AQA A LEVEL BIOLOGY PAPER 3
JUNE 18 2025 COMPLETE EXAM
PAPER AND MARK SCHEME 2026
VERIFIED ANSWERS AND
SOLUTIONS GRADED A+
◉ Use your knowledge of how myosin and actin interact to suggest the
myosin molecule moves the mitochondrion towards the presynaptic
membrane. Do not include the roles of calcium ions and tropomyosin in
your answer. Answer: 1. Myosin head attaches to actin and
bends/performs powerstroke
2. This pulls mitochondria past/along the actin
3. Other/next myosin attaches to actin and bends/performs powerstroke
◉ This movement of mitochondria happens when nerve impulses arrive
at the synapse. Suggest and explain one advantage of the movement of
mitochondria towards the presynaptic membrane when nerve impulses
arrive at the synapse. Answer: 1. (Mitochondria) supply (additional)
ATP / energy;
2. To move vesicles / for active transport of ions / for myosin to move
past actin
OR
Re-synthesis / reabsorption of neurotransmitter / named
neurotransmitter;
,◉ Give two examples of biological molecules containing nitrogen that
would be removed when a crop is harvested Answer: amino
acid/protein/
polypeptide/peptide;
2. nucleic
acid/nucleotide/base;
3. DNA;
4. RNA;
5. ATP/ADP;
6. NAD/NADP (reduced or
not);
7. Cyclic AMP/cAMP;
8. Chlorophyll;
◉ Outline a method the ecologists could have used to determine the
plant species richness at one site. Answer: 1. A method of selecting
sampling sites at random;
2. Use of quadrat;
3. Identify (plant) species (at site / in each quadrat)
OR
Count number of (different plant) species (at site / in each quadrat);
◉ Name two enzymes involved in the semi-conservative replication of
DNA Answer: 1. DNA helicase
,2. DNA polymerase
◉ Sometimes, damage occurs during DNA replication. One enzyme
involved in repairing damage to DNA is called ATR.
ATR works as follows.
• ATR phosphorylates other enzymes involved in repairing DNA.
• ATR also phosphorylates substrates required to repair DNA.
When ATR phosphorylates other enzymes, these enzymes become able
to bind to their substrates.
Use your knowledge of enzyme structure to suggest why. Answer: 1.
Changes tertiary structure of the enzyme;
2. (Enzyme) active site formed / able to be formed / active site becomes
complementary;
◉ The enzyme-catalysed reactions activated by ATR only occur if the
substrates have been phosphorylated.
Use your knowledge of energy changes in enzyme-catalysed reactions to
suggest why. Answer: (Phosphorylation / phosphate) makes substrates
more reactive / raises their energy level(s) / lowers activation energy for
the reaction;
◉ Sometimes, a mutagenic agent causes DNA to break. A different
enzyme called ATM binds to the broken DNA. This leads to the
activation of a protein coded for by a tumour suppressor gene. The effect
of ATM binding is to stop cell division until DNA is repaired.
A mutation could result in a person having non-functional forms of the
gene that produces ATM.
