AQA A-Level Biology Practice Exam | Complete
QUESTIONs, Mark Scheme Answers & Detailed
Explanations (2026/2027)
QUESTION 1
Which type of bond is formed during the condensation reaction
between two alpha-glucose molecules to form maltose?
• A. 1,4 glycosidic bond
• B. 1,6 glycosidic bond
• C. Ester bond
• D. Peptide bond
Correct Answer: A. 1,4 glycosidic bond
Detailed Rationale: Maltose is a disaccharide formed by a condensation
reaction between two alpha-glucose molecules, creating a 1,4 glycosidic
bond with the elimination of a water molecule.
QUESTION 2
Which statement correctly describes the action of a non-competitive
inhibitor on an enzyme-catalyzed reaction?
• A. It binds to the active site, preventing the substrate from
entering.
• B. It binds to an allosteric site, altering the shape of the active site
so the substrate can no longer bind effectively.
, • C. Increasing the substrate concentration can overcome the effect
of the inhibitor.
• D. It permanently denatures the enzyme by breaking covalent
peptide bonds.
Correct Answer: B. It binds to an allosteric site, altering the shape of
the active site so the substrate can no longer bind effectively.
Detailed Rationale: Non-competitive inhibitors bind away from the
active site at an allosteric site, causing a conformational change in the
tertiary structure of the enzyme's active site. Increasing substrate
concentration cannot overcome this type of inhibition.
QUESTION 3
What is the main advantage of using a transmission electron
microscope (TEM) compared to a light microscope?
• A. It allows live specimens to be observed in real time.
• B. It provides a much higher resolution due to the shorter
wavelength of electrons.
• C. It requires minimal preparation of thin tissue sections.
• D. It produces full-color three-dimensional images of cell surfaces.
Correct Answer: B. It provides a much higher resolution due to the
shorter wavelength of electrons.
Detailed Rationale: Transmission electron microscopes use a beam of
electrons that possess a much shorter wavelength than light photons,
providing a significantly higher resolving power to reveal internal
cellular ultrastructure.
,QUESTION 4
In the human ileum, how are sodium ions and glucose absorbed
together across the epithelial cell membrane?
• A. Simple diffusion through the phospholipid bilayer
• B. Active transport of glucose directly using ATP, followed by
passive diffusion of sodium
• C. Co-transport, where sodium ions move down their
concentration gradient via facilitated diffusion, driving the
movement of glucose against its concentration gradient
• D. Osmosis of water dragging both solutes through aquaporins
Correct Answer: C. Co-transport, where sodium ions move down their
concentration gradient via facilitated diffusion, driving the movement of
glucose against its concentration gradient
Detailed Rationale: Sodium-potassium pumps actively transport
sodium ions out of the epithelial cells into the blood, maintaining a low
intracellular sodium concentration. Sodium ions then enter the cell
from the lumen down their concentration gradient via a co-transporter
protein, simultaneously pulling glucose molecules inside against their
concentration gradient.
QUESTION 5
Which experimental observation from the Meselson-Stahl experiment
disproved the conservative model of DNA replication?
• A. After one generation in the nitrogen-14 medium, all DNA
molecules had an intermediate density.
, • B. After one generation in the nitrogen-14 medium, DNA
separated into two distinct bands: one heavy and one light.
• C. After two generations, only heavy DNA was detected.
• D. DNA replication was shown to require free ribonucleotides
instead of deoxyribonucleotides.
Correct Answer: A. After one generation in the nitrogen-14 medium, all
DNA molecules had an intermediate density.
Detailed Rationale: The conservative model predicted two distinct
bands after one generation (one fully heavy, one fully light). Instead, a
single hybrid intermediate band was observed, supporting the semi-
conservative model.
QUESTION 6
A cell sample is viewed under a microscope. Out of 250 cells counted,
45 are observed undergoing mitosis. What is the mitotic index of this
tissue sample?
• A. 0.05
• B. 0.18
• C. 0.22
• D. 5.56
Correct Answer: B. 0.18
Detailed Rationale: The mitotic index is calculated by dividing the
number of cells in mitosis by the total number of cells counted
(45/250 = 0.18).
