Biology A Past Paper 2 Exam Pack 2026 |
Verified Question Paper & Mark Scheme | A-
Level & AS-Level | Edexcel, AQA, OCR | A+
Graded
Section 1: Energy Transfers – Photosynthesis (Questions 1-40)
1. Which of the following correctly describes the immediate fate of electrons released
during photolysis of water in the light-dependent reactions of photosynthesis?
A) They reduce NADP directly to form reduced NADP
B) They replace electrons lost by photosystem II, which then excite photosystem I electrons
C) They combine with hydrogen ions to form hydrogen gas
D) They are used to phosphorylate ADP to ATP directly
Correct Answer: B
Rationale: Photolysis of water replaces electrons lost from photosystem II (P680). These
replacement electrons are passed along the electron transport chain, providing energy for
proton pumping and eventually replacing electrons lost by photosystem I (P700). Option A is
incorrect because electrons from photolysis do not directly reduce NADP—they must pass
through the electron transport chain first. Option C is incorrect as hydrogen gas is not
produced in photosynthesis. Option D is incorrect because electrons do not directly
phosphorylate ADP; chemiosmosis drives ATP synthesis .
, 2. During the Calvin cycle, for every 3 molecules of CO₂ fixed, how many molecules
of triose phosphate (TP) are produced, and how many leave the cycle to produce
hexose sugars?
A) 6 TP produced; 6 TP leave
B) 6 TP produced; 1 TP leaves
C) 3 TP produced; 3 TP leave
D) 3 TP produced; 1 TP leaves
Correct Answer: B
Rationale: For every 3 CO₂ molecules fixed, 6 molecules of TP are produced (via 6 turns of
the cycle involving 6 RuBP). However, only 1 TP molecule leaves the cycle to form hexose
sugars (requiring 2 TP to form 1 hexose). The remaining 5 TP molecules are used to
regenerate 3 RuBP molecules to maintain the cycle. Option A is incorrect because not all
TP leaves—regeneration is essential. Options C and D underestimate the total TP
production .
3. In oxidative phosphorylation, what is the role of oxygen?
A) To phosphorylate ADP directly to form ATP
B) To act as the final electron acceptor, forming water with protons
C) To pump protons across the inner mitochondrial membrane
D) To oxidize NADH and FADH₂ directly
Correct Answer: B
Rationale: Oxygen acts as the final electron acceptor at the end of the electron transport
chain, combining with electrons and protons (H⁺) to form water. This maintains the proton
gradient by removing electrons from the chain. Option A is incorrect—oxygen does not
phosphorylate ADP. Option C is incorrect—proton pumping is driven by electron transport,
not oxygen directly. Option D is incorrect—NADH and FADH₂ are oxidized by
dehydrogenase enzymes at complex I and II, not by oxygen .
, 4. A respirometer experiment shows an organism consumes 0.6 dm³ of O₂ and
produces 0.4 dm³ of CO₂ over the same time period. What is the respiratory quotient
(RQ)?
A) 0.67
B) 1.0
C) 1.5
D) 0.4
Correct Answer: A
Rationale: RQ = Volume of CO₂ produced ÷ Volume of O₂ consumed = 0.4 ÷ 0.6 = 0.67.
An RQ of 0.7 indicates lipid respiration; 1.0 indicates carbohydrate; >1.0 indicates anaerobic
respiration or conversion of carbohydrate to fat. Option B would indicate pure carbohydrate
metabolism. Option C is mathematically incorrect. Option D inverts the calculation .
5. Which statement correctly describes the relationship between gross primary
production (GPP) and net primary production (NPP)?
A) NPP = GPP + plant respiration losses
B) NPP = GPP − plant respiration losses
C) GPP = NPP − plant respiration losses
D) GPP = NPP + plant respiration losses
Correct Answer: B
Rationale: Net primary production (NPP) is the energy available to the next trophic level
after the plant has used some energy for respiration. Therefore, NPP = GPP − plant
respiration losses. Option A adds respiration, which is incorrect. Options C and D incorrectly
rearrange the relationship .
6. In the light-dependent reaction, what is the primary role of the electron transport
chain?
A) To produce glucose directly
, B) To generate a proton gradient for ATP synthesis
C) To fix carbon dioxide
D) To produce oxygen
Correct Answer: B
Rationale: The electron transport chain in the thylakoid membrane pumps protons into the
thylakoid space, creating a proton gradient. This gradient drives ATP synthesis via
chemiosmosis. Option A is incorrect—glucose is produced in the light-independent reaction.
Option C is incorrect—carbon fixation occurs in the Calvin cycle. Option D is incorrect—
oxygen is produced by photolysis of water, not the electron transport chain .
7. A scientist measures photosynthesis rate at different CO₂ concentrations at
constant light intensity and temperature. Rate plateaus above 0.4% CO₂. Explain why.
A) CO₂ becomes toxic at high concentrations
B) Light intensity becomes the rate-limiting factor above 0.4% CO₂
C) The plant stops respiring
D) Chlorophyll is destroyed at high CO₂ concentrations
Correct Answer: B
Rationale: From 0% to 0.4% CO₂, rate rises because CO₂ is the rate-limiting factor—more
CO₂ means more substrate for the Calvin cycle. At 0.4% CO₂, CO₂ stops being limiting.
Above 0.4%, a different factor becomes limiting—likely light intensity (since temperature is
constant). Adding more CO₂ doesn't increase rate because the Calvin cycle is now starved
of ATP and NADPH from the light-dependent reactions .
