Learner Guide for Cambridge AS and A Level Biology

Transcription

1 Learner Guide fr Cambridge AS and A Level Bilgy Hw t use this guide The guide describes what yu need t knw abut yur AS/A Level Bilgy examinatin. It can be used t help yu t plan yur revisin prgramme fr the thery examinatins and will explain what the we are lking fr in the answers yu write. It can als be used t help yu revise by using the table in Sectin 3, What yu need t knw?, t check what yu knw and which tpic areas f Bilgy yu have cvered. The guide cntains the fllwing sectins: Sectin 1: Hw will yu be tested? This sectin will give yu infrmatin abut the different types f thery and practical examinatin papers that are available. Sectin 2: Examinatin tips This sectin gives yu advice t help yu d as well as yu can. Sme f the tips are general advice and sme are based n the cmmn mistakes that learners make in exams. Sectin 3: What will yu be tested n? This sectin describes the areas f knwledge, understanding and skills that yu will be tested n. Sectin 4: What yu need t knw This shws the syllabus cntent in a simple way s that yu can check: the tpics yu need t knw abut the cntents f each syllabus - AS, A2 and the Optins details abut each tpic in the syllabus hw much f the syllabus yu have cvered Sectin 5: Useful websites Sectin 6: Appendices This sectin cvers the ther things yu need t knw, including: infrmatin abut the mathematical skills yu need infrmatin abut terminlgy, units and symbls, and the presentatin f data the imprtance f the cmmand wrds used in the examinatin papers Page 1 f 68

2 Sectin 1: Hw will yu be tested? 1.1 The examinatins yu will take There are three ways yu can gain an advanced level qualificatin. take the AS qualificatin nly fllw a staged assessment rute t the A Level by taking the AS papers and the A2 papers in different examinatin sessins. Usually this means taking the AS papers at the end f ne year f study and the A2 papers at the end f a secnd year f study. take all the examinatin papers in the same examinatin sessin leading t the full A Level AS Yu will be entered fr three examinatin Papers, tw thery Papers and ne practical Paper. Yu will take Paper 1 (thery, multiple chice), Paper 2 (thery, structured questins) and Paper 3 (practical test). A2 Yu will be entered fr tw examinatin Papers, Papers 4 and 5. Yu will take Paper 4 (thery) and Paper 5 (planning, analysis and evaluatin.). Page 2 f 68

3 1.2 Abut the examinatin Papers The table gives yu infrmatin abut the examinatin Papers Paper number 1 1 hur (40 marks) Hw lng and hw many marks? What s in the paper? Weighting % 40 multiple-chice questins. Yu chse ne answer yu cnsider crrect frm a chice f 4 pssible answers. AS A 2 1 hur 15 min (60 marks) 3 2 hurs (40 marks) 4 2 hurs (100 marks) 5 1 hur 15 min (30 marks) Structured questins. Yu shuld write yur answers in the spaces prvided. The Paper tests the AS syllabus nly. A practical test set and marked by CIE. It will include experiments and investigatins based n the AS syllabus. Structured questins, ttalling 85 marks plus a chice f free respnse questins that carry a further 15 marks. Based n the A2 syllabus, but a knwledge f the AS syllabus is required. A written paper that tests the practical skills f planning, analysis and evaluatin. It will include infrmatin abut experiments and investigatins frm bth AS and A Abut the practical Papers Twenty-three percent f the marks fr AS Bilgy are fr practical wrk. In Paper 3, yu will have t handle familiar and unfamiliar bilgical material and will be expected t shw evidence f the fllwing skills: planning implementing interpreting and cncluding When unfamiliar materials r techniques are invlved, yu will be given full instructins. Questins culd be set that will require the use f a micrscpe r hand lens. N dissectin will be set in Paper 3. Page 3 f 68

4 If yu cntinue t a full A level, after AS, the mark yu btained in Paper 3 will cntribute twelve percent f yur verall mark and Paper 5 will cntribute a further twelve percent. In Paper 5, there will be questins in which yu will be expected t design an investigatin and write ut a plan that yu will nt carry ut. T d this cnfidently yu need plenty f experience f practical wrk in the labratry. Questins invlving an understanding f the use f the t-test and the chi-squared test may be set. If they are, yu will be prvided with the frmulae fr these tests. Page 4 f 68

5 Sectin 2: Examinatin tips Much f this advice is given in respnse t the types f answers that learners have written in the past. These tips are presented under varius subheadings t help yu t prepare fr yur examinatins. Sme examples f questins and answers are included t illustrate sme f the tips. Make sure that yu read all the general tips. These can be imprtant in any f the papers that yu take. Have a cpy f the syllabus t lk at as yu read thrugh these tips. Nte that in Sectin 4 the first part is the AS syllabus and the secnd part is A2. Make sure that yu knw the examinatin papers that yu are taking befre yu lk at the tips fr the different papers. At AS, yu will take Paper 1, which is a multiple chice paper. Paper 2, which cnsists f shrt answer questins. Paper 3 which is the practical paper. There are different papers fr different time znes; fr example, 11, 12 and 13 are all multiple chice papers. At A2, yu will take Paper 4, which has a shrt-answer part fr 85 marks and an essay fr 15 marks. Paper 5, which tests yur skills f planning, analysis and evaluatin. It is nt a practical paper like Paper 3, but des require much experience f practical wrk. General Advice Use yur syllabus all the time while yu are revising and preparing fr the examinatin papers. Yu must knw which tpics yu will be tested n. Make sure yu have all the equipment yu will need fr the exam in a clear, plastic cntainer. Yu need tw pens, pencils (preferably HB r B), a clean eraser, a ruler (which measures in mm), a pencil sharpener and a calculatr. Answering questins. The questins are designed t test yur knwledge and understanding and yur ability t apply the skills yu have gained during the curse. When yu are writing yur answers remember that anther persn has t be able t read them. D nt waste time by writing ut the questin befre yu start t answer. Keep yur handwriting clear and legible. Keep yur answers n the lines n the questin paper. D nt write in the left hand side f the paper r in the clumn marked Fr Examiner s use. This is because papers are scanned and then marked nline. If yu write in the margin yur answers may nt be visible. If yu wish t change an answer, crss ut yur first answer and rewrite. D nt write ver what yu have already written. If yu have t crss ut smething, put a line thrugh it; d nt scribble ver it. Page 5 f 68

