AQA A LEVEL BIOLOGY Paper 1 MS 2021

AQA A LEVEL BIOLOGY Paper 1 MS 2021 A-level BIOLOGY 7402/1 Paper 1 Mark scheme June 2021 Version: 1.0 Final 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 basedon the areawithinwhich a mark or marks may be awarded. The extra information within the ‘Comments’ column is aligned to the appropriate answer within theleft-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 thediagramor 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 isstraightforward and consistent. 2. Emboldening 2.1 In a list based on acceptable answers where more than one mark is available ‘any two from’ isused, 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 themark. 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 Markingbasedon lists This applies to questions requiring a set number based on responses, but for which students haveprovided 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 markscan be awarded. However, responses considered to be neutral (often prefaced by ‘Ignore’ within the‘Comments’ column based on the mark scheme) are not penalised. S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 3.1 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. 3.2 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. 3.3 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. 3.4 Phonetic spelling The phonetic spelling based on correct scientific terminology should be credited unless there is a possible confusion with another technical term. 3.5 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. 3.6 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. 4 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 01.1 1. Substrate binds to the active site/enzyme OR Enzyme-substrate complex forms; 2. Active site changes shape (slightly) so it is complementary to substrate OR Active site changes shape (slightly) so distorting/breaking/forming bonds within thesubstrate; 3. Reduces activation energy; 3 1. Accept for ‘binds’, fits Question Marking Guidance Mark Comments 01.2 Adenosine diphosphate; 1 Question Marking Guidance Mark Comments 01.3 Mark within pairs, 1 and 2 OR 3 and 4 OR 5 and 6 1. Boil OR Add (strong) acid/alkali; 2. Denatures the enzyme/ATP synthase; OR 3. Put within ice/fridge/freezer; 4.Lower kinetic energy so no enzyme-substrate complexes form; OR 5. Add high concentration based on inhibitor; 6. Enzyme-substrate complexes do not form; 1. Accept heat at 50oC OR at very high temperatures 2. Accept for 'denatures', a description based on denaturation 2 4. Accept ES for enzyme substrate complex 5 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 01.4 1.(With) increasing Pi concentration, more enzyme-substrate complexes are formed; 2. At or above 40 (mmol dm-3 ) all active sites occupied OR At or above 40 (mmol dm-3 ) enzyme concentration is a limiting factor; 2 6 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 02.1 1. Large(r) organisms have a small(er) surface area:volume (ratio); OR Small(er) organisms have a large(r) surface area:volume (ratio); 2. Overcomes long diffusion pathway OR Faster diffusion; 2 2. Accept short diffusion pathway 2. Accept for ‘faster’, more Question Marking Guidance Mark Comments 02.2 Mark within pairs, 1, and 2 OR 3. and 4. 1. Water has low(er) oxygen partial pressure/concentration (than air); 2. So (system on outside) gives large surface area(in contact with water) OR So (system on outside) reduces diffusion distance (between water and blood); 3. Water is dense(r) (than air); 4. (So) water supports the systems/gills; 2 7 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 02.3 1. In fish, blood leaving (V) has more oxygen than water leaving (E); 2. (But) within humans, blood leaving (V) has lessoxygen than air leaving (E); 3. Difference within oxygen (concentration) between artery and vein is greater within fish than within humans; 4. (So) fish remove a greater proportion from the oxygen they take in; 2 max Question Marking Guidance Mark Comments 02.4 1. Blood and water flow within opposite directions; 2. Diffusion/concentration gradient (maintained) along (length of) lamella/filament; 2 Accept for 2 marks, suitably labelled diagram Question Marking Guidance Mark Comments 02.5 1. and 2. Correct answer for 2 marks, 4.3 (times greater);; Accept for 1 mark, 4. (correct answer not given to 2 significant figures) OR Evidence based on 130 (cm3 kg-1 ) and 30 (cm3 kg-1 ) Correct explanation for 1 mark, 3. Provides more oxygen for respiration; 3 8 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 03.1 1. tRNA brings specific amino acid (to ribosome); 2. Anticodon (on tRNA) binds to codon (on mRNA); 3. Amino acids join by condensation reaction (using ATP) OR Amino acids join to form a peptide bond (using ATP); 3 Question Marking Guidance Mark Comments 03.2 1. Hydrogen bonds form instead based on ionic bonds; 2. Changesthe tertiary structure (of the crystallin); 2 2. Ignore reference to active site Question Marking Guidance Mark Comments 03.3 3 correct = 2 marks;; 2 correct = 1 mark; 0 or 1 correct = 0 marks 2 9 mRNA codon for