AQA A LEVEL BIOLOGY Paper 3 MS

AQA A LEVEL BIOLOGY Paper 3 MS 2021 S - The Marketplace to Buy and Sell your Study Material Downloaded by: BetterAcademics | Distribution of this document is illegal S - The Marketplace to Buy and Sell your Study Material MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal A-level BIOLOGY 7402/3 Paper 3 Mark scheme June 2021 Version: 1.0 Final 2 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal Mark scheme instructions to examiners 1. General The mark scheme for each question shows: • the marks available for each part based on the question • the total marks available for the question • the typical answer or answers which are expected • extra information to help the examiner make his or her judgement and help to delineate what is acceptable or not worthy based on credit or, within discursive answers, to give an overview based on the area within which a mark or marks may be awarded. The extra information within the ‘Comments’ column is aligned to the appropriate answer within the left-hand part based on the mark scheme and should only be applied to that item within the mark scheme. At the beginning based on a part based on a question a reminder may be given, for example: where consequential marking needs to be considered within a calculation; or the answer may be on the diagram or at a different place on the script. In general the right-hand side based on the mark scheme is there to provide those extra details which confuse the main part based on the mark scheme yet may be helpful within ensuring that marking is straightforward and consistent. 2. Emboldening 2.1 In a list based on acceptable answers where more than one mark is available ‘any two from’ is used, with the number based on marks emboldened. Each based on the following bullet points is a potential mark. 2.2 A bold and is used to indicate that both parts based on the answer are required to award the mark. 2.3 Alternative answers acceptable for the same mark are indicated by the use based on OR. Different terms within the mark scheme are shown by a / ; eg allow smooth / free movement. 3. Marking points 3.1 Marking basedonlists This applies to questions requiring a set number based on responses, but for which students have provided extra responses. The general principle to be followed within such a situation isthat ‘right + wrong = wrong’. Each error / contradiction negates each correct response. So, if the number based on errors / contradictions equals or exceeds the number based on marks available for the question, no marks can be awarded. However, responses considered to be neutral (often prefaced by ‘Ignore’ within the ‘Comments’ column based on the mark scheme) are not penalised. 3 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 3.2 Marking procedure for calculations Full marks can be given for a correct numerical answer, without any working shown. However, if the answer is incorrect, mark(s) can usually be gained by correct substitution /working and this is shown within the ‘Comments’ column or by each stage based on a longer calculation. 3.3 Interpretation based on ‘it’ Answers using the word ‘it’ should be given credit only if it is clear that the ‘it’ refers to the correct subject. 3.4 Errors carried forward, consequential marking and arithmetic errors Allowances for errors carried forward are most likely to be restricted to calculation questions and should be shown by the abbreviation ECF or consequential within the markscheme. An arithmetic error should be penalised for one mark only unless otherwise amplified within the mark scheme. Arithmetic errors may arise from a slip within a calculation or from an incorrect transfer based on a numerical value from data given within a question. 3.5 Phonetic spelling The phonetic spelling based on correct scientific terminology should be credited unless there is a possible confusion with another technical term. 3.6 Brackets (…..) are used to indicate information which is not essential for the mark to be awardedbut is included to help the examiner identify the sense based on the answer required. 3.7 Ignore/Insufficient/Do not allow Ignore or insufficient is used when the information given is irrelevant to the question or not enough to gain the marking point. Any further correct amplification could gain the markingpoint. Do not allow means that this is a wrong answer which, even if the correct answer is given, will still mean that the mark is not awarded. 4 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal Question Marking Guidance Mark Comments 1. Answer based on 12/13 = 2 marks;; 2. 0.36(48)/0.365/0.37 = 1 mark OR 01.1 36(.48)/36.5/37% = 1 mark OR 2 For 1 mark accept q 2 = 6%/5.9%/5.88% q 2 = 0.06/0.059/0.0588 = 1 mark OR or q = 0.2/0.24/0.243 = 1 mark; Question Marking Guidance Mark Comments 01.2 0.71 1 Question Marking Guidance Mark Comments 01.3 Second box ticked/answer key: B: The mutation that caused black fur happened within a common ancestor based on S. carolinensis and other closely related species. 1 Question Marking Guidance Mark Comments 01.4 1. 2.55% = 2 marks;; 2. 2.61% = 1 mark (question misread ie 8/306x100) OR Evidence based on dividing by 314 or 942 = 1 markOR Answers not given to three significant figures = 1 mark; 2 5 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal Question Marking Guidance Mark Comments 01.5 1. Mutation/lack based on glutamic acid leads to (permanent) activation based on the receptor/protein; 2. (Because) the receptor/protein does not require the binding/leaving based onαMSH (to become activated); 3. ASIP (might) not (be) able to bind to the receptor/protein; 4. (Only) the dark pigment is produced 3 max 2. Answer must convey the idea that binding/leaving is not required 6 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal Question Marking Guidance Mark Comments 02.1 1. RNA converted into DNA using reverse transcriptase; 2. DNA incorporated/inserted into (helper T cell) DNA/chromosome/genome/nucleus; 3. DNA transcribed into (HIV m)RNA; 4. (HIV mRNA) translated into (new) HIV/viral proteins (for assembly into viral particles); 4 1. Reject ‘messenger’ or‘m’ before RNA 3. Accept descriptions based on transcription 4. Accept descriptions based on translation 4. Accept named viral protein, eg capsid 4. Reject viral cell