6 If yu run ut f space, use white space n anther part f the exam paper fr a cntinuatin answer; d nt try t squeeze in yur answer by using very small writing. If yu have t use a different space fr a rewritten answer r t cntinue an answer, put a nte t tell the Examiner where it is, e.g. see page 5 r see back page. Always try t write accurately using the crrect bilgical terms. Learners ften lse marks because they d nt use the apprpriate crrect terms in their answers. D nt use wrds like it, they, effect, affect withut any mre explanatin. A sentence like It has an effect n the bdy r They affect the prcess des nt say anything. If yu want t use the wrd it r they think what is it? r what are they? and then phrase yur answer mre precisely. If yu want t use the wrd affect r effect think hw d they affect r what is the effect that they have? Example 1 Questin Chrnic bstructive pulmnary disease (COPD) is a prgressive disease that develps in many smkers. COPD refers t tw cnditins: chrnic brnchitis emphysema. (i) State tw ways in which the lung tissue f smene with emphysema differs frm the lung tissue f smene with healthy lungs. [2] Crrect answer fr tw marks 1 There are fewer alveli than in a healthy lung. 2 The surface area fr gas exchange is much smaller. Frm the wrding f the questin it is clear that the answers refer t the lung tissue f emphysema. Ambiguus answers fr n marks 1 There are many air spaces. 2 There is less diffusin f xygen and carbn dixide. 3 There are fewer capillaries. Bth types f lung tissue have many air spaces. The technical term alveli shuld be used as in the crrect answers. Even thugh the third answer is crrect, it will nt be marked as the questin asks fr tw ways. D nt write the first answer that cmes int yur head. Yu are unlikely t think f exactly the crrect phraselgy r have all the necessary detail t answer the questin. Plan what yu intend t write befre yu start writing. Remember t read the questin carefully, plan an answer, write the answer clearly, reread the questin, re-read yur answer and then make any additins r crrectins clearly. Always re-read yur answers t check them against the questin. During yur curse yu will prbably have seen many mark schemes frm past papers. D nt learn them. It is unlikely that yur exam papers will have exactly the same questins as previus papers. If yu write ut a mark scheme that yu have learnt, it is unlikely t gain yu many marks and ften nne at all. Page 6 f 68

7 Be prepared fr questins n aspects f practical bilgy; they can appear n all the papers, nt just Papers 3 and 5. Terms. These are the technical wrds used in bilgy. Many f them are given in the syllabus. These terms will be used in questins. Yu will get mre marks if yu can use them crrectly in yur examinatin. Ask yur teacher if yu are unsure f the meanings f the bilgical terms used in the syllabus and in any textbk yu are using. Yu will ntice that many terms are defined in the syllabus, s that is a gd place t start when making yur wn dictinary. Many f the definitins in Sectin 5 f the syllabus are quite lng. It wuld be a gd idea t write mre cncise definitins fr yurself and use them t start yur wn bilgical dictinary using yur class ntes, web sites and the glssaries frm the back f text bks. Try t use the crrect spelling. If yu cannt remember hw t spell a wrd, write it dwn as best yu can. The Examiners will prbably recgnise what wrd yu mean; if the spelling is t far ut r ambiguus, then they cannt allw yu a mark. Sme bilgical terms have very similar spelling. Make sure yu write clearly and always try t spell as accurately as yu can. D nt try t mix the spellings f tw wrds when yu are nt sure which f them is the crrect answer. Fr example, yu might write meitsis when yu are nt sure whether the answer is mitsis r meisis. This answer will nt get a mark. Writing in yur wn wrds. Yu ften have t write tw r mre sentences t answer a questin. Use shrt sentences. If yu write lng sentences yu can becme cnfused and yur meaning is lst. Yu might als write smething cntradictry. It is hard fr the Examiner t find crrect statements in a muddled answer. Yu are ften asked t write dwn smething yu have learned. Make sure yu have learnt the meanings f the cmmn terms used in bilgy, e.g. active transprt, smsis, phtsynthesis and respiratin. During yur curse take every pprtunity t read and write as much as yu can t imprve the way yu express yurself. Check that yur glssary has al the terms that are used in the learning utcmes in the syllabus. What yu shuld lk fr in a questin The number f marks. Always lk t see hw many marks are available fr each questin. In Paper 1 there is ne mark fr each questin. The number f marks is printed n the examinatin papers fr Papers 2, 3, 4 and 5. The mark available fr each part questin ((a), (b), (c)(i), etc.) is printed in square brackets, e.g. [2]. The number f marks helps yu decide hw much t write. The ttal number f marks fr each questin is printed at the end f the last part questin, e.g. [Ttal: 12]. The number f marks is a guide t hw lng t spend n each part f a questin. D nt waste time and write a lng answer fr a questin which has ne r tw marks. Yu will nt get any extra marks even if yur answer is full f many crrect and relevant statements. Page 7 f 68