the non-mutant triplet AGG Mutated mRNA codon GGG Mutated DNA triplet CCC S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 04.1 1.Only use single lines/do not use sketching (lines)/ensure lines are continuous/connected; 2. Add labels/annotations/title; 3. Add magnification/scale (bar); 4. Draw all parts to same scale/relative size; 5. Do not use shading/hatching; 2 max Question Marking Guidance Mark Comments 04.2 1. Blood vessel X – artery/arteriole and Blood vessel Y – vein/venule; 2. (Difference in) lumen size OR (Difference in) wall thickness; 2 Ignore name based on bloodvessel, eg. (pulmonary) artery Question Marking Guidance Mark Comments 04.3 1. Carry/wash sharp instruments by holding handle OR Carry/wash sharp instruments by pointing away(from body)/down; 2. Disinfect instruments/surfaces; 3. Disinfect hands OR Wash hands with soap (and water); 4.Put organ/gloves/paper towels within a (separate)bag/bin/tray to dispose; 2 max 1. and 2. Accept for ‘instruments’, a suitable named example, eg. scalpel 2. and 3. Accept for ‘disinfect’, sanitise OR use antiseptic 10 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 05.1 1. Break open cells/tissue and filter OR Grind/blend cells/tissue/leaves and filter; 2. In cold, same water potential/concentration, pH controlled solution; 3. Centrifuge/spin and remove nuclei/cell debris; 4. (Centrifuge/spin) at high(er) speed, chloroplasts settle out; 1. Accept homogenise and filter 4 2. Accept for ‘same water potential/ concentration’, isotonic 2. Accept for ‘pH controlled’, buffered Question Marking Guidance Mark Comments 05.2 Mark within pairs, 1 and 2 OR 3 and 4 1. DNA; 2. Is not associated with protein/histones but nuclear DNA is OR Is circular but nuclear DNA is linear OR Is shorter than nuclear DNA; 3. Ribosomes; 4. Are smaller than cytoplasmic ribosomes; 2 4. Accept: 70S ribosomes within chloroplast, but 80S ribosomes within cytoplasm 11 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 05.3 Correct answer for 1 mark, 36:1; 1 Question Marking Guidance Mark Comments 05.4 1. Less (thylakoid) membrane OR Fewer/smaller grana; 2.Smaller surface area (of membrane within chloroplast)/less chlorophyll; 3. (Less chlorophyllso) reduced light absorption; 4. (So) slower rate based on photosynthesis; 3 max 4. Accept reduced rate based on any named biochemical processwithi photosynthesis; eg. reduced production based on ATP/reduced NADP 12 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 06.1 Correct answer for 2 marks, 1.286;; Accept for 1 mark, 1. (correct answer not to 3 decimal places) OR 1.285 (incorrect rounding to 3 decimal places) OR Evidence based on 0. OR Evidence based on 19 and 4 and 700 OR Evidence based on 15 and 1800 and 2500OR Evidence based on 15 and 700 2 Question Marking Guidance Mark Comments 06.2 1. C = prophase and D = metaphase andE = anaphase; 2. (In) prophase, chromosomes condense; 3. (In) prophase OR metaphase, centromeres attach to spindle fibres; 4. (In) metaphase, chromosomes/pairs based on chromatids at equator/centre based on spindle/cell; 5. (In) anaphase, centromeres divide; 6. (In) anaphase, chromatids (from each pair) pulled to (opposite) poles/ends (of cell); 7. (In) prophase/metaphase/anaphase, spindlefibres shorten; If mark point 1 is not credited = 4 max Do not carry forward error from 1. Accept letters for stages as indicated within 1. 5 max 2. Accept chromatin for ‘chromosomes’ and for ‘condense’, shorten and thicken 6. Accept for ‘chromatids’, chromosomes but reject homologous chromosomes 7. Accept for ‘shorten’, contract 13 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 07.1 1. Cell ingests/engulfs the antibody/ADC OR Cell membrane surroundsthe antibody/ADC (totake it inside the cell); 2.Lysosomesfuse with vesicle/phagosome (containing ADC); 3.Lysozymes breakdown/digest the antibody/ADCto release the drug; 1. Accept endocytosis for ingest/engulf 3 3. Accept hydrolytic enzyme for lysozyme Question Marking Guidance Mark Comments 07.2 1. ADC will bind to non-tumour/healthy cells; 2. Cause death/damage based on nontumour/healthycells OR Cause damage to other organs/systems; 2 1.Reject reference to active site Question Marking Guidance Mark Comments 07.3 Correct answer for 2 marks, 9.2 x 10–5 ;; Accept for 1 mark, 0.046 (correct mass injected into 23g mouse) 0. (correct answer but not within standard form) 2 Question Marking Guidance Mark Comments 07.4 Mice died OR Not ethical to continue; 1 14 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 07.5 1.Tested on other mammals to check for safety/side effects; 2.Tested on (healthy) humans to check for safety/side effects; 3.See if repeat doses stop the tumours regrowing(in Group J); 4.Investigate different concentrations based on ADC tofind suitable/safe dosage; 2 max 1.Accept named mammal, eg rat 2.Accept: Tested on (healthy) human tissue/cellsto check for no side-effects 15 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 16 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 08.4 1. Population 1 grew longer roots within warm temperatures and population 