A-level
BIOLOGY 7402/3
Paper 3
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 of the question
• the total marks available for the question
• the typical answer or answers which are expected
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
• 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.
3
3.2 Marking procedure for calculations
Full marks can be given for a correct numerical answer, without any working shown.
2
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
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.
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Question Marking Guidance Mark Comments
1. Answer of 12/13 = 2 marks;;
2. 0.36(48)/0.365/0.37 = 1
mark OR
01.1 36(.48)/36.5/37% = 1 mark 2
OR
2
q = 0.06/0.059/0.0588 = 1 mark OR
or q = 0.2/0.24/0.243 = 1 mark; For 1 mark accept q2
= 6%/5.9%/5.88%
Question Marking Guidance Mark Comments
01.2 0.71 1
Question Marking Guidance Mark Comments
Second box ticked/answer key: B:
01.3 The mutation that caused black fur happened in a 1
common ancestor of S. carolinensis and other
closely related species.
Question Marking Guidance Mark Comments
1. 2.55% = 2 marks;;
2. 2.61% = 1 mark (question misread ie
8/306x100)
OR
01.4 2
Evidence of dividing by 314 or 942 = 1 mark
OR
Answers not given to three significant figures = 1
mark;
4
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Question Marking Guidance Mark Comments
1. Mutation/lack of glutamic acid leads to
(permanent) activation of the receptor/protein;
2. Answer must
2. (Because) the receptor/protein does not convey the idea that
require the binding/leaving of αMSH (to become binding/leaving is not
activated); required
01.5 3 max
3. ASIP (might) not (be) able to bind to the
receptor/protein;
4. (Only) the dark pigment is produced
5
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
1. RNA converted into DNA using reverse 1. Reject ‘messenger’ or
transcriptase; ‘m’ before RNA
2. DNA incorporated/inserted into (helper
T cell) DNA/chromosome/genome/nucleus;
3. DNA transcribed into (HIV m)RNA;
3. Accept descriptions
4. (HIV mRNA) translated into (new) of transcription
02.1 HIV/viral proteins (for assembly into viral 4
particles); 4. Accept descriptions
of
translation
4. Accept named viral
protein, eg capsid
4. Reject viral cells
6
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
For Max 4 for reasons for or
against
1. (There appears to be) no virus/ HIV(-
1)/RNA/DNA, so could be a cure/effective; 1. Ignore virus is killed
2. No CCR5/receptor, so not get HIV(-1) in
2. Reject less CCR5/less
the future
HIV(-1) bind
OR
No CCR5/receptor, so nothing for HIV(-1) to
bind to;
3. Only one transplant/BSCT needed (shown
by patient Q) 5. Accept:
chemotherapy/radiotherapy
4. Would not need (daily) ART (16 months is toxic/harmful/has
after BSCT); sideeffects
Against 6. Accept: Might not work
in other types of HIV
5. Don’t know if chemotherapy/radiotherapy is
needed
OR
Do not know if BSCT alone would be effective;
02.2 5 max
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 in all people
OR 10. Accept stem cells/BSCT
Only worked/tried in 2 cases; (might be) rejected
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 of (suitable stem
cell/BSCT) donors;
7
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
1. Reject
Behaviour negative
1. (Positive photo) taxis; (photo) taxis
03.1 Advantage 2
2. Accept any suitable suggestion, eg to avoid 2. Neutral – to
competition, to find a mate, increase move into the open or
dispersal, to avoid predators; to move out of the
tree bark