8 If there are tw r mre marks d nt write the same thing in tw different ways, e.g. The leaf is very large. The leaf has a large surface area. Ntice that the secnd sentence is mre accurate and is preferable t the first ne. The instructins. These are called cmmand wrds and tell yu what t d. Yu can find all the cmmand wrds in the Glssary f terms used in science papers which is in Sectin 7 at the end f the syllabus. If a questin asks yu t Name r State tw things nly the first tw will be marked. Use the numbered lines fr yur answers if they are given n the questin paper. If yu write mre than tw and the first is crrect, the secnd ne is wrng, and the third ne crrect, yu will nly get ne mark (see Example 1). Sme questins have tw cmmands in the questin, fr example Predict and explain. This means that yu have t say what yu think will happen AND then say why yu think it will happen. Usually the wrd and is printed in bld type t help yu. See the sectin belw fr a tip abut answering questins that have tw cmmand terms and require an extended answer. The table belw has a list f terms used in bilgy papers t tell yu what t d in an answer. Make sure yu knw what yu shuld d in respnse t each cmmand wrd. Example 2 Questin A learner investigated the effect f increasing the cncentratin f sucrse n the rate f activity f sucrase. The results are shwn in Fig The graph in Fig. 4.1 shws that as the substrate cncentratin increases the rate f activity f sucrase increases t a cnstant level. Describe and explain the results shwn in Fig It is quite easy t frget that there are tw parts t this questin. Befre writing yur answer it is a gd idea t write descriptin at the beginning f the first f the answer lines and then explanatin abut half way dwn. Yu culd write these in pencil and rub them ut when yu have finished yur answer. Alternatively, yu may chse t write a descriptin f the first part f the graph (activity increases) and then explain it fllwed by a descriptin and explanatin f the plateau n the graph. That is als a perfectly acceptable way t answer the questin. What the questin is abut. Make sure yu knw which part f the syllabus is being tested. Read the whle f a questin carefully including all the stimulus material and parts (a), (b), (c) (i) and (c) (ii), etc. befre yu begin t answer. Sme f the parts may have similar answers s yu need t wrk ut the differences between them. If yu write exactly the same thing in different parts f the same questin, there is n way the answer can be crrect fr bth parts. Page 8 f 68

9 There is ften stimulus material fr each questin. This might be a phtgraph, diagram, drawing, flw chart, table f data, graph r just sme text. Read all f this infrmatin carefully and study any pictures, tables r graphs that are included. All f it is relevant t the questins. The stimulus material is ften abut smething yu have nt studied. D nt panic. There will be enugh infrmatin in the questin fr yu t wrk ut an answer. Yu are being tested n yur ability t apply yur knwledge t new infrmatin. All the different parts f a questin may be abut the same tpic, e.g. cells frm sectin A r bld frm sectin G, but yu shuld be prepared fr questins that test different tpics, e.g. the structure and functin f white bld cells (phagcytes and lymphcytes) invlving sectins f A, G and J. Lk fr clues in the wrding f the questins. If yu are nly given a Latin name r a name yu d nt recgnise, e.g. impala, lk t see if yu are tld anything abut it. If in a questin n sectin K yu are tld that impala are herbivres, then yu knw they eat plants. Answer each questin as far as yu can. D nt spend a lng time staring at a questin. If yu d nt knw the answer r hw t wrk it ut, then leave it and cme back t it later. It is best t put a mark by the side f the questin s yu can find it easily. An asterisk (*) is a gd idea r a large questin mark against the letter f the part questin. Nt all part questins have answer lines. Yu may nt realise that yu have left ut a part questin when yu check thrugh yur script twards the end f the examinatin. Try nt t leave blanks. Always check thrugh yur script twards the end f the examinatin. When yu cme back t a questin yu may remember what t write as an answer t a questin that yu left ut earlier in the exam. D nt waste time by writing abut things unrelated t the questin. Example 3 It helps t highlight the main features f a questin. Yu cannt use a highlighter pen, s the best thing t d is t underline r circle key wrds in the questins. Questin Aztbacter vinelandii is a bacterium fund in the sil that is able t fix atmspheric nitrgen. One feature f nitrgen-fixing bacteria is the ability t synthesise the enzyme nitrgenase, a mlybdenum- and irn-cntaining, prtein cmplex. Mlybdenum is a mineral in fund in the sil slutin. It enters the cell as mlybdate ins, thrugh membrane transprt prteins. The prteins have the ability t bind t, and hydrlyse, ATP. Name and describe the mechanism f transprt f mlybdate ins int the cell. [3] Underline r circle the imprtant wrds in the intrductry text especially thse that give a clue as t the tpics tested. Ntice enzyme and nitrgen which suggests the questins will be abut sectins C and K frm the syllabus. The first part questin began with tw cmmand wrds. Underline them t remind yurself that there are tw different tasks t write the answer active transprt and describe hw this ccurs. In, transprt prtein, membrane and ATP are all clues as t what t write. Page 9 f 68

10 Cmmand wrds Yu can find ut mre abut cmmand terms in the Glssary f terms used in science papers twards the end f the syllabus. These ntes shuld help yu respnd t each f the cmmand wrds. Cmmand wrds Define What d yu understand by the term...? State List Describe Explain Page 10 f 68 What yu shuld d in respnse t each cmmand wrd Give a definitin these shuld be cncise definitins Give a definitin r a fairly brief explanatin f what the term means. Yu can use an example t illustrate if this seems apprpriate Give a brief answer maybe ne wrd r a phrase A number f brief f answers shuld be given; usually yu are asked fr a specific number f pints. Yu d nt gain extra marks by writing mre than the number stated Yu may have t describe the steps in a prcess r describe the appearance f a bilgical structure. Yu may als have t describe sme data given in a table r a graph. Make sure yu have the crrect vcabulary fr such a descriptin. Fr example, use the wrds increase, decrease, cnstant, peak, maximum, minimum, etc. This is nt the same as describe. Yu shuld give an answer that has sme reasns. Yu may have t explain why smething happens r hw it happens Discuss Yu may be asked t discuss advantages and disadvantages s make sure yu give sme f bth. Much depends n the type f questin, but discuss usually means yu shuld give different sides f an argument Outline Predict Suggest Calculate Measure This is nt the same as describe. Yu shuld give the main imprtant pints withut any detail This means yu shuld state what yu think will happen. Yu may be asked t justify yur predictin r explain it; explanatin is nt required if all the questin says is predict... This is ften used when there is n ne crrect answer; yu shuld lk thrugh the infrmatin yu have been given fr sme clues as t what t suggest in respnse t the questin. Many prblem-slving questins use this cmmand wrd This is bvius; make sure yu knw hw t calculate means, percentages, percentage changes, rates and ratis (fr genetics). At A2, yu shuld als knw hw t use the frmulae fr standard deviatin, standard errr, the chi-squared test and the t-test. Always give yur wrking even if nt asked. Always make sure yu use the crrect units Yu shuld use a suitable measuring instrument t take a reading. Usually this invlves using a ruler t measure t the nearest mm. Make sure yu write dwn the unit after the numerical answer

