GCE Biology A H420/02: Biological diversity Advanced GCE Mark Scheme for Autumn 2021

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GCE Biology A H420/02: Biological diversity Advanced GCE Mark Scheme for Autumn 2021 Oxford Cambridge and RSA Examinations GCE Biology A H420/02: Biological diversity Advanced GCE Mark Scheme fo... r Autumn 2021Oxford Cambridge and RSA Examinations OCR (Oxford Cambridge and RSA) is a leading UK awarding body, providing a wide range of qualifications to meet the needs of candidates of all ages and abilities. OCR qualifications include AS/A Levels, Diplomas, GCSEs, Cambridge Nationals, Cambridge Technicals, Functional Skills, Key Skills, Entry Level qualifications, NVQs and vocational qualifications in areas such as IT, business, languages, teaching/training, administration and secretarial skills. It is also responsible for developing new specifications to meet national requirements and the needs of students and teachers. OCR is a not-for-profit organisation; any surplus made is invested back into the establishment to help towards the development of qualifications and support, which keep pace with the changing needs of today’s society. 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. 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 2021H420/02 October 2021 Annotations Annotation Meaning DO NOT ALLOW Answers which are not worthy of credit IGNORE Statements which are irrelevant ALLOW Answers that can be accepted ( ) Words which are not essential to gain credit __ Underlined words must be present in answer to score a mark ECF Error carried forward AW Alternative wording ORA Or reverse argumentH420/02 October 2021H420/02 October 2021 Question Answer Marks AO element Guidance 1 C  1 AO1.1 2 A  1 AO2.1 3 D  1 AO1.2 ALLOW A 4 C  1 AO2.5 5 B  1 AO1.2 6 A  1 AO1.2 7 A  1 AO1.1 8 B  1 AO2.1 9 C  1 AO2.2 10 B  1 AO1.2 11 C  1 AO2.4 12 B  1 AO2.4 13 D  1 AO2.7 14 B  1 AO1.1 15 C  1 AO2.1 Total 15H420/02 October 2021 Question Answer Marks AO element Guidance 16 (a) (i) phosphate  deoxyribose  guanine  3 1.1 2.1 IGNORE PO4 DO NOT CREDIT dioxyribose DO NOT CREDIT if any other sugar mentioned IGNORE G DO NOT CREDIT if any other base mentioned (ii) phosphodiester  condensation  2 1.1 1.2 16 (b) (i) 1 2 3 4 5 6 amplify (DNA fragment) with PCR  cut / digest , with restriction enzyme  separate / AW , using, electrophoresis / electric current through gel  transfer (fragments) to , paper / membrane / nylon  add , radioactive / fluorescent , probe  use , x-rays / UV light , to view (position of DNA fragments)  4 max 1.2 IGNORE steps in implausible sequence 4 ALLOW (Southern) blot 6 viewing method must not contradict probe used. (ii) Individual C  idea of highest number of matches (3) that cannot have come from mother 2 3.1 DO NOT CREDIT if bands are described as , genes / basesH420/02 October 2021 Question Answer Marks AO element Guidance or 5th (child) band (from left) can only have come from C  (iii) idea of assessing disease risk  classification / species identification  1 max 1.1 ALLOW reference to horsemeat in burgers ALLOW ascertain ancestry of (extinct) species 16 (c) (i) editing of primary , mRNA / transcript  not present in mature mRNA  not translated  regulatory , sequences / genes  2 max 1.2 IGNORE introns are non-coding (as this is not an explanation) ALLOW introns removed ALLOW used to make , tRNA / rRNA (ii) not selected against / AW  1 2.5 ALLOW doesn’t affect survival 16 (d) synthetic  Escherichia  phylogeny / phylogenetics  3 1.1 2.1 Question Answer Marks AO element Guidance 17 (a) (i) FIRST CHECK ON ANSWER LINE If answer = 8.85 x 109 award 2 marks 8.94 x 109 - 9.08 x 107 correct  2 2.6 If answer incorrect… ALLOW max 1 mark for 8.8492 x 109 / 8.84 x 109 / correct answer not in standard form (ii) measuring changes in dry mass over time / AW  1 3.3 ALLOW e.g, dry leaves after 24h and weigh them then repeat at different times of year.H420/02 October 2021 Question Answer Marks AO element Guidance (iii) misses , chloroplasts / parts that photosynthesize  (rate of photosynthesis) limited by another factor  1 max 1.1 ALLOW transmitted (iv) idea that heather is less easily digested  ora (because of) cellulose (cell walls) / lignin (in woody parts)  2 2.5 ALLOW only part of the plant is eaten 17 (b) (i) FIRST CHECK ON ANSWER LINE If answer = 767 or 768 award 2 marks 545 x 100/71  2 max 2.2 If answer incorrect ALLOW max 1 mark for 76.6 ALLOW max 1 mark for 1535 (quoting individuals rather than pairs) (ii) deliberate killing to maintain grouse numbers / pollution / pesticides / disease / loss of another food source / competition from new predator  1 2.5 Mark as prose IGNORE habitat loss ALLOW hunting 17 (c) (i) (species are conserved) in their (natural) habitat  1 2.1 (ii) controlled grazing  monitoring of