Please write clearly in block capitals.
Centre number Candidate number
A-level
Surname
Forename(s) BIOLOGY
Candidate signature
I declare this is my own work.
7402/1
Paper 1
A-level
Mark scheme
BIOLOGY June 2026
Paper 1 Version: 1.0 Final
Thursday 4 June 2026 Afternoon Time allowed: 2 hours
Materials For Examiner’s Use
For this paper you must have:
Question Mark
• a ruler with millimetre measurements
• a scientific calculator. 1
2
Instructions
3
• Use black ink or black ball-point pen.
• Fill in the boxes at the top of this page. 4
• Answer all questions. 5
• You must answer the questions in the spaces provided. Do not write 6
outside the box around each page or on blank pages.
7
• If you need extra space for your answer(s), use the lined pages at the end of
this book. Write the question number against your answer(s). 8
• Show all your working. 9
• Do all rough work in this book. Cross through any work you do not want
10
to be marked.
TOTAL
Information
• The marks for the questions are shown in brackets.
• The maximum mark for this paper is 91.
*jun *
IB/M/Jun26/G4005/V13 7402/1
, 2
MARK SCHEME – A-LEVEL BIOLOGY – 7402/1 – JUNE 2026
Do not write
outside the
Answer all questions in the spaces provided. box
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
0 1 Figure 1 shows a molecule of antidiuretic hormone (ADH).
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’
Figure 1
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.
No student should be disadvantaged on the basis of their gender identity and/or how they refer to the
gender identity of others in their exam responses.
A consistent use of ‘they/them’ as a singular and pronouns beyond ‘she/her’ or ‘he/him’ will be credited in
exam responses in line with existing mark scheme criteria.
Further copies of this mark scheme are available from
The ADH molecule is made up of nine amino acids joined by peptide bonds.
0 1 . 1 Use information in Figure 1 to describe two other structural features of ADH.
[2 marks]
1
2
information
retains the on all its publications. However, registered schools/colleges for are permitted to copy material from this booklet for their own internal
use, with the following important exception: cannot give permission to schools/colleges to photocopy any material that is acknowledged to a third party even for
internal use within the centre.
and its licensors. All rights reserved.
*02*
2
IB/M/Jun26/7402/1
, 3
MARK SCHEME – A-LEVEL BIOLOGY – 7402/1 – JUNE 2026
Do not write
outside the
0 1 . 2 Name the biochemical test used to detect ADH in a solution. box
Describe the positive result. Mark scheme instructions to examiners
[2 marks]
Name of test
1. General
Positive result The mark scheme for each question shows:
• the marks available for each part of the question
• the total marks available for the question
ADH is produced when enzymes hydrolyse the preproprotein, AVP. This hydrolysis • the typical answer or answers which are expected
produces three smaller polypeptides, ADH, Copeptin and NPII. • 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
0 1 . 3 A scientist determined that ADH contains 6.38% of the amino acids in an AVP which a mark or marks may be awarded.
preproprotein. He counted 39 amino acids in the Copeptin protein.
The extra information in the ‘Comments’ column is aligned to the appropriate answer in the
Calculate the number of amino acids in the NPII polypeptide. left-hand 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
Use Figure 1 to help you answer this question. consequential marking needs to be considered in a calculation; or the answer may be on the
[1 mark] 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
Answer
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
0 1 . 4 The hydrolysis of AVP by these enzymes always produces ADH, Copeptin and potential mark.
NPII polypeptides.
2.2 A bold and is used to indicate that both parts of the answer are required to award the
Explain why. mark.
[2 marks]
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’.
7 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.
Turn over for the next question However, responses considered to be neutral (often prefaced by ‘Ignore’ in the
‘Comments’ column of the mark scheme) are not penalised.
Turn over ►
*03*
3
IB/M/Jun26/7402/1
, 4
MARK SCHEME – A-LEVEL BIOLOGY – 7402/1 – JUNE 2026
Do not write
outside the
0 2 . 1 Explain why the genetic code is described as universal and degenerate. box
[2 marks]
3.2 Marking procedure for calculations
Universal 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.
Degenerate
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
Table 1 shows information about the genome of a human sperm cell. 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
Table 1 scheme.
An arithmetic error should be penalised for one mark only unless otherwise amplified in
Log10 (total number of nucleotide pairs) 9.5 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.
Percentage of nucleotide pairs not coding for polypeptide 98.5 3.5 Phonetic spelling
The phonetic spelling of correct scientific terminology should be credited unless there is a
Total number of genes coding for polypeptides 20 000
possible confusion with another technical term.
0 2 . 2 Use information in Table 1 to calculate the mean number of nucleotide pairs coding
3.6 Brackets
for a polypeptide per gene in a sperm cell. (…..) 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.
Show your working.
[3 marks] 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.
Answer
0 2 . 3 What term is used to describe nucleotide pairs within a gene that do not code for an
amino acid sequence?