11 Determine Estimate Sketch This is nt the same as measure. Often this means that yu shuld explain hw an experiment culd be set up t take measurements and hw yu calculate the answer frm the results. Yu d nt have t give an accurate answer but yur answer (which is usually numerical) shuld be apprximate This is usually used abut graphs. Yu shuld put a line (straight r curved) n a pair f axes. This may be a graph that has a line n it already r it may be pair f axes printed n the exam paper withut a line r curve Page 11 f 68

12 4 The style f questins We use a great variety f different styles f questins. If yu answer plenty f past papers during yur curse yu will gain lts f practice at these. Here are sme. Putting ticks and crsses in a table t make cmparisns. Fr example, cmparing the prperties f different bilgical mlecules. Cmpleting tables f infrmatin by writing in single wrds, numbers r shrt phrases, e.g. what happens t the fur valves in the heart during different phases f the cardiac cycle. Cmpleting a passage f text with the missing terms. Writing definitins make these as cncise as yu can; there is n need t use any examples unless asked. Making a list answers shuld als be cncise; detail is nt required. Matching pairs frm tw lists, e.g. matching the names fr the stages f mitsis with descriptins f what happens inside a cell during this type f nuclear divisin. Putting stages f a prcess int the crrect sequence, e.g. the stages f prtein synthesis. Labelling a diagram label lines may already be n the diagram r yu may have t add them yurself. Cmpleting a genetic diagram (Paper 4). Describing and/r explaining data frm a table r a graph. Explaining aspects f an investigatin, e.g. a learner investigatin that yu might have carried ut r a piece f research that has been adapted frm a scientific paper. Adding infrmatin t a flw chart. Writing a flw chart frm infrmatin that yu are given, e.g. drawing a fd web frm written descriptins f the feeding relatinships in a cmmunity. Use infrmatin given in the questin Questins may ask yu t Use examples frm... r Use nly the infrmatin in... r With reference t Fig If yu read instructins like these, find ut what yu are expected t use as examples r take infrmatin frm. Yu will nt get any marks if yu use examples frm smewhere else. The infrmatin can be given t yu in different ways: a diagram, such as a fd web, a set f apparatus r a bilgical structure; a graph, which culd be a line graph, a bar chart r a histgram always check the headings and units carefully; a table always read the headings f the clumns and/r rws carefully and lk fr any units. 5 Interpret tables and graphs The stimulus material may be in the frm f a table, line graph, bar chart r histgram. Always read the intrductry text very carefully befre yu study the table r graph. Underline key pints in the infrmatin that yu are given. In Papers 4 and 5, there may be quite a bit f intrductry text explaining hw the infrmatin was cllected. Tables Lk at the clumn and rw headings in a table and make sure yu understand them. If yu have read the intrductin carefully, then yu will. Page 12 f 68

13 Find the units that have been used. Make sure that yu use the units if yu give any figures in yur answer. Use a ruler t help read the table. Align the ruler with the the first clumn. This shuld be the independent variable and shuld increase in steps. Nw put the ruler t the right f the next clumn and lk at the figures in this secnd clumn that shuld be the dependent variable. Lk fr a pattern r trend in the figures. Identify the pattern r trend first befre thinking f an explanatin. Mve the ruler acrss t the right f the third clumn if there is ne and cntinue in the same way. It may help t sketch a little graph n the exam paper t help yu identify any pattern r trend. Line graphs Lk carefully at the x-axis which is the independent variable and make sure yu understand what has been changed. Lk carefully at the y-axis which is the dependent variable. Bth variables shuld be described in the intrductin t the questin. Put yur ruler against the y-axis and mve it gradually acrss the graph frm left t right. Fllw the pattern r trend f the line (r each line if there is mre than ne). Mark n the graph where smething significant happens. Fr example, the line might shw that the dependent variable becmes cnstant (gives a hrizntal line). Use yur ruler when taking figures frm the graph. If the graph is pltted n a grid, then the Examiners may allw ± ne small square r half a small square in taking yur readings. If yu use a ruler and rule lines n the graph, yu shuld take exact readings. Bar charts and histgrams Lk carefully at the x-axis and the y-axis t see what has been pltted. Again, it is a gd idea t mve a ruler acrss the bar graph r histgram frm left t right t help yu cncentrate n ne aspect at a time. Yu can identify the highest and lwest figures and see if there is any pattern. Yu shuld make yurself sme ntes abut the table, graph r histgram befre answering the questins. Calculatins. If yu are asked t d a calculatin: Yu may have t find the figures frm a table r graph. Write ut all the wrking fr yur calculatin. If yu make a mistake and give the wrng answer, yu may well be given marks fr shwing hw t d the calculatin. Make sure that yu shw the units in the calculatin. Make sure yu include the units if they are nt given n the answer line. Always express yur answer in the same way as ther figures prvided, e.g. in a table. If the ther figures are 5.6 and 4.6, then yur answer shuld be given t ne decimal place, e.g. 2.0 and 7.0, nt 2 and 7. Rund up r dwn the result n yur calculatr - d nt cpy all the figures after the decimal pint. Make cmparisns. If yu are asked t cmpare tw things make sure yu make it clear which thing yu are writing abut. Page 13 f 68