Question Marking Guidance Mark Comments
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 of
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 of movement, might not
just be walking speed;
03.2 4. Slowing of movement happens before 35 °C; 3 max
5. Slowing of movement could be due to beetles
preparing 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;
8
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
1. Low respiration; 1. Accept less
energy lost in
2. More growth/biomass/colonisation; respiration
04.1 2 2. Allow
examples of more
carboncontaining
molecules eg glucose
Question Marking Guidance Mark Comments
1. Less nitrification
OR
2. Order must be
Fewer/less active nitrifying bacteria; nitrite then nitrate
OR 2. Accept ammonia for
ammonium ions
Nitrification/nitrifying bacteria require
oxygen/aerobic conditions; 2. Accept correct
chemical formulae for
ions, eg there will be
2. (Less) oxidation/conversion of ammonium (ions)
little
to nitrite (ions) and to nitrate (ions);
oxidation/conversion
3. More denitrification + -
of NH4 → NO2 →
04.2 2 max
NO3-
OR
More/more active denitrifying bacteria 2. Ignore ‘breakdown’
for
OR oxidation/conversion
Denitrification/denitrifying bacteria do not require 4. Accept correct
oxygen chemical formulae eg
So more
OR NO3reduced/converted
to
Denitrification/denitrifying bacteria require N2;
anaerobic conditions;
4. (So more) nitrate (ions) reduced/converted to
nitrogen (gas);
9
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
1. Assumed that height is (directly) 1. Accept
proportional to biomass; descriptions of ‘is
proportional to’, eg
2. (Plants may put biomass into) other named correlates to, is
aspect of growth (other than height) equivalent to
04.3 OR 2. Examples of
2
other named aspects
Height does not include the roots of growth could
include root growth,
OR flower/seed/fruit
formation, lateral
Some increase in height results from water gain; growth, wider leaves
Question Marking Guidance Mark Comments
1. Answer of 12 days = 2 marks;;
2. 12.16 (12.15774433) = 1 mark
04.4 OR 2
4 days (used 387 and 268, ie not calculated
starting length) = 1 mark;
1. Exopeptidases hydrolyse peptide bonds at the
ends of a polypeptide/protein 1. Reference to
AND endopeptidases hydrolyse internal peptide 'hydrolyse' required at
bonds within a polypeptide/protein; least once
05.1 2. More ‘ends’ 2 2. Accept even if
via
OR action of incorrect
enzyme
More surface area;
Question Marking Guidance Mark Comments
10
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BIOLOGY 7402/3
Paper 3
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 of the question
• the total marks available for the question
• the typical answer or answers which are expected
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
• 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.
3
3.2 Marking procedure for calculations
Full marks can be given for a correct numerical answer, without any working shown.
2
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
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.
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
1. Answer of 12/13 = 2 marks;;
2. 0.36(48)/0.365/0.37 = 1
mark OR
01.1 36(.48)/36.5/37% = 1 mark 2
OR
2
q = 0.06/0.059/0.0588 = 1 mark OR
or q = 0.2/0.24/0.243 = 1 mark; For 1 mark accept q2
= 6%/5.9%/5.88%
Question Marking Guidance Mark Comments
01.2 0.71 1
Question Marking Guidance Mark Comments
Second box ticked/answer key: B:
01.3 The mutation that caused black fur happened in a 1
common ancestor of S. carolinensis and other
closely related species.
