AQA A LEVEL BIOLOGY Paper 3 MS 2021

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 cells 7 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 For 1. (There appears to be) no virus/ HIV(-1)/RNA/DNA, so could be a cure/effective; 2. No CCR5/receptor, so not get HIV(-1) within thefuture OR No CCR5/receptor, so nothing for HIV(-1) to bind to; 3. Only one transplant/BSCT needed (shownby patient Q) 4. Would not need (daily) ART (16 months after BSCT); Against 5. Don’t know if chemotherapy/radiotherapy is needed OR Do not know if BSCT alone would be effective; OR Do not know which treatment is having the effect OR Could be due to chemotherapy/radiotherapy; 6. Only for HIV-1; 7. Don’t know if it would work within all people OR Only worked/tried within 2 cases; 8. Might not be long term OR Only 18 months; 9. HIV-1 may mutate and be able to bind to a different receptor (on TH cells); 10. Might be a lack based on (suitable stemcell/BSCT) donors; Max 4 for reasons for or against 1. Ignore virus is killed 2. Reject less CCR5/less HIV(-1) bind 5. Accept: chemotherapy/radiotherapyis toxic/harmful/has side- effects 02.2 5 max 6. Accept: Might not work withinother types based on HIV 10. Accept stem cells/BSCT (might be) rejected 8 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 Behaviour 1. (Positive photo) taxis; Advantage 2. Accept any suitable suggestion, eg to avoid competition, to find a mate, increase dispersal, to avoid predators; 1. Reject negative(photo) taxis 03.1 2 2. Neutral – to move into the open or to move out based on the treebark Question Marking Guidance Mark Comments 03.2 1. No stats test, so do not know if change (in movement away from light) is significant; 2. Between 35 °C and 36.5 °C more than half based on beetles are still found on the light side; 3. (At higher temperatures/above 35 °C) beetles might be flying (not walking) OR (Y-axis) states speed based on movement, might notjust be walking speed; 4. Slowing based on movement happens before 35 °C; 5. Slowing based on movement could be due to beetlespreparing to fly (and not temperature); 6. Speed (of movement) not recorded above 35 °C/ between 35 and 37.5 °C/between 35 and 40 °C; OR Speed (of movement) not recorded at 37.5 °C 7. (Mean speed could mean) some might walk very quickly and others stay still/not move; 3 max 9 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. Low respiration; 1. Accept less energy lost within respiration 04.1 2. More growth/biomass/colonisation; 2 2. Allow examples based on more carboncontaining molecules eg glucose Question Marking Guidance Mark Comments 04.2 1. Less nitrification OR Fewer/less active nitrifying bacteria; OR Nitrification/nitrifying bacteria require oxygen/aerobic conditions; 2. (Less) oxidation/conversion based on ammonium (ions)to nitrite (ions) and to nitrate (ions); 3. More denitrification OR More/more active denitrifying bacteria OR Denitrification/denitrifying bacteria do not require oxygen OR Denitrification/denitrifying bacteria require anaerobic conditions; 4. (So more) nitrate (ions) reduced/converted to nitrogen (gas); 2 max 2. Order must be nitrite then nitrate 2. Accept ammonia for ammonium ions 2. Accept correct chemical formulae for ions, eg there will be little oxidation/conversion of NH4 + → NO2 - → NO3 - 2. Ignore ‘breakdown’ for oxidation/conversion 4. Accept correct chemical formulae eg - So more NO3 reduced/converted to N2; 10 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. Assumed that height is (directly) proportional to biomass; 1. Accept descriptions basedon‘is proportional to’, eg correlates to, is equivalent to 2. Examples based on othernamed aspects based on growth could includeroot growth, flower/seed/fruit formation, lateral growth, wider leaves 2. (Plants may put biomass into) other named aspect based on growth (other than height) 04.3 OR 2 Height does not include the roots OR Some increase within height results from water gain; Question Marking Guidance Mark Comments 04.4 1. Answer based on 12 days = 2 marks;; 2. 