raised of that the and biology ▲ is the structure transformed possibility molecules diverse of has and the of how than DNA they 50 years 1953 biological interact are in started understanding explaining interactions more of our with very old, it each still a a other. so revolution living processes complex, is of from The the It structure structures although relatively in organisms. are molecular young science. Figure 1 A molecular biologist at work in the laboratory Many molecules apparently are nucleic They are varied cell, The The and organisms that the make out a organisms most Nucleic to carry the varied acids genes. huge chemical of of and DNA are tasks the one complex Proteins range genes including and comprise reactions between molecular various down that we not and that and and RNA. astonishingly by proteins as molecules within cell the when that reductionist parts. has otherwise of is processes component biology approach properties system its in would though, biologist biochemical into productive emergent whole of the reductionist everything are and living the is the acting at the as heart biology. breaking immensely used controlling in but proteins. relationship approach considering water, and structure molecular important as chemicals including enzymes. of acids the in are simple of have. be insights involves has into biologists biologist parts studied it organism approach us Some molecular as living This given component cannot a argue cannot are without been whole explain combined looking at there the together. Synthsis f Urea as an example of a compound that is produced by living organisms but can also be ar ticially synthesized. Urea is a nitrogen-containing molecular where of it was amino from used the to structure acids can by out also are different the urea the it body, be A blood the as 3). body those a in is is produced of a relatively the of when urine there excreting happens to the the catalysed in the kidneys is liver. an this was excess nitrogen by where simple and enzymes, Urea it is is is then ltered out urine. articially. the with component reactions, This in a means of stream synthesized from It It cycle (gure the of compound 2). discovered. acids. produce passes Urea in amino transported and rst (gure liver and The chemical enzymes are reactions not used involved, but O that is produced ammonia + carbon is identical. dioxide → ammonium carbamate C → H N 2 ▲ 62 urea + water NH 2 Figure 2 Molecular diagram of urea About as a 100 million nitrogen tonnes fertilizer on are produced crops. annually. Most of this is used 2 . 1 M o l e c u l e s t o M e t a b o l i s M CO + NH 2 3 enzyme 1 carbamoyl phosphate ornithine urea enzyme 2 arginase citrulline arginine aspartate fumarate enzyme 3 enzyme 4 argininosuccinate ▲ Figure 3 The cycle of reactions occurring in liver cells that is used to synthesize urea u nd th fsitin f vitism Falsication of theories: the ar ticial synthesis of urea helped to falsify vitalism. Urea was assumed time in it was plants help of discovered to are due to of vital psyche and for the be was is forces. vital of with of different – a organic compounds achievement the vitalism Aristotle principle was that compounds made part and At phenomena which physical 1720s organic only This principle, or the kidneys. that could origin in the believed the chemical word urine principle”. that a in product animals “vital theory the a widely and a the purely be – life from used of vitalism. did not meaning breath, life or cause evidence accept that 1828 the synthesized isocyanate the rst vital articially was a principle Swedish a that I of using make animal, to be Jacob water. it be Wöhler step, in excitedly was because obvious deduction I can man no must without was to the or the that still as without a vital has been a well. to the for theory theory, but pieces biologists and it vitalism several most falsied theory Wöhler’s the abandon requires theory over and now there have that after to his of to sometimes continue for decades. accept that had principle, some make for as by in processes example, same compounds articially. proteins without components of the non-living organic complex synthesis chemistry mad. urea, into nowadays To tropical remarkable urea forces synthesized other one primeval kidneys to governed of It is such using cells. Wöhler Four wrote Berzelius: drives dog. if been and Organic you remain not impossible years are physical hemoglobin, this longer tell chemical it forest things; which me a almost appears full of the dreadful one dare not like a most endless enter, for been there synthesized a biologists jungle An falsify biologists usually organisms ribosomes the Berzelius: I living matter, This synthesized involved this urea to as against Greek silver chloride. speaking, chemical can any wrote Friedrich signicant been Jöns manner my very had Wöhler chemist hold of It chemist compound all It be soul. ammonium organic synthesis. In urea and articially. no German it could evidence helped against controversies in In It immediately. Although word was seems no way out. other 63 2 M O L E C U L A R B I O L O G Y cbn mpnds av Carbon atoms can form four bonds allowing a diversity c mp of compounds to exist. Can you nd an example of a biological molecule Carbon is in which a carbon atom is used make bonded to atoms of three organisms other elements or even four activities other elements? by Titin is a giant protein that Carbon acts as a molecular spring is in muscle. The backbone of electron the titin molecule is a chain bond between Each carbon most other to the only the a almost of their formed limitless of form when most range cells. properties atoms 15th huge abundant of different possibilities The diversity element for of on molecules. the Earth, This chemical carbon but has it can given composition compounds is be living and explained carbon. covalent two bonds adjacent contributed by atoms each so with atoms atom. stable other share a pair Covalent molecules atoms. of on covalent electrons, bonds based A are the carbon bond with one strongest can be type of produced. of 100,000 atoms, linked by atom can form up to four covalent bonds – more than single covalent bonds. Can you nd an example structures. of a molecule in your or body with a chain of over chains atoms 1,000,000,000 atoms? for covalent for can they found bonds example in can length. oxygen, or molecules bonds any atoms (alcohol so example. methane, H The of hydrogen, Carbon atoms, The bond and there the can or with also one wine). carboxyl carbon contain more be carbon be atoms chains with can of have to up other complex make to 20 rings carbon elements such as phosphorus. just to can other acids bonds bond beer or with Fatty nitrogen can in be containing other than The two group four single of element, one other bonds and ethanoic such can one acid as element all be double (the hydrogen as in in ethanol single covalent acid in bond, vinegar). methane cssifying bn mpnds H H H Life is based on carbon compounds including H H ethanol carbohydrates, lipids, proteins and nucleic acids. Living H organisms different use properties four and main so can classes be used of carbon for compound. different They have purposes. H O Carbohydrates C are characterized by their composition. of O carbon, hydrogen and oxygen, with hydrogen two hydrogen atoms to one oxygen, hence the Lipids H H and oxygen are in composed the ratio of H H H They ethanoic acid H H H H H H H H H H H H H H name are molecules a carbo hydrate broad that are class of insoluble in O water, C C C C C C C C C C C C C C C H H H H H H H fatty including acids and steroids, waxes, triglycerides. In OH H H H H common are linolenic acid – an omega-3 fatty acid fats language, if they temperature ▲ are or triglycerides solid oils if at they room are Figure 4 Some common naturally-occurring carbon compounds liquid Proteins amino and carbon, 64 composed in nitrogen, Nucleic of are acids these but acids two are hydrogen, nucleic acid: of one chains of the chains of oxygen, ribonucleic or more contain the twenty subunits acid chains of acids called and (RNA) room elements amino nitrogen at temperature. amino also All of hydrogen, the oxygen containsulphur. nucleotides, phosphorus. and acids. carbon, which There contain are deoxyribonucleic two types acid(DNA). 2 . 1 M o l e c u l e s t o M e t a b o l i s M Dwing ms Drawing molecular diagrams of glucose, ribose, a saturated fatty acid and a generalized amino acid. There is many different be able no to need draw important to memorize molecules diagrams but of the a a structure biologist few of the of atom should with most line is of with covalent double bonds C and bonds with an are two oxygen shown atom with a lines. molecules. atom symbol Single and Some Each represented O. in a the molecule element. is represented For Name of group example a using the carbon gives Full structure chemical atoms together groups and are shown bonds not with the indicated. Table 1 examples. Simplied notation hydroxyl –OH H amine –NH N 2 H O carboxyl –COOH C O H H –CH methyl 3 H ▲ T able 1 Ribose ● OH The formula for ribose is C H 5 ● The molecule is a 5 O 10 5 ve-membered ring with a side O chain. OH 4 C C H ● Four carbon atoms are in the ring and one forms the side chain. H H 3 ● The ● The carbon atoms hydroxyl can be groups numbered (OH) on starting carbon with atoms number 1, 2 and 1 3 on the point and down C C OH OH 2 right. up, Ribose ▲ down 1 H respectively. CH 6 OH 2 Glucose 5 C ● The formula for glucose is C H 6 H 6 4 ● The ● Five ● The molecule is a six-membered ring with a side chain. 1 C OH H atoms are in the ring and one forms the C C side atoms can be numbered starting with number 1 on the The hydroxyl down, down, glucose carbon used atom groups (OH) up down by 1 and plants points to on carbon atoms respectively, make cellulose 1, 2, 3 although the and in a hydroxyl 4 OH right. ▲ ● OH 2 chain. H carbon C HO 3 carbon C O H O 12 Glucose point form of group on upwards. 65 2 M O L E C U L A R B I O L O G Y Saturated fatty acids C ● The ● In ● The carbon saturated At one ● At the All fatty number ● ● atoms end of other other of form acids end carbon are atoms chain the unbranched they carbon the an the carbon atoms bonded is most carbon atom are is chain. to each commonly atom is bonded bonded other to two single between part to by of three a 14 hydrogen hydrogen C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H C H bonds. and carboxyl H 20. group atoms. atoms. Amino acids ● A carbon different ■ an ■ a atom group, carboxyl a ■ the the centre of the molecule is bonded to four things: amine ■ in hence group hydrogen the which term makes amino the acid; molecule an acid; atom; H R group, which is the variable part of amino acids. H O R ▲ R Full molecular diagram of a O H saturated fatty acid CH (CH 3 C N ) 2 C n COOH 2 H O H H OH H simplied molecular diagram full molecular diagram ▲ ▲ Molecular diagrams of an amino acid Simplied molecular diagram of a saturated fatty acid Idntifying ms Identication of biochemicals as carbohydrate, lipid or protein from molecular diagrams. The molecules proteins usually ● are so quite Proteins of carbohydrates, different easy to contain carbohydrates but ● not Many is C in H 6 a O 12 in O contain and Carbohydrates used H, Lipids N contain ratio and of 2:1, sucrose sulphur C, H and O (S) but donot. hydrogen for is C and example (the H sugar oxygen glucose commonly unsaturated O 22 relatively carbohydrates, for fatty 11 less example acid) is oxygen oleic C H 18 testosterone is C H 19 66 is 6 baking) contain steroid it whereas contain lipids 12 ● that them. and lipids and other N. proteins atoms C, lipids each recognize and carbohydrates ● from O 34 O 28 than acid (an and the 2 ▲ 2 Figure 5 A commonly-occurring biological molecule 2 . 1 M o l e c u l e s t o M e t a b o l i s M Mtbism Metabolism is the web of all the enzyme catalysed reactions in a cell or organism. All living organisms reactions. happen in reactions sum of These the Even 1,000 in digest consists another, reactions to reactions Metabolism into cytoplasm used all but in a They of are relatively Encyclopedia out of cells in pathways of small also simple are large but the by which one An chemical Most of extracellular, type of pathways example cells, maps the are intestine. These cycles. on different them such Metabolism as is the the organism. prokaryote and of enzymes. some an Global by small in steps. some available Genes numbers catalysed occur reactions. of are food that series there different complex. carry reactions is molecule are shown metabolism showing internet, all for is mostly in transformed chains gure consists reactions example in of are the of 3. over very Kyoto Genomes. anbism Anabolism is the synthesis of complex molecules from simpler molecules including the formation of macromolecules from monomers by condensation reactions. Metabolism Anabolism is is An easy are hormones energy, way often to is includes Protein ● DNA ● Photosynthesis, ● synthesis two up is body parts, larger by supplied these synthesis into build this promote usually ● and that remember that which Anabolism divided reactions anabolism molecules recalling building. in the that of catabolism. anabolic Anabolic form and from smaller ones. steroids reactions require ATP . processes: using during ribosomes. replication. including production of glucose from carbon dioxide water. Synthesis of complex carbohydrates including starch, cellulose and glycogen. ctbism Catabolism is the breakdown of complex molecules into simpler molecules including the hydrolysis of macromolecules into monomers. Catabolism broken in be some used is down in this the Digestion ● Cell part into cases ● and Digestion of metabolism energy cell. of of smaller ones. is in in the in includes mouth, which in which Catabolic captured Catabolism food respiration dioxide ● the the form these stomach glucose or larger reactions ATP , are energy which and can then processes: and lipids of molecules release are small intestine. oxidized to carbon water. complex carbon compounds in dead organic matter by decomposers. 67 2 M O L E C U L A R B I O L O G Y 2.2 W undstnding appitins ➔ Water molecules are polar and hydrogen bonds Comparison of the thermal proper ties of water ➔ form between them. with those of methane. ➔ Hydrogen bonding and dipolarity explain ➔ Use of water as a coolant in sweat. ➔ Methods of transpor t of glucose, amino acids, the adhesive, cohesive, thermal and solvent proper ties of water. cholesterol, fats, oxygen and sodium chloride ➔ Substances can be hydrophilic or hydrophobic. in blood in relation to their solubility in water. Nt f sin ➔ Use theories to explain natural phenomena: the theory that hydrogen bonds form between water molecules explains water ’s proper ties. H Hydgn bnding in wt H Water molecules are polar and hydrogen bonds form O between them. A water and tends to small pull the positive molecule two involves is is hydrogen unequal because the formed atoms. sharing nucleus of by The of covalent bond electrons the bonds between oxygen – it is atom a is between hydrogen polar more an oxygen and atom oxygen covalent bond. attractive to This electrons + electrons charge δ slightly on each in this hydrogen direction atom than the Because nuclei of hydrogen the of the hydrogen unequal atoms have sharing a partial atoms of (gure electrons positive 1). in water charge and molecules, oxygen has the a partial Corresponding negative charge negative 2δ Because water molecules are bent rather than linear, on oxygen atom the ▲ charge. two hydrogen atoms are on the same side of the molecule and form Figure 1 Water molecules one pole and Positively particles Water is still oxygen charged molecules enough is rather a ions) only to bond. opposite each partial signicant “hydrogen a the (positive attract have have than forms particles (negative molecules force the bond”. A ions) other and Strictly hydrogen negatively and charges, effects. pole. so The form the is the charged ionic attraction attraction speaking bond an it is is less between an force bond. but it water intermolecular that forms when water molecule a hydrogen atom of atom another in one polar polar molecule covalent is attracted to a slightly negative molecule. hydrogen bond Although ▲ a hydrogen bond is a weak intermolecular force, water Figure 2 The dotted line molecules are small, so there are many of them per unit volume of water indicates the presence of an intermolecular force between the molecules. This is called a hydrogen bond 68 and large water its numbers unique importance to of hydrogen properties living things. and bonds these (gure 2). properties Collectively are, in turn, they of give immense 2 . 2 W a t e r Hydgn bnds nd th pptis f wt Use theories to explain natural phenomena: the theory that hydrogen bonds form between water molecules explains water ’s proper ties. There is bonds, strong but between without it experimental remains water doubt that However, way explaining of the properties that of make they the water. water exist as properties is these useful to for they are are of a not water. distinctive the been that directly is useful proven science correct ifit solvent seem unwise natural predict They and might of prove very thermal living It hydrogen form cannot they bonds adhesive, It so that Scientists hydrogen cohesive, evidence theory molecules. visible. explain a if world to exist. works there behaviour, helps to – is to on base However we can if it understanding has for not natural this that is assume evidence explain our something it, that if been has the it not way a theory helps falsied to and phenomena. properties organisms. Pptis f wt Hydrogen bonding and dipolarity explain the cohesive, adhesive, thermal and solvent proper ties of water. Cohesive proper ties Cohesion type, for Water each This to molecules other, due property through the refers instance are to is xylem water the for vessels bonding top tallest at are this trees – they low not over of two cohere, bonding, water molecules pressure. happens a which described transport separated rarely – together of the same molecules. cohesive hydrogen molecules the water useful hydrogen of binding two in The by the plants. method the and hundred in means can can stick previous Water suction water they is section. sucked only forces. be to work Due pulled if to up to the metres. Adhesive proper ties Hydrogen causing useful If water in water to leaves, of nearest carbon can air form stick to where evaporates network the bonds xylem dioxide them. water from spaces, between the needed cell This for This is adheres adhesive vessel. water walls forces keeps and called to and polar adhesion. cellulose is cause the other lost This property molecules from water walls molecules, to the be in leaf drawn moist so they useful to living cell via the out can is walls. of absorb photosynthesis. Thermal proper ties Water ● has High water several specic bonds amount relatively ● energy. to air it or of To Water’s land, latent separates molecule. to so broken. needed in is a of down, to is stable do in needed the remains molecules bonds must vaporization. needed are restrict temperature raise water thermally other heat the Energy to temperature heat The be that Hydrogen increases cool it from properties capacity. and energy large. of High heat molecules hydrogen the thermal this lose motion require do this. liquid a for stable As large in of result, is amounts comparison organisms. evaporates becomes the a water aquatic molecule and called of relatively relatively habitat is to the water temperature When a of organisms: latent a vapour heat of 69 2 M O L E C U L A R B I O L O G Y vaporization. amounts bonds of have Sweating High ● to is boiling water has Water is 100 a are be an temperature to Evaporation heat point. high it This is the use boiling heat in of over has a cooling evaporate makes the reach liquid to This of The can latent therefore °C. broken. example that therefore needed of it a good water point a water, of liquid a broad temperature range range For its of Considerable hydrogen evaporative a is the the same boiling highest reasons point temperatures found in coolant. coolant. substance state. vaporization, a as effect. because most is that high. – from habitats on 0 °C Earth. Solvent proper ties Water has molecule important means preventing Water oxygen from is chemical is shells clumping bonds pole Cytoplasm the properties. forms attracted hydrogen dissolve. it hydrogen pole positive which them forms solvent that to is a together with polar positively attracted complex reactions of The around polar and ions negatively mixture of metabolism and keeping molecules. charged to nature charged them Its and the its water molecules, in solution. partially charged dissolved of polar negative partially ions, so both substances in occurs. toK Hydphii nd hydphbi How do scientic explanations dier Substances can be hydrophilic or hydrophobic. from pseudo-scientic explanations? The literal meaning of the word hydrophilic is water-loving. It is used to Homeopathy is a practice where describe substances that are chemically attracted to water. All substances remedies are prepared by dissolving that dissolve in water are hydrophilic, including polar molecules such things like charcoal, spider venom as glucose, and particles with positive or negative charges such as or deadly nightshade. This “mother sodium and chloride ions. Substances that water adheres to, cellulose for tincture” of harmful substance is diluted example, are also hydrophilic. again and again to the point where a Some substances are insoluble in water although they dissolve in other sample from the solution is unlikely to solvents such as describe them, propanone (acetone). The term hydrophobic is used to contain a single molecule of the solute. though they are not actually water-fearing. Molecules It is this ultra-dilute solution that is are hydrophobic if they do not have negative or positive charges and are claimed to have medicinal proper ties. nonpolar. All lipids are hydrophobic, including fats and oils The proper ties are referred to as the “memory of water ”. Despite the large number of practitioners of this practice, no homeopathic remedy has ever been shown to work in a large randomized placebo-controlled clinical trial. ▲ Figure 3 When two nonpolar molecules in water come into contact, weak interactions form between them and more hydrogen bonds form between water molecules 70 2 . 2 If a nonpolar form and the water as water though This each is a and are result, in are to water nonpolar each but to bonds forces tend bring that known form it is are is a if to nonpolar they are in water because water molecules contact molecules. water nonpolar in by behave attraction they the bonds molecule surrounded together, between together hydrophobic hydrogen nonpolar slight simply than join cause as There other the them signicantly, can to molecules, between molecules other. more each molecules are water not water-fearing: attracted The by but movements hydrogen they more nonpolar groups two attracted more groups. If random molecules, because larger into and other, are surrounded molecules, molecules. they not is water nonpolar molecules As the molecules between with molecule between W a t e r molecules. to to form join larger together interactions. cmping wt nd mthn Comparison of the thermal proper ties of water with those of methane. The properties waste product in habitats in swamps termites, and cattle single can form do and very other be it form lacking. wetlands sheep. used methane already as a are bonds. and They to bonds, in produce fuel to but the both described. certain the live guts in methane if allowed a prokaryotes animals, dumps escape with live live are digesters. into atoms are molecules result a including and anaerobic molecules methane As to is that the effect. molecules water of in Methane prokaryotes waste greenhouse small whereas bonds. in Methanogenic also However hydrogen been respiration is contributes hydrogen their linked polar are physical and by can nonpolar and properties are different. The data and water. methane a oxygen and covalent not have encouraged atmosphere Water water anaerobic where deliberately Methane of of higher higher liquid in table The and melting a shows water specic over 1 density in heat point range some and a liquid capacity, and of of 22 data latent boiling °C, water of of given that methane for water over methane 100 H O 2 16 18 3 Specic heat capacity 0.46g per cm 2.2 J per g per °C Latent heat of vaporization Melting point 760 J/g is °C. W 4 Density has vaporization, Whereas liquid CH Molecular mass are shows heat point. is M Formula properties capacity The higher Pp physical heat state. higher only the specic 3 1g per cm 4.2 J per g per °C 2,257 J/g −182 °C 0 °C −160 °C 100 °C ▲ Boiling point Figure 4 Bubbles of methane gas, produced by prokaryotes decomposing organic matter at ▲ T able 1 Comparing methane and water the bottom of a pond have been trapped in ice when the pond froze 71 2 M O L E C U L A R B I O L O G Y cing th bdy with swt Use of water as a coolant in sweat. Sweat is is secreted carried skin along where it evaporation tissues Blood of the skin, This body can as sodium, brain. in It are be is left temperature receptors glands to Usually the target secreted is because to is sweat to two the is of if we secreted body to of evaporation an of of example. water which from is of cooling these also water. useful in leaves; hot on Panting Transpiration plant other rely is it than heat in sweating, loss dogs evaporative has a due and cooling birds loss effect environments. of ions and hypothalamus If of methods many taste. the from body the sweat body when blood inputs stimulates are intense surface monitor the to is the heat salty the skin. if the are cooling sensory though even period cause by for from latent skin that though especially their litres secreted adrenalin a the the of high by There the therefore a receives temperature, we anticipates tend up sweat is sweat, on sweat of temperature. the in needed taken has hypothalamus secrete no skin receptors also is The surface heat their controlled and skin. the method detected has the the in temperature overheated sweat water the to The reducing Solutes secretion the out. effective because sometimes Sweat of an in ducts through is vaporization. such water owing cooled. glands spreads of the by narrow per is is sweat hour. below adrenalin already when cold. our activity is This brain that will overheat. Tnspt in bd psm Methods of transpor t of glucose, amino acids, cholesterol, fats, oxygen and sodium chloride in blood in relation to their solubility in water. Blood using and transports several ensure a wide methods that each variety to avoid of substance is Glucose substances, possible problems carried in water is and quantities for the body’s freely chloride soluble in is an water, ionic molecule. It dissolved is in freely blood soluble in plasma. is a nonpolar molecule. Because of the needs. small Sodium polar carried large Oxygen enough a is compound dissolving to that form is sodium only size of the sparingly oxygen at molecule and water relatively low it dissolves becomes in water saturated concentrations. but with Also, as + ions (Na carried ) in and chloride blood ions (Cl ), which are the temperature oxygen plasma. hold Amino acids have both negative and but Because their group, of solubility some of this they varies which are soluble depending are on hydrophilic decreases, much in the °C or hydrophobic. All amino acids are to be carried dissolved in lower. plasma can little provide while to plasma oxygen solubility at 37 than °C of can water The amount of oxygen that at blood transport for around aerobic the cell body is far respiration. too This others is overcome the use of Hemoglobin by has binding hemoglobin in soluble blood blood cells. sites for plasma. oxygen blood 72 blood dissolved the R red enough so rises, water problem are less water positive 20 charges. of and for greatly oxygen increases transport. the capacity of the 2 . 3 Fats molecules than oxygen carried These in are are and blood entirely are inside groups of nonpolar, insoluble in lipoprotein molecules are water. c a r b o h y d r a t e s a n d l i P i d s larger They phospholipid are complexes. with a single protein layer cholesterol of phospholipid hydrophilic on the phosphate outside heads and of fats the inside. The phospholipids triglyceride face the outwards blood plasma. tails face fats. There inwards are monolayer, is a not water small and also to hydrophilic in the are the at cholesterol transported one of the with This in fats in molecules monolayers, outwards the apart end. dissolve cholesterol facing heads with phospholipid hydrophobic, region The in lipoprotein. phospholipid region phosphate in water hydrocarbon contact name complexes. positioned in proteins is with hydrophobic the it contact are make instead the the The molecules are with in hydrophilic enough lipoprotein are and hence Cholesterol from and in the with region phospholipids. ▲ Figure 5 Arrangement of molecules in a lipoprotein complex 2.3 c p undstnding appitins ➔ Monosaccharide monomers are linked ➔ Structure and function of cellulose and starch together by condensation reactions to form in plants and glycogen in humans. disaccharides and polysaccharide polymers. ➔ ➔ Scientic evidence for health risks of trans-fats Fatty acids can be saturated, monounsaturated and saturated fats. or polyunsaturated. ➔ ➔ Lipids are more suitable for long-term energy Unsaturated fatty acids can be cis or trans storage in humans than carbohydrates. isomers. ➔ ➔ Evaluation of evidence and the methods used Triglycerides are formed by condensation from to obtain evidence for health claims made three fatty acids and one glycerol. about lipids. Nt f sin ➔ Evaluating claims: health claims made about Skis ➔ lipids need to be assessed. Use of molecular visualization software to compare cellulose, starch and glycogen. ➔ Determination of body mass index by calculation or use of a nomogram. 73 2 M O L E C U L A R B I O L O G Y cbhydts toK Monosaccharide monomers are linked together by i w mpg pgm gv xp pm, condensation reactions to form disaccharides and w w w ? polysaccharide polymers. Thomas Kuhn, in his book The Structure of Glucose, fructose and ribose are all examples of monosaccharides. The Scientic Revolutions adopted the word structure of glucose and ribose molecules was shown in sub-topic 2.1. ‘paradigm’ to refer to the frameworks that Monosaccharides can be linked are single together to make larger molecules. dominate the interpretation of information ● Monosaccharides ● Disaccharides sugar units. in a scientic discipline at a particular point in time. The paradigm impacts the kinds of questions that are supposed to example, be asked. Sucrose consist maltose is made is by of two made monosaccharides by linking a linked linking two glucose glucose and a together. molecules For together. fructose. Nutritionism is the reductionist paradigm Polysaccharides ● that the presence consist of many monosaccharides linked together. of indicator nutrients Starch, glycogen and cellulose are polysaccharides. They are all made are the key determinant of healthy by food. linking together glucose molecules. The differences between them Even highly processed food may are described later in this sub-topic. be advertised as healthy depending When monosaccha r i d e s combi ne , t hey do so by a pr oc e ss c al l ed on the degree to which it contains condensation (gur e molecule an 1). This i nvo lve s the l os s of an OH from one ‘healthy’ nutrients. Words like ‘carbs’, and H from another m o l e cul e , whi ch to g e th er fo rm ‘vitamins’ and ‘polyunsaturated fat’ have H entered the everyday lexicon. Some O. Thus, condensa ti o n i nvo lve s the c om bin a t io n of s u bun i t s and 2 yields water. argue that this aligns consumer anxiety with the commercial interests of food manufacturers. Linking together polysaccharides ATP supplies monosaccharides is an energy anabolic to the to form process and disaccharides energy monosaccharides and has this to and be used energy is to do then An alternative paradigm for determining when the condensation reaction occurs. the ‘healthiness’ of food is argued for by Michael Pollan in his book “In Defense of H Food”. It argues that food quality should H H H Monosaccharides, C H 6 O 12 6 be determined by cultural tradition which e.g. glucose, fructose, galactose tended to look at food more holistically: OH The sheer novelty and glamor of H O 2 the Western diet, with its seventeen Condensation thousand new food products every year and the marketing power – thirty-two Hydrolysis (water removed) (water added) billion dollars a year – used to sell us those products, has overwhelmed the Disaccharide, C H 12 O 22 11 force of tradition and left us where we e.g. maltose, sucrose, lactose now nd ourselves: relying on science HO O OH Glycosidic and journalism and government and bond marketing to help us decide what to eat Michael Pollan, In Defense of Food: An Condensation Hydrolysis Eater's Manifesto H H Polysaccharide e.g. starch, glycogen HO ▲ O O OH Figure 1 Condensation and hydrolysis reactions between monosaccharides and disaccharides 74 O it. used 2 . 3 c a r b o h y d r a t e s a n d l i P i d s Imging bhydt ms Use of molecular visualization software to compare cellulose, starch and glycogen. The most widely can be use JMol, available When which with JMol changes ● used downloaded Use to is to use. a There used, on the that you molecule function are software also Suggestions resources being of visualization charge. electronic image scroll of easier software the the are the molecular free of you mouse to be see JMol, able on make the that websites this to the which websites suitable accompany should that is many are book. make these screen: image larger orsmaller. ● Left ● Right of click and click move to molecular display model, continuously Spend then the some try or time these structure the menu label change to to that the the developing questions of a mouse rotate allows atoms, your skill your in skill image. you make background test the to the change the molecule style rotate colour. molecular level and visualization learn more and about polysaccharides. Questions 1 Select ● glucose What colours oxygen 2 Select ● is Select the amylose, amylose ● What ● How only 4 Select is must ● at a the How to stick show is is style glucose the to is between the a and overall and sucrose and style with carbon, a black hydrogen background. and a blue the glucose unbranched shape ring and the molecule? white then background. a form background. longer of [1] an molecules starch, possible with select the molecule? chain are [1] linked to with the branched where an different between extra about [1] styles form there third this glucose is and colours of starch. a branch. glucose linkage, molecules to that Zoom A to glucose make the compared in you in to prefer. look molecule branch. the unbranched parts molecule? many glucose in glucose the a one. amylose in of If glucose? position linkages ● the which other linked What of in chain many one sticks amylopectin, be used and [2] style the Amylopectin closely ball difference ring wireframe short are with the fructose 3 the atoms? sucrose What with [1] molecules amylopectin are linked molecule? to only one other ▲ [1] Figure 2 Images of sugars using molecular visualization software – (a) fructose, (b) maltose, (c) lactose 75 2 M O L E C U L A R B I O L O G Y 5 Select glycogen. amylopectin ● 6 What Select ● 7 at is it the glucose ● the is similar of starch. difference but not between identical glycogen to the and amylopectin? [1] cellulose. How Look is It form different oxygen molecule What pattern atoms along shape atom in do the in the that from forms the other part of polysaccharides? the ring in [1] each chain. you notice in the position of these oxygen chain? Pyshids Structure and function of cellulose and starch in plants and glycogen in humans. Starch, glycogen together glucose functions in the type type of could hand at top glucose in in Cellulose glucose is made atom group or 4 has 1 of to in the but link (on to link the is the 6 is right glucose) on atom on group it major from and left (shown used to form In points points atom Figure 3 Glucose molecule ▲ Figure 4 Cellulose 1 alpha downwards upwards. consequences together reactions the carbon ▲ for glucose. linking on and which downwards. OH Condensation carbon and polysaccharides. the by linking differences common (shown carbon OH made of atom (β-glucose) difference molecules. to the to them used diagrams) upwards (α-glucose) small on 4 by reactions, diagrams atom some due any most carbon OH have either beta The made structure molecules. actually molecular polysaccharides 1 groups, molecular The can on is make glucose are carbon of This to all their condensation OH branches pointing This in on side). Glucose but OH in them the side the side between ve of used are yet different. polysaccharides. OH hand cellulose glucose used three between the of has be make very linkage Glucose only are and molecules, next β-glucose link carbon β-glucose. atom The OH Cellulose groups on carbon atom 1 and 4 point in molecules β-glucose, directions: up on carbon 1 and down on bring these OH groups together and allow reaction to occur, each the are to the chain previous oriented one. has The to be positioned glucose alternately subunits upwards and at in 180° consequence of this is that the 76 is a straight chain, rather bonds bundles the have chains bundles of with linking are the called cellulose cellulose molecules. microbrils. very high tensile strength and are used as the of cellulose basis of plant cell walls. The tensile strength chain prevents plant cells from bursting, downwards. when very high pressures have developed cellulose inside molecule form to even The to β-glucose They added unbranched them a These condensation allowing carbon4. hydrogen To are opposite than curved. the cell due to entry of water by osmosis. 2 . 3 Starch is made molecules. As condensation carbon of the point in atom linking 1 of one can curved, starch. be In is Starch types this amylose and is only are has by the a helix. more plant are two In The amylopectin they of the shape. Molecules but is forms molecules globular cells. hydrophilic way. molecule α-glucose a both molecules same There on atom4 groups starch of are of too both large ▲ to be soluble in cells in where water. large They are amounts of therefore glucose Figure 5 Starch useful need to be glycogen stored, but a concentrated glucose solution too Starch is energy much used in water as seeds a to store and enter of a cell glucose storage by and organs it remove Starch is made as a therefore as of an in a unbranched glucose is being made faster store by it can Glycogen starch, animals liver the a and store cause ▲ exported very there more and similar is of energy in stores osmotic in It is in form leaf is at molecules both molecule or at any of ends the branched molecule. Starch and ends glycogen do not have a xed size and the cells form made of glucose molecules that they it in increased or contain decreased. in of by the acts glucose, be the Glycogen glucose both glucose done plant. making plants: of With the stored humans. dissolved problems. of branched Glycogen starch the of parts the be photosynthesis branching, fungi. muscles as other to more some function large to compact. also some same where is but molecule be extra can potato in can than add of number when to This osmosis. such temporary easy them. molecules cells. is would or cause l i P i d s by groups carbon OH the chain forms so made starch in that made OH glucose straight. the branched, of the are the and a n d α-glucose links These all is than unbranched chain glucose orientated of rather so the between glucose. downwards, starch together cellulose, reactions adjacent consequence is by in c a r b o h y d r a t e s has as cells would starch and Figure 6 Glycogen lipids Triglycerides are formed by condensation from three fatty acids and one glycerol. Lipids are of being of lipid. a diverse group of carbon insoluble in water. Examples of triglycerides compounds Triglycerides are the are fat one in that of share the adipose the property principal tissue in groups humans 77 2 M O L E C U L A R B I O L O G Y and the (37°C) both A oil in but body sunower solid gure condensation linkage This an of alcohol. acid In and well, by they Arctic is this an are used marine used room so fatty each the on as cell as fatty is body temperature whereas fatty linked and acid is acids to the molecules acid an reaction oils are liquid at the are with the one glycerol by produced. glycerol reacts between with glycerol is the an ester OH COOH a The bond. group group in on a glycerol. energy stores. respiration. heat at °C) three water when the liquid (20 temperature. acids three formed case are combining the OH aerobic are and between Fats temperature by of reaction, bond Triglycerides released made Each formed type fatty is 7). seeds. room temperature triglyceride (see at The energy Because insulators, for they from do example them not in can conduct the be heat blubber of mammals. Glycerol Fatty acids Triglyceride (fat) H H HO C (CH ) 2 CH n C O 3 (CH ) 2 CH n 3 H O O Condensation (water removed) H HO C (CH ) 2 CH n C O 3 (CH ) 2 O CH n 3 O H HO C (CH ) 2 CH n C O 3 (CH ) 2 CH n 3 H O 3H O H O 2 Ester ▲ bond Figure 7 Formation of a triglyceride from glycerol and three fatty acids engy stg Lipids are more suitable for long term energy storage in humans than carbohydrates. Lipids and storage for carbohydrates humans, long-term used of in are cells fats. called but energy They adipose immediately around some organs both are storage. are located are lipids The stored tissue. in used lipids the including that tissue skin the and greater energy used specialized Adipose beneath for normally cells are gram of groups grams is more can also kidneys. is are several r e a s o ns for us ing than carbo hy d r a tes f or The is lipids are around of we with of body have with us in whereas each about actually amount gram because and more bats important that amount of energy released in six energy mass. to two times that This carry our wherever we go. for animals such as y. Stored per gram of lipids is lipids have amount released could not be The from same a gram amount as lipid rather than adds the half mass as Be ca us e of hea t, insulators. l ip id s ar e by po or the y Thi s is ca n the be use d r e a so n f or as much carbohydrate much to body our stored advantage of lipids fat b e i ng in s ub- cuta ne ous mass. adipose fact r ol e s w el l energy of therefore as of of heat stored se cond ar y p e r f or me d double conductors carbohydrates. s o me cell carbohydrates. 78 droplets storage: respiration In pure associated the per stores even that the is so in form associated, l ong - ter m ● ● stored important, birds energy water, efcient be fats water li pi ds It rather no glycogen of energy There because with is even tissue next to the s ki n. B eca us e fat 2 . 3 is liquid as a at shock adipose other body te mp e r atur e, absorb e r. tissue T hi s aro und is the it the can a l so re a son ki dney s act can s om e it is in is the car b o hy dr ate tha t is energy muscles. term storage , in Although storage of the lipids ene r g y, l ive r ar e a nd i de a l g ly co ge n in fo r is storag e . T hi s is as in gl ucos e by the a d i pos e rapidl y. or to easily l i P i d s tis sue Glucos e ae r o b i c ce ll r ap id ly b lo od ca n to and wh e re can n ot be u se d r e sp ir a ti on be e it h e r wh er e a s and fatty acid s ca n onl y be use d in a e ro bi c so m e respiration. The of and li v e r s tor es up to 15 0 gr a m s lo n g- u s ed be ca us e dow n Fats anaerobic glycogen s o me m us cl es stor e up to for 2% short-term needed. a n d u se d fats for broken transported mobilized organs. Glycogen be then for a nd c a r b o h y d r a t e s glycogen by mass . gl yc og e n d- q: Emperor penguins 0.4 During the Antarcti c w inte r fe mal e 0.5 E m pe ro r 8.0 penguins live and feed at s ea , but m a le s h a ve 6.8 to stay on the ice to i ncuba te the s in g le egg the 18.2 female eat no and has laid. food. the Thr o ug hout After females 16 w e ek s r e tur n. thi s the W hil e time e ggs the th e 14.3 m al e s h at c h m a l es ar e 0.8 12.0 incubating groups of the eg g s about the y 3,000 s ta nd b ir ds . in To tig ht l y p ac k e d i nv e st i g at e the captive before reasons were for standi ng taken from a in g ro ups , co l o ny at 10 ma le Po inte captive after b i r ds G e ol og ie in 0.4 0.4 Antarctica. They ha d a l r e ad y s ur vi ve d 4 we e ks 6.9 without food. The y were ke pt fo r 14 m o re 7 .7 14.4 1 7 .3 weeks without where they conditions fo o d could were in no t kept f ence d for m the encl os u re s gr oups . s ame as Al l in ot h e r the w il d 11.8 colony. The mean air te mpe r atur e was 16.4 ° C. 2.2 The composition birds’ bodies 14-week of was period the ca ptiv e me a s ur e d of the a nd be for e the a nd ex pe ri me nt. w il d a f t er Th e the wild before wild after re s u lt s Key in kilograms are s ho w n a) Calculate the total in gure 8. water group of mass loss for each lipid birds. [2] protein other substances i) wild ▲ ii) b) captive Compare captive free c) Figure 8 in the birds the Besides another changes with lipid of content the birds of the living colony. being used function important in those for [2] as of an lipid penguin energy which survival. source, might state be [1] 79 2 M O L E C U L A R B I O L O G Y Bdy mss indx Determination of body mass index by calculation or use of a nomogram. The by body mass aBelgian needed to index, calculate height in BMI calculated is usually statistician, it: abbreviated Adolphe the mass to Quetelet. of the BMI, Two person in was developed measurements kilograms and are their metres. mass using in this formula: kilograms __ BMI = 2 (height in metres) 2 Units BMI can straight on the for also line based BMI is is kg found hand to too using a page on 81 whether or type height intersects on assess high m the scale questions used or be are between right data level, BMI too a low. of chart the the left BMI include person’s Table bMi 1 a called hand on the BMI body shows a nomogram. scale and central the scale. A mass The nomogram. mass how is at this a is healthy done: s av below 18.5 underweight 18.5–24.9 normal weight 25.0–29.9 overweight 30.0 or more obese emg pg To estimate body fat percentage, measure the thickness of a skinfold in millimetres using calipers in ▲ T able 1 In some these four places: parts of the world food supplies are insufcient or are unevenly Front of upper arm distributed and many people as a result are underweight. In other parts Back of upper arm of the world a likelier cause of being underweight is anorexia nervosa. Below scapula This is a psychological condition that involves voluntary starvation and Side of waist loss of body mass. The measurements are Obesity is an increasing problem added and then analysis in some countries. Excessive food tools available on the internet intake and insufcient exercise can be used to calculate cause an accumulation of fat in the estimate. adipose fat can tissue. be (gure the of coronary diabetes. the Figure 9 Measuring body fat heart It with skinfold callipers 80 overall countries are 9). such disease and costs is of life of body skinfold Obesity reduces where rising. using conditions signicantly ▲ amount estimated calipers risk The increases as and type 2 expectancy increasing health rates of care in obesity ▲ Measuring body mass. What was this person’s body mass index if their height was 1.80 metres? 2 . 3 c a r b o h y d r a t e s a n d l i P i d s d q: Nomograms and BMI Use gure 11 to answer these b) questions. Suggest could 1 a) State who the has body a mass mass of index 75 kg of a man and a height 4. of1.45metres. b) Deduce a) State the Outline and [1] body mass status of this man. the BMI two ways reduce her in relationship for a xed on the the body scales mass on the of the person the woman mass. between bodymass. [2] height [1] [1] body mass/kg 2 which body height/cm standing previouspage. 150 [1] 125 140 b) The person has a height of 1.8 metres. 130 Deduce their body mass status. 130 [1] body mass index 120 3 a) A woman has a height of 150 cm and 135 110 a BMI of 40. Calculate the minimum 50 100 amount of body mass she must lose 140 to 95 reach normal body mass status. Show 40 90 145 allof your working. [3] 85 80 150 30 75 155 70 65 160 60 20 165 55 170 50 175 45 180 40 185 10 190 35 195 30 200 205 210 25 ▲ Figure 10 Jogger ▲ Figure 11 Ftty ids Fatty acids can be saturated, monounsaturated or polyunsaturated. The a basic chain covalent chain is structure of bonds. the can be The length used carbon It acid is variable of living the fatty of as is the described a atoms hydrocarbon molecule. hydrocarbon the was hydrogen This is in sub-topic linked chain. a to At one carboxyl 2.1. them end group, There by is single of the which COOH. organisms feature acids with therefore part represented by of atoms, have bonding chain is variable between between 14 and the but 20 most carbon carbon of the fatty atoms. atoms. In acids Another some fatty 81 2 M O L E C U L A R B I O L O G Y acids C but C H H C C a carbon it C H C H C H C H C C H C H C C H C H hydrogen C C H H C H Fatty C H H C H C H C H is linked it can bonds H C C H C H is are linked are one there are linked linked than H C H H C H and names H C H C H C H H C H C C H H C H C C H C H C C H C H H H Figure it they 12 one bond double to all to to by or by single more double adjacent of have covalent positions covalent carbons one could one or less in specic and it fatty acids is is saturated fatty is more bond polyunsaturated of atom. atoms acid in atoms. adjacent bonds, in the chain bonds. the fatty therefore called than If carbon A double hydrogen fatty double shows an carbon one the to hydrogen hydrogen its contain bond, two bond one possibly that double C C a bond as acids H H also between because one by only more C atoms atom can C C H atoms acids chain by single H C C carbon fatty carbon bonds, H the C C If H of other OH O C in where C OH O all OH O a a carbon in the acid chain, with contains saturated bonds they are atom single as much fatty acid. unsaturated could. If monounsaturated there and is if it has polyunsaturated fatty acid, acid. IB It is one not monounsaturated necessary to remember Biology. unsttd ftty ids H Unsaturated fatty acids can be cis or trans isomers. In palmitic acid linolenic acid palmitoleic acid • saturated • polyunsaturated • monounsaturated • non-essential • all cis • cis • essential • non-essential • omega 3 • omega 7 unsaturated are nearly are double is for the acids. ▲ fatty always acids on bonded – hydrogens These two the in these to living same be are on organisms, side of called the cis-fatty opposite conformations are the two sides shown – hydrogen carbon acids. The called in atoms atoms that alternative trans-fatty gure 14. Figure 12 Examples of fatty acids In cis-fatty double fatty acids saturated with acids, bond. less fatty H C C C at acids, they acids the bond, double room solid H good Trans-fatty partial H – do so for use in bend in the triglycerides it fatty not hydrocarbon containing together lowers acids the are in regular melting therefore have a have bend a Trans-fatty of acids vegetable margarine in the higher the than liquid and or hydrocarbon melting are sh some point produced oils. other This at is chain and are room articially done to C Figure 13 Double bonds in fatty acids Figure 1 4 Fatty acid stereochemistry – (a) trans (b) cis at solid by produce processedfoods. trans 82 at Triglycerides usually H ▲ arrays point. cis ▲ chain cis-unsaturated oils. they temperature. a packing so are hydrogenation fats is makes cis-unsaturated temperature at there This 2 . 3 c a r b o h y d r a t e s a n d l i P i d s Hth isks f fts Scientic evidence for health risks of trans-fats and saturated fats. There on In have human this disease deposits, A rates low be There are Kenya of does amounts of blood not dietary example arteries that bre, that a is do with t fat by fatty the fat fatty acid nding disease. intake, It such as CHD. correlation. in of (CHD). However, cause causes rich blocked saturated saturated the is fats types disease attacks. programs. actually that different heart heart between saturated not of partially and research that diet effects coronary become found many correlated have the formation been in prove factor about concern clot has CHD populations for main coronary to another claims The correlation and correlation could many the leading positive intake a been health. meat, The fat, Maasai blood of and ▲ milk. They therefore have a high consumption of saturated Figure 15 Triglycerides in olive oil fats, contain cis-unsaturated fatty acids yet CHD is members Diets are almost of rich another in olive traditionally populations has been fatty of explain There is of the CHD also a and see can they therefore fatty these this concentrations rates of account do the of is genetic such that contains countries countries positive in in tribe as the show to the factors use of Figure this 17 shows trend. cis-monounsaturated around typically due the Maasai. in the have low intake these of rates of CHD in acids, The and it cis-monounsaturated populations, tomatoes fatty Mediterranean. many or other dishes could rates. probably deposits which that diet consumed if oil, However, the among Kenyan eaten claimed acids. aspects unknown correlation CHD. for the cause trans-fats, risk In arteries which amounts factors correlation, CHD. diseased between Other but patients have gives have none who been more of trans-fat been did. had found tested, died to evidence to Trans-fats from contain of a CHD, high causal narrowed fatty plaque causing lumen of ar tery thickening of the ar tery lining link. layer of muscle outer coat of ar tery and elastic bres ▲ ▲ Figure 16 Ar tery showing fatty plaque Figure 1 7 Samburu people of Nor thern Kenya. Like the Maasai, the Samburu have a diet rich in animal products but rates of hear t disease are ex tremely low 83 2 M O L E C U L A R B I O L O G Y evting th hth isks f fds Evaluating claims: health claims made about lipids need to be assessed. Many some health cases benet and harmful. when claims the in other Many they about claim are is cases claims tested foods that the it is have are made. food that been has the a food found similar In health to controlled be false health, would scientically. but be almost It is of relatively diet on numbers easy health of to test using claims about laboratory genetically uniform the of groups health Variables amount do not can be and them be other of than inuence designed of with selected exercise, strong effect of can diet, can the so factor be on of as can be be sex and that as exercise to eat a of animal Diets varies about the obtained nding food are by a of used what in the the but they health diet. It do effects would not are be tell on very into a control humans sex were It and used would other they also variables would controlled health cohort and be diet risks be such willing for nd associated of a long out their factors in their over can is involve measuring health increased must These procedures whether an food Evidence studies. people, Statistical with of approach. following years. to the different epidemiological large a then the diet frequency of a often particular interesting, few strictly use intake period be animal. experiments twins different. to age, period. therefore are Results and very Researchers they factor obtained of It of state and experiment. dietary terms identical genetically humans. groups bred experiments. so unless in with matched Large temperature the one thus the age, in controlled only can same use such results that evidence this the for select subjects impossible enough and to effects animals. animals experiments possible experimental is be might us with humans difcult of to disease. The analysis has to eliminate certainty a the effects of the disease. other factors that could be causing factor carry out Nature of science question: using volunteers in experiments. During were using as the Second conducted conscientious volunteers. sacrice their knowledge. 20 a The A eight War, to For six 70 help C to weeks mg months, of and were in the they US service willing were C. all given volunteers for in on the diet with 70 mg, seven had in The cross-linking reduced C. to All 10 of mg and these ten ten were their Three-centimetre thighs, with ve stitches. was also gums. These bleeding Some serious the of heart wounds wounds from the cuts hair The to follicles up 70mg of vitamin C fared heal. and 2 Is it vitamin protein killed The to well of acceptable perform where the this the C had bres and for doctors experiments or on there is a risk that the volunteers will be harmed? people are experiments, more or less paid such to as acceptable participate drug than trials. using mg and Is it better to use animals for experiments for vitamin C ethical objections the same Is it acceptable been ironically 84 done are using suitable real guinea-pigs, because which guinea-pigs, to kill animals, have experiment also or are did 4 requirements in Is unpaid as with humans? notdevelopscurvy. on less volunteers? more 10 Sometimes the Experiments and collagen strength. ethically medical There from given equally then tested. C, were in 3 or the urine no with developed groups restricted between and were was During developed made closed failed volunteers problems. were skin acid. vitamin were health scurvy. plasma of their given volunteers and with volunteers, vitamin blood ascorbic intakes guinea-pigs lower scientists dose various in bone guinea-pigs therefore synthesize with concentrations 1 kept cannot periods collagen involved Then, trial monitored. to medical England vitamin three in military extend trial humans, experiments England volunteers vitamin containing next in objectors health volunteers. diet the World both like can be done? so that an 2 . 3 c a r b o h y d r a t e s a n d l i P i d s anysis f dt n hth isks f ipids Evaluation of evidence and the methods used to obtain the evidence for health claims made about lipids. An evaluation implications claims two 1 is comes to Implications or 2 not the at IB scientic ask – about do the health as an assessment Evidence research. this of rigorous, There are or of the strongly, or – were are the there research rst question of the results or easiest if of is answered of a results – survey. are by ● methods used about type of statistical and ● the as visual Is there lipid a the between investigated health or is a usually graph How large benet? negative is slightly the rates in a of lipid be a are This a bar data, been is is shown scattergraph chart. the less The likely it signicant. done on the data, differences? answered points below questions by assessing refer to should the surveys be asked to experiments. was the necessary survey How and intake rate of of the to get sample to have reliable size? In surveys thousands of it is people results. even was the the This might be and less the sample other style? factors The in sex, can more age, affect even state the of sample, theresults. either If the sample was uneven, were the results a to eliminate the effects of other factors? correlation. difference of life disease between Were the the disease with intake? Small measurements of lipid intake and mean rates reliable? Sometimes people in a different differences do not report their intake accurately may and not have different large survey levels The controlled disease (average) on or ● ● data? on the signicant question adjusted positive bars differences tests used. usually ● or the points display. correlation being error show second health ● is data spread mean they How ● other If methods in analysing Analysis of widely that The experimental presented size of research weaknesses either spread spread is assess research results the the more moderately uncertainties because widely the do conclusions results How by methodology? The ● health research: results claim for all? Limitations the in limitations. from questions support dened and diseases are sometimes misdiagnosed. signicant. d- q: Evaluating evidence from a health sur vey The Nurses’ survey into factors. It Health the Survey health began in is a highly consequences 1976 with Health respected of 121,700 161:672–679. many in the USA and Canada, who completed questionnaire about their lifestyle assess CHD, medical been history. Follow-up completed every the the into two years since of diagnose by the reading Journal on the of in a Intake used heart research MJ and and Women: Oh, paper 20 K, of Years assess in FB, WC. is diet be 5 was effects of trans-fats participants five intake. the average American was freely energy (2005) Heart Follow-up and found Manson, Coronary of can the which Hu, Willett, Risk to disease Epidemiology, internet: Stampfer, Fat methods coronary doi:10.1093/aje/kwi085 in the on rates survey groups according to were their of available JE, Dietary Disease the Quintile 1 was the 20 % of then. participants Details Epidemiology, questionnaires trans-fat have of factors divided and Journal a of lengthy American female To nurses Study. Nurses’ with 20 % with intake of calculated, found intake. for assigned each a differences mass risk the the as a The 1. for percentage relative quintile, of intake highest trans-fats between index, lowest The the smoking, risk with risk and intake. each of of was alcohol The quintile dietary CHD Quintile quintiles quintile was 1 adjusted in age, intake, for body parental 85 2 M O L E C U L A R history affect of 18 energy quintiles CHD. risk of is a and graph from and The intake rates the confidence is other for adjusted of level of the 1.6 that factors. 1.4 percentage each of relative trans-fat statistically foods other showing trans-fats effect CHD of various the risk intake on significant DHC fo ksir evitaler of CHD, CHD Figure B I O L O G Y five of relative with a 1.2 1.0 0.8 0.6 0.4 99 % 0.2 1 Suggest reasons for using only female nurses 0 in this survey. [3] 1 2 State the trend 3 The mean was not age shown of in nurses the graph. 1.5 in the ve Explain the reasons 2.0 2.5 3.0 percentage of energy from trans-fats [1] quintiles Data for graph the same. for % of energy from adjusting the results to compensate for the 1.3 1.6 1.9 2.2 2.8 1.0 1.08 1.29 1.19 1.33 trans-fat effects of age differences. [2] Relative risk of CHD 4 Calculate tests, of the the chance, based differences in on the CHD statistical risk being due ▲ to factors trans-fat 5 Discuss factors other Figure 18 than intake. [2] evidence from the graph that other were having some effect on rates ofCHD. [2] d- q: Saturated fats and coronary hear t disease ainovalS edargleB roclaverC ninajnerZ 18 14 12 10 10 9 9 9 9 8 7 3 3 992 351 420 574 214 288 248 152 86 9 150 80 290 144 66 88 1727 1318 1175 1088 1477 509 1241 1101 758 543 1080 1078 1027 764 1248 1006 emoR eterC akubihsU ASU 19 saturated fat ufroC nehptuZ 19 by % calories as akileV dnalniF .W 22 ranked aitamlaD dnalniF .E uramihsunaT oigroigetnoM Populations % Calories as saturated fat Death CHD rate/ 100,000 All 1 yr ▲ 1 2 3 86 causes T able 2 a) Plot a b) Outline Compare a) East b) Crete scattergraph the the and Evaluate results West and the trend of the shown data by in the table 2. [5] scattergraph. [2] for: Finland; [2] Montegiorgio. evidence from this [2] survey for saturated fats as a cause of coronary heartdisease. [4] 2 . 4 P r o t e i n s 2.4 P undstnding appitins Amino acids are linked together by ➔ Rubisco, insulin, immunoglobulins, rhodopsin, ➔ condensation to form polypeptides. collagen and spider silk as examples of the There are twenty dierent amino acids in ➔ range of protein functions. polypeptides synthesized on ribosomes. Denaturation of proteins by heat or deviation of ➔ Amino acids can be linked together in any ➔ pH from the optimum. sequence giving a huge range of possible polypeptides. The amino acid sequence of polypeptides is ➔ Skis coded for by genes. Draw molecular diagrams to show the formation ➔ A protein may consist of a single polypeptide or ➔ of a peptide bond. more than one polypeptide linked together. The amino acid sequence determines the three- ➔ dimensional conformation of a protein. Nt f sin Living organisms synthesize many dierent ➔ Patterns, trends and discrepancies: most but ➔ proteins with a wide range of functions. not all organisms assemble polypeptides from Every individual has a unique proteome. ➔ the same amino acids. amin ids nd pypptids Amino acids are linked together by condensation to form polypeptides. Polypeptides amino a acids process are the chains of amino condensation called Polypeptides they are by translation, are the only and other The condensation main which contain reaction that will component component. proteins acids reactions. Some two or are This be of made happens described proteins proteins by on in and contain linking together ribosomes sub-topic in many one by 2.7. proteins polypeptide more. involves the amine group ( NH ) of one amino 2 acid and the carboxyl group ( COOH) of another. Water is eliminated, as peptide bond carboxyl amino group group H H N C H 1 C OH H H condensation O H H O O O H (water removed) N C H R H C N OH R H C C N C C OH H R R O 2 ▲ Figure 1 Condensation joins two amino acids with a peptide bond 87 2 M O L E C U L A R B I O L O G Y in all condensation amino acids, of amino two consisting called of fewer rather many amino acids can even amino one with any humans longer with so titin is 35,213 A bond. by number are far is is of a is a molecule the 34,350 is the two consisting is a molecule bonds. acids, to protein and between polypeptide referred which of A formed amino small acids chain is peptide usually titin, amino bond dipeptide linked amino a new peptide Insulin 21 discovered a acids polypeptides. polypeptide In contain 20 a bond. by polypeptides, muscle. peptide linked than than a and acids Polypeptides of reactions, amino contains with of chains oligopeptides that other part though as the 30. two The largest structure acids, but in of mice it is acids. Dwing pptid bnds Draw molecular diagrams to show the formation of a peptide bond. To a form a dipeptide, condensation of one other. amino This is two reaction acid and shown amino between the in acids the carboxyl gure are linked amine group ● by There group of the with peptide group at the showing showing bond amino how the is the acid same, carries. peptide formation chain of forming a atoms the repeating linked backbone sequence by of of single the N covalent oligopeptide, C C 1. ● The is bonds whatever To bonds test are of a in gure R your bond hydrogen to skill formed, peptide A each an try atom nitrogen oxygen one of the The amine linked atom atom two is is in the linked carbon by by a single bond backbone a double and bond to atoms. between ● ( NH ) and carboxyl ( COOH) 2 two of the amino acids 2. There are groups sixteen possible dipeptides that can be these four amino could amino also acids, try to linked draw by an three oligopeptide peptide of bonds. four and this correctly, you only should see these If These terminals in forming the peptide remain at the ends of the of are called the the amino and carboxyl chain. you ● do up acids. chain. You used produced bond from are The R groups of each amino acid remain and features: project outwards from the backbone. COOH OH H H N H C H C COOH H H 2 N H C H C COOH H N H C COOH H N C glutamic acid COOH 2 H H H serine H C 2 2 H ▲ H H C alanine glycine Figure 2 Some common amino acids Th divsity f min ids There are twenty dierent amino acids in polypeptides synthesized on ribosomes. The amino acids polypeptides in the group centre and group, 88 all a of that have the are is atom. different in together identical molecule hydrogen which linked some is bonded The each by ribosomes structural to carbon amino an amine atom acid. to features: is a make carbon group, also a bonded atom carboxyl to an R 2 . 4 Twenty different polypeptides. forming give a the the these of peptide to the Some and use proteins it between the The by the R ribosomes carboxyl it of the repertoire of R table is their 1. wide It is groups, to make groups of twenty used up acids to try that amino in that allows proteins. necessary remember the are amino range not important R to groups groups amazingly in but used and is an shown differences very so character. are differences chemically are groups bond, its make differences specic acids amine polypeptide organisms of amino The P r o t e i n s living Some to learn because acids are diverse. contain amino acids that are not in the basic repertoire av of twenty. In most cases this is due to one of the twenty being modied s v after a polypeptide modication provide walls. at of tensile been amino acids strength Collagen many has in in hydroxyproline, but at which collagen, tendons, polypeptides positions, synthesized. made some makes of a by is an structural ligaments, skin ribosomes these the There protein and more it is of used blood contain positions collagen example to Ascorbic acid (vitamin C) is vessel needed to conver t proline proline converted into hydroxyproline, so to ascorbic acid deciency stable. leads to abnormal collagen production. From your Eleven R groups are hydrophilic Nine R groups are hydrophobic knowledge of the role of with between zero and nine collagen, what eects do Seven R groups can become charged carbon atoms Four you expect this to have? hydrophilic Four R groups act as Three R groups act as an acid by giving up a a base by accepting a proton and becoming proton and becoming negatively charged positively charged Test your predictions by Three R Six R groups R groups are groups contain do not contain polar but never rings rings charged researching the symptoms of ascorbic acid deciency (scurvy). ▲ T able 1 Classication of amino acids amin ids nd igins Patterns, trends and discrepancies: most but not all organisms assemble polypeptides from the same amino acids. It is a remarkable proteins cases using amino fact the acids that same are most 20 organisms amino modied acids. after a In make will always some and do been synthesized, but the initial process together amino acids on All life has ribosomes bonds usually involves the same of for to it. exclude chance. Several the possibility There must hypotheses be that one have this or been trend more is by acids, reasons These by of 20 amino chemical life, so all continued have They been acids processes were on organisms to use used, them. if they the Earth used produced before them Other had ones and amino been the origin have acids might available. are way that ribosomes, are the ideal 20 amino wide range of proteins, so to change by new acids for natural is a it single 20 ancestral amino acids. polypeptides is difcult the for repertoire removing are any existing of amino ones or ones. complicated commonly been found normally (stop signal acid. code for science encountered. that codons) amino use the to For one end encode of of example, the discrepancies species three extra some and have codons polypeptide an selenocysteine and Some that synthesis non-standard species some use use UGA UAG to making code a a these proposed: to ● from used the either adding Biology ● acids. acids. can due them 20 organism We amino use with made amino evolved which Because peptide other that of species, linking use organisms polypeptide ● has not favour for pyrrolysine. selection 89 2 M O L E C U L A R B I O L O G Y d- q: Commonality of amino acids 1 a) Discuss 20 which amino of acids the by three most hypotheses organisms is for use of supported the by same the evidence. b) 2 Suggest Cell walls of of these Also, whereas ▲ of testing bacteria that Some 20. ways of compound [3] contain contains amino some the 20 of one them are are acids the hypotheses. peptidoglycan, sugars acids amino of and short different into complex chains from right-handed made a [2] of the carbon amino usual forms of polypeptides acids. repertoire amino are acids, always the Figure 3 Kohoutek Comet – 26 dierent left-handed forms. Discuss whether this is a signicant discrepancy amino acids were found in an articial comet that falsies the theory that living organisms all make polypeptides produced by researchers at the Institut using the same 20 amino acids. [5] d’Astrophysique Spatiale (CNRS/France), which suggests that amino acids used by the rst living organisms on Earth may have come from space Pypptid divsity Amino acids can be linked together in any sequence av giving a huge range of possible polypeptides. cg ppp v Ribosomes fully nm nm p m m q amino The link formed. acids, number amino The so of acids together ribosome any can sequence possible of amino one make amino acid at a time, peptide acids until bonds is sequences a polypeptide between any pair is of possible. can be calculated starting with dipeptides (table 2). Both amino acids in a dipeptide can be any 1 1 20 2 20 of the twenty so there are twenty times twenty possible sequences 2 (20 2 3 ). There are 20 × 20 × 20 possible tripeptide sequences (20 ). For 400 n apolypeptide 3 of n amino acids there are 20 possible sequences. 8,000 The number of amino acids in a polypeptide can be anything from 20 to 4 tens of thousands. one example, if a polypeptide has 400 amino 400 6 20 Taking 64 million acids, there bogglingly are 20 large possible number and amino some acid sequences. online This calculators is a simply mind- express it as 10.24 trillion innity. ▲ T able 2 Calculate the missing values acids, If the we add all number is the possible effectively sequences for other numbers of amino innite. Gns nd pypptids The amino acid sequence of polypeptides is coded for by genes. The number immense, these. Even different The in Some acid ▲ amino living so, a base acid genes have of and of other a sequences cell a of only that store each could actually produces must sequence sequence sequence acid organisms typical sequences amino the of but be polypeptides the produced produce is small with information polypeptide a thousands needed stored is fraction in a to do coded of of this. form gene. roles, but polypeptide. most They genes use the in a cell genetic store code the to amino do this. Figure 4 Lysozyme with nitrogen of amine groups shown blue, oxygen red and sulphur yellow. The active site is the cleft upper left Three the bases the polypeptide. require 90 of a gene gene In are theory with a needed a to code polypeptide sequence of 1,200 for with each 400 bases. In amino amino acid acids practice in should genes are 2 . 4 always longer, also at certain The base sequence molecular extra in as frames base the that biologists openreading ofa with points sequences only both ends and sometimes middle. actually the at P r o t e i n s codes open for reading occupy a a polypeptide frame. small One is known puzzle proportion of the is to that total DNA species. Ptins nd pypptids A protein may consist of a single polypeptide or more than one polypeptide linked together. Some or proteins more are single polypeptides polypeptides, linked but others are composed of two together. ▲ Figure 5 Integrin embedded in a membrane (grey) shown folded and inactive and open Integrin is a membrane protein with two polypeptides, each of which with binding sites inside and outside the cell has a hydrophobic portion embedded in the membrane. Rather like the indicated (red and purple) blade and adjacent to Collagen a handle three a folding other consists rope-like the each of of or can three molecule. the unfold long This polypeptides knife and polypeptides move polypeptides structure would two if has they apart wound greater were can when it is together tensile separate. either working. to strength The be form than av winding Molecular biologists are allows a small amount of stretching, reducing the chance of the investigating the numbers of molecule breaking. open reading frames in selected Hemoglobin structures. more consists The four effectively to of four parts of tissues polypeptides hemoglobin that need it with associated interact than if to they non-polypeptide transport were oxygen species for each of the major groups of living organism. It is still far from cer tain how many separate. genes in each species code for a polypeptide that the organism nm exmp bkg actually uses, but we can ppp compare current best estimates: Enzyme in secretions such as nasal mucus and 1 lysozyme tears; it kills some bacteria by digesting the • Drosophila melanogaster, the fruit y, has base peptidoglycan in their cell walls. sequences for about 14,000 Membrane protein used to make connections 2 polypeptides. integrin between structures inside and outside a cell. • Caenorhabditis elegans, a Structural protein in tendons, ligaments, skin nematode worm with less 3 collagen and blood vessel walls; it provides high tensile than a thousand cells, has strength, with limited stretching. about 19,000. Transpor t protein in red blood cells; it binds • 4 hemoglobin Homo sapiens has base oxygen in the lungs and releases it in tissues with sequences for about 23,000 a reduced oxygen concentration. dierent polypeptides. ▲ T able 3 Example of proteins with dierent numbers of polypeptides • Arabidopsis thaliana, a small plant widely used in research, has about 27,000. Ptin nfmtins Can you nd any species with The amino acid sequence determines the three-dimensional greater or lesser numbers of conformation of a protein. The conformation conformation and its is of a protein determined constituent open reading frames than these? is by its the polypeptides. three-dimensional amino Fibrous acid structure. sequence proteins such of as a The protein collagen 91 2 M O L E C U L A R B I O L O G Y are elongated, globular, or with usually an with intricate a repeating shape that structure. often Many includes proteins parts that are are helical sheet-like. Amino acids always added globular to R added in the proteins develop the are the groups the nal of the one same by one, to sequence polypeptides acids a make This that is polypeptide. a gradually conformation. amino form to particular fold up stabilized have been as They they by are polypeptide. are bonds brought In made, between together by thefolding. In globular Rgroups ▲ proteins on the that outside are of soluble the in water, molecule and there there are are hydrophilic usually Figure 6 Lysozyme, showing how a polypeptide hydrophobic groups on the inside. In globular membrane proteins there can be folded up to form a globular protein. are regions with hydrophobic R groups on the outside of the molecule, Three sections that are wound to form a helix which are attracted to the hydrophobic centre of the membrane. are shown red and a section that forms a sheet is shown yellow. Other parts of the polypeptide In brous proteins the amino acid sequence prevents folding up and including both of its ends are green ensures that the chain of amino acids remains in an elongated form. Dnttin f ptins Denaturation of proteins by heat or pH extremes. The is three-dimensional stabilized groups of of these weak bonds in protein, bonds amino and results by a acids and they which is interactions within the interactions can change conformation or be to the called proteins molecule. are disrupted of between or Most conformation of As This of the protein the denatured protein does not normally its former structure– the denaturation Soluble the form hydrophobic molecule by and proteins the Heat often cause vibrations break in in microorganisms that or water are near not higher. was National of this the it that Park. at heat live are is due centre the new ionic ionic water exceptions: and bonds to on R within form. structure that become contents normally acidic, with a pH as is the optimum pH for the of have insoluble. the low as stomach 1.5, but protein-digesting of water pepsin that works in the stomach. to the around best It in used causes lower it interactions. vents Some springs have example aquaticus , springs at causes can volcanic best in or that 80 is a in °C or in proteins temperatures hot works heat much by known Thermus widely because of 80 °C DNA prokaryote Yellowstone and because biotechnology. denaturation temperatures. of most ▲ Figure 7 When eggs are heated, proteins that were dissolved in both the white and the yolk are denatured. They become insoluble so both yolk and white solidify 92 bonds proteins often the can charges three-dimensional altered in alkaline, become This tolerance. in geothermal from Nevertheless, proteins bonds their discovered is to molecule denatured The polymerase that exposed the denaturation within vary in is and because breaking causing the is conformation. intermolecular Proteins hot precipitate. groups becoming change can R a or protein enzyme insoluble changed, heat, acidic This is this permanent. both return are to pH, dissolved There A are with been denaturation. of denaturation. groups the relatively broken. Extremes cause R 2 . 4 P r o t e i n s Ptin fntins av Living organisms synthesize many dierent proteins with d xpm a wide range of functions. A solution of egg albumen Other none to groups can the of compare worker functions carbon bees listed compounds with the that here versatility perform are have carried of almost out by important proteins. all the roles They tasks in in the can a be hive. cell, but compared All of the proteins. in a test tube can be heated in a water bath to nd the temperature at which it denatures. The eects of pH can be investigated by adding ● Catalysis – there are thousands of different enzymes to catalyse acids and alkalis to test tubes specic chemical reactions within the cell or outside it. of egg albumen solution. ● Muscle contraction musclecontractions – actin used in and myosin locomotion together and cause transport the To quantify the extent of around denaturation, a colorimeter thebody. can be used as denatured albumen absorbs more light ● Cytoskeletons – tubulin is the subunit of microtubules than dissolved albumen. that giveanimals cells their shape and pull on chromosomes duringmitosis. ● Tensile needed strengthening in skin, – tendons, brous proteins ligaments and give blood tensile vessel strength walls. av ● Blood clotting – plasma proteins act as clotting factors that cause bx blood to turn from a liquid to a gel in wounds. Botox is a neurotoxin ● Transport of nutrients and gases – proteins in blood help obtained from Clostridium transport oxygen, carbon dioxide, iron and lipids. botulinum bacteria. ● Cell adhesion – membrane proteins cause adjacent animal cells 1 tostick to each other within What are the reasons tissues. for injecting it into ● Membrane transport facilitateddiffusion and – membrane active proteins transport, and are also used for humans? for electron 2 transport during cell respiration and What is the reason for photosynthesis. Clostridium botulinum ● Hormones – some buthormones are such as insulin, chemically very FSH and LH are producing it? proteins, diverse. 3 ● Receptors hormones, – ● sites light and chromosomes make There are huge insulinfor this treating as Increasingly, microscopic it is eye the of to are most is still genetically protein for not and during uses to modied and injecting it rather than for taking it orally? also group with DNA in eukaryotes mitosis. of proteins, as cells can antibodies. for proteins antibodies treating cytoplasm smells, associated for Pharmaceutical easy and plants. diverse different diabetics. in condense monoclonal proteins tastes and biotechnological stains, different expensive, membranes histones numbers many forremoving many – – the of Immunity DNA in Packing help in neurotransmitters, receptorsfor ● binding What are the reasons for diseases. synthesize organisms including pregnancy companies These tend proteins are enzymes tests now to or produce be very articially. being used as factories. 93 2 M O L E C U L A R B I O L O G Y exmps f ptins Rubisco, insulin, immunoglobulins, rhodopsin, collagen and spider silk as examples of the range of protein functions. Six proteins which illustrate some of the functions of proteins are described r in table 4. i This name is an abbreviation for ribulose bisphosphate This hormone is produced as a signal to many cells in carboxylase, which is arguably the most impor tant the body to absorb glucose and help reduce the glucose enzyme in the world. The shape and chemical proper ties concentration of the blood. These cells have a receptor of its active site allow it to catalyse the reaction that xes for insulin in their cell membrane to which the hormone carbon dioxide from the atmosphere, which provides binds reversibly. The shape and chemical proper ties of the source of carbon from which all carbon compounds the insulin molecule correspond precisely to the binding needed by living organisms can be produced. It is site on the receptor, so insulin binds to it, but not other present at high concentrations in leaves and so is molecules. Insulin is secreted by β cells in the pancreas probably the most abundant of all proteins on Ear th. and is transpor ted by the blood. immg rp These proteins are also known as antibodies. They have Vision depends on pigments that absorb light. One of sites at the tips of their two arms that bind to antigens these pigments is rhodopsin, a membrane protein of rod on bacteria or other pathogens. The other par ts of the cells of the retina. Rhodopsin consists of a light sensitive immunoglobulin cause a response, such as acting as a retinal molecule, not made of amino acids, surrounded marker to phagocytes that can engulf the pathogen. The by an opsin polypeptide. When the retinal molecule binding sites are hypervariable. The body can produce absorbs a single photon of light, it changes shape. This a huge range of immunoglobulins, each with a dierent causes a change to the opsin, which leads to the rod cell type of binding site. This is the basis of specic immunity sending a nerve impulse to the brain. Even very low light to disease. intensities can be detected. cg sp k There are a number of dierent forms of collagen but all Dierent types of silk with dierent functions are are rope-like proteins made of three polypeptides wound produced by spiders. Dragline silk is stronger than steel together. About a quar ter of all protein in the human body and tougher than Kevlar™. It is used to make the spokes is collagen – it is more abundant than any other protein. of spiders’ webs and the lifelines on which spiders It forms a mesh of bres in skin and in blood vessel suspend themselves. When rst made it contains walls that resists tearing. Bundles of parallel collagen regions where the polypeptide forms parallel arrays. molecules give ligaments and blood vessel walls their Other regions seem like a disordered tangle, but when immense strength. It forms par t of the structure of teeth the silk is stretched they gradually extend, making the and bones, helping to prevent cracks and fractures. silk extensible and very resistant to breaking. Ptms Every individual has a unique proteome. A proteome organism. an organism. mixtures 94 is By of all of the contrast, To nd proteins proteins the out are produced genome how is many extracted all of by different from a a the cell, a genes tissue of proteins sample and a are are or cell, an a being then tissue or produced, separated 2 . 4 by gel electrophoresis. present, marker antibodies can Whereas because in a on the cell’s a unique, us has become ▲ but partly exception of an in of a identify protein the of cells the species differences If cell an in The there are the identical different of amino unique not what strong differences acid twins, none proteome. with of Even the vary in us the activity the variable Even is actually happen. of all individual also because With of is depending proteome identical proteome is what each proteins. have time but protein uorescent present. could of a proteins. reveals proteome of is to proteome over potentially sequence particular different therefore of a linked protein xed, make similarities The not been the made proteome differences. because is organism are or have uoresces, that organism, also whether that organism an proteins activities. in individuals, To the genome cell happening Within used. different single the be to P r o t e i n s the small possible proteins, identical is of so each twins can age. Figure 8 Proteins from a nematode worm have been separated by gel electrophoresis. Each spot on the gel is a dierent protein av av : gm pm We might expect the proteome of an organism to be smaller than its genome, as some genes do not code for polypeptides. In fact the proteome is larger. How could an organism produce more proteins than the number of genes that its genome contains? 95 2 M O L E C U L A R B I O L O G Y 2.5 e m undstnding appitins ➔ Enzymes have an active site to which specic Methods of production of lactose-free milk and ➔ substrates bind. its advantages. ➔ Enzyme catalysis involves molecular motion and the collision of substrates with the active site. ➔ Temperature, pH and substrate concentration aect the rate of activity of enzymes. ➔ Enzymes can be denatured. ➔ Immobilized enzymes are widely used in industry. Nt f sin ➔ Skis Experimental design: accurate quantitative Design of experiments to test the eect of ➔ measurements in enzyme experiments require temperature, pH and substrate concentration replicates to ensure reliability. on the activity of enzymes. Experimental investigation of a factor aecting ➔ enzyme activity. (Practical 3) ativ sits nd nzyms Enzymes have an active site to which specic substrates bind Enzymes are chemical reactions called up biological biochemical products an globular in proteins without catalysts because reactions. these The reactions enzyme-catalysed that being as they called catalysts – themselves. are substances are reaction work altered made that by they living enzymes substrates. A speed Enzymes cells and convert general up are often speed into equation for is: enzyme ______ → substrate Enzymes to work literally only Figure 1 Computer-generated image of the reactions enzyme hexokinase, with a molecule of its This substrate glucose bound to the active site. The difference enzyme bonds a second substrate, phosphate, found take property metals all of living them. one place cells, is are in called Many and are produce different biochemical nearly all in and catalytic also and need are of some to needed, be It catalysts cells enzymes thousands specicity . non-biological by different enzymes which converters secreted many reaction of enzyme–substrate enzymes used cells organisms catalyse between that in Living thousands enzymes ▲ are outside. product – as of catalysed. is a signicant such as the vehicles. to the glucose, to make glucose phosphate To be able to mechanism 96 explain by enzyme–substrate which enzymes speed specicity, up reactions. we must This look involves at the the 2 . 