AQA A-Level Biology Predicted Papers | Most Likely Exam
QUESTIONs with Model Answers (2026/2027)
QUESTION 1
Which of the following best describes the role of a competitive inhibitor
in enzyme-catalyzed reactions?
A. It binds to an allosteric site, causing a permanent conformational
change in the active site.
B. It has a similar shape to the substrate and temporarily binds to the
active site, reducing the reaction rate.
C. It permanently denatures the enzyme by breaking hydrogen bonds
within the tertiary structure.
D. It increases the maximum rate of reaction (𝑉𝑚𝑎𝑥 ) by stabilizing the
enzyme-substrate complex.
Correct Answer: B. It has a similar shape to the substrate and
temporarily binds to the active site, reducing the reaction rate.
Detailed Rationale: Competitive inhibitors have a molecular shape
complementary to the active site, allowing them to temporarily occupy
it and prevent the substrate from binding. However, their effect can be
overcome by increasing the substrate concentration. They do not alter
𝑉𝑚𝑎𝑥 permanently, nor do they bind to allosteric sites (which is
characteristic of non-competitive inhibition).
QUESTION 2
,Which component of the plasma membrane is primarily responsible for
determining its fluidity under varying temperature conditions?
A. Cholesterol
B. Glycoproteins
C. Peripheral proteins
D. Phospholipid polar heads
Correct Answer: A. Cholesterol
Detailed Rationale: Cholesterol molecules fit between phospholipid
molecules in the cell membrane. At high temperatures, they restrict
lateral movement of phospholipids, reducing fluidity; at low
temperatures, they prevent phospholipids from packing too closely
together, maintaining fluidity.
QUESTION 3
During the absorption of glucose in the human ileum, which mechanism
is directly responsible for moving glucose from the lumen into the
epithelial cell?
A. Facilitated diffusion via carrier proteins down a concentration
gradient.
B. Simple diffusion directly through the phospholipid bilayer.
C. Co-transport utilizing a sodium ion concentration gradient
established by active transport.
D. Active transport driven directly by ATP hydrolysis at the glucose
transporter.
,Correct Answer: C. Co-transport utilizing a sodium ion concentration
gradient established by active transport.
Detailed Rationale: Sodium-potassium pumps actively transport Na+
out of the epithelial cell into the blood, creating a low concentration of
Na+ inside the cell. Sodium ions then move down their concentration
gradient from the lumen into the cell via a co-transporter protein,
bringing glucose molecules along against their concentration gradient.
QUESTION 4
In cell fractionation and ultracentrifugation, which of the following
represents the correct order of organelle sedimentation from first to
last (heaviest to lightest)?
A. Nuclei → Mitochondria → Lysosomes → Ribosomes
B. Mitochondria → Nuclei → Ribosomes → Lysosomes
C. Nuclei → Ribosomes → Mitochondria → Endoplasmic reticulum
D. Ribosomes → Lysosomes → Mitochondria → Nuclei
Correct Answer: A. Nuclei → Mitochondria → Lysosomes → Ribosomes
Detailed Rationale: During ultracentrifugation, tissue is homogenized
and spun at increasing speeds. The largest and densest components
sediment first at lower speeds. Nuclei are the largest/heaviest, followed
by mitochondria and chloroplasts, then lysosomes/ER fragments, and
finally small structures like ribosomes at the highest speeds.
QUESTION 5
What structural feature distinguishes a molecule of messenger RNA
(mRNA) from a molecule of DNA?
, A. mRNA contains uracil instead of thymine and is typically single-
stranded.
B. mRNA contains deoxyribose sugar rather than ribose sugar.
C. mRNA is always found as a stable double helix in the cytoplasm.
D. mRNA lacks phosphodiester bonds between adjacent nucleotides.
Correct Answer: A. mRNA contains uracil instead of thymine and is
typically single-stranded.
Detailed Rationale: mRNA contains the sugar ribose (unlike deoxyribose
in DNA), utilizes the pyrimidine base uracil in place of thymine, and is
synthesized as a single-stranded molecule during transcription, whereas
DNA forms a stable double helix.
QUESTION 6
A student calculates the mitotic index of an onion root tip as 0.35. If the
total number of cells observed is 400, how many cells are actively
undergoing mitosis?
A. 114
B. 140
C. 260
D. 350
Correct Answer: B. 140
Detailed Rationale: The mitotic index is calculated using the formula:
Number of cells in mitosis
Mitotic Index = . Rearranging this gives:
Total number of cells
Cells in mitosis = 0.35 × 400 = 140.