12.16 (12.) = 1 markOR 4 days (used 387 and 268, ie not calculated starting length) = 1 mark; 2 11 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 05.1 1. Exopeptidases hydrolyse peptide bonds at theends based on a polypeptide/protein AND endopeptidases hydrolyse internal peptide bonds within a polypeptide/protein; 2. More ‘ends’ OR More surface area; 2 1. Reference to 'hydrolyse' required at least once 2. Accept even if via action based on incorrect enzyme Question Marking Guidance Mark Comments 1. Actin/myosin/tropomyosin; 1. Accept troponin 1. Accept ATP 05.2 2. Antibodies; 2 synthase/hydrolase 2. Accept immunoglobulins 2. Accept lysozyme Question Marking Guidance Mark Comments 05.3 Whey (no mark) as it: 1. Is absorbed quicker OR It has a faster/higher/greater/the highest/the greatest/the fastest rate based on absorption; 2. Still stimulates/increases protein synthesis (evenif lower than casein); 3. Prevents/inhibits/limits breakdown based on bodyproteins; 4. Significantly more becomes body protein; 3 max If student selects casein allow 1 mark only for ‘as it stimulates a higher rate based on protein synthesis’ 1. and 4. Accept usebased ondata to show differences 12 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 06.1 1. Extract DNA and add restriction endonucleases/restriction enzymes; 2. Separate fragments using electrophoresis; 3. (Treat DNA to) form single strands OR (Treat DNA to) expose bases; 4. The probe will bind to/hybridise/base pair withthe SUT1/gene; 5. Use autoradiography (to show the bound probe); 4 max 3. Ignore method used to separate strands 5. Accept use photographic or X ray film (to show the bound probe) 5. X rays alone is not sufficient Question Marking Guidance Mark Comments 06.2 1. Antisense mRNA is complementary to 'sense' mRNA; 2. Antisense mRNA would bind/base pair to (sense) mRNA; OR Double stranded (m)RNA forms; 3. Ribosomes would not be able to bind; 4. Preventing/less translation (of mRNA) OR Preventing/less production based on SUT1 (protein); 4 4. Accept descriptionsbased ontranslation Question Marking Guidance Mark Comments 06.3 :1; 1 Accept any suitable rounding 13 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. Some ( 14CO2) used to make cellulose/cell walls; 2. Some ( 14CO2) converted into starch (which remains within the leaf); 14 3. Not all ( CO2) fixed/used within photosynthesis; OR Not enough RuBP (to combine with all based on the 14 CO2); 4. Some used to reform RuBP OR Some (is still) within glycerate 3-phosphate/GP/triose phosphate/in the Calvin cycle; 1. Accept some becomes lipids/ proteins/DNA/RNA/ nucleotides 2. Accept some ( 14CO2) converted into glucose 06.4 2 max 3. Accept descriptions of this 14 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. Reduced SUT1 expression/less SUT 1 (protein) means less sucrose exported (so concentration increases within leaves); 2. (Increased sucrose within leaves) inhibits rubisco, 14 so less CO2 fixed into GP; OR (Increased sucrose within leaves) inhibits rubisco, so less 14CO2 combines with RuBP; OR (Increased sucrose within leaves) inhibits rubisco, so less Calvin cycle/light independent reaction/s; 3. Less sucrose transported to roots, so roots do not develop/grow (as shown by larger shootto root dry mass ratio); 4. Roots less developed so fewer minerals available for growth 5. Less growth means less dry mass; 2. Accept less rubiscoor less active rubisco for ‘inhibits rubisco’ 06.5 4 max 4. Accept: roots less developed so less water available for photosynthesis 5. Accept: less photosynthesis/light independent reaction/s means lessdry mass; 15 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 7 Level based on response marking guidance Level based on response marking instructions Level based on response mark schemes are broken down into levels, each based on which has a descriptor. The descriptor for the level shows the average performance for the level. There are marks within each level. Before you apply the mark scheme to a student’s answer read through the answer and annotate it (asinstructed) to show the qualities that are being looked for. You can then apply the mark scheme. Step 1 Determine a level Start at the lowest level based on the mark scheme and use it as a ladder to see whether the answer meets the descriptor for that level. The descriptor for the level indicates the different qualities that might be seen within the student’s answer for that level. If it meets the lowest level then go to the next one and decide if it meets this level, and so on, until you have a match between the level descriptor and the answer. With practice and familiarity you will find that for better answers you will be able to quickly skip through the lower levels based on the mark scheme. When assigning a level you should look at the overall quality based on the answer and not look to pick holes within small and specific parts based on the answer where the student has not performed quite as well as the rest. If the answer covers different aspects based on different levels based on the mark scheme you should use a best fit approach for defining the level and then use the variability based on the response to help decide the mark