5 substrate, enzyme or properties the substrates called of the substrate into to products then the active bind, while released, binding active site but they freeing site and not are the to a (see special gure the The substrate other to site the to on the shape match substances. bound active region 1). surface and each active catalyse site and another the chemical other. Substrates of e n z y M e s are the This allows converted products are reaction. d- q: Biosynthesis of glycogen The Nobel Gerty two Prize Cori and enzymes for her that Medicine husband convert was won Carl. in They glucose 1947 by glycogen. isolated phosphate of into ways, 4 Glycogen glucose called Curve B hadnot Explain why neededfor two the different synthesis enzymes of Describe b) Explain are and was a) Figure 2 Bonding in glycogen 1 1,4 a polysaccharide, bonded 1,6 together bonds obtained been noisrevnoc % ▲ is molecules (see using composed in two gure enzymes 2). that heat-treated. the the shape shape of of Curve Curve B. [2] B. 80 [2] B 60 glycogen 40 fromglucose 2 phosphate. The formation rate at which glucose of canbe linked on [2] side-branches to a increases phosphate growing 20 the molecules A 10 glycogen 20 30 40 50 min molecule. Explain the reason for this. [2] ▲ 3 Curve A was enzymes. obtained Explain the using shape heat-treated of curve Figure 3 shows the percentage conversion of glucose phosphate to glycogen by the two enzymes, over a A. [2] 50-minute period enzym tivity Enzyme catalysis involves molecular motion and the collision of substrates with the active site. Enzyme three The ● activity substrate have two While ● The site to is it. and we how With the to two of a reaction need by an enzyme. There are a substrate–active most reactions enzyme. can site of the different to the which the only enzyme. parts active are active bind together on a site of This road, about the Because bound from collision. think to the site, of site Some the they products leaving it enzymes active site. change of the vacant into reaction. for again. vehicles to are active bind substances, coming as the that separate bind molecule The known between to substrates products substrate close catalysis binds chemical substrates A the substrates the different ● is stages: but is in a active site if it molecule suggest that molecular substrates the substrate might collisions water to a a would motion high be in a moves and an velocity very active impact misleading liquids to image understand occur. are dissolved liquid state, in its water around molecules and all 97 2 M O L E C U L A R B I O L O G Y the particles dissolved in it are in contact with each other and are in toK continual motion. movement Each repeatedly particle changes can and move is separately. random, The which is direction the basis of of W k k m diffusion in liquids. Both substrates and enzymes with active sites are p able to move, though most substrate molecules are smaller than the - m? enzyme so their movement is faster. The lock and key model and the So, collisions between substrate molecules and the active site occur induced-t model were both developed because of random movements of both substrate and enzyme. The to help to explain enzyme activity. substrate may be at any angle to the active site when the collision Models like these are simplied occurs. Successful site correctly collisions are ones in which the substrate and active descriptions, which can be used to are aligned to allow binding to take place. make predictions. Scientists test these predictions, usually by performing experiments. If the results agree with the predictions, then the model is retained; if not then the model is water molecules modied or replaced. The German scientist Emil Fischer introduced the lock and key model in 1890. Daniel substrates Koshland suggested the induced-t model in 1959 in the United States. The conformational changes predicted by Koshland's model were subsequently observed using high-resolution X-ray analysis of enzymes and other newly active site developed techniques. Although much experimental evidence has part of enzyme accumulated conrming predictions ▲ Figure 4 Enzyme-substrate collisions. If random movements bring any of the substrate based on the induced-t model, it is molecules close to the active site with the correct orientation, the substrate can bind to the still just viewed as a model of enzyme active site activity. Fts ting nzym tivity Temperature, pH and substrate concentration aect the av rate of activity of enzymes. Mkg p Enzyme activity is aected by temperature in two ways Bacillus licheniformis lives ● In liquids, the particles are in continual random motion. When a liquid is in soil and on decomposing heated, the particles in it are given more kinetic energy . Both enzyme and feathers. What is the reason substrate molecules therefore move around faster at higher temperatures for it producing a protease and the chance of a substrate molecule colliding with the active site of the that works best at alkaline enzyme is increased. Enzyme activity therefore increases. pH? Make a hypothesis to explain the observations. ● When enzymes How could you test your the chance hypothesis? enzyme active to an enzyme typical 98 As rises the the has more are Figure has and shows changes, is called enzyme activity been for the vibrate When denatured, more reasons 5 enzyme enzyme been and the increased. enzyme enzyme there activity. of in is permanent denatured, when enzyme. is molecule reactions. temperature bonds breaking structure change become altogether, in the This heated, bonds enzyme catalyse solution are the break, site. When of is no of the longer in Eventually and able a it denatured. increases effects the including molecules falls. and in denaturation. it completely both more bonds stops So, as decreases temperature on a 2 . 5 e n z y M e s Enzymes are sensitive to pH rate at which reaction decreases owing to denaturation of enzyme molecules The pH The lower is due the the reducing solution ten times than pH used pH, at the measure more of the acid ion concentration. pH pH 7 by is and so one than A pH acidity the so pH makes pH 4 alkalinity alkaline the scale a solution 6, or less ions, The unit neutral. acidic or hydrogen the more 6, to presence hydrogen that A to is is is pH one a solution. solution the pH, 6 is ten hundred Acidity higher This times slightly is. the logarithmic. solution at a lower of acidic; times means more acidic. pH more noitcaer fo etar the scale 5 is acidic on. rate at which optimum reaction increases temperature owing to increased kinetic energy of substrate and enzyme molecules Most enzymes ha v e highest. If the pH enzyme activity an is op ti mum i ncr ea s e d or pH at wh ic h de c r e as e d th ei r fr om a c t ivi t y the is actual rate of o ptim u m , reaction the hydrogen d e cr e a s e s ion and ev en t ua ll y co nce ntr a ti on is h ig h e r s tops or al t og e t he r. l ower t ha n When t he le v el at 0 which the enzyme na tura l ly wor ks , the s tru c t u r e of t he enz ym e 10 20 30 40 50 60 is temperature/°C altered, of the including enzyme is the a cti ve s ite . ir r e v e rs ib ly Be y on d a lte re d. a T h is c e rt ai n is pH a n ot h er the s tru c t u r e ex am pl e ▲ of Figure 5 Temperature and enzyme activity denaturation. Enzymes a wide do not range. all This have the reflects same the pH wide optimum range of pH – in fact, there environments is Key in stomach which enzymes work. For example, the protease secreted by 1 Bacillus acidic hot springs licheniformis has a pH optimum between 9 and 10. This bacterium 2 is cultured to produce its alkaline-tolerant protease for use decaying plant matter in large intestine biological laundry detergents, which are alkaline. Figure 6 shows 3 small intestine the pH range of some of the places where enzymes work. Figure7 alkaline lakes 4 shows the neutral effects of pH on an enzyme that is adapted to work at pH. 5 6 Enzyme activity is aected by substrate concentration Enzymes site. This cannot catalyse happens reactions because of the until the random substrate movements binds of to the 7 active molecules in 8 liquids that result concentration will take place of in collisions substrates more is between substrates increased, frequently and the and active substrate–active rate at which site the sites. If the collisions 9 enzyme 10 catalyses its However, reaction there is increases. another trend that needs to substrate to be ▲ considered. an active After site, the the binding active site of is a occupied Figure 6 and Optimum pH at which enzyme unavailable to other substrate molecules until activity is fastest (pH 7 is products have been formed and released from the optimum for most enzymes). active more any site. and As the more moment. A substrate of the concentration active greater and sites are greater rises, occupied proportion at As pH increases or decreases from the of optimum, enzyme activity is reduced. For this reason, enzymes as If and increases concentration enzyme but is is in therefore the rate smaller at and blocked. which smaller rises. substrate plotted seen never are get between activity curve steeply, collisions reactions relationship distinctive less the catalyse substrate the site ytivitca emyzne substrate–active on (gure quite a 8), site is altered so the substrate does not t so well. Most enzymes are denatured by very high or low pH, so the enzyme no longer catalyses the reaction. concentration graph, rising reaching This is because the shape of the active a a less pH and maximum. ▲ Figure 7 pH and enzyme activity 99 2 M O L E C U L A R B I O L O G Y Dnttin Enzymes can be denatured. Enzymes are ytivitca emyzne irreversibly and both When high an can normally no like certain has been longer catalyses that and by temperatures enzyme substrate enzymes proteins, altered were does and proteins either or if its occur. dissolved in the In to or low the many structure process active binds, water their This high denatured, bind, not other conditions. is pH site can is cases be cause altered reaction become can denaturation that so the denaturation insoluble it. the enzyme causes and form a precipitate. substrate concentration ▲ Figure 8 The eect of substrate concentration on enzyme activity Qntittiv xpimnts Experimental design: accurate quantitative measurements in enzyme experiments require replicates to ensure reliability. Our on understanding evidence from evidence these designed and of enzyme activity experiments. experiments To must is be ● based obtain strong science ● the results of quantitative, some the basic just close be to accurate, the true which value; in and the experiment the replicate should be repeated, so that principles: experiment not should means carefully ● follow measurements should how be reliable results they can be compared to assess are. descriptive; d- q: Digesting jello cubes Figure 9 shows investigate apparatus that can be used to a) describing proteindigestion. cubes b) tube is taking whether colourless a sample the or of a the solution shade of around pink solution or the red and tight-tting lid measuring c) nding the electronic 2 If method would protease in a solution be its (c) absorbance mass of the in a cubes colorimeter using an balance. was [3] chosen, discuss whether it better gelatine cubes to nd the mass of all of the cubes of jello with known pH ▲ or the of the cubes are made from sugar-free jello If mass the the colouring that they contain will jello The as questions avoured 100 the jello protein below with whether the of digested assume red Explain rate is gradually colouring these protein that by one separately. have a mass of [2] it is accurate 0.5 enough grams, to be their mass to: protease. a) the nearest gram (g) b) the nearest milligram c) the nearest microgram strawberry- has methods digestion the cubes whether measure released each (jelly), state 1 nd Figure 9 Tube used to investigate the rate of digestion of gelatine 3 If together, are of been used! assessing acceptable: (mg) (µg). [3] 2 . 5 4 To obtain thejello accurate cubes, themfrom the it mass is measurements necessaryto tube and dry of 7 Draw a 8 Describe that there are no their the tube adhering. drying the surface drips of Explain of the 1 gives sugar-free the results jellocubes that the and a the Discuss the 5 from Discuss the esh whether of the Most of extract called the after this used to results protease ran out, obtain results were in table obtained one second more 1 Deduce which usingthe using pineapple, pineapple protease b) Suggest results second how the extractcould and [3] conclusions that can abouttheprecise be drawn optimum papain. [2] M (mg) for use were have of 80 87 77 3 122 127 131 an 4 163 166 164 5 171 182 177 6 215 210 213 7 167 163 84 8 157 157 77 9 142 146 73 but was in the obtained extract. use 2 are experiment. a) pH freshpineapples. from a between papain, [2] of [5] using reliable. 6 relationship data ph extracted table. [2] obtained protease the reason blocks. were in solution pHof Table results activity. fromthis for the surface 9 from of remove papain toensure graph e n z y M e s [1] a second affectedthe results. [2] ▲ T able 1 Dsigning nzym xpimnts Design of experiments to test the eect of temperature, pH and substrate concentration on the activity of enzymes. 1 The factor that independent ● you you with substrate a going variable. how obtain are are going You to investigate need vary it, with and the dilute to is clock the you ● example would to get what the units should be used independentvariable, temperature is for for lower ● measuring example measuredindegrees what range variable, levels 2 The fast need for includingthe and variable the you the that enzyme number you the and iscatalysing to the would be colour change; how variable. You many Other how the you are choice device, for of going to meter nd example an other be used variable, than for for for example minutes or measuring repeats you measuring need a hours rapid to get reliable that could variables. affect You need the to dependent are decide: ● what ● how ● what all the out each control of them variables can be are; kept constant; how is level they should be kept at, for the temperature should be kept at todecide: measure or time results. factors control the ● the levels. reaction need used measure change; should rather example dependent colour to lowest ofintermediate measure used Celsius; independent highest a be dependent enough 3 ● for units seconds concentrations; ● what the highest it could taken decide: for concentration solution concentration to it, including measuring electronic optimum investigated, enzymes for but should the enzyme factors be kept that at a if pH might is being inhibit minimum level. stop 101 2 M O L E C U L A R B I O L O G Y enzym xpimnts Experimental investigation of a factor aecting enzyme activity. There The are many method investigate worthwhile that the follows effect of enzyme can be used substrate constant experiments. concentration activity of investigating the effect of [2] on 4 the if substrateconcentration. to Predict whether the enzyme activity will catalase. change more if substrateconcentration is 3 Catalase It a is one catalyses toxic the of the most conversion by-product of widespread of hydrogen metabolism, into increased enzymes. peroxide, water by The apparatus shown in gure 10 same can to investigate the activity of catalase in Explain experiment could be repeated using the of yeast, but different concentrations. Another would concentrations in be to other assess cell isdecreased [2] tissues such as liver must be in before investigating catalase them. [2] goggles must Care be worn should be if this taken experiment not to get possible the types, it amount. why performed. hydrogen investigation if hydrogen is peroxide or same Safety concentration dm yeast. activity The mol be macerated used 0.2 and 5 oxygen. the by peroxide on the skin. catalase such as liver, oxygen kidney have at to the or germinating be macerated same seeds. and concentration These then as tissues mixed the would with water yeast. measuring cylinder yeast 1 Describe how the activity of the three-way tap enzyme water catalase could apparatus 2 Explain be be shown why a thoroughly measured in yeast gure using 10. suspension stirredbefore the a [2] must sample always of it is water 3 0.8 mol dm taken for use in an experiment. [2] hydrogen peroxide 3 State two factors, concentration, apart that from should enzyme bekept ▲ ▲ 102 Figure 11 Enzyme experiment Figure 10 Apparatus for measuring catalase activity 2 . 5 e n z y M e s d- q: Designing an experiment to nd the eect of temperature on lipase. Lipase converts therefore can be fats causes used to a into fatty decrease measure acids in the pH. and This activity of glycerol. pH 2 It a) Explain 12 shows suitable you would variable measure the accurately. [2] lipase. b) Figure how dependent change State the units for measuring the apparatus. dependent c) tube contents mixed when both Explain variable. the need [1] for at least three have reached target temperature replicate in this results for eachtemperature experiment. [2] thermometer 3 a) List the kept b) Explain be c) Suggest controlled sodium carbonate (an alkali) water bath and phenolphthalein a these suitable being lipids this that must be experiment. control [3] factors can [2] level for each factor. reasons milk milk mixed with factors in constant. Suggest a) lipase thermostatically how kept control 4 control constant in for: used this vegetable [3] to provide a source experimentrather of than oil. [1] (a pH indicator) b) ▲ the thermometer being placed in the Figure 12 Apparatus for investigating the activity of lipase tube Phenolphthalein but 7. becomes The used time to is pink colourless taken measure temperatures. for the in alkaline when this the colour activity Alternatively, of pH drops change at to can c) be followed using a pH probe changes and smaller, the substrate enzyme, different the larger, volume of rather than liquid [1] being rather added than the to the enzyme to substrate. [1] could 5 be the the conditions, lipase pH containing Sketch the shape of graph that you would data-logging expect from this experiment, with a software. temperature 1 a) State the independent experiment b) State the and units independent variable howyou for in would measuring this vary the it. [2] to the 6 variable. [1] State an appropriate range for and time colour 0 taken on the for whether expected to have from the to 80 the °C on indicator y-axis. germinatingcastor from lipase °C or [2] human oil seeds higher pancreas would optimum the temperature. independent from Explain be c) x-axis change range variable. [2] [2] Immbiizd nzyms Immobilized enzymes are widely used in industry. In 1897 extract the of alcohol. The processes Louis only Buchner yeast, door outside Pasteur occur if brothers, containing had was opened living cells yeast to the and Eduard, cells, use would of showed convert enzymes to that an sucrose catalyse into chemical cells. claimed living Hans no that were fermentation present. This of was sugars part of to alcohol the could theory of 103 2 M O L E C U L A R B I O L O G Y vitalism, which be under stated that substances in animals and plants can only toK made articial the synthesis inuence of urea, of a “vital described in spirit” or sub-topic “vital 2.1, force”. had The provided W w evidence against vitalism, but the Buchners’ research provided a clearer gm ? falsication of the theory. After the discovery in the 19th century More than 500 enzymes now have commercial uses. Figure 13 shows a of the conversion of sugar into alcohol classication of commercially useful enzymes. Some enzymes are used in by yeast, a dispute developed between more than one type of industry. two scientists, Justus von Liebig and Louis Pasteur. In 1860 Pasteur argued other industries 5% miscellaneous 4% that this process, called fermentation, agriculture 11% could not occur unless live yeast cells were present. Liebig claimed that the process was chemical and that living cells were not needed. Pasteur ’s medical 21% view reected the vitalistic dogma – that the substances in animals and biosensor 16% plants could only be made under the inuence of a “vital spirit” or “vital food & nutrition 23% force”. These contrasting views were as much inuenced by political and religious factors as by scientic biotechnology 46% evidence. The dispute was only resolved after the death of both men. In 1897 the Buchner brothers, Hans environment 13% and Eduard, showed that an extract of yeast, containing no yeast cells, did energy 3% indeed conver t sucrose into alcohol. The vitalistic dogma was over thrown ▲ Figure 13 and the door was opened to the use of enzymes to catalyse chemical The processes outside living cells. attachment so enzymes that doing them the movement this, in an aggregates Enzyme ● used of The in of including alginate of up to enzyme After being recycled, ● can 104 restricted. enzymes them to or into There a are glass together This to is aggregations, many surface, form ways of trapping enzyme several be advantages. separated reaction at from the the ideal products time and of the preventing products. from useful the cost reaction savings, mixture especially as the enzyme many may enzymes be are expensive. have to Substrates with the immobilized. material diameter. has the is the bonding mm retrieved giving temperature ● or usually another enzyme easily of Immobilization and gel, 0.1 stopping contamination very the are to attaching immobilization reaction, ● industry enzymes increases and be can dissolved pH, the stability reducing the of rate enzymes at which to changes they are in degraded replaced. be exposed enzymes, to higher speeding enzyme up concentrations reaction rates. than 2 . 6 s t r u c t u r e o f d n a a n d r n a lts-f mik Methods of production of lactose-free milk and its advantages. Lactose It can is be enzyme the sugar that converted lactase: into lactose is naturally glucose → present and glucose in galactose + milk. by ● the Lactose galactose. texture. are Lactase is obtained from Kluveromyces tends production type of yeast that Biotechnology extract it for the sale There lactase to are grows companies food from naturally culture the yeast manufacturing several reasons for crystallize ice soluble cream, glucose than during giving and lactose a the gritty galactose they remain lactis, in the and giving a smoother texture. milk. ● yeast, purify lactase Bacteria quickly companies. using to Because more dissolved, a of ferment than yoghurt and glucose lactose, cottage so and the cheese galactose production is more of faster. in Thailand food processing: South India ● Some people are lactose-intolerant and cannot Crete drink more than about 250 ml of milk per day, France unless it is lactose-reduced (see gure 14). Finland ● Galactose lactose, sweet and so less foods shakes or glucose sugar are containing fruit sweeter needs to milk, be than added such as Sweden to 0% milk 50% 100% lactose intolerance yoghurt. ▲ Figure 14 Rates of lactose intolerance 2.6 s dn a rn a undstnding appitins ➔ The nucleic acids DNA and RNA are polymers of ➔ Crick and Watson’s elucidation of the structure nucleotides. of DNA using model-making. ➔ DNA diers from RNA in the number of strands normally present, the base composition and the type of pentose. ➔ DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs. Nt f sin ➔ Using models as representation of the real Skis ➔ Drawing simple diagrams of the structure of world: Crick and Watson used model-making to single nucleotides and of DNA and RNA , using discover the structure of DNA . circles, pentagons and rectangles to represent phosphates, pentoses and bases. 105 2 M O L E C U L A R B I O L O G Y Ni ids nd ntids The nucleic acids DNA and RNA are polymers of nucleotides. Nucleic acids of hence cells, were rst their discovered name. There in material are two extracted types of from nucleic the acid: nuclei DNA O and O P RNA. linking 2 Nucleic together acids are very nucleotides to large form molecules a that are constructed by polymer. 5 O 1 O C C N Nucleotides consist of three parts: 4 ● a sugar, ● a phosphate OH OH nucleic ▲ has ve carbon atoms, so is a pentose sugar; group, acids; which is the acidic, negatively-charged part of and Figure 1 The par ts of a nucleotide ● a base atoms Figure and To 1 the sugar. of link the that in shows are Figure 2 A simpler representation of a together nucleotide them is shows a four in and along as a a has of either in one or two rings groups, of the base and This – phosphate the is for so can and base the The base pentose the base to used is ensures sugar. four to link therefore nucleic sequence backbone are of linked sugar key each there be are sugar molecule to sequence the bonds pentose linked RNA, phosphate information sugar a nucleotides molecule. the covalent and backbone Any to form. polymer, with DNA different nucleotide. RNA or together. bonds nucleotide strong both linked symbolic chain a are covalent one because genetic the in four every or a of they by creates bases The in and into phosphate DNA store and This sequence, same how linked phosphate different any the and nucleotide together the sugar and both nucleotide. information stable parts are nucleotides. are possible of 2 between different acting these nucleotides alternating nitrogen structure. phosphate next There contains its Figure formed ▲ which 2 3 is the that acids store the store secure. Dins btwn DNa nd rNa DNA diers from RNA in the number of strands normally present, the base composition and the type of pentose. HOH C OH O 2 There H H H are three 1 The sugar Figure OH sugar C 2 H H H two types of nucleic 3 within shows DNA that is deoxyribose deoxyribose has and one the sugar fewer in RNA is oxygenatom ribose. than The in full them names – of DNA and deoxyribonucleic RNA acid are and based on the ribonucleic type of acid. There are RNA. usually The two polymers polymers double-stranded and are RNA often of nucleotides is referred to as in DNA strands, but so only DNA one is single-stranded. OH 3 ▲ the H in OH between OH O 2 differences H ribose. HOH important acid: H The four bases in DNA ar e a de ni ne, cyt o si n e, gu a n in e and Figure 3 The sugar within DNA is thymine. The four bases in R NA a re ad eni n e, c yt o si n e, g ua ni n e deoxyribose (top) and the sugar in and uracil, so the RNA is ribose (bottom) thymine 106 in RNA. d i ff e r ence is tha t u r ac il is pr e se nt i n st e a d of 2 . 6 s t r u c t u r e o f d n a a n d r n a d- q: Charga’s data DNA samples analysed in by Edwin by others. from terms a of Chargaff, The data range their an is of species Austrian presented 3 were nucleotide biochemist, in Evaluate table the eukaryotes composition of and adenine and theamounts 1. claim and that in the DNA prokaryotesthe thymine of guanine are and of amount equal and cytosine areequal. 1 Compare the base Mycobacterium withthe shown 2 base composition tuberculosis in the table. Calculate the base humans Show and your (a composition for 4 prokaryote) of the Explain ofbases eukaryotes terms [2] ratio A+ G/T Mycobacterium + C, 5 for the in ratios the structure reasons thepolio between eukaryotes for basecomposition [2] Gp of Suggest tuberculosis . working. s dna [2] of of the amounts andprokaryotes of the in DNA. difference [2] in bacteriophage the T2 and virus. [2] a G c tm Human Mammal 31.0 19.1 18.4 31.5 Cattle Mammal 28.7 22.2 22.0 27.2 Salmon Fish 29.7 20.8 20.4 29.1 Sea urchin Inver tebrate 32.8 17.7 17.4 32.1 Wheat Plant 27.3 22.7 22.8 27.1 Yeast Fungus 31.3 18.7 17.1 32.9 Mycobacterium tuberculosis Bacterium 15.1 34.9 35.4 14.6 Bacteriophage T2 Virus 32.6 18.2 16.6 32.6 Polio virus Virus 30.4 25.4 19.5 0.0 ▲ T able 1 Dwing DNa nd rNa ms Drawing simple diagrams of the structure of single nucleotides and of DNA and RNA , using circles, pentagons and rectangles to represent phosphates, pentoses and bases. The structure using simple of ● circles ● pentagons ● rectangles Figure base 2 linked for to the C and for for for pentose molecules can be shown in diagrams subunits: the the sugar; bases. structure phosphate – RNA the phosphates; shows and DNA symbols are carbon of a nucleotide, linked atom on to the the using pentose right hand these sugar. side of symbols. The the base The is pentose 1 sugar. The phosphate is linked to C – the carbon atom on the side 5 ▲ Figure 4 Simplied diagram of RNA 107 2 M O L E C U L A R B I O L O G Y covalent bond P P chain these S A on the upper carbon left atoms side are of the shown in pentose gure sugar. The positions of 1. S T To show the structure of RNA, draw a polymer of nucleotides, with a P P line to show nucleotide the to covalent the bond pentose in linking the next the phosphate nucleotide. group The of each phosphate is S C S G linked to C of the pentose – the carbon atom that is on the lower left. 3 P P If you the have drawn polymer will the be structure different. of RNA They are correctly, referred the to as two the ends 3´ and of the 5´ S S A T terminals. ● P P The phosphate of another nucleotide could be linked to the C 3 atom of the 3´ terminal. S G S C ● The pentose phosphate P of of another the 5´ nucleotide could be linked to the terminal. P Hydrogen bonds are formed To show the structure of DNA, draw a strand of nucleotides, as with between two bases RNA, Key: then should – sugar S be a second run in strand the alongside opposite the direction, rst. so The that at second each P molecule, one strand has a C terminal and the other a C 3 A of the DNA terminal. The 5 C two – nitrogenous bases T G or strands names and ▲ strand end – phosphate are to linked indicate cytosine (C) by the only hydrogen bases. pairs bonds Adenine with between (A) guanine only the pairs bases. with Add letters thymine (T) (G). Figure 5 Simplied diagram of DNA 5 ´ end Stt f DNa 3 ´ end DNA is a double helix made of two antiparallel strands complementary S base pairs P S of nucleotides linked by hydrogen bonding between P A T S complementary base pairs. hydrogen P C S bonds Drawings of the structure of DNA on paper cannot show all features of P P the C three-dimensional structure of the molecule. Figure 6 represents S G S some of these features. P S A T S ● Each ● The two said to and the ● The two ● The strands strand consists of a chain of nucleotides linked by covalent bonds. P P S strands are parallel but run in opposite directions so they are P G S S P A T S antiparallel. other oriented strand in the P P T strands direction 3´ in to the direction 5´ to 3´ 5´. are wound together to form a double helix are held together by hydrogen P P bases. Adenine (A) is always paired between with the thymine sugar–phosphate (T) S and guanine (G) with cytosine (C). This is referred to as backbone P P C G complementary base pairing , meaning G that A and T complement S each other by forming base pairs each other by forming base pairs. and P S bonds S nitrogenous C S 3 ´ end P 5 ´ end 108 oriented S S ▲ is C S S is One S P G be Figure 6 The double helix similarly G and C complement 2 . 6 s t r u c t u r e o f d n a a n d r n a d- q: The bases in DNA Look at answer 1 the the State molecular following one theother 2 Each of atom left in this in gure 3 and the and between adenine 4 and to position, case nitrogen is in a DNA has hydrogen which in 7. when from its in in Deduce a 5 Guanine the [3] structure function how the is the bases each structure lower subunits. adenine of cytosine and [4] features, nucleotide between guanine. Although a the similarities thymine. nitrogen appears gure used a atom three Compare [1] bases each Identify questions. difference beingassembled ▲ 7 bases. bonded similar models one have has andshape. of bases DNA, each to a shared Remembering explain be some distinctive the chemical the importance distinctive. for [5] [2] Adenine Cytosine Thymine Figure 7 M mds Using models as representation of the real world: Crick and Watson used model-making to discover the structure of DNA. The word meaning plans, model showing dimensional impression Molecular but Models always they with what models what in science that are show in the not are of a building possible are a always They or a DNA, in but be to to a be more in theoretical which part took are in are three Crick two made attempts a help and do concepts to building us to not and feature be rejected and dimensions, is. common often Three- realistic whether models actually The modus, architects’ like. decide molecular be word constructed. give three-dimensional can science it Latin structure used processes. critical the originally would molecule proposals, models might future, of from were developed models systems played structure building proposed structures. architecture, the a derived Models then structure they Model-making of new also represent is a were reality the is method. architects’ propose can models how become discover English or models of whereas should in manner and Watson’s before of tested. As replaced. discovery they were successful. 109 2 M O L E C U L A R B I O L O G Y toK cik nd Wtsn’s mds f DNa stt W v Crick and Watson’s discovery of the structure of DNA mp p ? using model-making. Crick and Watson’s success in discovering the structure of DNA was Three prominent research groups based on using the evidence to develop possible structures for DNA openly competed to elucidate the and testing them by model-building. Their rst model consisted of a structure of DNA : Watson and Crick triple helix, with bases on the outside of the molecule and magnesium were working at Cambridge; Maurice holding the two strands together with ionic bonds to the phosphate Wilkins and Rosalind Franklin were groups on each strand. The helical structure and the spacing between working at Kings College of the subunits in the helix tted the X-ray diffraction pattern obtained by University of London; and Linus Rosalind Franklin. Pauling's research group was operating out of Caltech in the United States. A stereotype of scientists is that they take a dispassionate approach to investigation. The truth is that science is a social endeavour involving a number of emotion-inuenced interactions between science. In addition to the It was and be difcult it was enough strands. not of get all account the parts when magnesium Another take equals to rejected of Chargaff’s thymine this available deciency of of Franklin and the model pointed to this form rst nding amount to t out the cross model that of together that links was the there that equals not between is amount cytosine satisfactorily would that of it the did adenine the amount guanine. joy of discovery, scientists seek the To investigate the relationship between the bases in DNA pieces of esteem of their community. Within cardboard were cut out to represent their shapes. These showed that research groups, collaboration is A-T and C-G base pairs could be formed, with hydrogen bonds linking impor tant, but outside of their research the bases. The base pairs were equal in length so would t between group competition often restricts open two outer sugar-phosphate backbones. communication that might accelerate Another ash of insight was needed to make the parts of the to run the pace of scientic discovery. On the molecule t together: the two strands in the helix had in other hand, competition may motivate opposite directions – they must be antiparallel. Crick and Watson ambitious scientists to work tirelessly. were then DNA. able They together angles with constructed model just looked for DNA must ▲ Figure 8 Crick and Watson and their DNA model 110 right”. DNA. consist that 8 second and Bond shows model sheeting lengths Crick and of cut the to were structure shape all Watson to and scale with the of held and bond newly model. structure effects their rods clamps. Figure convinced copying code build metal small correct. The to used are all The It also of led triplets started still those who structure the quickly of saw to bases. great it. A immediately the In in comment suggested realization many molecular reverberating typical ways biology science and in a that the was “It mechanism the genetic discovery revolution, society. of with 2 . 7 d n a r e P l i c a t i o n , t r a n s c r i P t i o n a n d t r a n s l a t i o n 2.7 dn a p, p undstnding appitins ➔ The replication of DNA is semi-conser vative and ➔ Use of Taq DNA polymerase to produce multiple depends on complementary base pairing. copies of DNA rapidly by the polymerase chain ➔ Helicase unwinds the double helix and reaction (PCR). separates the two strands by breaking ➔ Production of human insulin in bacteria as an hydrogen bonds. example of the universality of the genetic code ➔ DNA polymerase links nucleotides together to allowing gene transfer between species. form a new strand, using the pre-existing strand as a template. Skis ➔ Transcription is the synthesis of mRNA ➔ copied from the DNA base sequences by RNA codon(s) corresponds to which amino acid. polymerase. ➔ Use a table of the genetic code to deduce which ➔ Translation is synthesis of polypeptides on Analysis of Meselson and Stahl’s results to obtain suppor t for the theory of semi- ribosomes. conser vative replication of DNA . ➔ The amino acid sequence of polypeptides is ➔ determined by mRNA according to the genetic Use a table of mRNA codons and their corresponding amino acids to deduce the code. sequence of amino acids coded by a shor t ➔ Codons of three bases on mRNA correspond to mRNA strand of known base sequence. one amino acid in a polypeptide. ➔ ➔ Deducing the DNA base sequence for the Translation depends on complementary mRNA strand. base pairing between codons on mRNA and anticodons on tRNA . Nt f sin ➔ Obtaining evidence for scientic theories: Meselson and Stahl obtained evidence for the semi-conser vative replication of DNA . Smi-nsvtiv pitin f DNa The replication of DNA is semi-conservative and depends on complementary base pairing. When a separate or cell template, formed by The result and a to gure for the adding is newly referred prepares (see two to 2). divide, these creation of a nucleotides, DNA being two of one strand. by strand. one, both For strands original new molecules, synthesized as the Each of The and double serves new linking composed this the strands reason, of an DNA helix as strands them a guide, are together. original strand replication is semi-conservative. 111 2 M O L E C U L A R B I O L O G Y The adenine base sequence the new strand. the next base on Only the a template nucleotide strand determines carrying a base the that is base sequence on complementary to thymine strand This is other, cytosine guanine to be that in guanine the because inserted, with the their the structure. hydrogen not another DNA base strand complementary would two template can successfully be added to the new 1). stabilizing nucleotide pairs on (gure is a bonding be added called to form hydrogen nucleotide between to the with bases chain. that the result parent from rule base DNA molecule bonds the with wrong would The complementary molecules sequences bases If not that occur one pairing. It replication that was each base started and base the always ensures are identical replicated. cytosine obtining vidn f th thy f smi- nsvtiv pitin thymine adenine Obtaining evidence for scientic theories: Meselson ▲ and Stahl obtained evidence for the semi-conservative Figure 1 replication of DNA. Semi-conservative replication seemed right, is an example of a scientic theory that Parental DNA with intuitively evidence. but Laboratories nonetheless around the needed world to be backed attempted to up conrm C experimentally C C A convincing replication evidence had been of DNA is semi-conservative and soon obtained. T In G that G G 1958 Matthew Meselson and Franklin Stahl published the results C of T exceedingly elegant experiments that provided very strong A 15 T A C evidence for semi-conservative replication. They used N, a rare G isotope of nitrogen that has one more neutron than the normal Replication fork A 14 T N G A G isotope, so methods T C of T In the stable C A T A T C denser. purifying 1930s C isotopes Harold that Urey could be had developed used as tracers in 15 biochemical T is C pathways. N was one of these. A A Meselson G and C Stahl devised a new method 15 containing of separating DNA 14 N in its bases from DNA with N. The technique is G C G called A T A caesium A gradient centrifugation. A solution T of caesium chloride spun in an ultracentrifuge at nearly 45,000 T revolutions G is T A per minute for 20 hours. The dense caesium ions tend sediment fully C C A density T A to move towards the bottom of the tube but do not T A T chloride A T because A T of diffusion. A gradient is established, with the greatest A G G Parental strand ▲ New strand New strand C caesium Parental strand Figure 2 Semi-conser vative replication concentration, the lowest at the caesium the top of chloride corresponding with Meselson Stahl and and the therefore tube. solution its density, Any at substance becomes the bottom centrifuged concentrated at a and with level density. cul tur ed the b act e r iu m E. coli for fourteen 15 generations Almost all in a me d i um nitrogen whe r e a to ms in the the o nl y b ase s of n i t ro ge n the DN A s ou r c e in the was N. b a c t e ri a 15 were therefore N. They then trans f e r r e d the b acte r ia abr u pt ly to a 14 medium to divided 112 in culture which them, and all the the ni tr og e n g e ne r atio n there f o r e r e pl ica te d was ti me N. wa s th e ir At 50 DN A the tempera tur e m i nu t e s on c e – e v e ry the 50 us e d b a c t e r ia m i n u t es . 2 . 7 Meselson culture and for Stahl severa l co l l ected ho ur s d n a r e P l i c a t i o n , s a mp l e s fr om the of tim e DNA t r a n s c r i P t i o n fr om whe n it the wa s a n d t r a n s l a t i o n b a c t e ri a l t r an s fe r re d av to nw xpm q 14 the N medium. They e x tr a cte d the DNA and m e a su r e d i ts de n s it y Meselson and Stahl used three by caesium chlori d e d e nsi ty g r ad ie n t ce n t r ifu ga t i on . Th e DNA techniques in their experiments could be detected b e ca use it a bs or bs u lt ra viol e t l ig ht , and so that that were relatively new. created a dark ban d w he n the tub es were il lu m in a t e d wi t h Identify a technique used by ultraviolet. Figure 3 s hows the r e sul ts. In th e ne xt pa r t of t h is them that was developed: sub-topic position there of the is g ui d a nce dar k in how to a n al yse the cha n g es in b a nd s. a) by Urey in the 1930s b) by Pickels in the 1940s c) by Meselson and Stahl themselves in the 1950s. av 0 0.3 0.7 1.0 1.5 2.0 2.5 3.0 4.0 Mg v generations To model helicase activity you ▲ Figure 3 could use some two-stranded rope or string and a split key ring. The strands in the rope are helical and represent the two strands in DNA. Open the key ring and put one Mssn nd Sth’s DNa pitin strand of the rope inside it. Close xpimnts the ring so that the other strand is outside. Slide the ring along the Analysis of Meselson and Stahl’s results to obtain suppor t string to separate the strands. for the theory of semi-conservative replication of DNA. What problems are revealed by this The data-based Meselson of and question Stahl’s below results will and guide help to you build through your the skills analysis in this model of the activity of helicase? of Use the internet to nd the solution aspect used by living organisms. science. d- q: The Meselson and Stahl experiment 14 In order for duplicated same to genetic process The cell of division ensurethat duplicating the occur, DNA progeny information Meselson–Stahl understand to as DNA is termed of be have theparent experiment mechanism cells must the cells. The replication. sought to replication. to in a conservative fashion, a N taken which medium. over density a Did Samples period gradient heavier inacentrifuge of of time the and centrifugation, molecules tube than settle bacteria by a in method further lighter were separated down ones. it 1 occur a The single band of DNA at the start semi-conservative -3 (0generations) fashion or in a dispersive fashion (see gure had a density of 1.724 g cm . 4)? The main had a band of DNA after four generations -3 Meselson and Stahl grew E. coli in a medium density of 1.710 g cm . Explain how 15 containing of “heavy” generations. nitrogen They then ( N) for transferred a number the bacteria DNA by with the a lower bacteria. density had been produced [2] 113 2 M O L E C U L A R 2 a) Estimate B I O L O G Y the density of the DNA after one generation. 6 Predict [2] the results mixtureofDNA of centrifuging from 0 a generations and 2generations. b) Explain one whether generation possible shown 3 a) density falsies mechanisms in Describe Explain gure the including b) the the DNA whether twogenerations three replication after the of two the results falsify any mechanisms generations, DNA. [3] after of the for DNA replication. 4 Explain the [3] results after three and four generations. 5 Figure (0 4 [2] after [3] density threepossible of DNA 4. results the any for of [2] shows generations) DNA and from after E. coli one at the start generation, 15 with strands of DNA containing N shown 14 red and Redraw strands either mechanism containing (a), that is (b) or N (c), shown green. choosing supported by the Meselson Dispersive and can Stahl’s be than be a red more experiment. shown helix and as and two the green. generations parallel colours Draw of Each the DNA lines do have for in Semi-conser vative Newly synthesized strand rather not DNA replication Conser vative molecule a Original template strand to two ▲ medium Figure 4 Three possible mechanisms for DNA replication 14 containing N. [3] His Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds. Before must of a DNA new enzymes in a that The use bonds donut shape. from the Double-stranded Helicase time it as energy from helicase The is DNA separates is the two act as carried ATP . The consists of the move of the between cannot be causes strands. split the by for molecule the required formation a group for of breaking bases. polypeptides with donut helicase bases into the helicases, is globular the of template energy assemble centre to bonds six strands a out complementary used therefore the each polypeptides through ATP occur, can separation hydrogen helical. can they between passing Energy breaking 114 that well-studied molecule it. so strand. hydrogen One replication separate along and two one and strand the the parting strands unwinding of the arranged of other DNA the the molecule, two while it helix at DNA outside stands. is still the same 2 . 7 d n a r e P l i c a t i o n , t r a n s c r i P t i o n a n d t r a n s l a t i o n DNa pyms DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template. Once helicase strands, for the formation carried DNA out the four of base brings but Each four the a making a new strand. group the is free DNA the It the have to the bond does this during the of the DNA acts the is template time. in Free the as new a into two template strands added has to the the base template where strand in nucleotides area where new that strand. base the is strand, can pair is each being only with the polymerase bonds pair same with DNA DNA hydrogen complementary so the base a the new the is the been is could form, formed, 3´ at polymerase moves of along sequence high the the and adds done of the on template delity into the the position bases, existing existing of is group complementary degree two This the terminal brought the strand. phosphate terminal very has between nucleotide DNA 3´ base formed of sugar the with correct end gradually a a the been of pentose with at between sugar to a split strands again. 5´terminal, strand along position and with nucleotide made the and two assembly available on helix the The nucleotide away the The the of into it polymerase new strand. are and are of polymerase. moves reached bonds links strand. DNA nucleotide happens covalent nucleotide a types double Each nucleotide bases time nucleotide polymerase new always one breaks hydrogen a the begin. enzyme position this nucleotide and of nucleotides unless Once can possible the at unwound the adding replicated. one by polymerase direction, of has replication DNA by the free end of the phosphate 5´terminal of strand. strand, to – the very assembling template few mistakes DNAreplication. Pcr – th pyms hin tin Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR). The polymerase technique used DNA sequence. DNA is into a needed PCR repeatedly DNA. This separated chain to Only at a the machine doubles two many very start. in (PCR) copies small The which the involves into reaction make a cycle of strands is a selected at of the loaded of the double-stranded single of a quantity DNA quantity is of one being stage high is cycle and single strands combining to DNA at another two strands hydrogen but in a in bonds. DNA DNA These molecule are are held weak there are at hold the by the cooled pair the most cells. the two strands strands again. If DNA is This is heated bonds separate. bonds together normally hydrogen hydrogen up two temperatures can called If to a eventually the form, DNA so the re-annealing. of PCR machine separates DNA strands by heating form to 95 °C for fteen seconds. It then cools stage. the The and strands them double-stranded they temperature, then The the so encountered break steps selected DNA them successfully together by interactions, large numbers DNA quickly annealing DNA. of to parent However, single-stranded a 54 °C. This strands large DNA to excess called would form of allow short primers re- double-stranded is sections present. of The 115 2 M O L E C U L A R primers large bind excess B I O L O G Y rapidly of re-annealing of single strands parent to primers the target is sequences present, parent then they strands. starts and Copying from as prevent the of strands. a of the 54 its the mixture primers. next stage in PCR is synthesis of DNA, using the single strands as templates. polymerase a is bacterium, including those °C. of Enzymes denature at of do aquaticus, to springs most high adapted It Yellowstone in Thermus enzyme this. aquaticus, these such be The to Thermus temperatures 80 used found organisms its heat-stable in National range hot this the DNA brief polymerase period at 95 is used °C 50 would but of to a very enough DNA it lower the 72 to temperature primers, °C. The this but reaction temperature polymerase adds rapid of by a the it can base is about rate of the of a help base be is 1,000 DNA elapsed cycles, Taq of by which DNA sequence be heating take huge for to completed billion, of production has sequence started can Thirty factor With are denaturation. separate cycle PCR minutes. of time selected next cycle to rapidly those the the The °C polymerase, resist because used is heated Taq temperature selected Taq when the attach temperature therefore minute, When from springs, Park. from DNA to at to for working. nucleotides replication. DNA obtained temperatures, including very Taq was work used with per primers is period is doubleAt stranded would that optimum the The It °C in to 95 less than the an polymerase, a of very °C. than amplify less numbers in replication complete, DNA hour. PCR copies short A two allows of a time. resist the DNA Select the DNA sequence to be copied Twice as many DNA Raise temperature 15 seconds Lower temperature 80 seconds 25 seconds Raise temperature to 72°C to allow rapid DNA replication by T aq DNA polymerase ▲ Figure 5 ▲ Figure 6 Tnsiptin Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase. This sequence characteristic sequence often of using the is strands ● 116 or Two base Transcription RNA in is acids DNA. enzyme of gene. in indirectly processes the gene a What RNA not, a RNA, transcription follows is to The an polymerase give most produce rst of using to DNA of a It is is as observable to specify proteins is a the that characteristics specic these occurs outline a any genes observable only binds itself, of polypeptide. the needed gene. of in function particular are of does The determine synthesis single-stranded, of a organism. sequence The a bases an amino directly individual. of in of an polypeptide, transcription. template. along one of Because the two transcription: site on the DNA at the start 2 . 7 RNA ● polymerase strands and on strand one a of in ● RNA polymerase ● The ● Transcription molecule The product that is base base separates is stops of uracil in sense strand is the a the gene is fashion no bonds of the with DNA into in RNA, so a n d t r a n s l a t i o n single complementary bases uracil adenine. between and t r a n s c r i P t i o n separating thymine with DNA end to the of DNA the gene molecule template to of strand strand. the a the thymine. strand complementary called is identical one is has is place of The called There the transcription that sequence at the nucleotides covalent from r e P l i c a t i o n , the double and RNA helix the nucleotides. reforms. completed RNA released. transcribed. and DNA. forms complementary is along RNA complementary sequence there up the pairs RNA moves pairing d n a a The base antisense So, the other RNA strand other to DNA with of of DNA. strand, make same strand to base This RNA the base a with an molecule, sequence with that acts the as of a the strand as the RNA has exception– copy sequence both RNA one other sequence the is RNA template and the sense strand RNA polymerase free RNA nucleotides antisense strand of DNA direction of transcription 3 ´ 5 ´ 5 ´ 3 ´ RNA molecule sense strand of DNA ▲ Figure 7 Tnstin NOITPIRCSNART Translation is synthesis of polypeptides on ribosomes. The second of polypeptide with an part of of this large in the of the amino acid RNA. is to is by a of by RNA gene produce the determined production determined takes place Ribosomes with translation. of large sequence The needed Translation the by was a specic synthesis base of a transcription described polypeptide, sequence in and the of a how its previous sub-topic. subunit, composed processes RNA to cell 9 (green) them sites shows molecules link structures complex binding Figure subunit acids, on are for each the two (pink is the in and site together the structures the a consist of and makes known of molecules subunits yellow) that into of cytoplasm that a a peptide and take ribosome. proteins as small that part Each (purple). bonds NOITA LSNART ribosomes. two translation. sequence Translation a the amino molecule base is is Part between polypeptide. ▲ Figure 8 117 2 M O L E C U L A R B I O L O G Y ▲ Figure 9 Large and small subunits of the ribosome with proteins shown in purple, ribosomal RNA in pink and yellow and the site that catalyses the formation of peptide bonds green Mssng rNa nd th gnti d The amino acid sequence of polypeptides is determined by mRNA according to the genetic code. RNA is that called mRNA carries molecules polypeptide In the to time certain will but be cell genes large the mRNA the pancreas Although transfer amino are acid structure that make most of is many need of a RNA is to ribosome. a the particular For of there are number genes some and is that of mRNA the other base and usually amino length acids 2,000 carry acid these only polypeptide The about Cells information sequence. types of many needed to for sequence ribosomal to At Only mRNA need or copies insulin-secreting referred the nucleotides. the that make types; of in polypeptides. certain polypeptide are of amino example, a mRNA. cytoplasm. translation They to specic the decoding during synthesize mammals make in copies in for the transcribed mRNA, involved to different polypeptide. many on with translation sequence the length therefore amounts for RNA are only for needed abbreviated depending polypeptide will available secrete a usually average there make a information RNA, varies an genome needed any the messenger make cells of in insulin. example, of mRNA RNA as is into part tRNA of and an the rRNA. d- q: Interpreting electron micrographs The electron micrographs transcription, 1 Deduce, with occurring 2 The in colour been 118 translation in added reasons, each the to in gure and DNA which 10 show process micrograph. electron micrographs the different up more clearly. Identify each of these structures: is electron make show replication. a) the red structure b) the thin in the central micrograph [5] has structures edge of blue the molecule right-hand near the lower micrograph 2 . 7 c) the blue molecules attached d) the red to this of thin molecule in d n a r e P l i c a t i o n , variable blue the t r a n s c r i P t i o n length e) molecule left-hand the a n d green t r a n s l a t i o n molecules in the left-hand micrograph. [5] micrograph Figure 10 ▲ cdns Codons of three bases on mRNA correspond to one amino acid in a polypeptide. The “translation dictionary” that enables the f cellular machinery to convert the base sequence s p t on p the mRNA the genetic into an amino acid sequence is called (5’ ) twenty amino one amino two bases, twenty use a A a code, amino codon. all to of the of one are still different base cannot sixteen too acids. with few Living groups to bases code for organisms of three U for combinations code all bases codon to codes the possible on the for a codons. is specic polypeptide. of The three codon second and Note that amino GUC both also for the Amino For code the that third designated three end of acids codons example for code in the 1 lists of tRNA. specic is the can the to are be code for codons amino said codons carried Each as acid the Cys U Phe Ser Tyr Cys C Leu Ser Stop Stop A Leu Ser Stop Trp G Leu Pro His Arg U Leu Pro His Arg C Leu Pro Gln Arg A Leu Pro Gln Arg G IIe Thr Asn Ser U IIe Thr Asn Ser C IIe Thr Lys Arg A Met Thr Lys Arg G rst, GUU valine. same and For “degenerate”. “stop” on amino which complementary particular Tyr codons this G Note that Val Ala Asp Gly U Val Ala Asp Gly C Val Ala Glu Gly A Val Ala Glu Gly G code translation. are tRNA, Ser an another kind of RNA, ▲ called Phe called bases table (3’ ) positions. different acid. reason, are G coding A mRNA a of amino Table c therefore bases mRNA u and C three added 64 four acid. Each be is are so There amino sequence acid acids, acid. triplet an There which the for code. p to amino has the acid a is carried three-base mRNA codon by T able 1 a anticodon for that acid. 119 2 M O L E C U L A R B I O L O G Y Dding bs sqns Use of a table of the genetic code to deduce which codon(s) corresponds to which amino acid; use of a table of mRNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a shor t mRNA strand of known base sequence; deducing the DNA base sequence for the mRNA strand. There code, is no but should need if be a to table able to try to memorize showing make it is the various base genetic available, sequence example, you from deductions. the strand 1 Which codons correspond to an amino the letters table acids of has are the used to genetic between one indicate code. and each Each six of amino the codons. 20 acid in off base from amino Read base of complementary codon the AUG sequence DNA. A in TAC longer to the mRNA on the mRNA. is For transcribed antisense example is that acid? the Three the sequence GUACGUACG CATGCATGC. thymine in DNA Note but that with is transcribed adenine uracil in pairs with RNA. the Questions three letters of each codon for the amino acid. For 1 example, Met 2 on the the What amino table, has amino translated strand of acid methionine, one acid from codon which sequence a shown is of rst three codons a) Tryptophan in b) Tyrosine c) Arginine are for the down the codon the left of a (Tyr) (Arg) [3] mRNA? bases in the mRNA sequence are Deduce the amino rst for amino the hand acid, second side of the base the next and table to three so on. nd codon, across the top of the table acid sequences that the to these mRNA sequences: [3] bases Look the a) to ACG b) CACGGG c) CGCGCGAGG [3] rst 3 base (Trp) a correspond codon for be codons 2 The the AUG. would sequence Deduce as nd If mRNA contains the base sequence the CUCAUCGAAUAACCC second third acid base base. and For alanine, down the example, which is right GCA hand codes abbreviated side for to to the Ala in nd the a) amino the deduce the table. the amino polypeptide acid sequence translated from of the mRNA 3 What base sequence transcribed strand of to give in the DNA base would sequence of b) a deduce strand of anti-sense mRNA strand is of produced the the antisense mRNA? the A [2] be DNA. by transcribing This therefore base strand sequence of transcribed the to produce mRNA. [2] the has a cdns nd ntidns Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA. Three ● components mRNA has sequence ● tRNA a of work sequence the molecules complementary corresponding ● ribosomes catalyse 120 act the together synthesize codons that polypeptides species the by amino translation: acid polypeptide; have an codon to as of to that the anticodon on mRNA three they bases carry that the binds amino to of the site for mRNA polypeptide. and tRNAs and a acid codon; binding assembly of and also 2 . 7 A summary 1 An 2 A A to The The the 6 The to peptide Stages added along 4, to 5 the and the the amino binds. the t r a n s l a t i o n follows: the ribosome. complementary binds to the maximum of to the rst ribosome. complementary A amino tRNA, carrying moves to two the second tRNAs can be along the binds a the acid by carried making chain of mRNA a two so by the new rst tRNA peptide amino the rst acids tRNA to bond. – a is the The dipeptide. released, rst. with an anticodon complementary to the next the rst mRNA. transfers amino 6 mRNA is the Mistakes mRNA anticodon second then the acid chain on repeated each the of amino second acids tRNA, by carried by making a new until a time stop again the and cycle codon is again, is with repeated. reached, one The when amino process the acid continues completed released. of translation anticodon are acids are chain accuracy between anticodon the then of a n d bond. polypeptide The the translation t r a n s c r i P t i o n time. becomes ribosome tRNA the tRNA on an r e P l i c a t i o n , subunit an on transfers is of small with with same ribosome second codon tRNA on tRNA Another 7 the acid second the mRNA ribosome amino 5 the at to events translated tRNA on bound of be second main binds molecule codon 4 the mRNA codon 3 of d n a very are rare, on so regularly depends each on tRNA polypeptides made with complementary and the with every a codon on sequence amino acid base pairing mRNA. of hundreds of correct. amino acid growing polypeptide chain large sub unit of ribosome tRNA tRNA mRNA anticodon ▲ Figure 11 Pdtin f hmn insin in bti Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species. Diabetes of cells insulin. the in in It blood. from the some the can individuals pancreas be that treated Porcine and pancreases of by is to hormone insulin insulin, and destruction the injecting bovine pigs due secrete cattle, into been widely difference insulin and extracted Shark have diabetics both in used. bovine insulin, in Porcine amino acid insulin which Japan, has has insulin has sequence has been three used seventeen only from one human differences. for treating differences. 121 2 M O L E C U L A R Despite the between to the of blood so it is human glucose modied E. production more coli amino an to allergy use was and have to been cause Since then developed safower bind some In 1982 available for genetically methods using yeast This may obvious, depends tRNA of these of cells having amino to it yeast (a plants. by species has transferring been the insulin to it. This is and the gene mRNA quantities exactly is is transcribed of the translated insulin. same to done to The amino for in use such a was and the being insulin transcribed a a plant) mRNA (an as animal). and is fortunate for ▲ Figure 12 harvestable produced sequence and same code as genetic engineers that organisms, has if translated all with very few exceptions, use the same genetic code as it makes gene transfer in possible human safower way the gene In coli, making produce produce acid E. genetically gene It the attached humans. prokaryote, humans that same words, genetic human anticodon acid in it each a the as other all modied on with fungus Each seem but particular insulins, insulin. using all lowering However, commercially produced sequence they animal human bacteria. recently acid insulin, receptor became It the concentration. develop time. in human insulin insulin rst and and preferable human the differences animal diabetics B I O L O G Y between widely differing species. cells. 2.8 c p undstnding appitins ➔ Cell respiration is the controlled release of ➔ Use of anaerobic cell respiration in yeasts to energy from organic compounds to produce produce ethanol and carbon dioxide in baking. ATP. ➔ ➔ Lactate production in humans when anaerobic ATP from cell respiration is immediately respiration is used to maximize the power of available as a source of energy in the cell. muscle contractions. ➔ Anaerobic cell respiration gives a small yield of ATP from glucose. ➔ Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose. Nt f sin ➔ 122 Assessing the ethics of scientic research: Skis ➔ Analysis of results from experiments involving the use of inver tebrates in respirometer measurement of respiration rates in germinating experiments has ethical implications. seeds or inver tebrates using a respirometer. 2 . 8 c e l l r e s P i r a t i o n rs f ngy by spitin Cell respiration is the controlled release of energy from organic compounds to produce ATP . Cell respiration Organic be used in breaking then In be is one compounds the cell. down used humans for is For the into muscle source the food functions broken down example, glucose the respiration of are of energy carbon life to that release is all released dioxide and living energy, in cells which muscle water. The perform. can then bres energy by can contraction. of the that organic we eat. compounds broken Carbohydrates and down lipids in are cell often ▲ used, but amino acids from proteins may be used if we eat more Figure 1 Breaking down 8 grams of glucose protein in cell respiration provides enough energy to than needed. Plants use carbohydrates or lipids previously made by sprint 100 metres photosynthesis. Cell respiration way, in a so that usable as form. triphosphate, phosphate is required is not supply. of life is carry of as This almost to all is out using is always linked organic the out possible form transferred This in carried group breakdown ATP is much enzymes the chemical adenosine reaction. in energy abbreviated to this a of a careful released substance to ATP . To make energy or comes controlled retained called diphosphate, The and is adenosine ATP , ADP . from a Energy the compounds. from reason cell for to cell cell and all respiration cells being require an a continuous essential function cells. aTP is s f ngy cell respiration ATP from cell respiration is immediately available as a source of energy in the cell. A DP 1 AT P Cells require energy ● Synthesizing ● Pumping ● Moving for large three main molecules types like of DNA, pho s pha te activity. RNA and proteins. active cell processes vesicles, molecules things or in or ions around muscle across inside cells the the membranes cell, such protein as bres by active transport. ▲ Figure 2 ▲ Figure 3 Infra red photo of toucan chromosomes, that cause muscle contraction. The energy for advantageof immediately and ATP all When cell as these an available. phosphate. by of ATP The processes energy It is ADP released and is supply supplied is that simply phosphate by can by the ATP . The energy splitting then be is ATP into ADP reconverted to respiration. energy from ATP is used in cells, it is ultimately all converted showing that it is warmer than its to heat. warm, Although it cannot environment. ATP for cell heat be This energy reused is the activities. for may cell reason be useful activities for cells to and keep is requiring an organism eventually a lost continual to surroundings due to heat generated the source of by respiration. Excess heat is dissipated by sending warm blood to the beak 123 2 M O L E C U L A R B I O L O G Y anbi spitin Anaerobic cell respiration gives a small yield of ATP from glucose. Glucose is oxygen. The quickly. broken ● when a ● when oxygen ● in The of Anaerobic short products in ATP cell but anaerobic is rapid that cell relatively respiration supplies environments waterlogged ▲ down yield burst run are is of out respiration small, but therefore ATP in production in without ATP useful respiring decient the in is can using be three any produced situations: needed; cells; oxygen, for example soils. of anaerobic respiration are not the same in all organisms. Figure 4 The mud in mangrove swamps is In humans, glucose is converted to lactic acid, which is usually in a decient in oxygen. Mangrove trees have evolved ver tical roots called pneumatophores which they use to obtain oxygen from the air dissolved to form ethanol excess, so d v mk m and carbon must produced av known in Summary be as lactate. dioxide. removed strictly limited In yeast Both from and lactate the cells plants and that glucose ethanol produce are is converted toxic them, or in be quantities. equations glucose lactate pm? ADP ATP There has been much debate about This occurs in animals including humans. bioethanol production. A renewable fuel that cuts down on carbon + emissions is obviously desirable. carbon dioxide What are the arguments against ADP ATP bioethanol production? This occurs in yeasts and plants. Yst nd its ss Use of anaerobic cell respiration in yeasts to produce ethanol and carbon dioxide in baking. Yeast is glucose It can a unicellular or other respire respiration renewable Bread is dough to is warm soon from ▲ Figure 5 124 yeast made to by then this the adding of occurs or basis for water to up so gas, it. naturally such as the anaerobically. production the the so produced dough that yeast yeast and our, Usually ingredient. encourage dioxide the that available, aerobically is baking bubbles often used carbon either are of in habitats surface of Anaerobic foods, where fruits. cell drinks and energy. and create Yeast in fungus sugars the After to by kneading ingredient baked bread kneading, respire. carries forms an out cell The a cell in is to the the texture. dough cannot the make dough kept respiration. respiration of to lighter dough oxygen swelling mixture added has the anaerobic anaerobic bubbles. Any the is is The escape dough due to 2 . 8 the is production also of produced bubbles by of carbon anaerobic cell dioxide is respiration, called but it rising. c e l l r e s P i r a t i o n Ethanol evaporates duringbaking. Bioethanol a is renewable utilized to as converts feed the rst The ethanol and various improve vehicles, its a nd ca ne brok e n i nto and ca n d o wn produce d metho d s by a re combus ti o n. sometime s in a l iv in g Al tho ug h e tha no l s ug a r s by v ar io us ma tte r in to Only be s o urce. su g a r sugars p ro duce d s to ck plant from respiration. must energ y a convert produced ethano l in e tha nol , p ur e puri e d to re m o ve is be by is Yea s t a nd c e l lu l os e u s in g enz ym e s . d is til l at i on wa t e r u s ed be u s ed a n ae r obic don e is an d by as c an ca n ye a st . s t a rc h is use b io et h a n ol us in g so Th i s bi oe th an ol s ta te m a t t er fe rm e n t er s suga rs . us e d Mos t m o st conv e r t ed , ye a sts then p la nt for or g an i sm s ( m a i z e ), l ar g e into the any l i vi n g cor n be o rg a nis m s , as s om et i m e s a fr om fu e l m ix ed it to in wit h gasoline(petrol). ▲ Figure 6 d- q: Monitoring anaerobic cell respiration in yeast The apparatus mass ask changes was in gure during placed on 7 the an was used brewing electronic to of monitor wine. balance, 2 Explain 3 Suggest connected to a computer for data-logging. mass two loss are shown in gure Calculate the total loss of mass during and the [3] reasons from for the the start increasing of the rate experiment 6. [2] Suggest two mean daily reasons for the mass remaining the constant experiment mass. 8. 4 1 of The untilday results loss which of was the The loss. from day 11 onwards. [2] [3] airlock to 560 prevent electronic entry balance of oxygen connected 555 g / ssam to a data- logging yeast in a computer 550 solution of sugar and 545 nutrients 555.00 0 1 2 3 4 5 6 7 8 9 10 11 12 13 time / days ▲ ▲ Figure 7 Yeast data-logging apparatus Figure 8 Monitoring anaerobic cell respiration in yeast anbi spitin in hmns Lactate production in humans when anaerobic respiration is used to maximize the power of muscle contractions. The lungs most and organs aerobic of blood the respiration system supply body rapidly to used, be oxygen enough but to resort for sometimes to reason we ATP anaerobic is very that cell respiration anaerobic rapidly for a in respiration short period muscles. can of The supply time. It is 125 2 M O L E C U L A R therefore power of used B I O L O G Y when muscle we need to maximize the contractions. After vigorous must be oxygen. In our ancestors maximally powerful will have been needed for allowing escape from a predator or during catching times occur in of our food respiration is training sport. or lives shortage. more weight ● short-distance lifters likely These ● today. to are These during used several minutes lactate the for use of enough be absorbed demand for for all lactate oxygen that to be broken builds a period of anaerobic respiration is up called events oxygen debt. anaerobic during examples: the runners Instead be take the involves of the rarely to The during prey can This survival down. by It contractions, down. muscle oxygen contractions muscle broken lift; in races up to 400 metres; ● long-distance during Anaerobic of lactate, the a cell so can is a respiration limit tolerate respiration short can timescale contractions a short to and it of the be distance and involves being in a how This which is the to rowers not more production supply muscle the the than body anaerobic reason We ATP , increases. that much power maximized. – the used concentration limits done. over can is lactate this be cyclists nish. when concentration There for runners, sprint of can for the muscle only ▲ sprint Figure 9 Shor t bursts of intense exercise are fuelled by ATP from anaerobic cell respiration 400metres. abi spitin Aerobic cell respiration requires oxygen and gives a large yield of ATP from glucose. If oxygen to release Whereas a available greater the anaerobic cell is yield cell to a cell, quantity of ATP is respiration, glucose of energy only it is dioxide waste cell respiration and water product humans are that about a involves to litre be cell respiration supplies its water needs 126 In eukaryotic including the more in fully anaerobic molecules than is all cells of series In thirty of most excreted, produced per per broken cell glucose glucose chemical organisms down respiration. with with but per the reactions. carbon water is aerobic most the of the reactions mitochondrion. often + to useful. is a In water ATP reactions that Carbon dioxide day. + ADP despite only eating dry foods, because aerobic a produced. has half glucose Figure 10 The deser t rat never needs to drink be than respiration. Aerobic ▲ two more can of produce aerobic carbon cell respiration, dioxide, happen inside 2 . 8 c e l l r e s P i r a t i o n rspimts Analysis of results from experiments involving measurement of respiration rates in germinating seeds or inver tebrates using a respirometer. A respirometer measure designs. ● A Most sealed An A One in or or plastic such as is that There these tissue carbon capillary the device rate. involve alkali, absorb ● any glass organism ● is respiration is used are in to many possible volume. the container in which the Respirometers potassium hydroxide, ● to the possible versions 11, uid, connected to ● the that it of is respirometer possible require only a to is syringe ● shown design tube attached to with and the respirometer the organisms cell respiration, is inside working are will correctly carrying volume reduce table out and tube will move of air the and organisms. carbon This dioxide is absorbed and the towards is uid the because produced by analyse in if the position several uid If is the times. the If the in rate even, temperature increase uid the relatively uctuates, an of the results air of different organisms temperature on respiration rate rates could be compared in active organisms. shows pea of the will be aerobic is the results of temperature an seeds was on experiment respiration in investigated. these repeats results at you each should rst temperature check are to close for you should to then decide that calculate the mean results results are for reliable. each used The next stage is to plot a graph of the cell results, are of graph the reliable. not be reliable causes an each line. respirometer temperature and vertical recorded movement results the of the oxygen by effect with temperature on the horizontal alkali. should inside rate container x-axis The various the mean respiration of below temperature. up perform aerobic inside You with to investigated; the germinating enough capillary be inactive which see respirometer used a bath. a To the be water inside using it. in If can controlled compared; respiration simpler The capillary be effect could design but temperature be controlled respiration could container. gure the should experiments: placed. containing possible thermostatically parts: dioxide. tube If respirometer because increase the y-axis. by rate plotting the temperature The graph relationship respiration is of movement Range bars lowest and will allow of the you the of be and joining between rate can on to highest them to uid added result with a conclude temperature germinating the the at ruled what and the the peas. Mvm pm 1 (mm m tmp 3 graduated 1 cm (°c) ) 1 2 3 g g g 5 2.0 1.5 2.0 10 2.5 2.5 3.0 15 3.5 4.0 4.0 20 5.5 5.0 6.0 25 6.5 8.0 7.5 30 11.5 11.0 9.5 syringe wire basket containing animal tissue lter paper rolled to form a wick capillary tube potassium hydroxide solution ▲ Figure 11 Diagram of a respirometer 127 2 M O L E C U L A R B I O L O G Y d- q: Oxygen consumption in tobacco hornworms Tobacco Adults hornworms of this from the are series a are species eggs laid of by larval the are larvae moths. the adult stages of Manduca Larvae female called b) sexta. trends moths. instars. above There grows and then changes into the next shedding its exoskeleton and developing researchers a air one. The exoskeleton includes the that supply oxygen to the graphs below (gure 12) rate using of 3rd, a simple 4th and show instar in below the and weight. [2] reared some oxygen tobacco content. hornworms They larvae moulted at a lower found body larvae reared in normal air with 20 % mass oxygen. tissues. respirometer 5th critical reduced instar Suggest a reason for earlier moulting in larvae measurements reared made difference tracheal 3 The with the than tubes the new that larger the for theperiods one in by reasons between Each The instar Suggest emerge of the larvae. in air withreduced oxygen content. [2] respiration Details after critical weight before critical weight of 5th instar the methods the biologists are given in the paper published by 0.12 0.16 who carried out the research. The 0.10 0.14 reference to the research is Callier V and Nijhout 0.08 0.12 H F (2011) “Control of body size by oxygen supply 0.06 0.10 reveals size-dependent and size-independent 0.04 mechanisms of molting and 0.08 metamorphosis.” 0.02 PNAS;108:14664–14669. on the internet at paper is freely 1 http://www.pnas.org/ content/108/35/14664.full.pdf+html. 2 and data respiration results low have to with are point the rate been of intermediate mass on is graphs one divided intermediate plotted body on body to referred larva. into and body graphs. to as the For the body each younger mass high separate shows mass. The instar larvae older mass the with larvae The results O lm( etar noitaripser Each 3 4 5 6 7 0.025 9 10 11 12 13 4th instar 0.030 0.020 0.028 0.026 0.015 0.024 0.022 0.010 0.020 0.005 0.018 0.20.30.40.50.60.70.80.9 1.0 intermediate critical 8 0.032 2 )nim/ available This 1.1 1.2 1.3 1.4 weight. 0.007 3rd instar 0.009 0.006 1 a) Predict, using the data in the graphs, how 0.008 0.005 the respiration rate of a larva will change 0.007 0.004 as it grows from moulting until itreaches 0.006 0.003 the critical weight. 0.005 [1] 0.002 0.004 0.001 b) Explain the change in respiration rate that 0.003 0.000 . 0 2 Figure 12 Respiration rates of tobacco hornworms (after Callier and Nijhout, 2011) e m pm Assessing the ethics of scientic research: the use of inver tebrates in respirometer experiments has ethical implications. It is important ethics of debate their about experiments. 128 for all scientists research. the ethics When There of to using discussing assess has been the we intense to animals ethical in issues, consider students consider do are the who consequences are intentions? harmed learning For such example, unintentionally as science? does if benets Do the that we animals change 6 . 0 2 4 ▲ . 0 [2] 2 weight (g) weight (g) in 2 rate weight. . 0 respiration 1 . 0 2 in critical 8 6 1 . 0 0 the 1 trends 4 the above . 0 larvae . 0 Discuss 1 a) . 0 2 0 . 0 0 0 . 2 6 4 0 . 1 [2] 0 described. 0 have 8 you 2 . 9 whether there the example, be can subject they experiment absolute to would principles we say was of that conditions encounter ethical right animals that in are their or and not? Are wrong: should outside natural 3 Can the never carrying involving be out animals answered to respirometer these help are to decide ethically Is the Is it acceptable natural can habitat they be to remove for safely Will the animals is the of or In be that be cause pain minimized particular, can or during contact prevented? animals is using particularly use in animals an returned from their experiment to their and habitat? suffer pain or any other use in International a there in an the experiment alternative method that animals? important to directive respirometer consider the An experiments Baccalaureate that investigations ethics of laboratory need important to be or eld of this has is in that an the issued experiments undertaken aspect because Organization and ethical experiments harm should during animals the way. 2 accidents acceptable: animal 1 of the alkali use avoids should whether the essential It experiments to habitat? experiments questions risk experiment? with what 4 Before the suffering for P h o t o s y n t h e s i s not be undertaken in schools that inict experiment? pain or harm on humans or other living animals. 2.9 P undstnding appitins ➔ Photosynthesis is the production of carbon ➔ Changes to the Ear th’s atmosphere, oceans and compounds in cells using light energy. rock deposition due to photosynthesis. ➔ Visible light has a range of wavelengths with violet the shor test wavelength and red the Skis longest. ➔ Chlorophyll absorbs red and blue light most ➔ other colours. ➔ ➔ ➔ Separation of photosynthetic pigments by chromatography. Oxygen is produced in photosynthesis from photolysis of water. Design of experiments to investigate limiting factors on photosynthesis. eectively and reects green light more than ➔ Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis. Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide. ➔ Temperature, light intensity and carbon dioxide Nt f sin concentration are possible limiting factors on ➔ Experimental design: controlling relevant the rate of photosynthesis. variables in photosynthesis experiments is essential. 129 2 M O L E C U L A R B I O L O G Y Wht is phtsynthsis? Photosynthesis is the production of carbon compounds in cells using light energy. Living organisms structure are able light of to The converted is into the that an complex and simple process compounds ▲ all and Photosynthesis is require cells make energy water. their to carbon this example chemical produced compounds life processes. of that substances is called energy energy include out compounds inorganic does carbon carry in they such as to build Some need the organisms using carbon only dioxide photosynthesis. conversion, carbon as light compounds. carbohydrates, proteins energy The and carbon lipids. Figure 2 The trees in one hectare of redwood forest in California can have a biomass of more than 4,000 tonnes, mostly carbon compounds produced by photosynthesis ▲ Figure 1 Leaves absorb carbon dioxide and light and use them in photosynthesis Spting phtsynthti pigmnts by hmtgphy Separation of photosynthetic pigments by chromatography. (Practical 4) Chloroplasts and other Because these wavelength us. may thin This is be light, can be done with with A containing tissue is solvent the 1 a is Tear in a a thin placed up separated a with plastic layer near types leaf a to of up that porous the of colour to chromatography gives of ranges chromatography. better has the results. been material. extracted end run chlorophyll pigments. different by strip of one of different a paper pigments allowed different look chromatography coated spot types accessory absorb they familiar layer several called pigments of Pigments You but contain pigments from strip. strip, to leaf A separate pigment. into small pieces and put them mortar. ▲ 2 130 Add a small amount of sand for grinding. Figure 3 Thin layer chromatography and 2 . 9 3 Add a small volume of propanone P h o t o s y n t h e s i s (acetone). Pgm c r 4 Use the pestle dissolve 5 If 6 the allow 7 Use the the the a in the all you to and has other off tissue just glass, turned into from a a pgm and 3–4 a little dark to the all of orange 0.98 Chlorophyll a blue green 0.59 Chlorophyll b yellow green 0.42 Phaeophytin olive green 0.81 Xanthophyll 1 yellow 0.28 Xanthophyll 2 yellow 0.15 then glass. the cells’ dry drops Carotene more. green, settle, watch off smear add add solids evaporate water have watch leaf evaporates, and drier the pigments. propanone hair When grind propanone sand propanone 8 the propanone When pour out to cytoplasm. pigments of propanone 12 9 and use a paint Use the paint brush brush to to dissolve transfer the a very of the pigment solution to the outside of the tube just below the level of the Take the spot on the TLC strip. small 13 amount Mark pigments. strip and cork out of the the tube. TLC strip. spot of Your aim pigment in is to the make middle a very of the small strip, 14 10 millimetres from one end. It should be Pour up dark. This small drop is achieved by repeatedly putting the strip and thenallowing to the dry before Place the adding another amount. You up dryingby using the blowing on the spot or When the it specime n will not tub e be of spot the the TLC so that is dark enough, slide the stripis strip into the slot in a cork or ts into The a slot tube that should is hold wider the than strip Insert the the TLC cork strip Leave and strip into a specimen str i p a nd of cor k into th e the just tub e is s e al e d d i p p i ng should extend nearly the tube, but not quite i nto and the the r unnin g must NOT tou c h th e spot. the tube to minutes, co mp l e tel y to allow the al one for s olv ent to a bou t run tube. through the TL C s tr i p. You can wa t c h the the bottom be nc h C ar e f u l ly TLC up The la b rmly. ve 11 a bung 16 strip. tube other pigment that on d i s tur be d. solvent.Thesolvent end specimen drier. TLC 10 the marked. by tube, hair into you can lower speed that it where to solvent level a 15 onto running very pigments sepa r a te , b ut DO NOT T OU CH touch. THETUBE. 17 sp c d r When the solvent has nearly reached the nm top m mv of the strip, remove it from the tube and pgm separate it from the cork. (mm) 18 Rule two pencil lines across the strip, one at 1 the level reached by the solvent and one at the 2 level of the initial pigment spot. 3 19 Draw a circle pigment 4 the around spots and a e a ch cr o s s of in the the s e pa ra t e d ce nt re of circle. 5 6 7 8 ▲ Table of standard R Figure 4 Chromatogram of leaf pigments values f 131 2 M O L E C U L A R 20 Using a ruler B I O L O G Y with millimetre markings, 21 Calculate the R for each pigment, where R f measure solvent and the (the the distance distance distance moved by between moved by the the each running two the lines) pigment distance between the lower line and the the centre of the by by the the pigment divided by the solvent. Show all your results in the table above, starting cross with in run is f run (the 22 distance distance the pigment that had moved least far. circle). Wvngths f ight Visible light has a range of wavelengths with violet the shor test wavelength and red the longest. Sunlight or radiation simply that wavelengths from very X-rays as our are short and infrared light eyes invisible. to very ultraviolet radiation wavelengths longer wavelengths of When droplets formed, a including of violet, by wavelengths plants the sun other in water of and of green the light so m W / ecaf rus s’ht raE visible light are separated sky and the and split of to electromagnetic us and electromagnetic wavelengths energy; lower longer energy. than other radiation such as wavelengths Visible infrared. light The such has range of nanometres. sunlight visible. which This we Violet up is see and and a rainbow because as sunlight different blue are is the is colours, shorter wavelength. detected for by this the is atmosphere particularly blue visible of shorter 700 reason Earth’s wavelengths Shorter have red. are A high are longest 2 eht gnihcaer noitaidar ralos Figure 5 In a rainbow the wavelengths of to light 1.5 ▲ have 400 that are the therefore spectrum wavelengths, is penetrate a waves the photosynthesis. wavelengths, is all is wavelengths. is in colours red of It ultraviolet light blue, and There radio than up detect. radiation different wavelengths The of made long and visible different mixture is can eye that in are also they larger are those used emitted quantities by than abundant. 5 450 500 nm green 5 525 575 nm red 700 nm 5 650 1.0 0.5 0 500 1000 1500 2000 2500 3000 wavelength /nm ▲ Figure 6 The spectrum of electromagnetic radiation reaching the Ear th’s surface light bsptin by hphy Chlorophyll absorbs red and blue light most eectively and reects green light more than other colours. The rst involves stage substance 132 in photosynthesis chemical does substances not absorb is the called visible absorption pigments. light. A Pigments of sunlight. white are or This transparent substances that do 2 . 