14 The questin may ask yu t cmpare tw structures r tw prcesses that yu have learnt abut. Smetimes yu may be expected t d this n answer lines in which case yu must make clear the items that yu are cmparing (see example 4). Yu may be given a table t cmplete. This may be blank and yu have t fill it in, r it may already have sme entries and yu cmplete it. If yu are given lines t make the cmparisn, it is perfectly acceptable t draw a table fr yur answer. Example 4 Questin State tw ways in which arteries differ frm veins. [2] Crrect answer: 1 Arteries have thicker walls than veins. 2 Veins have semi-lunar valves, but arteries d nt. Ambiguus answer: 1 They have thick walls. 2 They dn t have valves. N marks wuld be given t the last tw answers as the cmparisns have nt been made. Questin Cmplete the table t cmpare the structure f arteries with the structure f veins. [2] Crrect answer arteries veins have thick walls have thick muscle layer have thin walls have very thin muscle layer Incrrect answers as the cmparisns are nt made between the same features arteries thick wall n valves veins thin elastic tissue small amunt f muscle In cases like this, it is much better t have an extra clumn that gives the features t be cmpared: feature arteries veins thickness f wall thicker thinner valves absent present This extra clumn ensures that yu make direct cmparisns in each rw f the table. Yu can always add a first clumn if it is nt included in the questin. Page 14 f 68

15 Extended writing. Yu are required t write lnger answers t questins that have fur r mre marks. There are mre f these questins in Paper 4 than in the ther papers. Yu d nt have t write yur whle answer in prse. Yu can use labelled and anntated diagrams, flw charts, lists and bullet pints. Hwever yu present yur material, yu shuld write enugh t make yur meaning clear. Example 5 Questin frm Paper 2 Explain, in terms f water ptential, hw water mves frm the xylem in a leaf t the air utside a stma. [4] This questin requires a sequence, i.e. frm xylem t cell walls f mesphyll cells; frm walls t air spaces inside the leaf; frm air spaces thrugh the stma t the air utside the leaf. The mvement f water in each stage needs t be explained in terms f chesin-tensin, evapratin and diffusin. Writing ut the pathway n its wn des nt get any marks. Questins frm Paper 4 (a) Explain hw changes in the nucletide sequence f DNA may affect the amin acid sequence in a prtein. [7] (b) Explain hw natural selectin may bring abut evlutin. [8] [Ttal: 15] In (a), yu may find it easier t use sme examples t shw hw changes in nucletide sequences lead t changes in amin acid sequences. Yu d nt need t knw the genetic cde, but yu can use changes in DNA triplets t shw what will happen, e.g. AAA changes t TAA. In (b), yu shuld have learnt several key pints abut natural selectin that yu can write dwn in a lgical sequence. (a) Describe the part played by the prximal cnvluted tubules in the functining f the kidneys. [8] (b) Explain hw the cllecting ducts in the kidneys may reduce the lss f water frm the bdy. [7] [Ttal: 15] A diagram f a cell frm the prximal cnvluted tubule might help yur answer t (a). Yu can label and anntate yur diagram t illustrate yur answer. A feedback lp (a type f flw chart) wuld be a gd way t illustrate part (b). When yu answer these questins always use full sentences if yu can. If yu find it helps t write bullet pints, then make sure that each bullet pint is a full sentence. If yu abbreviate yur answer t much by writing ntes, then yu may nt cnvey enugh infrmatin t gain the marks. If yu are giving a sequence f events (as in Example 5), then yu shuld make sure they are in a lgical rder. If yu are explaining a bilgical principle r making cmparisns, then give the main pints first. Page 15 f 68

16 If yu are describing smething that mves frm ne place t anther as in the Paper 2 questin frm Example 5, then make sure yu include the directin f mvement. Fr example, water mves by smsis is unlikely t gain a mark unless yu include the directin; water enters the mesphyll cell dwn the water ptential gradient is a much better answer. The rest f these tips cncern the individual papers. Paper 1 Yu have abut ne minute t read and answer each questin. Each questin may test ne tpic r several tpics frm different parts f the AS syllabus. Sme questins test what yu knw and understand. Sme questins test if yu can apply what yu have learnt t understand new data. These questins will ften have a diagram, graph r table t use. Sme f the chices can be very similar; read carefully and underline wrds that make each chice distinct frm the ther three. Try t decide what the questin is testing as yu are reading it. The sequence f questins usually fllws the sequence f tpics in the syllabus. Therefre yu can expect the early questins t ask abut Sectin A n cells and thse at the end will be n Sectins J and K abut immunity and eclgy. D nt try t find a pattern in the rder f yur answers (e.g. A, B, C, D, A, B...) The same letter culd be the crrect answer fr several questins in a rw. Letter A might be the crrect answers fr mre questins than B, C r D. Or there culd be fewer crrect answers shwn by letter D than any f the thers. D nt let what yu have chsen fr the previus questins influence which letter yu chse. Sme questins may ask abut aspects f practical wrk, fr example abut different variables: independent, dependent and cntrlled. It is imprtant t understand hw t use terminlgy, e.g. hw t apply water ptential terminlgy t prblems n cells and smsis. Paper 2 This paper has a mix f shrt answers questins and thse requiring slightly lnger answers. There is n essay. Lnger answers will need fur r five sentences with tw r three different ideas. Always lk at the number f marks fr each part questin t help yu decide hw much t write. Lk at the number f cmmand wrds: ask yurself d yu have t d ne r tw things? See Example 2. Use the lines given. Stick t the pint and d nt write t much. Only give the number f answers that are asked. Use the numbered lines and give ne answer per line. There will nly be a few parts f questins that need extended writing. These will have fur [4] r five [5] marks. These questins will ften be related t sme infrmatin yu are given. Yu will need t write fur r five sentences in a sequence that makes sense. Page 16 f 68

