AQA A-level BIOLOGY (7402/1)
Paper 1 Mark scheme 2026
SPECIMEN V1
Course
AQA A-level BIOLOGY Paper 1 Mark scheme 2021 SPECIMEN V1
1. Biological Molecules
Question:
A student investigates a food sample using Benedict's reagent. The solution changes from blue
to orange after heating.
What does this result indicate?
Answer:
A reducing sugar is present.
Mark scheme:
1 mark — identifies a reducing sugar.
1 mark — states that Benedict's reagent changes colour when reducing sugar is present
after heating.
Rationale:
Reducing sugars such as glucose and maltose reduce copper(II) ions in Benedict's reagent. The
colour can progress from blue through green/yellow/orange to brick-red depending on the
amount present.
2. Protein Structure
Question:
Explain how a change in the amino acid sequence of a protein can alter its function.
Answer:
A change in the amino acid sequence can alter the interactions between amino acid side chains.
This changes the protein's tertiary structure and therefore its three-dimensional shape. If the
shape of an active site changes, the substrate may no longer bind effectively.
Mark scheme:
1 mark — different amino acid sequence.
, 1 mark — changes interactions between R groups.
1 mark — changes tertiary structure/shape.
1 mark — changes active-site shape or function.
3. Enzymes
Question:
Explain why increasing temperature initially increases the rate of an enzyme-controlled
reaction.
Answer:
Increasing temperature increases the kinetic energy of enzyme and substrate molecules. They
move faster and collide more frequently, increasing the number of successful enzyme-substrate
collisions.
Mark scheme:
1 mark — increased kinetic energy.
1 mark — increased frequency of collisions.
1 mark — increased successful enzyme-substrate complex formation.
4. Enzyme Denaturation
Question:
Why does a very high temperature reduce enzyme activity?
Answer:
High temperature disrupts bonds maintaining the enzyme's tertiary structure. The active site
changes shape, so the substrate is less complementary to it and fewer enzyme-substrate
complexes form.
Mark scheme:
1 mark — bonds/interactions disrupted.
1 mark — tertiary structure changes.
1 mark — active site changes shape.
1 mark — fewer successful enzyme-substrate complexes.
5. Water
, Question:
Give two properties of water that make it important in living organisms.
Answer:
Water is a good solvent.
Water has a high specific heat capacity.
Rationale:
Its solvent properties allow substances to be transported and reactions to occur in solution. Its
high specific heat capacity helps organisms resist rapid temperature changes.
6. DNA Structure
Question:
Describe the structure of a DNA molecule.
Answer:
DNA consists of two polynucleotide strands arranged as a double helix. The strands are held
together by hydrogen bonds between complementary bases. Adenine pairs with thymine and
cytosine pairs with guanine.
Mark scheme:
1 mark — two polynucleotide strands.
1 mark — double helix.
1 mark — hydrogen bonds between bases.
1 mark — complementary base pairing.
7. DNA Replication
Question:
Explain why DNA replication is described as semi-conservative.
Answer:
The two DNA strands separate and each original strand acts as a template for synthesis of a new
complementary strand. Each resulting DNA molecule therefore contains one original strand and
one newly synthesised strand.
Mark scheme:
1 mark — strands separate.
1 mark — each original strand acts as a template.
Paper 1 Mark scheme 2026
SPECIMEN V1
Course
AQA A-level BIOLOGY Paper 1 Mark scheme 2021 SPECIMEN V1
1. Biological Molecules
Question:
A student investigates a food sample using Benedict's reagent. The solution changes from blue
to orange after heating.
What does this result indicate?
Answer:
A reducing sugar is present.
Mark scheme:
1 mark — identifies a reducing sugar.
1 mark — states that Benedict's reagent changes colour when reducing sugar is present
after heating.
Rationale:
Reducing sugars such as glucose and maltose reduce copper(II) ions in Benedict's reagent. The
colour can progress from blue through green/yellow/orange to brick-red depending on the
amount present.
2. Protein Structure
Question:
Explain how a change in the amino acid sequence of a protein can alter its function.
Answer:
A change in the amino acid sequence can alter the interactions between amino acid side chains.
This changes the protein's tertiary structure and therefore its three-dimensional shape. If the
shape of an active site changes, the substrate may no longer bind effectively.
Mark scheme:
1 mark — different amino acid sequence.
, 1 mark — changes interactions between R groups.
1 mark — changes tertiary structure/shape.
1 mark — changes active-site shape or function.
3. Enzymes
Question:
Explain why increasing temperature initially increases the rate of an enzyme-controlled
reaction.
Answer:
Increasing temperature increases the kinetic energy of enzyme and substrate molecules. They
move faster and collide more frequently, increasing the number of successful enzyme-substrate
collisions.
Mark scheme:
1 mark — increased kinetic energy.
1 mark — increased frequency of collisions.
1 mark — increased successful enzyme-substrate complex formation.
4. Enzyme Denaturation
Question:
Why does a very high temperature reduce enzyme activity?
Answer:
High temperature disrupts bonds maintaining the enzyme's tertiary structure. The active site
changes shape, so the substrate is less complementary to it and fewer enzyme-substrate
complexes form.
Mark scheme:
1 mark — bonds/interactions disrupted.
1 mark — tertiary structure changes.
1 mark — active site changes shape.
1 mark — fewer successful enzyme-substrate complexes.
5. Water
, Question:
Give two properties of water that make it important in living organisms.
Answer:
Water is a good solvent.
Water has a high specific heat capacity.
Rationale:
Its solvent properties allow substances to be transported and reactions to occur in solution. Its
high specific heat capacity helps organisms resist rapid temperature changes.
6. DNA Structure
Question:
Describe the structure of a DNA molecule.
Answer:
DNA consists of two polynucleotide strands arranged as a double helix. The strands are held
together by hydrogen bonds between complementary bases. Adenine pairs with thymine and
cytosine pairs with guanine.
Mark scheme:
1 mark — two polynucleotide strands.
1 mark — double helix.
1 mark — hydrogen bonds between bases.
1 mark — complementary base pairing.
7. DNA Replication
Question:
Explain why DNA replication is described as semi-conservative.
Answer:
The two DNA strands separate and each original strand acts as a template for synthesis of a new
complementary strand. Each resulting DNA molecule therefore contains one original strand and
one newly synthesised strand.
Mark scheme:
1 mark — strands separate.
1 mark — each original strand acts as a template.