9 absorb all of There not light the are the For except sunlight therefore appear pigments others. colours and colours is absorb reected It the can some blue pass to they us. Pigments emit no wavelengths pigment appears and coloured because in to into a gentian us, because our eye, to of visible ower this be that absorb light. light but absorbs part of detected all the by cells in retina. Photosynthesizing photosynthetic chlorophyll red that example, blue. appear black, P h o t o s y n t h e s i s and much This less is being but blue organisms pigment they light all very effectively. the reason for is use a appear green effectively, main of of pigments, There to but Wavelengths the range chlorophyll. us. the This in but various is light the they green therefore ecosystems main forms because intermediate green colour are of absorb light are reected. dominated by ▲ Figure 7 Gentian owers contain the pigment delphinidin, which reects blue plants light and absorbs all other wavelengths. green. absptin nd tin spt Drawing an absorption spectrum for chlorophyll and an action spectrum forphotosynthesis. An of action spectrum photosynthesis An absorption percentage by a of pigment at is a graph each spectrum light or a is a graph absorbed group showing wavelength of at the of rate showing each It is not spectra light. the wavelength difcult are very to explain similar: occur in wavelengths other photosynthetic of why action and photosynthesis light that pigments When drawing can legend ● as the to 700 On of The should have nanometres should chlorophyll a chlorophyll b absorption extend the shown from 400 carotenoids nanometres. action for a spectrum measure photosynthesis. percentage from and x-axis with scale the pigments. action horizontal wavelength, units. an used the or absorb. noitprosba % spectra, both only chlorophyll 100 ● absorption can 0 to of the of the the This is y-axis relative often maximum should given rate, be 400 amount as with 500 a scale 600 700 wavelength (nm) a ▲ Figure 8 Absorption spectra of plant pigments 100%. 100 ● an absorption the from 0 legend to data should be not be y-axis absorption”, with should a scale 100%. Ideally curve “% the points plotted drawn possible, fo r a nd s p eci c the n thr o ug h the cur v e a wa vel e ng t h s smo ot h the m. fr om a If th is )etar xam fo %( have spectrum sisehtnysotohp ● On is publ i sh e d 400 spectrum could be 500 600 700 co p i e d. wavelength (nm) ▲ Figure 9 Action spectrum of a plant pigment 133 2 M O L E C U L A R B I O L O G Y d- q: Growth of tomato seedlings in red, green and blue light Tomato for seeds 30days green and different of photons light of of of In The each tested every the peak Plot Four two is table below, together with the mean you can put graph Do and height of the seedlings. Plants tall, when with they are weak stems receiving and small insufcient different and on left theother of height. scales the attempt relationship and to on on hand the plot the if y-axis side right the between Hint: of hand resultsfor LEDs. [6] in Using your graph, deduce the relationship leaf the leaf area of the seedlings and often their grow the area one not between area show leaf combinations of 2 the to needtwo side. intensity shown graph you the treatment wavelength a wavelength, orange, and same wavelength 1 grown red, diodes. were received light. by LED and by emitting colours. plants emitted produced light colours tomato germinated light blue combinations the were in height. [1] leaves light 3 for Evaluate of photosynthesis. the tomato considering Pk wvg g m data crops in in the table for greenhouses usingLEDs to a provide l g grower who is light. [3] hg g c led 2 led (m) Red (m 630 ) (mm) 5.26 192 Orange 600 4.87 172 Green 510 5.13 161 Blue 450 7.26 128 Red and Blue – 5.62 99 Red, Green and Blue – 5.92 85 Source: Xiaoying, Shirong, T aotao, Zhigang and Tezuka (201 2). “Regulation of the growth and photosynthesis of cherry tomato seedlings by dierent light irradiations of light emitting diodes (LED).” African Journal of Biotechnology Vol. 11(22), pp. 6 169-6 1 77 oxygn pdtin in phtsynthsis Oxygen is produced in photosynthesis from photolysis of water. One of of the water essential to release steps in electrons photosynthesis needed in is other the splitting of molecules stages. + H O → 4e + 4H + O 2 This and in reaction the word is 2 called lysis photosynthesis product and photolysis means comes diffuses because disintegration. from photolysis it only All of of happens the water. in oxygen Oxygen the light generated is a waste away. e p e Changes to the Ear th’s atmosphere, oceans and rock deposition due to photosynthesis. ▲ Figure 10 Photosynthesizing organisms seem Prokaryotes were but over billions of years they have changed it about million signicantly algae insignicant in relation to the size of the Ear th 134 3,500 and plants, the rst years which organisms ago. have They been to perform were joined carrying out photosynthesis, millions of starting years photosynthesis later ever by since. 2 . 9 One of consequence the 2% of atmosphere. by volume by photosynthesis This began 2,200 mya. is about This the rise 2,400 is in the million known as oxygen years the concentration ago Great P h o t o s y n t h e s i s (mya), Oxidation rising to av Event. d mp At the due to same to the a time the reduction rise in Earth in the experienced greenhouse oxygenation causing a its rst effect. glaciation, This decrease in could the presumably have been concentration P cmp due mp (%) of N CO methane carbon potent in the dioxide atmosphere and concentration. greenhouse photosynthesis Both methane causing and a carbon decrease dioxide in 2 are Venus increase in it to mya oxygen caused precipitate H 2 O 2 98 1 1 0 0 concentrations in the oceans between 2,400 0.04 78 1 21 0.1 96 2.5 1.5 2.5 0.1 and Mars 2,200 O gases. Ear th The Ar 2 the onto oxidation the sea of bed. dissolved A iron distinctive in rock the water, formation causing was What are the main dierences produced called the banded iron formation, with layers of iron oxide between the composition of the alternating with other minerals. The reasons for the banding are not yet Ear th's atmospheres and the fully understood. The banded iron formations are the most important atmosphere of the other planets. iron ores, so it is thanks to photosynthesis in bacteria billions of years What is the cause of these ago that we have abundant supplies of steel today. dierences? The oxygen 2,200 20% mya or concentration until more. multicellular about This of the 750-635 corresponds organisms were atmosphere mya. with There the remained was period then a when at about 2% signicant many from rise groups to of evolving. 50 erehpsomta fo %/negyxo 40 av 30 g 20 1500 10 1 h lomµ/ekatpu 0 4.0 3.0 2.0 1.0 0 Millions of years ago (×1,000) 500 2 Figure 11 OC ▲ 1000 0 75 150 225 300 200 2 light intensity /J dm 1 s Pdtin f bhydts ▲ Figure 1 2 The graph shows the results of an experiment in which the rate Energy is needed to produce carbohydrates and other of photosynthesis was found by carbon compounds from carbon dioxide. measuring the uptake of carbon dioxide Plants convert carbon dioxide and water into carbohydrates by 1 What is the reason for a CO 2 photosynthesis. The simple equation below summarizes the process: uptake rate of −200 in carbon To carry involves out this putting involving systems. dioxide the + water process, in Reactions energy energy production → is of carbohydrate is required. described oxygen involving as are combining A + chemical endothermic. usually darkness? oxygen reaction endothermic smaller that Reactions molecules to in living make 2 What can you predict about cell respiration and photosynthesis at the point where the net rate of CO uptake is zero? 2 larger such ones as are glucose also often are much endothermic larger than and molecules carbon dioxide of or carbohydrate water. 135 2 M O L E C U L A R B I O L O G Y The av co energy obtained for by the conversion absorbing occurring in disappear – the light. light. The of carbon This is energy the dioxide reason absorbed into for from carbohydrate photosynthesis light does is only not 2 is converted to chemical energy in the carbohydrates. 30 limiting fts 1 h 20 1 ah gk/ ssarg fo ssamoib ni esaercni 40 Temperature, light intensity and carbon dioxide 10 concentration are possible limiting factors on the 0 100 200 300 3 CO 2 /cm rate of photosynthesis. 400 3 m air 210 ▲ it The Figure 13 In this graph the rate of rate of photosynthesis in a plant can be affected by three externalfactors: photosynthesis was measured ● temperature; ● light ● carbon indirectly by measuring the change in plant biomass. 1 The maximum carbon intensity; dioxide concentration. dioxide concentration of the Each 3 atmosphere is 380 cm of these factors can limit the rate if they are below the optimal –3 m air. level. These three factors are therefore called limiting factors. Why is the concentration often According to the concept of limiting factors, under any combination lower near leaves? of 2 light In what weather conditions is one carbon dioxide concentration is likely to be the limiting factor to for photosynthesis? but of the intensity, the it this take the the is no is the other carbon limiting from its optimum, factors rises over limiting factors longer the will dioxide rate of optimum. the rate have as and the light one the the is of no moved a that limiting limiting intensity limiting carbon factor constant, the becomes presumably morning, limiting actually furthest to other factor intensity sun is the as the factor another is and If concentration, photosynthesis. the factor is photosynthesis effect, as they only This changed increases, are not the factor. course, keeping the that closer changing limiting Of factors factor make temperature factor. dioxide closer point is furthest factor. factor increases, As will the its optimum, reached from For for to be its optimum example, at temperature might will light When usually increases well and night, photosynthesis. temperature concentration while where during become the factor. cntd vibs in imiting ft xpimnts Experimental design: controlling relevant variables in photosynthesis experiments is essential. In any the The experiment, independent independent experiment 136 variable is affected by with what the it and is important dependent variable a range you is of the measure control variable one levels independent to that that during variable. that you you the all variables you are The experiment, than investigating. deliberately choose. other vary in the dependent to see if it is 2 . 9 It is essential during independent the dependent independent These an are questions Which to ● type the All will that variables need a be to be that sure be that the affecting might affect the controlled. answer limiting you to could when factor on investigate? you are designing photosynthesis: This will be your variable. How will your dependentvariable. How will optimal factor therefore you factor experiment other must that of only investigate limiting independent ● is variable. variable experiment ● this variable P h o t o s y n t h e s i s you measure you keep level? the the rate other Thesewill be of photosynthesis? limiting your factorsata controlled This will constant be and variables. Invstigting imiting fts Design of experiments to investigate limiting factors on photosynthesis. There used are to below. factor many possible investigate You or could you the effect either could experimental of carbon modify develop an designs. this to A dioxide that concentration investigate entirely method different a different can is be given limiting design. Investigating the eect of carbon dioxide on photosynthesis If a stem placed of gas of pondweed upside-down may be seen such in to as water Elodea, and escape. If the these Cabomba end are of or the Myriophyllum stem collected is and cut, av is bubbles tested, tmp they 100 found rate of be oxygen Factors nd to that out mostly production might what concentration oxygen, affect effect is can the this produced be rate has. In by measured of photosynthesis. by counting photosynthesis the method below can the be carbon etar mumixam fo % are The bubbles. varied to dioxide varied. 50 0 1 Enough water to ll a large beaker is boiled and allowed to cool. 0 10 20 30 40 50 temperature / °C This removes carbon dioxide and other dissolved gases. ▲ 2 The water is poured repeatedly from one beaker to another, Figure 14 In this graph the to rate of photosynthesis was oxygenate the water. Very little carbon dioxide will dissolve. measured indirectly by 3 A stem of pondweed is placed upside-down in the water and measuring the change in the plant biomass end of its stem is water contains water should illuminated. cut. No almost be about Suitable bubbles no 25 are carbon °C and apparatus is expected dioxide. the The water shown in to emerge, as temperature should gure be very the of the 1 brightly What was the optimum temperature for 16. photosynthesis in this plant? 4 Enough sodium hydrogen carbonate is added to the beaker to raise 3 the carbon emerge, until dioxide they two or are concentration counted three for consistent 30 by 0.01 seconds, results are mol dm repeating obtained. . If bubbles the counts 2 What was the maximum temperature for photosynthesis? 137 2 M O L E C U L A R B I O L O G Y 5 Enough sodium hydrogen carbonate is added to raise the –3 concentration in the same by another 0.01 mol dm . Bubble counts are done way. sodium 6 hydrogen The procedure increases carbonate in above carbon is repeated dioxide do again not and affect again the rate until of further bubble production. Questions 1 Why are the following procedures necessary? pondweed a) Boiling and b) Keeping c) Repeating then the cooling water bubble at 25 counts the °C water and until before brightly several the experiment. illuminating consistent it. counts have water at 25 °C been 2 What obtained. other pondweed factor and could how be would investigated you design using the bubble counts with experiment? light source 3 How could production ▲ Figure 15 Apparatus for measuring photosynthesis rates in dierent concentrations of carbon dioxide 138 you make more the measurement accurate? of the rate of oxygen Q u e s t i o n s Qstins 1 Lipase the is a digestive breakdown intestine. In of the enzyme that triglycerides laboratory, accelerates in the the rate a) (i) State small of in lipase can be detected by a decline in what causes the pH to units that are shown [1] State the mass units that are shown in pH. the Explain volume equation. activity (ii) of the the decline. equation. [2] [4] b) (i) Calculate the mass of ATP produced per 3 dm (ii) 2 Papain is a protease that can be extracted of of fruits. temperature experiment in water quantity of on was and Figure the 17 shows activity performed then Calculate that with had papain the been The c) Explain it to a solid surface. d) During dissolved immobilized The large percentage mixture that of the was protein digested in in results a the how masses a mass of ATP produced per 1. it is [4] of possible ATP to during synthesize such 100 m race, by 80 g races. of ATP [3] is needed 3 only 0.5 dm of oxygen is consumed. show Deduce the the table same but attaching in effect papain. using repeated papain of the [2] from race pineapple oxygen. how ATP is being produced. [3] reaction xed time. lg Vm x g m 3 /m 100 p g /m immobilized detsegid neitorp fo % papain 1500 36 10,000 150 42,300 700 80 dissolved 60 papain 40 20 ▲ T able 1 0 20 30 40 50 60 70 80 temperature / °C 4 ▲ Figure by a) (i) Outline the the activity effects of of temperature dissolved on papain. Explain the the effects activity of of leaves, Deduce on papain. (i) Compare the effect of activity of temperature immobilized the papain W (ii) effect on dissolved Suggest a reason for papain. the Explain have difference In some described. parts Explain Suggest body be 3 The pathways from + below the enzyme it + and would in a be used (ADP limiting factor for X at: (iii) Y (iv) Z. [4] why 1 curves and 7 I and units of II are light the same intensity. [3] the negative absorption values when for the carbon leaves a membranes. part the produce of of for the it ATP , → to [2] results glucose. Pi) light were intensities. in [3] body, membrane. to + in useful summarizes oxidation oxygen human of using Z OC fo etar glucose where the IV 0.4%CO at 30°C 2 13 12 11 10 9 III 0.4%CO at 20°C 2 8 7 Y X 6 5 II 0.13%CO 4 2 energy one of immobilized immobilized equation metabolic are dioxide [2] stinu yrartibra / noitprosba enzymes carbon temperatures. that low (iii) xed light absorption [2] dioxide you varying with c) (ii) and of dioxide on between the effects different, photosynthesis b) the the carbon [2] (i) b) at the [2] temperature dissolved shows on concentrations a) (ii) 18 intensity Figure 1 7 at 30°C 2 3 I 0.13%CO at 20°C 2 2 1 W 0 1 1 2 3 4 5 6 7 3 180 g 134.4 dm 18.25 kg light intensity / arbitrary units carbon dioxide + water + ATP ▲ Figure 18 3 134.4 dm 108 g 18.25 kg 139 2 M O L E C U L A R 5 Figure in 19 which shows the Chlorella wavelengths (far B I O L O G Y red). from The rate results cells 660 of of were nm an experiment given (red) oxygen light up to a) of 700 production nm was measured and the the relationship wavelength of when was there light no and between oxygen yield, supplementary light. Describe the effect of the supplementary yield light. of oxygen per photon of light was gives a measure of the [2] calculated. c) This Explain how photosynthesis at each experiment supplementary was light then with repeated nm at the same time a The probable was 0.125 wavelength from 660 to bars help in drawing experiment. [2] as each of 700 nm, maximum molecules yield per of oxygen photon of light. of how many photons are needed the to wavelengths this with Calculate 650 error from wavelength. d) The the efciency conclusions of but with produce one oxygen molecule in the photosynthesis. same overall intensity of [2] by b) photosynthesis Describe light as in the [2] rst e) experiment. Oxygen this production by photolysis involves reaction: with supplementary light + without supplementary light 4H O → O 2 thgil fo notohp rep selucelom negyxo fo dliey Each 0.15 of (raise Calculate how produced by during 0.05 0 680 700 wavelength (nm) Figure 19 Photon yield of photosynthesis in dierent light intensities 140 2H O + 4H + 4e 2 light it to a many is used higher times photolysis to excite energy each must be an level). electron excited 0.10 660 ▲ photon electron + 2 the reactions of photosynthesis. [2] 3 G E n E t I C s Iroducio Every life living from follows a linear of a its organism parents. patterns. sequence species. inherits The a blueprint inheritance Chromosomes that Alleles is shared segregate of carry by for genes genes in members during allowing fusion of new techniques cells and combinations gametes. for to Biologists articial be have formed by the developed manipulation of DNA, organisms. meiosis 3.1 Gene Uderadig Applicaio ➔ A gene is a heritable factor that consists of ➔ The causes of sickle cell anemia, including a a length of DNA and inuences a specic base substitution mutation, a change to the characteristic. base sequence of mRNA transcribed from it and ➔ A gene occupies a specic position on one type a change to the sequence of a polypeptide in of chromosome. ➔ The various specic forms of a gene are alleles. ➔ Alleles dier from each other by one or a few hemoglobin. ➔ Comparison of the number of genes in humans with other species. bases only. ➔ New alleles are formed by mutation. ➔ The genome is the whole of the genetic skill ➔ Use of a database to determine dierences in information of an organism. the base sequence of a gene in two species. ➔ The entire base sequence of human genes was sequenced in the Human Genome Project. naure of ciece ➔ Developments in scientic research follow improvements in technology: gene sequencers, essentially lasers and optical detectors, are used for the sequencing of genes. 141 3 G e n e t i c s Wha i a gee? A gene is a heritable factor that consists of a length of DNA and inuences a specic characteristic. Genetics is the information from parents before from the the the to word of Something living plants, fruit obvious middle made a can of of for DNA. therefore than a 19th of other was deduce that chromosome understood. eyes were and and It passed long came interested much be be biologists in more. passed on to that there were indeed characteristics passed on There to offspring was onwards and by intense and the factors that these pea research word gene factors. chemical there was each – gene that composition strong few example and by of can develop. specic century relatively for was features showed storage used Biologists again be the information was blue organisms. 20th the century are these would heritable cell origins. could with this genetics baldness, century early how storage inuenced They all the There human cause that question 20th word as features the concerned and meaning the and from the typical DNA the ies invented One be the The such heritable. genetics was in in biology information genesis, organisms were into of features must factors of organisms progeny. where Experiments in living method origins offspring branch in DNA yet are of a genes. that molecules there consists each of evidence in a cell thousands much chromosome By genes shorter carries – of the were just 46 genes. We length many of genes. Comparig umber of gee Comparison of the number of genes in humans with other species. How many bacterium, many see are genes a needed ourselves physiology Prokaryotes to it take plant make more or a to a so in we a and human? complex behaviour make bat, how We expect more true. It They structure, might have these to Nae of pece genes. gives are as The range based species numbers a on but these table of evidence are not are shows predicted not from precise yet Bef decpton whether gene the this is numbers. DNA counts of of gene known. Nube of gene Haemophilus inuenzae Pathogenic bacterium 1,700 scherichia coli Gut bacterium 3,200 Protoctista Trichomonas vaginalis Unicellular parasite Fungi Saccharomyces cerevisiae (Yeast) Unicellular fungus Plants Oryza sativa (Rice) Crop grown for food 41,000 Arabidopsis thaliana (Thale cress) Small annual weed 26,000 Populus trichocarpa (Black cottonwood) Large tree 46,000 Drosophila melanogaster (Fruit y) Larvae consume ripe fruit 14,000 Caenorhabditis elegans Small soil roundworm 19,000 Homo sapiens (Humans) Large omnivorous biped 23,000 Daphnia pulex (Water ea) Small pond crustacean 31,000 Animals 142 as and Goup does banana 60,000 6,000 3 . 1 G E N E s Where are gee locaed? Actvt A gene occupies a specic position on one type Etatng te nube of of chromosome. Experiments show of that the has of ten of are the different linked in chromosome linked groups humans which genes types groups in uan gene genes of in linked number of in fruit genes both varieties groups a species. ies and is of and and ten plant each For or animals group example, four types types of of are crossed corresponds there are to American published an estimate four chromosome. chromosome In October 1970 Scientic one and that the human genome might Maize consist of as many as 10 million in genes. How many times greater 23. than the current predicted number is this? What reasons Each gene occupies a specic position on the type of chromosome where can you give for such a huge it is located. This position is called the locus of the gene. Maps showing the overestimate in 1970? sequence were can of genes produced now be by along crossing produced in experiments, when the fruit but genome of ies much a and other more species is organisms detailed maps sequenced. 1.1 2q7 3.41q7 3.21q7 2.22q7 3.1 2q7 2.51q7 1.41q7 1.21q7 22.11q7 31.1 2q7 11.1 2q7 3.1 2q7 2.22q7 53q7 2.23q7 13.13q7 1.13q7 33.13q7 33q7 2.63q7 ▲ chromosomes Figure 1 Chromosome 7: an example of a human chromosome. It consists of a single DNA molecule with approximately 1 70 million base pairs – about 5% of the human genome. The pattern of banding, obtained by staining the chromosome, is dierent from other human chromosomes. Several thousand genes are located on chromosome 7 , mostly in the light bands, each of which has a unique identifying code. The locus of a few of the genes on chromosome 7 is shown Wha are allele? The various specic forms of a gene are alleles. Gregor Mendel varieties of is pea plants, white-owered the to differences different factors are two forms and the These a alleles, of the there gene As is gene are alleles One mice. the are are of A humans eye of occupy plant cells same locus in of of two There of these For one He dwarf crossed peas and deduced together pairs example making and the ABO that were of there pea due heritable are plants tall the more a than alleles colour There blood of has are for to two be three three groups. gene, gene, they gene copies be In alleles some example cases the ies. same – coat black. alleles fruit can multiple inuences grey different have that gene. examples chromosome the with Mendel crossed height, determines colour he genetics. dwarf. that forms of plants know alleles. rst yellow, that pea that now the called gene alternative type We plants of tall father purple-owered. varieties of the inuences the numbers one can and that mice inuences on allele animal in large that forms in with the the as example forms gene making making position one the gene. discovered for factors. alternative of regarded plants heritable other of pea between different alleles usually of have on each a they the occupy same chromosome. type of the locus. same Only Most chromosome, so ▲ Figure 2 Dierent coat colours in mice 143 3 G e n e t i c s we the can expect same two allele of copies the of gene a gene or two to be present. different These could be two of alleles. Dierece bewee allele Alleles dier from each other by one or a few bases only. A gene consists hundreds slight of of position in Positions in bases particular the are another in a gene nucleotide snips. Several gene length position single the a thousands variations number a or of DNA, bases base the for by a The sequence. different, in with long. base Usually in sequence different example sequence only one adenine one allele that alleles or might and of a a can very be be gene have small present cytosine at present are at that allele. where more than polymorphisms, snips differ of can only be a present few one base may abbreviated in a gene, to but be SNPs even and called pronounced then the alleles of bases. Comparig gee Use of a database to determine dierences in the base sequence of a gene in two species One that outcome the enabled allows of the techniques the gene Human that sequencing sequences Genome were of to developed other be Project ● have genomes. compared. is This this comparison can be used to The ‘Fast appear. Copy a .txt relationships. of sequences Also, the for exploring the allows function of species that Repeat to be chosen Go to the website called Choose ‘gene’ from the To have Enter the as name of a cytochrome run In search ● Select menu. gene plus the oxidase 1 (COX1) for pan the in your mouse File over transcripts, ‘Nucleotide Links’ and your Under the section products’ number compare of different and computer the save align into species the the software appears. le. choose Your ClustalX the that les. sequence called for ClustalX ‘Load Sequences’. sequences should show window. the Alignment ▲ menu Alignment.’ sequence ‘Genomic until Figure 3 144 a menu, organisms. regions, it it. the shows Move the Complete (chimpanzee). ● paste le. organism, ● such to download ● up ● and should GenBank (http://www.ncbi.nlm.nih.gov/pubmed/) ● sequence sequence notepad with want you, sequence. and ● the the identication ● conserved or and determine you evolutionary le A ’ results ● of Choose The choose example alignment of 9 ‘Do below different 3 . 1 G E N E s Data-baed queton: COX-2, smoking and stomach cancer COX-2 is a gene that cyclooxygenase. 6,000 nucleotides. polymorphisms codes The gene Three have for the single been 2 enzyme consists of a) of nucleotide discovered associated with gastric cancer occurs of at can survey copies stomach. nucleotide nucleotide large the of be in the One either COX-2 of The these base adenine involved gene developed gastric Explain in at or 3 this guanine. sequencing 357 patients Deduce, at A people who did adenocarcinoma not people smoked were have asked the conclusion the 1 shows the 357 they were whether they had nucleotide patients categorized whether and gene results they or copies (GG) or with that the with a reason, 1195 risk of is whether associated gastric did not A at shown this All had Discuss, using the data, adenocarcinoma Predict, all this of at COX-2 least one with whether is the increased risk of equally as (AG percentages. AG or AA 9.8% Non-smokers 9.5% 43.7% or Table copy of AA). The 2 40.0% G for the 985 T able 1 Patients with cancer shows people alleles the data, common 9.4% at which of bases nucleotide G 1195 are or if 12.6% 42.4% in [2] formed The in 35.6% T able 2 Patients without cancer Actvt changes out. AG or AA who controls. example, [2] cancer. using more base an [2] Smokers New aee New alleles are formed by mutation. One with A and Muaio carried or to ▲ random G smokers. Non-smokers New [2] of Smokers the drawn ever non-smokers position categorization have is be adenocarcinoma. GG same A can percentages. gastric according smokers two 1195 with are the 1 [2] in ▲ the patients cigarettes. adenocarcinoma at the percentage who disease. whether in GG Table of total weresmokers. difference nucleotide in these the the increased both gastric 985 that and SNPs 4 had percentage adenocarcinoma, 1195. China total smokers controls from a the were that b) are Calculate that over the – from there most is was of alleles by mechanism signicant sequence adenine other no a type gene present at of is a gene for a mutation. mutation replaced by particular Mutationsare particularmutation is a a base substitution. different point in the being base. base For sequence Recent research into mutation involved nding the base sequence of all genes in parents and their ospring. It showed that there was one base mutation per 8 it could be substituted by cytosine, guanine or 1.2 × 10 thymine. bases. Calculate how many new alleles a child is likely A random change to an allele that has developed by evolution over to have as a result of mutations perhaps millions of years is unlikely to be benecial. Almost all in their parents. Assume that mutations are therefore either neutral or harmful. Some mutations there are 25,000 human genes are lethal – they cause the death of the cell in which the mutation when the individual and these genes are 2,000 bases occurs. Mutations in body cells are eliminated dies, long on average. but mutations in cells that develop into gametes can be passed on to Source: Campbell, CD, et al. (201 2) offspring and cause genetic disease. “Estimating the human mutation rate using autozygosity in a founder population.” Nature Genetics, 44: 1 277 1 281. doi: 10.1038/ng.24 18 145 3 G e n e t i c s TOK sickle cell aemia Wat ctea can be ued to The causes of sickle cell anemia, including a base dtngu between coeaton and substitution mutation, a change to the base sequence caue and eect? There is a correlation between high frequencies of the sickle-cell allele of mRNA transcribed from it and a change to the sequence of a polypeptide in hemoglobin. in human populations and high rates Sickle-cell anemia is the commonest genetic disease in the world. of infection with Falciparum malaria. It Where a correlation exists, is due to a mutation of the gene that codes for the alpha-globin it may polypeptide in hemoglobin. The symbol for this gene is Hb. Most or may not be due to a causal link . A humans have the allele Hb . If a base substitution mutation converts Consider the information in gure 4 the sixth codon of the gene from GAG to GTG, a new allele is formed, to decide whether sickle-cell anemia S called Hb . The mutation is only inherited by offspring if it occurs in a causes infection with malaria. cell the When the codon sixth amino 15–20 s allele (%) 10–15 or testis 5–10 allele instead acid causes is that develops transcribed, of in GAG, the concentrations. formed are rigid sickle capillaries, cells the into an cause to is bundles distort damage them and mRNA when to this egg or sperm. to of the produced mRNA valine molecules The enough blocking and polypeptide hemoglobin oxygen These Key Hb sixth change Frequency of Hb ovary S b) a) of is instead stick red tissues reducing blood by of together hemoglobin tissues molecules cells ow. GUG glutamic in into becoming blood has transcribed, a with sickle This low are shape. in sickle its acid. that trapped When as the blood cells 0–5 return break to up high and oxygen the conditions cells return to in the their lung, normal the hemoglobin shape. These bundles changes occur Figure 4 Map (a) shows the frequency of time after time, as the red blood cells circulate. Both the hemoglobin red blood and the sickle cell allele and map the plasma membrane are damaged and the life of a cell can be cells at (b) shows malaria aected areas in shortened to as little as 4 days. The body cannot replace red blood Africa and Western Asia a rapid So, for a enough small rate change individuals that and to a anemia gene inherit therefore can the have gene. It develops. very is harmful not consequences known how often this S mutation has remarkably occurred common. have two copies have one copy These of so individuals but In the allele make only in some parts both suffer of and parts East of Africa develop normal mild the up world the to of severe 5% anemia. hemoglobin and anemia. Figure 5 Micrographs of sickle cells and normal red blood cells 146 Hb allele newborn Another the mutant is babies 35 % form. 3 . 1 G E N E s Wha i a geome? The genome is the whole of the genetic information of an organism. Among genetic DNA, of its ● biologists so a living DNA In today information the ● number of In plant species in the means Genetic is the the whole information entire base is of the contained sequence of in each in consists the This is the chromosomes nucleus the plus is the plus pattern in usually genome the of nucleus is DNA the 46 molecules the DNA other that form molecule animals, in the though the different. DNA molecules molecules in the of chromosomes mitochondrion and chloroplast. The in genome genome genome chromosomes the word organism. organism’s mitochondrion. ● the an molecules. humans the of genome the of circular prokaryotes is chromosome, much plus smaller any and plasmids consists that are of the DNA present. the Huma Geome Projec The entire base sequence of human genes was sequenced in the Human Genome Project. The Human base Genome sequence of improvements the in be Project entire base sequence to complete sequence sequencing published in began human much in 1990. Its genome. techniques, sooner aim This than was to project which nd allowed expected in the drove rapid a 2000 draft and a Actvt 2003. Etc of genoe eeac Although knowledge immediate what can and be total of entire base understanding regarded many as researchers for which sequences base the a rich years are to of mine human of come. sequence data, For has genetics, which example, protein-coding not genes. will it is it given has be are an given worked possible There us to Ethical questions about us genome research are wor th by predict discussing. approximately Is it ethical to take a DNA 23,000 of these in the human genome. Originally, estimates for the sample from ethnic groups number of genes were much higher. around the world and sequence it without their Another discovery was that most of the genome is not transcribed. permission? Originally that called within expression “junk these as DNA,” “junk” well as it is regions, highly being there repetitive increasingly are elements sequences, recognized that called affect gene satellite Is it ethical for a biotech DNA. company to patent the base sequence of a gene to The genome that was sequenced consists of one set of chromosomes – it prevent other companies is a human genome rather than the human genome. Work continues from using it to conduct to nd variations in sequence between different individuals. The vast research freely? majority unity, of but base there contribute to sequences are also human are many shared single by all humans nucleotide giving us genetic polymorphisms which Who should have access to this genetic information? diversity. Should employers, Since the publication other species of the human genome, the base sequence of many insurance companies and has been determined. Comparisons between these genomes law enforcement agencies reveal aspects of the evolutionary history of living organisms that were know our genetic makeup? previously of biology unknown. in the 21st Research into genomes will be a developing theme century. 147 3 G e n e t i c s techique ued for geome equecig Developments in scientic research follow improvements in technology: gene sequencers, essentially lasers and optical detectors, are used for the sequencing of genes. The idea seemed of sequencing impossibly improvements in the entire difcult at technology human one time towards uorescent genome ending but the end 20th century made it possible, though still These improvements continued The samples once copies was underway and draft sequences Further species completed advances to be much are sooner allowing sequenced at an than the ever expected. genomes of sequence small separately. of DNA, using a lengths genome, of To DNA. nd the it base single-stranded DNA is rst Each polymerase, of increasing broken these is sequence copies but of the it of up a the whole base sequence has An putting small quantities of a for the copies bases. together in and one all lane the of number of a gel nucleotides. scans along the markers lane to make the uoresce. optical is of a detector is used uorescence series of to along peaks each to of detect the the lane. uorescence, number of nucleotides stopped been A computer deduces the base sequence from copied the by mixed separated the corresponding ● before laser There fragment is A colours into made process four rate. sequenced are are are to uorescent other ● To used were ● therefore is the the according project of very DNA ambitious. marker each of ● the in sequence of colours of uorescence non-standard detected. nucleotide separately each of of DNA with copy of varying four samples of the sequence the are copy tracks bases in advance sequencing by in the in the is gel, DNA technology uorescent mark DNA it markers copies. A end a samples each each according band be number in just which the deduced. that is of each from can done produced, For there the is carrying Four separated automating Coloured the at are electrophoresis. in four of major gel bases. length bases This nucleotides DNA These nucleotides ● possible DNA by mixture. non-standard four of base reaction of length The the four to one 148 with the one copy. into speeded up this: are different used to colour of Figure 6 Sequencing read from the DNA of Pinor Noir variety of grape 3 . 2 C h r O m O s O m E s 3.2 Coooe Uderadig Applicaio Prokaryotes have one chromosome consisting ➔ Cairns’s technique for measuring the length ➔ of a circular DNA molecule. of DNA molecules by autoradiography. Some prokaryotes also have plasmids but ➔ Comparison of genome size in T2 ➔ eukaryotes do not. phage, Escherichia coli, Drosophila Eukaryote chromosomes are linear ➔ melanogaster, Homo sapiens and DNA molecules associated with histone Paris japonica. proteins. Comparison of diploid chromosome numbers ➔ In a eukaryote species there are ➔ of Homo sapiens, Pan troglodytes, Canis dierent chromosomes that carry dierent familiaris, Oryza sativa, Parascaris equorum. genes. Use of karyotypes to deduce sex and diagnose ➔ Homologous chromosomes carry the same ➔ Down syndrome in humans. sequence of genes but not necessarily the same alleles of those genes. skill Diploid nuclei have pairs of homologous ➔ chromosomes. Use of online databases to identify the locus of ➔ a human gene and its protein product. Haploid nuclei have one chromosome of ➔ each pair. The number of chromosomes is a characteristic ➔ naure of ciece feature of members of a species. Developments in scientic research follow ➔ A karyogram shows the chromosomes of ➔ improvements in techniques: autoradiography an organism in homologous pairs of was used to establish the length of DNA decreasing length. molecules in chromosomes. Sex is determined by sex chromosomes and ➔ autosomes are chromosomes that do not determine sex. Bacerial chromoome Prokaryotes have one chromosome consisting of a circular DNA molecule. The structure most molecule of of prokaryotic prokaryotes the there containing cell. sometimes The DNA described all in as is cells one the was described chromosome, genes bacteria is needed not in sub-topic consisting for the associated basic with of a life 1.2. In circular DNA processes proteins, so is naked. 149 3 G e n e t i c s Because is only usually present a briey preparation are one only moved after for to chromosome single cell copy the of present The poles and in gene. chromosome division. opposite is each has two the a prokaryotic Two identical been replicated, genetically cell then identical splits in cell, there copies but are this is a chromosomes two. Plamid Some do prokaryotes are small extra prokaryotes but circular and naked, but those not antibiotic when an a antibiotic are not of formed plas mids cell bu t eukaryot es of spread through natural a present or in a life the the cell same and a are commonly that processes. in They may For plasmids. environment replicated at genes located in that eukaryotes. few basic cell be This dies method to can at the rate. same may are be found usually useful example, These but as there not be not the may to in small, the genes genes are time Hence plasmid transferred population. barrier. biologists is its often always plasmids prokaryotic for are a in are at cell for benecial other times. chromosome be passed multiple to both cells division. Copies species molecules unusual containing cell plasmids by DNA very needed prokaryotic copies by are resistance Plasmids the have not . Plasmids of also of is It is happens absorbed gene transfer transfer genes from even if by a one plasmid a cell of between between cell possible a for that to is released different species. species another, plasmids to cross when species. Plasmids allowing are It is also a a used articially. Figure 1 (a) Circular DNA molecule from a bacterium (b) Bacterium preparing trimethoprim to divide genes to help the resistance plasmid spread penicillin family disinfectant resistance resistance streptomycin family resistance vancomycin resistance Figure 2 The pLW1043 plasmid Uig auoradiography o meaure DnA molecule Developments in scientic research follow improvements in techniques: autoradiography was used to establish the length of DNA molecules in chromosomes. Quantitative the hypothesis, that 150 data strongest type but provide in the is usually of considered evidence biology most it is for or to sometimes convincing be against Developments a images evidence. to be invisible. but in produced of These sometimes microscopy structures sometimes also change have that allowed were conrm our images previously existing ideas understanding. 3 . 2 Autoradiography the 1940s substances John way DNA time were Cairns in the was used not used to the biologists in where cells or technique He obtained from E. clear by discover located 1960s. molecules it was onwards coli in a of At than Cairns time. whole to the was one, a but answered revealed different images the more tissues. bacteria. whether chromosome from specic C h r O m O s O m E s single the this replication Cairns’s question. forks technique investigate the DNA molecule images in structure They DNA was used of or produced by also for the by rst others eukaryote chromosomes. bacterial Meaurig he legh of DnA molecule Cairns’s technique for measuring the length of DNA molecules by autoradiography. John from Cairns E.coli produced using this images of DNA The molecules technique: images molecule ● Cells a were culture grown medium thymidine. linked by to coli DNA make a replication ● The cells Tritiated the were membrane E. then and of DNA coli that of was cell the enzyme long cells 2 burst surface ● A thin of lm applied left in time to of some of and react At end the was surface the with of the At the of two researchers in contains hydrogen, a The of there given 1,100 µm. that the This length of is the E coli µm. to chromosomes. so the fruit that by y was the was then produce An image Drosophila 12,000 total µm melanogaster at least of a by of chromosome of This DNA chromosome, other eukaryotic melanogaster long. amount D. used images was from produced corresponded known so for to this be in a species a chromosome molecule. In contains contrast to one very long prokaryotes, was linear rather than the circular. the was membrane and During tritium energy in that the DNA electrons, lm. and is a of period examined point position of the DNA were onto emulsion two-month each that circular digested cells DNA the high the showed single dialysis were months. atoms emitted atomdecayed indicate for developed microscope. their Cairns a membrane. photographic the which lm release dialysis darkness decayed ● to the is length Autoradiography used uses produced onto only molecule gently by coli base is it is with walls lysozyme. a remarkably DNA using with E. in cells. placed their the and thymidine isotope labelled in consists nucleotides in tritiated deoxyribose radioactive radioactively generations containing to replication. tritium, two Thymidine thymine E. for produced chromosome where dark the the with a grain. a tritium These DNA. Figure 3 Eukaryoe chromoome Eukaryote chromosomes are linear DNA molecules associated with histone proteins. Chromosomes DNA with is a in single histone eukaryotes immensely proteins. are long Histones composed linear are of DNA globular DNA and molecule. in shape protein. It is and The associated are wider 151 3 G e n e t i c s than the DNA. with the DNA chromosome are not in There are of a many with string histone wound separated contact appearance are molecule by short histones. of beads molecules around them. stretches This gives during a in a chromosome, Adjacent of the histones DNA eukaryotic in molecule the that chromosome the interphase. Dierece bewee chromoome In a eukaryote species there are dierent chromosomes that carry dierent genes. Eukaryote chromosomes microscope during chromosomes Figure 4 In an electron micrograph the visible histones give a eukaryotic chromosome of the appearance of a string of beads during if become stains mitosis the chromatids, are that much bind identical narrow During shorter either chromosomes with too interphase. DNA can DNA be to be mitosis and or visible and fatter by proteins seen to molecules be with meiosis a light the supercoiling, are used. double. produced In so the There are rststage are two byreplication. interphase When can the be chromosomes seen. centromere can be They differ where positioned the are examined both two in during length and chromatids anywhere from are close to in mitosis, the held an different position together. end to the of types the The centromere centre of the chromosome. OH PH There are at least two different types in every eukaryote but in most phe 16S 7S DNA val species there are more than that. In humans for example there are 23S thr 23 types of chromosome. cyt b leu PL pro Every gene in eukaryotes occupies a specic position on one type of N1 ile chromosome, called the locus of the gene. Each chromosome type glu f-met therefore gln N6 N2 DNA carries molecule. a In specic many sequence of genes chromosomes this arranged sequence along the contains linear over a ala control loop asn ribosomal RNA trp N5 thousand genes. cys transfer RNAs OL tyr leu protein coding gene Crossing experiments were done in the past to discover the sequenceof ser his genes ser on chromosome types in Drosophila melanogasterand other species. OX1 The base sequence of whole chromosomes can now be found, allowing N4 asp a rg more accurate and complete gene sequences to be deduced. OX2 3 N gly lys OX3 ATPase Having the genes chromosome arranged allows parts in of a standard sequence chromosomes to be along a swapped type of during meiosis. Figure 5 Gene map of the human mitochondrial chromosome. There are genes on both of the two DNA strands. The chromosomes in the Homologou chromoome nucleus are much longer, carry far more genes and are linear rather than circular Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes. If two chromosomes homologous. each are If of other because, for at the same sequence chromosomes least some of are the of not genes genes usually on they are identical them, the to alleles different. two the eukaryotes are chromosomes chromosome 152 have Homologous in the members in one other. of of the them This same to allows be species, we homologous members of a can with species expect at to each least one interbreed. 3 . 2 C h r O m O s O m E s Data-baed queton: Comparing the chromosomes of mice Actvt and humans mcocope nvetgaton of gac Figure 6 shows all of the types of chromosome in mice and in coooe humans. Numbers and colours are used to indicate sections of mouse 1 chromosomes that are homologous to sections of human Garlic has large chromosomes so is an chromosomes. ideal choice for looking at chromosomes. Mouse and human genetic similarities Cells in mitosis are needed. Garlic bulbs Mouse chromosomes 1 2 3 4 5 Human chromosomes 6 7 8 9 19 10 8 1 2 3 4 5 6 grow roots if they are kept for 3 or 4 days 7 8 9 with their bases in water, at about 25°C. 11 7 8 19 6 19 9 7 8 3 Root tips with cells in mitosis are yellow 11 9 2 2 4 11 4 19 11 18 15 4 15 2 3 in colour, not white. 19 6 3 15 11 10 1 16 7 1 16 3 1 12 20 4 polystyrene 10 garlic bulb 1 13 11 10 10 11 12 13 14 15 16 1 7 11 12 13 14 15 16 1 7 18 disc with 18 hole cut 3 22 6 10 16 2 5 6 18 7 10 7 2 5 2 1 8 14 3 6 5 22 through 16 16 10 22 7 6 water at 25 °C 8 2 1 beaker 19 22 14 18 19 18 2 1 1 7 13 5 2 12 12 19 20 2 1 22 X Y 2 19 X Root tips are put in a mixture of a stain Y that binds to the chromosomes and 11 Y 9 acid, which loosens the connections X 10 between the cell walls. A length of about Figure 6 Chromosomes 5 mm is suitable. Ten parts of aceto- 3 orcein to one part of 1.0 mol dm 1 Deduce the number of types of chromosomes in mice and hydrochloric acid gives good results. in humans. [2] stain–acid mix ture 5 mm long garlic 2 Identify the similarto two human mouse chromosome types that are root tip most chromosomes. [2] watch glass 3 Identify mouse chromosomes nothomologous to human which contain sections that are chromosomes. [2] 3 4 Suggest reasons andhuman for the many similarities between the The roots are heated in the stain–acid mixture on a hot plate, to 80°C for mouse genomes. 5 minutes. One of the root tips is put [2] on a microscope slide, cut in half and 5 Deduce how chromosomes have mutated during the evolution the 2.5 mm length fur thest from the of animals such as mice and humans. [2] end of the root is discarded. root tip watch glass hot plate Comparig he geome ize set at 80 °C Comparison of genome size in T2 phage, Escherichia 4 coli, Drosophila melanogaster, Homo sapiens and A drop of stain and a cover slip is added and the root tip is squashed to spread Paris japonica. out the cells to form a layer one cell The genomes of living organisms vary by a huge amount. The smallest thick. The chromosomes can then be genomes are those of viruses, though they are not usually regarded as examined and counted and the various living organisms. The table on the next page gives the genome size of phases of mitosis should also be visible. one virus and four living organisms. thumb pressing down to squash root ti p One of the smallest four living genome. The organisms genome is size a prokaryote. of eukaryotes It has much depends on the the size cover and number of chromosomes. It is correlated with the complexity slip of the organism, reasons genes is for this. very but The is not directly proportion variable and also of the proportional. the DNA amount that of There acts gene as are microscope slide folded lter paper several functional duplication varies. 153 3 G e n e t i c s Ogan Genoe ze Decpton (on bae pa) T2 phage 0.18 Virus that attacks Escherichia coli Escherichia coli 5 Drosophila melanogaster Gut bacterium 140 Fruit y Homo sapiens 3,000 Humans Paris japonica 150,000 Woodland plant Fidig he loci of huma gee Use of online databases to identify the locus of a human gene and its protein product. The locus of homologous be used to a gene is its particular chromosomes. nd the locus of position Online human on databases genes. together can that with the total an example Mendelian by Johns of such a Inheritance Hopkins database in Man in the of gene loci on There Gene nae is number chromosome. Decpton of gene Online website, maintained DRD4 A gene that codes for a dopamine University. receptor that is implicated in a variety of neurological and psychiatric conditions. ● Search home for the abbreviation OMIM to open the page. CF TR A gene that codes for a chloride channel protein. An allele of this gene causes ● Choose ● Enter Search Gene Map. cystic brosis. the name of a gene into the Search HBB Gene Map box. This should bring up a gene, including The gene that codes for the beta-globin table subunit of hemoglobin. An allele of this with information about the its gene causes sickle cell anemia. locus, the starting gene genes is are with located. shown the chromosome Suggestions on the of on which human F8 The gene that codes for Factor VIII, one right. of the proteins needed for the clotting of blood. The classic form of hemophilia is ● An alternative to entering the name of a gene caused by an allele of this gene. is of to select the sex sequence a chromosome chromosomes of gene loci from X will or be Y. 1–22 A or one complete TDF Testis determining factor – the gene that displayed, causes a fetus to develop as a male. Haploid uclei Haploid nuclei have one chromosome of each pair. A haploid set of the humans contain Gametes are Gametes have contain 154 nucleus has one chromosomes 23 the 23 chromosome that are found chromosomes sex cells haploid that nuclei, chromosomes. fuse so for of in each its It has one Haploid full nuclei in example. together in type. species. humans during both sexual egg and reproduction. sperm cells 3 . 2 C h r O m O s O m E s Diploid uclei Diploid nuclei have pairs of homologous chromosomes. A diploid sets of humans When contain with cells consist a 46 two gametes with gametes are fuse found for is nuclei diploid of in each its during sexual When produced. apart type. species. It has two Diploid full nuclei in example. produced. are cells, sexual for together nucleus diploid of chromosomes that chromosomes diploid entirely produce has chromosomes haploid zygote more nucleus the from Many the reproduction, this divides animals cells that by and they a mitosis, plants are using to reproduction. Figure 7 Mosses coat the trunks of the laurel Diploid nuclei have two copies of every gene, apart from genes on the trees in this forest in the Canary Islands. sex chromosomes. An advantage of this is that the effects of harmful Mosses are unusual because their cells are recessive mutations can be avoided if a dominant allele is also present. haploid. In most eukaryotes the gametes are Also, organisms are often more vigorous if they have two different alleles haploid but not the parent that produces them of genes reason instead for of strong just one. growth of This F is known hybrid as crop hybrid vigour and is the plants. 1 Chromoome umber The number of chromosomes is a characteristic feature of members of a species. One of are a of the unlikely species The to need number species. if most fundamental chromosomes. splits It can occur. number to numbers be to of Organisms able decrease There to if are same so all number can change these are unchanged the of a over of is the number chromosomes interbreeding members of chromosomes. during that rare species number become mechanisms However, of different chromosomes also remain a interbreed the chromosomes double. tend to have characteristics with the evolution fused can events millions together cause and of the of a or increase chromosome Figure 8 Trillium luteum cell with a diploid chromosome years of number of 12 chromosomes. Two of each evolution. type of chromosome are present Comparig chromoome umber Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum The Oxford large of English volumes, information Dictionary each consists containing about the a origins large and of twenty and amount meanings eukaryotes. This information could have been have a smaller number of larger volumes or in a of smaller volumes. There is a eukaryotes the numbers and sizes of small large chromosomes ones. have so the at least diploid two different chromosome types of number at least four. In some cases it is over a hundred. parallel The with few larger is number many a published chromosome, in have of All words. others Some chromosomes table on the next page shows the diploid in chromosome number of selected species. 155 3 G e n e t i c s scentc nae Eng Dpod coooe of pece nae nube Parascaris horse equorum threadworm 4 Oryza sativa rice 24 Homo sapiens humans 46 Pan troglodytes chimpanzee 48 Canis familiaris dog 78 Figure 9 Who has more chromosomes – a dog or its owner? Data-baed queton: Dierences in chromosome number Pant Coooe nube Ana Haplopappus gracilis 4 Parascaris equorum (horse threadworm) Luzula purpurea (woodrush) 6 Aedes aegypti (yellow fever mosquito) Crepis capillaris 8 Drosophila melanogaster (fruity) Vicia faba (eld bean) 12 Musca domestica (house y) Brassica oleracea (cabbage) 18 Chor thippus parallelus (grasshopper) Citrullus vulgaris (water melon) 22 Cricetulus griseus (Chinese hamster) Lilium regale (royal lily) 24 Schistocerca gregaria (deser t locust) Bromus texensis 28 Desmodus rotundus (vampire bat) Camellia sinesis (Chinese tea) 30 Mustela vison (mink) Magnolia virginiana (sweet bay) 38 Felis catus (domestic cat) Arachis hypogaea (peanut) 40 Mus musculus (mouse) Coea arabica (coee) 44 Mesocricetus auratus (golden hamster) Stipa spar tea (porcupine grass) 46 Homo sapiens (modern humans) Chrysoplenum alternifolium (saxifrage) 48 Pan troglodytes (chimpanzee) Aster laevis (Michaelmas daisy) 54 Ovis aries (domestic sheep) Glyceria canadensis (manna grass) 60 Capra hircus (goat) Carya tomentosa (hickory) 64 Dasypus novemcinctus (armadillo) Magnolia cordata 76 Ursus americanus (American black bear) Rhododendron keysii 78 Canis familiaris (dog) T able 1 1 There are in table, the for of many example, the different but 5, species some 7, has 11, 13 chromosome numbers 13. are Explain numbers 3 missing, why species none chromosomes. of Discuss, using hypothesis organism 156 the that is, the data the in more more the table, complex why the cannot size be of the deduced genome from the of a number chromosomes. [1] [3] 4 2 Explain the in an chromosomes it Suggest, occurred has. [4] using the chromosome during data in structure human table that 1, a may evolution. change have [2] 3 . 2 C h r O m O s O m E s sex deermiaio Sex is determined by sex chromosomes and autosomes female male XX XY are chromosomes that do not determine sex. are two chromosomes in humans that determine sex: X X There ● the X the middle. chromosome the Y the end. is relatively large and has its centromere near X ● Y XX chromosome is m uch s ma ll e r and ha s its c e n t ro m e r e XX n e ar XY XY Because the X and chromosomes. All affect a whether Y chromosomes the other fetus determine chromosomes develops as a male sex are or they are autosomes called and the do sex not female. 1 female : 1 male The X chromosome has many genes that are essential in both males and Figure 10 Determination of gender females. The Y Y All humans chromosome chromosome has chromosome, but are on not found must only the the the therefore has a same small on at least number sequence genes X have the of as remainder of and are X genes. genes chromosome of one not a chromosome. A small small the Y part part of of the the X chromosome needed for female development. One Y male. male this A chromosome This called features, gene fetus have a the Females has TDF of their an X or a X by Y particular SRY one so X in mother. chromosome X two fertilization be two in testes X ovaries not The one egg chromosome and one sons Y Y fetus the no Y instead to develop a develops testes and of Because chromosome of as development production. chromosome and develop cell, gender the a initiates as a does of male. not female sex testosterone. Females so of a chromosome half It testosterone chromosomes. each causes TDF . and and chromosome. and or chromosomes produced, chromosomes from with gene are have gene either including fetus that hormones X is When all human is carried in sperm his Y on one inherit of an determined are chromosome. inherit pass offspring the sperm. formed, Daughters their X at the This half two chromosome moment can either contain inherit their the X father’s chromosome. Karyogram A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length. The chromosomes with to make type If cells a in the burst spread. cells by Often can usually can be an organism giving chromosomes distinctive dividing then of metaphase are they on the are visible clearest up. in cells view. Some that Stains stains give are have each in to mitosis, be used chromosome pattern. and the overlap found of show stained pressing be taken banding the with placed cover each no stained on slip, other, a microscope the but overlapping slide chromosomes with careful and are become searching chromosomes. A a cell micrograph chromosomes. 157 3 G e n e t i c s Originally analysis involved cutting out all the chromosomes and TOK arranging them chromosomes manually are but arranged this process according to can their now size be done and digitally. structure. The The To wat ex tent detenng gende position of the centromere and the pattern of banding allow chromosomes fo po tng copetton a centc that are of a different type but similar size to be distinguished. queton? As most cells are diploid, the chromosomes are usually in homologous Gender testing was introduced at pairs. They are arranged by size, starting with the longest pair and the 1968 Olympic games to address ending with the smallest. concerns that women with ambiguous physiological genders would have an unfair advantage. This has proven to be problematic for a number of reasons. The chromosomal standard is problematic as non-disjunction can lead to situations where an individual might technically be male, but might not dene herself in that way. People with two X chromosomes can develop hormonally as a male and people with an X and a Y can develop hormonally as a female. The practice of gender testing was discontinued in 1996 in par t because of human rights issues including the right to self-expression and the right to identify one's own gender. Rather than being a scientic question, it is more fairly a social question. Figure 11 Karyogram of a human female, with uorescent staining Karyoype ad Dow ydrome Use of karyotypes to deduce sex and diagnose Down syndrome in humans. A karyogram arranged property that at 1 Figure 12 Child with trisomy 2 1 or the in of is an organism deduce and 2 To one Y is pregnancy. sometimes 158 there called a be chromosomes of is number nuclei. used the of two is an length. and Karyotypes in individual type are organism, A karyotype of is a chromosomes studied by looking ways: male individual or is female. female If two XX whereas one X male. using are of decreasing the syndrome two, of other cells copies the 21. the Mental and fetal three trisomy features disorders. it its an done instead the present Down If component vision in indicate usually karyotype are of pairs – can whether diagnose This has They chromosomes Down syndrome image organism karyograms. To an homologous child of growth from the Down 21 in syndrome. individuals are abnormalities. uterus chromosome has While syndrome and chromosome taken vary, hearing retardation This some loss, are during the of heart also is the and common. 3 . 3 m E i O s i s Data-based questions: A human karyotype The 1 2 karyogram State shows which longest b) shortest. a) human b) the karyotype chromosome a) Distinguish the type of a fetus. is [2] between the structure chromosome human a X 3 Deduce with 4 Explain whether and reason the Y 2 and of chromosome 12 chromosome. the sex of karyotype the [4] fetus. shows any [2] abnormalities. [2] Figure 13 3.3 meo Uderadig Applicaio ➔ One diploid nucleus divides by meiosis to ➔ Non-disjunction can cause Down syndrome produce four haploid nuclei. and other chromosome abnormalities. Studies ➔ The halving of the chromosome number allows showing age of parents inuences chances of a sexual life cycle with fusion of gametes. ➔ DNA is replicated before meiosis so that all non-disjunction. ➔ chromosomes consist of two sister chromatids. ➔ Methods used to obtain cells for karyotype analysis e.g. chorionic villus sampling and amniocentesis and the associated risks. The early stages of meiosis involve pairing of homologous chromosomes and crossing over followed by condensation. ➔ chromosomes prior to separation is random. ➔ skill Orientation of pairs of homologous ➔ Drawing diagrams to show the stages of meiosis resulting in the formation of four Separation of pairs of homologous haploid cells. chromosomes in the rst division of meiosis halves the chromosome number. ➔ Crossing over and random orientation promotes naure of ciece genetic variation. ➔ ➔ Making careful obser vations: meiosis was Fusion of gametes from dierent parents discovered by microscope examination of promotes genetic variation. dividing germ-line cells. 159 3 G e n e t i c s the dicovery of meioi Making careful observations: meiosis was discovered by microscope examination of dividing germ-line cells. When in the cell improved 19th structures, specically revealed microscopes century it that was stained been detailed discovered the thread-like had gave nucleus structures that of in some the chromosome developed images cell. observation of a dyes These dividing halves dyes nuclei special named chromosomes. From the 1880s the group of German biologists carried out observations how mitosis of dividing and nuclei meiosis careful that can these that biologists they slides can a on bud or the we The must the be microscope or the images of the process. by shapes A key experts as during the the observation (Parascaris in it was egg of egg animals of there contains The must generation be that number. unlike during mitosis gamete had already development and plants. These divisions in were as the method used to halve the Suitable anthers cells in enough of cells from begins at of this birth out the between advantage of by 0 and were of 28 is occurs in careful ovaries species and they events named meiosis rabbits days that of ( Oryctolagus old. in slowly was observation The females over meiosis many days. to are show slides understand variety worked taken and squashed meiosis prepared number sequence eventually cuniculus) tissue inside locust. then The the bizarre meiosis. in are the two sperm four. a meiosis. of microscope and clear to every there gradually observations dissected with form that and a no difcult stages equorum) nuclei fertilized is not Even chromosomes of stained Often are the developing of in fertilization. that and achievements challenging. testis slide. details images is the xed, visible made repeat preparation from from to by occur. considerable try meiosis obtained tissue a if made. showing be lily The appreciate division divisions observed chromosome We doubled chromosome identied revealed is hypothesis onwards both detailed the that been a to nuclear Nuclear were number led horse chromosomes cells, This threadworm whereas indicated the that the Figure 1 ▲ Meioi i oulie one diploid cell 2n One diploid nucleus divides by meiosis to produce four meiosis I haploid nuclei. two haploid cells n n Meiosis is cell divide. can one of the The two ways other in which method is the nucleus mitosis, of a eukaryotic which was described twice. The rst in meiosis II sub-topic four haploid cells n n produces nuclei. 1.6. two The In meiosis nuclei, two the each divisions nucleus of are which divides divides known as again meiosis I to give and a division total meiosis of four II. Figure 2 Over view of meiosis The has nucleus two known by known The the 160 as undergoes has just involves as cells of homologous meiosis Meiosis that chromosomes a a of the by rst type. division chromosome of the of meiosis Chromosomes chromosomes. halving reduction produced halving one the each Each of of each the type chromosome of four – is the diploid same nuclei they number. are It is – it type are produced haploid. therefore division. meiosis I chromosome have one number chromosome happens in of the each rst type, so division, 3 . 3 not the second haploid two division. number of chromatids. four nuclei that chromosome The two nuclei chromosomes, These have but chromatids the consisting haploid of a produced each separate number single by meiosis chromosome during of I still meiosis the consists II, chromosomes, have m E i O s i s of producing with each chromatid. Meioi ad exual life cycle The halving of the chromosome number allows a sexual life cycle with fusion of gametes. The life life cycles cycle the genetically of living offspring identical. organisms have In of In organisms, eukaryotic from two different chromosome halved at number Meiosis it some can happens therefore Meiosis stage happen diploid is a in at the and complex What is and the it be sexual cycle there so reproduction of Fertilization It sex cycle. This as the is involves cells, or an the the the are cause the diversity. process number of so genetic number halving asexual between gametes, therefore if In parent differences there doubles would generation, life asexual. are parents, union every or chromosomes the occurs. the during during developed. time number happens is parents. each life sexual Fertilization chromosomes of offspring can same sexual chromosomes fertilization. the a the of usually of a doubling was not also chromosome meiosis. any stage process have two process clear of is during copies and that a creating it its is sexual the of most not at cycle, but Body in cells animals are genes. the evolution life gametes. moment was a clear critical how step in it the Figure 4 Fledgling owls (bottom) produced by origin of eukaryotes. Without meiosis there cannot be fusion of gametes a sexual life cycle have diploid body cells but and the sexual life cycle of eukaryotes could not occur. mosses (top) have haploid cells Data-baed queton: Life cycles Figure 3 mosses, number shows with of n the life being cycle used chromosomes of to humans represent and 2n to and the 1 haploid represent the number. main moss Sporophytes plant and of mosses consist of a grow stalk ve cycle a of similarities moss and of a between in which spores are life [5] Distinguish between a a the life cycles of on and moss and human by giving ve a differences. capsule the human. the 2 diploid Outline [5] produced. egg n sperm sperm egg n n n moss human male zygote human female 2n 2n 2n plant zygote n Key mitosis 2n spore sporophyte n 2n meiosis fer tilization Figure 3 161 3 G e n e t i c s Replicaio of DnA before meioi DNA is replicated before meiosis so that all chromosomes 2n interphase consist of two sister chromatids. During by the early supercoiling. chromosome stages As of soon consists meiosis as of they two the chromosomes become visible chromatids. This it is is gradually clear because that all shorten each DNA in 2n homologous the nucleus is replicated during the interphase before meiosis, so each chromosomes chromosome Initially the genetically 2n n n two of two chromatids identical. This sister that is chromatids. make because up DNA each chromosome replication is very are accurate and meiosis I the n consists n number of mistakes We might the second expect the chromosome the division in the DNA of to copying be meiosis, of the replicated but it does DNA again not is extremely between happen. the This small. rst and explains how meiosis II n n in which to produce one each number is halved chromosome four haploid during consists nuclei in of meiosis. two which One diploid chromatids, nucleus, divides eachchromosome twice consists of chromatid. Figure 5 Outline of meiosis Bivale formaio ad croig over The early stages of meiosis involve pairing of homologous chromosomes and crossing over followed by condensation. Some I of while a most of two pair of DNA and of the junction is at Because a and in each As the is us one occurred, A bivalent there at is pair with and a there mutual are each at the called the in up the can the be with each with other. consists associated in each chromosomes place. of the is is The very molecular important. homologous chromatid. Crossing chromosomes. At over least one several. same exchange homologous meiosis synapsis. takes be of seen chromosome outcome each start cannot molecules other along pair over but the and homologous crossing here, precisely chromatids of sometimes anywhere occurs DNA chromatid rejoins happen elongated four called concern meiosis chromosomes are process where of very already there process involved, chromatids. has positions crossover chromatids Figure 6 A pair of homologous a not breaks occurs still chromosomes. created random crossover so pairing need chromosomes occurs and synapsis, this events are homologous replication homologous after details Firstly chromatids bivalent Soon important chromosomes microscope. Because A the the position of but on genes not the two between identical, the some chromosomes contains four alleles of the exchanged genes are likely to be different. Chromatids with chromatids and is sometimes called new combinations of alleles are therefore produced. a tetrad. Five chiasmata are visible in this tetrad, showing that crossing over can occur more than once Radom orieaio of bivale Orientation of pairs of homologous chromosomes prior to separation is random. While pairs nucleus growing 162 of of a homologous cell from in the the chromosomes early poles of stages the cell. of are condensing meiosis, After the spindle nuclear inside the microtubules membrane has are 3 . 3 broken the down, these attachment The principles ● Each ● The two The The the The to the centromeres of spindle microtubules is not the same as in mitosis. is attached to one chromosomes pole in a only, not bivalent to are both. attached to poles. to which pair of of each of orientation section bivalents of of on chromosome chromosomes attaching consequences the the orientation chance ● attach these: homologous pole way of are chromosome different ● microtubules chromosomes. The ● spindle m E i O s i s to each one the is and bivalent is attached facing. random, pole, random genetic is This so each not orientation later in of affect of depends called the being other which has pulled an to are equal it. bivalents. bivalents this on orientation. chromosome eventually does diversity is The discussed MITOSIS in topic. Halvig he chromoome umber Separation of pairs of homologous chromosomes in the rst division of meiosis halves the chromosome number. either The movement of chromosomes is not the same in the rst division or of MEIOSIS meiosis as in chromatids mitosis. that Whereas make up a in mitosis the chromosome centromere move to divides opposite and poles, in the two Figure 7 Comparison of attachment meiosis of chromosomes to spindle the centromere does not divide and whole chromosomes move to the poles. microtubules in mitosis and meiosis Initially by the two chiasmata, then the The of one is cell rst the of halves division chromosome formed these called of separation the the to but chromosomes chromosomes moves chromosomes in of the chromosome, pairs so the of the homologous type moves division they are is of the the to are held separation of chromosomes the reduction each pole, contain to to cell. both of of each the bivalent other opposite It is division. one and homologous from chromosome of together chromosomes chromosome number meiosis both of This One other chromosome that bivalent end separate. and meiosis each rst can to each disjunction. poles the of slide in poles therefore Because the each pole. two one nuclei type of haploid. Obaiig cell from a feu Methods used to obtain cells for karyotype analysis e.g. chorionic villus sampling and amniocentesis and the associated risks. Tw o procedures containing producing passing wall, The a the a needle used is used fluid amniotic sac. obtaining to to the mother's guide withdraw containing fetal the a cells needed Amniocentesis through ultrasound amniotic for chromosomes karyotype. needle using are fetal The A second procedure sampling used abdomen membranes needle. from This to tool involves sample cells for obtain can be that cells from done of amniocentesis, the with which earlier but it is chorionic from the in is 1%, villus through the the chorion, placenta the whereas amniocentesis sampling is enters sampling. vagina one the risk is the develops. pregnancy with of of than miscarriage chorionic villus 2% 163 3 G e n e t i c s Diagram of he age of meioi Drawing diagrams to show the stages of meiosis resulting in the formation of four haploid cells. In mitosis prophase, Meiosis each four can stage second stage also be are in twice: meiosis mitosis usually anaphase divided happens time in stages metaphase, also II. into in happen main in actual telophase. these meiosis The Usually recognized: and I stages, and but then events of a a each showing prophase: condensation of visible even metaphase: attachment of spindle microtubules; is why rather ● anaphase: movement of often is worth Permanent in then meiosis it is chromosomes of we decondensation than draw stages to slides! of chromosomes. Cell has 2n chromosomes (double nuclear membrane chromatid): n is haploid number of chromosomes. spindle microtubules and centriole ● Homologous chromosomes pair (synapsis). ● Crossing over occurs. Prophase I metapae i Spindle microtubules move homologous pairs to equator of cell. bivalents aligned on the equator ● Orientation of paternal and maternal chromosomes on either side of equator is random and independent of other Metaphase I homologous pairs. Anapae i ● Homologous pairs are separated. One homologous chromosomes chromosome of each pair moves to each being pulled to opposite poles pole. Anaphase I Teopae i ● Chromosomes uncoil. During interphase that follows, no replication occurs. cell has divided across the equator ● Reduction of chromosome number from diploid to haploid completed. Telophase I ● 164 Cytokinesis occurs. down to slides but usually it have temporary interpret their construct Popae i ● from them attempting from The rst division of meiosis ● at microscope slides than thepoles; telophase: of difcult bivalents usually microscope ● structures looking is more mounts, the chromosomes; structure ● biological Preparation meiosis challenging. but ● draw microscope. cells meiosis: we specimens, appearance. diagrams from of specimens This meiosis on 3 . 3 m E i O s i s The second division of meiosis Popae ii ● Chromosomes, which still consist of two chromatids, condense and become visible. Prophase II metapae ii Metaphase II Anapae ii ● Centromeres separate and chromatids are moved to opposite poles. Anaphase II Teopae ii ● Chromatids reach opposite poles. ● Nuclear envelope forms. ● Cytokinesis occurs. Telophase II Meioi ad geeic variaio Crossing over and random orientation promotes genetic variation. When two parents unpredictable the have mixture unpredictability parent has genetic Apart there of the each will parent. new child, they know characteristics due to meiosis. combination of that from Every alleles – it will each of gamete meiosis is inherit them. an Much produced a source by of of a endless variation. from copies a is a of be genes gene. one There are on In copy the some of likely X cases that to be and Y chromosomes, the allele in two copies every thousands of are gamete genes humans in the have same produced the two allele by parent’s and the genome 165 3 G e n e t i c s where Actvt the chance a gene of two alleles being with the are passed alleles different. on A in and a Each gamete. a. Half of of Let the the us two alleles suppose gametes has that an there produced by equal is the If g is the number of genes parent will contain A and half will contain a. in a genome with dierent g alleles, 2 is the number of combinations of these alleles that can be generated by meiosis. If there were Let us now Again can aB half result and suppose of in ab. the that there gametes gametes There are will with two is another contain different processes B gene and with half b. combinations in meiosis the of that alleles However, these B and genes: generate b. meiosis this AB, Ab, diversity. just 69 genes with dierent alleles (3 in each of the B 23 chromosome types in a B A b a 50% humans) there would be probability b 590,295,810,358,705, A 700,000 combinations. B b telophase I Assuming that all humans A are genetically dierent, and a that there are 7,000,000 50% humans, calculate the a a b A B probability prophase I percentage of all possible B genomes that currently exist. A metaphase I ▲ Figure 8 Random orientation in metaphase I 1. Random orientation of bivalents In of metaphase one Random the orientation does not orientation variation For I bivalent every among genes additional combinations in of a bivalents that are bivalent, cell of bivalents inuence the is the on the produced is process different number by random orientation that and any the of possible doubles. orientation the generates chromosome of meiosis of others. genetic types. chromosome For a haploid number n of n, the number of possible combinations is 2 . For humans with a 23 haploid number of 23 this amounts to 2 or over 8 million combinations. 2. Crossing over Without crossing chromosomes chromosome these genes It over would carried combinations to be increases meiosis so in be the to number much that it I, combinations linked combination could reshufed, the prophase forever occur produce of is in allele together. CD and gametes. new alleles another carried over combinations that on example, Crossing combinations effectively of For such can be if one cd, allows as Cd only linked and generated cD. by innite. Ferilizaio ad geeic variaio Fusion of gametes from dierent parents promotes genetic variation. The fusion both Figure 9 166 for of ● It is ● It allows the new gametes individuals start of alleles individual. to and the produce for life from a zygote is a highly signicant event species. of two a new individual. different individuals to be combined in one 3 . 3 ● The ● Fusion ● Genetic combination of of gametes variation alleles is therefore is unlikely ever promotes essential for to have genetic existed variation in m E i O s i s before. a species. evolution. no-dijucio ad Dow ydrome Non-disjunction can cause Down syndrome and other chromosome abnormalities. Meiosis One is sometimes example of chromosomes is termed any of Both pairs the to gamete that the decient involved be an 47 to of in other separate a pole. has at The can human to result either 13. with pole will be If the 45 gamete the result abnormal born of babies by a having the syndrome or is in humans not with trisomy can sex also an 18 so and the numbers chromosomes XXY. only are trisomy in syndrome having serious Babies result abnormal by are survive. Klinefelter’s caused chromosome, is do with chromosomes. of is sex caused Turner’s one sex X. will or diploid parent cell with chromosomes. An trisomies offspring Non-disjunction birth and chromosome fertilization, with one other the sometimes This happen chromosomes. extra chromosome. individual that anaphase. This move an Most errors. homologous homologous either in to when chromosomes neither is fail subject is non-disjunction. the of this two chromosome 21 number of chromosomes non-disjunction will often lead syndrome, signs or to i.e. a a person collection symptoms. For possessing of a during meiosis gamete with no chromosome 21 physical gamete with two example chromosome 21 trisomy 21, also known as Down cell dies syndrome, event that is due leaves to a the non-disjunction individual with fusion of normal haploid × three of instead some chromosome of of two. the number While 21 individuals component features gametes gamete vary, of trisomy: zygote with the syndrome include hearing loss, three chromosome 21 heart and vision disorders. Mental and Figure 10 How non-disjunction can give rise to Down syndrome growth retardation are also common. trisomy 2 1 Pareal age ad o-dijucio all chromosomal abnormalities non-disjunction The data maternal presented age and chromosomal 1 Outline of in the gure 11 shows incidence of the relationship trisomy 21 and of between other abnormalities. the relationship chromosomal between abnormalities in maternal live age and the incidence births. )sht rib evil lla fo %( ecnedicni Studies showing age of parents inuences chances of 14 12 10 8 6 4 [2] 2 2 a) For mothers 40 years of age, a child determine the probability that 0 they will give birth to with trisomy 21. [1] 20 b) Using the mother of data 40 chromosomal in gure years of 11, age calculate will abnormality give other the birth than probability to a child trisomy 21. that with 40 60 maternal age (years) a a ▲ [2] Figure 11 The incidence of trisomy 2 1 and other chromosomal abnormalities as a function of maternal age 167 3 G e n e t i c s 3 Only are a small ever commonest. 4 Discuss having number found the of among Suggest risks possible live reasons parents chromosomal births, face for and these when trisomy abnormalities 21 is much the trends. choosing to [3] postpone children. [2] 3.4 inetance Uderadig Applicaio ➔ Mendel discovered the principles of inheritance ➔ Inheritance of ABO blood groups. ➔ Red-green colour-blindness and hemophilia as with experiments in which large numbers of pea plants were crossed. examples of sex-linked inheritance. ➔ Gametes are haploid so contain one allele of ➔ Inheritance of cystic brosis and Huntington’s each gene. disease. ➔ The two alleles of each gene separate into ➔ Consequences of radiation after nuclear dierent haploid daughter nuclei during meiosis. bombing of Hiroshima and Nagasaki and the ➔ Fusion of gametes results in diploid zygotes nuclear accidents at Chernobyl. with two alleles of each gene that may be the same allele or dierent alleles. ➔ alleles but co-dominant alleles have joint eects. ➔ Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. ➔ Comparison of predicted and actual outcomes of genetic crosses using real data. Some genetic diseases are sex-linked and some are due to dominant or co-dominant alleles. ➔ ➔ Many genetic diseases in humans are due to recessive alleles of autosomal genes. ➔ skill Dominant alleles mask the eects of recessive ➔ Analysis of pedigree char ts to deduce the pattern of inheritance of genetic diseases. The pattern of inheritance is dierent with sex-linked genes due to their location on sex chromosomes. naure of ciece ➔ Many genetic diseases have been identied in ➔ Making quantitative measurements with humans but most are very rare. replicates to ensure reliability: Mendel’s genetic ➔ Radiation and mutagenic chemicals increase crosses with pea plants generated numerical data. the mutation rate and can cause genetic disease and cancer. 168 3 . 4 i N h E r i T A N C E Medel ad he priciple of iheriace Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed. When living offspring. also blue this, whales on. However, tails of We in acquired their parents. of it the was not Mendel’s nd out many of pea inheritance In 1866 were was interest in biologists done same pea female that He also his did just an of used inheritance Mendel’s other plants explained the For pea in of the theories, and early earlier. theories characters between made in those the of ▲ in Figure 1 Hair styles are acquired characteristics and are for tunately not rst inherited by ospring inheritance, “Experiments of pea grown of plant, on its Plant result and with grew the of Mendel male variety. each seven each own. the another repeated over been plants that They with basis on cosmetic pollen He them cross to with different pairs principles of effect. have work. and a be resemble blending demonstrated isolated research. the transferring experiment reasons experiments as can available. owers Mendel reliably of inherit by paper when in seen and current biologists by than whale, Hippocrates varieties formed were. this his Various using Scars intermediate was together were of explained his their are characteristics. sometimes Many that More blue to to young inherited. offspring theory parts results not be characters of published with time parents. published were be children a attacks According which not of parents’ whale cannot observations could the the species. skin inherited. the that their characters pattern theory this. these alternative the ignored. the the the so his of since have Mendel rediscovered experiments Mendel’s of peas, that as than so seeds and Mendel such observed an their in largely factor examples be killer characters to pea by characteristics same the inherit cannot caused varieties plants. characters offspring on reproduce, the and that variety the on in had what of markings century crossed collected members discussed experiments one are more until reliably carefully pass inheritance, Some Hybridization” which are been parents 19th blue the whales blending both whales the Aristotle from from that grandparents involved half as characteristics has they when characteristics blue example, reproduce, they humans Inheritance their – such say some some surgery but example, variations, passed For organisms For thirty years suggested and species. quickly animals. there In These inheritance in was 1900 did his for ndings this. not several cross-breeding conrmed all One great plants that and animals. Replicae ad reliabiliy i Medel’ experime Making quantitative measurements with replicates to ensure reliability: Mendel's genetic crosses with pea plants generated numerical data. Gregor the Mendel father of attributed to for research is regarded genetics. being into His the by most success rst to inheritance. is use Peas biologists as sometimes pea plants have clear characteristics that to can the easily next. hybrids or such be They they as red or followed can can also be white from be ower one crossed allowed to colour generation to produce self-pollinate. 