17 Yu can think f it as telling a stry with a beginning, a middle and an end. Remember t refer t any infrmatin yu are given. Paper 3 General tips Success at Paper 3 requires yu t d plenty f practical wrk during yur curse and have several attempts at past paper questins t find ut hw t cmplete everything in the time available. During the practical exam yu will have t make sme decisins; if yu practice plenty f past questins yu will find ut what srt f decisins t expect. As yu revise, make sure yu knw exactly hw t carry ut the practical prcedures described in the AS syllabus. Yu will be assessed n yur skills at: manipulating apparatus t cllect results and make bservatins data presentatin analysis f results and bservatins evaluatin f prcedures and data Yu shuld make decisins, such as: identifying variables standardising the cntrl variables hw t change the independent variable chse the number f measurements t take decide the intervals between the values f the independent variable chsing a cntrl experiment identifying any risks and stating apprpriate precautins During the examinatin Read thrugh the questins carefully, lking t see hw many marks are given fr each questin. Read the instructins t the end; d nt start a practical prcedure withut reading carefully all the steps invlved. As yu read, check that yu have the apparatus and materials described. If nt alert the Supervisr. Think abut the apparatus that yu will use fr each step and imagine using it in yur mind. Make sure that yu have a sharp pencil t use fr making drawings and fr drawing graphs and charts. D nt draw in ink because yu cannt make changes as yu can when using a pencil. Make sure yu have a gd, clean eraser fr rubbing ut yur pencil lines if necessary. D nt press t hard when using a pencil fr making drawings, graphs r charts. Smetimes it is hard fr an Examiner t tell which is yur final line. Fllwing the instructins Fllw the instructins fr practical methds exactly. If yu make a change in the methd yu can alter the results. D nt take shrt cuts. Always label test-tubes and ther cntainers t help yu remember which is which. Page 17 f 68

18 If yu are tld t "Wash the apparatus thrughly after each use" make sure yu d. If there is anything left in the apparatus the next stage may nt wrk. It is a gd idea t put a tick by the side f each instructin when yu have cmpleted it. This helps yu t find the right place in the instructins, s that yu d nt leave ut a step r repeat a step when it is nt required. Keep yur exam paper n a part f the bench which yu can keep dry. D nt pur liquids r use syringes r pipettes ver yur exam paper. If yu keep ur exam paper away frm the wet part f yur bench yu are unlikely t spill anything n it. Recrding yur measurements and bservatins Yu are expected t make bservatins and recrd them. Yu can recrd yur bservatins: as statements in writing in tables by using drawings by cnstructing tally charts Yu will take readings frm different apparatus. Yu must make the measurements as accurately and reliably as yu can. Numerical readings will nrmally be cllected and presented in a table. Fllw the instructins belw abut drawing tables. Make clear descriptins f clurs and clur changes; refer t blue, range and purple when describing reagents used in bichemical tests. Yu may want t refer t slight differences, s use wrds like pale and dark. Make yur measurements as accurate and reliable as pssible. Accurate results are clse t the actual r true values; reliable results are thse that are repeatable. If yu can take repeat readings, then d s. There is nt always enugh time t d this. Yu can prcess yur bservatins by: carrying ut calculatins, e.g. percentages and percentage changes pltting graphs line graphs, bar charts and histgrams. Use all the space available n the paper fr yur bservatins. D nt write an explanatin until the questin asks fr ne. Use a sharp HB r B pencil. It can be rubbed ut easily if yu need t crrect a mistake. Use a gd eraser as traces f pencil lead are detected when yur paper is scanned. D nt frget headings fr the clumns and the rws in tables. Drawings These will be frm micrscpe slides r phtgraphs. Read the questin carefully, the drawing may have t be an accurate size e.g. twice the riginal. Make each drawing as big as the space allws, making sure that yu leave enugh space fr labels and anntatins, if asked fr. Use a ruler fr labelling lines. Draw and label in pencil. Use ne clear cntinuus utline nt an artistic drawing. D nt shade. Page 18 f 68

19 Observe details carefully, such as the relative number f chlrplasts in different cells and the thickness f cell walls in different cells in a vascular bundle. Shw these accurately n yur drawing. A plan diagram shws the distributin f tissues in a sectin. It als shws the prprtins f the different tissues. Althugh called a lw pwer plan diagram yu may use high pwer t identify the different tissues and t be sure yu are putting the bundaries f thse tissues in the right place. Yu d nt draw any cells in a lwer pwer plan diagram. When yu make a plan diagram, fllw these simple rules: make the drawing fill mst f the space prvided; leave space arund the drawing fr labels and anntatins (if required by the questin) use a sharp HB pencil (never use a pen) use thin, single, unbrken lines (ften called clear and cntinuus lines ) shw the utlines f the tissues make the prprtins f tissues in the diagram the same as in the sectin d nt include drawings f cells d nt use any shading r cluring Add labels and anntatins (ntes) t yur drawing nly if yu are asked fr these in the questin. Use a pencil and a ruler t draw straight lines frm the drawing t yur labels and ntes. Write labels and ntes in pencil in case yu make a mistake and need t change them. Yu may leave yur labels and ntes in pencil d nt write ver them in ink. High pwer drawings shuld shw a small number f cells and they shuld be drawn a reasnable size s yu can shw any detail inside them. When yu make a high pwer drawing, fllw these simple rules: make the drawing fill mst f the space prvided; leave space arund the drawing fr labels and anntatins (if required by the questin) use a sharp HB pencil (never use a pen) use clear, cntinuus lines (see abve) draw nly what is asked in the questin, e.g. three cell types r ne named cell and all cells adjining it shw the utlines f the cells the prprtins f the cells in the drawing must be the same as in the sectin yu are drawing plant cell walls shuld be shwn as duble lines with a middle lamella between the cells; the prprtins f cell walls shuld be drawn carefully. shw any details f the cntents f cells draw what yu see nt what yu knw shuld be present; fr example, in plant cells yu may see nuclei, chlrplasts and vacules d nt use any shading r cluring Page 19 f 68

