Please write clearly in block capitals.
Centre number Candidate number
Surname
Forename(s)
Candidate signature
I declare this is my own work.
A-level
BIOLOGY
Paper 3
Wednesday 18 June 2025 Morning Time allowed: 2 hours
Materials
For Examiner’s Use
For this paper you must have:
• a ruler with millimetre measurements Question Mark
• a scientific calculator. 1
2
Instructions
• Use black ink or black ball-point pen. 3
• 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
outside the box around each page or on blank pages. 6
• If you need extra space for your answer(s), use the lined pages at the end of 7
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
to be marked. 10
TOTAL
Information
• The marks for the questions are shown in brackets.
• The maximum mark for this paper is 91.
*jun237402201*
IB/M/Jun23/E13 7402/3
, 2
Do not write
outside the
Answer all questions in the spaces provided. box
0 1 . 1 Describe how an action potential in a presynaptic neuron leads to the transmission
of a nerve impulse across a cholinergic synapse.
In your answer, you should refer to:
[4 marks]
The role of calcium ions
The release of neurotransmitter
Events at the postsynaptic membrane
How the postsynaptic neurone is activated
0 1 . 2 A student investigated the effect of a drug that blocks calcium ion channels in the
presynaptic membrane.
Explain how this drug would affect communication between neurones at a synapse.
[2 marks]
6
*02*
IB/M/Jun23/7402/2
, 3
Do not write
outside the
0 2 . 1 box
Scientists have developed a herbicide that blocks the transfer of electrons
between electron carriers in the light-dependent reaction of photosynthesis.
Describe and explain the effect this herbicide would have on the light-dependent
reaction and the plant’s ability to synthesise sugars.
[5 marks]
In cyclic electron flow, only photosystem I is involved, and electrons are recycled
via ferredoxin and plastoquinone back to the cytochrome complex, generating ATP
without producing NADPH or oxygen. Additionally, the regulation of the light-
dependent reaction is more dynamic than traditionally taught — for instance, state
transitions allow chloroplasts to redistribute excitation energy between
photosystems in response to changing light conditions, optimizing efficiency.
0 2 . 2 Suggest two ways a plant could increase the rate of the light-dependent reaction
when light intensity is high.
[2 marks]
1
2
Question 2 continues on the next page
Turn over ►
*03*
IB/M/Jun23/7402/2
, 4
Do not write
outside the
box
0 2 . 3 Ziconotide was injected at 3 ng kg–1 h–1 for 8 days into each patient.
1 ng = 1 × 10–9 g
Calculate the total mass in grams of ziconotide injected after 8 days into a patient with
a body mass of 82 kg
Show your working.
[2 marks]
Answer g
0 2 . 4 When the patients recorded the intensity of pain, suggest two reasons why it was
important to use a statistically valid scale.
[2 marks]
1
2
11
*04*
IB/M/Jun23/7402/2
Centre number Candidate number
Surname
Forename(s)
Candidate signature
I declare this is my own work.
A-level
BIOLOGY
Paper 3
Wednesday 18 June 2025 Morning Time allowed: 2 hours
Materials
For Examiner’s Use
For this paper you must have:
• a ruler with millimetre measurements Question Mark
• a scientific calculator. 1
2
Instructions
• Use black ink or black ball-point pen. 3
• 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
outside the box around each page or on blank pages. 6
• If you need extra space for your answer(s), use the lined pages at the end of 7
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
to be marked. 10
TOTAL
Information
• The marks for the questions are shown in brackets.
• The maximum mark for this paper is 91.
*jun237402201*
IB/M/Jun23/E13 7402/3
, 2
Do not write
outside the
Answer all questions in the spaces provided. box
0 1 . 1 Describe how an action potential in a presynaptic neuron leads to the transmission
of a nerve impulse across a cholinergic synapse.
In your answer, you should refer to:
[4 marks]
The role of calcium ions
The release of neurotransmitter
Events at the postsynaptic membrane
How the postsynaptic neurone is activated
0 1 . 2 A student investigated the effect of a drug that blocks calcium ion channels in the
presynaptic membrane.
Explain how this drug would affect communication between neurones at a synapse.
[2 marks]
6
*02*
IB/M/Jun23/7402/2
, 3
Do not write
outside the
0 2 . 1 box
Scientists have developed a herbicide that blocks the transfer of electrons
between electron carriers in the light-dependent reaction of photosynthesis.
Describe and explain the effect this herbicide would have on the light-dependent
reaction and the plant’s ability to synthesise sugars.
[5 marks]
In cyclic electron flow, only photosystem I is involved, and electrons are recycled
via ferredoxin and plastoquinone back to the cytochrome complex, generating ATP
without producing NADPH or oxygen. Additionally, the regulation of the light-
dependent reaction is more dynamic than traditionally taught — for instance, state
transitions allow chloroplasts to redistribute excitation energy between
photosystems in response to changing light conditions, optimizing efficiency.
0 2 . 2 Suggest two ways a plant could increase the rate of the light-dependent reaction
when light intensity is high.
[2 marks]
1
2
Question 2 continues on the next page
Turn over ►
*03*
IB/M/Jun23/7402/2
, 4
Do not write
outside the
box
0 2 . 3 Ziconotide was injected at 3 ng kg–1 h–1 for 8 days into each patient.
1 ng = 1 × 10–9 g
Calculate the total mass in grams of ziconotide injected after 8 days into a patient with
a body mass of 82 kg
Show your working.
[2 marks]
Answer g
0 2 . 4 When the patients recorded the intensity of pain, suggest two reasons why it was
important to use a statistically valid scale.
[2 marks]
1
2
11
*04*
IB/M/Jun23/7402/2