169 3 G e n e t i c s In fact Mendel plants. was Thomas horticulturalist, Downton 18th in and Philosophical Knight had Castle century made not the Andrew rst conducted Transactions in the results the important pea cross pollinating peas: English research his of use an Herefordshire published some to Knight, to the stigma here at late in Royal pollen from another plant is dusted on the Society. discoveries: pollen is collected ● male the ● and female parents contribute equally to from the anthers offspring; characters that such apparently reappear in inheritance the is as white ower disappear next in colour offspring generation, discrete rather can showing than that blending; – called the keel ● one character can show “a alternative such as stronger red ower tendency” colour than self pollinating peas: the – if the ower is left untouched, the anthers inside the keel pollinate the stigma character. ▲ Although Mendel was not as pioneering in Figure 2 Cross and self pollination his (a) Prediction based on experiments as sometimes thought, he deserves blending inheritance credit for was pioneer in a another having seven Table in large different 1 shows aspect of obtaining numbers cross the his research. quantitative of replicates. experiments, results of his Mendel results He not also just tall plants and 3 dwarf plants did one. monohybrid crosses. pea plants with an It is now repeats standard in practice experiments to in science to demonstrate intermediate height include the (b) Actual results reliability of results. Repeats can be compared to tall plants see how close identied tests can and be differences they are. Anomalous excluded done to between from assess results analysis. the It is 3 dwarf plants be Statistical signicance treatments. can also of standard pea plants as tall practice to repeat whole experiments, using a as the tall parent different organism or different treatments, to test ▲ a hypothesis in different ways. Mendel Figure 3 Example of a monohybrid cross experiment. All the should hybrid plants produced by crossing two varieties together therefore be regarded as one of the fathers of had the same character as one of the parents and the genetics, but even more we should think of him character of the other parent was not seen. This is a clear as a pioneer of research methods in biology. Paenta pant Tall stem × dwarf stem Round seed × wrinkled seed Yellow cotyledons × green cotyledons Purple owers × white owers Full pods × constricted pods Green unripe pods × yellow unripe pods Flowers along stem × owers at stem tip ▲ 170 T able 1 hbd pant falsication of the theory of blending inheritance Opng fo ef-ponatng te bd rato All tall 787 tall : 277 dwarf 2.84 : 1 All round 5474 round : 1850 wrinkled 2.96 : 1 All yellow 6022 yellow : 2001 green 3.01 : 1 All purple 705 purple : 224 white 3.15 : 1 All full 882 full : 299 constricted 2.95 : 1 All green 428 green : 152 yellow 2.82 : 1 All along stem 651 along stem : 207 at tip 3.14 : 1 3 . 4 i N h E r i T A N C E Gamee Gametes are haploid so contain one allele of each gene. Gametes are start new of a produced gametes cells when are than gamete moves smaller Parents one male the pass and less in or genes only female and has female at to gametes, It all. usually In cell so are each and the sex fuse The able humans, in a its gene. The This is parents Male is the to of make the female sperm to has the a egg. contain of a both an cell female generally Gametes true the and swim nucleus is single whereas tail gametes. that the gamete move example, uses cell and zygote. male to haploid. female single cells, is for and offspring of male called motility. egg type allele so produce gametes is the their each one and one. than on of to sometimes size not volume together are female chromosome therefore fuse They different smaller much that life. Figure 4 Pollen on the anthers of a ower gamete contains the male gamete of the plant. The male equal male gametes contain one allele of each of genetic the plants contribution to their offspring, despite being very different in overall size. Zygoe Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or dierent alleles. When the male and chromosomes each If female chromosome of each The type so fuse, their nucleus is of diploid. nuclei the It join zygote contains there were of Aa Some also two either and alleles allele or of a one gene, of A and a, each. The three the zygote two doubling two alleles of possible contain two combinations are aa. genes blood could possible have more than two alleles. For example, A ABO together, contains gene. copies AA, gametes number. groups in humans combinations of has three alleles: I the gene for B , I and i. This gives six alleles: A ● three with two of ● three with two different the same allele, I A alleles, I A I B I B , I B I and A , I i ii B and I i. segregaio of allele The two alleles of each gene separate into dierent haploid daughter nuclei during meiosis. During nuclei. meiosis The haploid ● ● If nuclei two a copies will alleles were two of different receive either every alleles one of of copy a of gamete were the twice two to copies produce of each four gene, haploid but the one. allele one divides contains only one receive PP , nucleus nucleus contain nuclei If diploid diploid gene were this allele. will receive present, alleles present, or each the For one copy haploid other each of example, of if the the P . nucleus allele, haploid two not will both. For Figure 5 Most crop plants are pure-bred strains example, if the two alleles were Pp, 50 % of the haploid nuclei would with two of the same allele of each gene receive P and 50% would receive p. 171 3 G e n e t i c s The separation of alleles into different nuclei is called segregation. It TOK breaks up existing combinations to combinations form in the of alleles in a parent and allows new offspring. Dd mende ate eut fo pubcaton? In 1936, the English statistician Domia, receive ad co-domia allele R.A. Fisher published an analysis Dominant alleles mask the eects of recessive alleles but of Mendel’s data. His conclusion was that “the data of most, if not all, of the experiments have been falsied so as to agree closely with Mendel’s expectations.” Doubts still persist about Mendel's data – a recent estimate put the chance of co-dominant alleles have joint eects. In each plant, the of all other. pea plant, the Mendel’s of the For all parents example, the is seven offspring crosses showed in a offspring due to one between the cross were gene between tall. with different character The two a of tall varieties one pea difference of the plant in of pea parents, and height a not dwarf between alleles: getting seven ratios as close to 3:1 as ● the ● the ● they tall parents have two copies of an allele that makes them tall, TT Mendel’s at 1 in 33,000. 1 dwarf parents have two copies of an allele that makes them dwarf, tt To get ratios as close to 3:1 as Mendel's would have required a “miracle of chance”. What are the of each each pass allele, on one allele to the offspring, which therefore has one Tt possible explanations apar t from a ● when the two alleles are combined in one individual, it is the allele miracle of chance? for 2 Many distinguished scientists, is tallness that determines the height because the allele for tallness dominant including Louis Pasteur, are ● the other allele, that does not have an effect if the dominant allele is known to have discarded results present, is recessive. when they did not t a theory. Is it acceptable to do this? How can we In distinguish between results that was are due to an error and results that effect falsify a theory? What standard do well-known you use as a student in rejecting plant each of Mendel’s recessive. when is crosses However, they are present example crossed with one some is a the of the genes together. ower alleles have They colour white-owered was pairs are of dominant of alleles called Mirabilis plant, the and where the co-dominant jalapa. offspring If a have other both have alleles. an A red-owered pink owers. anomalous data? R ● there is an allele for red ● there is an allele for white ● these alleles owers, C W owers, C R The a usual protein allele are reason that codes is for co-dominant for dominance active a and so of carries non-functional C one out W C a gives allele is 172 that function, protein. Figure 6 There are co-dominant alleles of the gene for coat colour in Icelandic horses. pink owers. this allele whereas the codes for recessive 3 . 4 i N h E r i T A N C E parents: Pue grid genotype tt TT phenotype dwarf stem tall stem Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses. Monohybrid height with two of a two of crosses pea only plant, so pure-breeding the produces same just allele, one involve they parents. not type of one involve two character, only This means different gamete, one for that alleles. containing example gene. Most the parents Each one the parent copy of eggs or pollen crosses T t start have therefore the allele. F hybrids genotype Tt 1 Their offspring are also identical, although they have two different tall stem phenotype alleles. The offspring obtained by crossing the parents are called F 1 hybrids or the F generation. different alleles of the gene, so they can each g two g have 1 s hybrids T F T The e 1 TT produce two types of gamete. If two F hybrids are crossed together, 1 or if an F plant is allowed to self-pollinate, there are four possible 1 outcomes. after the cross This can geneticist between two be shown who F rst plants using used are a 2 this × 2 type called the of F 1 To make a Punnett table, called table. The a Punnett offspring and outcomes overall both should ratio be below Tt tall of a tt dwarf generation. 2 grid the tT tall grid as clear as possible the gametes should be ▲ labeled t t tall alleles and shown the on the the Punnett character grid. It is of the also four useful Figure 7 Explanation of Mendel’s 3:1 ratio possible to give an grid. parents: Figure 7 shows Mendel’s cross between tall and dwarf plants. It R genotype explains the F ratio of three tall to one dwarf plant. phenotype C W R W C C C white owers red owers 2 Figure plants 8 shows of the Mirabilis results jalapa. of It a cross explains between the F red ratio and of white one red owered to two pink 2 R F hybrids genotype C 1 phenotype years in a of the similar 20th way century, to those many of crossing Mendel. The experiments French geneticist used the house mouse, Mus musculus, to see C Cuénot C R Lucien whether R C the principles that Mendel had discovered also operated in red C crossed normal grey-coloured mice with albino mice. R C animals. W He The hybrid C R W C C pink mice that were produced were all grey. These grey hybrids were W together and produced 198 grey and 72 albino W C pink C crossed e early done W C pink owers g the were C R Data-baed queton: Coat colour in the house mouse In W C plant. g owered s white C one R to W C offspring. white 1 Calculate your 2 3 ratio between grey and albino offspring, showing working. Deduce two the the colour reasons for Choose suitable and the list symbols, [2] of your together of that is due to a recessive allele, for the [3] alleles combinations with alleles. the coat Figure 8 A cross involving co-dominance with answer. symbols possible combination coat ▲ of for grey alleles colours of and mice associated albino using with coat your each [3] 173 3 G e n e t i c s 4 Using 5 Punnett grid, explain how albino mice was produced. The albino mice had red how ▲ a and one gene can eyes determine the observed ratio of grey [5] in addition whether to the white mice coats. had Suggest grey fur Figure 9 and black eyes or white fur and red eyes. [2] Data-baed queton: The two-spot ladybird Adalia ▲ Figure 10 F bipunctata called ladybugs. There is a rarer is a species The of ladybird. commonest form called form annulata. In of North this Both America species forms are is ladybirds known shown as in are typica. gure 9. hybrid ospring 1 1 Compare 2 The the differences gene. If male offspring annulata are When is annulata the female typica. are that typica and between and forms conclusions 3 typica two typica Similarly, mated can be mated forms are forms are the all of Adalia are mated due bipunctata. to a together, offspring annulata. single all produced Explain [2] the when the drawn. with [2] annulata, the F hybrid offspring are 1 not ▲ Figure 11 F identical to either parent. Examples of these F hybrid 1 ospring 2 offspring are shown in gure 10. Distinguish between the F 1 hybrid offspring and the typica and annulata parents. [3] Actvt 4 If F hybrid offspring are mated with each other, the offspring 1 ABO bood goup include It is possible for two parents to have the both same typica wing and case annulata markings as forms, the F and also hybrid offspring with offspring. 1 an equal chance of having a child with a) Use a genetic b) Predict diagram to explain this pattern of inheritance. [6] blood group A, B, AB or O. What would be the genotypes of the parents? the expected ratio of phenotypes. [2] ABO blood group Inheritance of ABO blood groups. A The ABO example blood of nd out system co-dominance. importance: to group before the blood blood It is in is humans of great of a an medical transfused, group is it patient is vital recessive alleles being that it is matched. Unless this is may be complications due to being I B and I . co-dominant recessive are as The and reasons the for other two allele follows: All of the three alleles cause the production of done, a there both and ● ensure to glycoprotein in the membrane of red blood coagulation cells. of red blood cells. One gene determines the ABO A A blood group of a person. The genotype B blood group A and the genotype I I A ● I gives gives group B I I alters the glycoprotein galactosamine. This by altered addition of acetyl- glycoprotein is A A B. Neither I B nor I is dominant over the A allele a and a different person blood with group, the genotype called AB. I absent other B I so has There is a allele of the ABO blood group gene, exposed i. A person with the genotype ii is I alters in A O. The genotypes I 174 A and B they not make have anti-A the allele I antibodies. the glycoprotein This altered by addition glycoprotein of is not B in people who do not have the allele I B i and I i give blood so groups it do blood present group to who usually galactose. called people B ● third if from respectively, showing that i is if exposed to it they make anti-A antibodies. 3 . 4 A ● The be genotype altered by I B i N h E r i T A N C E A I causes addition of the glycoprotein either to acetyl-galactosamine the of the I B or glycoprotein I is alleles is altered also by present addition A and galactose. anti-A nor As a anti-B consequence antibodies neither are acetyl-galactosamine produced. therefore give the or same galactose. I phenotype, of A I A and as do I i B B I I B This genotype therefore A phenotype to I A gives B I and I a different B I and I i The allele A so the alleles I and ● i is recessive because it does not B I are co-dominant. A cause the production of a glycoprotein. I A I A ● The allele i is recessive because it and causes I i do I therefore B production of the basic glycoprotein: if so B I give I same phenotype and i Group A Group O anti-A anti-B anti-A anti-B Group B Group AB anti-A ▲ the B and anti-B anti-A anti-B Figure 12 Blood group can easily be determined using test cards teig predicio i cro-breedig experime Comparison of predicted and actual outcomes of genetic crosses using real data. It is in the principles not just nature that to of science explain describe to natural individual try to nd general phenomena examples of one face and Mendel discovered showing that have great principles predictive can still use them to predict the important crosses. Table 2 lists outcomes possible predictions actual usually outcomes This is chance involved tossing of a coin of genetic exactly because in is the a crosses with there the is coin to to t, either the element of analogy. results, genes. We of The due land 50% of times with each An uppermost, not bi ol og y of an is d ecid ing ex pe ri men t pre d i cti o ns the resul ts but if we toss it 1,000 expect it to land precisely 500 obvio us difference to for us to ar e c l os e a cc e pt d iffe r ence s a re t ha t too or the p re di ct i on s gr e at must the less chance predictions do tr e nd bet w e e n lik e l y and no t tha t the t is tha t ob se r ve d the mor e the the and g re a ter e xpe c t e d di ffe re nc e l ik el y t ha t is the r e sul ts . expect of its assess objectively times times whether results t two statistical tests are used. For genetic we crosses do in whethe r predictions, faces skil l resul ts the or false. the not predicted an inheritance simple do To the the crosses. correspond outcomes. other in be The the of and monohybrid with power. they genetic times of enough We 500 showing. whether inheritance and a An phenomenon. face the chi-squared test can be used. This test with is described later in the book in sub-topic 4.1. 175 3 G e n e t i c s Co Pedcted outcoe Exape Pure-breeding parents one with All of the ospring will have the same All ospring of a cross between pure- dominant alleles and one with character as the parent with dominant breeding tall and dwarf pea plants recessive alleles are crossed. alleles. will be tall. Pure-breeding parents that have All of the ospring will have the same All ospring of a cross between red dierent co-dominant alleles character and the character will be and white owered Mirabilis jalapa are crossed. dierent from either parent. plants will have pink owers. Two parents each with one Three times as many ospring have 3:1 ratio of tall to dwarf pea plants dominant and one recessive the character of the parent with from a cross between two parents allele are crossed. dominant alleles as have the character that each have one allele for tall of the parent with the recessive height and one allele for dwarf alleles. height. A parent with one dominant and Equal propor tions of ospring with 1:1 ratio from a cross between a one recessive allele is crossed the character of an individual with a dwarf pea plant and a tall plant with with a parent with two recessive dominant allele and the character of one allele for tall height and one for alleles. an individual with recessive alleles. dwarf height . T able 2 Data-baed queton: Analysing genetic crosses 1 Charles majus pure Darwin plants, breeding symmetric. cr o s s e d which pla nts All the pure hav e w ith F bre e din g b i l ate ra l ly pe lo ri c offspring wil d- t ype s ymm et ri c o w e r s produced t h at Antirrhinum owe rs , a re wit h r a di al l y b i l a ter a ll y sy m m et r i c 1 owers. Darwin the n cro ss e d the F plants together. In the F 1 generation owers Figure 13 Antirrhinum owers – there and 37 were with 88 p la nts p e l or ic 2 wi t h bi la t e ra ll y s ym m et r i c owe rs. (a) wild type, (b) peloric a) Construct between a Punnett the F grid to predict the outcome of the cross plants. [3] 1 b) Discuss whether enough c) Peloric to There are called light, together, three only buff pheasants a) crossed Discuss enough 176 a with of and 141 the support all cross close [2] feather offspring buff there rare for pheasants produced. the are extremely reasons with light with [1] bred Similarly, were wild coloration were were in this. ring. 75 when When light to predict the outcome of pheasants. actual the are Suggest were the buff. grid buff of outcome. pheasant ring, Punnett whether plants When crossed together to majus species. buff. results predicted offspring were ring Construct breeding b) and light were 68 this varieties ring ring offspring, of actual the Antirrhinum populations 2 the support results predicted [3] of the cross outcome. are close [2] 3 . 4 3 Mary and character of the are Herschel called fungus shown Mitchell poky grow in the more table mae paent in investigated fungus slowly the inheritance Neurospora than the crassa. wild-type. of Poky The i N h E r i T A N C E a strains results 3. Feae paent Wild type Wild type Poky Nube of wd Nube of pok tpe opng opng 9,691 90 Poky 0 10,591 Wild type Poky 0 7,905 Poky Wild type 4,816 43 T able 3 a) Discuss table b) 1 whether (page Suggest a between male c) data ts any of the Mendelian ratios in reason wild [2] for type all the and offspring poky strains being when poky a in wild a cross type is the parent. Suggest cross is the 170). a [2] reason between the female for wild a small type number and poky of poky strains offspring when a in wild a type parent. [1] Figure 14 Feather coloration from a bu pheasant Geeic dieae due o receive allele Many genetic diseases in humans are due to recessive alleles of autosomal genes. A genetic diseases only usually person has will recessive Genetic in as this. one not allele they do illness a allele to they for that have the by a parents show probability of of do a the have gene. the of disease of a gene. but recessive one allele the a can are pass called If the a allele, on the carriers. Aa must they child of allele. appear disease disease, having therefore allele dominant they usually the genetic disease dominant individuals with Most The the and disease, child parents by a copies These symptoms of not recessive of these caused two offspring. caused Both is allele genetic symptoms their not that recessive individuals show diseases The an by because unexpectedly. but is caused develops gene, they disease are are with be unaware the Aa carriers, disease of is 25 a per cent caused (see by a gure 15). recessive Cystic allele. It brosis is is an described example later in of this a genetic A disease sub-topic. Oher caue of geeic dieae AA Aa aA aa not carrier Some genetic diseases are sex-linked and some are due carrier to dominant or co-dominant alleles. A small It is not proportion possible dominant allele to of genetic be then a diseases carrier they of are these themselves caused diseases. will do not develop the disease by If develop a a dominant person the has disease. allele. one If one develops the genetic disease ▲ Figure 15 Genetic diseases caused by a recessive allele 177 3 G e n e t i c s Bb parent bb is 50 has per genetic b the cent allele (see disease for the gure caused disease, 16). by a A very small alleles. An disease dominant proportion example was is of genetic sickle-cell is bb does not develop Hb a It is child is an inheriting example described later of in it a this described in diseases sub-topic 3.1. possible the sickle cell combinations allele of is alleles the disease The Hb and . caused by molecular normal Figure the co-dominant basis allele that characteristics have as one those for of this hemoglobin shows the three that result. S Hb who 17 characteristics A Figure 16 Genetic diseases caused are The S and Individuals ▲ of disease allele. anemia. A Bb disease chance sub-topic. b develops the the Huntington’s and have one two Hb allele copies of do not either have allele, the so same the by a dominant allele alleles Most some This are co-dominant. genetic show is diseases a called red-green affect different sex males pattern linkage. The colour-blindness of and inheritance causes and females of sex in in the males linkage hemophilia, same are and and way but females. two described examples, later in this sub-topic. A A alleles : Hb A Hb alleles : Hb s Hb S alleles : Hb S Hb characteristics : characteristics : characteristics : - susceptible to - increased resistance - susceptible to malaria malaria - severe anemia to malaria - not anemic - mild anemia normal red blood sickle-cell shape cell shape A Figure 1 7 Eects of Hb ▲ S and Hb alleles Cyic broi ad Huigo’ dieae Inheritance of cystic brosis and Huntington’s disease. Cystic brosis in parts of the of CFTR channel mucus the gene. chromosome ion is Europe. and 7 is This and that commonest It is the due to gene digestive is gene involved a genetic located product in disease recessive allele a secretion mucus and on is secretions, chloride of sweat, recessive chloride alleles channels function properly. up pancreatic enzymes reach the them in the very lungs duct is usually secreted small viscous. causing by the Sticky infections blocked of of this being gene result produced Sweat sodium do intestine. that containing do some have in not excessive is an parts recessive, have of allele any a Europe for cystic single effects. one copy The in twenty brosis. of the chance of As people the allele two allele does chloride is produced, but both being a carrier of the allele not parents 1 __ amounts so pancreas juices. In The the digestive not making builds is 1 __ × 20 , 20 1 ___ digestive juices and mucus are secreted with which is . The chance of such parents having 400 insufcient enough 178 sodium water chloride. moves by As a osmosis result into not the a child with Punnett cystic grid. brosis can be found using a 3 . 4 Because father Cc with of late Huntington’s children. A symptoms C the i N h E r i T A N C E onset, many disease have genetic would test can develop people diagnosed already show had before whether a young c person at risk has the choose dominant not to allele, have the but most people test. Cc CC C About normal one in 10,000 people have a copy of normal (carrier) the mother Cc for cC c cc Huntington’s two can normal cystic (carrier) brosis one parents both nonetheless of their allele, to so is have develop parents it has the the a very unlikely copy. disease allele A if person only because it is dominant. ratio 3 normal : 1 cystic brosis father Hh Huntington’s allele of the HTT chromosome named still disease 4 gene. and huntingtin. being is due This the to dominant gene gene The a is located product function of is a on protein huntingtin H h is researched. Hh hh h The dominant allele of HTT causes Huntington’s normal degenerative disease changes in the brain. Symptoms usually start mother hh when a person is between 30 and 50 years old. Hh hh Changes to behaviour, thinking and emotions h Huntington’s normal become the increasingly start of severe. symptoms is Life about expectancy 20 years. A after disease person ratio 1 normal : 1 Huntington’s disease with and or the disease usually some eventually succumbs other to infectious needs heart full nursing failure, care pneumonia disease. sex-liked gee The pattern of inheritance is dierent with sex-linked genes due to their location on sex chromosomes. Plants such female which same ● pea were in When plants the the are in same female hermaphrodite Thomas the late Andrew 18th whichever gamete. – For they can Knight century, character example, he was produce did crossing discovered in these both the two the gamete crosses and experiments that male male gave and the results: pollen plant ● peas gametes. between results as with pollen plant from plant purple from with a a green stems placed onto on the stigma of a stems; plant green with with purple stems placed onto on the stigma of a stems. 179 3 G e n e t i c s Plants white eye r X red eye r are always carried give out, the but same in results animals the when reciprocal results are crosses sometimes such as different. these An R X X Y inheritance X r X One r X sex pattern where the ratios are different in males and females is linkage R called of the rst examples of sex linkage was discovered by Thomas R X Morgan the fruit y, Drosophila. This small insect is about 4 mm long X Y r red in r r X R X X and Y completes its life cycle in two weeks, allowing crossing experiments white red to be done quickly with large numbers of ies. Most crosses in Drosophila r Y X do not show sex linkage. For example, these reciprocal crosses give the white same red eye R X white eye R results: ● normal-winged ● vestigial-winged males × males vestigial-winged × females; normal-winged females. r X X Y These gave different ● red-eyed ● white-eyed males white-eyed males. males × results: white-eyed females gave only red-eyed × females gave red-eyed offspring; r R X crosses X R X R X red-eyed females and X Y R red R X r R X X red Y red Geneticists had obs e r v e d tha t the inhe ri t a n c e of g e n es an d of R X Y chromosomes sho we d cle a r pa r a ll el s and so g en e s wer e l ik e ly to be red located have on two chromo s o me s . copies of a It wa s a l so chro mos ome kn o wn c a l le d X t ha t an d fe m a l e m al e s Drosophila on l y h ave one Key copy. R X Morgan ded uce d that se x li nka g e of eye c o lo u r cou ld t h e r efor e X chromosome with allele be for red eye (dominant) due to the eye co l o ur g e ne b ei n g lo c a t ed on the X ch r om o so m e . r X X chromosome with allele Male Drosophila also have a Y chro mo s ome , but th i s do es not ca r ry for white eye (recessive) the Y eye-colour Y chromosome Figure ▲ ge ne . 18 explains the inheritance of eye colour in Drosophila. In crosses Figure 18 Reciprocal sex-linkage involving sex linkage, the alleles should always be shown as a superscript crosses letter on should a letter also be X to represent shown though it the X does chromosome. not carry an The allele Y of chromosome the gene. Red-gree colour-blide ad hemophilia Red-green colour-blindness and hemophilia as examples of sex-linked inheritance. Many examples discovered to genes are very X of few of genes recessive cone specic They the on X the allele cells of a the wavelength all Y as chromosome. described due to here: due there Two genes on red-green hemophilia. gene proteins. in been almost conditions are and have are chromosome, colour-blindness photoreceptor by on chromosomes Red-green linkage sex-linked colour-blindness a sex humans. located examples the in is caused for one These retina of ranges the proteins the of of by eye visible are and made detect light. ▲ Figure 19 A person with red-green colour-blindness cannot clearly distinguish between the colours of the owers and the leaves 180 3 . 4 proteins involved expectancy is is untreated. puried The only for the recessive. allele is be of carriers they The only 1 in by of VIII the In theoretically practice, girls ▲ with is there ( the hemophilia VIII, the if X hemophilia hemophilia therefore Females both The the can allele of but their X frequency in 2 = ) been due Factor hemophilia allele. 10,000 have Life hemophilia on is boys. disease the if causes This 1 _____ girls years of in recessive carry blood. infusing located that 10,000. the of donors. is allele disease develop chromosomes ten frequency the of clotting is blood The about frequency the about Factor chromosome. is in Treatment from gene i N h E r i T A N C E to 1 in even lack 100,000,000. fewer of cases Factor of VIII Figure 20 Blood should stop quickly owing from a pricked than this. One reason is that the father would nger but in hemophiliacs bleeding continues for much longer have as blood does not clot properly on Males have inherit only from one their X chromosome, mother. If that X which to the be hemophiliac condition to his and decide to risk passing children. they H chromosome h X H X X Y KE Y H carries the the son red-green will be colour-blindness red-green allele colour-blind. In then X X chromosome carrying the allele for normal parts blood clotting of northern Europe the percentage of males with h h this disability is as high as 8 %. Girls are H X red-green H X X Y X X chromosome carrying the allele for hemophilia. blind and carrying if their they the also father is inherit recessive red-green an gene X colour- chromosome from their mother. predict that the percentage of girls X can X H We with H H X colour-blindness in the same parts of Europe to H colour-blind X be normal 8% = 0.64%. The actual percentage is about X Y × h 8% 0.5%, tting this prediction H well. X h H X X Whereas red-green disability, colour-blindness hemophilia is a is a mild life-threatening genetic h X disease. the to Although disease, an most inability to there cases are of make some rarer hemophilia Factor VIII, forms are one Y normal carrier of Y hemophiliac due of the Pedigree char Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases. It isn’t possible genetic experiments. to to diseases deduce investigate in humans Pedigree the pattern charts of the by inheritance carrying can be out used inheritance. ● of cross instead These are conventions for constructing pedigree to affected by males are shown as females are shown are the shaded whether or an cross- individual is disease; parents top and bar children of the T are linked between using the a T, with parents; squares; ● ● circles indicate charts: the ● and hatched the ● usual squares as Roman numerals indicate generations; circles; 181 3 G e n e t i c s ● Arabic each numbers are used for individuals their in generation. children expect large Example 1 Albinism in humans 1 in see will that numbers 2 that to is not our of be if unexpected are we the children. deductions albinism albino, ratio The and about could parents actual does the only had very ratio not of show inheritance of incorrect. generation I 1 2 Example 2 Vitamin D-resistant rickets Deductions: ● generation II 1 2 3 4 Two unaffected children but children with suggesting Key: dominant parents two vitamin that only affected this have parents D-resistant disease is unaffected have rickets, caused by a allele. normal pigmentation ● The are albino offspring all This Deductions: of suggests offspring Two of the parents both suggests allele children that (m) dominant have are normal albinism and is normal allele albino and yet by a pigmentation This ● recessive by If vitamin dominant a father (M). There are both daughters and sons of suggesting that the condition is only if Both they albinism have allele males two and females copies of the in his are data The albino (mm). children ● Similarly have inherited for albinism from both Both parents must also have one allele pigmentation parents therefore as they have The chance are the not of is . a child of Although these on parents average 1 having in 4 of data the Key: vitamin D-resistant rickets not aected 182 caused would the would inherit the a the his dominant have by of X allele, so disease. in the pedigree shows that this and the theory. if by vitamin a D-resistant dominant with the rickets X-linked disease in allele, generation is the have one X chromosome II carrying the allele recessive for the allele. disease All of her and one offspring have a 50% chance of inheriting this Mm. 4 ▲ is daughters albino. alleles 1 albinism I carrying daughters chromosome ● rickets allele, generation dominant would The number the for with normal the of parents. the ● sure an would allele D-resistant X-linked supports caused must be albino recessive mother ● although to I sons. not so sex-linked. small generation unaffected with This albinism linkage too in and pattern. chromosome all ● parents the pigmentation. caused the daughters sex is inheritance ● of affected Figure 2 1 Pedigree of a family with cases of vitamin D-resistant rickets in the theory. and of pedigree having ts this the disease. and so The supports X 3 . 4 i N h E r i T A N C E Data-baed queton: Deducing genotypes from pedigree char ts The pedigree chart in I gure22 shows ve 1 generations of a 2 3 4 family II affected by a genetic disease. 1 1 Explain, using 2 3 4 5 6 7 9 8 10 11 12 13 14 15 evidence III from the pedigree, 1 whether 2 3 4 the IV condition is due to a 1 recessive or a 2 3 4 5 6 7 8 dominant V allele. [3] ? 1 ? ? ? 2 3 4 unaected male unaected female 2 Explain what the aected male probability is of the aected female individuals generation a) two in V copies recessive b) having: one of ▲ Figure 22 Example of a pedigree char t a allele; recessive 3 and one Deduce, dominant a) 1 in b) 13 with reasons, generation the possible alleles of: III; allele; c) two copies of the in generation II. [2] dominant 4 allele. Suggest two examples of genetic diseases that [3] would t this inheritance pattern. [2] Geeic dieae i huma Many genetic diseases have been identied in humans but most are very rare. Several genetic including disease. (PKU), There research more genetic from no any of by inheritance. small chance It is but of now rare cause to 75 genome. An to reason of the disease that the individual can that that one as sub-topic, Huntington’s phenylketonuria large most most of genetic us do not must any be of suffer diseases Mendelian for diseases number genetic follow alleles 4,000 this allele a genome and large This typical Current alleles is than Given which two such this and are patterns specic of disease inherited and the small. comparisons. 200 this inheriting quickly alleles more surprising for in hemophilia syndrome. found. alleles sequence and disease. and be described examples, identied to recessive been brosis, Marfan’s seem extremely allow genetic between might chance cheaply to and already The already cystic well-known remain develop is recessive a it rare The this sequenced of has possible relatively other them. very have anemia, disease doubt diseases, caused is are Tay-Sachs Medical and diseases sickle-cell only an research individual estimates among of the individual numbers are a is or child human humans revealing carrying that 25,000 produce is of the so that number genes with are the a in could is the genetic being number ▲ human disease Figure 23 Alleles from two parents come together when they have a child. There is a small chance that two recessive alleles will come together and cause a genetic disease due the to one same of rare these recessive alleles if the other parent of the child has allele. 183 3 G e n e t i c s Caue of muaio Radiation and mutagenic chemicals increase the mutation rate and can cause genetic disease and cancer. A gene consists hundreds ▲ or of a length thousands of of DNA, bases with long. a The base sequence different that alleles of can a be gene have Figure 24 Abraham Lincoln’s features slight variations in the base sequence. Usually only one or a very small resemble Marfan’s syndrome but a more number of bases are different. New alleles are formed from other alleles recent theory is that he suered from MEN2B, by gene mutation. another genetic disease A mutation types ● of is factor Radiation cause from can increases are all tobacco First Mutations mutation be benecial. harmful. a cell to Mutations eliminated into Almost diseases. It Figure 25 The risk of mutations due to of radiation from nuclear waste is minimized estimates by careful storage humans, is mutations of body can cause of of a gene. Two if it has enough rays and ultraviolet energy alpha to particles radiation and chemical changes gas used and as a in DNA and nitrosamines chemical so are found weapon in the – there random perhaps mutations the genes and adding cells, are that including individual passed one to no mechanism millions to of into a an is either cell for allele years therefore control develop on those dies, to particularly or the two risk new of that but a particular that has unlikely neutral division tumour. cause can to or cause Mutations This important cells in is to the mutations genetic cancer, mutations offspring. gamete-producing that is change are cancer. the be A over all therefore in are rate Gamma benzo[a]pyrene mustard out. endlessly when gametes sequence rate. short-wave changes evolution cause in are and carried Mutations a mutation DNA. substances random divide therefore ▲ by in base War. being developed the mutation isotopes, smoke are the changes Examples World the to mutagenic. chemical mutagenic. change increase radioactive Some in random chemical X-rays ● a the in are cells that origin minimize ovaries occur diseases in and each of the develop genetic number testes. Current generation in children. Coequece of uclear bombig ad accide a uclear power aio Consequences of radiation after nuclear bombing of Hiroshima and Nagasaki and the nuclear accidents at Chernobyl. The of common Hiroshima accidents that at potentially of the Nagasaki Three radioactive environment to feature and Mile Island isotopes and as a nuclear and were result dangerous the and levels of into were is the exposed radiation. has the atomic b o mb s we r e de to na t e d The been Effects 26,000 followed people 2011 184 and Na g a s a k i have the d i r e ctl y of or s i nce we r e be e n us e d survi v o r s as ha d by in no t a fe w 1 00, 000 the n Fo und atio n who wi thi n nea r ly the Ra di a t io n Jap a n . ex po s ed a su r vivor s co ntro l de ve lo pe d An ot h e r to gr oup. 17, 448 over tumours, Hiroshima died health Research radiation By When either months. Chernobyl released people people bombing nuclear 1 50, 00 0– 250 ,00 0 but only 853 of the s e coul d be 3 . 4 attributed atomic to the e f fe cts of r ad ia tion fro m the into the atmosphere widespread bombs. i N h E r i T A N C E and in total. The effects were severe: 2 Apart from radiation leading cancer that to the was other main predicted stillbirths, was effect of the ● mutations, malformation or death. of 10,000 children that were fetuses km of ginger Horses and atomic bombs were detonated and that Nagasaki been found There but has are the were born been monitored. of later mutations likely to number is have too in Hiroshima No caused been small for by it and evidence some even with the large the be Lynx, cattle their eagle around radiation. in the owl, to the felt the that of evidence bombs, they potential were wives them or for genetic Bioaccumulation of mutations survivors stigmatized. husbands have Some were of due found reluctant fear that their children lamb accident as from boar and thrive from other in which a wildlife zone humans were caused caesium in high sh as levels far of away that and Germany was banned and as with for consumption radioactive some time as far away Concentrations of radioactive iodine in the might rose and resulted in drinking diseases. at Chernobyl, explosions reactor. Ukraine, in and a re in the fatal Workers doses of at the core plant radiation. and milk with unacceptably high levels. 1986 of More than 6,000 cases of thyroid cancer a been reported that can be attributed quickly to received died Wales. have nuclear plant glands. to ● involved the to contaminated caesium sometimes water The wild started environment have reactor of ● marry the study. lack atomic of died. statistically numbers Scandinavia Despite near thyroid Chernobyl radioactive children and excluded. mutations, to to subsequently has ● signicant downwind brown 77,000 ● children forest when damage the pine turned The ● health 4 radioactive iodine released during the Radioactive accident. isotopes of xenon, krypton, iodine, caesium and ● tellurium were released and spread over According Health, parts of Europe. other About radioactive six tonnes metals in of fuel was broken up into small explosions particles GBq of and escaped. radioactive An estimated material Legacy Socio-Economic was is produced no clearly by The Chernobyl demonstrated Forum, increase in by cancers or leukemia due to radiation in 5,200 the million “Chernobyl’s and the solid the report uranium from there reactor the Environmental Impacts”, and to large most affected populations. released Incidence per 100,000 in Belarus 12 Actvt adults (19–34) Cangng ate of tod cance 10 adolescents (15–18) When would you expect the cases children (0–14) 000,001 rep sesaC of thyroid cancer in young adults to 8 star t to drop, based on the data in gure 26? 6 4 2 0 1984 ▲ 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 v Figure 26 Incidence of thyroid cancer in Belarus after the Chernobyl accident 185 3 G e n e t i c s Data-baed queton: The aftermath of Chernobyl Mutations 6.7 at due 4,000 Green a report to cancer from to c a n c e r. a of UN the 1950 warheads. It as at was gave of exposures, of the an among those published by an “up but of estimate as the Nagasaki to in leukemia exposed the that of commissioned such due of station d i s a s t e r, estimate and deaths release numbers stated of obtaining Hiroshima analysis 1990 Forum The power large Parliament way radiation of result which One cell. nuclear cause a European warheads and the the die scientist, an tumour Chernobyl deaths. is a from therefore previous nuclear below become ultimately extra from of data these The may to material radiation between Research cell was members data The a 1986 60,000 detonation 1945. in from to use cause radioactive people” Party 30,000 is of Chernobyl deaths to can tonnes to Radiation and radiation Effects Foundation. radaton Nube of deat Etate of exce doe ange n peope expoed deat ove conto Pecentage of deat attbutabe to (sv) to adaton goup adaton expoue 0.005–0.2 70 10 0.2–0.5 27 13 48 0.5–1 23 17 74 56 47 3391 63 2 0.2–0.5 646 76 12 0.5–1 342 79 23 308 121 39 Leukemia ▲ Figure 27 Humans have been excluded from a large zone near the Chernobyl reactor. Some >1 Cancer plants and animals have shown deformities 0.005–0.2 that may be due to mutations >1 1 Calculate due to you have the 186 in and effect due with acceptable type to of Sv of graph the to There radiation control 0.005-0.02 groups Sv radiation. or table, cancer (a) over chart to [4] represent including should be the two two what the y-axes, for deaths in the deaths. on data percentages [4] due to leukemia cancer. reasons, the deaths exposed of of the excess >1 calculated. Compare Discuss, (b) column deaths deaths of people suitable leukemia and 4 a in radiation right-hand that 3 of Construct the percentage leukemia (sieverts) 2 the [3] level environment. of radiation might be [4] 3 . 5 G E N E T i C m O D i F i C A T i O N A N D B i O T E C h N O l O G y 3.5 Genetc odcaton and botecnoog Uderadig Applicaio ➔ Gel electrophoresis is used to separate proteins Use of DNA proling in paternity and forensic ➔ or fragments of DNA according to size. investigations. ➔ PCR can be used to amplify small amounts of DNA. ➔ DNA proling involves comparison of DNA . ➔ Genetic modication is carried out by gene Gene transfer to bacteria with plasmids using ➔ restriction endonucleases and DNA ligase. Assessment of the potential risks and benets ➔ transfer between species. ➔ associated with genetic modication of crops. Clones are groups of genetically identical Production of cloned embryos by somatic-cell ➔ organisms, derived from a single original nuclear transfer. parent cell. ➔ Many plant species and some animal species skill have natural methods of cloning. ➔ Design of an experiment to assess one factor ➔ Animals can be cloned at the embryo stage by aecting the rooting of stem-cuttings. breaking up the embryo into more than one ➔ group of cells. ➔ Analysis of examples of DNA proles. Methods have been developed for cloning adult ➔ Analysis of data on risks to monarch butteries animals using dierentiated cells. of Bt crops. naure of ciece ➔ Assessing risks associated with scientic research: scientists attempt to assess the risks associated with genetically modied crops or livestock . DNA samples Gel elecrophorei negative electrode Gel electrophoresis is used to separate proteins or sample well fragments of DNA according to size. Gel electrophoresis eld, in is a according gel. The applied. to gel is involves their size separating and immersed Molecules in the in charged charge. a that molecules Samples conducting sample gel are are uid and charged in placed an will an in electric wells electric move cast eld through 1 the gel. Molecules directions. with Proteins negative may be and positive positively or charges negatively move in opposite charged so can positive electrode be large fragments separated according to their charge. direction of The gel resists used the in gel electrophoresis movement of molecules consists in a of a sample. mesh DNA of laments molecules that migration from small fragments eukaryotes are too long to move through the gel, so they must be 1 broken charges up so into smaller move in the fragments. same All DNA direction molecules during gel carry negative electrophoresis, but not ▲ Figure 1 Procedure for gel electrophoresis 187 3 G e n e t i c s at the move to same rate. further separate in Small a fragments given fragments time. of move Gel DNA faster than electrophoresis according to large can ones so therefore they be used size. DnA amplicaio by PCR PCR can be used to amplify small amounts of DNA . The polymerase of of technique this amount a ▲ DNA. chain copies of single It DNA is are is reaction almost described needed molecule. is Within used always at in the an to make simply sub-topic start hour or of large called 2.7. the two, numbers PCR. The Only a process millions – of very in of details small theory copies just can Figure 2 Small samples of DNA being be made. This makes it possible to study the DNA further without ex tracted from fossil bones of a Neander thal the risk of using up a limited sample. For example, DNA extracted for amplication by PCR from fossils from blood, can be amplied semen or hairs using can PCR. also be Very small amplied amounts for use in of DNA forensic investigations. PCR is such the not as used blood person sperm PCR from cells is in used copying by a to primer The selectivity a presence primer is of that amplied whom a of by to blood semen DNA that set blood allows or to greater but if a man’s is A in and entire of a sample chromosomes the together genome. sequence start is Instead selected desired of the for sequence. pairing. desired mixture in modied there all example, the ingredients genetically PCR, for base molecules contain sequences. particular even DNA contain binds modied the of cells came, complementary genetically the of primer PCR binds entire White specic genome by the the sample copy binds whole copy semen. using The from to or none sequences of DNA. foods DNA. be the such PCR copied test involves Any present to One for the use DNA has the of no effect. Data-based questions: PCR and Neander thals The be evolution studied DNA. species time. If a in species base The number Samples of fossil of living the base separates sequence accumulate “evolutionary from groups into two over differences the long can be Neanderthal can sequences between gradually of organisms groups, two periods used as of an clock”. DNA were bones neanderthalensis). of a recently obtained Neanderthal They were ( Homo amplied using and between the humans and the chimpanzees. of fo ycneuqerf differences of comparing % / secnereid fo rebmun their by 25 human–Neander thal 20 human–human 15 human–chimp 10 PCR. 5 A section was of the sequenced Neanderthal and mitochondrial compared with DNA sequences 0 from 994 humans and 16 chimpanzees. 0 The bar chart sequence sample 188 of in gure differences humans, 3 shows were how found between the many within ▲ the humans and the 5 10 15 20 25 30 35 40 45 50 55 60 65 number of dierences in base sequence base- Figure3 Number of dierences in base sequences between humans, chimps and Neander thals a present 3 . 5 1 State in 2 the base most Humans in the common sequence and genus classied in number between pairs Neanderthals Homo the and genus are G E N E T i C of of differences humans. both Discuss this [1] the classied chimpanzees Pan. m O D i F i C A T i O N 3 A N D classication bar a supported by the data in [3] limitation conclusion whether is chart. Suggest are B i O T E C h N O l O G y from to the drawing any human–Neanderthal comparison. [1] DnA prolig DNA proling involves comparison of DNA . DNA ● proling A sample from ● involves of Sequences are DNA another in selected these is obtained, source the and ● The copied ● The fragments ● This produces is are a such DNA are DNA stages: as that copied split vary from or a a known crime considerably individual or scene. between individuals PCR. fragments separated of fossil by into pattern either a using bands using gel that restriction endonucleases. electrophoresis. is always the same with DNA ▲ taken from one individual. This is the individual's DNA Figure 4 DNA proles are often referred to as prole. DNA ngerprints as they are used in a similar ● The proles bands are of the different same individuals and which are can be compared to see which way to real ngerprints to distinguish one individual from all others different. Paeriy ad foreic iveigaio Use of DNA proling in paternity and forensic investigations. DNA proling is used in forensic DNA investigations. proling is investigations. ● Blood stains on a suspect’s clothing could to come from the Blood from stains the at the victim crime could scene be that shown to are not come a A single come each the of a hair to at the come from from scene sample If of the a crime from sexual the example crime victim. Men the highly scene could be the is crime could be shown to DNA a prole compared taken pattern of with from bands that the two the same father to of a nd out child. paternity There investigations are being person. who of material the the DNA suspect matches samples This can committed from ● prole or the exactly claim now of DNA have many the databases criminal to raise to that avoid they are the having to not pay the the child. A provide crime. of DNA cases to who wish to have ha d identi f y mul ti ple the pa rtn e r s bio lo gi cal fa th e r of child may man was they are wish their their to prove father in that order a to deceased show that heir. proles of the mother, the child and the are very are needed. DNA proles of each of patterns of the strong are prepared and the bands Some proles, be compared. If any bands in the child’s prole which do allowed child it are countries a child. samples of of Women may suspect. DNA likely evidence have for sometimes mother man from the suspect. DNA is is requested. ● Semen In paternity suspect. shown ● man reasons father ● in done from ● the are victim. various ● used be whether shown also These not occur in the prole of the mother or solved. man, another person must be the father. 189 3 G e n e t i c s Aalyi of DnA prole Analysis of examples of DNA proles. Analysis two if of DNA the DNA proles samples pattern of are in very bands on forensic likely the to investigations have prole is come the is straightforward: from the same person same. victim specimen 1 2 suspects 3 ▲ Figure 5 Which of the three suspects’ DNA ngerprints matches the specimen recovered from the crime scene? Analysis Each in of the of DNA the biological prole must prole or more proles bands be in do prole paternity child’s mother not, in the checked the bands in or to of DNA father’s make the another investigations prole prole. sure man man that must Every it have to more the band occurs presumed must is be be been in the either the the complicated. same in as a band child’s the father. If mother’s one biological or father. Geeic modicaio Genetic modication is carried out by gene transfer between species. Molecular be to transferred another genetic the code amino is Genetic to milk crop the was daodil plants to rice, to make the rice produce be These genes involved transfer genes from that the from so of from are that allow genes It is from possible transferred them is genes one to species because between unchanged – the species, the same of been silk has gene large used protein. to for bacteria. making quantities also been as purple of it been of One of human this the insulin hormone to can silk used have is new characteristics produced that immensely secrete strong, but commercially. to produce genetically rather three introduce have Spider produce known transfer to goats snapdragons are the to diabetics. used are eukaryotes that example, spider not fruits when transfer has For modication example The modication. translated done treating species. plant. Figure 6 Genes have been transferred from rice for could Genetic of was This containing spiders so transferred modication animal species. techniques produced. examples produced developed genetic sequence been bacterium. as universal, Genes be 190 between acid have have known is a produce a yellow pigment in its seeds is polypeptide early ▲ biologists been than genes, many modied or transferred red. two The from new GM to tomatoes production daffodil varieties crops. of plants For to golden and 3 . 5 one in from the a rice bacterium, so that the G E N E T i C yellow m O D i F i C A T i O N pigment β-carotene is A N D B i O T E C h N O l O G y produced grains. Actvt Scientists have an obligation to consider the ethical implications of their research. Discuss the ethics of the development of golden rice. β-carotene is a precursor to vitamin A . The development of golden rice was intended as a solution to the problem of vitamin A deciency, which is a signicant cause of blindness among children globally. techique for gee rafer o baceria Gene transfer to bacteria with plasmids using restriction endonucleases and DNA ligase. Genes of can be transferred techniques. engineering. Together Gene from these transfer one species techniques to bacteria to another are known usually by as involves a Bacterial cell variety genetic Plasmid plasmids, mRNA extracted from restriction ● A enzymes plasmid is a and DNA small ligase. extra circle of DNA. The smallest plasmids Plasmid obtained have about 1,000 base pairs (1 kbp), but they can have over from bacteria 1,000 kbp. They occur commonly in bacteria. The most mRNA abundant Plasmid plasmids are those with genes that encourage their replication in cut with the cytoplasm are therefore pathogenic advantage and transfer some and on parallels natural a from one with selection bacterium bacterium viruses but favours rather than a to another. plasmids plasmids are that disadvantage. There restriction cDNA not confer an mRNA treated with reverse Bacteria transcriptase use plasmids to exchange genes, so naturally absorb them them into their main circular DNA molecule. Plasmid and cDNA fused and to make incorporate enzyme Plasmids using DNA ligase complementary Recombinant are very useful in genetic DNA (cDNA) engineering. plasmid introduced into ● Restriction enzymes, also known as endonucleases, are enzymes host cells that cut used to DNA cut molecules open at plasmids specic and base also to sequences. cut out They desired can genes be from Bacteria larger DNA molecules. Some restriction enzymes have the useful multiply in property of cutting the two strands of a DNA molecule at different a fermenter points. sticky This ends leaves single-stranded created complementary by base any one sections particular sequences so can be called sticky restriction used to ends. enzyme link The and produce insulin have together Separation and pieces of DNA, by hydrogen bonding between the bases. purication of human insulin ● DNA by ligase making is an enzyme that sugar–phosphate joins bonds DNA molecules between together nucleotides. rmly When Human insulin the desired there are gene still has nicks been in inserted each into a plasmid sugar–phosphate using backbone sticky of the ends can be used by diabetic DNA patients but An DNA obvious ligase can be requirement transferred. It is usually used for to gene easier to seal these transfer obtain is nicks. a copy messenger of the RNA gene being transcripts of ▲ genes than the genes themselves. Reverse transcriptase is an Figure 7 shows the steps involved in one enzyme example of gene transfer. It has been used that makes DNA copies of RNA molecules called cDNA. It can be used to create genetically modied E. coli bacteria to make the DNA needed for gene transfer from messenger RNA. that are able to manufacture human insulin, for use in treating diabetes 191 3 G e n e t i c s Aeig he rik of geeic modicaio Assessing risks associated with scientic research: scientists attempt to assess the risks associated with genetically modied crops or livestock . There of when Paul Figure 8 The biohazard symbol indicates any the rst many fears was an going expressed expressed These experiments planned SV40 biologists been modication. Berg virus ▲ have genetic fears in gene experiment to be be in which into concerns the possible traced transfer inserted serious about can back were being DNA the from SV40 the 1970s conducted. the bacterium because dangers to E. was monkey coli. Other known to organism or material that poses a threat to the cause cancer in mice and E. coli lives naturally in the intestines of health of living organisms especially humans humans. There bacterium Since have then been scientists safety of many therefore cancer other identied. and the organisms. with was causing research potentially has a risk risks led useful to the associated has been scientists and of genetically engineered humans. There between This in the and of being applications genetic debate using GM among about genetically imposed of modication both non-scientists safety bans with erce in crops some or the modied countries, livestock left undeveloped. Almost everything eliminate risk lives. natural It is whether assess The ▲ or the risks not ● What ● How is for go risks can that entirely, we the assessed chance carries in humans ahead of assess it. with in This their two an risks science to with associated be do either or the is and in it is other risk what of not possible aspects an action scientists research before of to our and must do carrying it decide – out. ways: accident or other harmful consequence? Figure 9 GM corn (maize) is widely grown in harmful would the consequence be? Nor th America If there chance is of a high very chance harmful of harmful consequences consequences then or research a signicant should not bedone. Rik ad bee of GM crop is disagreement, because gene transfer to crop Assessment of the potential risks plants and benets associated with genetic GM crops have that by GM opponents and such reduce been many publicized produce issues 192 have been as of potential widely seed, the contested. It is the they technology. whether pesticide but benets. by GM and not are questioned Even crops These corporations basic increase herbicide surprising use that yields have there a involved takes modication of crops. is relatively are very decades Potential for benets environmental agricultural crops be are assessed evidence. available It complex disputes can a IB and to in be the science and Economic benets of be because basis students to they using impossible assess often into benets here, issues it resolved. grouped scientic would procedure, health included on for be benets, benets. not recent in experimental the all GM cannot time claimed 3 . 5 benets for one claim one crop. all GM from Much benets and Claims about GM ● also Instead given the to evidence risks is it here is better and freely to assess relating to crop transferring the plants. sprayed other Use for on of GM of select it for of of can be making so then fewer are toxin has bees to be and harmed. reduces spraying produced a crops, the so need less fuel is machinery. fruit reducing that and vegetables wastage have to and be can be reducing the grown. ▲ Claims about the health benets Figure 10 Wild plants growing nex t to a crop of GM maize of crops: These ● B i O T E C h N O l O G y potential benets insecticide crop varieties farm crops for insects and shelf-life improved, area the crop for varieties gene Less to plowing The a benecial needed GM A N D available. environmental Pest-resistant to ● of list m O D i F i C A T i O N crops: by ● crops. the G E N E T i C The nutritional improved, vitamin for value of example crops by can diseases signicantly be increasing of the control killing content. cur r e ntl y and is to insect t he red uce vecto r s re duce o nly cr op cur re nt tr a ns mis s ion of the yi el ds met h od v ir us e s by w it h insecticides. ● Varieties of allergens in crops or could toxins that be produced are lacking naturally present A wide have them. effect ● GM crops could be engineered that vaccines so by eating the on crop a be vaccinated against a GM about agricultural benets of The health about resistant to drought, ground s cold risks, be produced by gene and be transfer, range over which crops the safety assessed increasing total can be a A gene for case resistance can crop to the be killed with plants allowing all by kill all in the herbicide. crop plants growing With crop less is ● but yields can conditions they are be higher. used to is look to for cannot can m a ke GM o ve ra ll cr ops , e a ch usi ng al l a nd ju dg m e n t s r is k the ne e ds a va i la ble evid e nce . basis Thi s as it ne e ds is not to be d on e p os si ble risks and b e ne ts of one GM to c ro p sowing be used be diseas e s by on a no t h er on e. no consensus yet among about GM all scientists crops and it or is at important the for evidence as for many the of us claims as possible and risks that rather are than included the here publicity. could be Any of selected non-GM once p r oduce d ca use d p e r f o r med Herbicides the detailed tha t are vi ru s es . scrutiny. crop Claims varieties resistant gr oupe d create growing. Crop be r i sk s by for crops r el e v a n t can weed the weed-free of case counter-claims, that not other to competition To experiments therefore spraying ar e care ful l y, non-scientists plants so co nce rns be There to the yields. herbicide transferred as as s es s ed produced from ● be salinity assess and c ro ps expending on the GM s uc h ca nno t e nv i r o nme ntal risks. experimental can ab out the s e, i nco me s, remaini ng agricultural crops: Varieties of disease. to ● S o me farmer’s scientic into Claims co nce rns person here. would of raised. produce on edible variety been ● made Proteins about produced translation of health by risks of transcription transferred genes GM crops: and could be 193 3 G e n e t i c s toxic or cause livestock that allergic eat GM reactions in humans or plants, crops. feed crops ● Antibiotic during resistance gene pathogenic ● used as could spread genes to Claims unexpected GM could problems during mutate that and were development of them are made about ● cause not GM made Some risk- environmental seed crops. plants organisms than that non-GM risks agricultural risks of from that to a must very crop become be is always controlled, difcult spilt unwanted if the but crop and volunteer this could contains of resistance genes. crops: Non-target organisms toxins are could be affected Widespread that intended to control pests crop them transferred herbicide plants, GM crops containing a that of kills insect resistance pests to the will lead toxin in to the the pests plants. that Genes of in spread GM use by toxin ● about germinates ● ● and rather beinggrown. herbicide GM GM crops: become Claims insects where markers bacteria. Transferred assessed transfer genes plant-eating on turning to crop resistant them plants could into to make spread to were spread wild the of the initial problem secondary toxin but were pests and that previously also are to the resistant to scarce. uncontrollable ● Farmers are not permitted by patent law to super-weeds. save ● Biodiversity proportion could of be reduced sunlight energy if a lower passes to and have weed re-sow grown, conditions so GM seed strains cannot be from adapted crops to they local developed. Aalyig rik o moarch buerie of B cor Analysis of data on risks to monarch butteries of Bt crops. Insect but pests that protein. ies, It kills Bt Bt varieties In North as maize, pests toxin toxin or corn toxin in to 194 is cob. insect. This from Data for toxin. contain are while particular from toxin butteries, corn is the a moths, varieties including Zea in it larvae about engineering pollen. attacked the The engineered produced, is insecticides genetic transferred including corn, crop with by was Bt that expressed One Britain by of the species is various the of of known insect moth effects mays. Ostrinia Bt concern corn is on the plexippus. buttery that feed sometimes with the monarch corn from gene plant been The plant GM A orders which dusted risk spraying codes called been by produced genetically the have Danaus a that of crop monarch therefore pollen insects. The borers, of been insect parts the become experimentally. of ants. have curassavica. crops is corn the controlled kills crops on species of all this buttery, larvae There in Concerns monarch Asclepias and many including non-target that members bees of be recently thuringiensis America nubilalis. corn a can been Bacillus beetles, produce crops have produce bacterium The of varieties crops. these on leaves grows of close milkweed, enough wind-dispersed larvae This risk experiments might has is corn be been to pollen. poisoned by Bt investigated available for analysis. 3 . 5 G E N E T i C m O D i F i C A T i O N A N D B i O T E C h N O l O G y )%( eavral hcranom fo lavivruS Data-baed queton: Transgenic pollen and monarch lar vae To investigate monarch collected spatula old from of dusting. by effect the of the was leaves plants gently were buttery larvae pollen from following milkweed pollen The monarch eaten the butteries were tapped larvae was and placed Bt corn procedure in were over on was lightly the placed over on to tubes. each four larvae leaf. days. of Leaves misted leaves water-lled monitored the used. with water. deposit Five The The were a A ne three-day- area mass of of leaf 100 75 50 25 0 the 1 2 3 4 Time (days) larvae was measured monitored treatments each The survival of the larvae was days. were 2 included in the experiment, with ve repeats treatment: ● leaves not ● leaves dusted ● days. fael evitalumuC of four four leaves dusted with with dusted with pollen non-GM pollen (blue) pollen from Bt (yellow) corn avral rep noitpmusnoc Three over after 1.5 1 0.5 (red) 0 The results are shown in the table, bar chart and graph on the 1 right. 2 3 4 Time (days) 1 a) List the variables that were kept constant in the Source: Losey JE, Rayor LS, Carter ME (May 1999). experiment. [3] “Transgenic pollen harms monarch larvae”. 2 b) Explain the a) Calculate need the to total keep these number of variables larvae constant. used in [2] the Treatment experiment. b) Explain the Nature 399 (6733): 214. need for replicates in experiments. [2] Mean mass of surviving larvae (g) [2] Leaves not dusted 0.38 with pollen 3 The bar Explain chart how and the error graph bars help show in mean the results analysis and and error bars. Not available evaluation non-GM pollen of data. [2] 0.16 4 Explain the conclusions that can be drawn from the pollen from Bt corn percentage 5 Suggest survival reasons between the for three of larvae the in the differences three in treatments. leaf [2] consumption treatments. [3] Actvt 6 Predict with the mean non-GM mass of larvae that fed on leaves dusted Etatng te ze of a cone pollen. [2] A total of 130,000 hectares of Russet 7 Outline this differences experiment might by any Bt affect and between processes whether the that monarch procedures occur larvae are in used nature, actually Burbank potatoes were planted in in Idaho in 2011. The mean density which of planting of potato tubers was harmed pollen. [2] 50,000 per hectare. Estimate the size of the clone at the time of planting and at the time of harvest. Cloe Clones are groups of genetically identical organisms, derived from a single original parent cell. A zygote, the rst sexual and produced cell of a by new reproduction, develops into an the fusion organism. they are adult of a male Because all and genetically organism. If female zygotes it are gamete, produced different. reproduces A zygote sexually, is by grows its 195 3 G e n e t i c s offspring Actvt also identical The a will different. When they In some do this, species they organisms produce can genetically organisms. of Although identical of genetically genetically we do twins result develop genetically asexually. production group the be reproduce of a into not is usually the identical identical think smallest human zygote separate organisms organisms of clone or an in can into is called them that dividing embryos, is this two cloning and clone. way, exist. embryo called a a They cells, pair are which splitting into of either each two How many potato clones are there in parts which each develop into a separate individual. Identical twins this photo? are not identical different rarely in all ngerprints. identical their A triplets, characteristics better term for quadruplets and them and have, is even for example, monozygotic. quintuplets More have beenproduced. Sometimes For a clon e example, Large but clones even so ca n cons i st com me r c ia ll y are all fo r me d the of ve ry gr own by cloning o r g a ni sms la rg e pot a t o ma y n u m be r s v a ri e t ie s h ap pe n in g be t r ac ed a g a in back of a re to o rg a n is m s . hu g e and one c l on e s. a ga i n, or ig i n al parentcell. naural mehod of cloig Many plant species and some animal species have natural methods of cloning. Although identical the produced ▲ Figure 11 Identical twins are an example of cloning twig. by ● by Many plants Two plants very examples A a single A at they garlic of are a end. or the growing Natural are bulb, ● and can for in It any the comes method involve group early from of of 20th the cloning. stems, genetically century Greek The roots, for plants word for methods leaves or used bulbs. here: planted, produce plant the uses enough bulbs g r o ws in l ong p l a ntl e ts us i ng plan t. genetical l y the its food food by group stores to grow photosynthesis are genetically to grow identical A hor i zon t a l g r ow the i r roo t s le a ve s, he a lthy i d e ntica l so can s tr awbe r ry ne w st e m s i nt o p la nt s th e with s oi l b e c om e p la nt in t h is p la n t le t s and in d ep en d en t c an way pr oduc e du r in g t en a season. do of cloning are less common in animals but some species it. Hydra clones gure 1, Female ▲ to natural when All These methods able used used clone. parent more a given photosynthesize of now rst reproduction. varied bulbs. is was leaves strawberry the it have are These group so clone asexual are leaves. ● word organisms, itself page aphids by a process called budding (sub-topic 1.6, 51). can give birth to offspring that have been produced Figure 12 One bulb of garlic clones itself to produce a group of bulbs by the end of the growing season 196 entirely meiosis. from The diploid egg offspring cells are that were therefore produced clones of their by mitosis mother. rather than 3 . 5 G E N E T i C m O D i F i C A T i O N A N D B i O T E C h N O l O G y Iveigaig facor aecig he rooig of em-cuig Design of an experiment to assess one factor aecting the rooting of stem-cuttings. Stem-cuttings used to from clone the stem, independent 1 are Many the new plants Ocimum short plants lengths articially. cutting can of If stem roots that ● are develop become whether the cutting is placed in water or compost an ● what ● how ● whether type of compost is used plant. can be basilicum cloned roots from warm the cuttings are kept cuttings. particularly easily. a plastic bag is placed over the cuttings 2 Nodes are positions on the stem where leaves ● are attached. below 3 a Leaves the 4 The most species the stem is cut whether holes are cut in the plastic bag. node. are stem. upper With removed If half there they lowest from are can third of the many also the be lower large half leaves of in You should you design or water. about these questions when experiment: the 1 What 2 How is your independent variable? reduced. cutting is inserted Compost should be will you measure the amount into of compost think your root formation, which is your dependent sterile variable? and contain plenty of both air and water. 3 5 A clear plastic bag with a few holes cut in Which variables should you keep it constant? prevents excessive water loss from cuttings 4 inserted in How you 6 Rooting normally takes a few weeks. new different types of plant should leaves usually indicates that use? Growth 5 of many compost. the How many cuttings should you use for each cutting treatment? has Not to all developed gardeners clone plants gardeners ngers” the carry have using sometimes for an success root biologist their about cuttings out factors your a evidence whether the are but reason give roots. success. root the list to or have “green this that You or can determine can design investigate below, as Experiments not. to trying Successful reject factors experiment on said would the when cuttings. one another and of factor of own. Possible factors ● whether ● how ● whether the long callus to stem the the investigate: is cut cutting end of above or below a node is the stem is left in the air to over ● how ● whether many a leaves are hormone left on rooting the cutting powder is used 197 3 G e n e t i c s Cloig aimal embryo Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cells. At an early stage pluripotent theoretically and each This cells one is embryo most separated Only to a an ▲ in all to an animal types divide separate or by of two individual up this It or with Coral breaking because embryo tissue). into fragmentation. presumably egg still has at embryo can could not into be of are is therefore more all embryos into parts body smaller increases parts. have groups the of chance of little stage interest it is not vitro can be and be this and in allowed separated into obtained cells successful method possible cloning by naturally. articially embryo most in as this transplanted can the do splitting, However, some cases it the embryos. in cells and clones usually to embryos fertilized divisions is regarded multiple pluripotent of be appear Individual number been do animal develop embryos There the a themselves twins up embryo. are of into cells, species number Splitting clone break limited certain embryo splitting identical parts they a the cells into surviving. multicellular while to all developing for called single of livestock, of develop animal possible In is even Formation but to observed or development possible part process been of (capable to at of assess develop the surrogate this are to from way, no the articial stage. cloning a after pluripotent. eight-cell whether a mothers. because longer into embryo new because individual Figure 13 Sea urchin embryo (a) 4-cell stage produced by sexual reproduction has desirable characteristics. (b) blastula stage consisting of a hollow ball of cells Cloig adul aimal uig diereiaed cell Methods have been developed for cloning adult animals using dierentiated cells. It is relatively is impossible easy to characteristics. assess This are their is the undifferentiated biologist nuclei cells the as from from nuclei carried tissues Prize of for Figure 14 Xenopus tadpoles 198 body cell there cells the using Xenopus or had interest in out in the frog. cells for an it to is easy clone adult new during and to them. animal animal as and his on cloning the body The though egg they differentiation Gurdon was pioneering proved mammal to was uses therapeutic be them cells were to the He frog removed into into zygotes. form awarded all egg which They the the Nobel research. much Dolly of in 1950s. transplanted removed. reproductive it of a it desirable adults difcult experiments 2012 for stage needed. tadpoles In in that have into body Oxford been at will more tissues developed cloned obvious are growth Medicine first up but grown much the cells differentiated The is all Xenopus cell embryos have make carried transplanted the also of it student nucleus division, normal from is Gurdon Physiology mammals. Apart ▲ a that pluripotent John were but embryos, the embryos produce postgraduate which out Cloning in a cells To animal whether the characteristics, because Xenopus clone know Once differentiated. The to this reasons. more the type If difficult sheep of this in 1996. cloning, procedure 3 . 5 was done stem with cells, Because adult the from rejection humans, which cells could the be would whom the embryo used be to would was m O D i F i C A T i O N consist regenerate genetically nucleus G E N E T i C identical obtained of tissues to they A N D B i O T E C h N O l O G y pluripotent for those would the of adult. the not cause problems. Mehod ued o produce Dolly Production of cloned embryos by somatic-cell nuclear transfer. The production development was used somatic a is The Adult a normal were Dorset laboratory, the cells ● of a a of was cell method the were that with that transfer. a A diploid stages: medium so The nuclear nutrients. eggs Scottish pioneering from and inactive Unfertilized a these taken using differentiation body has ewe concentration in was cloning. somatic-cell method cells Finn Dolly animal called cell nucleus. ● is of in udder grown of in the containing This the made a low genes pattern of lost. were taken Blackface ewe. from The the ovaries nuclei were ▲ removed cells to from each around of gel. cause 10% into from egg the A an Finn cell, egg, small the of the two the these eggs. Dorset inside which electric cells fused One to cells the is a was the cultured placed zona pellucida was the team that produced her ● coating used together. developed to a The embryos seven could About like Figure 15 Dolly with Dr Ian Wilmut, the embryologist who led next protective pulse fuse of zygote embryo. in the days act as same embryos through were old then into injected uteri of surrogate mothers. way IVF . as implanted a the normal in when other This about ewes was that done Only one of successfully and developed gestation. This was the 29 Dolly. egg without a nucleus fused with donor cell using a pulse of electricity cell taken from udder of donor adult and cultured embryo resulting from in laboratory for six days fusion of udder cell and egg transfered to the surrogate mother uterus of a third sheep gives birth to lamb. which acts as the Dolly is genetically surrogate mother identical with the sheep that donated the udder cell unfertilized egg taken from another (the donor) sheep. Nucleus removed from the egg ▲ Figure 16 A method for cloning an adult sheep using dierentiated cells 199 3 G e n e t i c s Queio 1 Human while somatic our chimpanzee, have the 48 the primate human 12 and have primate the gorilla chromosomes. human from cells closest of ancestor. two The chromosome 13 and from the orangutan number 2 2 below compared is was chromosomes in Compare the formed part a from chromosome the two study gene this 19 The (Felis true, many chromosomes, is repeats If the predict region of of endangered and variation out. samples analysed In were for with samples Gel the East of the one taken the electrophoresis. compared blood an protein The electrophoresis from 19 domestic electrophoresis used to separate proteins using the can same as in DNA proling. The bands on [3] of sequence. gel is South carried blood sylvestris). called gel which the fusion what the of same be chromosome hypothesized to short hypothesis would have represent forms of the protein telomeres, transferrin have using level was and in chromosomes 17). ends the pool jubatus) found 2 the b) of study, for principles (gure cat cheetahs were patterns chromosome chimpanzee of results be with A (Acinonyx large transferrin chimpanzee. human of cheetah that cats a) cheetah Africa. all shows to The species the hypothesis image 3 chromosomes, the One chromosome fusion 46 relatives, indicated. were found where are DNA in the the fusion occurred. [2] transferrin C H ▲ Figure 1 7 origin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 7 18 19 cheetahs 2 The pedigree groups I of in three gure 18 shows generations of a the ABO family. AB B O B 1 2 3 4 B A B O 1 2 3 4 O A B O ? 1 2 3 4 5 transferrin II III ▲ O 5 Figure 18 origin 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 7 18 19 domestic cats a) Deduce the genotype of each person in the family. b) Deduce [4] the individual of possible III 5, blood with the groups ▲ of percentage chance each. Using Deduce the percentage (i) of of is 200 possible chance children partner (ii) gure 19, deduce with reasons: [2] a) c) Figure 19 who children in of blood of groups each blood individual is of blood also III group 2 in her the and for his group partner O the b) [2] who [2] number number group: 1 blood and AB. III and the in c) domestic transferrin gene number the of cheetahs number the the in the of gene of of of the heterozygous of of [2] the transferrin domestic alleles pool and were gene; alleles pool cats that of the cats; transferrin cheetahs. gene [2] gene [1] 4 E c o l o g y Intrdutin Ecosystems energy to energy lost of carbon require fuel as and ecosystems life a continuous processes heat. and Continued other depends chemical on supply to availability elements cycles. of replace The in future survival depends of living on Concentrations signicant Earth’s organisms sustainable of effects gases on including ecological in the climates humans communities. atmosphere experienced have at the surface. 4.1 Sps, s sss Understandin Skis ➔ Species are groups of organisms that can ➔ Classifying species as autotrophs, consumers, potentially interbreed to produce fer tile ospring. detritivores or saprotrophs from a knowledge of ➔ Members of a species may be reproductively their mode of nutrition. isolated in separate populations. ➔ ➔ Testing for association between two species Species have either an autotrophic or using the chi-squared test with data obtained heterotrophic method of nutrition (a few by quadrat sampling. species have both methods). ➔ ➔ Recognizing and interpreting statistical Consumers are heterotrophs that feed on living signicance. organisms by ingestion. ➔ ➔ Setting up sealed mesocosms to try to Detritivores are heterotrophs that obtain organic establish sustainability. (Practical 5) nutrients from detritus by internal digestion. ➔ Saprotrophs are heterotrophs that obtain Nature f siene organic nutrients from dead organic matter by external digestion. ➔ A community is formed by populations of dierent species living together and ➔ Looking for patterns, trends and discrepancies: plants and algae are mostly autotrophic but some are not. interacting with each other. ➔ A community forms an ecosystem by its interactions with the abiotic environment. ➔ Autotrophs and heterotrophs obtain inorganic nutrients from the abiotic environment. ➔ The supply of inorganic nutrients is maintained by nutrient cycling. ➔ Ecosystems have the potential to be sustainable over long periods of time. 201 4 E c o l o g y Speies Species are groups of organisms that can potentially interbreed to produce fer tile ospring. Birds of paradise islands. In courtship to the dances, display their that they reason is show to Papua season repeatedly exotic female the are New the carrying plumage. t that and One would they Guinea males are out a a series for type of this suitable same other elaborate reason be the and do Australasian and is to show partner. of distinctive movements bird of to a Another paradise as female. There these are each forty-one usually between of the the characters types ▲ inhabit breeding of only different different forty-one that are organism types reproduces types types are of different such as of with of paradise. of its rarely bird to bird others of those these type produced. paradise of other species . For Each and this remains types. Although of hybrids reason distinct, Biologists few with call species have Figure 1 A bird of paradise in Papua as elaborate courtship rituals as birds of paradise, most species have New Guinea some method members When they two are of trying their members This paradise. is However, are species becoming The almost reproductive species being distinguish summary, fertile of called species a it a to ensure that they reproduce with other species. the interbreeding. together. of of same species Occasionally cross-breeding. the always offspring infertile, mate and members It of happens produced which by produce different offspring species occasionally cross-breeding prevents the genes breed with of birds between two mixed. separation recognizable from even species is a the between type of most group of species is organism closely the with related organisms that reason for characters other each that species. interbreed to In produce offspring. Pps Members of a species may be reproductively isolated in separate populations. A population same area at a the group same they are unlikely they are different still If members two of to they and difcult decide to biologists different time. same of a in are interbreed If If two species each same species live other. potentially never in This could interbreed characters. considered fertile whether sometimes the populations with they of who live different does not interbreed, in the areas mean they that are species. their produce species. organisms interbreed the differences differences, of species. populations develop 202 is be the offspring. two disagree to Even same In populations about if then there species practice have whether they are it may gradually recognizable until can reached populations they be this are cannot very point the and same or 4 . 1 S P e c i e S , c o m m u n i t i e S a n d e c o S y S t e m S aph hph av Species have either an autotrophic or heterotrophic Gápgs ss method of nutrition (a few species have both methods). The tor toises that live on All organisms amino acids. obtaining need They these a supply are of needed carbon organic for nutrients, growth compounds can and be such as glucose reproduction. divided into two and Methods the Galápagos islands are of types: the largest in the world. They have sometimes been grouped together into one some ● organisms make their own carbon compounds from carbon species, Chelinoidis nigra, dioxide and other simple substances – they are autotrophic, which but more recently have been means self-feeding; split into separate species. some ● organisms obtain their carbon compounds from other Discuss whether each organisms – they are heterotrophic, which means feeding on others. of these observations Some unicellular gracilis there by for is organisms example sufcient endocytosis. has light, use both methods chloroplasts and but feed Organisms can that also are not of carries on nutrition. out photosynthesis detritus exclusively Euglena or smaller autotrophic indicates that populations when organisms on the various islands are separate species: or ● heterotrophic are The Galápagos tor toises mixotrophic. are poor swimmers and cannot travel from one island to another so they do not naturally interbreed. ● Tor toises from dierent islands have recognizable dierences in their characters, including shell size and shape. ● ▲ Figure 3 Arabidopsis ▲ Figure 4 Humming birds ▲ Tor toises from dierent Figure 5 Euglena – an islands have been mated in zoos and thaliana –the autotroph are heterotrophic; the plants unusual organism that molecular biologists from which they obtain as it can feed both use as a model plant nectar are autotrophic autotrophically and hybrid ospring have been produced but they heterotrophically have lower fer tility and higher mor tality than the ospring of tor toises ts p g from the same island. Looking for patterns, trends and discrepancies: plants and algae are mostly autotrophic but some are not. Almost all complex plants organic substances. algae is A obtain therefore and supply by algae are compounds of autotrophic using energy absorbing light. photosynthesis is carbon needed Their and they – they to do method carry make dioxide it and this, of out their other which plants autotrophic in own simple and nutrition chloroplasts. ▲ This by trend for plants photosynthesis However the there trend, in are because and algae to chloroplasts small make is numbers although they their followed of are both own by carbon the plants majority and recognizably algae plants Figure 2 Galápagos tor toise compounds of that or species. do algae, not t they 203 4 E c o l o g y do not These them To contain species and cause decide algae and are whether groups are The and It is 1% almost alga were them. all they different of this autotrophs, plant can the and out from parasitic. theory whether to photosynthesis. compounds that they consider plants are how and just many minor species the easily parasitic This is relatively ancestral parasitic be lost species pattern from species species from are suggests photosynthetic ecologists number algae of small – only species. original that quite Also, families. small the or need algal and repeatedly a falsify we carry carbon therefore species plants and that evidence, with not evolved. developed. evolved do obtain are plants parasitic Chloroplasts many Because They autotrophic certain be have harm. autotrophic easily they plants, discrepancies of of and other parasitic of how number about ● on them insignicant there ● chloroplasts grow regard plants exceptional of cells, diverse that plant evolved but and from cannot and occur parasitic species. and algae species as that groups are of parasitic. d-bs qss: Unexpected diets Although animals and to9 do we to not show usually be expect consumers, always four conform organisms plants living to our with to be autotrophs organisms are very expectations. diets that are and varied Figures 6 unexpected. 