Biology - Past Papers

1 GCEB iology Advanced GCE A2 7881 Advanced Subsidiary GCE AS 3881 Mark Schemes for the Units June 2007 3881/7881/MS/R/07 OCR (Oxford, Cambridge and RSA Examinations) is a unitary awarding body, established by the University of Cambridge Local Examinations Syndicate and the RSA Examinations Board in June 1998. OCR provides a full range of GCSE, A level, GNVQ, Key Skills and other qualifications for schools and colleges in the United Kingdom, including those previously provided by MEG and OCEAC. It is also responsible for developing new syllabuses to meet national requirements and the needs of students and teachers. This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which marks were awarded by Examiners. It does not indicate the details of the discussions which took place at an Examiners meeting before marking commenced.

2 All Examiners are instructed that alternative correct answers and unexpected approaches in candidates scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes should be read in conjunction with the published question Papers and the Report on the Examination. OCR will not enter into any discussion or correspondence in connection with this mark scheme. OCR 2007 Any enquiries about publications should be addressed to: OCR Publications PO Box 5050 Annesley NOTTINGHAM NG15 0DL Telephone: 0870 870 6622 Facsimile: 0870 870 6621 E-mail: CONTENTS Advanced GCE Biology (7881) Advanced Subsidiary GCE Biology (3881) MARK SCHEMES FOR THE UNITS Unit Content Page 2801 Biology Foundation 1 2802 Human Health and Disease 9 2803/01 Transport - Written Paper 17 2803/03 Practical Examination 25 2804 Central Concepts 37 2805/01 Growth, Development and Reproduction 47 2805/02 Applications of Genetics 59 2805/03 Environmental Biology 69 2805/04 Microbiology and Biotechnology 81 2805/05 Mammalian Physiology and Behaviour 93 2806/01 Unifying Concepts in Biology - Written Paper 103 2806/03 Practical Examination 111 * Grade Thresholds 121 1 Mark Scheme 2801 June 2007 2 ADVICE TO EXAMINERS ON THE ANNOTATION OF SCRIPTS 1.

3 Please ensure that you use the final version of the Mark Scheme. You are advised to destroy all draft versions. 2. Please mark all post-standardisation scripts in red ink. A tick (9) should be used for each answer judged worthy of a mark. Ticks should be placed as close as possible to the point in the answer where the mark has been awarded. The number of ticks should be the same as the number of marks awarded. If two (or more) responses are required for one mark, use only one tick. Half marks ( ) should never be used. 3. The following annotations may be used when marking. No comments should be written on scripts unless they relate directly to the mark scheme. Remember that scripts may be returned to Centres. x = incorrect response (errors may also be underlined) ^ = omission mark bod = benefit of the doubt (where professional judgement has been used) ecf = error carried forward (in consequential marking) con = contradiction (in cases where candidates contradict themselves in the same response) sf = error in the number of significant figures 4.

4 The marks awarded for each part question should be indicated in the margin provided on the right hand side of the page. The mark total for each question should be ringed at the end of the question, on the right hand side. These totals should be added up to give the final total on the front of the paper. 5. In cases where candidates are required to give a specific number of answers, ( give three reasons ), mark the first answer(s) given up to the total number required. Strike through the remainder. In specific cases where this rule cannot be applied, the exact procedure to be used is given in the mark scheme. 6. Correct answers to calculations should gain full credit even if no working is shown, unless otherwise indicated in the mark scheme. (An instruction on the paper to Show your working is to help candidates, who may then gain partial credit even if their final answer is not correct.) 7. Strike through all blank spaces and/or pages in order to give a clear indication that the whole of the script has been considered.

5 8. An element of professional judgement is required in the marking of any written paper, and candidates may not use the exact words that appear in the mark scheme. If the science is correct and answers the question, then the mark(s) should normally be credited. If you are in doubt about the validity of any answer, contact your Team Leader/Principal Examiner for Mark Schemes June 2007 2 Abbreviations, annotations and conventions used in the Mark Scheme / = alternative and acceptable answers for the same marking point ; = separates marking points NOT = answers which are not worthy of credit ( ) = words which are not essential to gain credit = (underlining) key words which must be used to gain credit ecf = error carried forward AW = alternative wording ora = or reverse argument Question Expected Answers Marks 1 (a) (i) Each of the following to be labelled with a clear label line.

6 Allow P and E as letters inside the appropriate cell. P / palisade mesophyll cell ; E / lower epidermal cell ; C / cuticle ; 3 (ii) award two marks if correct answer (150) is given incorrect answer (or no answer) but correct working = 1 mark (x) 150 ;; R units A in the range 147 153 answer should not exceed 1 if answer incorrect or to too many , then allow 1 working mark for (mm) or equivalent 2 (b) if describing organ, max 1 made up of , more than one / two / a few , types of cell ; A named cell types (vessel / fibre / parenchyma) working together / AW ; with a , specific / particular / same , function / role / purpose / job ; A named function A transport minerals R transport nutrients 2 max [Total: 7]2801 Mark Schemes June 2007 3 Question Expected Answers Marks 2 (a) one mark for each correct row if only ticks, assume that spaces are crosses.