, What can you predict about the possible effects of having a non-
functional form of ATM? Answer: 1. ATM will not bind to (broken)
DNA;
2. DNA not repaired/ cell still has broken DNA;
3. Cell division continues/tumour forms;
4. Tumour suppressor (gene) not effective/ not
activated;
5. May have no effect in diploid/heterozygous
(organism);
6. (Which) still has a functional ATM/ATM gene;
◉ The student wanted to determine the rate of water loss per mm2 of
surface area of the leaves of the shoot in Figure 5. Outline a method she
could have used to find this rate. You should assume that all water loss
from the shoot is from the leaves. Answer: 1. Method for measuring
area;
e.g. draw round (each) leaf on graph paper and count squares;
2. Of both sides of (each) leaf;
3. Divide rate (of water loss / uptake from potometer) by (total) surface
area (of leaves);
◉ The rate of water movement through a shoot in a potometer maybe
not be the same as the rate of water movement through the shoot of a
whole plant. Suggest one reason why. Answer: Plant has roots
Xylem cells very narrow
JUNE 18 2025 COMPLETE EXAM
PAPER AND MARK SCHEME 2026
VERIFIED ANSWERS AND
SOLUTIONS GRADED A+
◉ Use your knowledge of how myosin and actin interact to suggest the
myosin molecule moves the mitochondrion towards the presynaptic
membrane. Do not include the roles of calcium ions and tropomyosin in
your answer. Answer: 1. Myosin head attaches to actin and
bends/performs powerstroke
2. This pulls mitochondria past/along the actin
3. Other/next myosin attaches to actin and bends/performs powerstroke
◉ This movement of mitochondria happens when nerve impulses arrive
at the synapse. Suggest and explain one advantage of the movement of
mitochondria towards the presynaptic membrane when nerve impulses
arrive at the synapse. Answer: 1. (Mitochondria) supply (additional)
ATP / energy;
2. To move vesicles / for active transport of ions / for myosin to move
past actin
OR
Re-synthesis / reabsorption of neurotransmitter / named
neurotransmitter;
,◉ Give two examples of biological molecules containing nitrogen that
would be removed when a crop is harvested Answer: amino
acid/protein/
polypeptide/peptide;
2. nucleic
acid/nucleotide/base;
3. DNA;
4. RNA;
5. ATP/ADP;
6. NAD/NADP (reduced or
not);
7. Cyclic AMP/cAMP;
8. Chlorophyll;
◉ Outline a method the ecologists could have used to determine the
plant species richness at one site. Answer: 1. A method of selecting
sampling sites at random;
2. Use of quadrat;
3. Identify (plant) species (at site / in each quadrat)
OR
Count number of (different plant) species (at site / in each quadrat);
◉ Name two enzymes involved in the semi-conservative replication of
DNA Answer: 1. DNA helicase
,2. DNA polymerase
◉ Sometimes, damage occurs during DNA replication. One enzyme
involved in repairing damage to DNA is called ATR.
ATR works as follows.
• ATR phosphorylates other enzymes involved in repairing DNA.
• ATR also phosphorylates substrates required to repair DNA.
When ATR phosphorylates other enzymes, these enzymes become able
to bind to their substrates.
Use your knowledge of enzyme structure to suggest why. Answer: 1.
Changes tertiary structure of the enzyme;
2. (Enzyme) active site formed / able to be formed / active site becomes
complementary;
◉ The enzyme-catalysed reactions activated by ATR only occur if the
substrates have been phosphorylated.
Use your knowledge of energy changes in enzyme-catalysed reactions to
suggest why. Answer: (Phosphorylation / phosphate) makes substrates
more reactive / raises their energy level(s) / lowers activation energy for
the reaction;
◉ Sometimes, a mutagenic agent causes DNA to break. A different
enzyme called ATM binds to the broken DNA. This leads to the
activation of a protein coded for by a tumour suppressor gene. The effect
of ATM binding is to stop cell division until DNA is repaired.
A mutation could result in a person having non-functional forms of the
gene that produces ATM.
, What can you predict about the possible effects of having a non-
functional form of ATM? Answer: 1. ATM will not bind to (broken)
DNA;
2. DNA not repaired/ cell still has broken DNA;
3. Cell division continues/tumour forms;
4. Tumour suppressor (gene) not effective/ not
activated;
5. May have no effect in diploid/heterozygous
(organism);
6. (Which) still has a functional ATM/ATM gene;
◉ The student wanted to determine the rate of water loss per mm2 of
surface area of the leaves of the shoot in Figure 5. Outline a method she
could have used to find this rate. You should assume that all water loss
from the shoot is from the leaves. Answer: 1. Method for measuring
area;
e.g. draw round (each) leaf on graph paper and count squares;
2. Of both sides of (each) leaf;
3. Divide rate (of water loss / uptake from potometer) by (total) surface
area (of leaves);
◉ The rate of water movement through a shoot in a potometer maybe
not be the same as the rate of water movement through the shoot of a
whole plant. Suggest one reason why. Answer: Plant has roots
Xylem cells very narrow