1 Which of the organisms is autotrophic? [4] 2 Which of the organisms is heterotrophic? [4] 3 Of organisms the consumer, which that a are heterotrophic, detritivore and deduce which a which saprotroph. is a [4] ▲ Figure 6 Venus y trap: grows in swamps, with green leaves that carry out photosynthesis and also catch and digest insects, to provide a supply of nitrogen ▲ 204 Figure 7 Ghost orchid: grows ▲ Figure 8 Euglena: unicell underground in woodland, feeding that lives in ponds, using its o dead organic matter, occasionally chloroplasts for photosynthesis, growing a stem with owers above but also ingesting dead organic ground matter by endocytosis ▲ Figure 9 Dodder: grows parasitically on gorse bushes, using small root-like structures to obtain sugars, amino acids and other substances it requires, from the gorse in plants 4 . 1 S P e c i e S , c o m m u n i t i e S a n d e c o S y S t e m S css Consumers are heterotrophs that feed on living organisms by ingestion. Heterotrophs source them of in. are divided organic One Consumers group feed into molecules off of groups that heterotrophs other by they is organisms. ecologists use and called These the according method to of the taking consumers. other organisms are either ▲ still alive or have only been dead for a relatively short time. A feeds on Figure 10 Red kite (Milvus milvus) is a mosquito consumer that feeds on live prey but also sucking blood from a larger animal is a consumer that an on dead animal remains (carrion) organism a that is still alive. A lion feeding off a gazelle that it has killed is consumer. Consumers material ingest from digestion. lions Consumers to and take what are other autotrophs; In practice, because inside their sometimes secondary their it into organisms most that digest such as up into do feed not t material they and by on a undigested the take into variety in of by such it. according feed consumers of food consumers groups any products the consumers primary neatly in swallowing trophic Primary from take absorb Multicellular system consume. consumers it Paramecium vacuoles. divided includes means They digestive they consumers diet This consumers digest food food. organisms. Unicellular endocytosis as their other one of trophic on and so these on. ▲ groups Figure 11 Yellow-necked mouse (Apodemus avicollis) is a consumer that feeds mostly on living plant matter, especially seeds, but also groups. on living inver tebrates dvs Spphs Detritivores are heterotrophs that obtain Saprotrophs are heterotrophs that obtain organic nutrients from detritus by organic nutrients from dead internal digestion. organic matter by external digestion. Organisms discard matter, example: for large quantities of organic Saprotrophs organic absorb ● dead leaves and other parts of the feathers, hairs and other dead parts of animal bodies ● feces This from dead ecosystems of nutrition digest it ingest Large earthworms Unicellular The larvae is groups dead and known the organisms rolled and as fungi are digestion. into the They Many saprotrophic. decomposers carbon compounds release elements so they as a dead then types in such because dead as They they organic nitrogen are of break matter into the also down and ecosystem dung into that can be used again by other organisms. source heterotroph – organic absorb dead ingest beetles matter the and products detritivores matter it into feed by into food then of such their as gut. vacuoles. ingestion of ▲ feces of enzymes externally. accumulates used of multicellular ingest of products it saprotrophs. internally digestion. rarely instead two and Detritivores matter and by detritivores digestive digest animals. organic in and plants bacteria ● secrete matter a ball by their Figure 12 Saprotrophic fungi growing over the surfaces of dead parent. leaves and decomposing them by secreting digestive enzymes 205 4 E c o l o g y TOK Identifin mdes f nutritin t h x h ss Classifying species as autotrophs, consumers, detritivores sss (bs gs) or saprotrophs from a knowledge of their mode of nutrition. s s s h pv? By answering a series of simple questions about an organism’s mode of There are innite ways to divide up nutrition it is usually possible to deduce what trophic group it is in. These our observations. Organisms can be questions are presented here as a dichotomous key, which consists of a organized in a number of ways by series of pairs of choices. The key works for unicellular and multicellular scientists: by morphology (physical organisms but does not work for parasites such as tapeworms or similarity to other organisms), fungi that cause diseases in plants. All multicellular autotrophs are phylogeny (evolutionary history) and photosynthetic and have chloroplasts containing chlorophyll. niche (ecological role). In everyday language, we classify organisms such Feeds on living or recently Feeds on dead organic killed organisms = CONSUMERS matter = DETRITIVORES as domesticated or wild; dangerous or harmless; edible or toxic. Either ingests organic matter by endocytosis (no cell walls) or by taking it into its gut. START HERE av cg Cell walls present. No ingestion of organic matter. No gut. Secretes enzymes into Enzymes not secreted. its environment to digest Only requires simple dead ions and compounds organic matter = SAPROTROPHS such as CO 2 ▲ Figure 14 = AUTOTROPHS In a classic essay written in 1972, the physicist Philip Anderson stated this: The ability to reduce everything to simple fundamental laws does not cs imply the ability to start from those laws and reconstruct the universe. At A community is formed by populations of dierent each level of complexity entirely new species living together and interacting with each other. properties appear. An important part of ecology is research into relationships between Clearcutting is the most common organisms. These relationships are complex and varied. In some cases and economically protable form of the interaction between two species is of benet to one species and logging. It involves clearing every tree harms the other, for example the relationship between a parasite and its in an area so that no canopy remains. host. In other cases both species benet, as when a hummingbird feeds With reference to the concept of on nectar from a ower and helps the plant by pollinating it. emergent proper ties, suggest why the ecological community often fails to recover after clearcutting. 206 All species are dependent long-term survival. never in live For isolation. on this relationships reason Groups of a with other population populations of live species one for species together. A their can group 4 . 1 of is populations known in hundreds ▲ living ecology or even together as a in an area community. thousands of S P e c i e S , and interacting Typical species c o m m u n i t i e S with communities living together in each consist an a n d e c o S y S t e m S other of area. Figure 13 A coral reef is a complex community with many interactions between the populations. Most corals have photosynthetic unicellular algae called zooxanthellae living inside their cells Fied wrk – assiatins between speies Testing for association between two species using the chi-squared test with data obtained by quadrat sampling. Quadrats out are using involves a square quadrat repeatedly sample frame. areas, usually Quadrat placing a marked ● sampling positions in a quadrat habitat and frame The usual quadrats ● of A procedure is base ● the way table is using Random a present for each randomly placed the precisely two at random the distances numbers. this procedure is followed correctly, with a large the number of replicates, reliable estimates of time. positioning this: line habitat all organisms is by at recording enough numbers quadrat determined If random The marked a along the numbers or a out along measuring edge are random tape. of the obtained number the It edge must of the extend habitat. using either generator on a calculator. ● A a ● rst random distance number along the distances along A random a second distance to the must out tape. be the tape must the distances equally used number across All is measuring likely. is to be All equally used habitat across determine tape. to at the likely. determine right angles habitat ▲ Figure 15 Quadrat sampling of seaweed populations on a rocky shore 207 4 E c o l o g y population suitable not sizes for are plants motile. obtained. and Quadrat populations of other sampling most The method organisms animals, is not for is that suitable obvious only 2 are for Calculate the exp e cte d fr e que nci es , assuming independ e nt d is tr i butio n, each of Each reasons. the presence or absence of more than four expected values If the on the sp e ci e s f or co mbi na ti on s. fre q ue ncy is conti ng e ncy ca lcul a t e d ta bl e us i n g f r om th is one equation: species is recorded sampling of a in every habitat, it is quadrat possible during to test for row total × column total ___ an expected often frequency = association unevenly between species. distributed Populations because some are parts of 3 habitat are more suitable for a species than two they This species will is occur tend to known as in be a the same found in positive parts the of same a Calculate be negative or the degrees There species can be of degrees of freedom of freedom = (m 1)(n 1) can distribution m and n ar e the numbe r of ro w s of and two number equation. habitat, quadrats. association. associations, the this where also total others. using If grand the number of co l umns in the co ntin g e n c y independent. table. There are two possible hypotheses: 4 H : two species are distributed Find the table independently of critical region chi-squared for chi-squared values, using the from a degrees 0 (the null of hypothesis). freedom that signicance H : two species are associated (either region they tend to occur together or negatively tend to occur can test these is any value in value the hypotheses using a – the (5 %). and The a critical of chi-squared larger than table. Calculate chi-squared chi-squared using this equation: statistical (f procedure calculated 0.05 apart). 5 We of so the they have (p) positively 1 so you level test. f o e _ 2 X )2 = Σ f e The chi-squared expected sample test is frequencies was taken at only are 5 valid or random if all larger from the and the where the f is the observed frequency o population. f is the expected frequency and e Method for chi-squared test Σ 1 Draw up a contingency table of 6 frequencies, which are the numbers of or not containing the sum of. Compare the two the calculated value of chi-squared quadrats with containing is observed the critical region. species. ● Species A Species A Row present absent totals If the calculated region, for We an there is value reject in evidence association can is at between the the critical the 5% the hypothesis level two species. H Species B present 0 ● If the calculated value is not in the critical Species B absent region, because it is equal or below the Column totals value obtained squared Calculate the row and column totals. row the same totals or Adding the column totals should no evidence 208 total in the lower right is the table not of chi- rejected. at the 5% level for There an give association grand H 0 is the from values, cell. between the two species. 4 . 1 S P e c i e S , c o m m u n i t i e S a n d e c o S y S t e m S d-bs qss: Chi-squared testing Figure 16 Caradoc, The hill shows a area hill is an in grazed walkers area on the Shropshire, cross by it sheep on summit of Caer 3 Calculate 4 Find in grassy summer paths. There hummocks growing in suggested of moss with them. that A heather visual in heather this (Calluna survey Rhytidiadelphus growing these with area, of of the hummocks. heather and this 6 site a State a sample of 100 the quadrats, presence moss was , the and of freedom. [2] positioned region level of for chi-squared at a 5%. [2] chi-squared. [4] two alternative evaluate them hypotheses, using the H and calculated 1 value for chi-squared. [4] or Suggest ecological reasons for an association recorded the heather and the moss. [4] randomly. 8 Explain used Results area Sps degrees 0 H species associated The critical Calculate between in of are 7 absence number vulgaris) squarrosus, was the signicance and 5 raised the England. to of the methods position that should quadrats have randomly in been the study. [3] Fq Heather only 9 Moss only 7 Both species 57 Neither species 27 Questions 1 Construct a contingency table of observed values. 2 [4] Calculate the association expected between values, the assuming no species. [4] ▲ Figure 16 Caer Caradoc, Shropshire Statistia siniane Recognizing and interpreting statistical signicance. Biologists often signicant” experiment. a statistical alternative use when This the refers hypothesis types phrase discussing of to the test. “statistically results of outcome There are that an a of H is the null and is the belief range be false. of critical hypothesis: hypothesis is the of region. two to ● it results If A possible the the and is is a nd v a l ues calcul a te d region, false s ta ti s ti c rese a r ch nul l ca l cul a te d is ca ll e d sta ti stic the cr it i c a l is r e je cte d, th e wi t h ex c ee d s hyp othes i s the r e f or e u si n g comp ar e d the con si de r ed t h ou g h that 0 we there is no relationship, for example that cannot say tha t thi s ha s be e n p ro ved two withcertainty. means or are equal correlation or that between there two is no association When variables. a biologist statistically ● H is the alternative hypothesis and is states signicant that it results means were that if the null the 1 hypothesis belief that there is a relationship, for two means are different or that there is between two usual procedur e hypothesis, with t he is to true, the probability of as extreme as the observed results getting would very small. A decision has to be made about variables. how The was an be association ) 0 example results that (H tes t the e x pe ctatio n nu ll of sh owin g small known point as for this the the probability signicance probability needs level. of to It be. is rejecting This the the is cut-off null 209 4 E c o l o g y hypothesis 5% is one when often in in chosen, twenty. signicance That level in fact so is it was the the true. A probability minimum published level is ● of less In than the example between acceptable pages, research. there two the is a If there is a difference between the less for the two treatments in a statistical test results will level. of If such means the it a is, large arising population is difference there population a is chance, are than 5% between even equal. signicant means signicant less difference by means statistically is 5% test association on shows probability the observed previous whether of the and being as large as it the is the species being either positively or show negatively whether an an without experiment, than between for described mean expected results testing chi-squared difference ● of species, at We 5% When probability the when say evidence the sample on the a results bar usually there a letter differ. is and such not biological letters are signicance. statistically the of chart, statistical that that associated. b, a indicate and statistically a often Two signicant as research are used different mean indicates to with Two that indicate letters, results difference. displayed of any a the same difference signicant. Esstems A community forms an ecosystem by its interactions with the abiotic environment. A community organisms living is composed could not surroundings surroundings as In the some cases organisms. specialized the rock There For are also the and So, their not also The can where loose abiotic and many sand wave organisms community therefore known ecosystems of be and an an up an on area. their Ecologists are wind complex and and of an be ecosystem. interactions a to it These non- refer to these area Ecologists between survive. inuence more within their the develop plants stabilize sand to abiotic On studyboth the cliffs, can nest. abiotic along grow the be in sand deposited. there environment components them. Autotrophs and heterotrophs obtain inorganic nutrients from the abiotic environment. ● ▲ organisms Carbon, need hydrogen a supply and of oxygen chemical are elements: needed to make carbohydrates, Figure 1 7 Grasses in an area of developing sand dunes 210 lipids and other carbon compounds on which life is are interacting ig s Living the very environment. non-living complex over a birds communities, the highly creates which They plants and and single can specialized encourage inuence shore on this. these organisms in to powerful rocky ledges of interactions between a organisms shore roots a adapted there the The organisms the on living considered as exerts example the there in depend rock. are leaves are or where blown living they action whether cases interactions soil environment sand. only – environment. only break organisms water, the dunes is all isolation wind-blown many system, air, example Sand of in abiotic determines environment. coasts of the habitat type live based. of 4 . 1 Nitrogen ● and phosphorus are also S P e c i e S , needed to c o m m u n i t i e S make many of a n d e c o S y S t e m S these compounds. Approximately ● organisms. are fteen Some nonetheless Autotrophs nutrients obtain from Heterotrophs several however obtain environment, of the abiotic the as other them elements are used in are needed minute by traces living only, but they essential. all the on others of other part of other elements hand the obtain carbon elements including that environment, as sodium, they need including these two compounds inorganic potassium as and elements in their nutrients and inorganic carbon nitrogen. and food. from They the do abiotic calcium. n s The supply of inorganic nutrients is maintained by Reserves of an element in the nutrient cycling. abiotic environment There living they are limited organisms have endlessly have run to Earth using This is the from the of the chemical supplies because Organisms nutrients them on been out. recycled. inorganic return not supplies absorb abiotic environment elements. for chemical the three with elements the billion elements environment, atoms that use Although can they them years, be require and as then Element forming part of a living unchanged. organism Recycling diagram before vary of and it is from nitrogen often element cycle nutrient in this for carbon it element back to the into The is is rarely passed The described an as from in shown organism cycle refer is as environment. to often element an cycle simple carbon nutrient means as abiotic Ecologists word nitrogen is the element. simply cycle and elements example. cycles. context topic4.2 an released as The chemical of an a details from schemes ambiguous in the collectively biology organism nutrient this organism The different these that example Option is to in but needs. cycle in sub- C. Ssb f sss Ecosystems have the potential to be sustainable over long periods of time. The it is concept clear that Something fossil fuels carry fuels are on Natural that our of is is sustainability some current sustainable an nite, example are not if risen human it of has can an to uses prominence of continue resources being are indenitely. unsustainable currently recently activity. renewed and because unsustainable. Human Supplies cannot use of of fossil therefore indenitely. ecosystems children requirements for ● nutrient ● detoxication ● energy can and teach us how grandchildren sustainability in to can live live in as a sustainable we do. There way, are so three ecosystems: availability of waste products ▲ Figure 18 Living organisms have been recycling for billions of years availability. 211 4 E c o l o g y Nutrients not be a products species. Energy ▲ Figure 19 Sunlight supplies energy to a forest ecosystem and nutrients are recycled recycled the one and species used Dust does supply light the it not from be to in the energy an recycled, sun. The of toxic as released source but by is done life a is resource by because there based. should The by of the waste another decomposers Nitrosomonas sustainability Most reduced only energy eruption causing was to this which exploited ions importance the atmosphere supplies so ecosystems. the This energy if on are bacteria action in of the these accumulate. afterwards, starvation. usually potentially consequences months are and elements ammonium for is indenitely chemical example, cannot energy by be of Ammonium bacteria as of For absorbed soil. can lack a the crop of in is supply Mount intensity the on supplied this failures temporary ecosystems of depends and phenomenon, of ecosystems be in sunlight globally form to can Tambora of continued illustrated 1815. for some deaths due however, sunlight will to and continue av for billions of years. cv sss Organisms have been found living in total darkness in Messms caves, including eyeless sh. Discuss whether Setting up sealed mesocosms to try to establish ecosystems in dark caves sustainability. (Practical 5) are sustainable. Mesocosms are sma l l e x pe ri menta l ar e as t ha t ar e set up as Figure 20 shows a ecological experime nts . Fe nce d- off e nc l os u re s in g r as s la n d or small ecosystem with forest could be us e d as te r re s tr ia l m es oc os m s ; t a nk s s et up in photosynthesizing plants the laboratory can be use d as a qua t ic me s oc os m s. E c o lo gi c a l near ar ticial lighting in a experiments can be d o ne in r e pli cat e m es oc o sm s, to nd ou t th e cave that is open to visitors effects of varying o ne or mo re co nditi on s . For ex am pl e, t an ks cou ld in Cheddar Gorge. Discuss be set up with and wi tho ut s h, to i nv e s t ig a t e the e f fe c t s of sh on whether this is more or aquatic ecosystems . less sustainable than Another possible use of mesocosms is to test what types of ecosystems ecosystems in dark caves. are sustainable. together You or ● with should also soil or these sealing water up a inside questions community a of organisms container. before setting up either aquatic mesocosms: glass be involves and consider terrestrial Large This air jars used. are ideal Should the but transparent sides of the plastic container containers be could transparent or opaque? ● Which a of these sustainable groups of community: organisms must autotrophs, be included consumers, to make saprotrophs up and detritivores? ● How can we organisms will ● be How ▲ Figure 20 212 able can placed in in ensure the to we the that the mesocosm oxygen as once supply it is is sufcient sealed, no for more all the oxygen enter. prevent any mesocosm? organisms suffering as a result of being 4 . 2 e n e r G y F l o w 4.2 eg Understandin Skis ➔ Most ecosystems rely on a supply of energy Quantitative representations of energy ow ➔ from sunlight. using pyramids of energy. ➔ Light energy is conver ted to chemical energy in carbon compounds by photosynthesis. ➔ Nature f siene Chemical energy in carbon compounds ows through food chains by means of feeding. ➔ Use theories to explain natural phenomena: ➔ the concept of energy ow explains the limited Energy released by respiration is used in living length of food chains. organisms and conver ted to heat. ➔ Living organisms cannot conver t heat to other forms of energy. ➔ Heat is lost from ecosystems. ➔ Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels. Suniht and esstems Most ecosystems rely on a supply of energy from sunlight. For most sunlight. Three biological Living groups eukaryotic organisms can autotroph carry of algae cyanobacteria. communities, including These the initial harvest out are energy of by photosynthesis: seaweeds organisms this source that grow often on referred energy is photosynthesis. plants, rocky to by shores, and ecologists asproducers. Heterotrophs dependent on consumers, almost harvested The the and in all by amount world. for becomes their light are food in as the of The energy percentage example, the redwood in the Sahara to the a producers in of are to this other they are indirectly heterotroph in of carbon them energy. compounds ecosystems energy that organisms of In use most will the energy in is also sunlight because California more of of All but ecosystems: ecosystems originally have all been producers. intensity of much groups source carbon organisms forests but to directly, detritivores. supplied available available energy several and photosynthesis In because use There energy therefore Desert, it. not saprotrophs compounds or do is there varies harvested varies. very are intensity becomes sunlight high very of In by Sahara but to little of it producers. sunlight available producers the few around is less than organisms abundant. 213 4 E c o l o g y d-bs qss: Insolation av Insolation is a measure of solar radiation The two maps in gure 2 cb vs show Cyanobacteria are annual (upper map) mean and insolation at the at Earth’s the top surface of the (lower Earth’s atmosphere map). photosynthetic bacteria that are often very abundant Questions in marine and freshwater 1 State the relationship between distance from the equator and ecosystems. Figure 1 insolation at the top of the Earth’s atmosphere. [1] shows an area of green 2 State the mean annual insolation in Watts per square metre cyanobacteria on an area for the most northerly part of Australia of wall in a cave that is illuminated by articial light. a) at the top of the b) at the Earth’s atmosphere [1] The surrounding areas are surface. [1] normally dark. If the articial 3 Suggest reasons for differences in insolation at the Earth’s light was not present, what surfacebetween places that are at the same distance from other energy sources could theequator. [2] be used by bacteria in caves? 4 Tropical rainforests continents. Evaluate They the insolation. are have found very hypothesis Include equatorial high that named in this parts rates is of of due the regions of all photosynthesis. to very world in high your answer. ▲ [5] Figure 1 2 0 ▲ 214 40 Figure 2 80 120 160 200 240 280 320 360 400 w/m 4 . 2 e n e r G y F l o w Ener nversin av Light energy is conver ted to chemical energy in carbon Bsh fs s compounds by photosynthesis. Producers absorb pigments. This make carbohydrates, Producers can respiration is sunlight converts eventually lipids release and then lost to using the and energy use the chlorophyll light it energy all the from for cell to other their and carbon carbon activities. environment as other chemical photosynthetic energy, compounds compounds Energy waste which to cell in However, used producers. by released heat. in is this only way some ▲ of the carbon compounds in producers are used in this way and Figure 3 the Figure 3 shows a bush re in largest part remains in the cells and tissues of producers. The energy in Australia. these carbon compounds is available to heterotrophs. What energy conversion is happening in a bush re? Ener in fd hains Bush and forest res Chemical energy in carbon compounds ows through food occur naturally in some ecosystems. chains by means of feeding. Suggest two reasons for this A food chain is a sequence of organisms, each of which feeds on the previous hypothesis: There are fewer one. There are usually between two and ve organisms in a food chain. It is heterotrophs in ecosystems rare for there to be more organisms in the chain. As they do not obtain food where res are common from other organisms, producers are always the rst organisms in a food compared to ecosystems chain. The subsequent organisms are consumers. Primary consumers feed where res are not common. on producers; consumers the last feed therefore falls ▲ in on organism compounds Figure secondary 4 in is an secondary in the indicate a food on direction of a feed on consumers, chain. organisms the example northern consumers primary and Consumers which of they energy food chain so on. obtain feed. consumers; No consumers energy The tertiary from arrows in feed the a on carbon food chain ow. from the forests around Iguazu Argentina. Figure 4 Respiratin and ener reease Energy released by respiration is used in living organisms and conver ted to heat. Living organisms ● Synthesizing ● Pumping ● Moving or ATP in need large things or around cells energy for molecules molecules muscle supplies energy the for ions like inside the activities DNA, across protein these cell RNA such that activities. as cause Every as and membranes cell, bres such by these: proteins. active transport. chromosomes muscle cell or vesicles, contraction. produces its own ATPsupply. 215 4 E c o l o g y All cells can produce compounds oxidation in reason such as The are ATP second never in Energy have is law not of is cell be molecules respiration. and make and the and other for in cell to may heat. reside such eventually of states the Some warm for as a digested is time the is in carbon cell, but large energy is the ATP . The chemical transformations the to oxidation ATP . but for as ATP is example. when when released The when contract molecules proteins, to compounds produced they used activities. energy from also when and in transferred heat up DNA the that is transfers compounds different energy carbon These released respiration energy by process oxidized. energy cell many respiration Muscles synthesized, all this are carbon usable directly Not the So chemical immediately used In lipids ATP . thermodynamics activities. are to efcient. ATP cell exothermic that converted from been by glucose is compounds remainder used this can 100% carbon are from doing glucose in ATP carbohydrates reactions energy for energy as reactions endothermic chemical of such they these heat. d-bs qss 20 Figure shows the r e s ul ts yellow-bill e d of ma g p ie s an e x pe ri m e n t (Pica nuttalli) in were 1 be in a cage in controlled. was The measured from 30 ° C 10 ° C the w hi ch at to b i r ds ’ seven + 40 ° C. magpies temperature, the but temp e rat u r e r ate of tem pe r at u r e s, Between mai nta i ned above 30 ° C c o ul d r e spi ra tio n d iffe r ent 10 ° C constant body 15 g Wm( etar noitaripser put ) which 5 and body temperatur e 10 5 increased. a) Describe the temperature relationship and between respiration rate external in 0 yellow- 0 10 billed b) magpies. Explain the 10 [3] change in respiration rate 20 30 40 50 temperature (°C) ▲ as Figure 5 Cell respiration rates at dierent temperatures in yellow-billed magpies temperature c) Suggest a drops reason respirationrate from 30 °C to from for as the +10 °C to change temperature 10 °C. [3] in d) increased 40 °C. Suggest two respiration [2] reasons rate for the between variation the birds at in each temperature. [2] Heat ener in esstems Living organisms cannot conver t heat to other forms of energy. Living energy can chemical various Light ● Chemical energy to kinetic ● Chemical energy to electrical ● Chemical energy to heat cannot to perform ● They 216 organisms convert heat energy in energy in into conversions: photosynthesis. in energy energy energy energy muscle in contraction. nerve cells. heat-generating any other form adipose of tissue. energy. 4 . 2 e n e r G y F l o w Heat sses frm esstems av Heat is lost from ecosystems. thkg b g Heat This resulting heat can from be cell useful respiration in making makes living cold-blooded organisms animals warmer. more hgs active. What energy conversions Birds and mammals increase their rate of heat generation if necessary to are required to shoot a maintain their constant body temperatures. basketball? According to the laws of thermodynamics in physics, heat passes from What is the nal form of the hotter to cooler lost the bodies, so heat produced in living organisms is all eventually energy? a to while, abiotic but ultimately atmosphere. in cell environment. Ecologists activities will is lost, The for assume ultimately heat may example that be all lost remain when energy from heat in is released an the ecosystem radiated by into respiration for the for use ecosystem. expg h gh f f hs Use theories to explain natural phenomena: the concept of energy ow explains the limited length of food chains. If we consider chain, we leading that can up fed to on in the There are might expect branches the that occur how which carnivore many if fed than chains innitum. science, of of top example, more length a an on that stages osprey is at there the are feeds on phytoplankton, end in the sh of food food such there a are chain as salmon four chain. food concept of out For food ad of restricted is work it. rarely another diet shrimps, stages by the we energy between to be This try food four stages limitless, not explain chains trophic ve does to ow or using along levels with in one happen. natural that chain. species In and provide the an We being ecology, theories. chains can food phenomena scientic food a as eaten in such In this all as the case energy it losses explanation. ▲ Figure 6 An infrared camera image of an Ener sses and esstems African grey parrot (Psittacus erithacus) shows how much heat is being released to the Energy losses between trophic levels restrict the length environment by dierent par ts of its body of food chains and the biomass of higher trophic levels. Biomass tissues is of the those compounds energy, added the be per energy year The they has by per added square Most of for the organisms a of of the is by each in loss food trophic to of is the measure their so how that by and other much level carbon energy is are trophic is and chemical results always is cells levels found: less. always In less per consumers. between digested the have The energy primary released is trophic of of different trend amount in and biomass. same energy is consists compounds successive than that level can the It carbohydrates carbon ecosystem ecosystem is the done, example, trend organisms. Because organisms this for of Ecologists biomass energy in of metre metre this group including energy. When to a contain. consumers, reason of groups square compared. secondary ● year mass organisms, that biomass per calculated can total trophic levels. absorbed them in by respiration ▲ for Figure 7 The osprey (Pandion halietus) is a sh-eating top carnivore 217 4 E c o l o g y use in cell available av activities. to It is organisms carbohydrates and therefore in the other next carbon lost as heat. trophic The level compounds is that only energy chemical have not energy been in used S s up in cell respiration. Most salmon eaten by The ● humans is produced in sh by farms. The salmon have organisms organisms sometimes traditionally been fed on parts sh meal, mostly based on the anchovies harvested o the of bodies trophic next of their in all plants passes organisms have become scarce and a the consume some material coast of South America. These in in to the level the are prey such in usually For an bones or or entirely example, area Predators as trophic not level. plants eaten. saprotrophs next are trophic but more may not hair. Energy detritivores eat rather consumed locusts usually material in only from uneaten than passing to level. expensive. Feeds based on Not ● all parts of food ingested by the organisms in a trophic level are plant products such as soy digested and absorbed. in Energy Some material is indigestible not on and is egested beans are increasingly being feces. in feces does pass along the food chain and used. In terms of energy ow, instead passes to saprotrophs or detritivores. which of these human diets is Because of these losses, only a small proportion of the energy in most and least ecient? 1 thebiomass of organisms in one thebiomass of organisms in the trophic level will ever become part of Salmon fed on sh meal 2 Salmon fed on soy beans 3 Soy beans. often quoted, variable. less As energy stages in enough trophic a to but the the losses available food in food measured to carbon food of of chain higher levels. of trophic level the in is or levels all, of trophic is of in a energy The chain, level. this of 10 %is levels there After remaining For gure trophic food trophic level. only would reasonthe is is lessand a few not be number of restricted. also diminishes water from therefore a level. between stage undigested is than each loss successive and generally of at grams, uneaten trophic energy amount chains dioxide trophic There each another Biomass, loss of occur to chain support levels level next higher any parts of usually biomass other along food respiration trophic loss organisms. smaller of chains, and The than producers, the biomass that the due from of lower lowest level. secondary consumer decomposers 2 (200 kJ m 2 (16,000 kJ m Pramids f ener 1 yr ) 1 yr ) Quantitative representations of energy ow using primary consumer 2 (2,500 kJ m 1 yr ) pyramids of energy. plankton The 2 of energy converted to new biomass by each trophic level in ) an ▲ amount 1 yr (150,000 kJ m ecological Figure 8 An energy pyramid for an aquatic This ecosystem (not to scale) The is a type community can of with amounts bar of chart energy be a should represented horizontal be per unit with bar a for area pyramid each per are kilojoules should lowest be per metre stepped, bar. The not bars squared per triangular, should be year (kJ starting labelled m with Often energy. level. the units 1 yr the producer, trophic year. 2 of ). The pyramid producers rst in consumer, the second secondary consumer 2 (3,000 MJ m consumer 1 yr and so on. If a suitable scale is chosen, the length of each bar ) can be proportional to the amount of energy that it shows. primary consumer 2 (7,000 MJ m 1 yr ) Figure 8 shows ecosystem. To an be example more of a pyramid accurate, the bars of energy should be for an aquatic drawn with relative producers 2 (50,000 MJ m 1 yr widths Figure 9 Pyramid of energy for grassland 218 match the relative energy content at each trophic level. Figure ) 9 ▲ that shows a pyramid of energy for grassland, with the bars correctly to scale. 4 . 2 e n e r G y F l o w d-bs qss: a simple food web A sinkhole cavern a sinkhole due in is a surface collapses. lled part to feature Montezuma with the water. which Well It extremely is an high forms in the when an Sonoran aquatic underground desert ecosystem concentrations of in that Arizona lacks dissolved is sh, CO . The 2 dominant grow to Figure 1 top 70 mm 10 Compare 3 4 Deduce 7 a using P b) what is the a bakeri, a giant water of that can for Montezuma Belostoma bakeri Well. and Ranatra montezuma [2] which organism occupies more level. [2] values: be the most preferred pyramid the of common prey of energy B. for food chain in this web [2] bakeri? the rst [1] and second the trophic levels. Outline energy lost between the rst and [2] of classifying organisms into [2] additional the of levels. difculties the complete [3] percentage trophic Discuss pyramid information of energy that for would the third be and required to fourth level. [1] Ranatra montezuma 1 235,000 kJ ha 2 P = 1.0 gm insect levels. Calculate trophic web reason, would Construct Belostoma web. trophic what second 6 roles a) trophic 5 food food with one is length. a the the Deduce, than in shows within 2 predator Belostoma bakeri 1 1 yr 588,000 kJ ha 1 2 yr P = 2.8 gm 1 yr 1 yr Telebasis salva 1 1,587,900 kJ ha 2 P = 7.9 gm 1 yr 1 yr Hyalella montezuma 1 30,960,000 kJ ha 2 P = 215 gm phytoplankton - Metaphyton 1 234,342,702 kJ ha 2 P = 602 g C m ▲ 1 yr 1 yr piphyton 1 yr 1 427,078,320 kJ ha 1 yr 1 yr 2 P = 1,096 g C m 1 yr Figure 10 A food web for Montezuma Well. P values represent the biomass stored in the population of that organism each year. Energy values represent the energy equivalent of that biomass. Arrows indicate trophic linkages and arrow thickness indicates the relative amount of energy transferred between trophic levels 219 4 E c o l o g y 4.3 cb g Understandin Appiatins ➔ Autotrophs conver t carbon dioxide into ➔ Estimation of carbon uxes due to processes in carbohydrates and other carbon compounds. the carbon cycle. ➔ In aquatic habitats carbon dioxide is present as ➔ Analysis of data from atmosphere monitoring a dissolved gas and hydrogen carbonate ions. stations showing annual uctuations. ➔ Carbon dioxide diuses from the atmosphere or water into autotrophs. ➔ Skis Carbon dioxide is produced by respiration and diuses out of organisms into water or the ➔ Construct a diagram of the carbon cycle. atmosphere. ➔ Methane is produced from organic matter Nature f siene in anaerobic conditions by methanogenic archaeans and some diuses into the ➔ atmosphere. ➔ ➔ Making accurate, quantitative measurements: it is impor tant to obtain reliable data on the Methane is oxidized to carbon dioxide and concentration of carbon dioxide and methane water in the atmosphere. in the atmosphere. Peat forms when organic matter is not fully decomposed because of anaerobic conditions in waterlogged soils. ➔ Par tially decomposed organic matter from past geological eras was conver ted into oil and gas in porous rocks or into coal. ➔ Carbon dioxide is produced by the combustion of biomass and fossilized organic matter. ➔ Animals such as reef-building corals and molluscs have hard parts that are composed of calcium carbonate and can become fossilized in limestone. carbn xatin Autotrophs conver t carbon dioxide into carbohydrates and other carbon compounds. Autotrophs it into that absorb carbon carbohydrates, they require. This the dioxide lipids has concentration of atmosphere currently and the all from the effect atmosphere. of The the atmosphere other carbon reducing mean CO the and convert compounds carbon dioxide concentration of the 2 mole is (µmol/mol) photosynthesis 220 but rates it approximately is have lower been above high. 0.039 % parts of or the 390 micromoles Earth’s surface per where 4 . 3 c a r B o n c y c l i n G d-bs qss: Carbon dioxide concentration The by two maps NASA. in They concentration above the gure show of the surface of 1 were the atmosphere the 4 produced carbon Earth, a) Deduce lowest eight between in kilometres May part mean May State whether fall(autumn) 2 a) October in Distinguish the in the Suggest a) Distinguish dioxide the in in spring hemisphere. October that had the concentration 2011. [1] Suggest reasons for carbon May and for the between the concentrations and the Suggest being the carbon lowest in dioxide this area. [2] [1] dioxide October [1] difference. [2] carbon in May between southern hemisphere. b) and Earth dioxide or hemisphere. reasons northern the southern northern b) is between concentrations 3 the 2011. concentration 1 of carbon and b) October the dioxide [1] reasons for the difference. Figure 1 [2] carbn dixide in sutin In aquatic habitats carbon dioxide is present as a dissolved gas and hydrogen carbonate ions. Carbon dioxide is soluble in water. It can either remain in water as av a dissolved gas or it can combine with water to form carbonic acid pH hgs k ps (H CO 2 ). Carbonic acid can dissociate to form hydrogen and hydrogen 3 + carbonate ions (H and HCO ). This explains how carbon dioxide can Ecologists have monitored 3 reduce the pH of pH in rock pools on sea water. shores that contain animals Both dissolved carbon dioxide and hydrogen carbonate ions are absorbed and also photosynthesizing by aquatic plants and other autotrophs that live in water. They use them algae. The pH of the to make carbohydrates and other carbon compounds. water rises and falls in a 24-hour cycle, due to changes in carbon dioxide Absrptin f arbn dixide concentration in the water. Carbon dioxide diuses from the atmosphere or water The lowest values of about pH 7 have been found during into autotrophs. the night, and the highest Autotrophs use carbon dioxide in the production of carbon compounds values of about pH 10 have by photosynthesis or other processes. This reduces the concentration been found when there was of carbon dioxide inside autotrophs and sets up a concentration bright sunlight during the gradient between cells in autotrophs and the air or water around. day. What are the reasons for Carbon dioxide therefore diffuses from the atmosphere or water into these maxima and minima? autotrophs. The pH in natural pools or In land plants stomata surface so in of with the the diffusion leaves underside leaves can be and this of diffusion the stems through leaves. is any usually In usually part of happens aquatic plants permeable these parts to of through the entire carbon the dioxide, ar ticial aquatic mesocosms could be monitored using data loggers. plant. 221 4 E c o l o g y Reease f arbn dixide frm e respiratin Carbon dioxide is produced by respiration and diuses out of organisms into water or the atmosphere. Carbon dioxide produced grouped in all is a waste cells according that to trophic ● non-photosynthetic ● animal ● saprotrophs Carbon into cells of out level in aerobic aerobic of the cell cell respiration. respiration. It is These can be organism: producers for example root cells in plants cells dioxide the product carry such as fungi produced atmosphere or by that decompose respiration water that dead diffuses surrounds organic out these of cells matter. and passes organisms. d-bs qss: Data-logging pH in an aquarium Figure 2 shows the pH and light intensity pH sensor (pH) in an aquarium containing a varied 7.50 100 light intensity community of organisms including 90 pH newts and other animals. 7.45 The data was obtained by stinu yrartibra/ ytisnetni thgil pondweeds, data 80 logging 70 using a pH electrode and a light meter. 7.40 The aquarium was illuminated 60 articially 50 to give a 24-hour cycle of light and dark 7.35 using a lamp controlled by a 40 timer. 30 1 Explain the changes in light 7.30 intensity during the experiment. 20 [2] 10 2 Determine how many days the 0 7.25 data logging covers. [2] 0.14:02:31 0.23:13:11 06 February 2013 3 a) Deduce the trend in pH 3.08:23:50 14:02:31 4.17:34:30 6.02:45:09 absolute time (d.hh:mm:ss) in Figure 2 the light. [1] 4 b) Explain this trend. a) Deduce the b) Explain trend in pH in darkness. [1] [2] this trend. [2] Methanenesis Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans and some diuses into the atmosphere. In a 1776 reed was on this it is a Three name. waste Bacteria Volta He product had is of groups that collected margins Methane different alcohol, 222 the inammable. it 1 Alessandro bed hydrogen Lake of bubbles discovered type of anaerobic and in and though anaerobic from found Volta mud that did not in it give environments, as respiration. into dioxide. emerging Italy, prokaryotes matter carbon gas in methane, widely anaerobic organic of Maggiore produced a convert of a are involved. mixture of organic acids, 4 . 3 2 Bacteria carbon 3 that use dioxide Archaeans acetate. that They CO + CH organic this → CH out → in CH this Mud along ● Swamps, peat the + mires, ● Guts of ● Landll sites from chemical 2H to produce acetate, carbon dioxide, hydrogen and reactions: O CO group in are many and in mangrove are termites alcohol 2 third shores deposits and 2 methanogenesis ● or + 4 archaeans carry two 4 3 The methane by 2 COOH acids c y c l i n G hydrogen. produce do 4H 2 the and c a r B o n therefore anaerobic the bed forests of and methanogenic. They environments: lakes. other wetlands where the soil waterlogged. and where of ruminant organic mammals matter is in such wastes as that cattle and have sheep. been buried. Some of the methane environments in the atmosphere Methane produced diffuses is produced into the between from by archaeans atmosphere. 1.7 organic and 1.85 waste in in these anaerobic Currently the micromoles anaerobic concentration per mole. digesters is Figure 3 Waterlogged woodland–a typical not habitat for methanogenic prokaryotes allowed to escape and instead is burned as a fuel. oxidatin f methane Methane is oxidized to carbon dioxide and water in the atmosphere. Molecules on of average the methane for only stratosphere. released 12 years, Monatomic into the because oxygen atmosphere it is (O) naturally and persist there oxidized highly in reactive • hydroxyl explains amounts human radicals why of (OH ) are atmospheric production of involved in methane concentrations methane by are both oxidation. not high, natural This despite processes large and activities. Peat frmatin Peat forms when organic matter is not fully decomposed because of anaerobic conditions in waterlogged soils. In many soils eventually obtain the in the of soils cannot In thrive saprotrophs in and matter such saprotrophic they need these conditions also dead so tend methanogens leaves and respiration water waterlogged conditions as bacteria for environments become Acidic m a t t e r. by that some they decomposed. organic organic oxygen soil. so all digested and is to organic develop, that from unable to anaerobic. dead might from fungi. plants is Saprotrophs air spaces drain out Saprotrophs matter further break is not fully inhibiting down the Figure 4 Peat deposits form a blanket on a boggy hill top at Bwlch Groes in Nor th Wales 223 4 E c o l o g y d-bs qss: Release of carbon from tundra soils Soils in tundra amounts of carbon accumulates of dead ecosystems plant this, from of in Alaska. the of organic investigate areas in because form low matter ecologists tussock Some of typically of rates by peat. of areas and This samples Toolik been and To of the soil nitrogen and phosphorus every or 15°C. others the Some were carbon amount 5 shows of the eight years (TF) and some soils were incubated for had 100-day were with the kept water soils was dioxide monitored. moist (W). The measured given The (M) bar off during chart in results. fertilized year for a) State the effect not of increasing the the of the soils on the rate (TC). of The of carbon was temperature previous samples saturated content experiment gure Lake 1 with 7 initial decomposition near had either large saprotrophs. collected vegetation the contain periods release of carbon. [2] at b) Explain the a) Compare reasons for this effect. [2] 40 2 the rates of release of carbon in TC C laitini fo egatnecrep moist 30 soils with those in soils saturated TF with b) water. Suggest [2] reasons for the differences. [2] 20 3 Outline release the of effects carbon of fertilizers from the on rates of soils. [2] 10 4 Discuss whether amount of differences water in the in soil or temperature, amount of 0 7M 7W 15M fertilizer 15W treatment group release have of the greatest impact on the carbon. [2] Figure 5 Large quantities of partially accumulated in brown material is acidic covered the total by some peat called and quantities of decomposed ecosystems as peat. the this and organic become About depth material is 3% ten are matter have compressed of the metres to Earth’s or more form land in a dark surface some places, immense. Fssiized rani matter Par tially decomposed organic matter from past geological eras was conver ted into oil and gas in porous rocks or into coal. Carbon can and remain are large the result in ● deposits Coal is compounds of that coal. coal Large coastal buried left a the of from were Carboniferous. formed level coal. past chemically of of very millions geological of peat compressed deposits the are hundreds eras. organic of These matter stable years. and There deposits and its are burial rock. deposits is swamps when seam peat carbon for decomposition when The of rocks carbon became formed of in incomplete sediments. falls; 224 of sediments period Figure 6 Coal at a power station some unchanged rose are and formed There buried heated, during was a as the level and the sea the cycle fell under turning Pennsylvanian of and spread other gradually sea level were inland. rises and destroyed Each into sub- cycle and has 4 . 3 Oil ● and lakes. natural incomplete. As decomposed which We largest these part that above more formed of other or compressed mixtures crude gas. them the mud mud is natural below the anaerobic complex hold in usually mixtures can and are are matter produce call rocks gas Conditions oil of porous rocks are are gas. found that and of seas deposited Chemical carbon natural shales bottom decomposition heated. liquid and as the so sediments and Deposits such at and prevent the compounds the and partially there are deposit’s occur, or forms impervious c y c l i n G often changes Methane where also is c a r B o n gases. the porous rocks escape. cmbustin Carbon dioxide is produced by the combustion of biomass and fossilized organic matter. If organic of matter oxygen it is will heated set light to its and ignition burn. The temperature oxidation in the reactions presence that occur Figure 7 Carbon dioxide is released by are called dioxide In and some forests the combustion. biomass rapidly In other are Coal, in are areas rainforest leaves of complete combustion are carbon combustion of the leaves of sugar cane the the world forest often it Carbon or well is natural dioxide is grassland. adapted to for there released In these res and to be from periodic the areas the res in combustion trees communities and of other regenerate afterwards. sometimes cane of grassland. organisms products water. parts or The for due them planting traditionally burn oil res cause off, and to to oil palms burned leaving natural natural occur. the gas causes Fire or is for shortly cattle before harvestable are are used different very to unusual, clear areas ranching. they are but of humans tropical Crops of sugar harvested. The dry stems. forms of fossilized organic Figure 8 Kodonophyllum–a Silurian coral, in matter. They are all burned as fuels. The carbon atoms in the carbon limestone from Wenlock Edge. The calcium dioxide released may have been removed from the atmosphere by carbonate skeletons of the coral are clearly photosynthesizing plants hundreds of millions of years ago. visible embedded in more calcium carbonate that precipitated 420 million years ago in shallow tropical seas limestne Animals such as reef-building corals and molluscs have hard par ts that are composed of calcium carbonate and can become fossilized in limestone. Some animals (CaCO have hard body parts composed of calcium carbonate ): 3 ● mollusc ● hard corals calcium When shells contain that build calcium reefs carbonate; produce their exoskeletons by secreting carbonate. these animals die, their soft parts are usually Fig u r e decomposed 9 E ng la nd. quickly. In acid conditions the calcium carbonate dissolves away but or alkaline conditions it is stable and deposits of it from parts can form on the sea bed. In shallow tropical seas cl i f f s is a on the f or m of sou th coast l i mestone of that a l most enti r ely of 90 - m i l l ion- yea r- hard old animal Cha l k in cons i sts neutral Cha l k s hel l s of ti ny u n icel l u la r a n i ma l s ca l led calcium fo r a m i n i fe r a 225 4 E c o l o g y carbonate is limestone rock, visible as also of carbon the by precipitation deposited hard in the parts water. of The animals result are is often fossils. Approximately 12% deposited where the are 10% mass of locked of the up all sedimentary calcium in rock carbonate limestone rock on is on Earth carbon, is so limestone. huge About amounts of Earth. carbn e diarams Construct a diagram of the carbon cycle. Ecologists recycling studying of other the carbon elements cycle use the and the terms Diagrams pool cycle. and arrows ux. for diagram ● A pool is a reserve of the element. It can or inorganic. dioxide in the of carbon. ecosystem The is For example atmosphere biomass an of organic is an the A ux one ux is pool is the to the transfer another. of in be An absorption of element example carbon of the atmosphere and its to plant to be represent used Figure can be 10 for shows converted shows ecosystems. a for combined the A labeled diagram diagram cycle separate marine or of for all for diagram aquatic and reserve of aquatic could ecosystems, ecosystems. ecosystems, the In inorganic carbon carbon conversion hydrogen is dissolved carbonate, carbon which is dioxide and by various means biomass. the water. in cell respiration in saprotrophs and detritivores s le u f cell respiration li s s o f carbon in in consumers organic compounds fo in producers n o it s u b m o c death feeding egestion carbon in dead organic matter incomplete decomposition and fossilization of organic matter and absorbed by by 2 226 a and illustrated dioxide CO Figure 10 Carbon cycle an to carbon atmosphere oil carbon arrows. only marine into coal the pools from producers photosynthesis and constructed and from 10 terrestrial an pool. the can uxes. which boxes Figure pool or ● used carbon inorganic producers be boxes be text organic can Text gas is released back 4 . 3 c a r B o n c y c l i n G carbn uxes Estimation of carbon uxes due to processes in the carbon cycle. The carbon cycle diagram in gure 10 shows F x/ggs Pss processes another uxes. uxes but It is it transfer does not them. not but scientists Estimates individual carbon show possible precisely interest, in that as global quantities on or 1 to of these are of 120 Cell respiration 119.6 great Ocean uptake 92.8 Ocean loss 90.0 for measurements in Photosynthesis carbon estimates many ecosystems pool quantities produced based natural the one measure these have are to from mesocosms. Deforestation and land use 1.6 changes Global carbon estimates are gigatonne based on is uxes in 1,015 Ocean are extremely gigatonnes grams. large (petagrams). Table Biogeochemical 1 shows Dynamics, so Burial in marine sediments 0.2 Combustion of fossil fuels 6.4 One estimates Sarmiento T able 1 and Gruber, 2006, Princeton University Press. d-bs qss: Oak woodland and carbon dioxide concentrations Carbon uxes deciduous in England. robur and have been woodland The at trees Quercus measured Alice are Holt mainly petraea, with since 1998 Research oaks, some in 1 on Quercus ash, They were planted in 1935 and are 20 metres more Deduce dioxide times a concentrations are net is second. ecosystem the net From these forest indicate the an forest decrease and production ux of the can carbon be dioxide atmosphere. increase and due in the negative to shows net the the months in Explain for net year. [1] the in which forest was the carbon pool highest of Positive carbon values loss daily pool indicate carbon average the reasons net pool of several years ecosystem for and biomass increases in the in the forest part of the year and decreases in between parts. [4] values 4 of the annual carbon ux to or from forest. a dioxide. State the [2] The Suggest a reason based on the data for ecosystem also the planting of more the oak cumulative the [2] encouraging production in decreases deduced. 5 graph or measurements other the the pool lowest. during This in carbon increases measured carbon the the forest tall. 3 20 days biomass and Carbon the now of nearly whether of Fraxinus 2 excelsior. Calculate biomass Forest forests. [1] production. 20 25 1 ) 20 1 1 ) h 15 15 ah ah 10 5 5 0 0 0 50 100 150 200 250 300 530 −5 OC t( PEN evitalumuc 2 OC gk( PEN egareva yliad 2 10 −5 −10 −10 −15 day of year 227 4 E c o l o g y Envirnmenta mnitrin Making accurate, quantitative measurements: it is impor tant to obtain reliable data on the concentration of carbon dioxide and methane in the atmosphere. Carbon in the dioxide and atmosphere effects. Carbon methane have dioxide photosynthesis rates the pH of above affect seawater. inuence global temperatures and as a 600 extent of ice sheets at the poles. therefore affect sea levels and data lines. Through their effects the on position heat the energy affect in ocean the oceans currents, and the and extreme also the weather the such and as these hypotheses and The carbon dioxide atmosphere time in the is severity past twenty over can Human activities dioxide and have Data on higher million of than the prerequisite predictions methane long of by a the period past human the at any Research now years. of Organization, for of such concentration as possible and possible future of gases in the Atmosphere atmosphere Watch increased the the on World agency in Meteorological of the various atmosphere, Hawaii has United parts of but Nations. the world Mauna records from carbon concentrations in period. Carbon dioxide concentrations the been measured activity will cause atmospheric records from are of 1984. from 1959 These immense and onwards value other and to reliable scientists. Analysis of data from atmosphere monitoring stations showing annual uctuations. freely it. atmosphere available There are uctuations data and stations are in monitoring allowing both in Observatory of the data. Hawaii data any long-term from available The person trends for and to and Mauna produces this stations analyse annual Loa vast other is amounts monitoring analysis. Figure 11 Hawaii from space. Mauna Loa is near the centre of the largest island 228 Loa the Trends in atmspheri arbn dixide from are before atmosphere. Human Data as atmospheric activity. Global the an stations monitor methane ● level century. predictions: have Earth’s and concentrations collected longest methane and as evaluate Observatory ● from a of hurricanes. concentration currently essential measurements dioxide programme ● the to of is Consider rise atmosphere distribution frequency events an hypotheses consequences rainfall of to 2014 amount we they end in of needed of are Reliable carbon coast the mole Indirectly these. they by per result evaluating the concentrations Both Reliable gases dioxide 397micromoles important concentrations and carbon concentrations very 4 . 4 c l i m a t e c H a n G e 4.4 c hg Understandin Appiatins Carbon dioxide and water vapour are the most ➔ Correlations between global temperatures and ➔ signicant greenhouse gases. carbon dioxide concentrations on Ear th. Other gases including methane and nitrogen ➔ Evaluating claims that human activities are not ➔ oxides have less impact. causing climate change. The impact of a gas depends on its ability to ➔ Threats to coral reefs from increasing ➔ absorb long-wave radiation as well as on its concentrations of dissolved carbon dioxide. concentration in the atmosphere. The warmed Ear th emits longer-wave radiation ➔ (heat). Nature f siene Longer-wave radiation is reabsorbed by ➔ Assessing claims: assessment of the claims ➔ greenhouse gases which retains the heat in the that human activities are not causing climate atmosphere. change. Global temperatures and climate patterns are ➔ inuenced by concentrations of greenhouse gases. There is a correlation between rising atmospheric ➔ concentrations of carbon dioxide since the star t of the industrial revolution two hundred years ago and average global temperatures. Recent increases in atmospheric carbon ➔ dioxide are largely due to increases in the combustion of fossilized organic matter. greenhuse ases Carbon dioxide and water vapour are the most signicant greenhouse gases. The in Earth the is kept atmosphere likened to that of therefore known retention is The are ● not carbon Carbon that the as the greenhouse in much dioxide living retain glass than heat. that it The retains greenhouse gases, otherwise effect heat of in though a would these be gases greenhouse the by gases has been and mechanism of they are heat same. gases dioxide warmer that and is have water released organisms and the largest warming effect on the Earth vapour. into also by the atmosphere combustion of by cell biomass respiration and fossil 229 4 E c o l o g y fuels. It is removed dissolving Water ● in the vapour transpiration and Water liquid back continues the explains areas formed in the atmosphere by photosynthesis and by plants. by It evaporation is removed from from the the oceans and atmosphere also by rainfall snow. water to is from oceans. in Earth’s why with to retain clouds. the clear heat The surface and temperature skies than after water in it condenses absorbs also reects drops areas heat so the much with to form energy heat more cloud droplets and of radiates energy back. quickly at it This night in cover. other reenhuse ases Other gases including methane and nitrogen oxides have less impact. Although carbon dioxide and water vapour are the most signicant Figure 1 Satellite image of Hurricane Andrew in greenhouse gases there are others that have a smaller but nonetheless the Gulf of Mexico. Hurricanes are increasing in frequency and intensity as a result of increases signicant effect. in heat retention by greenhouse gases Methane ● from sites is where extraction Nitrous ● vehicle two are radiation. than 1% All of fossil by is most other signicant wastes fuels bacteria in have and another greenhouse waterlogged been from ice It in greenhouse habitats and gas. and dumped. melting signicant some habitats also It from is emitted released polar gas. by is landll during regions. It is released agriculture and exhausts. most nitrogen, third and organic of oxide naturally The the marshes abundant not of the gases greenhouse the in the gases greenhouse Earth’s as gases they atmosphere, do not together oxygen absorb and longer-wave therefore make up less atmosphere. Assessin the impat f reenhuse ases The impact of a gas depends on its ability to absorb long-wave radiation as well as on its concentration in the atmosphere. Two factors ● how ● the For readily carbon atmosphere The the its water there atmosphere for as a it enters nine in days twelve the much is at a long the on years more on lower is a greenhouse gas: and the rate average average, at it molecule is which it remains is in the methane dioxide for released there. immensely whereas carbon per concentration less. atmosphere and of radiation; warming much on impact atmosphere. warming depends how warming long-wave global gas and the gas causes on vapour only the but impact of absorbs of methane atmosphere which remains 230 gas dioxide, concentration into the the determine concentration example, than at together The rapid, rate but remains even longer. it in 4 . 4 c l i m a t e ln-waveenth emissins frm Earth c H a n G e TOK The warmed Ear th emits longer-wave radiation. Qss xs b h The warmed sun and then re-emitted The peak Figure 2 through and the pass re-emits the the it, is wavelength shows of through range of temperature of much of but at solar range the Earth of to with longer the peak is and of expected the wavelength of of 10,000 radiation emitted to Most the f s ph. wh the sqs gh hs hv f h nm. pb pp sg f s? surface The from nm. solar Earth’s (blue). energy wavelengths. 400 wavelengths atmosphere Earth a wavelengths reach short-wave longer radiation wavelengths the absorbs much infrared, atmosphere range the of radiation the out show surface and by smooth be the red emitted that pass warm Earth and by it involves entities and concepts beyond that blue bodies Much of what science investigates (red) everyday experience of the world, curves of such as the nature and behaviour the of electromagnetic radiation or the sun. build-up of invisible gases in the atmosphere. This makes it dicult for scientists to convince the general ytisnetni lartceps public that such phenomenon actually exist – par ticularly when the consequences of accepting their existance might run counter to value systems or entrenched beliefs. UV Visible Infrared 1 0.2 10 70 wavelength (µm) Figure 2 greenhuse ases Longer-wave radiation is reabsorbed by greenhouse gases which retains the heat in the atmosphere. 25–30% the is sun of the that absorbed of light, which much the of passing before Most radiation is short-wavelength solar is it radiation absorbed therefore this is through reaches by reaches converted radiation the the atmosphere Earth’s absorbed ozone. the to is surface. ultraviolet 70–75 % Earth’s heat. from of solar surface and A far higher percentage radiation re-emitted absorbed before 70% the and 85% is atmosphere. towards Without surface the it it This would the be longer-wavelength surface by out effect is the is Earth space. global at is Between gases re-emitted, temperature about of to greenhouse energy The mean the passed captured Earth. the by has of in some warming. the Earth’s 18°C. Key short-wave radiation from the sun long-wave radiation from earth Figure 3 The greenhouse eect 231 4 E c o l o g y Greenhouse only absorb Figure of 4 below radiation shows gases the in energy by the in shows the bands Earth’s specic total percentage atmosphere. of atmosphere individual wavebands. The wavelengths the absorption graph absorbed Earth carbon also is a some The wavelengths between dioxide, absorb by gases. are of 5 and methane these greenhouse re-emitted 70nm. and Water nitrous wavelengths, oxide so by vapour, each all of them gas. 100 tnecrep 75 Total absorption 50 and scattering 25 0 0.2 1 10 70 Water vapour stnenopmoc rojam Carbon dioxide Oxygen and ozone Methane Nitrous oxide 0.2 1 10 70 wavelength (µm) Figure 4 gba temperatures and arbn dixide nentratins Correlations between global temperatures and carbon dioxide concentrations on Ear th. If the in concentration the size atmosphere of its change can contribution and test this global To is drilled than trapped to in in nd the greenhouse can expect greenhouse using to the atmosphere, in the rise gases carbon fall. to We dioxide because it past, ice can columns years, the can be so isotopes in ice has ice built deeper and water up down of air analysed concentration. from ratios 5 shows results for an Global the present. They were year obtained carbon – when the ice core plateau 232 by drilled the in Dome European C on Project the for same Data that the to of trend this the current of higher was Age periods periods striking concentration of Ice rapid longer very repeatedly Earth rises in of correlation and global carbon coincide with warmer. past that some in dioxide the 800,000 It is case in the ice we does is a temperature must increase always not know cores. hypothesis concentration dioxide years other with important correlation this carbon of found consistent effect. that but been are carbon remember least has type greenhouse causation, At prove from other greenhouse variation therefore gas. over have been period to rises and from Antarctic Ice a periods periods of pattern much is dioxide the concentration concentrations. an part by There dioxide due before this repeating followed temperatures research of molecules. 800,000 a cooling. between the Figure During been warming gradual The have has of has and Bubbles extracted deduced the of ice from surface. dioxide be The Antarctica. there the effect or concentrations Antarctic. near carbon temperatures hydrogen the of ice the dioxide the thousands older to the we temperatures the carbon temperatures over of of considerably. deduce been any hypothesis concentration changed of changes, Coring in falls in atmospheric carbon dioxide 4 . 4 c l i m a t e c H a n G e 300 vmpp/ 250 OC 2 200 erutarepmet( -380 warm )yxorp 9°C -410 %/Dδ ° -440 cold 800,000 600,000 400,000 200,000 0 age (years before present) Figure 5 Data from the European Project for Ice Coring in the Antarctic Dome C ice core d-bs qss: CO concentrations and global temperatures 2 Figure 6 shows atmospheric measurements The points ice at show concentrations polar The red line Mauna carbon carbon shows Loa 0.6 dioxide direct )C°( ylamona erutarepmet concentrations. Observatory. dioxide measured from trapped air in cores. 380 Annual average 0.4 Five year average 0.2 0 -0.2 emulov yb noillim rep strap Direct measurments 360 Ice core measurments -0.4 340 1880 1900 1920 1940 1960 1980 2000 320 Figure 7 300 2 Compare the trends in carbon 280 dioxide 260 concentration temperatures 1750 1800 1850 1900 1950 and between global 1880 and 2008. [2] 2000 3 Estimate the change in global average Figure 6 temperature Figure 7 shows temperatures Institute annual for a Space averages ve-year from 1961 1990. 1 Discuss carbon ice global the average NASA The red are is a) 1900 and 2000 [1] b) 1905 and 2005 [1] Goddard green curve values mean points a given temperature are rolling as 4 a) the Suggest the between measurements concentration consistent measurements at with Mauna years of b) from during trend Discuss indicate direct Loa. reasons temperatures overall whether are the The the dioxide cores of by Studies. and average. deviation and record compiled between a global for rising whether that global period of does average few an temperatures. [2] falls dioxide not temperatures. a with these carbon concentration [2] for falling inuence [2] 233 4 E c o l o g y greenhuse ases and imate patterns evaporation of water from the oceans and Global temperatures and climate therefore patterns are inuenced by frequent bursts surface of the Earth is warmer than and delivered concentrations of greenhouse gases. The is be with no greenhouse gases in Mean temperatures are estimated 32°C higher. greenhouse and we If the gases should concentration rises, expect more an heat increase of will in any be of global average The not all mean that global likely are gas directly inuence, orbit and proportional Other Milankovitch variation in increases in greenhouse and to also Global of cause higher more global frequent cycles sunspot gas temperatures climate. Higher very and more of rain other intense signicantly. temperatures cause In tropical to be faster more wind frequent and speeds. of any rise unlikely become to in be global evenly warmer. Scotland might The average spread. west become Not coast colder in activity. heat other temperatures Atlantic Current brought less if warm from the Gulf distribution of Stream rainfall to north-west would also be Europe. likely to the with some areas becoming more prone Even droughts and other areas to intense periods of will and ooding. Predictions about changes to temperatures intense inuence amount have concentrations average and with are and North rainfall tend be to factors to so, ocean hurricanes would change, Earth’s increase to average concentrations. including and powerful, areas The an to consequences water greenhouse The thunderstorms higher Ireland the temperatures during temperature of does protracted. likely the retained temperatures. This are to more be rain the storms atmosphere. of it addition, would periods weather patterns that a are very uncertain, but it is clear waves. aspects increase just profound few degrees changes to of the warming Earth’s would cause very climatepatterns. the d-bs qss: Phenology Phenologists of seasonal the are biologists activities opening of tree in who animals leaves and study and the the laying temperature timing plants, of such as 35 of birds. Data climate The date such as changes, in the these can including spring when provide global new was been chestnut recorded Figure year’s 8 trees in shows date of Germany the leaf (Aesculus warming. leaves open hippocastaneum) every difference opening year since between and the Identify the a) the opening between 1970 and indicate earlier than that b) mean 1951. 2 Use the mean. date The of leaf graph date between each year’s mean March the and for April these and two the in [1] at their March the in the relationship [1] graph to deduce the and between April and the temperatures date of in opening leaves on horse chestnut trees. [1] the whether there is evidence of global of the temperature The towards the end mean data century. [2] for Figure 8 The relationship 15 4 between temperature and 5 1 0 0 1 5 2 10 syad / gninepo fael C° / erutarepmet naem ni ecnereid 10 2 fo etad ni ecnereid 3 horse chestnut leaf opening in Germany since 1951 Key: temperature 3 15 4 1970 234 and lowest. was shows overall months. earliest temperatures data 20th temperature opened were warming during which: of b) difference in Negative opening also of following: of the year leaves March values records has each mean 2000. the on a) leaf from stations. evidence April horse obtained climate eggs 1 by German 1980 1990 2000 leaf opening 4 . 4 c l i m a t e c H a n G e Industriaizatin and imate hane There is a correlation between rising atmospheric concentrations of carbon dioxide since the star t of the industrial revolution two hundred years ago and average global temperatures. The graph 800,000 of uctuations. 180 parts rose as atmospheric years During per high shown 300 carbon gure 5 glaciations million as in by the volume. ppm. The dioxide concentrations indicates there concentration During rise that warm during over have dropped to interglacial recent times to the been past large as low periods as they concentrations Figure 9 During the industrial revolution nearing 400 ppm is therefore unprecedented in this period. renewable sources of power including Atmospheric carbon 280ppm until probably started initially very the In the late second and 18th but half is carbon strong century. the Much the of century. coal, oil increases and in for factors is to say the a when has More countries natural gas an global effect the when was an by burning fossil fuels ever dioxide between was rise 1950. in was some in the industrialized, more rapidly, concentration. atmospheric temperatures, so wind were replaced with power generated and unnatural starting globally increased rise since became carbon correlation as happened revolution 260 concentrations but exactly rise between industrialization and have were levels, atmospheric concentration other of industrial impact 20th This natural impossible evidence dioxide explained, main of consequent There is began. the combustion with it concentrations above century the of 18th rise slight, concentrations countries late to in dioxide temperatures but as are not already TOK directly since proportional the start of the to carbon industrial dioxide concentration. revolution the Nevertheless, correlation between wh ss pb rising atmospheric carbon dioxide concentration and average global v f sk? temperatures is very marked. In situations where the public is at risk, scientists are called upon to advise governments on the setting of policies Burnin fssi fues or restrictions to oset the risk. Because Recent increases in atmospheric carbon dioxide are scientic claims are based largely on largely due to increases in the combustion of fossilized inductive observation, absolute certainty is dicult to establish. The precautionary organic matter. principle argues that action to protect As the industrial revolution spread from the late 18th century the public must precede certainty of onwards, increasing quantities of coal were being mined and burned, risk when the potential consequences causing carbon dioxide emissions. Energy from combustion of the coal for humanity are catastrophic. Principle provided a source of heat and power. During the 19th century the 15 of the 1992 Rio Declaration on the combustion of oil and natural gas became increasingly widespread in Environment and Development stated addition to coal. the principle in this way: Increases 1950s in in the onwards atmospheric that the burning and carbon burning factor in the levels than this rise of fossil dioxide. fuels It of fossil of atmospheric experienced fuels coincides on were with seems has been carbon Earth the for most hard a to major dioxide more rapid period than of from the steepest doubt the Where there are threats of serious or rises irreversible damage, lack of full scientic conclusion contributory concentrations 800,000 certainty shall not be used as a reason for postponing cost-eective measures to higher to prevent environmental degradation. years. 235 4 E c o l o g y d-bs qss: Comparing CO emissions 2 The bar chart in gure 10 shows the cumulative CO were higher Arab Emirates, in the year 2000: Qatar, United 2 emissions and ve from fossil individual 2000. It also forest clearance fuels of the countries shows the total European between CO Union 1950 emissions reasons and for Kuwait the and Bahrain. Suggest difference. [3] including 2 3 Although cumulative CO emissions from 2 and other land use changes. combustion 1 Discuss reasons for higher cumulative CO Brazil of fossil between fuels 1950 and in Indonesia 2000 were and relatively 2 emissions from combustion of fossil fuels in low, total CO emissions were signicantly 2 the 2 United States than Although cumulative 1950 2000 and were in Brazil. [3] emissions higher in between the higher. 4 United Suggest Australia reasons ranked emissions of for seventh CO in this. in 2000, [3] the but world fourth for when 2 States four than any countries other in country, which there emissions were per all capita greenhouse reason for the gases are included. Suggest a difference. [1] 30% Figure 10 CO from fossil fuels CO from fossil fuels & land-use change 2 25% 2 latot dlrow fo tnecrep 20% 15% 10% 5% 0% U.S. EU-25 Russia China Indonesia Brazil Assessin aims and unter-aims Assessing claims: assessment of the claims that human activities are not causing climate change. Climate almost change any internet views, has other will area quickly expressed Michael scientists as use murder novel State of more vociferously. eco-terrorists of Fear. A search The climate who promote What debated diametrically portrayed to hotly science. reveal very Crichton mass been were their reasons of than ● the and opposed the author be prepared could in to for such erce opposition to climate climate is tipping and for what defend reason their do ndings climate so questions many factors ● Scientists are that are worth could trained to having be The and to base their an are inuence: about if are expected to admit for 236 evidence and is this can weaker on changes about increases patterns occur. in There This can where makes difcult. could be of changes very severe in global for climate humans other is a species give it need for so many immediate feel that remain Companies and oil natural in make gas action climate huge and it even change prots is in from their their for fossil fuel combustion to continue evidence. when than climate more coal, there grow. the It would not be reports to be written impression actually surprising if they paid are risks that in science. for uncertainties even uncertainties to They points complex change There cautious ideas further concentrations. consequences interests claims of very predictions vigorously? discussing. be are make there there These to change and scientists gas massive prediction patterns science patterns difcult consequences sudden his ● be it greenhouse change work Global is. of climate change. that minimized the 4 . 4 c l i m a t e c H a n G e oppsitin t the imate hane siene Evaluating claims that human activities are not causing climate change. Many claims climate that change television and human have on activities been the made internet. are in not One Global causing newspapers, example of this warming increases on is: dioxide each by evidence “Global warming stopped in 1998, dioxide concentrations have rise, so human carbon dioxide be causing global claim Earth are ignores greenhouse and cycles variations factors, also gas in from 1998 than that many currents year was of fact by to an temperatures factors, they year. some cause Because activity year and have have been be base is such years would on just signicant of warm recent otherwise not Volcanic can unusually them fuels dioxide not with emitting and there causes equal carbon is strong warming, is not supported by the so evidence. that human change activities will are continue not and causing these claims need warming.” concentrations. ocean because cooler the inuenced fossil carbon but are emissions to This Humans continued climate cannot burning that claim Claims to continuing yet the carbon is year. evaluated. our now evaluations gases Not all and we gases and sources need websites reliable been. always considerable greenhouse these As the careful and to the climate are of effects of patterns. distinguish that There trustworthy assessments others should emissions about internet we evidence. about changing objective evidence reliable humans, about be science, evidence by on to with on in between based show on bias. d-bs qss: Uncer tainty in temperature rise projections Figure for 11 shows average computer-generated global temperatures, forecasts based on 6 eight AIB 5 different scenarios for the changes in the AIT emissions AIFI of greenhouse gases. The light green band includes 4 A2 the full range of forecasts from research centres B1 3 around the world, and the dark green band shows B2 IS92a the range forecasts of for most of arctic the forecasts. temperatures, Figure based 12 on shows two 2 of 1 the emissions 1 Identify scenarios. 0 the emissions code for the least optimistic scenario. 1 [1] 9 9 0 2 0 0 0 0 1 0 2 2 0 2 0 2 0 3 0 2 0 4 0 2 0 5 0 2 0 6 0 2 0 7 0 2 0 8 0 2 0 9 0 2 1 0 0 Figure 11 Forecast global average temperatures 2 State for the minimum average global and maximum temperature forecasts change. [2] 7 Discuss whether forecasts 3 Calculate and B2 the difference forecasts temperature of between global the Compare average 8 rise. the [2] forecasts for Discuss average with those whether environmental or in temperature inaction. [4] livelihood it is risks risks possible with or to balance socio-economic whether priorities need arctic to temperatures uncertainty action A2 and 4 the justies for be established. [4] global temperatures. [2] 7 6 A2 5 Suggest uncertainties, apart from B2 5 greenhouse gas emissions, which 4 affect forecasts for average global 3 temperatures over the next 100 years. [2] 2 6 Discuss in how forecasts much based more on condent data from a we can number be of 1 0 2000 different research centres, rather than one. 2020 2040 2060 2080 2100 [3] Figure 12 Forecast arctic temperature 237 4 E c o l o g y cra reefs and arbn dixide Threats to coral reefs from increasing concentrations of dissolved carbon dioxide. In addition emissions on the its pH century surface to when to 500 there 8.104 in and warming, make be billion tonnes of calcium since the dissolved of the been the little mid-1990s current in Earth’s in the of the is In 2012 global This seemingly small acidication. are that it severe if Ocean the change dioxide atmosphere continues to There is corals and animals such deposit calcium carbonate need The is to absorb will low, because interrelated reacts with dissociates ions. they carbon concentration are even water into ions, very as a react result reducing in already island coral of agreed monitoring evidence reefs. Ischia releasing thousands In their corals, their place and seawater than to ocean 20 set up a acidication. for concerns Volcanic vents about near in the carbon Gulf dioxide of Naples into the have water of the years, area reducing of acidied the pH water of the there sea skeletons other reefs continues from algae. around to be or other calcium organisms invasive coral urchins could world emitted from that carbonate. ourish This the animals are if such be as the In sea their grasses future carbon burning make of dioxide fossil fuels. carbonate of some Carbon acid, dioxide which hydrogen with that soluble. the carbonic and corals seawater. ions reactions. form and more of skeletons from makes hydrogen ions their ions lower to in not Seattle for existing threatened. rise. carbonate dioxide chemical Hydrogen carbonate of from so are to existing become concentration reef-building carbonate concentration Dissolved as in dissolve, corals ceases ions, a no Marine met scheme seawater. the to oceanographers seawater approximately represents acidication carbon tends reef-building if carbonate had for more of industrialization. been 30% of Also, solution carbonate countries 18th skeletons. saturated skeletons oceans. oceans late showed levels carbon start a the 8.069. their effects 8.179 had the global having have been to are humans layers have Measurements fallen by revolution of estimated dioxide Over released industrial contribution carbon oceans. dioxide The to of carbonate dissolved concentration. + CO + H 2 O H CO 2 + CO → H + HCO 3 HCO 3 If → 3 2 + H → 2 carbonate difcult for ion 3 concentrations reef-building corals drop to it is absorb more them to Figure 1 3 Skeleton of calcium carbonate from a reef-building coral TOK av Draw a graph of oceanic wh h p ps f fg bs? pH from the 18th century The costs of scientic research is often met by grant agencies. Scientists submit onwards, using the gures research proposals to agencies, the application is reviewed and if successful, given in the text above, and the research can proceed. Questions arise when the grant agency has a stake in extrapolate the curve to the study's outcome. Fur ther, grant applications might ask scientists to project obtain an estimate of when outcomes or suggest applications of the research before it has even begun. The the pH might drop below 7. sponsor may fund several dierent research groups, suppressing results that run counter to their interests and publishing those that suppor t their industry. For example, a 2006 review of studies examining the health eects of cell phone use revealed that studies funded by the telecommunications industry were statistically least likely to repor t a signicant eect. Pharmaceutical research, nutrition research and climate change research are all areas where claims of funding bias have been prominent in the media. 