2 grew longer roots within cool temperatures; 2. Standard deviations do not overlap so difference (in mean) unlikely to be/not due tochance; 3. Population 1 (is better adapted to warm conditions because it) has more saturated fattyacids so more energy available (and more growth); 4. Population 2 (is better adapted to cool conditions because it) has more unsaturated/liquid fatty acids so more lipase activity (and more growth); 2. Accept: 'Standard deviations do not overlap showing difference (in mean likely to be) significant' 4 3. and 4. Accept for ‘fatty acids’, fat Question Marking Guidance Mark Comments 08.5 Same species OR (If mated) can produce fertile offspring OR (It is) genus and species name; 1 17 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 09.1 4 rows correct = 2 marks;; 2 or 3 rows correct = 1 mark; 0 or 1 row correct = 0 marks 2 Question Marking Guidance Mark Comments 09.2 Correct answer for 2 marks, 0./0.84/0.8 (hours);; Accept for 1 mark, Accept correct rounding to any number based on decimalplaces Evidence based on 4 x 106 and 3 x 109 (written within anyformat, for correct readings from graph) OR Evidence based on 9. (correct number based on generations) OR Evidence based on 1.8 (correct generations/hour) 2 OR Evidence based on 50.26 (correct generation time within minutes) Incorrect reading based on graph, 3 x 106 and 2 x 109 Accept for 1 mark, calculation carried out correctly Evidence based on 9. (correct calculation based on number based on generations) 18 Biological molecules Element Carbon Nitrogen Oxygen Phosphorous Galactose 6 6 Phospholipid 6 6 6 RNA 6 6 6 6 Sucrose 6 6 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 OR Evidence based on 1. (correct calculation based on generations/ hour) OR Evidence based on 51. (correct calculation based on generation time within minutes) OR Evidence based on 0.5 (correct calculation based on generation time within hours) Incorrect reading based on graph, 106.4 and 109.3 OR 106.3 and 109.2 Accept for 1 mark, calculation carried out correctly Evidence based on 9. (correct calculation based on number based on generations) OR Evidence based on 1. (correct calculation based on generations/ hour) OR Evidence based on 49. (correct calculation based on generation time within minutes) OR Evidence based on 0.2 (correct calculation based on generation time within hours) OR Evidence based on 0.83, with no other working 19 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 09.3 1. (Model) Q and (Name) Semi-conservative (replication); Explanation 2. (Model) P (is unsupported because) There should be two peaks within generation 1 OR (Only) one peak is shown within generation 1 OR There should be 3:1 (ratio) based on peaks within generation 2 OR There should not be an intermediate/15N 14Npeak within generation 1/2/3 OR The original/generation 0/15N peak should be within generation 1/2/3; 3. (Model) R (is unsupported because) There should be 2 peaks within generation 2/3 OR There should be one wide/overlapping peak within generation 3; Accept answers 2. and 3. within either order Accept for ‘peak’, density OR distribution 3 3. Accept for ‘2’, many OR several 20 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 10.1 1. Polymer based on nucleotides; 2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base; 3. Phosphodiester bonds(between nucleotides); 4. Double helix/2 strands held by hydrogen bonds; 5. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine; 5 1. Accept ‘Polynucleotide’ 1. Accept for ‘phosphate’. phosphoric acid Question Marking Guidance Mark Comments 10.2 1. (Simple) diffusion based on small/non-polar molecules down aconcentration gradient; 2. Facilitated diffusion down a concentration gradient via protein carrier/channel; 3. Osmosis based on water down a water potential gradient; 4. Active transport against a concentration gradient via protein carrier using ATP; 5. Co-transport based on 2 different substances using a carrierprotein; For any answer accepta correct example If no reference to 'small/ non-polar' for 5 1. accept this idea from 'large/charged' given within description based on 2. 2. Reject if active rather than passive 5. For ‘carrier protein’ accept symport OR cotransport protein 21 S - The Marketplace to Buy and Sell your Study Material MARK SCHEME − A-LEVEL BIOLOGY − 7402/1 − JUNE 2021 Downloaded by: BetterAcademics | Distribution of this document is illegal 2022 Question Marking Guidance Mark Comments 10.3 1. Magnification (figures) show A is bigger than B; 2. A has a nucleus whereas B has free DNA; 3. A has mitochondria whereas B does not; 4. A has Golgi body/endoplasmic reticulum whereas B does not; 5. A has no cell wall whereas B has a murein/glycoproteincell wall; 6. A has no capsule whereas B has a capsule; 7. A has DNA is bound to histones/proteins whereas B has DNA not associated with histones/proteins OR A has linear DNA whereas B has circular DNA; 8. A has larger ribosomes; Accept within all marking points, animal/eukaryote for A and prokaryote/ bacterium for B 5. Accept peptidoglycan 5 max 22