QUESTIONs with Model Answers (2026/2027)
QUESTION 1
Which of the following best describes the role of a competitive inhibitor
in enzyme-catalyzed reactions?
A. It binds to an allosteric site, causing a permanent conformational
change in the active site.
B. It has a similar shape to the substrate and temporarily binds to the
active site, reducing the reaction rate.
C. It permanently denatures the enzyme by breaking hydrogen bonds
within the tertiary structure.
D. It increases the maximum rate of reaction (𝑉𝑚𝑎𝑥 ) by stabilizing the
enzyme-substrate complex.
Correct Answer: B. It has a similar shape to the substrate and
temporarily binds to the active site, reducing the reaction rate.
Detailed Rationale: Competitive inhibitors have a molecular shape
complementary to the active site, allowing them to temporarily occupy
it and prevent the substrate from binding. However, their effect can be
overcome by increasing the substrate concentration. They do not alter
𝑉𝑚𝑎𝑥 permanently, nor do they bind to allosteric sites (which is
characteristic of non-competitive inhibition).
QUESTION 2
,Which component of the plasma membrane is primarily responsible for
determining its fluidity under varying temperature conditions?
A. Cholesterol
B. Glycoproteins
C. Peripheral proteins
D. Phospholipid polar heads
Correct Answer: A. Cholesterol
Detailed Rationale: Cholesterol molecules fit between phospholipid
molecules in the cell membrane. At high temperatures, they restrict
lateral movement of phospholipids, reducing fluidity; at low
temperatures, they prevent phospholipids from packing too closely
together, maintaining fluidity.
QUESTION 3
During the absorption of glucose in the human ileum, which mechanism
is directly responsible for moving glucose from the lumen into the
epithelial cell?
A. Facilitated diffusion via carrier proteins down a concentration
gradient.
B. Simple diffusion directly through the phospholipid bilayer.
C. Co-transport utilizing a sodium ion concentration gradient
established by active transport.
D. Active transport driven directly by ATP hydrolysis at the glucose
transporter.
,Correct Answer: C. Co-transport utilizing a sodium ion concentration
gradient established by active transport.
Detailed Rationale: Sodium-potassium pumps actively transport Na+
out of the epithelial cell into the blood, creating a low concentration of
Na+ inside the cell. Sodium ions then move down their concentration
gradient from the lumen into the cell via a co-transporter protein,
bringing glucose molecules along against their concentration gradient.
QUESTION 4
In cell fractionation and ultracentrifugation, which of the following
represents the correct order of organelle sedimentation from first to
last (heaviest to lightest)?
A. Nuclei → Mitochondria → Lysosomes → Ribosomes
B. Mitochondria → Nuclei → Ribosomes → Lysosomes
C. Nuclei → Ribosomes → Mitochondria → Endoplasmic reticulum
D. Ribosomes → Lysosomes → Mitochondria → Nuclei
Correct Answer: A. Nuclei → Mitochondria → Lysosomes → Ribosomes
Detailed Rationale: During ultracentrifugation, tissue is homogenized
and spun at increasing speeds. The largest and densest components
sediment first at lower speeds. Nuclei are the largest/heaviest, followed
by mitochondria and chloroplasts, then lysosomes/ER fragments, and
finally small structures like ribosomes at the highest speeds.
QUESTION 5
What structural feature distinguishes a molecule of messenger RNA
(mRNA) from a molecule of DNA?
, A. mRNA contains uracil instead of thymine and is typically single-
stranded.
B. mRNA contains deoxyribose sugar rather than ribose sugar.
C. mRNA is always found as a stable double helix in the cytoplasm.
D. mRNA lacks phosphodiester bonds between adjacent nucleotides.
Correct Answer: A. mRNA contains uracil instead of thymine and is
typically single-stranded.
Detailed Rationale: mRNA contains the sugar ribose (unlike deoxyribose
in DNA), utilizes the pyrimidine base uracil in place of thymine, and is
synthesized as a single-stranded molecule during transcription, whereas
DNA forms a stable double helix.
QUESTION 6
A student calculates the mitotic index of an onion root tip as 0.35. If the
total number of cells observed is 400, how many cells are actively
undergoing mitosis?
A. 114
B. 140
C. 260
D. 350
Correct Answer: B. 140
Detailed Rationale: The mitotic index is calculated using the formula:
Number of cells in mitosis
Mitotic Index = . Rearranging this gives:
Total number of cells
Cells in mitosis = 0.35 × 400 = 140.
