A-level BIOLOGY 7402/3 Paper 3 Mark scheme June 2022 Version: 1.0 Final

A-level BIOLOGY 7402/3 Paper 3 Mark scheme June 2022 Version: 1.0 Final *226A7402/3/MS* MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2022 2 Mark schemes are prepared by the Lead Assessment Writer and consider ...

A-level BIOLOGY 7402/3 Paper 3 Mark scheme June 2022 Version: 1.0 Final *226A7402/3/MS* MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2022 2 Mark schemes are prepared by the Lead Assessment Writer and considered, together with the relevant questions, by a panel of subject teachers. This mark scheme includes any amendments made at the standardisation events which all associates participate in and is the scheme which was used by them in this examination. The standardisation process ensures that the mark scheme covers the students’ responses to questions and that every associate understands and applies it in the same correct way. As preparation for standardisation each associate analyses a number of students’ scripts. Alternative answers not already covered by the mark scheme are discussed and legislated for. If, after the standardisation process, associates encounter unusual answers which have not been raised they are required to refer these to the Lead Examiner. It must be stressed that a mark scheme is a working document, in many cases further developed and expanded on the basis of students’ reactions to a particular paper. Assumptions about future mark schemes on the basis of one year’s document should be avoided; whilst the guiding principles of assessment remain constant, details will change, depending on the content of a particular examination paper. Further copies of this mark scheme are available from aqa.org.uk Copyright information AQA retains the copyright on all its publications. However, registered schools/colleges for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to schools/colleges to photocopy any material that is acknowledged to a third party even for internal use within the centre. Copyright © 2022 AQA and its licensors. All rights reserved. MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2022 3 Mark scheme instructions to examiners 1. General The mark scheme for each question shows: • the marks available for each part of 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 of credit or, in discursive answers, to give an overview of the area in which a mark or marks may be awarded. The extra information in the ‘Comments’ column is aligned to the appropriate answer in the lefthand part of the mark scheme and should only be applied to that item in the mark scheme. At the beginning of a part of a question a reminder may be given, for example: where consequential marking needs to be considered in a calculation; or the answer may be on the diagram or at a different place on the script. In general the right-hand side of the mark scheme is there to provide those extra details which confuse the main part of the mark scheme yet may be helpful in ensuring that marking is straightforward and consistent. 2. Emboldening 2.1 In a list of acceptable answers where more than one mark is available ‘any two from’ is used, with the number of marks emboldened. Each of the following bullet points is a potential mark. 2.2 A bold and is used to indicate that both parts of the answer are required to award the mark. 2.3 Alternative answers acceptable for the same mark are indicated by the use of OR. Different terms in the mark scheme are shown by a / ; eg allow smooth / free movement. 3. Marking points 3.1 Marking of lists This applies to questions requiring a set number of responses, but for which students have provided extra responses. The general principle to be followed in such a situation is that ‘right + wrong = wrong’. Each error / contradiction negates each correct response. So, if the number of errors / contradictions equals or exceeds the number of marks available for the question, no marks can be awarded. However, responses considered to be neutral (often prefaced by ‘Ignore’ in the ‘Comments’ column of the mark scheme) are not penalised. MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2022 4 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 in the ‘Comments’ column or by each stage of a longer calculation. 3.3 Interpretation of ‘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 in the mark scheme. An arithmetic error should be penalised for one mark only unless otherwise amplified in the mark scheme. Arithmetic errors may arise from a slip in a calculation or from an incorrect transfer of a numerical value from data given in a question. 