population(s)  restricting human access  remove / AW , invasive species  1 max 2.1 ALLOW cutting heather ALLOW prevention of grazing IGNORE fence off the area ALLOW maintaining footpaths IGNORE ‘don’t allow building’ ALLOW remove weedsH420/02 October 2021 Question Answer Marks AO element Guidance 17 (d)* Please refer to the marking instructions on page 4 of this mark scheme for guidance on how to mark this question. Level 3 (5–6 marks) Describes some stages of succession with reference to general principals and key terms AND explains why heather moorland is deflected succession. There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated. Level 2 (3–4 marks) Describes some stages of succession with reference to general principles OR describes one stage of succession with reference to general principles AND explains why heather moorland is deflected succession OR describes some stages of succession AND explains why heather moorland is deflected succession. There is a line of reasoning presented with some structure. The information presented is relevant and supported by some evidence. Level 1 (1–2 marks) Mentions some stages of succession OR outlines the general principles OR explains why heather moorland is deflected succession. 6 1.2 2.5 Indicative points may include AO1.2 Stages Pioneer community • begins with bare rock • arrival as seeds or spores • pioneer species have certain adaptations, e.g. nitrogen-fixation Intermediate community • herb species, including grasses • followed by shrubs and trees Climax community • dominance by a few tree species • little change over time General principles • seral stages • community and decomposition changes composition of soil • increased organic, nitrate or water content AO2.5 Heather moorland is deflected succession because…H420/02 October 2021 Question Answer Marks AO element Guidance There is an attempt at a logical structure with a line of reasoning. The information is in the most part relevant. 0 marks No response or no response worthy of credit. • climax community is prevented from developing As a result… • plagioclimax • heather is a shrub Question Answer Marks AO element Guidance 18 (a) phosphate (on head), is hydrophilic / bonds with water (molecules)  (two) fatty acid tails are hydrophobic  heads orientate towards water / tails orientate towards other fatty acids / tails orientate away from water , (so a bilayer forms) 3 2.1 2.5 DO NOT CREDIT reference to incorrect bond, e.g. covalent This point is for a description of why a bilayer forms and key terms are not required 18 (b) (i) ruled lines and a border and correct numbers in each column and absorbance and pH and mean in headings  pH in left hand column  units (%) in headings and not within table  means recorded to one decimal place  4 3.3 3.4 ALLOW means recorded as whole numbers (ii) (low pH) denatures / changes tertiary structure of , (membrane) proteins  2 max 2.1H420/02 October 2021 Question Answer Marks AO element Guidance therefore membrane permeability (to pigment) is increased  CREDIT only in the context of membrane protein structure having been changed (iii) use pH buffer range with narrower intervals  pH (buffers) , close to pH6 / between pH5 and pH6 / between pH5 and pH7  2 3.3 ALLOW stated values (must be more than one) at interval of less than 1 ALLOW stated value of buffer within the range pH5 to pH7 ‘test more values between pH5 and pH6’ = 2 marks. ‘test at pH 6.5’ = 1 mark (mp2) Question Answer Marks AO element Guidance 19 (a) (i) (bird) females have two different (sex) chromosomes / AW  ora 1 2.1 ALLOW human females are homozygous IGNORE male mammals have X and Y chromosomes DO NOT CREDIT chromosomes described as , alleles / genes (ii) Parents’ phenotype red male blue female  Gametes ZA, Zb ZB, W  Offspring genotypes ZAZB, ZBZb, ZAW, ZbW  Offspring phenotypes red male, blue male, red female, brown female  4 2.1 ALLOW ECF if no sexes given for mp1 or mp4 but colours correctH420/02 October 2021 Question Answer Marks AO element Guidance 19 (b) (i) phenotypes observed number (O) expected number (E) O-E (OE)2 (OE)2 E healthy female 5 4.5 0.5 0.25 0.056 healthy male 3 2.25 0.75 0.56 0.249 haemophilia male 1 2.25 -1.25 1.56 0.693   χ2 = 0.998 2 2.6 IGNORE decimal places (ii) 5.991  1 2.2 ALLOW number circled or otherwise indicated in table (iii) student is incorrect because , chi-squared / calculated , number below critical value  greater than , 5% / 10% , probability that any difference is due to chance  idea that statistical tests only gives a probability  2 max 3.2 ALLOW no significant difference between observed and expected ALLOW numbers too low to be confident about conclusion 19 (c) (hypophosphatemic rickets allele is) dominant  because occurs in daughter of an affected father  2 max 3.1 ALLOW it / gene , is dominantH420/02 October 2021 Question Answer Marks AO element Guidance on X chromosome / not on Y chromosome , because , it occurs in females (and males) / affected fathers always pass to daughters  Question Answer Marks AO element Guidance 20 (a) (i) -1.8  1 2.2 (ii) FIRST CHECK ON ANSWER LINE If answer = 0.24 award 2 marks 0.8 / 3.4  2 2.2 If answer incorrect… ALLOW max 1 mark for 0.2 / correct answer to >2 s.f. / 24% (iii) 12 3 4 5 67 supports because… two peaks  (at) 0 and , 1.2 / 1.4  does not support because… second / AW , peak is not much higher than background  second / AW , peak represents a small number of birds  idea that there could be other explanations for more birds between 1.2 and 1.4 (a.u.)  