AQA A-Level Biology Practice Exam | Complete
QUESTIONs, Model Answers & Mark Scheme
(2026/2027
QUESTION 1
Which of the following describes the chemical bond formed between
two monosaccharides during a condensation reaction?
• A. Peptide bond
• B. Glycosidic bond
• C. Ester bond
• D. Phosphodiester bond
Correct Answer: B. Glycosidic bond
Detailed Rationale: A glycosidic bond forms between two
monosaccharides when a molecule of water is removed during a
condensation reaction. Peptide bonds are found in proteins, ester
bonds in lipids, and phosphodiester bonds in nucleic acids.
QUESTION 2
Which organelle is primarily responsible for the modification and
packaging of proteins into vesicles for secretion?
• A. Mitochondrion
• B. Rough endoplasmic reticulum
• C. Golgi apparatus
, • D. Nucleolus
Correct Answer: C. Golgi apparatus
Detailed Rationale: The Golgi apparatus receives proteins from the
rough endoplasmic reticulum, modifies them (e.g., by adding
carbohydrate chains to form glycoproteins), and packages them into
vesicles for transport. The rough endoplasmic reticulum synthesizes
proteins, while mitochondria produce ATP.
QUESTION 3
Which of the following processes requires ATP to transport substances
across a cell membrane against a concentration gradient?
• A. Simple diffusion
• B. Facilitated diffusion
• C. Osmosis
• D. Active transport
Correct Answer: D. Active transport
Detailed Rationale: Active transport moves substances against a
concentration gradient using carrier proteins and energy derived from
ATP hydrolysis. Simple diffusion, facilitated diffusion, and osmosis are
passive processes that do not require metabolic energy.
QUESTION 4
During which phase of the cell cycle does DNA replication occur?
• A. G1 phase
• B. S phase
, • C. G2 phase
• D. Mitosis (M phase)
Correct Answer: B. S phase
Detailed Rationale: DNA replication takes place during the synthesis (S)
phase of interphase, ensuring that each daughter cell receives an
identical copy of the genetic material. G1 and G2 are growth and
preparation phases, while mitosis involves nuclear division.
QUESTION 5
What is the role of RNA polymerase during transcription?
• A. To unwind the DNA double helix and join free RNA nucleotides
to form a pre-mRNA strand
• B. To translate mRNA codons into a specific sequence of amino
acids
• C. To catalyze the formation of peptide bonds between adjacent
amino acids at the ribosome
• D. To replicate the entire DNA molecule prior to cell division
Correct Answer: A. To unwind the DNA double helix and join free RNA
nucleotides to form a pre-mRNA strand
Detailed Rationale: RNA polymerase binds to the promoter region,
unwinds the DNA strands, and catalyzes the condensation reactions
joining complementary RNA nucleotides to synthesize pre-mRNA.
Translation is carried out by ribosomes and tRNA.
QUESTION 6
, Which property of water makes it an effective buffer against sudden
temperature changes?
• A. High latent heat of vaporization
• B. High specific heat capacity
• C. Cohesive properties
• D. Ability to act as a metabolite
Correct Answer: B. High specific heat capacity
Detailed Rationale: Water has a high specific heat capacity because a
lot of energy is required to break hydrogen bonds between water
molecules. This buffers aquatic and cellular environments against rapid
temperature fluctuations.
QUESTION 7
How does a competitive inhibitor affect enzyme action?
• A. It binds to an allosteric site, altering the shape of the active site.
• B. It permanently destroys the tertiary structure of the enzyme.
• C. It has a similar shape to the substrate and competes for binding
at the active site.
• D. It increases the activation energy required for the reaction to
proceed.
Correct Answer: C. It has a similar shape to the substrate and competes
for binding at the active site.
Detailed Rationale: Competitive inhibitors have a molecular shape
complementary to the active site, allowing them to occupy it and block
QUESTIONs, Model Answers & Mark Scheme
(2026/2027
QUESTION 1
Which of the following describes the chemical bond formed between
two monosaccharides during a condensation reaction?
• A. Peptide bond
• B. Glycosidic bond
• C. Ester bond
• D. Phosphodiester bond
Correct Answer: B. Glycosidic bond
Detailed Rationale: A glycosidic bond forms between two
monosaccharides when a molecule of water is removed during a
condensation reaction. Peptide bonds are found in proteins, ester
bonds in lipids, and phosphodiester bonds in nucleic acids.
QUESTION 2
Which organelle is primarily responsible for the modification and
packaging of proteins into vesicles for secretion?
• A. Mitochondrion
• B. Rough endoplasmic reticulum
• C. Golgi apparatus
, • D. Nucleolus
Correct Answer: C. Golgi apparatus
Detailed Rationale: The Golgi apparatus receives proteins from the
rough endoplasmic reticulum, modifies them (e.g., by adding
carbohydrate chains to form glycoproteins), and packages them into
vesicles for transport. The rough endoplasmic reticulum synthesizes
proteins, while mitochondria produce ATP.
QUESTION 3
Which of the following processes requires ATP to transport substances
across a cell membrane against a concentration gradient?
• A. Simple diffusion
• B. Facilitated diffusion
• C. Osmosis
• D. Active transport
Correct Answer: D. Active transport
Detailed Rationale: Active transport moves substances against a
concentration gradient using carrier proteins and energy derived from
ATP hydrolysis. Simple diffusion, facilitated diffusion, and osmosis are
passive processes that do not require metabolic energy.
QUESTION 4
During which phase of the cell cycle does DNA replication occur?
• A. G1 phase
• B. S phase
, • C. G2 phase
• D. Mitosis (M phase)
Correct Answer: B. S phase
Detailed Rationale: DNA replication takes place during the synthesis (S)
phase of interphase, ensuring that each daughter cell receives an
identical copy of the genetic material. G1 and G2 are growth and
preparation phases, while mitosis involves nuclear division.
QUESTION 5
What is the role of RNA polymerase during transcription?
• A. To unwind the DNA double helix and join free RNA nucleotides
to form a pre-mRNA strand
• B. To translate mRNA codons into a specific sequence of amino
acids
• C. To catalyze the formation of peptide bonds between adjacent
amino acids at the ribosome
• D. To replicate the entire DNA molecule prior to cell division
Correct Answer: A. To unwind the DNA double helix and join free RNA
nucleotides to form a pre-mRNA strand
Detailed Rationale: RNA polymerase binds to the promoter region,
unwinds the DNA strands, and catalyzes the condensation reactions
joining complementary RNA nucleotides to synthesize pre-mRNA.
Translation is carried out by ribosomes and tRNA.
QUESTION 6
, Which property of water makes it an effective buffer against sudden
temperature changes?
• A. High latent heat of vaporization
• B. High specific heat capacity
• C. Cohesive properties
• D. Ability to act as a metabolite
Correct Answer: B. High specific heat capacity
Detailed Rationale: Water has a high specific heat capacity because a
lot of energy is required to break hydrogen bonds between water
molecules. This buffers aquatic and cellular environments against rapid
temperature fluctuations.
QUESTION 7
How does a competitive inhibitor affect enzyme action?
• A. It binds to an allosteric site, altering the shape of the active site.
• B. It permanently destroys the tertiary structure of the enzyme.
• C. It has a similar shape to the substrate and competes for binding
at the active site.
• D. It increases the activation energy required for the reaction to
proceed.
Correct Answer: C. It has a similar shape to the substrate and competes
for binding at the active site.
Detailed Rationale: Competitive inhibitors have a molecular shape
complementary to the active site, allowing them to occupy it and block