3.5 Phonetic spelling The phonetic spelling of 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 awarded but is included to help the examiner identify the sense of 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 marking point. 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. MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2022 5 Question Marking Guidance Mark Comments 01.1 Two marks for three correct answers, one mark for two correct answers;; (Left amino acid) Serine (Middle amino acid) Alanine (Right amino acid) Aspartic (acid) 2 (2 x AO2) Accept phonetic spellings Question Marking Guidance Mark Comments 01.2 One mark for each correct row DNA ATP Reverse transcriptase Phospholipid  ;     ;   ; 3 (3 x AO1) Question Marking Guidance Mark Comments 01.3 Correct answer of 574 (amino acids) = 2 marks;; 573.99936 = 1 mark OR 146/145.99986 = 1 mark OR 287 = 1 mark OR 292 = 1 mark; 2 (2 x AO2) Question Marking Guidance Mark Comments 01.4 Accept curve drawn to the right, following the same pattern and starting at Y = 0 and finishing at the same percentage saturation as original curve; 1 (AO3) MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2022 6 Question Marking Guidance Mark Comments 01.5 1. During exercise OR At low pO2 (in the tissues); 2. (Allowing) more oxygen for respiration OR (Allowing) more aerobic respiration OR To delay anaerobic respiration; 2 (2 x AO3) 1. Accept ‘high altitude’ or ‘lack of red blood cells’ for ‘exercise’ 1. Accept when there is a high pCO2 (in the tissues) 1. Accept at low concentration of O2 (in the tissues) 2. Accept descriptions of aerobic respiration, eg more oxygen to act as a terminal electron acceptor 2. Accept oxygen can unload/dissociate easier/more readily for respiration Question Marking Guidance Mark Comments 02.1 Two marks for three correct structures, one mark for two correct structures;; P = Capsule/lamella(e) Q = Axon (membrane) R = Schwann cell(s) OR R = Myelin (sheath) 2 (2 x AO1) P – accept connective tissue Q – accept (sensory) neurone Q – accept nerve cell Q – ignore nerve MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2022 7 Question Marking Guidance Mark Comments 02.2 1.27% (second box) ticked; 1 (AO2) Question Marking Guidance Mark Comments 02.3 1. The student started to move/close her hand before the ruler was released; 2. The ruler did not fall vertically/was not placed vertically; 3. The ruler stuck to her skin; 4. (Student B) held the ruler too high/higher; 1 max (AO3) 1. Accept any descriptions of a pre-emptive strike Ignore answers related to student A having their eyes open Ignore student B misread the ruler; Question Marking Guidance Mark Comments 02.4 Correct answer of 12.9 / 13 (m s–1 ) = 2 marks;; Use of reaction time of 136 (ms)/0.136 (s) in answer = 1 mark OR • 14.583 (answer including Trial 3) = 1 mark OR 1.29 = 1 mark 2 (2 x AO2) For 2 marks accept any correct rounding of 12.8676471 Question Marking Guidance Mark Comments 02.5 1. Synaptic transmission OR Transmission at neuromuscular junction; 2. Time for muscle contraction; 3. Time taken for (stretch-mediated) sodium ion channels to open (in the Pacinian corpuscle); 4. Student may have been distracted/not concentrating; 5. Time taken for coordination/comprehension (by the brain); 3 max (3 x AO3) Ignore answers relating to the estimate of the length of the nerve pathway involved 1. Accept (involves) synapses For 1 mark, accept correct reference to student conditions/medication eg tiredness, antidepressants MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2022 8 Question Marking Guidance Mark Comments 03.1 1. To break down links between cells/cell walls OR To separate cells/cell walls OR To break down/hydrolyse cellulose/cell wall; 2. Allowing the stain to pass/diffuse into the cells OR Allowing the cells to be (more easily) squashed; 3. To stop mitosis; 2 max (2 x AO2) 1. Ignore references to any bonds 3. Accept to stop cell division/cell cycle Question Marking Guidance Mark Comments 03.2 1. To create a single/thin layer of cells OR To spread out cells; 2. So that light could pass through; 2 (2 x AO3) Question Marking Guidance Mark Comments 03.3 1. Anaphase; 2. Chromatids moved/pulled to opposite poles/ends; 2 (1 x AO1, 1 x AO2) 1. Reject ‘Anaphase I (of meiosis)’ 2. Accept ‘chromosomes’ for ‘chromatids’ 2. Reject homologous chromosomes for chromatids