AQA BIOLOGY PAPER 3 STUDY GUIDE 2026 QUESTIONS WITH COMPLETE SOLUTIONS

AQA BIOLOGY PAPER 3 STUDY GUIDE 2026
QUESTIONS WITH COMPLETE SOLUTIONS

◉ 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;