20 Taking measurements f specimens and phtgraphs Using an eyepiece graticule An eyepiece graticule is a scale that fits inside the eyepiece n yur micrscpe. It allws yu t take measurements f the specimens yu view with the micrscpe. Yu can measure simply in graticule units, but yu may be asked t make an actual measurement which invlves calibrating the graticule using a stage micrmeter. This is dne by lining up the graticule with the divisins n the micrmeter. Make yur measurements as accurate as yu can. Yu will prbably be able t measure t the nearest divisin n the graticule. Yu may be asked t take several measurements and then calculate a mean. Taking measurements frm phtgraphs Yu may have t measure an bject n a phtgraph and calculate the actual size f a structure r the magnificatin f an image. Always measure phtgraphs in millimetres, nt centimetres. If yu have t use yur measurements in a calculatin, write neatly and shw yur wrking. The persn marking yur paper might be able t give yu marks fr knwing what t d even if yu make a mistake r d nt finish the calculatin. Presenting data and bservatins Tables Befre yu start t draw a table, decide what yu wish t recrd. Decide n hw many clumns and hw many rws yu will need. Make sure yu have read all the instructins befre yu draw the table utline. Fllw these rules: use the space prvided, d nt make the table t small leave sme space t the right f the table in case yu decide yu need t add ne r mre clumns make the table ready t take bservatins r readings s that yu can write them directly int the table rather than n anther page and then cpy them int the table (tables need t shw all the raw data yu cllect) draw the table utlines in pencil rule lines between the clumns and rws rule lines arund the whle table write brief, but infrmative headings fr each clumn clumns headed with physical quantities shuld have apprpriate SI units when tw r mre clumns are used t present data, the first clumn shuld be the independent variable; the secnd and subsequent clumns shuld cntain the dependent variables entries in the bdy f the table shuld be brief they shuld be single wrds, shrt descriptive phrases r numbers data shuld be recrded in the table in the rder in which it is cllected this is because the table is prepared befre the data cllectin. Fr example, if the instructins state that results frm the highest temperature r highest ph is t be recrded first then these g at the tp f their respective clumns. It is mre usual t arrange the values f the independent variable in ascending rder (e.g. frm 0 t 100) s that patterns are easier t fllw and that is hw data in tables fr papers 1, 2, 4 and 5 is usually presented Page 20 f 68

21 numbers written int the bdy f the table d nt have units (units nly appear in the clumn headings) Yu may have t prcess yur results by calculating rates f reactin, changes in length, percentage changes r means f repeat readings. These prcessed results can appear in the same table with the raw data that yu have cllected r can be in a separate table with the independent variable. The slidus r slash (/) meaning per shuld nt be used in units. Fr example, if yu have t include cncentratins as in a table yu d nt write g per 100 cm 3 as g/100 cm 3. It shuld always be written ut in full using per r, better, as g 100 cm -3. The negative expnent, cm -3, means per. Nte that the slidus is used t separate what is measured frm the unit in which it is measured. Yu may ntice that text bks and examinatin papers use brackets arund the units in tables. This is als an accepted cnventin, but the slidus is the cnventin used in CIE AS/A Bilgy. Crrect and incrrect ways f shwing units in tables and graphs Crrect either: rate / mm cm -3 r: rate (mm cm -3 ) either: cncentratin / g 100 cm -3 r: cncentratin (g 100 cm -3 ) Incrrect rate mm/cm 3 cncentratin g/100 cm 3 A nte n the uses f ticks and crsses in tables D nt use ticks and crsses in tables f results, which shuld shw bservatins, such as the clurs btained in bichemical tests. Ticks and crsses may be used in tables f cmparisn if there is a key t explain what they mean, e.g. = present; = absent. Yu may want t shw anmalus results in tables. If s circle them and put a nte underneath the table t explain that they are anmalus results. Yu may be asked t cmpare specimens viewed in the micrscpe and/r in phtgraphs. These cmparisns must be rganised int a table. Draw yur table s that it has a first clumn fr the features that yu have bserved. Yu can then present bth similarities and differences: feature specimen A specimen B similarities Charts and graphs Bar charts have separate clumns that d nt tuch there are gaps in between; histgrams have clumns that d tuch each ther. Bar charts are used t shw data n Page 21 f 68

22 discntinuus variables, fr example bld grups, eye clur, etc.; histgrams are used t shw data n cntinuus variables, e.g. length, mass, speed, vlume, etc. Bar charts Bar charts shuld be used if the independent variable is qualitative. If yu are investigating the rate f respiratin f yeast when given different substrates, the independent variable is the type f substrate, e.g. glucse, maltse, sucrse, etc. In this case there is n cntinuus scale fr the independent variable and a bar chart is the apprpriate way t present the results. The dependent variable is cntinuus as it is the rate f respiratin and wuld be measured in units such as rate f carbn dixide prductin / cm 3 s -1. Rules fr drawing bar charts: use mst f the grid prvided, d nt make the chart t small. draw the chart in pencil bar charts can be made f lines, r mre usually, blcks f equal width. There must be space between the lines r bars. They d nt tuch the intervals between the blcks n the x-axis shuld be equidistant the y-axis shuld be prperly scaled with equidistant intervals; the scale shuld usually start at 0 and this shuld be written at the base f the axis. If all the numbers are large a displaced rigin may be used but the start number shuld be clear at the base f the y-axis the y-axis shuld be labelled with the headings and units taken frm the table f results the lines r blcks shuld be arranged in the same rder as in the table f results each blck shuld be identified; there is n need t shade the blcks r clur cde them Histgrams D nt cnfuse bar charts with histgrams. A histgram is drawn fr cntinuus data that is subdivided int classes. A gd example is cllecting data n cntinuus variables, such as linear measurements r mass. Smetimes the intervals can be whle numbers, fr example the numbers f seeds in fruits. If yu are analysing data then yu may wish t draw a frequency histgram t see if the data shws a nrmal distributin. Histgrams are used when the independent variable is numerical and the data are cntinuus. They are smetimes referred t as frequency diagrams. First the raw data needs t be rganised int classes. The number f classes needs t be established. This will largely depend n the type and nature f the data. The rule fr determining the number f classes is 5 x lg 10 ttal number f readings. The range within each class needs t be determined; this is usually the ttal range divided by ne less than the number f classes. There shuld be n verlap in the classes, e.g t 5.20 r 4.01 < t 6.40 r 5.21 < 6.41 (< = less than) The data shuld be rganised using a tally chart and drawing five bar gates as in //// = 5 Fllw these rules when drawing a histgram: use mst f the grid prvided, d nt make the histgram t small draw the histgram in pencil the x-axis represents the independent variable and is cntinuus. It shuld be labelled clearly with an apprpriate scale the blcks shuld be drawn tuching Page 22 f 68