238 Q u e S t i o n S Questins 4 The total solar 5 5 × energy 2 l0 kJ received m is yr 5 . The net × energy is grassland production 2 is 10 kJ 6 passed × m yr on to and 2 10 kJ of the 1 2 production a 1 2 grassland by xednI thguorD 1 gross 1 m yr primary its . The total consumers yr passed a) 1 m on . Only to Calculate the the 10 per cent secondary energy lost of this energy consumers. by plant respiration. b) Construct [2] a pyramid of energy for this grassland. [3] mk/ytilat rom eert fo aerA is kJ 2 1 0 –1 –2 –3 Cool/moist is 2 2 60 3 2000 1500 1000 500 0 1930 1940 1950 1960 1970 1980 1990 2000 Figure 15 Tree mor tality and drought index 2 Figure 14 shows temperate the forest. energy The ow energy through ow 2 square metre per year (kJ is a) a shown index per 1 m yr Identify the two remained periods high when for the three or drought more years. ). lost b) (i) [2] Compare the beetle outbreaks in the 5,223,120 1970s (ii) and Suggest 1990s. reasons [2] for the differences sunlight between respiration the outbreaks. [2] energy 24,024 5,266,800 c) Predict rates of destruction of spruce 1 72 green consumers trees in the future, your answer. with reasons for plants [4] storage 14,448 decomposers (e.g. wood) 5,036 4 Figure 16 shows monthly average carbon Figure 14 dioxide a) The chart sunlight shows energy that in 99.17 the per cent temperate of the forest Zealand concentrations and Alert, for Baring Head, New Canada. is 390 or Predict lesser would b) Only of be a with a reason percentage lost small plants in in a greater energy of [2] the net temperate the forest reasons passes for to this. [2] OC Explain production 385 Key 380 Aler t station, 375 Canada 370 Baring Head, 365 New Zealand 360 2 herbivores. whether sunlight desert. part the of mpp/noitartnecnoc lost. 355 350 345 340 3 Warmer temperatures favour some 335 species 330 of pest, for example the spruce beetle. Since 76 78 80 82 84 86 88 90 92 94 96 98 00 02 04 the rst major outbreak approximately Alaska and 400,000 the in 1992, hectares Canadian it of Yukon. has trees The year killed in Figure 16 beetle a) normally cycle, needs but it two has years recently to complete been able to its do Suggest why areas Mauna it year. drought and The graphs index, a gure combination precipitation, destroyed in and the 15 of area show Loa, have Baring chosen Head such and the locations for monitoring Alert stations. [1] the temperatures of as in as one scientists life spruce b) Compare the trends illustrated in both graphs. trees [2] annually. c) Explain why patterns. the graphs show different [3] 239 4 e c o l o G y 5 Figure 17 shows the concentration of CO in the tundra above taiga 2 root ground atmosphere, In a forest, measured in parts concentrations of per CO million change (ppm). over above the 2 ground course top of of the the day forest and is change referred to with as height. the The root canopy. soil soil m/thgieh 310 ppm 30 320 Top forest canopy grasslands deciduous forest 20 above above ground ground 305 330 10 root root 340 soil soil 350 350 0 0 6 12 18 24 time of day / hours savannah equatorial forest Figure 1 7 a) (i) State the highest concentration of above above ground ground CO 2 reached in the canopy. [1] soil (ii) Determine found in the the range of concentration canopy. soil root root [2] Figure 18 The distribution of nitrogen in the three organic b) (i) State the time of day (or night) matters compar tments for each of six major biomes when the highest levels of CO are 2 detected. [1] a) Deduce what the compartment (ii) The highest levels of CO are “above consists of ground” in an ecosystem. [1] detected 2 just above reasons c) Give an the why ground. this example of is an Deduce the two b) case. hour [2] when CO State which ground” c) Explain biome has the largest “above compartment. why it is difcult [1] to grow crops in 2 concentrations the full range are of reasonably uniform over heights. an [1] cleared d) State by 6 Within an ecosystem, nitrogen can be area where of the one above Figure in the of three ground, 18 organic in shows three roots the organic matter and in matter the soil. of of six major has been of the and [2] process detritus carried feeders out that stored CO e) nitrogen compartments into the atmosphere. [1] 2 Suggest tundra why most ecosystem of is the in nitrogen the in a soil. [1] for f) each name compartments: distribution forest vegetation. decomposers releases in its equatorial Explain why warming due to climate biomes. change might cause a release of CO from 2 tundra 240 soil. [2] 5 Ev O Lu t I O n a n d B I O d I v E r s I t Y Iocio There that is the overwhelming diversity continues ancestry to of of evolve groups evidence life by of has for the evolved, natural species selection. can be theory and comparing Species The deduced are their base named internationally or and agreed amino acid classied sequences. using an system. by 5.1 Edee e ueig applicio ➔ Evolution ours when heritale harateristis ➔ Comparison of the pentadatyl lim of of a speies hange. mammals, irds, amphiians and reptiles ➔ The fossil reord provides evidene for with dierent methods of loomotion. evolution. ➔ ➔ Seletive reeding of domestiated Development of melanisti insets in polluted areas. animals shows that ar tiial seletion an ause evolution. ➔ radiation explains similarities in struture when there are dierenes in funtion. ➔ ➔ ne of ciece Evolution of homologous strutures y adaptive ➔ Looking for patterns, trends and disrepanies: there are ommon features in the one Populations of a speies an gradually diverge struture of ver terate lims despite their into separate speies y evolution. varied use. Continuous variation aross the geographial range of related populations mathes the onept of gradual divergene. 241 5 E v o l u t i o n a n d b i o d i v E r s i t y Eolio i mmy Evolution ours when heritale harateristis of a speies hange. There time. is strong scientic should the evidence Biologists this for be drawn of from of between an characteristics process understanding lifetime passed call the parent to natural acquired individual of evolution. and offspring. It species lies world. at An heart important characteristics heritable changing the that only a distinction develop characteristics Evolution over of that concerns during are heritable characteristics. The ▲ mechanism of evolution is now well understood – it is natural Figure 1 Fossils of dinosaurs show there were selection. Despite the selection, there still robustness of evidence for evolution by natural animals on Ear th in the past that had dierent is widespread disbelief among some religious characteristics from those alive today groups. evolve There than evolution. are to It stronger the is logic objections of therefore the to the mechanism important to concept that look at that species inevitably the can causes evidence for evolution. Eiece fom foil The fossil reord provides evidene for evolution. In the or strata eras rst were various 20th ages of ● layers the The ago and would and It of has of that was out the a fossils us in in which and fossils strong is of dating them. which the the fossils. has branch evidence in In revealed There the layers geological found sequence radioisotope fossils, given sequence worked there the into Many that been of the the a science evolution on back very ts land, and worms bony matches with later sh mya, 110 in appear evolve, 340 appearing sequences with over 60 similar of the bacteria and land appeared reptiles sequence and vertebrates about 320 420 mya, in simple later million birds which algae 250 still. years mya mya. with before plants fossils their members rhinoceroses now totally ex tinct and mammals also to the ecology animal, suitable of plants for the on insect groups, land with before pollination before pollinators. zebras, hundreds of millions of years but the group is fungi amphibians fossils organisms and fossils vertebrates, sequence insect which expected rst, placental The in be the (mya), animals 242 – methods research the was obvious different strata of sequence plant Figure 2 Many trilobite species evolved over were century, became palaeontology. Among ▲ It reliable rock appearing ● 19th deposited occurred. they ● the were named. amount called of rock century, huge has half of and a likely known, ancestors. of the genus tapirs. An extensive million to are years, links rhinoceros. which For Equus, link example, are most sequence them to together of existing horses, closely fossils, Hyracotherium, asses related to extending an animal 5 . 1 E v i D E n c E f o r E v o l u t i o n Daa-baed qe: Missing links An objection been for gaps in example to fossil the a evidence record, link called between for evolution missing reptiles has The links, and discovery particularly fossils that for ll in these gaps is biologists. birds. 1 Calculate from (a) of exciting its the length head to the of tip Dilong of its paradoxus, tail. [2] (b) (g) (c) 2 (d) Deduce three paradoxus Earth similarities and reptiles between that live Dilong on today. [3] (i) (h) 3 Suggest a function for the protofeathers of 100 mm Dilong paradoxus. [1] (j) (e) (f) 4 Suggest would ▲ Figure 3 Drawings of fossils recently found in Western two have features had capable of Explain why to which evolve Dilong to paradoxus become ight. [2] China. They show Dilong paradoxus, a 130-million-year-old 5 it is not possible to be certain tyrannosauroid dinosaur with protofeathers. a–d: bones of whether the protofeathers of Dilong paradoxus skull; e–f: teeth; g: tail ver tebrae with protofeathers; h–j: are homologous with the feathers of birds. [2] limb bones Eiece fom elecie beeig Seletive reeding of domestiated animals shows that ar tiial seletion an ause evolution. Humans have thousands the wild of species Consider the junglefowl of Western other It is clear The that that very have to cause in Asia, by of articial but naturally, with it or to does that breeds have for process selection is is prove Blue and that by over It the in the that of has is been selection. time changes that selection species evolution and individuals considerable of aurochs their change periods shows the cattle breeds. articial evolution for and existed the breeding called time. mechanism that huge. the sheep, between for with often and cattle of always is shown animals geological not not are hens breeds variation species compared differences Belgian selecting animal are egg-laying explanation This the the different much domesticated comparison particular livestock between repeatedly in of modern many credible uses. used resemble, or also livestock, human evolution, occurred most are only and breeds between domesticated The occurred short, they There simply suited bred modern Southern Asia. effectiveness that ▲ of form. achieved If differences domesticated current most deliberately years. has natural are can actually selection. Figure 4 Over the last 15,000 years many breeds of dog have been developed by ar ticial selection from domesticated wolves 243 5 E v o l u t i o n a n d b i o d i v E r s i t y Daa-baed qe: Domestication of corn Homology A eolio wild grass probably is grown called the as teosinte ancestor a crop, it of that grows cultivated gives yields in corn, of Central Zea about America mays. 150 kg When per was teosinte hectare. This Looking for patterns, trends compares and disrepanies: there are at the Corn with start was of a world the 21st average century. domesticated at yield Table least 7,000 of 1 corn gives years of 4,100 the kg lengths per of hectare some cobs. ago. ommon features in the one struture of ver terate lims 1 Calculate and the Silver percentage difference in length between teosinte Queen. [2] despite their varied use. 2 Vertebrate limbs are used Calculate and many different walking, running, swimming, These ways, varied uses such and world percentage average yields difference of in yield between teosinte corn. [2] as jumping, grasping the in ying, 3 Suggest factors 4 Explain why apart from cob length, selected for by farmers. [3] digging. require joints improvement slows down over generations of that selection. articulate velocities different be in different of movement amounts reasonable have but very there features found in Patterns are all the As a common vertebrate piece of Teosinte – wild relative of orn 14 Early primitive orn from Colomia 45 Peruvian anient orn from 500 bc 65 Imriado – primitive orn from Colomia 90 common only far legh b (mm) to that are Silver Queen – modern sweetorn limbs. require The so c aey ad g would structure, structure this also It them bone fact evolution ancestor. expect [3] different and force. vertebrate like explanation is in bone explanation. case to of different of ways, T able 1 ▲ Figure 5 Corn cobs reasonable proposed from ▲ 170 a in this common consequence, bone limbs structure has evidence for become of a classic evolution. Eiece fom homologo ce Evolution of homologous strutures y adaptive radiation explains similarities in struture when there are dierenes in funtion. Darwin pointed structure dugong those between and 244 a very in the When or tail we different. The Origin organisms whale, between structures. are out ns study An are between of of Species supercial, a whale whales them that and closely evolutionary some for and a shes we similarities example sh. are nd interpretation between Similarities known that is these that in as a like analogous structures they have had 5 . 1 different same or origins a Homologous may look which of what could in the digit that be limb, same are that many the without Darwin called function. of These of and have a an teeth the of or found pelvis easily that and – of so are a the structures function, gave the bat that same appearing they pentadactyl because asked the surface is that but example and “include structures. have or they but they ve- perform thigh bone the are are found gradually that as reveal to serve of the in that no them despite in prove not structures examples appendix not do difcult the whales, evolution do and structures and baleen course They ancestry organs by E v o l u t i o n radiation. reduced being are and the interesting embryo explained and had evolution, and on different vestigial in He explanation common organs” They they perform f o r evolution. different type”. that adaptive of a despite Particularly snakes, are nd had they porpoise homologous called small function to become called this. of horse, ancestor have is of perform “unity than evolved now a mole, mechanism some structures longer This and because convergent converse positions”, evolution. are toothless, whales from they similar called evolutionary “rudimentary They beginnings being The is called examples explain the curious have about are different human, origin, organisms This relative functions. anything the a more and become Darwin of different. same different There what the completely had structures forelimbs bones, have function. supercially have the and similar E v i D E n c E are adults body wall humans. structures that no lost. Pecyl limb Comparison of the pentadatyl lim of mammals, irds, amphiians and reptiles with dierent methods of loomotion. The pentadactyl limb consists of these structures: classes birds Be e femb that and have a mp hib ia ns, Ea ch of the m r e pti le s , h as Hdmb pentadactyl single one in the l i mb s : mamma l s . humerus limbs : femur ● crocodiles walk or crawl on land and use their proximal par t webbed two ones in the radius and ulna hind limbs for swimming tiia and ula ● penguins use their hind limbs for walking and distal par t their group of wrist/ arpals forelimbs ● ankle ones echidnas also series of ones in metaarpals and metatarsals eah of ve digits phalanges and phalanges ● use frogs use pattern present in mammals, of all bones or a modication amphibians, whatever the reptiles, function of birds of it use photos in one example gur e of ea ch 6 s how of ippers for swimming all the the four four four for limbs forelimbs limbs for for walking and digging for walking the relative and their jumping. is Differences can thicknesses of be seen in lengths and and their the bones. Some metacarpals and limbs. phalanges The all their hindlimbs The as tarsals s ke le t o ns of the have penguin’s been lost during the evolution of forelimb. v ert ebr at e s 245 5 E v o l u t i o n a n d b i o d i v E r s i t y Ay Peaday mb mamma mole horse ▲ Figure 6 porpoise speciio Populations of a speies an gradually diverge into separate speies y evolution. If two not populations interbreed of and a species natural become selection separated then acts so that they differently on do the two bat populations, human the two will populations recognizably ▲ they evolve will different. If in different gradually the ways. diverge. populations The After a characteristics time subsequently they will merge of be and have Figure 7 Pentadactyl limbs (not to scale) the chance clear that of interbreeding, they have evolved but do into not actually separate interbreed, species. This it would process is be called Choose a olour ode for speciation. the types of one in a pentadatyl lim and olour Speciation the diagrams in gure 7 to by often show the type of eah one. species on How is eah lim used? certain geographical What features of the ones are in eah lim make them well of adapted to the use? different migrating an the occurs an islands. example of archipelago. species, divergence. 246 to after island. An population explains endemic area. this. On a This The One six formed species lava species smaller by is of to species the is found of is all a island the and by range in a Islands main closely its endemic only Galápagos on there extends numbers that the present islands migration a large one lizards is of the islands related but subsequent 5 . 1 E v i D E n c E f o r E v o l u t i o n Eiece fom pe of iio Pinta Genovesa Continuous variation aross the geographial Marchena range of related populations mathes the Santiago onept of gradual divergene. If populations gradually diverge over time to become separate Santa Cruz Fernandina species, to nd then at any examples of one all moment stages of we would expect divergence. This is to be San Cristóbal able indeed Santa Fe what we nd in nature, as Charles Darwin describes in Isabela Chapter II of The Origin of Species. He wrote: a Español Santa Maria Many years ago, when comparing, and seeing others compare, key the birds both from one with mainland, is the the I separate another , was distinction islands and much with struck between of those how species the Galápagos from entirely and the Archipelago, T.albemarlensis T.delanonis T.habelii T.duncanensis T.pacicus T.bivittatus T.grayii American vague and arbitrary varieties. ▲ Figure 8 Distribution of lava lizards in the Galápagos Islands Darwin gave different, species. but One ptarmigan species Because there is being split The to his two for can sudden separate into They therefore species are species and as have gradually be origin of variation were new the clearly it been classied provides of separate This is a organisms. time one populations and species to together or arbitrary. distinct their as willow lagopus. of populations as the living periods lump rather and Lagopus classify long between by separate Britain populations to created species of and over two across recognizably species name remains Instead of are grouse decision constant unchanging. are sometimes being species in they diverge the species that red who from species, that that the varieties switch should the is biologists range belief populations extent separate continuous the the Norway. species no of examples sometimes problem them either and not of of and common examples does types geographic evidence for of not range the match organism or TOK that evolution of t wha ex e a mpe mde be ed e hee? evolution. The usefulness of a theory is the degree to whih it explains Iil melim phenomenon and the degree to whih it allows preditions to e Development of melanisti insets in polluted areas. made. One way to test the theory Dark varieties of typically light-coloured insects are called melanistic. of evolution y natural seletion is The most famous example of an insect with a melanistic variety through the use of omputer models. is Biston betularia, the peppered moth. It has been widely used as The Blind Watchmaker omputer an example of natural selection, as the melanistic variety became model is used to demonstrate how commoner in polluted industrial areas where it is better camouaged omplexity an evolve from simple than the pale peppered variety. A simple explanation of industrial forms through ar tiial seletion. The melanism is this: Weasel omputer model is used to ● Adult and Biston betularia moths y at night to try to nd a demonstrate how ar tiial seletion mate an inrease the pae of evolution reproduce. over random events. What features ● During ● Birds the day they roost on the branches of trees. would a omputer model have to they and nd other them. animals that hunt in daylight predate moths if inlude for it to simulate evolution y natural seletion realistially? 247 5 E v o l u t i o n a n d b i o d i v E r s i t y ● In unpolluted lichens ● and Sulphur dioxide blackens ● ● tree moths polluted areas. In polluted ▲ kills are well covered in pale-coloured camouaged lichens. are well the camouaged melanic variety over a Soot from against variety of relatively ▲ Figure 9 Museum specimen of the against coal them. burning dark Biston short tree branches betularia time, but in replaced not in non- Figure 10 The ladybug Adalia bipunctata peppered form of Biston betularia has a melanic form which has become mounted on tree bark with lichens common in polluted areas. A melanic male from an unpolluted area is mating with a normal female here have evolution by ndings been into criticized and selection ever Michael book in pale been and used careful in to a The predation cast classic of example this, design of doubt evaluation Biston Naturalist His nding melanism factors attacked. and as because the of some moths over of research early has whether been natural occurs. a New 2002). though of has gives causing Perhaps repeatedly melanism the melanism selection. actually of HarperCollins pollution industrial camouage this Majerus development strong, used natural have experiments rates are areas. Biologists his branches moths pollution areas peppered polluted tree branches. Melanic the in areas peppered other melanic in series is that Biston than of betularia evidence and (Moths, the other camouage the of Michael evidence betularia about species and can for other also moth Majerus, industrial species of inuence moth is survival varieties. Daa-baed qe: Predation rates in Biston betularia One into of the moths trunks roost. were and The suitable of placed that 1980s the moths is but the original betularia exposed not were some tested were in this moths on the of Biston positions persisted 248 criticisms predation able even to so effect placed. that positions normally websites. the experiments was move the on where to Experiments of the position Peppered and tree they have done in in which melanic (fty in and two the in the a of oak woods, polluted Midlands. in area The percentage a trunk. Forest of of Biston positions below tree New each) exposed millimetres at more criticisms forms placed the joint This one near procedure in an were trunks a major was in eaten gure and 11 in 50 branch area and out of another the show moths and carried unpolluted England Stoke-on-Trent plots moths tree between southern box betularia on the surviving. 5 . 2 1 a) Deduce, with a reason from the n A t u r A l data, peppered whether the moths were more s E l E c t i o n likely to Stoke on Trent and New Forest be New Forest/melanic/BJ eaten if trunk or branch they were below and the placed the on the junction of a 60 main trunk. New Forest/melanic/ET 38 62 [2] New Forest/peppered/BJ b) Suggest a a) Compare reason for the difference. 74 and contrast the 68 in b) of the peppered New Explain rate and melanic the the Stoke/melanic/ET [3] difference two in Stoke/peppered/BJ survival varieties in Forest. Distinguish between New woodlands rates Forest of peppered the and Stoke-on-Trent Pollution in relative melanic survival moths. due near to 50 50 industry has Stoke-on-Trent 0% 42 20% 58 40% 60% 80% 100% key not eaten [2] eaten BJ = branch junction decreased ▲ greatly 40 and ET = exposed trunk 4 60 [3] melanic 3 28 the Stoke/peppered/ET New 72 moths Forest. between 32 survival Stoke/melanic/BJ rates 26 [1] New Forest/peppered/ET 2 40 exposed since the Figure 11 1980s. Source: Howlett and Majerus (1987) The Understanding of Predict the consequences of this change for industrial melanism in the peppered moth (Biston betularia) Biston betularia. [4] Biol. J.Linn.Soc. 30, 31–44 5.2 naa ee ueig applicio ➔ Natural seletion an only our if there is ➔ Changes in eaks of nhes on Daphne Major. ➔ Evolution of antiioti resistane in ateria. variation amongst memers of the same speies. ➔ Mutation, meiosis and sexual reprodution ause variation etween individuals in a speies. ➔ Adaptations are harateristis that make an ne of ciece individual suited to its environment and way of life. ➔ ➔ Speies tend to produe more ospring than the environment an suppor t. ➔ Individuals that are etter adapted tend to survive Use theories to explain natural phenomena: the theory of evolution y natural seletion an explain the development of antiioti resistane in ateria. and produe more ospring while the less well adapted tend to die or produe fewer ospring. ➔ Individuals that reprodue pass on harateristis to their ospring. ➔ Natural seletion inreases the frequeny of harateristis that make individuals etter adapted and dereases the frequeny of other harateristis leading to hanges within the speies. 249 5 E v o l u t i o n a n d b i o d i v E r s i t y viio Natural seletion an only our if there is variation amongst memers of the same speies. Charles causes his voyage the to Figure 1 Populations of bluebells (Hyacinthoides of of theory and 20 to in the understanding years, world on selection for 1859. presents 30 his many evidence Species, previous over natural accumulate his developed around theory Origin ▲ Darwin evolution it. In HMS in the book Beagle. the He 1830s, published of evidence of returning late Darwin this the after nearly for it England probably but his 500 that mechanism to he then great developed worked work, pages, had that from he found The explains over the years. non-scripta) mostly have blue owers but One of the observations on which Darwin based the theory of evolution white-owered plants sometimes occur by natural respects. blood may it is all selection Variation group not be there. and so in variation. human many other immediately Natural individuals some is in a individuals populations populations features. obvious selection were favoured is obvious With but depends population being Typical other careful on than – in many height, species the observation variation identical, more vary within there skin colour, variation shows that populations would be no – way if of others. soce of iio Mutation, meiosis and sexual reprodution ause variation etween individuals in a speies. The 1 causes of Mutation by 2 gene Meiosis an Sexual The a ▲ the in new is usually combination of in a over reproduction of are diploid to carry and the involves come alleles from New alleles Every different fusion of different two understood: pool by cell alleles of a are breaking produced male and individuals. by the the meiosis alleles, of bivalents. female so This up of orientation parents, produced population. combination independent the from well gene of cell. a the now variation. enlarges combinations likely crossing gametes source which combination of populations original individual because 3 is mutation, produces existing in variation gametes. offspring allows has mutations Figure 2 Dandelions (Taraxacum ocinale) that occurred in different individuals to be brought together. appear to be reproducing sexually when they disperse their seed but the embryos in the In seeds have been produced asexually so are of genetically identical species that variation not is generate survival do not carry mutation. enough during times It out is variation of sexual generally to be reproduction assumed able environmental to that evolve the only such source species quickly will enough for change. apio Adaptations are harateristis that make an individual suited to its environment and way of life. One of the structure correlated 250 recurring and themes function. with its diet For and in biology example, method is the of the close structure feeding. The relationship of a bird’s thick coat between beak of a is musk 5 . 2 ox is obviously habitats. The infrequent correlated water rainfall with storage in the tissue desert low in temperatures the habitats. In stem of a biology in its cactus n A t u r A l s E l E c t i o n northerly is related characteristics Ay to such as Adapa bd’ beak these that make an individual suited to its environment or way of life The four photographs of are called adaptations. irds show the eaks of a The term and thus this process. natural suited one adaptation that species its as acquired not to that It the important direct They Characteristics acquired is characteristics evolutionary with environment. individual. known evolve. According selection, to implies do that characteristics characteristics cannot do theory of develop a to over imply making during during widely an woodpeker. To what diet by individual lifetime lifetime accepted heron, maaw, hawk and in develop the a time purpose adaptations develop and be not purpose not develop and method of feeding is eah adapted? of are theory is that inherited. Oepocio of opig Speies tend to produe more ospring than the environment an suppor t. Living An organisms example southern every other so in of three their species nucifera in which on do have a a bacteria, there It can number with a and However pair faster could the be as needs a rate. breeding as 7 For 20 raises for of 60 the in within living out a a be a the at as least 70 two years offspring. coconut per in the giant palm, year. fungus puffball be variation there is an produced can that for population. for for will will the Darwin tend to existence There resources individual more than support. this in overall organisms struggle competition every may is edgling (7,000,000,000,000). environment pointed the huge to of long twenty rate, offspring to as called spores breeding lead rate one coconuts all body Despite trend It example, rate trillion produce. breeding raise and fruiting they cooperation live theoretically huge many slow the can between fastest produces offspring leadbeateri . they breeding produces of relatively Bucorvus average this. usually gigantea. the hornbill, lifetime Cocos from to in species years Most Calvatia a ground adults Apart vary will and obtain be not enough ▲ to allow them to survive Figure 3 and reproduce. ▲ Figure 4 The breeding rate of pairs of southern ground hornbills, Bucorvus leadbeateri, is as low as 0.3 young per year 251 5 E v o l u t i o n a n d b i o d i v E r s i t y dieeil il epocio Ay Individuals that are etter adapted tend to survive and sma aa ee ● Make ten or more produe more ospring while the less well adapted tend to die or produe fewer ospring. ar tiial sh using Chance plays a part in deciding which individuals survive and reproduce modelling lay, or some and which do not, but the characteristics of an individual also have an other malleale material. inuence. In the struggle for existence the less well-adapted individuals Drop eah of them into tend to die or fail to reproduce and the best adapted tend to survive and a measuring ylinder of produce many offspring. This is natural selection. water and time how long An example that is often quoted is that of the giraffe. It can graze on eah takes to reah the grass and herbs but is more adapted to browse on tree leaves. In the wet ottom. season ● its food is abundant but in the dry season there can be periods Disard the half of of food shortage when the only remaining tree leaves are on high the models that were branches. Giraffes with longer necks are better adapted to reaching slowest. Pair up the these leaves and surviving periods of food shortage than those with fastest models and shorter necks. make intermediate shapes, to represent their ospring. Random Iheice new shapes an also e introdued to simulate mutation. ● Test the new generation and repeat the elimination of the slowest and the reeding of the fastest. Does one shape gradually emerge? Desrie its features. Individuals that reprodue pass on harateristis to their ospring. Much of the offspring of their – is blackcap some Spain Not all of the broken of an tusk person atricapilla are signicant in and not the of children of skin on are to not skin evolution with colour a to Those broken from to to skin colour north behaviour sites differences in in can the their Germany genes, to Britain. acquired inherited. through Acquired of Due offspring. in overwintering southwestwards usually on dark Variation northwestwards calves inherited. to passed the light-skinned colour. example. others be inherit migration an have darker not and light can children migrate passed individual does is a is species winter develops skin example inherit individuals Maasai direction this features lifetime darker The Sylvia birds for for parents heritable. between heritable. parents European be variation it An tusks for exposure characteristics during elephant example. to are the with If sunlight, therefore a a the not species. Pogeie chge Natural seletion inreases the frequeny of harateristis that make individuals etter adapted and dereases the frequeny of other harateristis leading to hanges within the speies. Because pass on adapted leads 252 to better-adapted characteristics have an lower increase individuals to their survival in the survive, offspring. rates and proportion less of they can Individuals reproduce that reproductive individuals in a are and less success. well This population with 5 . 2 characteristics that characteristics of natural make the them well population adapted. gradually Over change the – n A t u r A l generations, this is s E l E c t i o n the evolution by Ay selection. The impulse to reprodue and pass Major and evolutionary many them colours air. this generations, during signicant in Two our that has examples of are we but there been beaks antibiotic of to occur not are are in many resistance on in to the long be in time able examples The industrial described nches over expect observed. observed evolution to likely should have been of changes development so lifetime, changes moths book: changes to of the of with next Galapagos but dark wing Islands pattern have evolved in lions and with two or more males so their litters of and infantiide. How ould this ehaviour other speies? Female heetahs mate polluted sections on harateristis an e very strong. It an ause adult males to arry out observe smaller evolution areas periods the have multiple paternity. How does this protet the young against infantiide? bacteria. Daa-baed qe: Evolution in rice plants The bar charts evolution in in rice gure 6 plants. show F the hybrid results plants of an were investigation bred by of crossing together 1 two in rice varieties. Japan. collected Each from These year the the hybrids date plants, of for were then owering re-sowing F grown was at ve recorded that site F 3 at in different and the seed following F 4 sites was year. F 5 ▲ Figure 5 A female cheetah’s cubs inherit Sapporo characteristics from her and from one of 43° N the several males with whom she mated Fujisaa 40° N onasu 36° N iratsua singe 35° N origina popuation panted iugo out at 33° N iyaai 31° N 56 70 84 98 112 126 68 82 96 110 124 138 54 68 82 96 110124 138 51 65 79 93 10712 1 135 days to owering ▲ 1 Figure 6 Why was single 2 the investigation pure-bred Describe the done using hybrids rather than a variety? changes, [2] shown in the chart, between the F and 3 F generations of rice plants grown at Miyazaki. [2] 6 3 a) State in the the F relationship between owering time and latitude generation. [1] 6 4 b) Suggest a) Predict until a reason the the for results F if this the relationship. investigation [1] had been carried on generation. [1] 10 b) Predict the results of collecting seeds from F plants grown at 10 Sapporo and from F plants grown at Miyazaki and sowing 10 them together at Hiratsuka. [3] 253 5 E v o l u t i o n a n d b i o d i v E r s i t y Glápgo che Changes in eaks of nhes on Daphne Major. Pinta (5) Genovesa (4) Rabida (8) Marchena (4) Santiago (10) Daphne Major (2/3) Santa Cruz Fernandina San Cristóbal (9) (9) (7) (a) G. fortis (large beak) (b) G. fortis (small beak) (c) G. magnirostris Santa Fe (5) Isabela (10) Española (3) Santa Maria (8) ▲ Figure 7 The Galápagos archipelago with the number of species of nch found on each island Darwin and were 14 species diet. and (see of in From Galápagos has since particular, that related and also. particular Grant’s small ground called Both G. fortis can of competition G. fortis is Daphne Major of Peter a in than birds “one of might birds taken and Major. feed G. on Grant diet the are this small seeds. fuliginosa size other (c) G. magnirostris does of a is the for the small island, seeds, In and (a) G. for tis (large beak). (b) G. for tis (small beak). on fuliginosa, the almost though absence small beak Figure 8 Variation in beak shape in Galápagos nches. have Rosemary fortis, ▲ closely other and On on body nches. population Geospiza larger from smaller the and their into Darwin’s and Geospiza eat research as Rosemary been nch, species also been did islands paucity had changes, focus nch, absent. intense one Daphne ground species and has between that are sizes as Galapagos original characters when research medium island beak the varied, hypothesized an known Peter shown that There ends”. been become the 1835 which nches. similarities one different as in birds, nches over from Islands small observed the Darwin that for have A of overall archipelago, modied what 7), fancy There Darwin beaks the of identied distribution gure this all. the their really In the specimens subsequently shapes in visited collected seeds, size on islands. among there months supply seeds. 1977, a drought on Daphne Major of of G. of 254 larger, small harder seeds, individuals are population died seeds, so G. fortis able in to which crack that year, the fed open. with small, with El soft bred small that seeds, year, and only they and seeds breeding 37 per were in population. In fewer With of G. 1982–83 a to fortis hard the return until those eight increased large, reduced random 1987, an response stopped a In causing result greatly cent not a and availability. and beaks. event, as rapidly, conditions of food shorter Niño rain in to 1987. alive in sample had dry supplies In 1983 of the longer and a beaks than the 1983 averages, correlating instead with on heavy fortis narrower shortage severe weather bred caused a increase 1983 In individuals was the reduction in supply of small seeds. larger-beaked Most of highest the mortality Variation gure 8) in is the shape mostly due and to size of genes, the beaks though the (see 5 . 2 environment the has variation Using and the data breed, The the between predictions. by beak µm 1983 10 and µm and beak 1987 and were to by even was predicted 6 decrease 120 by expect the by the observed and increased of to µm. selection natural actually huge if it had linked to theory to have It have followed 1859, but have of evolution signicant selection changes natural the that occurring. been in to is changes published signicant s E l E c t i o n objections natural caused to predicted. to was predicted decreased by width survived length length One of heritability. close actually was proportion length had very beak actually The called that mean and width is beak are Average Average of in results increase effect. genes birds changes observed 130 to heritability about the width some due n A t u r A l not is changes been unreasonable occurred since in the in a Darwin’s case occurred of that theory G. are to species, fortis, clearly selection. by µm. Daa-baed qe: Galápagos nches When Peter nches there on and the were Rosemary island breeding of Grant Daphne began Major populations of to in two study the 1973, G. fortis and Geospiza scandens. established a breeding Daphne Geospiza island in 1982, initially with population just two Major is 100 three males. Figure 9 shows the m. G. magnirostris and G. fortis on 1997 and has an area and of 1 0.34 km hectare is . 100 the maximum × and females population densities of G. fortis numbers Daphne 1997–2006. [4] Major Table between [3] hectares Calculate during of of on minimum and population 2 km 100 the the 2 1 magnirostris in species, 2 Geospiza changes magnirostris. 2 shows the percentages of three types of 2006. seed in the Daphne 1500 diets Major. of the Small three seeds nch are species produced on by 22 G. for tis plant G. magnirostris species, srebmun echios, 1000 and Tribulus medium large seeds seeds, by which the are cactus very Opuntia hard, by cistoides. 500 3 a) Outline the of on nch diet of each Daphne of the species Major. [3] 0 1996 1998 2000 2002 2004 b) 2006 There was a very severe drought on year Daphne ▲ Figure 9 Changes in numbers of G. for tis and G. magnirostris Deduce between 1996 and 2006 a) Describe of G. and the changes magnirostris in the between 1997 4 2006. Compare the [2] changes in Figure G. population fortis between spee ▲ 1997 and 2006 10 fortis the during in the 2003 diet the and of the 2004. nches drought, using table. [3] shows from an 1973 assigned the index to of 2006, value beak with zero size the and of adult size the in sizes in of other G. data in population 1973 b) how changed the 1 Major years shown in comparison to this. with Geospiza fortis Geospiza magnirostris Geospiza scandens Yea 1977 1985 1989 2004 1985 1989 2004 1977 1985 1989 2004 sma 75 80 77 80 18 5.9 4.5 85 77 23 17 Medm 10 0.0 5.1 11 0.0 12 26 15 22 70 83 lage 17 19 16 8.2 82 82 69 0.0 0.0 0.0 0.0 T able 2 255 5 E v o l u t i o n a n d b i o d i v E r s i t y c) 1 In the beak 0.5 rst size severe of G. second drought, data this in xedni ezis kaeb selection drought, fortis it decreased. question, could the increased, cause in Using explain these mean but how the the natural changes in 0 beak 5 The size in intensity of the two droughts. natural selection [3] on Daphne 0.5 Major was droughts. calculated The during calculated the values two are called 1 selection for beak differentials. length They during the range second from –1.08 drought, 1.5 to 1975 1980 1985 1990 1995 2000 with year ▲ +0.88 for beak length in the rst drought, 2005 similar width and These are selection depth and differentials overall beak for beak size. Figure 10 Relative beak size in G. for tis between very large selection differentials, 1973 and 2006 compared The graph change in shows mean correspond two beak with periods size, droughts of both on very of rapid Suggest Major. beak on a) State in b) two mean Suggest beak two changing a periods size of of reasons most most G. [2] mean when reasons size the of of G. island in other evolution. for natural fortis of calculated being Daphne selection unusually on the intense Major. [2] change fortis. for rapidly rapid values investigations which Daphne to beak there 6 Discuss of size for is drought. few being [2] the advantages evolution over long long-term of investigations periods and the reasons investigations done. [3] nl elecio ibioic eice Use theories to explain natural phenomena: the theory of evolution y natural seletion an explain the development of antiioti resistane in ateria. Antibiotics medicine rst in the a it but antibiotic of have resistance trends great of been in triumphs When expected method there following the century. was permanent diseases, The one 20th introduced, offer of were they that they were would controlling bacterial increasing problems pathogenic have development of become an of the of develops what established: is antibiotic evolution. theory understanding of bacteria. example terms of of very should of It can natural how useful be resistance be done it to therefore explained selection. antibiotic as is A in scientic resistance gives an reduce understanding the problem. 16 14 ● After an antibiotic patients, ● a bacteria few Resistance and more to introduced showing and resistance used on 12 appear tnatsiser % within is years. the antibiotic species of spreads pathogenic to more bacteria. 10 8 6 4 ● In each species the proportion of infections 2 that are caused by a resistant strain increases. bacteria. ▲ The Figure 11 Percentage resistance to ciprooxacin between 1990 and 2004 4002 3002 2002 there antibiotic of 1002 populations 0002 the 9991 of diseases in 8991 properties bacterial changes 7991 treat 6991 cumulative 5991 used been antibiotics 4991 been have which 3991 to over 2991 time have resistance 256 the 1991 during 0991 0 So, 5 . 2 n A t u r A l s E l E c t i o n aibioic eice Evolution of antiioti resistane in ateria. Antibiotic resistance is due to genes in bacteria population with no and antibiotic-resistant bacteria so it can be antibiotic inherited. resistance The to mechanism become more that causes prevalent or antibiotic resistance to diminish The is summarized evolution of multiple in gure antibiotic resistance 12. antibiotic gene received from a gene formed by bacterium in another mutation in one resistance population has occurred evolution is in just due to a few the decades. following This bacterium rapid causes: population with some antibiotic-resistant bacteria ● There has been antibiotics, very both for widespread treating use of diseases and in antibiotic is used therefore animal feeds used on farms. there is strong natural selection for resistance ● Bacteria can generation reproduce time of very less than rapidly, an with a population with more hour. antibiotic-resistant bacteria ● Populations increasing of the bacteria chance are of a often gene huge, for antibiotic is not used therefore antibiotic there is natural selection resistance being formed by mutation. (weak) against resistance ● Bacteria can pass genes on to other bacteria in population with slightly several ways, including using plasmids, fewer which antibiotic-resistant bacteria allow one resistance species genes of bacteria from to another gain antibiotic species. ▲ Figure 12 Evolution of antibiotic resistance Daa-baed qe: Chlor tetracycline resistance in soil bacteria Bacteria were distances collected from a site on from a soil pig at farm different in 3.0 Minnesota 2.5 from feed manure an had animal given to pen the subtherapeutic out rates. what and pigs low chlortetracycline, growth been on this of order of farm the to bacteria percentage to overow accumulate. doses in The allowed The contained antibiotic promote were them )%( ecnatsised where faster tested was to nd resistant 2.0 1.5 1.0 0.5 to 0.0 this antibiotic. chart. The The yellow chlortetracycline results bars are show resistant shown the in the percentage bacteria that bar 5 m of grew 20 m 100 m distance from animal pen on Source: " The eects of subtherapeutic antibiotic use in farm animals nutrient-rich the medium percentage on a and the orange nutrient-poor bars show medium that on the proliferation and persistence of antibiotic resistance among soil bacteria", Sudeshna Ghosh and Timothy M LaPara, The International Society for Microbial cology Journal (2007) 1, 191–203 encouraged 1 a) different State the types of relationship bacteria to between grow. percentage 2 antibiotic resistance and distance from Predict whether resistance animal pen. Explain the difference in between the pen populations of and far been antibiotic lower from the than at 100 at 200 metres metres. [3] Discuss the pen. use of subtherapeutic doses of bacteria antibiotics near percentage have antibiotic 3 resistance would [1] from b) the the in animal feeds. [2] [4] 257 5 E v o l u t i o n a n d b i o d i v E r s i t y 5.3 caa bd ey ueig applicio The inomial system of names for speies is ➔ Classiation of one plant and one animal ➔ universal among iologists and has een agreed speies from domain to speies level. and developed at a series of ongresses. External reognition features of ryophytes, ➔ When speies are disovered they are given ➔ liinophytes, oniferophytes and sienti names using the inomial system. angiospermophytes. Taxonomists lassify speies using a hierarhy ➔ Reognition features of porifera, nidaria, ➔ of taxa. platyhelminthes, annelida, mollusa and ➔ All organisms are lassied into three domains. ➔ The prinipal taxa for lassifying eukaryotes are ar thropoda, hordata. Reognition of features of irds, mammals, ➔ kingdom, phylum, lass, order, family, genus amphiians, reptiles and sh. and speies. In a natural lassiation the genus and ➔ skill aompanying higher taxa onsist of all the speies that have evolved from one ommon Constrution of dihotomous keys for use in ➔ anestral speies. identifying speimens. Taxonomists sometimes relassify groups ➔ of speies when new evidene shows that a ne of ciece previous taxon ontains speies that have Cooperation and ollaoration etween groups ➔ evolved from dierent anestral speies. of sientists: sientists use the inomial Natural lassiations help in identiation ➔ system to identify a speies rather than the of speies and allow the predition of many dierent loal names. harateristis shared y speies within a group. Ieiol coopeio clicio Cooperation and ollaoration etween groups of sientists: sientists use the inomial system to identify a speies rather than the many dierent loal names. Recognizable biologists many as different language. of plant has cows jack and French 258 For lo ca l to called in bulls, is o rg a ni sms s ame na me s , in e ve n as willy als o a de vi ls l i ly a nd v a r ie ty kn o wn can wit h i n Eng la nd s ci e nti sts p ul p i t, are sp ec i e s the Arum lo r d s - a nd- la di e s, the there of T he exa mp l e , known been pint, group s speci e s . o ne sp ec ie s maculatum chandelle, la Sainte-Vierge, Spanish species de del a ng e ls , s na ke ’s meat. of n am e s: l oc a l la In le there of plant are de p i l e tte even the s e other le la de ma n t e au va ch ot t e . names j us t v el a na me in or mor e ar e b a rb a fue g o , The maculatum in la alcatra x , hojas quemado. Arum pi e d - d e - ve a u, which culebra, menor, cu c ko o- a nd to ha ve a a r ón, de l fo r fe w : lang ua g e s . but for t h is o ne c om ida dr a go nt ia d ia b lo pr ima ve ra s Spanish de In a is and ye r ba u se d for d i ffe r ent 5 . 3 Local names culture of venture may an so be area, a valuable but scientic science names understood throughout system has that cooperation The credit naming for is Linnaeus who part names the genius is a still in style many there each was the use of (used groups to in anagallis for In the of group το name, λενκον (used by of as in and of a was to jambu bol different and by Fuchs), (used jambu species of by chilli Eugenia). of that in that name specic for name Ancient anagallis Pliny), Malayan Malays (used mynte of used αδιαυτου Latin by water mirroring the the and Seeblumen and two- system so Turner) geel mynte of recognizes species, wild B i o D i v E r s i t Y scientists. stroke been style consists Threophrastus), This and English (applied o f biologist system had The example Swedish a are binomial system binomial that that The good Linnaeus similar group femina the the fact needed modern Seeblumen the international between century. before. a αδιαυτου by 18th today. species Greek to nomenclature are a introduced basis languages attached our given Carl in is of an world. collaboration devising species are the developed and part is c l A s s i f i c A t i o n το μεαυ mas German and Figure 1 Arum maculatum ▲ weiss deelopme of he biomil yem The inomial system of names for speies is universal among iologists and has een agreed and developed at a series of ongresses. To ensure that organisms, held for at and International late 1753 19th be plants 150 avec Botanical as fungi the to Linné, the as by There same system delegates are separate then the Species The Congresses The IBC starting this book 19 vasculaires.” the attended intervals. century. kingdom votes use of from names around congresses for the for living world animals are and fungi. taken and Plantarum, plant biologists congresses regular plants the all was that gave that IBC (IBC) in both when consistent “La IBC of held in genera binomials Vienna be 1753) in every 1892 in pour year proposed and Linnaeus nomenclature (ann. will were Genoa for year The Plantarum 19th point the known. rule held species published for all 1905 Shenzhen, of Species accepted in of the by commence groupes China, that species botanique les during de plantes ▲ Figure 2 Linnaea borealis. Binomials are often chosen to honour a biologist, or to describe a feature of the organism. Linnaea borealis is named 2017. in honour of Carl Linnaeus, the Swedish The rst International Zoological Congress was held in Paris in 1889. biologist who introduced the binomial It was recognized classifying and subsequent valid names Systema The 4th animal of Natura current edition scientists that internationally species congresses. animal in he rene there the will needed 1758 species which International and were as gave Code no methods accepted was this and doubt that for Zoological be they as when binomials for these chosen was rules more use for were the agreed starting Linnaeus all species in naming and at date this system of nomenclature and named many plants and animals using it for published known Nomenclature editions for naming the is then. the future as species. 259 5 E v o l u t i o n a n d b i o d i v E r s i t y the biomil yem When speies are disovered they are given sienti names using the inomial system. The the system Linnaea a borealis group is that biologists international the of name (gure species species or use of a 2). that The share specic is called species rst name certain name. binomial consists of is nomenclature, two the words. genus characteristics. There are various An name. The rules because example A genus second about is is name binomial nomenclature: ● The genus species ● In ● After name name typed a or ● The binomial to or for text, a used letter example: for an upper-case (small) binomial been initial published 1758 with lower-case has the name, earliest plants a printed abbreviated species begins with L. name animals, once of shown in the letter and the a in piece genus italics. of text, name it with can the be full borealis for is is (capital) letter. a the species, correct from 1753 onwards for one. ALLIGATORIDAE the hiechy of x mississippiensis Taxonomists lassify speies using a hierarhy of taxa. Alligator sinensis The word taxa. crocodilus is of Caiman In taxon biology, classied the into genera is Greek species a and are genus. and means Genera species a arranged in a are group or of grouped family is something. classied into into shown in The taxa. families. gure 3. plural Every An is species example Families are latirostris grouped yacare kingdom taxa and Melano- into or from orders, domain. the larger orders level The taxa below. numbers of into classes form Going species, a up and on hierarchy, the which so up as fewer the each hierarchy, share to the and level taxon taxa of includes include fewer larger features. niger suchus palpebrosus the hee omi Paleo- suchus All organisms are lassied into three domains. trigonatus Traditional ▲ classication systems have recognized two major categories Figure 3 Classication of the alligator family of organisms based classication have been sequence there are of two Members of the but so the eukaryotes. biologists very as eukaryotes was groups of and inappropriate diverse. RNA systems Eubacteria, of types: In prokaryotes. because particular, determined, prokaryotes. it the when became They This prokaryotes the base apparent were given that the names Archaea. domains, some be distinct and organism, shows 260 to cell regarded ribosomal classication called and now found of Eubacteria Most is on all therefore Archaea organisms features that domains are Bacteria and archaeans are now and are can Eukaryota. classied be usually used less are well three These into to referred eukaryotes often recognize three major categories domains. distinguish to as known. are Table between bacteria, relatively categories archaeans familiar to 1 them. most 5 . 3 c l A s s i f i c A t i o n feae o f B i o D i v E r s i t Y Dma Baea Histones assoiated Ahaea Asent Ekaya Proteins similar to histones with DNA Present ound to DNA Presene of introns Rare or asent Struture of ell walls Present in some genes Made of hemial alled Not made of peptidoglyan peptidoglyan Frequent Not made of peptidoglyan; not always present Cell memrane Glyerol-ester lipids; Glyerol-ether lipids; Glyerol-ester lipids; dierenes unranhed side hains; unranhed side hains; l-form unranhed side hains; d-form of glyerol of glyerol d-form of glyerol ▲ T able 1 Archaeans deep are ocean Earth. with They very are high methanogens of their of termites Viruses have found in sediments also salt are are range even in oil responsible classied coding for in for any proteins habitats fairly or anaerobes Methanogens of deposits some concentrations obligate are not genes broad found metabolism. and a and such below extreme the give in the off the close intestines three the the of such to of surface, of as a The waste cattle and gas” in Although genetic code the water boiling. as “marsh domains. same ocean surface methane production using as the habitats temperatures and live of far as product the guts marshes. they living Ay organisms they have too few of the characteristics of life to be regarded ideyg a kgdm as living organisms. This is a denition of the Bacteria Archaea Eukaryota harateristis of organisms in Green lamentous one of the kingdoms. Can you Slime bacteria molds Spirochetes dedue whih kingdom it is? Animals Gram Methanobacterium Proteobacteria positives Fungi Halophiles Multicellular; cells typically Methanococcus Plants Cyanobacteria held together by intercellular Ciliates junctions; extracellular Flagellates matrix with fibrous proteins, typically collagens, between two dissimilar epithelia; sexual with production of an egg cell that is fer tilized by a ▲ Figure 4 Tree diagram showing relationships between living organisms based on base smaller, often monociliated, sequences of ribosomal RNA sperm cell; phagotrophic and osmotrophic; without cell wall. Ekyoe clicio The prinipal taxa for lassifying eukaryotes are kingdom, phylum, lass, order, family, genus and speies. Eukaryotes into phyla, genera. are The phylum, classied which are hierarchy class, order, into kingdoms. divided of taxa family, into for Each classes, classifying genus and kingdom then orders, is divided families eukaryotes is thus up and kingdom, species. ▲ Most biologists recognize four kingdoms of eukaryote: of the plants, animals, Figure 5 Brown seaweeds have been classied in the kingdom Protoctista fungi as and protoctista. protoctists kingdoms. At are very present The last diverse there is these and no is should be consensus most controversial divided on how up into this more should be done. 261 5 E v o l u t i o n a n d b i o d i v E r s i t y Exmple of clicio Classiation of one plant and one animal speies from domain to speies level. Animals shows and the kingdom plants are classication down to kingdoms of one of plant the domain and one Eukaryota. animal Table species 2 from species. tax Gey w Dae pam Kingdom Animalia Plantae Phylum Chordata Angiospermophyta Class Mammalia Monootyledoneae Order Carnivora Palmales Family Canidae Areaeae Genus Canis Phoenix Speies lupus dactylifera ▲ T able 2 Daa-baed qe: Classifying car tilaginous sh All the sh shown Chondrichthyes. found sh in in gure They this class are in 6 are the in most the class 1 State frequently north-west in the gure kingdom 6 to which all of the species belong. [1] Europe. 2 a) Four the of the same sh in genus. gure Deduce 6 are classied which these are. b) c) [1] Deduce with sh in: are whether these four same or different species [2] (ii) the same or different families. [2] State The sh two that characteristics are of possessed these by the four other [2] four sh Deduce, are not sh. other orders. Figure 6 Car tilaginous sh in seas in nor th-west Europe reason the four ▲ a (i) sh 3 in sh split are with into a two classied reason, into how two the four orders. [2] nl clicio In a natural lassiation, the genus and aompanying higher taxa onsist of all the speies that have evolved from one ommon anestral speies. Scientic that evolved. of a closely of the of a or is common natural to this higher This is follows Following genus ancestor. 262 consensus most the a in should natural ancestry to species way convention, taxon called group classify we share can in a which all have way species members a common classication. expect many the Because members characteristics. An example classication and all insects y. and as differ to in unnatural be one grouped evolved do many classify an would are Flight they of not them separately It articial which together, share ways. or in a together in these common would not other birds, because groups ancestor be than bats they they appropriate to place them 5 . 3 all in in the the one time they an animal phylum classied have It cell articial separately are is no share can a be and do classication to clear common move, cell which other so of natural Convergent but this walls than distantly bats were at because shows groups and fungi presumably their each birds and research ancestor, problematic. both not as molecular similar always and Plants together, walls and more not kingdom Chordata. c l A s s i f i c A t i o n to organisms adaptive visible of some in sub-topic was have signicant groups. More can supercially make different. In attempted characteristics methods caused appear radiation appear classication many have animals. species related molecular they B i o D i v E r s i t Y organisms and as evolved that related similar natural is o f been as by possible, of to the this past, looking introduced changes details closely the but and at new these classication are given later, do 5.4. classication evolution can make TOK Wha a ee he deepme a e e? Carl Linnaeus’s 1753 ook Species Plantarum introdued genera and speies. This was inorporated in the Amerian onsistent two-part names (inomials) for all speies of “Rohester Code” of 1883 and in the ode used at the Berlin the vegetale kingdom then known. Thus the inomial Botanihes Museum and supported y British Museum of Physalis angulata replaed the osolete phrase-name, Natural History, Harvard University otanists and a group Physalis annua ramosissima, ramis angulosis glabris, of Swiss and Belgian otanists. The International Botanial foliis dentato-serratis. Linnaeus rought the sienti Congress of Vienna in 1905 aepted y 150 votes to 19 nomenlature of plants ak to the simpliity and revity the rule that “La nomenlature otanique ommene ave of the vernaular nomenlature out of whih it had grown. Linné, Speies Plantarum (ann. 1753) pour les groupes de Folk-names for speies rarely exeed three words. In plantes vasulaires.” groups of speies alike enough to have a vernaular 1 Why was Linnaeus’s system for naming plants adopted group-name, the speies are often distinguished y a as the international system, rather than any other single name attahed to the group-name, as in the Anient system? Greek αδιαυτου το λενκον and αδιαυτου το µεαυ 2 Why do the international rules of nomenlature state (used y Threophrastus), Latin anagallis mas and anagallis that genus and speies names must e in Anient femina (used y Pliny), German weiss Seelumen and geel Greek or Latin? Seelumen (used y Fuhs), English wild mynte and water 3 mynte (used y Turner) and Malayan jamu ol and jamu Making deisions y voting is rather unusual in siene. Why is it done at International Botanial Congresses? hilli (applied y Malays to dierent speies of Eugenia). What knowledge issues are assoiated with this The International Botanial Congress held in Genoa in 1892 method of deision making? proposed that 1753 e taken as the starting point for oth reiewig clicio Taxonomists sometimes relassify groups of speies when new evidene shows that a previous taxon ontains speies that have evolved from dierent anestral speies. Sometimes common closely from The one related, genus species. assigned been to much family. so species to classication other this evidence ancestor, Conversely be new so two or another of in all should taxa the of a up are more group into if any, of the great apes were two or not or species share more found are a taxa. to moved taxa. controversy procedures, family do sometimes united, higher caused and split taxa are taxonomic which, the be between Primates Originally members different has standard about that more or humans order debate group classied Using the the shows humans Hominidae. great placed than apes in any are There to has include another in family, 263 5 E v o l u t i o n a n d b i o d i v E r s i t y the Pongidae, are closer same if research This also classication that and be in is than would suggests humans should but humans family. evidence so to has to just leave chimpanzees a separate shown in that are are so closer placed genus. gure chimpanzees and orang-utans chimpanzees FAMILY A in should in the than of SPECIES gorillas in the Pongidae. gorillas different summary and be to Most humans, genera, this gorillas scheme for human 7. Hominidae GENUS AND ▲ shown orang-utans Pongidae Gorilla Homo Pan Pan Pongo gorilla sapiens troglodytes paniscus pygmaeus (gorilla) (human) (chimpanzee) (bonobo) (orang-utan) Figure 7 Classication of humans age of l clicio Natural lassiations help in identiation of speies and allow the predition of harateristis shared y speies within a group. There is great of biologists to nd new out 1 in are identied ▲ species Identication and the it into of is by moment areas are sometimes research found at surveying what species helpful interest are present. species is Even assigning it It If what rst to biodiversity research in a the specic specimen it is, kingdom, world. been done parts classication two species its of has well-known Natural has easier. obvious the little discovered. biodiversity. not in where of of Groups before, the world species is very advantages. of the an organism specimen then the is can phylum be within Figure 8 Members of the Hominidae the kingdom, class within the phylum and so on down to species and Pongidae level. Dichotomous process Ay would example, colour cg pa bgh was if not keys work owering and a can so be used to well with an plants were white-owered discovered, it would not with articial classied bluebell be help this This classication. according Hyacinthoides identied process. to For ower non-scripta correctly as the species Phytophthora infestans, the normally has blue owers. organism that auses the disease potato light, has hyphae and was lassied as a fungus, ut moleular iology has shown that it is not a true fungus and should e lassied in a dierent kingdom, possily the Prototista. Potato light has proved to e a diult disease to ontrol using fungiides. Disuss reasons for this. 2 Because have of the within is a found to be was in mammary bats For mammalian were a a that if in a features. in this related a is of these with all useful the bat about heart predictions other ying a species drug are species will similar of as chemicals new predictions correct: inherit characteristics that If classication they four-chambered None articially or natural the genus. many are a of a species, chemical the make they placenta, classied group genus, species could certainty glands, in a ancestral prediction example, plant we of common allows other discovered, reasonable if one in a This group. found members from characteristics. other 264 all evolved it of with have and likely bat hair, many could be made organisms. 5 . 3 c l A s s i f i c A t i o n o f B i o D i v E r s i t Y dichoomo key Constrution of dihotomous keys for use in identifying speimens Dichotomous keys are often constructed to use for 1 identifying species within a group. A Fore and hind lims visile, an emerge on land Only fore lims visile, annot live on land is a division into two; a dichotomous key a of these the numbered series should other of clearly should pairs of match clearly be descriptions. the species wrong. The the designer of the key chooses to Fore and hind lims have paws ..................................... 3 One and Fore and hind lims have ippers ................................. 4 features 3 that use in Fur is dark ............................................................ visible. should Each of to another of in the or key, the the to therefore pair of reliable descriptions numbered an be pairs of and leads example of a polar ears easily either 4 descriptions External ear ap visile ........... No external ear ap sea lions and fur seals ........................................................... 5 identication. 5 An key is shown in table 3. We Two long tusks ..................................................... it to identify the species in gure 9. In the of visible. 6 of has key, They the a the key. are We blowhole. we must not, so must It decide we now does are if directed decide not, so hind it if is a limbs to the Mouth reathing, no lowhole ... dugongs and manatees are Breathing through lowholes stage species dugong true seals rst 6 stage walruses can No tusks ............................................................... use sea otters the Fur is white ........................................................ descriptions ................ 6 consists 2 of ..... 2 dichotomy or 7 ......................................... 7 Two lowholes, no teeth ......................... aleen whales a One lowhole, teeth ........ dolphins, porpoises and whales manatee. to A separate fuller key dugongs would and have another stage ▲ manatees. T able 3 Key to groups of marine mammals Ay cg dhm key Keys are usually designed for use in a par tiular area. All the groups or speies that are found in that area an e identied using the key. There may e a group of organisms in your area for whih a key has never een designed. ● You ould design a key to the trees in the loal forest or on your shool ampus, using leaf desriptions or ark desriptions. ● You ould design a key to irds that visit ird-feeding stations in your area. ● You ould design a key to the inver terates that are assoiated with one par tiular plant speies. ● You ould design a key to the footprints of mammals and irds (gure 10). ▲ Figure 9 Manatee They are all right front footprints and are not shown to sale. bear duck ▲ wolf rabbit / hare fox squirrel cat deer dog heron Figure 10 Footprints of mammals and birds 265 5 E v o l u t i o n a n d b i o d i v E r s i t y Pl External reognition features of ryophytes, liinophytes, oniferophytes and angiospermophytes. All In plants the life gametes formed which of classied cycle are of it The and into embryo is. together every formed develops this plant into are plant, fuse an in different The depends types of example kingdom. and together. embryo. develops one male The way on main female one phyla of the smaller phyla. The four are: ● Bryophyta ● Filicinophyta ● Coniferophyta ● Angiospermophyta – mosses, liverworts and hornworts in type are – ferns put – conifers phyla. Most plants are in one of four phyla, but other smaller phyla. The Ginkgo – owering plants. there The are in zygote the plants is plant biloba tree are Byphya Vegetative organs – par ts Rhizoids ut no of the plant onerned true roots. Some with growth rather than with simple stems reprodution and leaves; others external recognition features of these phyla for shown fphya in table 4. cephya Agpemphya Roots, stems and leaves are usually present have only a thallus Vasular tissue – tissues No xylem or with tuular strutures used phloem Xylem and phloem are oth present for transpor t within the plant Camium – ells etween No amium; no true trees and Present in onifers and most angiosperms, xylem and phloem that shrus allowing seondary thikening of stems and an produe more of these roots and development of plants into trees tissues and shrus Pollen – small strutures Pollen is not produed ontaining male gametes Pollen is produed Pollen is produed in male ones y anthers in that are dispersed Ovules – ontains a female owers No ovaries or ovules gamete and develops into a seed after fer tilization Seeds – dispersile unit Ovules are produed Ovules are enlosed in female ones inside ovaries in owers No seeds Seeds are produed and dispersed onsisting of an emryo plant and food reserves, inside a seed oat Fruits – seeds together with No fruits Fruits produed for a fruit wall developed from dispersal of seeds the ovary wall y mehanial, wind or animal methods ▲ 266 T able 4 5 . 3 c l A s s i f i c A t i o n o f B i o D i v E r s i t Y aiml phyl Reognition features of porifera, nidaria, platyhelminthes, annelida, mollusa and ar thropoda, hordata. Animals table 5. are Two divided up examples into of over each Phym 30 are phyla, shown Mh/a based in on gure their characteristics. Six phyla are featured in 11. symmey skee ohe ex ea eg eae Porifera – fan sponges, No mouth or up sponges, tue anus None Internal spiules Many pores over the surfae (sketetal needles) through whih water is drawn sponges, glass sponges in for lter feeding. Very varied shapes Soft, ut hard Tentales arranged in rings jellysh, orals, sea orals serete around the mouth, with stinging anemones CaCO ells. Polyps or medusae Cnidaria – hydras, Mouth only Radial 3 (jellysh) Platyhelminthes – Mouth only Bilateral atworms, ukes, Soft, with no Flat and thin odies in the shape skeleton of a rion. No lood system or tapeworms system for gas exhange Mollusa – ivalves, Mouth and gastropods, snails, anus Bilateral Most have shell A fold in the ody wall alled made of CaCO the mantle seretes the shell. A 3 hard rasping radula is used for hitons, squid, otopus feeding Annelida – marine Mouth and ristleworms, anus Bilateral oligohaetes, leehes Internal avity Bodies made up of many ring- with uid under shaped segments, often with pressure ristles. Blood vessels often visile Ar thropoda – insets, Mouth and arahnids, rustaeans, anus Bilateral myriapods ▲ 1 Segmented odies and legs or other appendages with joints hitin etween the setions T able 5 Characteristics of six animal phyla Study and 2 External skeleton made of plates of List the organisms assign the each one organisms a) bilaterally b) radially shown to that its in gure 11 phylum. 3 List the organisms not symmetric symmetric symmetrical in have: a) jointed b) stinging appendages c) bristles. are: 4 List the their structure. tentacles [3] organisms pumping c) that [7] water that lter through feed tubes by inside [3] their bodies. [2] 267 5 E v o l u t i o n a n d b i o d i v E r s i t y veebe Reognition of features of irds, mammals, amphiians, reptiles and sh. Most Adocia cinerea species of chordate belong to one of ve major classes, each of Alcyonium glomeratum which are not are about 5,700 bony ve Nymphon gracilis Pycnogonum littorale contains are certain more and 10,000 mammals. sh, with largest vertebrates, By ay- new bird All of a thousand species species, of more classes than these than 9,000 30,000 they Amphba still classes chordate because are are species. sometimes reptiles, are species. a 6,000 The in repe numbers amphibians by the recognition table backbone the discovered, outnumbered shown have Although 6. All of composed and ray-nned features the of Bd there of the organisms vertebrae. Mamma ed h Lepidonotus clara Corynactis viridis Sales whih Soft moist Impermeale Skin with Skin has are ony skin skin overed feathers made folliles with plates in the permeale in sales of of keratin hair made of skin to water and keratin keratin gases Polymastia mammiliaris Cyanea capillata Gills overed Simple lungs Lungs with Lungs with Lungs with y an with small extensive para-ronhial alveoli, operulum, folds and folding to tues, ventilated with one gill moist skin for inrease the ventilated using slit gas exhange surfae area using air sas ris and a diaphragm No lims Tetrapods with pentadatyl lims Fins Four legs Four legs (in Two legs and Four legs in suppor ted y when adult most speies) two wings most (or two Procerodes littoralis rays legs and two wings/arms) Loligo forbesii Arenicola marina Eggs and sperm released for Sperm passed into the female for internal external fer tilization fer tilization Remain Larval stage Female lays Female lays Most give in water that lives in eggs with soft eggs with hard ir th to live throughout water and shells shells young and their life yle adult that all feed usually lives young with on land milk from mammary Prostheceraeus vittatus glands Swim ladder Eggs oated Teeth all of Beak ut no Teeth of ontaining gas in protetive one type, with teeth dierent for uoyany jelly no living par ts Caprella linearis types with a living ore Do not maintain onstant ody temperature Maintain onstant ody Gammarus locusta temperature ▲ Figure 11 Inver tebrate diversity ▲ 268 T able 6 5 . 4 c l A D i s t i c s 5.4 cad ueig applicio ➔ A lade is a group of organisms that have Cladograms inluding humans and other ➔ evolved from a ommon anestor. primates. ➔ Evidene for whih speies are par t of a lade Relassiation of the gwor t family using ➔ an e otained from the ase sequenes evidene from ladistis. of a gene or the orresponding amino aid sequene of a protein. ➔ skill Sequene dierenes aumulate gradually so there is a positive orrelation etween the Analysis of ladograms to dedue evolutionary ➔ numer of dierenes etween two speies relationships. and the time sine they diverged from a ommon anestor. ne of ciece ➔ Traits an e analogous or homologous. ➔ Cladograms are tree diagrams that show the Falsiation of theories with one theory eing ➔ superseded y another: plant families have most proale sequene of divergene in een relassied as a result of evidene from lades. ladistis. ➔ Evidene from ladistis has shown that lassiations of some groups ased on struture did not orrespond with the evolutionary origins of a group of speies. Cle A lade is a group of organisms that have evolved from a ommon anestor. Species can happened there are ancestor. evolve now a Clades very include a They ten member can with the and be just thousand common been group all species small about of and some groups groups A time with of split species species of to highly can organisms form new successful all be derived from identied evolved species. species, by from a a This so has that common looking for common shared ancestor is clade. ancestral extinct. large These characteristics. called over repeatedly of other ancestral a clade species species any very a large few. living For that and The clade together evolved include example, evolved this today, that species species. in alive species all 270 are form they Ginkgo about but it million now of one have biloba the and thousands birds because tree with from is all became species, large only ago. or clade evolved the years common then with from living There have extinct. 269 5 E v o l u t i o n a n d b i o d i v E r s i t y Ay the EDGE Exee pje The aim of this projet is to identify animal speies threatened or have lose relatives. In some ases speies that have few or no lose relatives and are therefore are the last memers of a lade that has existed for tens memers of very small lades. The onservation status or hundreds of millions of years and it would e tragi for of these speies is then assessed. Lists are prepared of them to eome extint as a result of human ativities. speies that are oth Evolutionarily Distint and Gloally What speies on EDGE lists are in your par t of the world Endangered, hene the name of the projet. Speies and what an you do to help onserve them? on these lists an then e targeted for more intense http://www.edgeofexistene.org/speies/ onservation eor ts than other speies that are either not ▲ Figure 1 Two species on the EDGE list: Loris tardigradus tardigradus (Hor ton Plains slender loris) from Sri Lanka and Bradypus pygmaeus (Pygmy three-toed sloth) from Isla Escudo de Veraguas, a small island o the coast of Panama Ieifyig membe of cle Evidene for whih speies are par t of a lade an e otained from the ase sequenes of a gene or the orresponding amino aid sequene of a protein. It is not always ancestor The and most amino objective acid ancestor 270 to evidence from have of expected Conversely, diverged likely be which therefore sequences can sequence. but obvious should a many species be comes proteins. to have species common have included from sequences that look tens of from a common clade. have differences might ancestor differences. a base Species few that evolved in in a of base similar genes recent in millions or amino certain of or common years acid respects ago are 5 . 4 c l A D i s t i c s Molecl clock Sequene dierenes aumulate gradually so there is a positive orrelation etween the numer of dierenes etween two speies and the time sine they diverged from a ommon anestor. Differences acid gradually occur clock. long For in the sequence at over a long species four sequence are periods of split a mitochondrial related primates DNA result time. rate so differences from of the of constant number example, and base proteins roughly The ago of DNA evidence be used can the that as be in They a amino accumulate mutations molecular used to deduce how ancestor. from been is can sequence common has therefore mutations. There they in and of three humans European completely Japanese sequenced. From hypothetical in gure 2. the ancestry Using differences has been differences in base sequence, constructed. in base It is sequence a shown as African a Common chimpanzee molecular between clock, groups ● 70,000 ● 140,000 ● 5,000,000 these have years ago, years been dates for splits deduced: Pygmy chimpanzee (bonobo) European–Japanese ago, years approximate split Gorilla African–European/Japanese ago, human–chimpanzee split split ▲ Figure 2 alogo homologo i Traits an e analogous or homologous. Similarities between Homologous ● example the Analogous ● human Problems in structures For this and but reason rarely base or the they are wing, are are used amino acid similar eye led to identifying sequences arm homologous of and because of similar other because they (form and trusted in in and a clade for forelimbs. evolution. structure The and independently. analogous classication structure) of analogous. ancestry; evolved homologous mistakes or pentadactyl convergent similarities members is be because show between morphology for either human analogous sometimes the can similar octopus distinguishing have now structures chicken structures eye function organisms of and in the past. organisms evidence is from more. cornea iris lens retina photoreceptors optic nerve ▲ Figure 3 The human eye (left) and the octopus eye (right) are analogous because they are quite similar yet evolved independently 271 5 E v o l u t i o n a n d b i o d i v E r s i t y sruasonid sdrib naiva-non sdrazil sekans seltrut selidocorc Clogm Cladograms are tree diagrams that show the most proale sequene of divergene in lades. ancestral species A A cladogram is a tree diagram based on similarities and differences between ancestral species B the or species amino in a acid clade. Cladograms sequences. are Computer almost always programs have now based been on base developed that ancestral species C calculate number ▲ how of species changes in of a clade base or could amino have acid evolved with sequence. the This is smallest known as the Figure 4 A cladogram showing the principle of parsimony and although it does not prove how a clade actually hypothesized relationship between birds and evolved, it can indicate the most probable sequence of divergence in clades. the traditional taxonomic group “the reptiles” The branching branch off at points a node on but cladograms sometimes are called there are nodes. three or Usually more. two The clades node Ay represents Figure 5 shows an ar tist’s impression species. of two pterosaurs, whih were the rst base a hypothetical Option B sequences ancestral includes using species instructions computer for that split to form constructing two or cladograms more from software. hordates to develop powered ight. Figure 4 is an example of a cladogram for birds and reptiles. It has been They were neither irds nor dinosaurs. based on morphology, so that extinct groups can be included. Where might pterosaurs have tted into the ladogram shown in gure 4? ● ● Birds, non-avian called dinosauria. Birds, non-avian part a Lizards, ● This or clade reptiles are and either be closely ancestral crocodiles species and A form ancestral a clade species B species that divided related birds into to C should two birds form or than a clade be more to called regarded groups, other squamates. as as reptiles some reptiles. Figure 5 Two pterosaurs in ight Pime clogm Cladograms inluding humans and 45,000 4.5 Myr ago other primates. The closest and bonobos. species has evidence (gure relatives been for 6). estimates The the The of of humans entire sequenced population splits occurred. clock with These on sizes are of the a these very cladogram dates on a Figure 7 is mutation rate a cladogram for of 10 are when 27,000 molecular –9 a three strong cladogram and based chimpanzees of giving construction numbers are genome 1 Myr ago –1 yr primates and the most 12,000 closely are for an related order climbing gibbons 272 and other of groups mammals trees. that Humans, lemurs are of mammal. have primates. Primates adaptations monkeys, baboons, are archosaurs. ancestral suggests should more and dinosaurs, called snakes cladogram that reptiles ▲ of dinosaurs Bonobo ▲ Figure 6 Chimpanzee Human 5 . 4 c l A D i s t i c s Cavies and Coypu alyi of clogm Porcupines Mice and Rats Analysis of ladograms to dedue evolutionary Beavers relationships. Chipmunks The pattern of branching in a cladogram is assumed to match the Rabbits evolutionary origins of each species. The sequence of splits at nodes is Primates therefore a diverged. If hypothetical sequence in which ancestors of existing clades Treeshrews two clades on a cladogram are linked at a node, they are Figure 7 ▲ relatively of nodes, Some in related. are cladograms base are closely they or amino assumed to less If include acid occur two closely species numbers sequence at a are only connected via a series related. or to in relatively indicate genes. numbers Because constant rate, of genetic these Ay differences changes numbers A adgam he gea ape can The great apes are a family of be used to estimate how long ago two clades diverged. This method primates. The taxonomi name is of estimating times is called a molecular clock. Some cladograms Hominidae. There are ve speies are drawn to scale according to estimates of how long ago each split on Ear th today, all of whih are occurred. dereasing in numer apar t from Although cladograms history a of group, constructed of on mutations sequence and using the to of be different cannot to were in versions the for for proof. smallest base or is convoluted. of cladograms been the produced humans. Figure 6 is a ladogram evolutionary Cladograms possible assumption more have as current this analysis that evidence regarded that account evolution strong be Sometimes cautious several provide assumption occurred pathways compare they differences. important can for three of the speies. Use are this information to expand the number amino ladogram to inlude all the great acid apes: the split etween humans incorrect It is and and gorillas ourred aout therefore where 10 million years ago and the split possible etween humans and orang- independently utans aout 15 million years ago. genes. Daa-baed qe: Origins of tur tles and lizards Cladograms based on morphology the suggest short-tailed opossum or to the duck-billed platypus. that this turtles and hypothesis, compared for lizards are not microRNA nine species a clade. genes of To have been chordate. 2 Calculate found The but results were gure8. which used The to construct numbers microRNA on genes the are the cladogram cladogram shared by a clade example, humans but not there and members are six short-tailed of other show 3 microRNA opossums genes but not Discuss other chordates on the the Deduce, whether using evidence humans are microRNA clade on genes the are cladogram clades. the supports any in of 4 Evaluate tetrapod are not the evidence the a [2] in the hypothesis that turtles clade. traditional chordates [3] and into mammals classication amphibians, using evidence of reptiles, from the cladogram. cladogram. 1 other whether lizards birds the in many mammal For found in not how the cladogram members clades. in in and of [2] test from more the [3] cladogram, closely related to 273 5 E v o l u t i o n a n d b i o d i v E r s i t y African clawed frog 043 176 167 588 Human Short-tailed opossum 681 095 378 3 1521 7931 6 Duck-billed platypus 1971 1541 0641 7641 9551 7651 1461 9661 9271 3471 4471 6571 9571 1871 4871 9871 3081 1312 1 4592 4692 094 7931 19 Zebra nch Chicken Alligator 7761 1 Painted turtle ▲ 0935 1935 2935 3935 4 Lizard Figure 8 Clogm eclicio Evidene from ladistis has shown that lassiations of some groups ased on struture did not orrespond with the evolutionary origins of a group of speies. The construction only the became sequence been has classication. classication evolutionary been data developed identication Cladistics of group and to truly to 274 is is from groups groups cases and The as of and 20th amino acid century. computer of sequences Before software construction in plant cladograms does not species. have species base the had that not cladograms and cladistics. morphology of of revolutions clear Some some analysis. known on end available some on origins of groups disruptive natural have some be the now classications They not based the have animal traditional always As been and that a merged, been match result some others transferred the groups have from have been one another. potentially also do based in towards clades caused It Reclassication a cladograms was to reclassied. divided new of possible based of some signicant organisms biologists, on classication revealed similar. for cladistics so their unnoticed differences is but it are time-consuming is certainly likely predictive be value similarities between to much will between species and worthwhile. be closer higher. groups previously The to and assumed 5 . 4 c l A D i s t i c s Clogm flicio Falsiation of theories with one theory eing superseded y another: plant families have een relassied as a result of evidene from ladistis. The is a reclassication good theories and theories. on their Laurent revised example of The of of on replacement Jussieu repeatedly was in the important classication morphology de plants an of of Genera of theories discoveries in science: found to be angiospermophytes begun during basis process by the French plantarum , the 19th false into in cladistics testing with of new families botanist published in the based Antoine 1789 and century. Clicio of he gwo fmily Relassiation of the gwor t family using evidene from ladistis. There Until are more recently than the Scrophulariaceae, gwort family. proposed by It de 400 eighth commonly was one Jussieu in name Scrophulariae and based on in more until similarities plants there 5,000 were were families largest of 1789. 