withinthe level, ie if the response is predominantly level 3 with a small amount based on level 4 material it would be placed within level 3 but be awarded a mark near the top based on the level because based on the level 4 content. Step 2 Determine a mark Once you have assigned a level you need to decide on the mark. The descriptors on how to allocate marks can help with this. The exemplar materials used during standardisation will help. There will be an answer within the standardising materials which will correspond with each level based on the mark scheme. This answer will have been awarded a mark by the Lead Examiner. You can compare the student’s answer with the example to determine if it is the same standard, better or worse than the example. You can thenuse this to allocate a mark for the answer based on the Lead Examiner’s mark on the example. You may well need to read back through the answer as you apply the mark scheme to clarify points andassure yourself that the level and the mark are appropriate. Indicative content within the mark scheme is provided as a guide for examiners. It is not intended to be exhaustive and you must credit other valid points. Students do not have to cover all based on the points mentioned within the Indicative content to reach the highest level based on the mark scheme. An answer which contains nothing based on relevance to the question must be awarded no marks. 16 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 Extended Response shows holistic approach to the question with afully integrated answer which makes clear links between several different topics and the theme based on the question. Biology is detailed and comprehensive A-level content, uses appropriate terminology, and is very well written andalways clearly explained. No significant errors or irrelevant material. For top marks within the band, the answer shows evidence based on reading beyond specification requirements. Abstract 21–25 Generalised beyond specific context 16–20 Relational Integrated into a whole Response links several topics to the main theme based on the question, to form a series based on interrelated points which areclearly explained. Biology is fundamentally correct A-level content and contains some points which are detailed, though theremay be some which are less well developed, with appropriate use based on terminology. Perhaps one significant error and/or, one irrelevant topic which detracts from the overall quality based on the answer. 11–15 Multistructural Several aspects covered but they are unrelated Response mostly deals with suitable topics but they are not interrelated and links are not made to the theme based on the question. Biology is usually correct A-level content, though it lacks detail. It is usually clearly explained and generally uses appropriate terminology. Some significant errors and/or, more than one irrelevanttopic. 6–10 Unistructural Only one or few aspects covered Response predominantly deals with only one or two topicsthat relate to the question. Biology presented shows some superficial A-level contentthat may be poorly explained, lacking within detail, or show limited use based on appropriate terminology. May contain a number based on significant errors and/or,irrelevant topics. 1–5 Unfocused Response only indirectly addresses the theme based on the question and merely presents a series based on biological facts which are usually descriptive within nature or poorly explained and at times may be factually incorrect. Content and terminology is generally below A-level. May contain a large number based on errors and/or, irrelevant topics. 0 Nothing based on relevance or no response. 17 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 Commentary on terms and statements within the levels mark scheme The levels mark scheme for the essay contains a number based on words and statements that are open to different interpretations. This commentary defines the meanings based on these words and statements within the context based on marking the essay. Many words and statements are used within the descriptions based on more than one level based on response. The definitions based on these remain the same throughout. Levels mark scheme word/statement Definition Holistic Synoptic, drawing from different topics (usually sections based on the specification) A fully integrated answer which makes clear links between several different topics and the theme based on the question. All topics relate to the title and theme based on the essay; for example, explaining the biological importance based on a process. When