QUESTION 7
QUESTIONs, Mark Scheme Answers & Detailed
Explanations (2026/2027)
QUESTION 1
Which type of bond is formed during the condensation reaction
between two alpha-glucose molecules to form maltose?
• A. 1,4 glycosidic bond
• B. 1,6 glycosidic bond
• C. Ester bond
• D. Peptide bond
Correct Answer: A. 1,4 glycosidic bond
Detailed Rationale: Maltose is a disaccharide formed by a condensation
reaction between two alpha-glucose molecules, creating a 1,4 glycosidic
bond with the elimination of a water molecule.
QUESTION 2
Which statement correctly describes the action of a non-competitive
inhibitor on an enzyme-catalyzed reaction?
• A. It binds to the active site, preventing the substrate from
entering.
• B. It binds to an allosteric site, altering the shape of the active site
so the substrate can no longer bind effectively.
, • C. Increasing the substrate concentration can overcome the effect
of the inhibitor.
• D. It permanently denatures the enzyme by breaking covalent
peptide bonds.
Correct Answer: B. It binds to an allosteric site, altering the shape of
the active site so the substrate can no longer bind effectively.
Detailed Rationale: Non-competitive inhibitors bind away from the
active site at an allosteric site, causing a conformational change in the
tertiary structure of the enzyme's active site. Increasing substrate
concentration cannot overcome this type of inhibition.
QUESTION 3
What is the main advantage of using a transmission electron
microscope (TEM) compared to a light microscope?
• A. It allows live specimens to be observed in real time.
• B. It provides a much higher resolution due to the shorter
wavelength of electrons.
• C. It requires minimal preparation of thin tissue sections.
• D. It produces full-color three-dimensional images of cell surfaces.
Correct Answer: B. It provides a much higher resolution due to the
shorter wavelength of electrons.
Detailed Rationale: Transmission electron microscopes use a beam of
electrons that possess a much shorter wavelength than light photons,
providing a significantly higher resolving power to reveal internal
cellular ultrastructure.
,QUESTION 4
In the human ileum, how are sodium ions and glucose absorbed
together across the epithelial cell membrane?
• A. Simple diffusion through the phospholipid bilayer
• B. Active transport of glucose directly using ATP, followed by
passive diffusion of sodium
• C. Co-transport, where sodium ions move down their
concentration gradient via facilitated diffusion, driving the
movement of glucose against its concentration gradient
• D. Osmosis of water dragging both solutes through aquaporins
Correct Answer: C. Co-transport, where sodium ions move down their
concentration gradient via facilitated diffusion, driving the movement of
glucose against its concentration gradient
Detailed Rationale: Sodium-potassium pumps actively transport
sodium ions out of the epithelial cells into the blood, maintaining a low
intracellular sodium concentration. Sodium ions then enter the cell
from the lumen down their concentration gradient via a co-transporter
protein, simultaneously pulling glucose molecules inside against their
concentration gradient.
QUESTION 5
Which experimental observation from the Meselson-Stahl experiment
disproved the conservative model of DNA replication?
• A. After one generation in the nitrogen-14 medium, all DNA
molecules had an intermediate density.
, • B. After one generation in the nitrogen-14 medium, DNA
separated into two distinct bands: one heavy and one light.
• C. After two generations, only heavy DNA was detected.
• D. DNA replication was shown to require free ribonucleotides
instead of deoxyribonucleotides.
Correct Answer: A. After one generation in the nitrogen-14 medium, all
DNA molecules had an intermediate density.
Detailed Rationale: The conservative model predicted two distinct
bands after one generation (one fully heavy, one fully light). Instead, a
single hybrid intermediate band was observed, supporting the semi-
conservative model.
QUESTION 6
A cell sample is viewed under a microscope. Out of 250 cells counted,
45 are observed undergoing mitosis. What is the mitotic index of this
tissue sample?
• A. 0.05
• B. 0.18
• C. 0.22
• D. 5.56
Correct Answer: B. 0.18
Detailed Rationale: The mitotic index is calculated by dividing the
number of cells in mitosis by the total number of cells counted
(45/250 = 0.18).
QUESTION 7