7 If only crosses, assume that spaces are ticks R hybrid ticks statement substance use heat use biuret reagentuse Benedict s reagent boil with a dilute acid a positive result is a blue-black colour a positive result is an emulsion lipid 8 8 8 8 8 9 protein 8 9 8 8 8 8 ; starch 8 8 8 8 9 8 ; reducing sugar 9 8 9 8 8 8 ; non-reducing sugar 9 8 9 9 8 8 ; 4 (b) (i) glycosidic ; A covalent / C-O-C / oxygen bridge R oxygen bond / glucosidic 1 (ii) hydrolysis / hydrolytic ; if qualified, needs to be correct 1 (c) 1 2 3 4 5 6 no (suitable) enzyme (in gut) to digest sucralose / sucrase will not act on sucralose / AW ; enzymes , are specific / only act on one substrate ; complementary shape ; idea that (Cl on sucralose instead of OH) gives different , shape / structure ; no ESC (enzyme substrate complex) / substrate will not fit into active site ; AVP ; further detail of enzyme-substrate interaction 4 max [Total: 10]2801 Mark Schemes June 2007 4 Question Expected Answers Marks 3 (a) (i) U A C C G G A U U C A C ; ; 1 error = 1, 2 errors = 0 allow 1 mark for giving T throughout instead of U ( T A C C G G A T T C A C = 1 mark) 2 (ii) transcription / transcribed ; R transcriptase 1 (b) (i) J anticodon ; R anticodons K transfer RNA / tRNA ; L ribosome / rRNA ; M codon ; R codons 4 (ii) 1 2 3 4 5 6 7 8 9 10 DNA triplet / codon / M / mRNA triplet , codes for specific amino acid ; order of , triplets / bases , determines the order of amino acids.

8 TRNA / K , has , corresponding / complementary , triplet / anticodon ; (tRNA / K) attached to specific amino acid ; activation of amino acid ; 2 (tRNA) binding sites on the ribosome ; codon and anticodon bind ; A match A to U and C to G ; adjacent amino acids join ; peptide bond ; 4 max (c) 1 2 3 4 5 6 7 attaches to ribosome ; removes , base / portion , of ribosome ; A stops ribosome assembling / changes shape of ribosome prevents ribosome , attaching to / reading , mRNA ; prevents codons being exposed ; prevents , tRNA / anticodon , attaching to , mRNA / codon ; prevents / inhibits enzyme responsible for , formation of peptide linkages ; AVP ; further detail of any of the above points 2 max [Total: 13]2801 Mark Schemes June 2007 5 Question Expected Answers Marks 4 (a) credit comparative statements on the same line ~ must refer to both do not credit ref to size of cell ignore vacuoles / slime layer prokaryotic eukaryotic no , nucleus / nucleolus / nuclear membrane / nuclear envelope A free DNA nucleus / nucleolus / nuclear membrane / nuclear envelope A DNA enclosed ; circular DNA A loop linear DNA ; no , histones / (true) chromosome A naked DNA histones / chromosome A DNA + protein.

9 No membrane-bound organelles membrane-bound organelles/ named (Allow up to 2 marks) ; cell wall may have cell wall ; peptidoglycan / murein , cell wall cellulose cell wall (if present) ; ribosomes , 18 nm / 70S / smaller ribosomes , 22 nm / 80S / larger ; plasmids no plasmids (except inside organelles) ; AVP no cytoskeleton flagellum not 9+2 pili fimbrae capsule mesosome AVP cytoskeleton flagellum 9+2 no pili no fimbrae no capsule no mesosome ; 3 max 2801 Mark Schemes June 2007 6 4 (b) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 max 7 for the process of genetic engineering max 2 for the advantages identify / find , gene (for insulin) / length of DNA coding for insulin ; obtain / isolate / extract , gene / length of DNA (for insulin) ; obtain / isolate / extract , mRNA (for insulin) ; restriction enzyme / named ;reverse transcriptase ; cut plasmid ; cut plasmid ; use same restriction enzyme ; use restriction enzyme / named ; ref to , complementary ends / sticky ends / described ; insert , gene / AW , into plasmid ; recombinant DNA ; plasmid uptake by bacteria ; identify those bacteria that have taken up the plasmid ; provide with , raw materials / nutrients ; fermenter / bioreactor ; bacteria produce insulin ; extract and purify / downstream processing ; AVP.

10 Detail of uptake by bacteria method of identifying those that took up plasmid PCR ligase 7 max advantage 1 ; more reliable supply advantage 2 ; greater / faster , production overcomes ethical problem described less risk of disease less risk of , rejection / side effects human insulin so more effective 8 max QWC clear, well organised using specialist terms ; award QWC mark if four of the following are used 1 gene plasmid restriction enzyme complementary named of a restriction enzyme sticky end reverse transcriptase recombinant DNA fermenter / bioreactor [Total: 12]2801 Mark Schemes June 2007 7 Question Expected Answers Marks 5 (a) R I and II throughout (i) prophase ; 1 (ii) interphase / S phase ; 1 (iii) telophase ; ignore cytokinesis 1 (b) 1 2 3 4 5 6 7 8 attach to spindle ; by centromere ; centromere , divides / splits ; R breaks spindle fibres shorten / AW.