23 the area f each blck is prprtinal t the size f the class. It is usual t have similar sized classes s the widths f the blcks are all the same the blcks shuld be labelled, e.g. 3.0 t 3.9 which means that 3.0 is included in this class, but 4.0 is nt. 4.0 will be included in the next class: 4.0 t 4.9 the y-axis represents the number r frequency and shuld be prperly scaled with equidistant intervals. It shuld be labelled with apprpriate units Line graphs Line graphs are used t shw relatinships in data which are nt immediately apparent frm tables. The term graph applies t the whle representatin. The term curve shuld be used t describe bth curves and straight lines which are used t shw trends. Fllw these guidelines: use at least half the grid prvided, d nt make the graph t small draw the graph in pencil the independent variable shuld be pltted n the x-axis the dependent variable shuld be pltted n the y-axis each axis shuld be marked with an apprpriate scale. The rigin shuld be indicated with a 0. The data shuld be examined critically t establish whether it is necessary t start the scale(s) at zer. If nt, yu may have a displaced rigin fr ne r bth axes, but this must be made bvius by labelling the displaced rigin very clearly each axis shuld be scaled using multiples f 1, 2, 5 r 10 fr each 20 mm square n the grid. This makes it easy fr yu t plt and extract data. Never use multiples f 3 each axis shuld be labelled clearly with the quantity and SI unit(s) r derived (calculated) units as apprpriate, e.g. time / s and cncentratin / g dm -3 ; the axes labels and units must be the same as thse in the table pltted pints must be clearly marked and easily distinguishable frm the grid lines n the graph. Dts in circles ( ) r small, neatly drawn saltire crsses (x) shuld be used; dts n their wn shuld nt. If yu need t plt three lines, vertical crsses (+) can als be used label each line carefully r use a key. Use a pencil fr bth lines; d nt use a blue r black pen r different clurs as these d nt shw up n scanned scripts in Paper 3 there are usually five r six results t plt After pltting the pints yu need t decide if any f them are anmalus. Ask yurself the questin d they fit the trend? But what is the trend? Yu shuld knw smething abut the thery behind the investigatin s yu shuld be aware f the likely trend. If yu think ne r mre f the results are anmalus, then it is a gd idea t ring them. Put a circle n the graph away frm the line and put a key t state that the circled pint(s) represent anmalus result(s). The next thing t decide is hw t present the curve. It may be bvius that the pints lie n a straight line; fr example, the effect f enzyme cncentratin n the rate f an enzyme-catalysed reactin. If yu have a result fr the rigin (0, 0) then that must be included and yu can place a clear plastic ruler n the grid and draw a straight line frm the rigin making sure that there is an even number f pints n either side f the line. If yu d nt have a result fr the rigin, then start the line at the first pltted pint. D nt cntinue the line past the last pltted pint. Yu shuld nly draw a smth curve if yu knw that the intermediate values fall n the curve. Yu may be expecting the relatinship t be a smth curve and if the pints seem t fit n a curve then draw ne. Again decide whether the rigin is a pint and, if nt, start at the first pltted pint. The curve shuld g thrugh as many pints as pssible, but try t make sure there is an even number f pints n either side f the line. D nt cntinue past the last pltted pint. Page 23 f 68

24 In the practical examinatin yu may nly have five r six results. These are likely t be single results rather than means f replicate results. Therefre yu cannt be sure f the relatinship and shuld nt draw a straight line r a curve as described abve. Yu shuld draw straight lines between the pints. This indicates uncertainty abut the results fr values f the independent variable between thse pltted. If a graph shws mre than ne line r curve, then each shuld be labelled t shw what it represents. Bar charts, histgrams and line graphs shuld nrmally have infrmative titles. There is n need t give titles in the exam as it is bvius what they are. In all ther circumstances give infrmative titles. If yu have times in minutes and secnds, never use minutes as the unit n a graph. It is very difficult t use a scale with each small square representing 3 r 6 secnds. Always plt results in secnds unless the unit fr time is whle minutes. Analysis, cnclusins and evaluatin As part f analysis yu shuld be able t: identify anmalus results. Anmalus results are thse that d nt fit the trend. prcess yur results t calculate means, percentages, changes in mass r length, calculate percentage changes and rates f reactins find unknwn quantities by using axis intercepts r estimating frm clur standards using knwn cncentratins describe the pattern r trend in data make cnclusins t cnsider whether experimental data supprts hyptheses r nt. Prcessing results Yu shuld be prepared t calculate: means percentages percentage changes rates f reactin by calculating 1/t r 1000/t; the unit used is s -1 Yu shuld knw hw t use line graphs t: find an intercept where a line yu have drawn crsses a key value n the x-axis; fr example, finding the water ptential f a tissue using percentage change in length f plant tissues find the rate f a reactin by calculating the gradient f a line yu have drawn. As part f evaluatin yu shuld be able t: identify systematic and randm errrs systematic errrs are thse that affect all the results in the same way randm errrs d nt affect all the results in the same way identify the significant errrs in yur investigatin estimate the uncertainty in measurements. The actual errr is half the smallest divisin n the apparatus yu are using. assess hw effective yu have been at standardising variables suggest imprvements t the prcedure yu have fllwed suggest ways in which the investigatin might be extended t answer a new questin. Page 24 f 68