OR if marking points 3, 4 or 5 have not been awarded does not support because… there is only one peak  3 max 3.1 3.2 1 ALLOW not a normal distributionH420/02 October 2021 Question Answer Marks AO element Guidance idea that more likely directional selection as peak closer to left hand side  20 (b) (i) sympatric  1 1.2 (ii) idea that individuals choose to mate only with other individuals with similar sized beaks  1 1.2 CREDIT sexual selection ALLOW different , mating seasons / courtship rituals (iii) (DNA) found in all organisms  some / AW , sequences highly conserved  comparison (of DNA between species)  similar (base) sequence indicates recent common ancestor  ora 2 1.1 ALLOW look at similarities in DNA IGNORE closely relatedH420/02 October 2021 Question Answer Marks AO element Guidance 20 (c)* Please refer to the marking instructions on page 4 of this mark scheme for guidance on how to mark this question. (c) Level 3 (5–6 marks) Explains how genetic variation, differential survival and the passing on of alleles to the next generation act to increase the proportion of the population with a beak length of around 11mm and makes appropriate use of the graph data to support explanation. There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated. Level 2 (3–4 marks) Explains how natural selection acts to increase the proportion of the population with a beak length of around 11mm. There is a line of reasoning presented with some structure. The information presented is relevant and supported by some evidence. Level 1 (1–2 marks) Explains how natural selection favours those in the population with an average phenotype OR that natural selection favours finches with a beak length of around 11 mm. 6 2.5 3.2 Indicative points may include AO2.5 Genetic variation • pre-existing • sexual reproduction • meiosis • mutation Differential survival • overproduction of offspring • finches with extreme beak depth less likely to survive • reason for birds with very small or large beaks not surviving Inheritance • survivors possess alleles for average beak depth • alleles for average beak depth more likely to be inherited by offspring • increase frequency of these alleles from one generation to the next AO3.2H420/02 October 2021 Question Answer Marks AO element Guidance There is an attempt at a logical structure with a line of reasoning. The information is in the most part relevant. 0 marks No response or no response worthy of credit. Use of figures from graph • bell-shaped curve • skewed to right • beak depth with peak survival is 11.2 mm • no birds survived with beaks of 7.4 mm or less • no birds survived with beaks of 11.6 mm or more (d) similar ideas to Darwin  arrived at independently  presented / published (paper) , together  idea of increased weight of evidence  2 max 1.1 3.2 Question Answer Marks AO element Guidance 21 (a) suckers / stolons / tubers / rhizomes / bulbs  1 1.1 ALLOW other correct methods 21 (b) meristem(atic)  1 1.1 21 (c) 2 max 1.2 All marks are for the idea of multiplication – key terms, such as explant are not essentialH420/02 October 2021 Question Answer Marks AO element Guidance many / AW, explants taken from , original / parent , plant  calluses subdivided  (meristems from) plantlets can be subdivided  21 (d) (i) FIRST CHECK ON ANSWER LINE if answer is 48(%), award 2 marks. 16.1/33.8  2 2.7 If answer incorrect… ALLOW max 1 mark for correct answer (47.633) to > 2 s.f. (ii) Independent variable BAP concentration  Dependent variable shoot length  Controlled variables Any two from… time light intensity lighting regime temperature (named) nutrient availability (in growth medium) water availability concentration of other plant hormones pH (of growth medium)  3 3.3 IGNORE mean Mark the first two answers only ALLOW composition of , growth medium / agarOCR (Oxford Cambridge and RSA Examinations) The Triangle Building Shaftesbury Road Cambridge CB2 8EA OCR Customer Contact Centre Education and Learning Telephone: 01223 553998 Facsimile: 01223 552627 Email: [email protected] [Show More]

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