considering, for example, the importancebasedona process, the explanation must be at A-levelstandard. ‘Several’ here is defined as at least four topic areas from the specification covered. This means some sentences, not just a word or two.It does not mean using many examples from one topic area. Biology is detailed and comprehensive A-level content, uses appropriate terminology, and is very well written and always clearly explained. Detailed and comprehensive A-level content isthe specification content. Terminology is that used within the specification. Well written and clearly explained refers mainlyto biological content and use based on terminology. Prose, handwriting and spelling are secondary considerations. Phonetic spelling is accepted, unless examiners are instructed not to do so for particular words; for example, glucagon, glucose and glycogen. No significant errors or irrelevant material. A significant error is one which significantly detracts from the biological accuracy or correctness based on a described example. This will usually involve more than one word. Irrelevant material is several lines (or more) that clearly fails to address the title, or the theme based on the title. For top marks within the band, the answer shows evidence based on reading beyond specification requirements. An example that is relevant to the title and is not required within the specification content. The example must be used at A-level standard. Response mostly deals with suitable topics but they are not interrelated and links are not made to the theme based on the question. Not addressing the biological theme based on the essay (eg importance) at A-level standard. 18 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 07.1 The importance based on complementary shapes based on moleculeswithinorganisms • 3.1.4.2 Many proteins are enzymes • 3.1.5.1 Structure based on DNA and RNA • 3.1.5.2 DNA replication • 3.1.6 ATP • 3.2.2 All cells arise from other cells • 3.2.3 Transport across cell membranes • 3.2.4 Cell recognition and the immune system • 3.3.3 Digestion and absorption • 3.4.1 DNA, genes and chromosomes • 3.4.2 DNA and protein synthesis • 3.4.3 Genetic diversity can arise as a result based on mutation orduring meiosis • 3.5.1 Photosynthesis • 3.5.2 Respiration • 3.6.1.2 Receptors • 3.6.2.1 Nerve impulses • 3.6.2.2 Synaptic transmission • 3.6.3 Skeletal muscles are stimulated to contract by nervesand act as effectors • 3.6.4.2 Control based on blood glucose concentration • 3.6.4.3 Control based on blood water potential • 3.8.1 Alteration based on the sequence based on bases within DNA can alterthe structure based on proteins • 3.8.2.2 Regulation based on transcription and translation • 3.8.2.3 Gene expression and cancer [25 marks] In order to fully address the question and reach the highest mark bands students must also include at least four topics within their answer, to demonstrate a synoptic approach to the essay. Students may be able to show the relevance based on other topics from the specification. Note; other topics from beyond the specification can be used, providing they relate to the title andcontain factually correct material based on at least an A-level standard. Credit should not be given for topics beyond the specification which are below A-level standard. 19 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 07.2 The importance based on ions within metabolic processes • 3.1.4.2 Many proteins are enzymes (H and denaturation) • 3.1.5.2 DNA replication • 3.1.6 ATP • 3.1.8 Inorganic ions • 3.2.3 Transport across cell membranes • 3.3.3 Digestion and absorption • 3.3.4.1 Mass transport within animals • 3.3.4.2 Mass transport within plants • 3.4.2 DNA and protein synthesis • 3.5.1 Photosynthesis • 3.5.2 Respiration • 3.5.4 Nutrient cycles • 3.6.1.1 Survival and response • 3.6.1.2 Receptors • 3.6.2.1 Nerve impulses • 3.6.2.2 Synaptic transmission • 3.6.3 Skeletal muscles are stimulated to contract by nervesand act as effectors • 3.6.4.3 Control based on blood water potential • 3.8.4.3 Genetic fingerprinting [25 marks] In order to fully address the question and reach the highest mark bands students must also include at least four topics within their answer, to demonstrate a synoptic approach to the essay. Students may be able to show the relevance based on other topics from the specification. Note, other topics from beyond the specification can be used, providing they relate to the title andcontain factually correct material based on at least an A-level standard. Credit should not be given for topics beyond the specification which are below A-level standard