275 as He the gave families it sixteen family with using the morphology. genera, Taxonomists evolutionary the original included their angiosperms. known the discovered, over of was the compared the genes large in a traditionally As genera that grew than in and One base in into the sequences to related the of one of three in project chloroplast genera Scrophulariaceae families. clades family research species the gwort ve the gwort important assigned that investigated of number closely species clade combined species. origins cladistics. genera, more recently family had It was were and found not incorrectly a true been family. Two small families were merged with the gwort family: the buddleja family, Buddlejaceae and the myoporum family, Myoporaceae Two genera were moved to Nearly fty genera have a newly-created family, been moved to the The gwort the calceolaria family, plantain family, family Calceolariaceae Plantaginaceae Scrophulariaceae Thirteen genera have ▲ been About twelve genera of transferred to a newly-created parasitic plants have been family, the lindernia family, moved to the broomrape Linderniaceae family, Orobanchaceae Figure 9 275 5 E v o l u t i o n A major Less in ▲ half family, largest b i o d i v E r s i t y reclassication than the a n d of the which among the has species is now now only angiosperms. carried been the A out. retained thirty-sixth summary of the Figure 10 Antirrhinum majus has been transferred from the gwor t family to the plantain family 276 been have changes has before of is been that species ▲ shown in welcomed the gure as it 9. was This Scrophulariaceae rather than a reclassication widely natural appreciated had been a rag-bag group. Figure 11 Scrophularia peregrina has remained in the gwor t family Q u E s t i o n s Qeio The bar three at charts in gure populations different came from Rhosneigr copper an in undersides of the The that growth Ectocarpus concentrations. ships copper-containing show alga, unpolluted Wales. of 12 an One environment other had two been anti-fouling 4 of siliculosus, Which of copper tolerance the following to processes develop in a are required for population? population (i) variation in (ii) inheritance (iii) failure copper tolerance at came from painted the with of copper tolerance a of algae with lower copper paint. tolerance to survive or reproduce. 500 emulov lagla ni esaercni % Rhosneigr a) i) only b) i) and ii) c) i) and iii) d) i), only 0 only M.V. San Nicholas 500 ii) and iii). 0 M.V. Amama 5 In gure species. 13, The each number closer that represents two numbers a are on 500 the diagram The 0 0.0 0.01 0.05 0.1 0.5 1.0 5.0 circles the more represent similar the taxonomic two species. groups. For 10.0 example, the diagram shows that 2, 3, 4 and -3 concentration of copper (mg dm ) 5 are in the same genus. Figure 12 1 How much higher concentration was the tolerated by maximum the algae copper from 34 2 3 1 ships than the algae from an unpolluted 6 7 4 5 environment? a) 0.09 times higher b) 0.11 times higher 8 9 10 c) 1.0 times higher d) 10 times 11 higher. 12 13 19 24 14 20 25 15 2 1 16 22 1 7 26 27 28 18 29 23 30 2 What is the reason for results lower than zero 31 on the bar 32 charts? 33 a) The volume b) The algae c) Increases d) Results of all in algae decreased. died. Figure 13 volume were less than 100 % a) State with were too small to b) State with c) What was the reason for the difference tolerance between the The algae on the ships the The algae can develop absorbed it on to their State The d) The copper in copper tolerance selection in the for that are in a family species [2] that are in an order families. [2] State the species that are in a class with orders. [2] Deduce whether species 8 is more closely offspring. the the [1] and paint caused paint higher caused levels of to species 16 or species 6. mutations. f) copper genus genera. two related c) a copper. e) pass in species. species two three b) is algae? d) a) other that in with copper no species measure accurately. 3 one natural copper tolerance. Explain been why drawn diagram. three concentric around species circles 34 on have the [2] 277 5 E v o l u t i o n 6 The map in in the in Britain a n d gure 1950s of and b i o d i v E r s i t y 14 two shows forms Ireland. the of distribution Biston Biston betularia betularia is a Key species of moth that ies at night. It spends Non-melanic the daytime roosting on the bark of trees. The Melanic non-melanic with black wings. the a) spots. Before melanic wind form form is wings, melanic very from has revolution, rare. the form peppered The black the prevailing Atlantic Ocean, to west. State the maximum of Outline the the forms in c) white industrial was percentages b) The the direction has two gure Explain moths the trends of and minimum melanic in the Biston form. [2] distribution betularia, of shown 14. how such [2] natural as Biston selection betularia can to cause develop Figure 14 camouaged d) 278 wing Suggest reasons the forms. two markings. for the distribution [4] of [2] 6 H U m A N p H y S I o l o g y Intrductin Research into foundation are carried The blood to it to and by of medicine. specialized the move, system cells physiology modern out structure allows human of wall digest of continuously simultaneously functions systems. small absorb intestine food. transports collects products. the organ the and is Body The substances waste The continuous lungs are exchange the actively can message, Hormones widely skin threat and of ventilated occur used resist pathogens. ensure that Neurons modulate when system by to passively. synapses are immune invasion the signals the The gas transmit message. need to be distributed. 6.1 Ds d s Understandin Aicatins ➔ The contraction of circular and longitudinal ➔ Processes occurring in the small intestine that muscle layers of the small intestine mixes the result in the digestion of starch and transpor t of food with enzymes and moves it along the gut. the products of digestion to the liver. ➔ The pancreas secretes enzymes into the lumen ➔ Use of dialysis tubing to model absorption of of the small intestine. digested food in the intestine. ➔ Enzymes digest most macromolecules in food into monomers in the small intestine. ➔ over which absorption is carried out. ➔ ➔ Production of an annotated diagram of the digestive system. Villi absorb monomers formed by digestion as well as mineral ions and vitamins. ➔ Skis Villi increase the surface area of epithelium ➔ Identication of tissue layers in transverse sections of the small intestine viewed with a Dierent methods of membrane transpor t are microscope or in a micrograph. required to absorb dierent nutrients. Nature f science ➔ Use models as representations of the real world: dialysis tubing can be used to model absorption in the intestine. 279 6 H u m a n p H ys i o l o g y Structure f the diestive sste Production of an annotated diagram of the digestive system. The can part be through the of human which anus. break the described The down role the in that several of the food, can to that ions Surfactants by mouth large and For digestion in digestion tube system of absorbed. occur a the digestive mixture polysaccharides stages for as from yield be used terms passes diverse compounds and body simple food compounds lipids in to to to absorption is carbon smaller proteins, involves different parts the place some small through small in e nzy mes tha t sy s te m. the the s ma l l stoma ch are se c r et e d d ucts C ontro ll ed, nutr i e nts molecul e s , the ha ve l e ad ing s e le ct i ve r el e as e d inte stine notab ly l i ning by a nd a lcohol , be for e di g es ti on c ol on , but di ffu se r ea ch in g t he intestine. of 1 is a diagram of the human digestive gut. system. Digestion droplets require s and Glandular and of takes o the r gland s digestive Figure the and accessory s ur f a ctants enzy me s cells intestines in the to ca ta l yse l ining prod uce to s ome of of br ea k up li pi d re a ct io n s. the the s tom a c h e n z ym e s . The part through the diagram can functions of functions is of thorax be the has esophagus been annotated different given in table Sc Mouth to parts. 1 that omitted. indicate A passes This the summary of below. Fc Voluntary control of eating and mouth swallowing. Mechanical digestion of food by chewing and mixing with saliva, which contains lubricants and enzymes that star t starch digestion Esophagus Movement of food by peristalsis from the mouth to the stomach esophagus Stomach Churning and mixing with secreted water and acid which kills foreign bacteria and other pathogens in food, plus initial stages of protein digestion gall bladder Small intestine Final stages of digestion of lipids, carbohydrates, proteins and nucleic liver acids, neutralizing stomach acid, stomach plus absorption of nutrients pancreas Pancreas Secretion of lipase, amylase and protease small intestine Liver Secretion of surfactants in bile to break up lipid droplets Gall bladder Large intestine Storage and regulated release of bile Re-absorption of water, fur ther digestion especially of carbohydrates by symbiotic large intestine bacteria, plus formation and storage of feces anus ▲ 280 Figure 1 The human digestive system ▲ T able 1 6 . 1 D i g e S t i o n a n D a b S o r p t i o n Structure f the wa f the sa intestine Identication of tissue layers in transverse sections of the small intestine viewed with a microscope or in a micrograph. The wall of the of living to distinguish outside small tissues, of in the intestine which are sections wall going is made usually of the wall. inwards of quite layers easy From there the are fourlayers: ● serosa ● muscle it ● – an outer layers circular ● lymph mucosa with its – the inner longitudinal muscle and inside muscle sub-mucosa and – coat – a tissue layer containing blood vessels the lining epithelium of the that small intestine, absorbs ▲ nutrients on Figure 2 Longitudinal section through the wall of the small intestine. Folds are visible on the inner surface and on these folds are nger-like projections called villi. All of the surface. four main tissue layers are visible, including both circular and longitudinal par ts of the muscle layer. The mucosa is stained darker than the sub-mucosa peristasis acv The contraction of circular and longitudinal muscle layers tss ds f of the small intestine mixes the food with enzymes and s w moves it along the gut. To practice your skill at identifying tissue layers, The circular and longitudinal muscle in the wall of the gut is draw a plan diagram of the smoothmuscle rather than striated muscle. It consists of relatively short tissues in the longitudinal cells, not elongated bres. It often exerts continuous moderateforce, section of the intestine wall interspersed with short periods of more vigorous contraction, rather in gure 2. To test your skill than remaining relaxed unless stimulated to contract. fur ther, draw a plan diagram Waves of muscle contraction, called peristalsis, pass along the intestine. to predict how the tissues Contraction of circular muscles behind the food constricts the gut to of the small intestine would prevent it from being pushed back towards the mouth. Contraction of appear in a transverse longitudinal muscle where the food is located moves it on along the gut. section. The the contractions enteric Swallowed one from stomach circular In the the nervous food continuous away time and for system, moves longitudinal the food progression of the the The muscle is main of is in moved through the gut a to of to the are brain but by complex. to occurs the in stomach one mouth used few in direction, from rather centimetres is much peristalsis mix the the than the wall. intestine function food muscles only the and only returned the by esophagus Peristalsis food not extensive abdominal semi-digested process is down wave. When vomiting, unconsciously which quickly peristaltic digestion. up controlled mouth. intestines churning speed the during overall are it with in at slower, the a time intestine enzymes so allowing and is thus digestion. 281 6 H u m a n p H ys i o l o g y pancreatic juice The pancreas secretes enzymes into the lumen of the small intestine. The the pancreas synthesizes to a eating the the The on of is the wave of muscle contraction (brown) in the larger ducts, nally pancreatic by juice ducts, are by 4. gland into by the synthesized reticulum. exocytosis. secreted in are Ducts day into duct, in secrete the response structure of round the secreted. cells on in pancreas through lumen of secreted cluster processed the cells gut and The gland then within the the cells are pancreatic pancreatic per system. enzymes They into gland of remainder synthesized nervous of groups The enzymes groups which Small blood. hormones enteric one tissue. the digestive Small into forming is the gure secreted of secretes endoplasmic and types glucagon mediated also enzymes rough apparatus is in called digestive the and two and and This shown tubes Figure 3 Three-dimensional image showing of meal. stomach tissue ends esophagus during swallowing. Green indicates insulin pancreas by ▲ contains hormones of which the ribosomes the Golgi merge about small into a litre intestine. when the muscle is exer ting less force. Time Pancreatic juice contains enzymes that digest all the three main types of is shown left to right. At the top the sphincter macromolecule between the mouth and the esophagus is found in food: shown permanently constricted apar t from a ● amylase to ● lipases ● proteases digest starch brief opening when swallowing star ts to digest to triglycerides, digest proteins phospholipids and peptides. secretory vesicles Diestin in the sa intestine Enzymes digest most macromolecules in food into one acinus monomers in the small intestine. The enzymes small basement membrane secretory cells wall of duct secreted intestine ● starch ● triglycerides acids is carry out digested and are by to the pancreas these hydrolysis maltose digested to monoglycerides into by lumen of the reactions: amylase fatty by the acids and glycerol or fatty lipase lumen of duct phospholipids ● ▲ are digested to fatty acids, glycerol and Figure 4 Arrangement of cells and ducts in a par t of phosphate byphospholipase the pancreas that secretes digestive enzymes proteins ● and polypeptides are digested to shorter peptides by protease. This does enough a variety enzymes in not to be of membrane off 282 other and the juice of ● Nucleases ● Maltase by b ut and to wa ll mo st be DNA ce ll s wi th and maltose the RNA into m or e in nucleotides. S om e be s e c r et e d p la sma The y fo od. small p ro du c e s may the e pi t h el iu m s e m i -d ig e st e d glucose. w al l int e s t in e . th e m o le c u le s s u bs t a n c es . int e st i n e the into i nt o in t e s t in e i m m obil i z ed wh e n the s ma l l di g es t l ining a cti ve d ig e st i on the in r e mai n ce l ls of of which g l and mi x e d digest digests pr oces s The epithe l i um continue lining the e nzy me s, produce d intestinal there comp l e te abso r b e d . a re c e l ls act i ve are a bra de d 6 . 1 ● Lactase ● Sucrase ● Exopeptidases amino until Because pass acids only be of not are digest cannot that a b S o r p t i o n fructose. peptides or amino by removing terminal of single the chain left. of time the on into the for amino small remain the of most largely necessary to acids. intestine, digestion substances passes digest a n D galactose. and carboxy dipeptides synthesize and and glucose the is length Some digested into from dipeptide great glucose proteases allowing completed. into sucrose either a the through, humans lactose digests Dipeptidases ● is digests D i g e S t i o n large food takes hours macromolecules undigested, enzymes. intestine because Cellulose as one to to of for the example main ▲ components of dietary Figure 5 Cystic brosis causes the pancreatic bre. duct to become blocked by mucus. Pills containing synthetic enzymes help digestion in the small intestine. The photograph shows one Vii and the surface area fr diestin day’s supply for a person with cystic brosis Villi increase the surface area of epithelium over which absorption is carried out. The process of absorption. taking In the substances human into digestive cells and system the blood nutrients are is called absorbed epithelium principally the in surface small the area intestine 25–30 small of in the intestine. epithelium adults millimetres The wide is rate that there are absorption carries approximately and of out seven folds on the process. metres its depends long inner on The and surface, layer of microvilli giving on surface of epithelium a large Villi surface are small area. This nger-like area is increased projections of the by the presence mucosa on the of lacteal (a branch of the lymphatic system) villi. inside of the blood capillary intestine be as They wall. many as increase A villus 40 of the is between them surface per 0.5 square area by a and 1.5 mm millimetre factor of of about long and small there intestine can wall. 10. goblet cells (secrete mucus) Absrtin b vii Villi absorb monomers formed by digestion as well as mineral ions and vitamins. The epithelium substances, useful Villus nutrients cells glucose, ● any ● fatty ● bases but of covers the pass the from twenty mineral ions ● vitamins must being form a barrier permeable to harmful enough to ▲ Figure 6 Structure of an intestinal villus ▲ Figure 7 Scanning electron micrograph of villi allow through. products galactose amino digestion absorb villi time of of and acids monoglycerides needing ● the same these fructose, acids, also not at to absorb ● They that while digestion other used and of macromolecules in food: monosaccharides to make proteins glycerol nucleotides. substances required by the body and present in foods digestion: such such as as calcium, ascorbic acid potassium (vitamin and sodium C). in the small intestine 283 6 H u m a n p H ys i o l o g y Some harmful subsequently harmless of those Small but that substances removed unwanted give numbers removed from food of pass from blood substances its colour bacteria the through the blood pass by are and the epithelium and detoxied also absorbed, avour. through phagocytic the These and by in the liver. including pass epithelium cells are the out but in are Some many urine. quickly liver. methds f absrtin Dierent methods of membrane transpor t are required to absorb dierent nutrients. To be the absorbed small must part rst of be the microvilli. plasma The of and ● of be pass Fatty acid ● of simple into are inside into the its pass pass in from the through surface out inwards the move of this the villi. the area towards nutrients can digested are villus fatty be lumen The cell the of nutrients exposed enlarged with through lacteal before acids phospholipids the and blood absorbed are by they and the using in fatty can be simple plasma the two villus transport different absorbed. cells, to triglycerides, diffusion as there membrane acids The which as can they membrane. diffusion the epithelium produce of active monoglycerides, by facilitated proteins out glucose. cells in and diffusion, illustrated and epithelium which into facilitated triglycerides be also monoglycerides out faces methods must transporters, Once it cells has then diffusion, digestion between acids that must lacteals epithelium must where or villus. absorption: absorbed can into membrane These Triglycerides nutrients capillaries mechanisms cells: products ● the exocytosis. examples body, the nutrients different epithelium the to absorbed plasma membrane capillaries Many into intestine are which of are the combined cannot fatty microvilli. with diffuse back lumen. lumen of small intestine interior villus epithelium of villus + Na + 3Na blood + low Na capillary concentration + 2K glucose fatty acids and monoglycerides lacteal lipoprotein triglyceride ▲ 284 Figure 8 Methods of absorption in the small intestine 6 . 1 Triglycerides ● diameter and lipoprotein plasma They or then enter either the on the it inside pump interstitial opposite a sodium lumen to gradient Glucose ● to form become from into pumps This the in droplets coated in with a b S o r p t i o n a phospholipids sodium channels glucose is allow to capillaries are villus plasma carried active the a away membrane in the cells. the lymph, low part transport villus by simple hydrophilic. inwards-facing by through epithelium villi. and of from the the potassium concentration of the the it by the of plasma cytoplasm ions in sodium active glucose to microvilli from cells. depends interstitial the in together epithelium but created the in proteins molecule passive ions cytoplasm exocytosis the ions cells. cytoplasm diffusion by the therefore the ions of and the co-transporter a side and creates epithelium the blood in inside and of the polar spaces released lacteal through is ion facilitated are inner the sodium direction. villus Sodium–glucose ● which capillaries pass because membrane the enter Sodium–potassium to cholesterol µm, particles blood cannot diffusion ● with 0.2 membrane Glucose ● coalesce about a n D protein. These ● of D i g e S t i o n on the This the transfer intestinal type of concentration transport. move spaces by facilitated inside the diffusion villus and on villus. Starch diestin in the sa intestine Processes occurring in the small intestine that result in the digestion of starch and transpor t of the products of digestion to the liver. Starch digestion processes illustrates including some catalysis, CH important enzyme OH CH 2 specicity O OH and membrane permeability. Starch is OH a OH macromolecule, composed of many OH 2 O O O α-glucose OH monomers linked together in plants OH by CH OH CH 2 condensation reactions. It is a major plant-based pasta. Starch membranes intestine to foods such molecules so must allow be as bread, cannot potatoes pass digested in OH CH 2 O O of CH 2 OH 2 constituent OH and through the OH OH OH O OH ▲ O OH O small absorption. O O OH O OH OH Figure 9 Small por tion of an amylopectin molecule showing six α-glucose molecules, all linked bv 1,4 bonds apar t from All of the reactions involved in the digestion of one 1,6 bond that creates a branch starch are happen at molecule exothermic, very in slow but rates. without There a are catalyst two they types of The starch: enzyme forms ● amylose has unbranched chains of of by 1,4 amylopectin by1,4 the has bonds, molecule the amylase. digestion Saliva of both contains but most starch digestion occurs in the bonds; small ● begins is α-glucose amylase linked that starch chains with of some branched. α-glucose 1,6 bonds linked that make intestine, Any1,4 by this least bond in enzyme, four catalysed starch as glucose long by pancreatic molecules as there monomers. is can a amylase. be broken chain Amylose is of at therefore 285 6 H u m a n digested p H ys i o l o g y into fragments a mixture called of maltose two- and and three-glucose capillaries glucose maltotriose. enter Because of the specicity of its active site, break 1,6 bonds in amylopectin. the the amylopectin molecule containing single that dextrins. Digestion three on enzymes villus and amylase in the epithelium dextrinase dextrins of into cannot starch digest is digest of Maltase, maltose, layer is Blood by in glucosidase maltotriose the villus co-transport by facilitated with sodium the epithelium into ions. the It then uid in inside the villus. The dense walls that to consist of cells, with pores capillaries between have aiding the entry of larger glucose. glucose though The of blood hepatic glucose can be other villus the in portal and wall these vein to products capillaries of the absorbed is liver, by of venules small venules the to carried where to glycogen for storage. liver cells Glycogen and is moves in structure to amylopectin, but with interstitial more spaces ensures distance cells similar diffusion usual, ows converted by short Capillary these sub-mucosa intestine. and via into thin but carrying digestion microvilli glucose. absorbed of cells, than excess Glucose system. a called completed membranes cells. are epithelium travel a pores 1,6bond blood the to Fragments adjacent of to has amylase a cannot close only network 1,6 bonds and therefore more extensive of branching. mdein hsiica rcesses Use models as representations of the real world: dialysis tubing can be used to model absorption in the intestine. Living systems experiments inuence control out the all becomes are are of results. the experiments carried rather much out approach model of a process. Gastric the and can A Model, human is used very and in of factors difcult analysis it is parts of in results to carry has tissue can to systems. physiology cells of better to use a model Because it is For been culture investigate example is to that digestion carries of real represent much specic the out food simpler, aspects Dynamic computer-controlled stomach chemical to recent a when many organisms. system. be be only clones whole living a can research part a and them, Sometimes Another of It using using than on variables difcult. example, complex done model ▲ of Figure 10 The Dynamic Gastric Model with its inventor, Richard Faulks, adjusting the antrum mechanism mechanical samples. It can mimic be used to investigate the effects of diet, the permeable alcohol and other factors on simpler made from water freely, 286 example and but is cellulose. small not the use Pores molecules large to of the small gut, rather which than is also large more particles. digestion. Dialysis A wall drugs, of in or dialysis the tubing ions molecules. tubing to These allow pass through properties by tubing passive model occur active in can be diffusion used and transport living cells by and to model osmosis. other absorption It cannot processes that 6 . 1 D i g e S t i o n a n D a b S o r p t i o n mdein the sa intestine Use of dialysis tubing to model absorption of digested food in the intestine. To make a model length of dialysis a in the knot thread. of the tubing Pour in small tubing a or and tying suitable intestine, seal one with a mixture cut end piece of a by of foods Suggest tying cotton an improvements entirely need for different to the method method, of or suggest investigating the digestion. and 2 Investigating membrane permeability using seal the open end by tying with a piece of cotton a model of the small intestine thread. made Two in experiments this way are using model intestines suggestedhere: 1 Investigating the need for digestion using a model of the small intestine Cola drinks with different to represent tubing the Set it up for the one apparatus shown in gure 11 and contain is wall a mixture particle food in sizes. the small semi-permeable of the small of substances They so can be intestine. can be used Dialysis used to model intestine. leave hour. Predictions Cola contains glucose, phosphoric acid and Results caramel, To obtain the results for the experiment, bags out of each tube, open them complex and a brown solutions from them into separate test the liquids have four in the tubes. You should your samples starch into and two the of uid. halves other Divide and half for test each one of half Predict which to of will diffuse out of the bag, these with predictions. Predict whether the reasons bag will now gain samples colour. tubes for from added pour substances the carbohydrate take produce the a or lose mass during the experiment. these for Instructions sugars. 1 Make the model 2 Rinse the outside traces of cola intestine and of the then with bag dry to the cola inside. wash off any bag. 10 ml of tube 1% starch 10 ml solution of 1% top of bag sealed and 1 ml starch with cotton thread of 1% solution amylase cola, left to go at and 1 ml solution before being put of water water into the tube dialysis tubing maintained at 40°C pure water – minimum volume water water to surround the bag base of bag knotted of dialysis to prevent leaks (Visking) tubing ▲ Figure 11 Apparatus for showing the need for digestion Record all the results in the way that you think is spotting most appropriate. tile Conclusions and evaluation State make carefully from Discuss method the of all your the conclusions that you can results. strengths and investigating weaknesses the need for of this pH indicator digestion. ▲ Figure 12 Apparatus for membrane permeability experiment 287 6 H u m a n 3 Find p H ys i o l o g y the mass of the bag using an vary electronic for these instructions balance. concentration 4 When place you the are bag ready in to pure start water the in a Test the water around the bag test tube. 6 After at suitable 16 A minutes. suggested At each range is time lift mix the of the Follow out the the glucose water. testing 1, the 2, 4, bag 8 the the bag, water dry it for the and last nd its time, mass again time with intervals. strips. work experiment, remove 5 test and the electronic balance. and up and Conclusions down a few times to water in the a) tube, then do these Explain about ● Look it ● is Use carefully still a drops clear dropping of spotting the tile indicator. the at or the has with a water a to become pipette water Use and to see them narrow-range colour chart from brown. remove test whether to a in Dip the the change few b) a conclusions pH work out the permeability tests in Compare and that of mass and the of you the can in wall intestine. the villus dialysis and draw from tubing the bag. the [5] dialysis membranes absorption of the water contrast plasma of that epithelium tubing carry cells out in the [5] pH. c) ● the tests: a glucose record the test colour strip that into it the turns. water and Instructions Use the the results direction osmosis of of across your experiment movement villus of to water epithelium predict by cells. [5] TOK W s f vs c scvs s w s “”? In some adult humans, levels of lactase are too low continue to consume milk into adulthood are therefore to digest lactose in milk adequately. Instead, lactose unusual. Inability to consume milk because of lactose passes through the small intestine into the large intolerance should not therefore be regarded as abnormal. intestine, where bacteria feed on it, producing carbon The second argument is a simple mathematical one: a dioxide, hydrogen and methane. These gases cause high propor tion of humans are lactose intolerant. some unpleasant symptoms, discouraging consumption The third argument is evolutionary. Our ancestors were of milk . The condition is known as lactose intolerance. It almost cer tainly all lactose intolerant, so this is the has sometimes in the past been regarded as an abnormal natural or normal state. Lactose tolerance appears condition, or even as a disease, but it could be argued to have evolved separately in at least three centres: that lactose intolerance is the normal human condition. Nor thern Europe, par ts of Arabia, the Sahara and eastern The rst argument for this view is a biological one. Female Sudan, and par ts of East Africa inhabited by the Tutsi and mammals produce milk to feed their young ospring. Maasai peoples. Elsewhere, tolerance is probably due to When a young mammal is weaned, solid foods replace migration from these centres. milk and lactase secretion declines. Humans who 288 6 . 2 t h e b l o o D S y S t e m 6.2 t d ss Understandin Aicatins ➔ Ar teries convey blood at high pressure from the ➔ William Har vey’s discovery of the circulation of ventricles to the tissues of the body. the blood with the hear t acting as the pump. ➔ Ar teries have muscle and elastic bres in ➔ Causes and consequences of occlusion of the their walls. coronary ar teries. ➔ The muscle and elastic bres assist in ➔ Pressure changes in the left atrium, left maintaining blood pressure between pump ventricle and aor ta during the cardiac cycle. cycles. ➔ Blood ows through tissues in capillaries Skis with permeable walls that allow exchange of materials between cells in the tissue and the ➔ blood in the capillary. ➔ capillaries or veins from the structure of Veins collect blood at low pressure from the their walls. tissues of the body and return it to the atria of ➔ the hear t. ➔ Identication of blood vessels as ar teries, Recognition of the chambers and valves of the hear t and the blood vessels connected Valves in veins and the hear t ensure circulation to it in dissected hear ts or in diagrams of of blood by preventing backow. hear t structure. ➔ There is a separate circulation for the lungs. ➔ The hear tbeat is initiated by a group of Nature f science specialized muscle cells in the right atrium ➔ Theories are regarded as uncer tain: William called the sinoatrial node. Har vey over turned theories developed by the ➔ The sinoatrial node acts as a pacemaker. ➔ The sinoatrial node sends out an electrical ancient Greek philosopher Galen on movement of blood in the body. signal that stimulates contraction as it is propagated through the walls of the atria and then the walls of the ventricles. ➔ The hear t rate can be increased or decreased by impulses brought to the hear t through two ner ves from the medulla of the brain. ➔ Epinephrine increases the hear t rate to prepare for vigorous physical activity. 289 6 H u m a n p H ys i o l o g y Wiia Harve and the circuatin f bd William Harvey’s discovery of the circulation of the blood with the hear t acting as the pump. William Harvey discovery he of combined research theory is the earlier ndings for usually blood to produce ow in opposition and touring by experiments provided theory became Harvey the to of high for being be veins. It blood He too small tissues had of that the not eye been blood to the be seen capillaries about until the 1660, owing as he had circulation after from his of blood death, arteries to veins predicted. results theories As a ow vessels in heart, and result his the too body after theories to the heart that the heart of with arteries the far earlier and presence valves that was as showed through with return arteries seen linked though was not overcame his showed consumed the overall blood theory was accepted. major the that own his It demonstrate theory. therefore in 1628. it returns numerous in ne contemporary to veins in the body. capillaries naked to in as his He published the convincing body. also Harvey out with publishing that He by predicted equipment Blood must a with blood unidirectional, be out recycled. vessels the to pumped pumps is the previous his generally through blood proposed. and for backow. ow by falsied vessels prevent the Europe demonstrated larger rate that evidence of discoveries widespread also credited circulation are or too with a invented narrow hand by the to be seen with lens. Microscopes time that Harvey ▲ Figure 1 Har vey’s experiment to demonstrate that blood ow in the veins of the arm is unidirectional overturnin ancient theries in science Theories are regarded as uncer tain: William Harvey over turned theories developed by the ancient Greek philosopher Galen on movement of blood in the body. During in the the stimulated ways Renaissance, classical it almost writings literature hampered impossible interest of and the progress to was Greece arts, in question reawakened and but Rome. in science. the It This some became doctrines vital spirits arteries. to be then writers as Aristotle, Hippocrates, is from to Galen, pumped right passes 290 by vital to “animal the the body spirits ow spirits”, nerves to the by to the the which brain, are body. Harvey was unwilling to accept these Ptolemy without evidence. He made careful Galen. According the into distributed observations and the of doctrines and distributed of converted William such are Some and ventricle into the to the lungs blood of left and fro the is formed between heart. ventricle, becomes A in the little where “vital it the liver liver and blood meets spirits”. air The he deduced pulmonary the not that and existence veins, even and of did blood circulates systemic the enough him of to which through linking lenses for from circulations. capillaries, though powerful experiments, He the predicted arteries the see time and were them. 6 . 2 The following Generation was of extract is Animals, from Harvey’s published in book 1651 On when others: the he 73. hence it is that admonition of observation and our mind and to. goes senses, astray We are are, experience, in a science. I Isay, not to to rely of frequent science, be my the and what experience to of and truth actually so or you your in be natural therefore, own The on trust so have of as of at erroneous many said, things eyes method pursued held which the properly of Generation commonly to can anything the to one branch have take others whether no any judge. is foolish, things ask not appeal therefore almost personal I witness time to of concerning pursuing is appealed after would reader, me S y S t e m which student Animals: phantoms to strive from observation every frequently due experiment, after Diligent requisite senses the without reiterated appearances. therefore the the without b l o o D without become gentle And t h e this and enquire and omit themselves be not. Arteries Ar teries convey blood at high pressure from the ventricles acv Dscss qss to the tissues of the body. W h v’s ds Arteries the are body. They The The have arteries, vessels main thick walls Elastic and Elastic tissue a blood in pressure with tissue in from chambers muscle high work muscle convey pumping strong reaching artery that the their at heart heart that peak to walls the walls the heart the of the of used the tissues are the ventricles. pumps each facilitate are to do into pumping and to blood control of 1 to accept doctrines the without evidence. Are cycle. blood William Harvey refused there academic contexts ow. where it is reasonable to this. accept doctrines on the contains elastin bres, which store the energy that stretches basis of authority rather them at the peak of each pumping cycle. Their recoil helps propel the than evidence gathered blood on down the artery. Contraction of smooth muscle in the artery from primary sources? wall determines the diameter of the lumen and to some extent the 2 rigidity of the arteries, thus controlling the overall ow through Harvey welcomed them. questions and criticisms Both the elastic and muscular tissues contribute to the toughness of the of his theories when walls, which have to be strong to withstand the constantly changing and teaching anatomy intermittently high blood pressure without bulging outwards (aneurysm) classes. Suggest why he or bursting. The blood’s progress along major arteries is thus pulsatile, not might have done this. continuous. The pulse reects each heartbeat and can easily be felt in arteries 3 that pass near the body surface, including those in the wrist and the Can you think of examples neck. of the “phantoms and Each organ of the body is supplied with blood by one or more arteries. appearances” that Harvey For example, the hepatic each kidney is supplied by a renal artery and the liver by refers to? artery. The powerful, continuously active muscles of the 4 heart itself are supplied with blood by coronary Why does Harvey arteries. recommend “reiteration” of experiments? Arter was 5 Harvey practised as a doctor, but after the Ar teries have muscle and elastic bres in their walls. publication in 1628 of The wall of the artery is composed of several layers: his work on the ● tunica externa ● tunica media – a tough outer layer of connective circulation of the blood, tissue far fewer patients – a thick layer containing smooth muscle and elastic consulted him. Why bres made of the protein elastin might this have been? ● tunica intima – a smooth endothelium forming the lining of the artery. 291 6 H u m a n tunica externa p H ys i o l o g y tunica media tunica lumen intima (endothelium) ▲ Figure 3 Structure of an ar tery acv ms d sss Because ar teries are distensible, blood pressure in those that pass near the body surface can be measured relatively easily. A common method is to inate an arm cu until it squeezes the tissues (skin, ▲ Figure 2 The cardiovascular system. The main ar tery that supplies oxygenated blood to supercial fat as well as the tissues of the body is the aor ta, shown as the red vessel that emerges from the hear t the vessels themselves) and forms an arch with branches carrying blood to the arms and head. The aor ta continues enough to stop blood through the thorax and abdomen, with branches ser ving the liver, kidneys, intestines and ow. The pressure is then other organs released slowly until ow resumes and the operator Arteria bd ressure or instrument can hear the pulse again. The pressures at which blood ow stops and The muscle and elastic bres assist in maintaining blood pressure between pump cycles. resumes are the systolic and The blood entering an artery from the heart is at high pressure. The peak diastolic pressures. They are pressure reached in an artery is called the systolic widening the lumen pressure. It pushes the measured with a pressure wall of the artery outwards, and stretching elastic monitor. According to the bres in the wall, thus storing potential energy. American Hear t Association the desired blood pressures for adults of 18 years or older measured in this way are: At the for end the of mechanism the each stretched artery, heartbeat elastic saves called energy the the bres and diastolic to pressure squeeze prevents in the pressure, the the arteries blood in minimum from falls the sufciently lumen. pressure becoming too This inside low. Because systolic 90-119 mmHg it is relatively high, blood ow in the arteries is relatively steady and diastolic 60-79 mmHg continuous The circular contract, and in the the high muscles a density to of is driven in process lumen arterioles the wall called muscle control restricts of cells blood blood a pulsating of the heart. artery vasoconstriction, narrowed. Branches by Vasoconstriction arteries that ow ow to to called respond part the a to of ring increases opposite process, called vasodilation, when a body is they reduced pressure particularly hormone tissues. increases blood have various the so circumference arterioles downstream the form and neural Vasoconstriction that Figure 4 Blood pressure monitor the 292 in arteries. signals ▲ although it. they supply of and 6 . 2 t h e b l o o D S y S t e m Caiaries acv Blood ows through tissues in capillaries with permeable bss walls that allow exchange of materials between cells in Bruises are caused by the tissue and the blood in the capillary. damage to capillary walls and leakage of plasma and Capillaries are the narrowest blood vessels with diameter of about blood cells into spaces 10μm. They branch and rejoin repeatedly to form a capillary network between cells in a tissue. with a huge total length. Capillaries transport blood through almost all The capillaries are quickly tissues in the body. Two exceptions are the tissues of the lens and the repaired, hemoglobin is cornea in the eye which must be transparent so cannot contain any broken down to green and blood vessels. The density of capillary networks varies in other tissues yellow bile pigments which but all active cells in the body capillary wall consists are close to a capillary. are transpor ted away and The of one layer of very thin endothelium cells, phagocytes remove the coated by a lter-like protein gel, with pores between the cells. The remains of the blood cells wall is thus very permeable and allows part of the plasma to leak out by endocytosis. When you and form tissue uid. Plasma is the uid in which the blood cells are next have a bruise, make suspended. Tissue uid contains oxygen, glucose and all other substances observations over the days in blood plasma apart from large protein molecules, which cannot after the injury to follow the pass through the capillary wall. The uid ows between the cells in a healing process and the tissue, allowing the cells to absorb useful substances and excrete waste rate at which hemoglobin products. The tissue uid then re-enters the capillary network. is removed. The permeabilities particular not proteins others. repair and tissues of capillary and other Permeabilities remodel that they walls large can also themselves differ between particles change to over continually in tissues, reach time enabling certain and response tissues but capillaries to the needs of perfuse. Veins Veins collect blood at low pressure from the tissues of the body and return it to the atria of the hear t. Veins transport heart. By arteries. and the now Veins wall therefore than Blood by ow shorter sitting Each is this other carry in because the of falls arms The the it a by in heart. It is on by It carries regarded carries is at vein by as low veins bres. of was is the in as the arteries They more blood like venous can blood in the and unusual from portal pressure it veins from on them muscle Walking, ow. example the because head it than relatively blood in does stomach rather is a pump. For the vein so a exerted makes blood veins. veins blood a it wall pressures more is atria exercise. improves subclavian a Contraction adjacent portal the than hold person’s and or to thick thus vigorous one as elastic and muscles. greatly the and gravity back pressure have sedentary skeletal hepatic to wider during served lower muscle squeezes is networks need much assisted it liver. much fewer dgeting to blood at 80 % body the back to the is so just veins. blood intestines far especially the from is become veins wider of jugular to capillary therefore Around even part blood not proportion and or from contains tissues carried the the do dilate arteries. though blood not and an artery thin. 293 6 H u m a n p H ys i o l o g y Vaves in veins acv Valves in veins and the hear t ensure circulation of blood Sd d by preventing backow. Pocket valves and vein walls become less ecient Blood with age, causing poor backow pressure venous return to the hear t. heart. Have you ever performed three To in veins towards the maintain cup-shaped is sometimes capillaries circulation, aps of and so low that there insufcient veins contain is return pocket a of danger blood valves, of to the consisting of tissue. gymnastic moves such as If ● blood starts to ow backwards, it gets caught in the aps of the headstands or handstands, pocket valve, which ll with blood, blocking the lumen of the vein. or experienced very high g-forces on a ride at an When ● sides amusement park? Young ow people can mostly do any blood of the ows vein. towards The the pocket heart, valve it pushes therefore the aps opens and to the blood can freely. of these activities easily These valves allow blood to ow in one direction only and make but older people may not efcient use of the intermittent and often transient pressures provided be able to. What is the by muscular and postural changes. They ensure that blood circulates in explanation? the body rather than owing to and fro. Identifin bd vesses Identication of blood vessels as ar teries, capillaries or veins from the structure of their walls. Blood at vessels their can structure. be identied Table 1 as below a Diameter Larger than 10 μm arteries, gives capillaries differences or that veins may looking beuseful. C Around 10 μm by V Variable but much larger than 10 μm ▲ Figure 5 Which veins in this gymnast will need valves to help with venous return? Relative Relatively thick thickness wall and narrow wall with variable of wall and lumen but often wide Extremely thin wall diameter of Relatively thin lumen lumen Number of Three layers, Only one layer – the Three layers – layers in wall tunica externa, tunica intima which tunica externa, media and intima. is an endothelium media and intima These layers may consisting of a be sub-divided to single layer of very form more layers thin cells Abundant None Small amounts None None Present in many Muscle and elastic bres in the wall Valves ▲ Figure 6 Ar tery and vein in transverse section. veins The tunica ex terna and tunica intima are stained more darkly than the tunica media. Clotted blood is visible in both vessels 294 ▲ T able 1 6 . 2 t h e b l o o D S y S t e m The dube circuatin lungs There is a separate circulation for the lungs. pulmonary There are valves in the veins and heart that ensure a one-way ow, circulation so blood single circulates circulation. oxygenated. pressure body for to and gas Blood through Blood After ow then is back exchange to are capillaries pumped owing directly, in arteries, the high the heart. In with cannot the slowly, contrast, blood and veins. pressure gills relatively supplied lungs at through but capillaries by withstand to blood Fish their still gills has other organs the lungs used separate high to a be enough to a have of by the mammals circulation. pressures so blood is heart pumped to capillaries to the them of heart therefore the to at lungs be have relatively the pressure. pressure pumped two low again separate of the before it After blood goes passing is to low, other through so it must organs. the return Humans circulations: systemic circulation ● the pulmonary ● the systemic circulation, to and from the lungs other circulation, to and from all other organs, including the organs heart Figure 7 muscles. shows pulmonary from that the has essential mixed. systemic been that The different the double circulation circulation, oxygenated blood heart circulation receives is pressures by owing and the to therefore a simplied the from double to the blood systemic pulmonary and a separately in deoxygenated these two It receives is Figure 7 The double circulation returned blood therefore circulations delivering ▲ The has circulation circulation. pump, two form. that blood is not under circulations. semilunar valve aorta Heart structure pulmonary artery Recognition of the chambers and valves vena cavae of the hear t and the blood vessels pulmonary veins connected to it in dissected hear ts or in diagrams of hear t structure. ● The heart pump has blood two to sides, the left systemic and and right, that pulmonary circulations. semilunar valve ● Each a side ventricle arteries the ● of Each that and veins side the an and of heart has pumps atrium passes the atrioventricular it heart valve the ventricle and a the ventricle and the two blood that to out into collects the has chambers, from ventricle. two between semilunar the blood valves, the an atrium valve and between atrioventricular right atrium ● Oxygenated blood valve artery. ows into the left side of left ventricle right ventricle the heart through the lungs and the pulmonary veins from septum out through the aorta. ▲ Figure 8 Structure of the hear t 295 6 H u m a n ● p H ys i o l o g y Deoxygenated of the heart blood through ows the into vena the left cava side and out 4 Left ventricle in Identify the pulmonary with The heart is structure. is a by a complicated The doing a a way heart, are three-dimensional learn A fresh with dissecting instruments to dissection. mammalian attached, best about or structure specimen blood dish its vessels board scalpel, line by the removing around and the has a if vessels Identify thin-walled in have incision gure Look cut an at blood smooth 9. This the vessels. wall, as shown should thick Using by open muscular a the up wall the that through. 5 Atrioventricular valve membranes them. It of dissecting needed. blood ventricle. pattern make X ventricle. Extend up left tree-like dashed you still and a sharp left of 1 Ar teries and veins Tidy the arteries. attached and the to other the heart tissue thick-walled from arteries the incision necessary until further you can of the atrioventricular to the sides inverting towards see valve. of the left into the atrium. the the two Tendons ventricle atrium thin aps attached prevent the valve veins. 6 Left atrium and pulmonary vein 2 Pulmonary ar tery and aor ta Push into a glass the heart through of the the rod artery, rod or through wall has other of reached. through which right through you left the the thinner-walled which blunt-ended arteries heart to Identify you will ventricle, will reach instrument and where the the the end pulmonary reach and feel the the thicker-walled ventricle. the heart so that side uppermost underneath. The as the artery, now there as surface of Extend the either in dorsal aorta is 9. the side its atrium. is no wall has incision with the the wall atrium the and (there a of the look it. left of outer already scissors, atrium the surprisingly The appearance. have with at opening be you or Look may will inside wrinkled that scalpel vein. It blood thin the as to far wall made, cut as of the the pulmonary vein or two). 7 Aor ta gure and left pulmonary veins pulmonary is the small through aorta, 3 Dorsal and ventral sides Lay Identify of behind The dorsal an the ventral side animal is itsback. Find of its the through and the aorta lumen, the smooth and of the towards inner the measure millimetres. wall working stretching again in aorta, the left surface wall to of see the Using diameter scissors, starting at ventricle. the how aorta tough end Look and it cut its at try is. 8 Semilunar valve aorta Where the will three be aorta exits the cup-shaped left ventricle, aps in the there wall. These pulmonary form the semilunar valve. Try pushing a blunt artery right instrument artrium into the aps to see how blood left atrium owing closing backwards the pushes the aps together, valve. X 9 Coronary ar tery coronary artery Look carefully aorta, near the at the inner semilunar surface valve. A of the small hole Y should be visible, coronaryarteries. lumen ▲ 296 Figure 9 Ventral view of the ex terior of the hear t the of wall this of which the Measure artery. the is heart The the opening diameter coronary with to oxygen the of arteries and the supply nutrients. 6 . 2 t h e b l o o D S y S t e m 10 Septum Make near line in a transverse the base marked of Y millimetres ventricles and (gure10). bres, in through ventricles, gure 9. the walls of the septum septum help to the along Measure of The which section the of the the left stimulate dotted thickness and between contains heart the right them conducting the ventricles left ventricle right ventricle tocontract. septum ▲ Figure 10 Transverse section through the ventricles acv Atherscersis Sc d fc f Causes and consequences of occlusion of the coronary ar teries. Discuss the answers to One of the commonest development of fatty current tissue health called problems atheroma in is atherosclerosis, the artery wall the these questions. adjacent 1 to the endothelium. Low density lipoproteins (LDL) containing fats Why are the walls of the and atria thinner than the cholesterol accumulate and phagocytes are then attracted by signals walls of the ventricles? from fats endothelium and cells cholesterol migrate bulges cells into to the by form smooth endocytosis a lumen and tough cap muscle. and over narrowing it The grow the and phagocytes very large. atheroma. thus Smooth The impeding engulf artery blood the muscle 2 What prevents the atrioventricular valve wall from being pushed into ow. the atrium when the Small traces of atheroma are normally visible in children’s arteries ventricle contracts? by the age of ten, but do not affect health. In some older people 3 atherosclerosis becomes much more advanced artery becomes but often Why is the left ventricle goes wall thicker than the unnoticed until a major so blocked that the tissues it right ventricle wall? supplies become compromised. 4 Coronary occlusion is a narrowing of the arteries that supply Does the left side of the blood hear t pump oxygenated containing oxygen and nutrients to the heart muscle. Lack of oxygen or deoxygenated blood? (anoxia) ability blood cap to causes contract, circulation covering formation heart The pain, and of atheroma heart some angina, beats of its blood that acute heart can are shown not the to faster are be sole impairs as out ruptures, block problems. atherosclerosis been but clots and muscle sometimes of have the with as atheromas cause causes factors so known not This yet of tries of is muscle’s The in to Various increased risk brought by the coronary the sub-topic understood. an own supply of blood, the blood Why does the wall of the hear t need its brous stimulates supplying with 5 maintain described fully the to action. which arteries associated causes it the of ar teries? 6.3. 6 Does the right side of the hear t pump a greater volume of blood condition: per minute, a smaller ● high ● chronic blood concentrations of LDL (low density lipoprotein) volume, or the same obesity high or blood glucose concentrations, due to overeating, volume as the left? diabetes 297 6 H u m a n p H ys i o l o g y acv ● chronic other high blood pressure due to smoking, stress or any cause C d c ccs ● consumption of the of trans fats, which damage the endothelium artery. A chemical called carnitine that is found in cer tain foods There are also some more recent theories that include microbes: is conver ted into TMAO by ● infection ● production of the artery wall with Chlamydia pneumoniae bacteria in the gut. Find out what foods contain the highest concentrations of trimethylamine N-oxide (TMAO) by microbes in theintestine. of carnitine and discuss whether this nding should inuence dietary advice. ▲ Figure 11 A normal ar tery (left) has a much wider lumen than an ar tery that is occluded by atheroma (right) The sinatria nde The hear tbeat is initiated by a group of specialized muscle cells in the right atrium called the sinoatrial node. The heart is stimulation meaning heart almost is a that muscle adjacent The cells, region cause the 298 cardiac the of generated they the also The at heart of in as node. its the rate the other sinoatrial of cells muscle node its rate have are of of the The cells without myogenic, membrane and this of a activates therefore the spontaneous wall few but therefore cells called contracts fastest. in cells, contract is contracts group the cells itself. cell fastest muscle These A of can contraction muscle when the muscles The contract. with membranes cycle. in the special sinoatrial the body neurons. depolarizes contraction because Figure 12 The sinoatrial node is so group membranes. ▲ it cell in motor simultaneously small called unique from of they of the have initiates rst the to beating right atrium, proteins that extensive each heartbeat, depolarize in each 6 . 2 t h e the pace for If becomes b l o o D S y S t e m Initiatin the heartbeat The sinoatrial node acts as a pacemaker. Because the the beating defective, articial with sinoatrial of its the output electrodes in be This is implanted place of initiates and may pacemaker. heartbeat node heart the is each often regulated an in or the wall of the even electronic sinoatrial heartbeat, called sets replaced device, the it pacemaker. entirely placed heart that it under by the initiate an skin each node. Atria and ventricuar cntractin The sinoatrial node sends out an electrical signal that stimulates contraction as it is propagated through the walls of the atria and then the walls of the ventricles. The sinoatrial sends This out can across a which so to After to a the the initiates the of of a the for electrical be signal cells signal contracting throughout interconnections can the all by spreads are signal passes second heartbeat that there electrical bre a signal because each tenth propagation atria node electrical happen branched than an in propagated. on the causes to the to Also the others. receive whole simultaneously walls between several atria and the of the bres It the both of atria. adjacent takes signal. left bres are and less This right contract. time delay ventricles. blood that propagated contract they about time are throughout and stimulation of The pump of the 0.1 seconds, delay holding the blood allows into walls out heartbeat of into are the the the the electrical time for the ventricles. ventricles, arteries. included in signal atria The to is conveyed pump signal is stimulating Details Option of the ▲ then them to Figure 13 Hear t monitor displaying the hear t rate, the electrical activity of the hear t and the percentage saturation with oxygen of the blood electrical D. TOK W s c dcs k: csqcs? There are some circumstances in which prolonging the life of an individual who is suering brings in to question the role of the physician. Sometimes, an active pacemaker may be involved in prolonging the life of a patient and the physician receives a request to deactivate the device. This will accelerate the pace of the patient’s death. Euthanasia involves taking active steps to end the life of a patient and it is illegal in many jurisdictions. However, there is a widely accepted practice of withdrawing life-sustaining interventions such as dialysis, mechanical ventilation, or tube feeding from terminally ill patients. This is often a decision of the family of the patient. The withdrawal of life suppor t is seen as distinct from euthanasia because the patient dies of their condition rather than the active steps to end the patient’s life in the case of euthanasia. However, the distinction can be subtle. The consequence is the same: the death of the patient. The intent can be the same: to end the patient’s suering. Yet in many jurisdictions, one action is illegal and the other is not. 299 6 H u m a n p H ys i o l o g y The cardiac cce Pressure changes in the left atrium, left ventricle and aor ta during the cardiac cycle. The pressure chang e s ventricle of a cycle cardiac understand what the are them occurs below he a r t at Typical it a is ea ch heart volumes the in r a te g ur e of of 75 To wi th per is a l so of the d i r e ctio n of blo od o w to achamber of the semilunar arterial – 0.1 The contract relatively which blood small causing pressure pumps blood ventricles, drains a rapid – 0.45 The semilunar from through the in – them 0.15 are arteries as but in the atri a as into the m fr om the ve ins seconds and of the pressure ventricular inside the muscles ventricles drops below the pressure in closed and blood gradually causing the semilunar valves no continues more is to The atrioventricular valves remain contract, build up atrioventricular 0.45 in. – 0.8 seconds Pressure in the ventricles pressure in the atria with a so drops the below that valves causes to semilunar valves the Blood and close. remain open. from from slow the there increase veins into in drains the into the ventricles, pressure. closed. vein 25 ml atrium 45 ml atrium contracts 25 ml atrioventricular valve atrioventricular valve closed open atrioventricular valve valve open ventricle ventricle relaxing contracting ventricle relaxing ventricle 70 ml semilunar valve artery valve closed valve open diastolic systolic semilunar valve closed diastolic the body 0 0.1 0.15 0.4 0.45 0.8 time (seconds) Figure 1 4 One cardiac cycle is represented on the diagram, starting on the left with contraction of the atrium. Vertical arrows show ows of blood to and from the atrium and ventricle 300 the atrioventricular rapid a ▲ closed. to ow pumped close. blood drops ● tissues of the seconds ventricles pressure The ris e s ll. contraction valves ● the the valves. valves the minimum The maximizing open ● ● blood into atria the ● pressure 0.1 and increase, to along open ventricles so but arteries, atrioventricular its rises arteries pressure. slowly they rapidly the The the transiently Pressure wanes ● valves from the seconds atria ● to ventricles in hea r t. 0.4 ● the or and 0.0 in pressure pumped blood from the an ● indication seconds pressure arteries, m in u t e . a nd 0.4 the Fi g ur e 1 4 tim in g s s hown – The above ap pr e cia t e cy c le . be a ts ar e 0.15 ● d u ri n g 15 . to the e ve nts, blood an d a or ta ne ces s ar y s ta g e the of a tr ium the s ho wn summarize s assuming in a nd atria causing 6 . 2 t h e b l o o D S y S t e m D-sd qss: Hear t action and blood pressures Figure 15 ventricle during one second Deduce from the when the start 2 Deduce 3 The the artery in the to the when one blood atrium and pressures on of atrium, the the heart, heart. pumped ventricle. Give both times. ventricle atrioventricular the of being the end the life is in side valve [2] starts is to the contract. ventricle gH mm / erusserp 1 shows and [1] 120 ar tery 100 valve 80 between when the the atrium and the atrioventricular ventricle. valve State closes. [1] 60 4 The semilunar the ventricle the semilunar valve and is the the valve artery. between State when 40 valve 5 Deduce when the 6 Deduce when blood opens. [1] semilunar valve closes. [1] 20 from the ventricle is to being the pumped artery. atrium Give 0 both 7 the Deduce start and when the the end volume times. of [2] blood in the –20 ventricle is: 0 a) at a maximum 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 [1] time / s b) at a minimum. [1] Figure 15 Pressure changes during the cardiac cycle ▲ Chanin the heart rate acv ls sds The hear t rate can be increased or decreased by impulses Sounds produced by blood brought to the hear t through two nerves from the medulla ow can be heard with a of the brain. The sinoatrial simple tube or stethoscope node responds to signals branches of two brain cause called the healthy rate. Signals act reects Low the rate other the centre its the pH carbon pressure, in the can nerve and the region in and to inputs the of the from of a times of the from for the ow of blood out of nerves the hear t can be felt as the pulse in a peripheral ar tery. resting two hear t. The consequences of this whole cardiac cycle the In the These placed on the chest near the heart signals heartbeats. rate. of the medulla one three brake of include from frequency decrease beating These Signals oxygen dioxide low a increase throttle receives for heart. centre. increase the like and its blood outside rhythm originating to people cardiovascular pressure the cardiovascular rather blood ● nerves from blood sets from pacemaker young branches The the that nerve (a) car. receptors concentration. that The pH monitor of the concentration. oxygen concentration and low pH all (b) suggest rate of carbon that the blood to heart the rate needs tissues, to deliver speed more up, to increase the oxygen and remove concentration and high ow more dioxide. ▲ ● High blood indicators pressure, that the high heart oxygen rate may need to slow pH are all Figure 16 T aking the pulse: (a) radial pulse (b) carotid pulse down. 301 6 H U M A N P H YS I O L O G Y Epinephrine Epinephrine increases the hear t rate to prepare for vigorous physical activity. The by sinoatrial increasing called adrenalin secretion when In of or ▲ Figure 1 7 Adventure spor ts such as rock is Thi s p ro duce d phy s i ca l is to ep ine ph r in e h or m o n e by the contr ol l e d acti vi ty ma y be th e in al s o a dr e na l by e pi ne phr in e is g la n ds . br a in n e c es s ar y has the the b l ood , s ome t im es an d Th e r is es be c a us e nic kn am e of a “ g h t or hormone”. the past prey athletes so and re s ponds r ate . opportuni ty. S o when epinephrine for also he a r t epinep hr i ne vigorous threat ight nod e the that or when often their activity huma ns woul d ha v e wer e be e n thr e a tened use hear t p r e - r a ce r a te is hun t e r- ga t h e re r s se cret e d by a p re da t or. ro utine s a l re a dy whe n to In the s tim u la t e inc r ea s ed ra t h e r hu m an s th an we re mo de rn a dr e na l in wh en vi g or ou s fa r m e r s, hu n t i ng wo rl d se c r et i on ph ys ic a l begins. climbing cause epinephrine secretion 6.3 Def ence against inf ectious disease Understanding Applications ➔ The skin and mucous membranes form a ➔ Causes and consequences of blood clot primary defence against pathogens that cause formation in coronary ar teries. infectious disease. ➔ ➔ Cuts in the skin are sealed by blood clotting. ➔ Clotting factors are released from platelets. ➔ The cascade results in the rapid conversion of Eects of HIV on the immune system and methods of transmission. ➔ Florey and Chain’s experiments to test penicillin on bacterial infections in mice. brinogen to brin by thrombin. ➔ Ingestion of pathogens by phagocytic white Nature of science blood cells gives non-specic immunity to diseases. ➔ ➔ ➔ Production of antibodies by lymphocytes in Florey and Chain’s tests on the safety of response to par ticular pathogens gives specic penicillin would not be compliant with current immunity. protocols on testing. Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells. ➔ Viral diseases cannot be treated using antibiotics because they lack a metabolism. ➔ Some strains of bacteria have evolved with genes which confer resistance to antibiotics and some strains of bacteria have multiple resistance. 302 Risks associated with scientic research: 6 . 3 D e F e n C e a g a i n S t i n F e C t i o u S D i S e a S e Skin as a barrier t infectin The skin and mucous membranes form a primary defence against pathogens that cause infectious disease. There are inside the are many different human opportunistic commonly inside The a live primary entry of and defence is damage. it. of the and Sebaceous can that are environment Some invade cause against a body and disease against associated can called is the and hair they only barrier physical with can are pathogens physical that grow microorganisms the specialized provides protection glands the disease. are body and in a they Others Microbes tough pathogens cause although body. layer microbes and outside human outermost body also survive pathogens. skin. Its against the chemical follicles and they Figure 1 Scanning electron micrograph of secrete a slightly and lowers called skin pH. sebum, The which lower pH maintains inhibits the skin moisture growth of and bacteria on the surface of teeth. Mucous bacteria membranes in the mouth prevent these and other microbes from invading body tissues fungi. Mucous areas and chemical membranes such as foreskin the and are nasal the a thinner passages vagina. and and The softer other mucus type of airways, that these skin the that head areas of is of found the skin in penis acv secrete i sk is a sticky solution of glycoproteins. Mucus acts as a physical barrier; A digital microscope can be pathogens and harmful particles are trapped in it and either swallowed used to produce images of or expelled. It also has antiseptic properties because of the presence of the dierent types of skin the anti-bacterial enzyme lysozyme. covering the human body. Figure 2 shows four images Cuts and cts produced in this way. Cuts in the skin are sealed by blood clotting. When The the clotting. a skin bleeding The semi-solid blood the and is blood gel. pathogens to blood stops seals up pressure. infection until vessels after emerging This blood barrier cut, usually new a from the tissue has it a are cut is by grown and of from Clots heal the start a to bleed. process being prevents important skin. to and because changes also the severed time wound Clotting provided in short a further because prevent called liquid loss cuts entry to of breach of cut. pateets and bd cttin Clotting factors are released from platelets. Blood a clotting catalyst for important blood The that vessels process Platelets smaller than forming trigger a off next cascade is clotting either damage clots only to temporary or plug. clotting can result vessels They platelets cells. occurs, then of clots because which very if it produces rapidly. occurs It is inside blockages. circulate blood each blood control, cause if that white blood reactions, a strict occurs fragments red of As under resulting cellular the a reaction. clotting the of are involving involves the release in the When platelets release the clotting blood. a cut or are other aggregate clotting factors. They at injury the factors site that process. ▲ Figure 2 303 6 H u m a n p H ys i o l o g y Fibrin rductin The cascade results in the rapid conversion of brinogen to brin by thrombin. platelets red blood cell The cascade from thrombin. into lymphocyte of platelets the reactions quickly Thrombin insoluble platelets and also exposed to Figure shows the that in turn brin. blood air it occurs results in after brin cells. to The the the a hard of soluble forms a clot of an clotting enzyme protein mesh resulting form release production converts The dries the in is cuts factors called brinogen that initially a traps gel, more but if scab. phagocyte 4 red blood cells trapped in this brous mesh. Figure 3 Cells and cell fragments from blood. Lymphocytes and phagocytes Crnar thrbsis are types of white blood cell Causes and consequences of blood clot formation in coronary ar teries. In patients in the coronary with to the semilunar supplyingthe respiration. thrombosis If the heart then coronary arteries. oxygen The is the and arteries to of disease, arteries carry glucose name formation deprived unable They medical coronary is valve. heart These of for produce blood to needed by clot blood clots blocked and in ATP by off sometimes from wall of cardiac is the by nutrients. sufcient clots the a blood become oxygen blood branch a a the the muscle blood Cardiac aerobic close heart, bres thrombus. coronary form aorta for cell Coronary arteries. clot, part muscle of cells respiration the are and their Figure 4 Scanning electron contractions become irregular heart quivering and uncoordinated. The wall of the micrograph of clotted blood with makes movements called brillation that do not pump brin and trapped blood cells blood effectively. naturally or Atherosclerosis atheroma damaged and a of the risk There of are increased calcium some risk the of Patches of fatal unless arteries coronary the the of occlusion, it resolves and arteries. arteries artery tends wall atheroma is Where to become hardened sometimes damage to the rupture of atheroma coronary ● smoking ● high blood cholesterol ● high blood pressure ● diabetes ● obesity ● lack factors that thrombosis are and correlated heart rupture all increase with an attacks: concentration Figure 5 Early inter vention during a of exercise. heart attack can save the patient’s life so it is important to know what to do by being trained 304 Of course correlation nonetheless advise does not patients to prove avoid causation, these risk but by capillary thrombosis. well-known of in especially, salts. hardening prove endothelium Coronary coronary can intervention. occlusion the roughened; lesion. epithelium, condition medical causes develops deposition causing This through doctors factors if possible. 6 . 3 D e F e n C e a g a i n S t i n F e C t i o u S D i S e a S e phactes Ingestion of pathogens by phagocytic white blood cells gives non-specic immunity to diseases. If microorganisms membranes of defence. and to that sites digest infected, of formation of past are the with white physical white different out infection. There of liquid called the are and When attracted, mucous the blood walls next cell. of pathogens lysosomes. phagocytes skin provide white in engulf of cells of pores they from barriers blood types through enzymes numbers a the body, many squeeze them large get enter There phagocytes move and line Some are capillaries by and endocytosis wounds resulting become in the pus. Antibd rductin Production of antibodies by lymphocytes in response to par ticular pathogens gives specic immunity. If microorganisms the body, recognized response. to as an as Any in antigen Antibodies Each can small The are a There array are body. However, the small group a A to Antibodies variable that helps of types just the they an of the skin surface stimulate immune response is pathogen. that for too a of a and invade pathogens specic response the The on are immune is referred production antibodies to antibodies. few the to ght that a that produce has and have the two of bind to in lymphocytes. our many initially not bodies because the to we cell cells of produce infected division appropriate type are quantities have types previously of of produced of the infection. functional antigen pathogen is plasma enough clear but stimulate the called large called of lymphocytes specic the This each pathogen that cell antibody, producing secrete proteins blood of pathogen pathogen binds white type lymphocytes they the large of of one different antigens and body a pathogen readily preventing enter on and one regions: another of a a hyper- region number of ways, these: making more ● the by lymphocytes control are particular control clone days region including ● large few antibody of and immune therefore to the within a barriers stimulates lymphocytes antibodies antibody. that produces of body specic to physical molecules pathogen. vast numbers enough the produced lymphocyte antibody. by response that the other chemical on produce past and foreign antigen. antibodies an get proteins the Antibodies more recognizable to phagocytes so they are engulfed viruses from docking to host cells so that they cannot cells. only persist in the body for a few weeks or months Figure 6 Avian inuenza viruses. In this and electron micrograph of a virus in transverse the plasma cells that produce them are also gradually lost after the section, false colour has been used to infection has been overcome and the antigens associated with it are no distinguish the protein coat that is recognized longer present. However, some of the lymphocytes produced during an as antigens by the immune system (purple) infection are not active plasma cells but instead become memory cells from the DNA of the virus (green) 305 6 H u m a n p H ys i o l o g y that the are very same active and infectious or long-lived. pathogen divide to disease memory cells These infects the produce involves that memory body plasma either allow cells again, cells having rapid remain in which very rapidly. antibodies production inactive case of unless they become Immunity against the to an pathogen, theantibody. Huan iundecienc virus Eects of HIV on the immune system and methods of transmission. The production system types is of human and is a a of antibodies complex process lymphocyte, including immunodeciency destroys helper progressive antibodies. In loss the by the early The diseases The a invades of infection, to system makes antibodies against can be detected in a person’s body, to be HIV is HIV . and uses of its they spreads retrovirus reverse once that has genes transcriptase it has to entered a made make host of DNA which helper T-cells are cell. destroyed blood people. RNA can copies considerably and anti-retroviral so antibody ineffective infections by a called said syndrome to have (AIDS). HIV the infection. body for The a virus short only time normally only occurs if there is and blood can be slowed contact There drugs. In that strike, production most a group which down of healthy immune sexual be ways in and uninfected which this the intercourse, mucous during which membranes of abrasions the penis and by can cause transfusion becomes products opportunistic system. infected various minor bleeding HIV-positive eventually would between are HIV easily of such infected as blood, Factor or blood VIII fought ● off is is conditions The by ● patients by outside vagina using person of for several occur: to varies the of together syndrome deciency infection, HIV-positive. genes at existing the present, HIV collection are ● rate is of A If to a When immune infection said stages sarcoma. conditions HIV survives these latter the AIDS immune or acquired produce the Kaposi’s syndrome. due consequence to for example different T-cells. (HIV) capacity stages diseases immune includes helper virus T-cells. of the and Several sharing of hypodermic needles by intravenous of drugusers. these are normally so rare that they are marker Antibitics Antibiotics block processes that occur in prokaryotic cells but not in eukaryotic cells. An antibiotic Most in is prokaryotes kill The a antibiotics bacteria chemical are but inside processes transcription, not the antibacterial fungi on which example is by with they fungi antibiotics ribosome penicillin. It is were feed. the growth are harm and discovered By secreting by in bacteria of their some microorganisms. that therefore bacterial function of processes can causing growth produced the block and saprotrophic both inhibit They without antibiotics compete saprotrophic inhibits eukaryotes body targeted These matter in translation, Many that antibacterial. to occur used human DNA cell be replication, wall formation. saprotrophic for the dead antibacterial bacterial strains of to cells. fungi. organic antibiotics, competitors. the Figure 7 Fleming's petri dish which rst fungus, but only when nutrients showed the inhibition of bacterial growth by penicillin from a mycelium of Penicillium 306 bacteria would be harmful. are scarce and An Penicillium competition with 6 . 3 D e F e n C e a g a i n S t i n F e C t i o u S D i S e a S e acv Testin eniciin Wd aiDS D Florey and Chain’s experiments to test penicillin on The red AIDS awareness bacterial infections in mice. ribbon is an international Howard Florey in the late to control 1930s Ernst that bacterial penicillin, Chain’s and formed investigated infections. discovered team Chain by developed the The a method research use most Alexander a of chemical promising Fleming of team in growing of Oxford symbol of awareness and substances these 1928. the in Florey fungus support for those living with was HIV . It is worn on World AIDS and Day each year – December 1st. Penicillium Are you aware how many in liquid culture in conditions that stimulated it to secrete penicillin. people in your area are They also developedmethods for producing reasonably pure samples aected and what can be of penicillin from the cultures. done to suppor t them? The test rst penicillin whether tested infected all the was on Larger rose sadly to of eye. the of in brain He were died. had and He companies larger that incurable it in was a a do the hours were tests on acute of life- the face on for policeman and four days penicillin from and ran his out and infection. were small of the and cured child wall United of the ve of who the more their States had an infection carrying the child died burst. then more effective patients infections, artery infection, artery allowing highly penicillin next 43-year-old scratch supplies the of 24 quantities. penicillin cured quantities, bacterial a when the a They with Four Within given an produced All was although had by infected should larger the weakened hemorrhage much but were tested. four to humans. penicillin. they He given in needed pneumonia. produced, test. from penicillin the that caused was died with much been human and them conrmed previously required they deliberately from but considerably, This brain Pharmaceutical penicillin of dead but infections were decided had plates, death injections infection bush. infections one the suddenly rst relapse quantities behind which the mice were which agar bacterial cause Chain improved acute blood mice bacterial a Eight that given and on control penicillin for a suffered but were enough condition with mice. patients, chosen thorn he on Florey threatening a would untreated human bacteria bacteria mice healthy. When it it Streptococcus killed began to extensive treatment for produce testing, many infections. Figure 8 Penicillin – the green ball represents a variable part of the molecule 307 6 H u m a n p H ys i o l o g y peniciin and dru testin Risks associated with scientic research: Florey and Chain’s tests on the safety of penicillin would not be compliant with current protocols on testing. When any new that will prove it patients These or that risks are are it that of tests the will is introduced ineffective cause on it strict must animals humans. tested is on to side and a with on drug last testing. that there Also small pure passes the disease very large whether the drug tocheck that numbers is there of effective are no patients in all severe to after could the there a very was easily samples and methods tested a have that could the that brief new on period type been they drug of used human of animal drug severe side they were using have been side and effects. were effects not from impurities. the other were all on hand, were cured the the point patients of death that and they used several and of their infections as a result of the common treatment. Because of expeditious effects. testing There are problems some famous during cases testing or of drugs after be causing Thalidomide was quickly release. introduced in the a treatment for various mild when sickness for that drug more birth on it in was found pregnant purpose. the than The fetus deformities relieve side had 10,000 to women been children would in be than possible June would introduced 1944 far today. now more During penicillin was the used to wounded bacterial soldiers and infection the was number greatly of deaths reduced. prescribed of the tested were the than landings was morning was effects not before it risk-taking conditions from but greater penicillin 1950s treat as with allowed, D-day ● only Penicillin experimental side the They test patients or with tests On involve today penicillin. patients effects. the The for all Initial then if drug risks or protocols Only treat. are some follow. patients intended there in harmful by companies healthy drug is be performed numbers these to minimized pharmaceutical tests drug and born problem with was recognized. In ● 2006 six TGN1412, of leukemia. All long-term very have six rapidly organ recovered, damage unlikely been volunteers protein that allowed to to diseases became failure. they their Florey carry were developed autoimmune multiple volunteers is new treatment suffered It healthy a may and very and ill and Although have immune out given for systems. Chain tests on the suffered would a new Figure 9 Wounded US troops on Omaha beach 6 June 1944 Viruses and antibitics Viral diseases cannot be treated using antibiotics because they lack a metabolism. Viruses living instead own 308 are non-living cells. of They having means of use a and the can only chemical metabolism transcription or of reproduce processes their protein of own. when a They synthesis they living do and are host not they inside cell, have rely their on the 6 . 3 host cell’s These enzymes processes for ATP cannot be synthesis targeted and by D e F e n C e other drugs as a g a i n S t metabolic the host i n F e C t i o u S D i S e a S e pathways. cell would also acv bedamaged. Dss w All of the commonly chloramphenicol not effective prescribe antibiotics and against them and used for antibiotics tetracycline viruses. a viral increases Not control only infection, in such is but antibiotic as penicillin, bacterial it it streptomycin, infections inappropriate contributes resistance in for to and are doctors the How can a doctor distinguish to overuse c d v fcs of bacteria. between bacterial and viral infections, without prescribing an antibiotic and seeing if it cures the There are a few viral enzymes which can be used as targets for drugs to infection? control been viruses without discovered known as or harming developed antivirals rather to than the host control cell. Only viruses in a few this drugs way. have These are antibiotics. Resistance t antibitics Some strains of bacteria have evolved with genes which confer resistance to antibiotics and some strains of bacteria have multiple resistance. In 2013 the government’s chief medical ofcer for England, Sally Davies, Figure 10 Many viruses cause said this: a common cold. Children lack The danger along with action, where able The to posed we in discovered huge may infections a lot kill of development described soon of used or after unless surgical antibiotics. tuberculosis worldwide some all us be as 5.2. the a resistance of back a threats in result to of Another of the or of of WHO operations. organ by we an ranked don’t immunity to most of them so frequently catch a cold. take Antibiotics do not cure them environment We natural won’t be selection resistance antibiotic. This resistance, (MRSA) and which resists problem reported reaching be transplants. with patients has disease If 19th-century multiple this should nation. bacteria aureus example the to routine develops hospital The antibiotics almost introduction of to antibiotics Staphylococcus with an treatments Strains strain wounds year list cancer (MDR-TB). per a resistance methicillin-resistant blood on our sub-topic concern growing terrorism then do by is are is for has all is usually not of example infected the commonly multidrug-resistant more than epidemic 300,000 cases proportions in areas. Antibiotic resistance is an avoidable problem. These measures are required: ● doctors ● patients prescribing antibiotics completing courses only of for serious antibiotics to bacterial eliminate infections infections completely ● hospital staff maintaining high standards of hygiene to prevent cross- infection ● farmers ● pharmaceutical new not types using have antibiotics companies been in animal developing introduced since feeds new the to stimulate types of growth antibiotic – no 1980s. 309 6 H u m a n p H ys i o l o g y D-sd qss: Antibiotic resistance Bacterial resistance consequence of to the antibiotics overuse of is a these b) direct drugs. USA, visits for currently upper more than respiratory half tract of the a reason for the pattern shown. Calculate the antibiotic resistance percentage difference in doctor infections between 2002 and (URIs) 1992. are prescribed most URIs are antibiotics, caused by despite knowledge the early 1990s, 3 viruses. Finnish public Evaluate began discouraging of the claim that erythromycin reduction has led to a in the reduction health in authorities [2] that use In the use of theincidence of antibiotic resistance in the S.pyogenes. antibiotic the bacterial national capita The resistance Finland, gure over a antibiotic, consumption the incidence for the 2002 responsible 0 1002 antibiotic 0002 is the 9991 pyogenes to 5 7991 resistant Streptococcus 10 8991 that S. of 15 6 991 period, in 20 5991 10-year are and per cent. shows [3] to 3991 erythromycin. 11 per response 4991 strains 43 the in 2991 pyogenes in by URIs to erythromycin dropped data for ecnatsiser citoibitna % rising erythromycin [2] In 2 the Suggest year condition known as “strep throat”. Figure 11 The incidence of Streptococcus 1 a) Describe the pattern of erythromycin pyogenes strains that are resistant to the resistance to over the period from 1992 2002. antibiotic erythromycin over a 10-year period [3] in Finland 6.4 gs c Understandin Aicatins ➔ Ventilation maintains concentration gradients ➔ External and internal intercostal muscles, of oxygen and carbon dioxide between air in and diaphragm and abdominal muscles as alveoli and blood owing in adjacent capillaries. examples of antagonistic muscle action. ➔ Type I pneumocytes are extremely thin alveolar ➔ Causes and consequences of lung cancer. ➔ Causes and consequences of emphysema. cells that are adapted to carry out gas exchange. ➔ Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the sides Skis of the alveolus adhering to each other by ➔ Monitoring of ventilation in humans at rest and reducing surface tension. after mild and vigorous exercise. (Practical 6) ➔ Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles. ➔ Muscle contractions cause the pressure Nature f science changes inside the thorax that force air in and ➔ Obtain evidence for theories: epidemiological out of the lungs to ventilate them. studies have contributed to our understanding ➔ Dierent muscles are required for inspiration and expiration because muscles only do work when they contract. 310 of the causes of lung cancer. 6 . 