[1 mark]
*04*
4
IB/M/Jun26/7402/1
Centre number Candidate number
A-level
Surname
Forename(s) BIOLOGY
Candidate signature
I declare this is my own work.
7402/1
Paper 1
A-level
Mark scheme
BIOLOGY June 2026
Paper 1 Version: 1.0 Final
Thursday 4 June 2026 Afternoon Time allowed: 2 hours
Materials For Examiner’s Use
For this paper you must have:
Question Mark
• a ruler with millimetre measurements
• a scientific calculator. 1
2
Instructions
3
• Use black ink or black ball-point pen.
• Fill in the boxes at the top of this page. 4
• Answer all questions. 5
• You must answer the questions in the spaces provided. Do not write 6
outside the box around each page or on blank pages.
7
• If you need extra space for your answer(s), use the lined pages at the end of
this book. Write the question number against your answer(s). 8
• Show all your working. 9
• Do all rough work in this book. Cross through any work you do not want
10
to be marked.
TOTAL
Information
• The marks for the questions are shown in brackets.
• The maximum mark for this paper is 91.
*jun *
IB/M/Jun26/G4005/V13 7402/1
, 2
MARK SCHEME – A-LEVEL BIOLOGY – 7402/1 – JUNE 2026
Do not write
outside the
Answer all questions in the spaces provided. box
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
0 1 Figure 1 shows a molecule of antidiuretic hormone (ADH).
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’
Figure 1
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.
No student should be disadvantaged on the basis of their gender identity and/or how they refer to the
gender identity of others in their exam responses.
A consistent use of ‘they/them’ as a singular and pronouns beyond ‘she/her’ or ‘he/him’ will be credited in
exam responses in line with existing mark scheme criteria.
Further copies of this mark scheme are available from
The ADH molecule is made up of nine amino acids joined by peptide bonds.
0 1 . 1 Use information in Figure 1 to describe two other structural features of ADH.
[2 marks]
1
2
information
retains the on all its publications. However, registered schools/colleges for are permitted to copy material from this booklet for their own internal
use, with the following important exception: cannot give permission to schools/colleges to photocopy any material that is acknowledged to a third party even for
internal use within the centre.
and its licensors. All rights reserved.
*02*
2
IB/M/Jun26/7402/1
, 3
MARK SCHEME – A-LEVEL BIOLOGY – 7402/1 – JUNE 2026
Do not write
outside the
0 1 . 2 Name the biochemical test used to detect ADH in a solution. box
Describe the positive result. Mark scheme instructions to examiners
[2 marks]
Name of test
1. General
Positive result The mark scheme for each question shows:
• the marks available for each part of the question
• the total marks available for the question
ADH is produced when enzymes hydrolyse the preproprotein, AVP. This hydrolysis • the typical answer or answers which are expected
produces three smaller polypeptides, ADH, Copeptin and NPII. • 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
0 1 . 3 A scientist determined that ADH contains 6.38% of the amino acids in an AVP which a mark or marks may be awarded.
preproprotein. He counted 39 amino acids in the Copeptin protein.
The extra information in the ‘Comments’ column is aligned to the appropriate answer in the
Calculate the number of amino acids in the NPII polypeptide. left-hand 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
Use Figure 1 to help you answer this question. consequential marking needs to be considered in a calculation; or the answer may be on the
[1 mark] 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
Answer
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
0 1 . 4 The hydrolysis of AVP by these enzymes always produces ADH, Copeptin and potential mark.
NPII polypeptides.
2.2 A bold and is used to indicate that both parts of the answer are required to award the
Explain why. mark.
[2 marks]
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’.
7 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.
Turn over for the next question However, responses considered to be neutral (often prefaced by ‘Ignore’ in the
‘Comments’ column of the mark scheme) are not penalised.
Turn over ►
*03*
3
IB/M/Jun26/7402/1
, 4
MARK SCHEME – A-LEVEL BIOLOGY – 7402/1 – JUNE 2026
Do not write
outside the
0 2 . 1 Explain why the genetic code is described as universal and degenerate. box
[2 marks]
3.2 Marking procedure for calculations
Universal 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.
Degenerate
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
Table 1 shows information about the genome of a human sperm cell. 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
Table 1 scheme.
An arithmetic error should be penalised for one mark only unless otherwise amplified in
Log10 (total number of nucleotide pairs) 9.5 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.
Percentage of nucleotide pairs not coding for polypeptide 98.5 3.5 Phonetic spelling
The phonetic spelling of correct scientific terminology should be credited unless there is a
Total number of genes coding for polypeptides 20 000
possible confusion with another technical term.
0 2 . 2 Use information in Table 1 to calculate the mean number of nucleotide pairs coding
3.6 Brackets
for a polypeptide per gene in a sperm cell. (…..) 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.
Show your working.
[3 marks] 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.
Answer
0 2 . 3 What term is used to describe nucleotide pairs within a gene that do not code for an
amino acid sequence?
[1 mark]
*04*
4
IB/M/Jun26/7402/1