Question Marking Guidance Mark Comments
1. 2.55% = 2 marks;;
2. 2.61% = 1 mark (question misread ie
8/306x100)
OR
01.4 2
Evidence of dividing by 314 or 942 = 1 mark
OR
Answers not given to three significant figures = 1
mark;
4
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
1. Mutation/lack of glutamic acid leads to
(permanent) activation of the receptor/protein;
2. Answer must
2. (Because) the receptor/protein does not convey the idea that
require the binding/leaving of αMSH (to become binding/leaving is not
activated); required
01.5 3 max
3. ASIP (might) not (be) able to bind to the
receptor/protein;
4. (Only) the dark pigment is produced
5
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
1. RNA converted into DNA using reverse 1. Reject ‘messenger’ or
transcriptase; ‘m’ before RNA
2. DNA incorporated/inserted into (helper
T cell) DNA/chromosome/genome/nucleus;
3. DNA transcribed into (HIV m)RNA;
3. Accept descriptions
4. (HIV mRNA) translated into (new) of transcription
02.1 HIV/viral proteins (for assembly into viral 4
particles); 4. Accept descriptions
of
translation
4. Accept named viral
protein, eg capsid
4. Reject viral cells
6
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
For Max 4 for reasons for or
against
1. (There appears to be) no virus/ HIV(-
1)/RNA/DNA, so could be a cure/effective; 1. Ignore virus is killed
2. No CCR5/receptor, so not get HIV(-1) in
2. Reject less CCR5/less
the future
HIV(-1) bind
OR
No CCR5/receptor, so nothing for HIV(-1) to
bind to;
3. Only one transplant/BSCT needed (shown
by patient Q) 5. Accept:
chemotherapy/radiotherapy
4. Would not need (daily) ART (16 months is toxic/harmful/has
after BSCT); sideeffects
Against 6. Accept: Might not work
in other types of HIV
5. Don’t know if chemotherapy/radiotherapy is
needed
OR
Do not know if BSCT alone would be effective;
02.2 5 max
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 in all people
OR 10. Accept stem cells/BSCT
Only worked/tried in 2 cases; (might be) rejected
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 of (suitable stem
cell/BSCT) donors;
7
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
1. Reject
Behaviour negative
1. (Positive photo) taxis; (photo) taxis
03.1 Advantage 2
2. Accept any suitable suggestion, eg to avoid 2. Neutral – to
competition, to find a mate, increase move into the open or
dispersal, to avoid predators; to move out of the
tree bark
Question Marking Guidance Mark Comments
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 of
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 of movement, might not
just be walking speed;
03.2 4. Slowing of movement happens before 35 °C; 3 max
5. Slowing of movement could be due to beetles
preparing 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;
8
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
1. Low respiration; 1. Accept less
energy lost in
2. More growth/biomass/colonisation; respiration
04.1 2 2. Allow
examples of more
carboncontaining
molecules eg glucose
Question Marking Guidance Mark Comments
1. Less nitrification
OR
2. Order must be
Fewer/less active nitrifying bacteria; nitrite then nitrate
OR 2. Accept ammonia for
ammonium ions
Nitrification/nitrifying bacteria require
oxygen/aerobic conditions; 2. Accept correct
chemical formulae for
ions, eg there will be
2. (Less) oxidation/conversion of ammonium (ions)
little
to nitrite (ions) and to nitrate (ions);
oxidation/conversion
3. More denitrification + -
of NH4 → NO2 →
04.2 2 max
NO3-
OR
More/more active denitrifying bacteria 2. Ignore ‘breakdown’
for
OR oxidation/conversion
Denitrification/denitrifying bacteria do not require 4. Accept correct
oxygen chemical formulae eg
So more
OR NO3reduced/converted
to
Denitrification/denitrifying bacteria require N2;
anaerobic conditions;
4. (So more) nitrate (ions) reduced/converted to
nitrogen (gas);
9
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MARK SCHEME – A-LEVEL BIOLOGY – 7402/3 – JUNE 2021
Question Marking Guidance Mark Comments
1. Assumed that height is (directly) 1. Accept
proportional to biomass; descriptions of ‘is
proportional to’, eg
2. (Plants may put biomass into) other named correlates to, is
aspect of growth (other than height) equivalent to
04.3 OR 2. Examples of
2
other named aspects
Height does not include the roots of growth could
include root growth,
OR flower/seed/fruit
formation, lateral
Some increase in height results from water gain; growth, wider leaves
Question Marking Guidance Mark Comments
1. Answer of 12 days = 2 marks;;
2. 12.16 (12.15774433) = 1 mark
04.4 OR 2
4 days (used 387 and 268, ie not calculated
starting length) = 1 mark;
1. Exopeptidases hydrolyse peptide bonds at the
ends of a polypeptide/protein 1. Reference to
AND endopeptidases hydrolyse internal peptide 'hydrolyse' required at
bonds within a polypeptide/protein; least once
05.1 2. More ‘ends’ 2 2. Accept even if
via
OR action of incorrect
enzyme
More surface area;
Question Marking Guidance Mark Comments
10
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