4 g a S e x C h a n g e Ventiatin Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood owing in adjacent capillaries. All organisms different dioxide to process. carbon gases This use in dioxide the inside one gas process is from absorb oxygen produced air. the In by this humans lungs the called photosynthesis Humans with alveoli absorb one. and for environment exchange. release use in process. gas (gure gas the cell release oxygen absorb occurs and small by release organisms in a carbon produced respiration Terrestrial exchange and Leaves this the exchange air sacs called 1). type I pneumocytes in alveolus wall phagocyte m 0 0 1 network of blood type II pneumocytes capillaries in alveolus wall Figure 1 Gas exchange blood there owing is a the in of blood gradients removed. the by fresh This the air and a capillary. must process be is between capillaries. gradient: oxygen in diffusion adjacent concentration concentration than happens the lower To in in the gases the into alveolus these the alveoli only concentration maintain pumped called air air The of and diffuse has a carbon because higher dioxide concentration alveoli and stale air must be ventilation. 311 6 H u m a n p H ys i o l o g y D-sd qss: Concentration gradients Figure 2 shows atmospheric dissolved in pulmonary the air, air typical air in the returning composition alveoli to the and of 1 gases lungs in Explain the the why alveoli is the oxygen not as concentration high as in fresh air in that inhaled. is [2] arteries. 2 a) Calculate the difference in oxygen oxygen concentration between air in the alveolus carbon dioxide nitrogen and blood arriving at the alveolus. [1] 700 b) Deduce the process caused by this 598 600 concentration 570 570 difference. [1] 565 gH mm / erusserp lait rap 500 c) (i) Calculate the difference dioxide concentration inhaled and air Explain this difference. in carbon between air 400 exhaled. [1] 300 (ii) [2] 200 d) 159 Despite the high concentration of 120 105 nitrogen in air in alveoli, little or none 100 45 40 40 27 diffuses from reasons for the air to the blood. Suggest 3 0 atmospheric air air in alveoli blood travelling this. [2] air exhaled to alveoli that is inhaled Figure 2 Partial pressures of gases in the pulmonary system Ventiatin exerients Monitoring of ventilation in humans at rest and after mild and vigorous exercise. (Practical 6) In an investigation ventilation, the the type independent parameter that of the or of and measured is exercise Either on or variable in ventilation exercise on the dependent measured of exercise is enough variable. A simple approach for the is to choose these can be the of the investigation ventilation carrying reach given rate. a on an constant below They effect a of should activity rate. include dependent The be for long example simple and a more independent advanced variable an of after to methods ● both the intensity variable is effect levels of activity technique that could be used for the ranging investigation. from inactive down, and to the rates, a for A same parameters per to active, standing, more be at allows during lying walking, at 1 jogging approach is Ventilation ● measured different the correlated minute as different running This such quantitative activity example treadmill. joules very and sprinting. do on sitting to work speeds rate rate most straightforward ventilation Count ventilation with The or in as in a maintained slow as is by number inhaled be exercise. the rate of times minute. at a possible way simple to measure observation. air is exhaled Breathing natural rate, without should which getting out is of breath. Ventilation of some fresh air some of of drawn in and number of times air The expelled 312 the per the lungs into stale the air is carried lungs from expelled minute that is the and the air out then lungs. is is by the expelling The tidal drawn ventilation drawing volume volume. in or rate. ● Ventilation by is data rate can logging. placed An around pumped in with pressure sensor also the a is be measured inatable thorax bladder. then A used chest and air belt is differential to measure 6 . 4 pressure chest can variations expansions. be deduced ventilations inside The and may the also the rate of belt relative be due to To ventilations size ensure rigorous, of and recorded. Tidal e x C h a n g e experimental apart variables parameters times at all should should levels of design from the be be is independent kept constant. measured exercise with each volume person Simple ● the variables dependent Ventilation several 2 that all g a S One the apparatus normal breath delivery volume this is tube shown is air for as in a It vessel is not repeatedly the gure exhaled into measured. apparatus exhaling is CO 3. in possible the trial. should be As many different people through and safe the to use inhaling and concentration will bell jar with 2 rise too as tested. high. graduations delivery tube ● Specially designed available for measure lungs ow and volumes use rate from can spirometers with into these be data are logging. and out of They pneumatic trough the measurements lung Figure 3 deduced. Te I neuctes bronchiole Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange. The lungs area for cells, I contain diffusion. called the The and of wall thin are μm of They are of each Most alveoli with alveolus of the attened cells, capillaries also a very consists cells in with this the of large a total single epithelium thickness of surface layer are only of Type about cytoplasm. of cells. numbers wall epithelium. pneumocytes. 0.15 huge The the The therefore carbon adjacent air less in the than dioxide alveolus 0.5 has to μm and apart. diffuse is consists the The blood of in distance therefore very a single the layer alveolar over which small, of very capillaries oxygen which is an alveolus adaptation to increase the rate of gas 0.25 mm exchange. Te II neuctes epithelium of alveolus wall Type II pneumocytes secrete a solution containing nucleus of epithelium cell surfactant that creates a moist surface inside the alveoli basement membrane to prevent the sides of the alveolus adhering to each other endothelium of capillary by reducing surface tension. Type II pneumocytes alveolar surface area. are rounded They cells secrete a that uid occupy which about coats 5% the of inner alveolus the surface blood plasma of the alveoli. This lm of moisture allows oxygen in the alveolus to erythrocyte dissolve provides and be and an then area diffuse from to the which blood carbon in the dioxide alveolar can capillaries. evaporate into It also the air 1 µm exhaled. Figure 4 Structure of alveoli 313 6 H u m a n p H ys i o l o g y The uid secreted by the Type II pneumocytes contains air in alveolus water monolayer of surface a pulmonary surfactant. Its molecules have a structure surfactant similar They lining Figure 5 Pulmonary surfactant molecules on the surface of the the to the a and the causing air exhaled collapse phospholipids of with the the the the in of the cell membranes. surface of hydrophilic tension sides from the on hydrophobic surface from is of monolayer alveoli, water reduces lm of moisture lining the alveoli that form tails and the facing prevents alveoli lungs. the This moisture heads to facing the the adhere helps to air. This water when prevent lung. trachea Premature babies pulmonary respiratory giving the are often surfactant distress baby and born can syndrome. oxygen and with suffer insufcient from Treatment also one or infant involves more doses intercostal muscle of surfactant, extracted from animal lungs. right bronchus Airwas fr ventiatin Air is carried to the lungs in the trachea bronchioles right lung and bronchi and then to the alveoli in ribs diaphragm bronchioles. Air enters the ventilation system through the nose or Figure 6 The ventilation system mouth rings air and of then cartilage pressure tissues is bronchi, passes in inside high. also is The with its down wall low or trachea walls to the trachea. keep it pressure divides This open in to even when surrounding form strengthened has with two cartilage. (a) inspiration One ver tebral bronchus Inside the leads lungs the to each bronchi lung. divide repeatedly to column form ribs a tree-like structure of narrower airways, called ribs bronchioles. bres to diaphragm in vary. groups The their At of bronchioles walls, the end alveoli, allowing of the where have the smooth width narrowest gas of muscle these bronchioles exchange airways are occurs. pressure chanes durin ventiatin (b) expiration Muscle contractions cause the pressure changes inside the thorax that force air in and out of the lungs to ventilate them. Ventilation If particles volume, air movement of of the Conversely, the gas lungs spread pressure if a gas is of involves out the to some occupy gas basic a becomes compressed to physics. larger lower. occupy a smaller ribcage movement volume, the pressure rises. If gas is free to move, it diaphragm movement will always ow from regions Figure 7 Ventilation of the lungs regions 314 of lower pressure. of higher pressure to 6 . 4 During thorax ventilation, to drawn into pressure cause drop the has risen out from to the the the thorax lungs to cause pressure. atmosphere atmospheric inside from contractions atmospheric lungs pressure forced muscle below the rise a pressure Muscle above atmosphere inside consequence, (inspiration) pressure. to the As until contractions atmospheric, so e x C h a n g e the air the g a S is lung then air is (expiration). Antanistic usces Dierent muscles are required for inspiration and expiration because muscles only do work when they contract. Muscles can Muscles ● be do (tension) when they two work that they Muscles ● in do when causes not they contract particular while lengthen elongated state a force pushing a contracting and by relaxing. exerting movement. a They pulling force become shorter this. lengthen do states: by they are relaxing, themselves. the Most contraction (compression) of but another while this muscles happens are pulled muscle. relaxing so do They no passively into do work not at – an exert this time. Figure 8 Dierent muscles are used for bending the leg at the knee and for the opposite movement of straightening it Muscles therefore movement two in muscles movement, opposite the rst known the be Inspiration directions second is caused When is needed by pair the of as in at one and is direction. different muscle second work elongated muscle together in times, contracts by If at and the rst. contracting this way least causes they a The while are muscles. involve working one relaxes muscles expiration required, movement When muscle antagonistic and are cause required. movement an only opposite will relaxes. as muscles can opposite movements, antagonistic so different pairs. Antanistic usce actin in ventiatin External and internal intercostal muscles, and diaphragm and abdominal muscles as examples of antagonistic muscle action. Ventilation pressure involves inside the two pairs of opposite movements that change the volume and therefore is e Diaphragm Moves downwards and attens Moves upwards and becomes more domed Ribcage Moves upwards and outwards Moves downwards and inwards Antagonistic pairs the thorax: of muscles are needed to cause these is movements. e Volume and pressure The volume inside the thorax The volume inside the thorax decreases and changes increases and consequently the consequently the pressure increases pressure decreases 315 6 H u m a n p H ys i o l o g y Movement The diaphragm contracts and so it The diaphragm relaxes so it can be pushed of the Diaphragm moves downwards and pushes the upwards into a more domed shape diaphragm abdomen wall out Abdomen Muscles in the abdomen wall relax Muscles in the abdomen wall contract pushing wall allowing pressure from the diaphragm the abdominal organs and diaphragm upwards muscles to push it out Movement External The external intercostal muscles The external intercostal muscles relax and are of the intercostal contract, pulling the ribcage upwards pulled back into their elongated state. ribcage muscles and outwards Internal The internal intercostal muscles The internal intercostal muscles contract, pulling intercostal relax and are pulled back into their the ribcage inwards and downwards muscles elongated state Eidei Obtain evidence for theories: epidemiological studies have contributed to our understanding of the causes of lung cancer. Epidemiology causes of is observational it is rarely disease the disease. in study Most rather possible human than to of the incidence epidemiological experimental investigate populations the by also and studies are because causes carrying and factor a risk of lung in other elds causes of of scientic a disease research, are evidence for or against a collected that allows the theory, association disease For example, and its survey theoretical causes lung test cancer, the cause the who have developed who have not are epidemiological evidence cancer for are a theory smoking lung needed. surveys link to in and be course correlation between a of smoking risk of people very large try to not prove that the factor apart are usually lung account the and causes confounding increased associated smoking is a spurious a the factors compensate from the to risk. with cause of Smoking leanness lung association one for reduces and cancer. between being to single recorded on carried factors factors. and data This leanness Age out and and sometimes factors many investigated. be confounding of confounding collect procedures of effect This to try sex it is factors allows take to isolate are almost epidemiological disease include only males or females or only in sub- disease. people There an is necessary surveys does so cancer. statistical strong and To usually 1.6. factor with the lung always A that signicantly tested. people provided sub-topic increased showed smoking Examples that not by an between habits cancer between included that analysis is example, found and can disease For been leanness Careful leanness it. a data and to cause repeatedly between cancer. and explains the not They between To of is incidence. theories proposed. appetite obtain the does has smokers associated the on associations that association among about effect epidemiologists out experiments. As an spurious an of have cause in a specic age range. which Causes f un cancer Causes and consequences of lung cancer. Lung cancer world, the 316 both number is in of the most termsof deaths common the due cancer number to of in the cases thedisease. and The general causes topic1.6. The considered of cancer specic here. are described causes of lung cancer are 6 . 4 and smoke organic ● Radon in gas that granite. ● from causes of leaks out It Asbestos, silica cancer inhaled. The if This in of and wood or dust of or usually of other other difculties with cases as it. solids on can of cause them are construction factories. cancer be such particles or of radioactive ventilated inhale other mines a rocks happens can is badly then lung them in numbers It certain some quarries, Some disease: world. people consequences severe. the or coal, signicant the accumulates and sites burning parts buildings lung e x C h a n g e matter. some gas g a S are used often to help breathing, very diagnose persistent Figure 9 A large tumour (red) is coughing, coughing up blood, chest pain, loss of visible in the right lung. The tumour appetite, weight loss and general fatigue. is a bronchial carcinoma In ● Smoking causes about 87% of cases. many when smoke contains many mutagenic patients chemicals. it is cigarette carries a risk, the incidence cancer increases with the number day and the number of years of Passive smoking happens smoke cases when exhaled will banned causes about non-smokers by decline indoors smokers. in The countries and in 3% public Air pollution lung are probably cancers. most nitrogen The cases. This number early be tobacco where oxides are from of about air diesel all with secondary tumours in the elsewhere. of Mortality patients with rates lung are high. cancer is enough, removed with of smoking than one Other 5 years. all or If part surgically. or more patients a of the This courses are tumour is of treated is survive discovered affected usually lung may combined chemotherapy. with radiotherapy. places. causes sources signicant or 15% more The ● large have smoking. of inhale already also smoked for ● is may As Only per and of brain lung tumour discovered metastasized, every the Tobacco 5% pollution exhaust vehicle that fumes, exhaust minority cancer, of fumes are but likely to difculties, possible of patients have lost continue fatigue return of who some to and the of have also are cured their of lung pain, anxiety lung tissue, breathing about the disease. Ehsea Causes and consequences of emphysema. In healthy group of lung small emphysema of larger total air tissue these sacs surface each thin-walled are with area for bronchiole alveoli. replaced much gas by In a thicker exchange a leads smaller walls. is to patient a ● with infections number elastase, The them and the distance over which gases occurs is increased, and so a therefore An enzyme much less less elastic, so effective. gas The ventilation is molecular mechanisms lungs more though there is involved some inhibitor are from by to kill endocytosis. called prevents alpha elastase 1-antitrypsin and digesting lung tissue. other In also the number not evidence increases and of they phagocytes produce in the more elastase. fully Genetic factors affect the quantity and for effectiveness these enzyme, formed lung produce difcult. ● understood, vesicles prevent and exchange lungs The the usually smokers, become normally bacteria diffusion proteases is alveoli engulng protein-digesting inside (A1AT) of inside by considerably ● reduced Phagocytes of A1AT produced in the lungs. theories: 317 6 H u m a n p H ys i o l o g y In about in the of proteases walls 30% of alveolus are is smokers wall not by digestion the prevented weakened and of increased and than proteins nd alveolus eventually normal result quantity the even onerous. destroyed. during Emphysema is a chronic disease because to alveoli oxygen is usually saturation in irreversible. the blood and In dioxide lacks such mild concentrations. energy as cases and climbing there exercise is but may stairs As a eventually too shortness eventually of breath even mild the It causes it. Ventilation is laboured and tends causes to low tasks vigorous activity damage carbon patient be more rapid than normal. higher D-sd qss: Emphysema and gas exchange Figure 10 shows healthy emphysema, at emphysema. Breathing 1 a) Place times a b) 2 Explain the why tissue polluted of and magnication. air each the several the are tissue makes crosses for from Smoking the micrograph ruler times results suitable Explain lung across edge this that using same ruler the Repeat way the each a a disease and gas count State with causes worse. how exchange micrograph, comparable. lung usually in your many surface. such a results units. [3] conclusions people who that have you draw from emphysema feel the results. tired all the time. 3 Suggest and Figure 10 Healthy lung tissue (top) and lung tissue showing emphysema (bottom) 318 [3] [3] why strained people right with side of emphysema the heart. often have an enlarged [1] 6 . 5 n e u r o n S a n D S y n a p S e S 6.5 ns d sss Understandin Aicatins ➔ Neurons transmit electrical impulses. ➔ The myelination of ner ve bres allows for ➔ Secretion and reabsorption of acetylcholine by neurons at synapses. saltatory conduction. ➔ Neurons pump sodium and potassium ions ➔ Blocking of synaptic transmission at cholinergic synapses in insects by binding across their membranes to generate a resting of neonicotinoid pesticides to acetylcholine potential. receptors. An action potential consists of depolarization ➔ and repolarization of the neuron. Skis Ner ve impulses are action potentials ➔ ➔ Analysis of oscilloscope traces showing resting propagated along the axons of neurons. potentials and action potentials. Propagation of ner ve impulses is the result of ➔ local currents that cause each successive par t of the axon to reach the threshold potential. Nature f science Synapses are junctions between neurons and ➔ ➔ Cooperation and collaboration between groups between neurons and receptor or eector cells. of scientists: biologists are contributing to When pre-synaptic neurons are depolarized ➔ research into memory and learning. they release a neurotransmitter into the synapse. A ner ve impulse is only initiated if the threshold ➔ potential is reached. Neurns Neurons transmit electrical impulses. Two systems endocrine of the a nd tha t consists of glands consists of nerve neurons in the electrical Neurons also by use d for ne r vous r e le a se ca l le d in t e r na l s ys t e m . hor m o n es . ne ur ons . ner vous tr a ns mitti ng Th e Th e r e s yste m . ner ve c o m m u ni c a t io n : T he en d oc r in e n e r vo u s a re a bou t N eu r on s i m pu l se s . h e lp A the s yst e m sys t em 85 bil li on wit h n e r ve in t e rn a l im pu ls e is signa l . have have ce l l s ar e the huma n communication an body system a cell narrow body with outgrowths cytoplasm called and nerve a nucleus bres along but they which nerve impulsestravel. ● Dendrites are totransmit spinal ● Axons short branched impulses between nerve bres, neurons in for one examples part of those the used brain or cord. are impulses very from elongated the tips of nerve the bres, toes or for the example ngers to those the that spinal transmit cord. 319 6 H u m a n p H ys i o l o g y cell body axon skeletal muscle (eector) dendrites ▲ Figure 1 Neuron with dendrites that transmit impulses to the cell body and an axon that transmits impulses a considerable distance to muscle bres meinated nerve bres The myelination of nerve bres allows for saltatory conduction. The basic structure transmitted membrane most A ▲ cases nerve is of very enclosing is about bre with speed of about Some nerve called myelin. 1 a nerve simple: 1 a µm, this are per is which a cylindrical region though simple along bre narrow metre bres bre the of some The bres conducts impulse shape, cytoplasm. nerve structure nerve in are with plasma diameter wider nerve is a in than impulses this. at a second. coated along most of their length by a material Figure 2 Ner ve bres (axons) transmitting It consists of many layers of phospholipid bilayer. Special electrical impulses to and from the central cells called Schwann cells deposit the myelin by growing round and ner vous system are grouped into bundles round the double more There myelin sheath nucleus of Schwann cell nerve layer layers is a of bre. when gap Each time phospholipid the Schwann between the they bilayer cell myelin is grow around deposited. stops the There nerve may bre be 20 a or growing. deposited by adjacent Schwann cells. node of Ranvier The gap is impulse can saltatory along a called a jump node from conduction. nerve much more much as bre rapidly so It of Ranvier. one is node much myelinated Ranvier quicker myelinated than of In nerve unmyelinated to than the bres next. continuous bres nerve nerve transmit bres. This is nerve called transmission nerve The the impulses speed can be axon ▲ 100 metres per second. Figure 3 Detail of a myelinated ner ve bre showing the gaps between adjacent Schwann cells (nodes of Ranvier) ▲ Figure 4 Transverse section of axon showing the myelin sheath formed by the Schwann cell's membrane wrapped round the axon many times (red) 320 as 6 . 5 Restin tentias n e u r o n S a n D S y n a p S e S uid outside neuron Neurons pump sodium and + Na + potassium ions across their Na + Na channel + K + Na + membranes to generate a resting K closed + Na potential. + Na + Na + A neuron that is not transmitting a Na signal + has a potential membrane This and difference that potential negative is is called due to charges or voltage the an resting across imbalance across the Na its of positive membrane. + Na Sodium–potassium ● pumps transfer + sodium (Na + Na potential. + /K pump + ) and potassium (K ) ions + across the membrane. Na ions are pumped + out and K numbers ions of are ions pumped pumped is in. + The + + K unequal – K K channel when + K + three Na are pumped out, only two closed + + ions + K K Na + K + K ions are pumped in, + creating K + K + concentration gradients for both K ions. + + + K K K + Also ● the membrane is about 50 times K more + + permeable to K + K ions than Na ions, leak back across the K K protein ions + + so + K + K membrane + faster than Na ions. As a result, cytoplasm the + Na concentration gradient across the ▲ Figure 5 The resting potential is generated by the sodium–potassium pump + membrane creating In ● a is steeper charge addition negatively to than the K gradient, imbalance. this, there charged are (organic proteins anions), inside which the nerve increases bre the that are charge imbalance. These factors about 70 together give the neuron a resting membrane potential of mV . Actin tentias An action potential consists of depolarization and repolarization of the neuron. An of action two potential is a rapid change in membrane potential, consisting phases: ● depolarization ● repolarization Depolarization is – – a a due change change to the from back negative from opening of to positive positive sodium to negative. channels in the + membrane, allowing Na ions to diffuse into the neuron down the + concentration imbalance the across outside. about +30 gradient. This the The entry membrane, raises the of so Na the membrane ions inside reverses is potential the positive to a charge relative positive to value of mV . 321 6 H u m a n p H ys i o l o g y uid outside neuron uid outside neuron + + + Na Na Na + + Na Na + channel + + K + K K + channel + K Na + K K open + + closed Na Na + Na + Na + + Na Na + + + + Na K K K + K + K + K + Na + + + Na /K + /K Na pump pump + + + K + + K Na + Na K + K + Na - Na - channel + + Na K + + + K + closed K + K Na Na + - - - - + - + + K - Na K K - - + + - K + - - + + + + Na - + + + - - Na K + + K Na + + + Na K - + Na + - K + K K Na + K - - + K K K Na K + K + K + + K K protein Na protein + + Na K cytoplasm cytoplasm ▲ open + - K K + channel Figure 6 Neuron depolarizing Figure 7 Neuron repolarizing ▲ Repolarization to the closing channels in out of the the inside the the of the down ce l l channe l s potential ra pi dl y s o di um me mb r ane. neuron, potassium a ha p p e ns of close T hi s thei r ne g ativ e r e m a in to 70 a fte r de pol a ri z a t io n channe l s al l ow s o pe n in g pot a s si u m conce n t r at i on a ga i n op en mV . a nd The re la t i ve unt i l the diffusi o n and of io ns gr a di en t , to the d ue to diffu s e w h ic h out s ide . mem bra n e of is pot a s si u m has pota ss ium m a ke s T he fa l le n to re p ola r iz e s impulse movement + + + + + + + + + – – – – – – – – – the neuron, but it does not r e stor e the re s t in g p ote n t ia l as the cell membrane A concentration gra d i e nts of s od ium a nd p ot a s si u m ion s h a ve n ot y et cytoplasm been + + + + + + + + + – – – – – – – – + + + + + – – – – – B then re-established . transmit T hi s ano the r tak e s ne rv e a few m il li s ec o n ds and t he neu r on c an imp ul se . + Na praatin f actin tentias + + + + – – C Nerve impulses are action potentials propagated along + Na the axons of neurons. + K A + + + + + – + + – D – + nerve impulse is an action potential that starts at one end other end of of a neuron + – – and is then propagated The propagation along the axon to the the neuron. + Na movements + that of the action depolarize potential one part of happens the because neuron the trigger ion depolarization K + + + – – – + + + in – – – + E + + – – the neighbouring part of the neuron. – + Na Nerve ▲ Figure 8 Action potentials are propagated along axons 322 impulses and other one terminal always vertebrates. of a move This neuron is in one direction because and can an only along impulse be passed neurons can on only to in be other humans initiated neurons at or 6 . 5 different after a cell types at depolarization backwards along an the other that terminal. prevents Also, there propagation of is an a n e u r o n S refractive action a n D S y n a p S e S period potential acv axon. ns s d s lca currents Anemonesh have a nervous system similar to ours, with a Propagation of nerve impulses is the result of local central nervous system and currents that cause each successive par t of the axon to neurons that transmit nerve impulses in one direction reach the threshold potential. only. Sea anemones have The propagation of an action potential along an axon is due to no central nervous system. movements of sodium ions. Depolarization of part of the axon is due to Their neurons form a simple diffusion of sodium ions into the axon through sodium channels. This network and will transmit reduces the concentration of sodium ions outside the axon and increases impulses in either direction it inside. The depolarized part of the axon therefore has different sodium along their nerve bres. They ion concentrations to the neighbouring part of the axon that has not yet both protect each other from depolarized. As a result, sodium ions diffuse between these regions both predators more eectively inside and Inside the outside the axon. than they can themselves. axon depolarized to the part the that are currents has not is the part shown reduce yet a higher axon part gradient polarized movements Local of neighbouring concentration from there that is in in sodium is still the back the so sodium to ions gure part 10. This diffuse that has are the so in in the inside the axon sodium just called gradient makes along Outside direction They concentration depolarized. concentration polarized. opposite the ion the diffuse These currents. part membrane axon the ions depolarized. local Explain how they do this. the of the potential neuron rise from ▲ the resting potential of 70mV to about 50 mV . Sodium channels in Figure 9 Anemonesh among the the tentacles of a sea anemone axon of membrane 50mV Opening Thus is of local a voltage-gated reached. the to hundred This sodium currents repolarization and are (or therefore channels cause be is a open of as a the per membrane threshold potential potential. depolarization. depolarization along metres when known causes wave propagated more) and the axon at and a then rate of between one second. impulse movement + N a di us io n outside inside membrane N a ▲ + dius n o par t that has just depolarized par t that has not yet depolarized (action potential) (resting potential) Figure 10 Local currents 323 6 H u m a n p H ys i o l o g y action potential peak Anasin scisce traces ira taz noi noi taz 0 Analysis of oscilloscope traces showing resting ope er lop iral d ecnereid laitnetop )Vm( enarbmem ssorca +35 potentials and action potentials. Membrane threshold potential potenti a l s in ne ur ons ca n be m e a su r e d by pla c i n g 50 electrodes on each side of the me m br a n e. The po t en t i al s can be 70 displayed resting potential using an o s ci ll os co pe . Th e di s pla y is s im il a r to a g ra ph undershoot with 0 1 2 3 4 5 6 time on the x-axis a nd the me mbr an e p ot e n t ia l on the y -a xi s . 7 If there is a resting p o te nti a l, a hor iz on t al li ne ap pe a rs on the time/ms oscilloscope stimulus ▲ Figure 11 Changes in membrane polarity resting screen potential at of a l ev el of 70 mV , assuming tha t this is the the ne ur on. during an action potential If an action potential and falling The oscilloscope the phases 70 mV changes showing trace depolarization repolarization occurs, until does not immediately gradually may narrow the show the threshold usually is seen, is a resting and the is with rising in potential which is rising before reached. membrane phase the repolarization. potential potential return there the spike depolarization also the and until a The potential the to potential reached. D-sd qss: Analysing an oscilloscope trace The a oscilloscope digital in a trace oscilloscope. mouse in It gure shows hippocampal 12 an was taken action pyramidal from 1 potential neuron pulse of after the neuron was stimulated the resting hippocampal potential pyramidal of the mouse neuron. [1] that 2 happened State with Deduce with a reason the threshold a potentialneeded to open sodium in this voltage-gated current. 3 channels Estimate the time )Vm( egatlov enarbmem depolarization, neuron. taken and the for [2] the repolarization. [2] 50 4 Predict the time depolarization taken for the from the resting end of the potential 0 to be regained. [2] resting potential 5 Discuss how many action potentials 50 could be stimulated per second in this neuron. 0 50 [2] 100 6 time (ms) Suggest a potential ▲ reason rising for the briey at membrane the end of the Figure 12 repolarization. [1] Snases Synapses are junctions between neurons and between neurons and receptor or eector cells. Synapses are there synapses the are brain neurons. 324 junctions and In between between spinal muscles cord and cells sensory there are glands in the nervous receptor immense there are cells system. and numbers synapses In sense neurons. of In synapses between organs both between neurons and 6 . 5 muscle bres effectors, Chemicals synapses. and or secretory because they called This only cannot about 20 Muscles (carry out) neurotransmitters system post-synaptic impulses cells. effect is cells pass nm used are at all This a are glands used by gap is are response synapses separated across. and a to to the a n D S y n a p S e S called stimulus. signals the uid-lled called sometimes a send where n e u r o n S across pre-synaptic gap, so synaptic electrical cleft and is wide. Snatic transissin When pre-synaptic neurons are depolarized they release ▲ Figure 13 Electron micrograph of a synapse. a neurotransmitter into the synapse. False colour has been used to indicate the Synaptic transmission occurs very rapidly as a result of these events: pre-synaptic neuron (purple) with vesicles of neurotransmitter (blue) and the post-synaptic A ● nerve impulse is propagated along the pre-synaptic neuron neuron (pink). The narrowness of the synaptic until it reaches the end of the neuron and the pre-synaptic cleft is visible membrane. Depolarization ● of the pre-synaptic membrane causes pre-synaptic cell nerve 2+ calcium ions membrane Inux ● of (Ca into ) the calcium neurotransmitter membrane and to diffuse through channels in impulse the neuron. causes to vesicles move fuse with to containing the 2+ pre-synaptic Ca it. diuses into knob synaptic knob synaptic vesicles Neurotransmitter ● is released into the synaptic cleft by exocytosis. pre-synaptic The ● neurotransmi tte r cleft and binds to d i ffus es r e ce p tor s acr os s on the the s y n ap t ic membrane neurotransmitter pos t - syn a pt ic (e.g. acetylcholine) membrane. synaptic cleft neurotransmitter The ● binding causes ● of the adjacent neurotransmitter sodium Sodium ions into post-synaptic the synaptic diffuse membrane ion down channels their neuron, to to reach the to open. concentration causing the 20nm approximately receptors the threshold gradient ion channel opened post- potential. post-synaptic membrane An ● action potential membrane and is is triggered propagated in on the post-synaptic along the neuron. post-synaptic cell The ● neurotransmitter removed from the is rapidly synaptic broken down and cleft. ▲ Figure 14 A ner ve impulse is propagated across a synapse by the release, diusion and post-synaptic binding of neurotransmitter D-sd qss: Parkinson’s disease Dopamine that are is used Parkinson’s one at of the many synapses disease, in there is neurotransmitters the a brain. loss of In metabolic and neurons, initiating in many which movement, cases causes muscular shaking. slowness rigidity Figure15 of involved in the formation dopamine. dopamine1 secreting pathways breakdown Explain how symptoms of Parkinson’s disease in are relieved a) L-DOPA by giving the following drugs: and shows the [1] 325 6 H u m a n b) p H ys i o l o g y selegeline, which is an inhibitor of tyrosine tyrosine L-DOPA COOH COOH monoamine oxidase-B (MAO-B) hydroxylase [1] CH CH HO CH 2 c) tolcapone, which is an 2 inhibitor NH NH (FOOD) of catechol-O-methyl 2 2 COMT transferase dopa (COMT) d) dopamine [1] ropinirole, which is an agonist CH CH CH of 3 dopamine decarboxylase COOH 2 2 NH 2 2 NH [1] 2 HO HO e) sanamide, of which dopamine by inhibits MAO-B reuptake O pre-synaptic C 2 neurons. [1] H aldehyde 2 Discuss how a cure for Parkinson’s disease dehydrogenase might in the future be developed by: COMT CH O CH 3 a) stem cell therapy b) gene therapy. CH 2 COOH 2 [3] HO HO [2] Figure 15 The formation and breakdown of L -DOPA and ▲ dopamine. The enzymes catalysing each step are shown in red Acetchine Secretion and reabsorption of acetylcholine by neurons at synapses. Acetylcholine including in the diet, choline The used synapses with an during binding group loaded synaptic receptors site for to the neuron acetyl is as neurotransmitter between pre-synaptic acetylcholine cleft is neurons by produced into and combining vesicles many muscle It is absorbed aerobic then synapses, bres. choline, during and in produced from respiration. released into the the The synaptic transmission. acetylcholine which in the acetylcholine post-synaptic will bind. The membrane have acetylcholine a only acetyl group remains ▲ Figure 16 Acetylcholine one action because cleft The bound acetyl enzyme rapidly choline converted the potential the and to is is receptor initiated breaks into in a short the acetylcholine into active the time, during post-synaptic acetylcholinesterase reabsorbed back for is present down into pre-synaptic neurotransmitter by which neuron. in the choline neuron, only This is synaptic and acetate. where recombining it it is with group. Nenictinids Blocking of synaptic transmission at cholinergic synapses in insects by binding of neonicotinoid pesticides to acetylcholine receptors. Neonicotinoids bind to central 326 the are synthetic acetylcholine nervous system compounds receptor of insects. in similar cholinergic to nicotine. synapses Acetylcholinesterase in does They the not an 6 . 5 break down receptors neonicotinoids, are blocked, so so the binding acetylcholine is is irreversible. unable to bind n e u r o n S a n D The S y n a p S e S acv and rsc ds synaptic transmission is prevented. The consequence in insects is cds paralysis and death. Neonicotinoids are therefore very effective There are currently insecticides. intense research eor ts One of the advanta g e s of ne oni co ti n oid s as pe s tic i de s is t h at t h ey to try to discover whether are not highly tox i c to huma ns a nd ot h e r m a m m a ls . Th i s is be c a u se neonicotinoids are to blame a much greater pr o p o r ti on of sy na ps es in t he cen t r a l n er vou s for collapses in honeybee system are choline r g i c in i ns e cts tha n in m am m al s and a l so be c a us e colonies. What are the most neonicotinoids bind much l es s str ongl y to a c e t yl c h ol in e re c e pt or s in recent research ndings mammals than ins e cts . and do they suggest that Neonicotinoid pes ti ci d e s particular neoni cotinoi d, one insecticide the insects. the in effects of the There evidence government world. thes e has of are no w been Howe ve r, on h u g e a re a s d is pute d is conc e r n s by c ro ps . mos t wid e ly h ave be en ra i se d and con t r over s y the of the ho ne ybee s consi de ra ble is on i midaclo pr id, i ns e ctici de s ha r m us e d ot h e r ove r us ed be banned? a bo u t b en e c ia l t h is ma n u fa c t u r er s these insecticides should In and and so m e agenci e s . Threshd tentias ▲ Figure 1 7 Research has shown that the neonicotinoid A nerve impulse is only initiated if the threshold pesticide imidacloprid reduces potential is reached. Nerve impulses initiated do if the follow voltage-gated opening of some start channels and positive At membrane therefore a synapse, always the depolarization the threshold The that of a pumps effect. full of to be and open, causing inward more action only this is of sodium channels potential is only potential depolarization. diffusion sodium threshold potential at to The ions open reached – there depolarization. membrane reached does in not post-synaptic the the An because neurotransmitter membrane the to the causing If pre-synaptic potential entered potassium be amount the post-synaptic have potential feedback principle. reached, channels the will is sodium there a all-or-nothing potential sodium increases is an threshold growth of bumblebee colonies the then neuron post-synaptic secreted may not following be post-synaptic depolarize. are to cause membrane. The pumped membrane enough sodium out returns by to ions sodium– the resting potential. A typical not just post-synaptic with necessary time for for the be initiated be used help in to one but several with of threshold in the process neuron in many these to potential post-synaptic information the brain or pre-synaptic release to be cord neurons. It neurotransmitter reached neuron. from spinal This different and type a has may at nerve of synapses be the same impulse mechanism sources in the to can body to decision-making. 327 6 H u m a n p H ys i o l o g y Research int er and earnin Cooperation and collaboration between groups of scientists: biologists are contributing to research into memory and learning. Higher only functions partly actively. but being science ▲ have used are medicine, the understood They increasingly are of also at including present traditionally the to brain techniques unravel making the and been of and are being and molecular work. contributions, computer by biology at learning researched investigated mechanisms important pharmacology memory are very psychologists and biochemistry Other branches including of biophysics, science. Figure 18 Many synapses are visible in this The Centre for Neural Circuits and Behaviour at Oxford University is scanning electron micrograph between the cell an excellent example of collaboration between scientists with different body of one post-synaptic neuron and a large areas of expertise. The four group leaders of the research team and the number of dierent pre-synaptic neurons (blue) area of science that ● Professor ● Dr Martin ● Dr Korneel ● Professor Gero they Miesenböck Booth Hens Scott originally – studied are: medicine and – engineering – chemistry Waddell – and and optical physiology microscopy biochemistry genetics, molecular biology and neurobiology. The centre Neurons specializes are transmission genetically or an brain tissue visible. in brain tissue respond There that are are to allows be many there group to research is a element to national boundaries. of the cerebrum—the folded upper par t of undoubtedly 328 scientic be of groups memory, sometimes make Figure 19 Memory and learning are functions countries patterns They to a emit making are light activity optogenetics. in synaptic specic engineered signal in as during activity also light known the with an neurons so specic action of living studied. investigating Although rst This to potential, in tissue techniques engineered action neurons brain the brain research neurons potential. ▲ in the research. there This in the and is world. brain between also extends of throughout other a across many of world to be the collaborative scientic how groups the functions. scientists strongly understanding achievement throughout universities competition discovery, Success in learning the disciplines brain scientists works in and will many 6 . 6 h o r m o n e S , h o m e o S t a S i S a n D r e p r o D u C t i o n 6.6 hs, sss d dc Understandin Aicatins Insulin and glucagon are secreted by α and ➔ Causes and treatment of type I and type II ➔ β cells in the pancreas to control blood glucose diabetes. concentration. Testing of leptin on patients with clinical ➔ Thyroxin is secreted by the thyroid gland to ➔ obesity and reasons for the failure to control regulate the metabolic rate and help control the disease. body temperature. Causes of jet lag and use of melatonin to ➔ Leptin is secreted by cells in adipose tissue ➔ alleviate it. and acts on the hypothalamus of the brain to The use in IVF of drugs to suspend the ➔ inhibit appetite. normal secretion of hormones, followed Melatonin is secreted by the pineal gland to ➔ by the use of ar ticial doses of hormones to control circadian rhythms. induce superovulation and establish A gene on the Y chromosome causes ➔ a pregnancy. embryonic gonads to develop as testes and William Har vey’s investigation of sexual ➔ secrete testosterone. reproduction in deer. Testosterone causes prenatal development ➔ of male genitalia and both sperm production Skis and development of male secondary sexual characteristics during puber ty. ➔ ➔ Annotate diagrams of the male and female Estrogen and progesterone cause prenatal reproductive system to show names of development of female reproductive organs structures and their functions. and female secondary sexual characteristics during puber ty. Nature f science The menstrual cycle is controlled by negative ➔ ➔ and positive feedback mechanisms involving Developments in scientic research follow improvements in apparatus: William Har vey ovarian and pituitary hormones. was hampered in his obser vational research into reproduction by lack of equipment. The microscope was invented 17 years after his death. Cntr f bd ucse cncentratin Insulin and glucagon are secreted by α and β cells in the pancreas to control blood glucose concentration. Cells the in the glucose pancreas respond concentration to changes deviates in blood substantially glucose from the levels. set If point of 1 about 5 mmol hormones L insulin , homeostatic and glucagon mechanisms are mediated by the pancreatic initiated. 329 6 H u m a n p H ys i o l o g y The is pancreas exocrine leading called to islets of small directly Alpha (α level breakdown the Beta ● ▲ blood, Figure 1 Fluorescent light micrograph of the cells glucose tissue into falls blood below glycogen cells) the digestive small stream. and set Most the The of enzymes regions of pancreas two secrete point. glucose cell the into pancreas ducts endocrine that tissue secrete types in the islets glucagon This in if hormone liver cells the blood stimulates and its release into concentration. synthesize concentration are organ. hormones. into the one through synthesize increasing (β dotted the in secretes There different cells) of glands that intestine. secrete cells glucose two Langerhans Langerhans ● effectively glandular the hormones of is rises insulin above and the secrete set point. it when This the blood hormone pancreas showing two islets of Langerhans stimulates uptake of glucose by various tissues, particularly skeletal surrounded by exocrine gland tissue. Alpha muscle and liver, in which it also stimulates the conversion of cells in the islets are stained yellow and beta glucose to glycogen. Insulin therefore reduces blood glucose cells are stained red concentration. cells it acts within Like upon, minutes so of most its hormones, secretion eating and insulin must may be is broken ongoing. continue for down by Secretion several the begins hours after ameal. Diabetes Causes and treatment of type I and type II diabetes. Diabetes is the consistently during of glucose also it is in If in impairs drinks, There the of whether are two body urinate feels for have main their in urine an and craves in and this the years. while Until is but the of prolonged to and diabetes. lack factors The last in that treatment go the affect of in over are due 65s. not two is to are a slow for this many form under The well 50 causes of and of understood sugary, habitual together energy the people of glucose decades, factors exercise, or Onset unnoticed few diabetes obesity of cells. rare risk because receptors may very main insulin target the only form to insulin on was common this disease: of disease diabetes increase urine respond transporters sugary the or deciency proteins. frequently, glucose of even presence elevated from developed types process dehydration. more tired test they the resulting and has levels to particularly kidney, should person glucose leading reabsorption urine to a Continuously tissues, thirsty, they blood urine. needs constantly where fasting, water in volume person check the damages forming the a elevated prolonged glucose It condition fatty diets, overeating with genetic metabolism. types of diabetes is different: ● Type I diabetes, characterized sufcient destruction causes are In by the and usually of still beta children severe disease inability this being of disease of Langerhans more early-onset an quantities autoimmune system. or by insulin. arising cells in body’s and start ● an Type too people food the of suddenly. the The diseases researched. last can Type II diabetes, sometimes called is characterized by an and too a because in the high are it or often of insulin blood. is testing likely blood to become before glucose Timing is a as the very do not treatments are implanted insulin necessary. blood injecting molecules Better using the and done absorbed. exogenous when by regularly peak and developed A devices into the that blood permanent cure late-onset inability be achievable by coaxing stem cells to to become 330 is digested release may diabetes, it prevent long being treated Injections important as ● when to is is concentration high. meal autoimmune diabetes insulin of immune symptoms I glucose the islets own rather other is from the is produce It young obvious and diabetes, to fully functional replacement beta cells. 6 . 6 ● Type diet II to diabetes reduce glucose. eaten Small Foods avoided. treated peaks amounts frequently meals. be is the rather with high Starchy by adjusting and of troughs food than should content should h o m e o S t a S i S the of blood be infrequent sugar food h o r m o n e S , be it it is be large has r e p r o D u C t i o n low included are eaten a digested foods. should only if a n D glycemic slowly. to slow Strenuous benecial as index, indicating High-bre the digestion exercise they foods and improve of that should other weight insulin loss uptake andaction. D-sd qss: The glucose tolerance test acv The glucose tolerance test is a method used to diagnose diabetes. Fds f ii dcs In this test, the patient drinks a concentrated glucose solution. The Discuss which of the foods blood glucose concentration is monitored to determine the length of in gure 2 are suitable for a time required for excess glucose to be cleared from theblood. person with type II diabetes. mc 001 gm / noitartnecnoc 3– 400 They should be foods with a 350 low glycemic index. 300 250 diabetic 200 150 unaected 100 50 0 0 0.5 1 2 3 4 5 time after glucose ingestion / h ▲ Figure 3 A person with diabetes and an unaected person give very dierent responses to the glucose tolerance test With reference metabolism a) The to to gure the concentration consumption of of 3, person b) The length c) The maximum d) The time of the time glucose required at person with time with normal respect zero, i.e. glucose to: before the drink. to level glucose the diabetes glucose glucose before compare with return to the level at time zero. ▲ reached. levels start to Figure 2 fall. t Thyroxin is secreted by the thyroid gland to regulate the metabolic rate and help control body temperature. The hormone chemical atoms of prevents almost structure iodine. the all metabolic active, Higher and it in rate, such is as so metabolic all of as the cells are to and supports generation more in hormone Thyroxin are but the protein body gland heat. so the is the a also most Its four therefore unusual as body’s metabolically targets. and person secretion body neck. contains diet synthesis In the regulatesthe main thyroxin production in molecule iodine respond increased heat of This brain of thyroid thyroxin targets. need triggers the deciency muscle stimulates by thyroxin. body rate the cooling which secreted unusual the liver, increases is Prolonged synthesis cells physiology, gland, thyroxin growth with by normal the temperature thyroid rises. 331 6 H u m a n p H ys i o l o g y Thyroxin thus regulates the metabolic rate and also helps to control bodytemperature. The importance deciency ● lack of energy ● forgetfulness ● weight gain broken ▲ of thyroxin is revealed by the effects of thyroxin (hypothyroidism): and and feeling to all the time depression despite down tired loss of release appetite energy by as less cell glucose and fat are being respiration Figure 4 Structure of thyroxin with atoms of ● feeling cold all ● constipation the time because less heat is being generated iodine shown purple slow impaired ● because contractions of muscle in the wall of the gut down. brain development in children. letin Leptin is secreted by cells in adipose tissue and acts on the hypothalamus of the brain to inhibit appetite. Leptin The the is a amount groups of control cells. of If The inactive They type mice and had of new Leptin a body Figure 5 Mouse with obesity due to lack of were injected leptin and a mouse with normal body mass increased of that recessive with and weight, a ob body about allele was mass of that in food feed ob. In by by showed the early of is the these causing with that in a tissue. wild the 1990s When energy with become adipose the cells leptin. a to rise, research compared Adipose in and hormone membrane increased declined, 30 % cells). intake contribute supported produce appetite this ravenously, experiments leptin. storage food intake. grams, gene by of that the (fat concentrations through 100 allele, cannot dropped brain leptin this named their target demonstrated 1950s Breeding alleles the cells controlled The reduced recessive leptin of mainly of is receptors was the weight wild-type hormone two in to adipose body. blood and system grams. copies the binds by blood the increases, this body the in inhibition 20–25 have tissue discovered two that of secreted in hypothalamus tissue gain to leptin the appetite grow shown of appetite. mice mice ▲ in adipose of hormone adipose importance strain a of cells long-term of protein concentration it obese was synthesis mice that ob/ob mice expenditure month. letin and besit Testing of leptin on patients with clinical obesity and reasons for the failure to control the disease. The by a discovery lack soon this in led to way. to that leptin obesity and attempts Amgen, California, rights 332 of paid leptin a to treat mice by a obesity million large could leptin biotechnology $20 and in cured for clinical be caused injections in humans company the in based commercial trial was carried out. Seventy-three themselves or with used, so knew were a either placebo. neither who was analysed. obese with A the volunteers one double of blind researchers injecting injected several leptin leptin procedure nor until the the doses was volunteers results 6 . 6 The leptin swelling The 7.1 a eight kg loss injections and of of only patients body 1.3 injecting the receiving in on the the highest volunteers dose the in the results tissue lost with of inevitably fails are group from a loss of 15 kg to a gain of 5 body mass lost during the trial was rapidly are afterwards. frequent in Such drug kg. very mice of humans and other is small are contrast humans leptin to have ob/ob to concentrations. leptin so fail to concentrations. and food most The have – high in many obesity insulin prevents extra if the leptin cause injections early-stage type II is alone diabetes. to of cases mutations in of obesity the genes in or its various receptors on for target Trials in people weight with loss such while obesity the leptin have shown injections ways continuing. to is cells it, even More and and However in shown the of at leptin inhibited of adipose to be to have leptin injected affect in has the children not solving the most refused reproductive suitable high not the has consequently treatment resistant therefore excessive. day blood target respond is of the obese become Appetite intake leptin disappointing research different mice, may blood is a short-lived rodents. exceptionally hypothalamus as proportion due synthesis protein In with in resistance Injection control just rise usually are from to a leptin Also signicant physiology appetite. ineffective cells. outcomes the very leptin regained causing resistance, humans any r e p r o D u C t i o n but inhibition A widely develops, leptin were varied a n D concentration trial. dose who h o m e o S t a S i S and the compared However, highest irritation completed average 12 placebo. the skin patients receiving mass kg induced 47 h o r m o n e S , it. several of those Also leptin development system, and fullled human so young its early obesity times a offered and has functioning injections adults. this been are All promise as in a not all means problem. meatnin Melatonin is secreted by the pineal gland to control circadian rhythms. Humans are behaviour They can the Circadian light daily the of evening rapidly The most night. night. time drop the drops the obvious levels in core kidney, a 24-hour are person is because cycle known placed an and as have rhythms circadian system in rhythms. experimentally internal to grown brain a low by body and of two the at dawn liver, changes of is is no in used as to as Melatonin of the increases the the cells cues set about hormone in hormone concentrations the sleep-wake and the is rise rapidly and fall at blocking the the rise during have in production at end to through of the the night- melatonin the been High sleep contributes articially urine cycle. promote waking receptors decreased in secretion. melatonin melatonin cells These external secretion and encourage that of (SCN). secretion blood in temperature, that the drowsiness levels shown temperature. with control groups nuclei Melatonin melatonin giving suggesting they feelings have on culture level these effect in gland. blood to depend suprachiasmatic melatonin core it if cause Falling reduces in a These humans the the Experiments drop levels if pineal response melatonin the In the from in in even day. by and removed in darkness called rhythm time live cycle. even or rhythms melatonin to this rhythm. hypothalamus a t continue continuous control adapted that day causes discovered night may a in be ▲ another effect of this Figure 6 Until a baby is about three months old hormone. it does not develop a regular day-night rhythm When light humans cues are placed indicating the experimentally time of day, the in an SCN environment and pineal without gland usually of melatonin secretion so sleep patterns do not t those of the baby’s parents 333 6 H u m a n p H ys i o l o g y maintain a timing the day. of A of rhythm special type wavelength indicates to melatonin of rhythm of slightly is ganglion 460–480 the SCN secretion longer normally nm the so cell and timing that it than 24 adjusted in the passes of hours. by a few retina of impulses dusk and corresponds to the to dawn the This indicates minutes eye cells and that so each detects light in or the allows day-night SCN. it to This adjust cycle. Jet a and eatnin Causes of jet lag and use of melatonin to alleviate it. Jet has lag is a common crossed three travel. The awake during sleeping to and continuing rather of more to day than are daylight understand: timing experience symptoms through headaches or the the hours night, set a SCN someone who Jet air impulses are used gland rhythm point to of be are suit the try that it eastwards few is to and days, cells detect regime. prevent time helping a ganglion new to the for they commencing. and destination. by when at shown the departure lasts sent to to orally easy only SCN adjust irritability, causes lag the remaining difculty pineal the during in fatigue, and at and The circadian night for zones difculty indigestion. and the time or when Most light trials crossing help reduce at jet the jet is ve It is melatonin more taken have sleep especially or to ideally promoting lag, to body sometimes lag. should of which retina the Melatonin sleep effective reduce during in if time ying zones. Sex deterinatin in aes A gene on the Y chromosome causes embryonic gonads to develop as testes and secrete testosterone. Human egg reproduction from embryos or a and testes. whole ● If the of SRY is SRY ● 50% have of a embryos embryonic codes factor). testis copy on of develop pathway the present, located determining cause is on fusion a for of the the Y a or sperm of that presence the TDF of development gonads depends gene gene the the developmental baby embryos. that involves Initially embryonic The the This female. the could embryonic embryonic the of gonads DNA-binding a either absence chromosome, stimulates from male embryo so is is the with become gonads an same in all ovaries and thereby onegene. develop only protein called expression into present of TDF other testes. in 50 % (testis genes development. have the gonads two SRY X chromosomes gene. develop as TDF is and therefore no not Y so they produced do not and the ovaries. Teststerne Testosterone causes prenatal development of male genitalia and both sperm production and development of male secondary sexual characteristics during puber ty. The of testes about ▲ Figure 7 X and Y chromosomes 334 develop pregnancy, early 30mm stage at long. and from the the time The these embryonic when testes the develop produce gonads embryo is in about becoming the a testosterone-secreting testosterone until about the eighth fetus week and cells at fteenth is an week 6 . 6 of pregnancy. genitalia At to puberty the production males. During develop, in of secretion the pubic hair also during and weeks are of testes, Testosterone characteristics the which of h o r m o n e S , secretion, shown in testosterone which causes puberty deepening is the the the testosterone gure increases. primary as This sexual of enlargement voice due causes a n D r e p r o D u C t i o n male 8. development such of h o m e o S t a S i S to stimulates sperm characteristic secondary of the growth penis, of the of sexual growth larynx. Sex deterinatin in feaes Estrogen and progesterone cause prenatal development of female reproductive organs and female secondary sexual characteristics during puber ty. If the gene SRY Ychromosome, is therefore not progesterone, by the not the present are always ovaries and the female reproductive During puberty the but the include enlargement the organs of of the in of by female female as the rst In estrogen and are they the and shown sexual growth of is no Testosterone estrogen are of fetal progesterone, in gure 9. increases, characteristics. pubic and secreted absence progesterone secondary and At placenta. which there ovaries. hormones, pregnancy. estrogen breasts because develop maternal develop of embryo two later presence development an gonads present and secretion causing in embryonic secreted, mother’s testosterone is and These underarm hair. mae and feae rerductive sstes Annotate diagrams of the male and female reproductive system to show names of structures and their functions. The tables female on the next reproductive page indicate systems are functions that should be included when diagrams of male and annotated. seminal vesicle bladder bladder sperm duct sperm duct prostate seminal vesicle gland erectile tissue prostate gland penis penis epididymis testis epididymis urethra urethra scrotum testis foreskin scrotum ▲ Figure 8 Male reproductive system in front and side view 335 6 H u m a n p H ys i o l o g y oviduct ovary oviduct opening to uterus uterus cervix ovary oviduct bladder vagina cervix large urethra intestine vagina vulva labia (vulva) ▲ Figure 9 Female reproductive system in front and side view m dcv ss Testis Scrotum F dcv ss Produce sperm and testosterone Ovary Produce eggs, estrogen and progesterone Hold testes at lower than core body Oviduct Collect eggs at ovulation, provide a site temperature for fer tilization then move the embryo to the uterus Epididymis Store sperm until ejaculation Sperm duct Transfer sperm during ejaculation Uterus Provide for the needs of the embryo and then fetus during pregnancy Seminal vesicle Secrete uid containing alkali, and prostate proteins and fructose that is added Cervix Protect the fetus during pregnancy and then dilate to provide a bir th canal gland to sperm to make semen Urethra Transfer semen during ejaculation Vagina Stimulate penis to cause ejaculation and provide a bir th canal and urine during urination Vulva Penis Protect internal par ts of the female Penetrate the vagina for ejaculation reproductive system of semen near the cervix menstrua cce The menstrual cycle is controlled by negative and positive feedback mechanisms involving ovarian and pituitary hormones. The menstrual menopause, it gives called the ovary. lining most In of chance each the The second of corpus of uterus half luteum. because egg is The a rst group stimulated (endometrium) breaks women from pregnancies. is open, Each half of to puberty time of the follicles grow. repaired releasing and its occurs cycle developing the starts egg the cycle menstrual is At until the same to into in time thicken. the is the the The oviduct. degenerate. of follicle most pregnancy. an follicle follicles the a in during phase follicle developed other occurs from follicular The wall 336 the cycle apart the that cycle is called released Continued an the egg luteal phase becomes development of the a because body called endometrium the the prepares 6 . 6 it for the implantation of an embryo. h o r m o n e S , If h o m e o S t a S i S fertilization does not a n D r e p r o D u C t i o n occur TOK the corpus luteum endometrium in in the the ovary uterus breaks also breaks down. The thickening down and is shed of the during t w d vs menstruation. w jd f c? Figure 10 including typical shows one for measured so woman in mass progesterone, estrogen of a the is hormone complete who per FSH measured ovary and of levels is not and the LH a woman cycle. The pregnant. millilitre. in in menstrual The are The actual (pg). a 36-day in of are levels very nanograms Figure 10 also period, changes hormone masses measured picograms over pattern Human eggs can be obtained by is using FSH to stimulate the ovaries, are then collecting eggs from the ovaries small, (ng) shows using a micropipette. Women have and the sometimes undergone this procedure state to produce eggs for donation to endometrium. another woman who is unable to produce eggs herself. The four cycle by hormones both hormones receptors are in negative produced in ovarian gure the and by the all help positive of gland follicle produced to control feedback. pituitary membranes hormones, 10 by cells. the FSH that the and bind to Estrogen wall of menstrual the LH are FSH and protein and Recently stem-cell researchers have LH used eggs in therapeutic cloning progesterone follicle and corpus experiments. The nucleus of an egg is removed and replaced with a nucleus from an adult. If the resulting cell developed as an embryo, stem cells 1000 could be removed from it and cloned. LH It might then be possible to produce tissues or organs for transplanting to 600 400 noitaurtsnem noitaurtsnem lm gn/ level enomroh 1– FSH 800 the adult who donated the nucleus. There would be no danger of tissue rejection because the stem cells would be genetically identical to 200 the recipient. 0 There is a shor tage of eggs both for donation to other women and for research. In 2006, scientists in England got permission to oer to develop mature corpus luteum 8 lm gp/level negortse 1– 400 progesterone 6 300 estrogen 200 4 100 2 women cut-price IVF treatment, if they lm gn/level enoretsegorp follicle nearly 1– follicle starting were willing to donate some eggs for research. In Sweden only travel and other direct expenses can be paid to egg donors, and in Japan egg donation is banned altogether. 1 Is there a distinction to be drawn between donating eggs for 0 26 28 2 4 5 8 10 12 14 16 18 20 22 24 26 28 days of menstrual cycle 4 therapeutic cloning experiments and donating eggs to a woman muirtemodne fo ssenkciht who is unable to produce eggs ovulation herself, for example because her ovaries have been removed? Can the same act be judged dierently depending on motives? 28 ▲ 2 7 14 21 28 Figure 10 The menstrual cycle 337 6 H u m a n p H ys i o l o g y luteum. they FSH ● They rises and towards uid. FSH to the a receptive more the LH rises to follicular a of It in end of the the follicles, partial follicle estrogen Progesterone and Progesterone of LH female body, where development. menstrual each cycle containing secretion after rise It of and an oocyte estrogen (negative of by the at the to the follicle the into a start low of the level thickening inhibits FSH the and and stimulates end of meiosis allowing corpus the in it of the to burst the luteum which progesterone. luteal by the and LH after the production the of wall make development and phase. estrogen feedback) towards feedback) that levels completion the follicular endometrium estrogen high peak the the receptors (negative the of of boosting ovulation back also FSH promotes (positive drop end reaches sharp also promotes endometrium. it FSH and in FSH, digestion levels then to the thickening stimulates ovulation. the secretes sudden phase. and at gland cells therefore stimulates increase When secretion secretion. oocyte an feedback). LH peak of towards and follicles wall and the also peak repair and open many development menstruation inhibits ● peak rises stimulates (positive ● by expression wall. Estrogen It a the follicular follicle absorbed gene to stimulates ● are inuence phase, end of reach this maintenance secretion by a phase. of the the pituitary feedback). D-sd qss: The female athlete triad The of female three female and athlete athletes: menstrual bone triad interrelated mineral is a syndrome disorders osteoporosis, disorders. density. It that can can be caused runners is in calcium, vitamin D or energy, a) higher bone a density in runners cycles b) lower by per parts had year. for of The shows the above the the femur for numbers t-score young Outline 11 different deviations mass a) Figure is or the bone a) Suggest b) bone mean the density than the mean [2] density between than the mean. [4] reasons or for no female athletes menstrual low one reason body for cycles. weight in eating [2] disorders female athletes. [1] of peak women. relationship Suggest and menstrual number below of mineral female of some low number )DS( erocs-t 1 two who standard bone levels. for diet havingfew estrogen reasons having: eating by or the reduced 3 low Explain affect disordered Osteoporosis 2 consisting 1 neck of femur trochanter of femur 0.5 0 0.5 of menstrual cyclesper year and bone 1 density. [3] menstrual cycles per year b) Compare femur the with results the for results the for neck the of the trochanter. 0–3 4–10 ▲ Figure 11 Bone mass in women grouped by number of menstrual cycles 338 11–13 [3] 6 . 6 h o r m o n e S , h o m e o S t a S i S a n D r e p r o D u C t i o n In vitr fertiizatin The use in IVF of drugs to suspend the normal secretion of hormones, followed by the use of ar ticial doses of hormones to induce superovulation and establish a pregnancy. The in natural vivo, tissues method meaning of outside the the conditions. of that body. body This occurs carefully called in in inside Fertilization in is fertilization it can humans the also controlled vitro a is consequence usual. living as happen Twelve many always abbreviated to IVF . This been used extensively to the in either the male overcome or the are rst woman spray, or is takes to LH. several stage a stop drug her Secretion therefore different usually female also protocols day, pituitary of for This usually gland estrogen stops. IVF , as a secreting and the cycle and allows doctors to embryo. wall is nasal to timing and amount of egg given much than is mm by in an diameter injection they of is normally secreted HCG, eggs at is 37 passed out 50,000 in °C mounted of to a the through follicles. 100,000 shallow until the on by the next uterus Each sperm dish, an egg cells which is in then day. fertilization is successful then one or more control production in are placed in the uterus when they are the 48 hours old. Because the woman has not ovaries. Intramuscular follicles 18 that scanner with incubated gone then IVF normal about woman’s are mature micropipette conditions embryos the A wash mixed sterile FSH progesterone suspends to hormone ultrasound but The If menstrual of be parent. down-regulation. each stage than can fertility the There This there superovulation. follicles stimulated another problems follicles. develop and procedure are has called follicles unusual fertilization, When almost more not twenty therefore laboratory far is to injections daily for develop. higher during of about The FSH ten FSH concentration a normal and days, LH to of this menstrual progesterone are in stimulate injections give and the grow from as a is vagina, maintained. a hormone cycle through then a normal usually to If the menstrual given ensure the that embryos pregnancy pregnancy that as the a cycle tablet uterus implant that began by placed lining and follows extra is natural is continue no to different conception. Wiia Harve and sexua rerductin William Harvey’s investigation of sexual reproduction in deer. William Harvey circulation life is into sexual the William from remembered but it mixes to he also generation reproduction. He which with was the for had to a discovery generation taught male menstrual his lifelong the blood. and “seed produces The a egg of the obsession with pioneered and soil” seed, theory which develops how research of forms into a an fetus mother. Harvey are chiey blood, according when inside Deer is the transmitted Aristotle, egg of tested seasonal Aristotle’s breeders and theory only using become a natural sexually experiment. active during the ▲ autumn. Harvey examined the uterus of female deer during the Figure 12 IVF allows the earliest stages in a mating human life to be seen. This micrograph shows a season by slaughtering and dissecting them. He expected to nd eggs zygote formed by fer tilization. The nuclei of the developing in the uterus immediately after mating, but only found signs egg and sperm are visible in the centre of the of anything developing in females two or more months after the start of zygote. There is a protective layer of gel around the mating season. the zygote called the fer tilization membrane 339 6 H u m a n p H ys i o l o g y He of regarded his reproduction proceed from commixture was false, during sexual ▲ of was false seed that or today or Although that that he “neither have as female intercourse) aware deer concluded male seed”. (sexual well of with and conclusion reproduction: yesterday of the Harvey’s coitus Harvey experiments was had in not nor “seed did not theory neither yet and from soil” result any theory from events false. discovered philosophers satisfactorily Aristotle’s doth coition, fetus also that fetus Aristotle’s the was the proof “the the nor explained, or basis the of physicians solved the of problem Aristotle.” Figure 13 William Har vey’s book on the reproduction of animals Exercitationes de Generatione Animalium published in 1651 Irveents in aaratus and research breakthruhs Developments in scientic research follow improvements in apparatus: William Harvey was hampered in his observational research into reproduction by lack of equipment. The microscope was invented seventeen years after his death. Harvey publish but was he 73 was his did into eventually years Generatione solved understandably research the old in do his Animalium. mystery of reluctant sexual so in work He to reproduction, 1651 when Exercitationes knew sexual that he he reproduction: Harvey because effective when and de had William not I remain more plainly in than sensation, Let the the see nothing uterus remains ... I in have learned after the at braine invented and all doth coition, this ingenious ... of subsequent after of an stage of it; let the supercilious the for the laugh scofng their ticklish swinge. generation, Because I is no sensible thing in the coition; and yet there is a by research something 340 render the should be animal has deciencies being will made Harvey’s sperm, eggs there, were death, and in often been apparatus, early hampered with for a discoveries into the improvements. future and we can uterus forward to further transformations in necessity, fruitful. the small Microscopes after following continue of the natural world as new which techniques may in embryos. understanding that choice embryos let look after remained his microscopically period. of available say, This there not gametes it: only them of with because years discovery mystery development remain long fusion unlucky animal used the were men reject time and was seventeen Scientic consider he solve so embryo He unusually invented allowing Fable. ock that to microscopes working, experimental for no was undiscovered. deer When he failed and technology are invented. our Q u e S t i o n S Questins 1 Using the data in table accidents 1: during disrupted a) outline the relationship between of the mother and the success percentage IVF as a result Figure of 15 oxygen saturation of shows arterial during a night of sleep in a patient with [3] severe b) daytime tiredness. rate blood of the and the the age sleep outline the relationship between obstructive sleep apnea. the 100 number of embryos transferred and 1 70 the of chance of having a baby as a result IVF [3] 100 2 c) discuss how should be many allowed embryos to fertility 70 centres transfer. [4] 100 3 70 pc f cs iVF cc ccd f s sfd a f 100 4 1 2 single twins 70 single twins sruoh single 3 triplets < 30 10.4 20.1 9.0 17.5 3.6 0.4 30–34 13.4 21.8 7.9 18.2 7.8 0.6 35–39 19.1 19.1 5.0 17.4 5.6 0.6 O % 2 100 5 70 100 6 70 > 39 4.1 12.5 3.5 12.7 1.7 0.1 100 T able 1 7 70 100 2 Figure 14 shows variations in liver glycogen 8 70 over the course of one day. 0 a) Explain the variation in 10 20 30 liver 40 50 60 minutes glycogen. [3] Figure 15 b) Evaluate the contribution of glycogen to a) blood sugar homeostasis. Hour 8 shows a typical pattern due to [2] obstructive sleep level negocylg revil (i) Explain the (ii) Explain apnea. causes the of causes falls of in saturation. [2] rises in saturation. (iii) Calculate falling lunch dinner Estimate that 12:00 16:00 how and long rising each cycle saturation of takes. [2] breakfast b) 8:00 [2] 20:00 24:00 4:00 the the minimum patient oxygen experienced saturation during the 8:00 night, and when it occurred. [2] Figure 14 c) Deduce during the the sleep night patterns when of the the trace patient was taken. 3 Sometimes This is is the the called ventilation apnea. blockage of One the of the lungs possible airways by cause the soft 4 palate sleep during apnea. sleep. It consequences, has This some including is called The action potential of a squid axon was obstructive potentially an [2] stops. recorded, with The was the axon in normal sea water. harmful increased risk + axon then placed in water with a Na of concentration of one-third of that of sea water. 341 6 h u m a n The p h yS i o l o g y action potential was recorded again. a) Using only the data in gure 17, outline the + Figure 16 shows these recordings. effect of reduced Na )Vm( laitnetop ebarbmem (i) the magnitude (ii) the duration concentration of of on: depolarization the [2] action +40 potential. sea water [2] +20 + b) Explain the effects of reduced Na 0 concentration on the action potential. [3] 33% 20 + c) Discuss the effect of reduced Na 40 concentration on the time taken to return 60 to the resting potential. [2] 80 1 2 d) Compare the action potentials of shaker time (ms) and normal fruit ies. [3] Figure 16 e) Explain action 5 Geneticists y that with discovered shakes ether. a mutant vigorously Studies have variety when shown of fruit anaesthetized that the shaker + mutant has properly. normal K channels Figure fruit 17 ies that shows and in do not action shaker function potentials in mutants. 40 wild-type drosophila normal action potential 0 Vm/laitnetop ebarbmem 40 4 8 12 16 40 shaker mutant abnormal action potential 0 40 4 8 12 time (ms) Figure 1 7 342 16 the differences potentials. between the 7 N U C L E I C A C I D S ( A H L ) Introduction The discovery of revolutionized coded form in the structure biology. DNA is of DNA Information copied onto structure stored mRNA. in a The of Information translated DNA is ideally transferred into an suited from amino acid to DNA its to function. mRNA is sequence. 7 .1 DN A and an Understanding Applications ➔ DNA structure suggested a mechanism for DNA ➔ Rosalind Franklin’s and Maurice Wilkins’ replication. investigation of DNA structure by X-ray ➔ Nucleosomes help to supercoil the DNA . ➔ DNA replication is continuous on the leading diraction. ➔ Tandem repeats are used in DNA proling. ➔ Use of nucleotides containing strand and discontinuous on the lagging strand. ➔ DNA replication is carried out by a complex dideoxyribonucleic acid to stop DNA replication system of enzymes. ➔ in preparation of samples for base sequencing. DNA polymerases can only add nucleotides to the 3’ end of a primer. Skills ➔ Some regions of DNA do not code for proteins but have other impor tant functions. ➔ Analysis of results of the Hershey and Chase experiment providing evidence that DNA is the genetic material. Nature of science ➔ ➔ Utilization of molecular visualization software Making careful obser vations: Rosalind to analyse the association between protein and Franklin’s X-ray diraction provided crucial DNA within a nucleosome. evidence that DNA is a double helix. 343 7 N U C L E I C A C I D S ( A H L ) The Hershey–Chase experiment Analysis of the results of the Hershey–Chase experiment providing evidence that DNA is the genetic material. From that and the late 1800s, chromosomes that the hereditary nature. Aware of protein both that contenders Until the 1940s, class due of to to specic proteins. two nucleic be the the view was functions properties requirements and that for acid, that that had great been the was variety Further, identied of function to as be for were essential and was known protein that cells becoming bound then bursts, (see gure certain with The simple T2 while and cell. The are to the often virus they It has DNA a is coat portion which of new by their of the cell viruses environment specic chose to to because inside a work of composed found was factories infected numbers them it injecting An bacteriophage structure. protein the of 1950s, particles non-genetic Viruses type. the cells large releasing cell was the infectious host outside 1). In wanted material virus-producing to manufactures and Chase genetic DNA. are into material. remains the or viruses transform genetic Martha whether viruses of material. Hershey ascertain virus a sub-units expected hereditary was it sub-units. had composed molecules material. as Alfred to chemical were protein specicity the a both occurring were convinced heredity had genetic nucleotide Variety in favoured, naturally four were role material macromolecules opposed many to material twenty a chromosomes and were hereditary scientists played its very entirely the coat. DNA protein ▲ Figure 1 Coloured transmission electron micrograph (TEM) of T2 viruses (blue) bound to an Escherichia coli bacterium. Each virus consists of a large DNA-containing head and a tail composed of a central sheath with several bres. The bres attach to the host cell ▲ surface, and the virus DNA is injected into the cell through the sheath. Figure 2 Diagram illustrating the structure of the T2 virus It instructs the host to build copies of the virus (blue, in cell) Daa-bad qn: The Hershey–Chase experiment Alfred Hershey scientists the In who chemical their and Martha worked nature experiment, the fact that not sulphur but not DNA of to resolve the they took proteins phosphorus. They were the genetic contains while Chase phosphorus. two debate over material. advantage phosphorus contain cultured of but with the blender of the the two to infected types separate virus culture pellet. They sulphur a viruses radioactive from of The cells viruses. the the solution separately They used non-genetic cell to and then concentrate were genetic bacteria expected component to of a component centrifuged the cells have the in the virus in 35 that contained sulphur and proteins they with separately radioactive cultured ( S) viruses them. pellet They and measured the the radioactivity supernatant. Figure3 in represents 32 that 344 contained DNA with radioactive ( P) the process and results of the the experiment. 7. 1 D N A s t r u c t u r e A N D r e p l i c A t i o N 35 radioactive protein ( S) 35 virus radioactivity ( S) in supernatant 35 protein coat with S bacterium bacteria 32 radioactive DNA ( P) virus DNA with 32 P bacterium bacteria 32 radioactivity ( P) in pellet Questions Explain what b) Explain why found in the a supernatant the genetic pellet and is. material not the should be supernatant. 32 c) Determine the percentage of remains in the supernatant. Determine the percentage the P that 35 d) in e) the of S that remains supernatant. Discuss which the evidence transforms that the DNA bacteria is the into tnatanrepus ni epotosi fo % a) percentage of isotope in supernatant after 8 minutes agitation 100% 80% 60% 40% 20% 0% 35 infected 32 S chemical ▲ P Figure 3 cells. X-ay dan an a vdn f ma Making careful observations: Rosalind Franklin’s X-ray diraction provided crucial evidence that DNA was a helix. Two names connection Watson. they are Flashes could not experimental other His of usually with DNA is of have the described insub-topic2.6 led achieved and One into remembered discovery insight work scientists. research the of of to it careful these in the their was Erwin base and success, without data-based 107). Crick but skilled observations percentage (page Another in DNA, by Chargaff. composition question key gure Rosalind Franklin. associate in London. The structure had the of already institute in the discovery 1950, biophysics unit DNA was by she unit other of DNA became at King’s a diffraction. X-ray College, carboncompounds the Franklin techniques diffraction was research alreadyinvestigating X-ray becomeskilledin crystallographyand researching in In of while at an Paris. 345 7 N U C L E I C At of King’s a A C I D S College camera, so measurements ( A H L ) she she of improved could the make X-ray the resolution more diffraction diffraction the detailed had previously been possible. She high quality samples of aligned in narrow DNA bres. Franklin’s with Watson By and of humidity two types of pure be produced and as Franklin was represented investigated the normal after Franklin starting had work obtained diffraction images have described been beautiful ever X-ray taken”. the next her ndings of at structure the of the or permission, best the calculations based diffraction on publish her results it. Crick Before and had used structure. It them is to build widely their accepted model that of Rosalind DNA, deserved in Their was there embarked on are strong rigorous is described to a Nobel in evidence. of happened. prizes aged in 1962, Prize posthumously, we can discoveries serendipity more for her or She foundations the techniques but research, of of science and of Prizes Rosalind from be life made but rigorous were cancer cannot in be Franklin prize her insight, are diligent Watson died many sometimes ashes and she Nobel than remember may Crick but thirty-seven. remembered What publish analysis never awarded They most substance unwilling was a the any implications She until of 1958, X-ray existence. “amongst this awarded College, sharpest DNA as King’s photographs section. therefore knowledge shown both. but Soon was could Franklin she calculate unsure DNA which to sample Watson could her helix. careful Franklin control allowed DNA the pattern molecules that the also James produced of patterns Without than patterns dimensions winners. is that through the real experimental observation. Rosalind Franklin’s investigation of DNA structure Rosalind Franklin and Maurice Wilkins’ investigation of DNA structure by X-ray diraction. If a beam most by is of the of it X-ray s passes particles called in them by particles d i re cte d the diffractio n. makes the is thr o ug h at T he a m a ter ia l , s ome m ate ri al . is Thi s wav el e ng th parti cul a r l y in but s e ns itive b i o l o gi ca l to sc at t e r ed s c at t e r in g of X- r ays d iffr a c t io n mo le cul es includingDNA. In a crystal repeating regular way. molecules array in pattern the particles pattern, so DNA were be cannot be in samples obtained, arranged diffraction arranged Franklin’s to are the in a crystallized an for rather orderly a regular occurs in but a the enough diffraction than random scattering. ▲ An to X-ray collect rotated the be detector the in of recorded placed scattered three pattern is rays. different scattering. using close X-ray The to the sample dimensions Diffraction lm. to can be investigate patterns Franklin can From was high resolution camera containing the able structure X-ray obtain from these 346 very DNA. clear Figure diffraction 4 images shows patterns. of diffraction the most of make a pattern series of in gure 4 deductions Franklin about the DNA: The cross in the centre of the pattern indicated lm that to diffraction to developed ● a Figure 4 Rosalind Franklin’s X-ray diraction photograph of DNA sample the molecule was helical in shape. patterns famous of ● The angle (steepness of of the cross angle) of shape the showed helix. the pitch 7. 1 ● The distance showed between turns of the the horizontal helix to be 3.4 D N A s t r u c t u r e bars nm the apart. A N D repeats. distance r e p l i c A t i o N This turned between out adjacent to be base the pairs vertical in the helix. ● The distance diffraction there was a molecule, between pattern the and repeating with a middle the top structure distance of of the showed that within 0.34 nm These the deductions diffraction between in the that pattern discovery of of the The Watson and Crick model suggested semi- were DNA made were structure from the critically of X-ray important DNA. toK conservative replication Wha n d n hav DNA structure suggested a mechanism for DNA replication. whn h and dn dn’ fy mah xmna Several lines of experimental evidence came together to lead to the vdn? knowledge by the Nobel discerned base of the structure prize from winner the composition DNA: Linus careful studies of molecular Pauling, photographs of Erwin modelling X-ray of diffraction Rosalind Chargaff. pioneered But Franklin insight Charga wrote about his patterns and and observations: the imagination the results serve to disprove the played a role as well. tetranucleotide hypothesis. One of Watson and wrapped around Rosalind Franklin nitrogen bases phosphate Crick’s one rst another countered were with this relatively backbone and models the had the nitrogen model with hydrophobic would likely sugar-phosphate the in point bases facing to the that to centre the of noteworthy cannot yet be said the sugar- the however, It is, - whether this is more than accidental, outwards. knowledge comparison in strands helix. - that in all deoxypentose nucleic acids examined thus far the molar ratios of total purines to total pyrimidines Franklin’s X-ray diffraction studies showed that the DNA helix was and also of adenine to thymine and tightly packed so when Watson and Crick built their models, their choices of guanine to cytosine were not far required the bases to t together such that the s