8. In the light-independent reaction, what is the role of ATP and NADPH?
A) They are used to fix CO₂ to RuBP
B) They provide energy and reducing power to convert GP to TP
C) They are produced during the Calvin cycle
D) They are used to regenerate RuBP
Verified Question Paper & Mark Scheme | A-
Level & AS-Level | Edexcel, AQA, OCR | A+
Graded
Section 1: Energy Transfers – Photosynthesis (Questions 1-40)
1. Which of the following correctly describes the immediate fate of electrons released
during photolysis of water in the light-dependent reactions of photosynthesis?
A) They reduce NADP directly to form reduced NADP
B) They replace electrons lost by photosystem II, which then excite photosystem I electrons
C) They combine with hydrogen ions to form hydrogen gas
D) They are used to phosphorylate ADP to ATP directly
Correct Answer: B
Rationale: Photolysis of water replaces electrons lost from photosystem II (P680). These
replacement electrons are passed along the electron transport chain, providing energy for
proton pumping and eventually replacing electrons lost by photosystem I (P700). Option A is
incorrect because electrons from photolysis do not directly reduce NADP—they must pass
through the electron transport chain first. Option C is incorrect as hydrogen gas is not
produced in photosynthesis. Option D is incorrect because electrons do not directly
phosphorylate ADP; chemiosmosis drives ATP synthesis .
, 2. During the Calvin cycle, for every 3 molecules of CO₂ fixed, how many molecules
of triose phosphate (TP) are produced, and how many leave the cycle to produce
hexose sugars?
A) 6 TP produced; 6 TP leave
B) 6 TP produced; 1 TP leaves
C) 3 TP produced; 3 TP leave
D) 3 TP produced; 1 TP leaves
Correct Answer: B
Rationale: For every 3 CO₂ molecules fixed, 6 molecules of TP are produced (via 6 turns of
the cycle involving 6 RuBP). However, only 1 TP molecule leaves the cycle to form hexose
sugars (requiring 2 TP to form 1 hexose). The remaining 5 TP molecules are used to
regenerate 3 RuBP molecules to maintain the cycle. Option A is incorrect because not all
TP leaves—regeneration is essential. Options C and D underestimate the total TP
production .
3. In oxidative phosphorylation, what is the role of oxygen?
A) To phosphorylate ADP directly to form ATP
B) To act as the final electron acceptor, forming water with protons
C) To pump protons across the inner mitochondrial membrane
D) To oxidize NADH and FADH₂ directly
Correct Answer: B
Rationale: Oxygen acts as the final electron acceptor at the end of the electron transport
chain, combining with electrons and protons (H⁺) to form water. This maintains the proton
gradient by removing electrons from the chain. Option A is incorrect—oxygen does not
phosphorylate ADP. Option C is incorrect—proton pumping is driven by electron transport,
not oxygen directly. Option D is incorrect—NADH and FADH₂ are oxidized by
dehydrogenase enzymes at complex I and II, not by oxygen .
, 4. A respirometer experiment shows an organism consumes 0.6 dm³ of O₂ and
produces 0.4 dm³ of CO₂ over the same time period. What is the respiratory quotient
(RQ)?
A) 0.67
B) 1.0
C) 1.5
D) 0.4
Correct Answer: A
Rationale: RQ = Volume of CO₂ produced ÷ Volume of O₂ consumed = 0.4 ÷ 0.6 = 0.67.
An RQ of 0.7 indicates lipid respiration; 1.0 indicates carbohydrate; >1.0 indicates anaerobic
respiration or conversion of carbohydrate to fat. Option B would indicate pure carbohydrate
metabolism. Option C is mathematically incorrect. Option D inverts the calculation .
5. Which statement correctly describes the relationship between gross primary
production (GPP) and net primary production (NPP)?
A) NPP = GPP + plant respiration losses
B) NPP = GPP − plant respiration losses
C) GPP = NPP − plant respiration losses
D) GPP = NPP + plant respiration losses
Correct Answer: B
Rationale: Net primary production (NPP) is the energy available to the next trophic level
after the plant has used some energy for respiration. Therefore, NPP = GPP − plant
respiration losses. Option A adds respiration, which is incorrect. Options C and D incorrectly
rearrange the relationship .
6. In the light-dependent reaction, what is the primary role of the electron transport
chain?
A) To produce glucose directly
, B) To generate a proton gradient for ATP synthesis
C) To fix carbon dioxide
D) To produce oxygen
Correct Answer: B
Rationale: The electron transport chain in the thylakoid membrane pumps protons into the
thylakoid space, creating a proton gradient. This gradient drives ATP synthesis via
chemiosmosis. Option A is incorrect—glucose is produced in the light-independent reaction.
Option C is incorrect—carbon fixation occurs in the Calvin cycle. Option D is incorrect—
oxygen is produced by photolysis of water, not the electron transport chain .
7. A scientist measures photosynthesis rate at different CO₂ concentrations at
constant light intensity and temperature. Rate plateaus above 0.4% CO₂. Explain why.
A) CO₂ becomes toxic at high concentrations
B) Light intensity becomes the rate-limiting factor above 0.4% CO₂
C) The plant stops respiring
D) Chlorophyll is destroyed at high CO₂ concentrations
Correct Answer: B
Rationale: From 0% to 0.4% CO₂, rate rises because CO₂ is the rate-limiting factor—more
CO₂ means more substrate for the Calvin cycle. At 0.4% CO₂, CO₂ stops being limiting.
Above 0.4%, a different factor becomes limiting—likely light intensity (since temperature is
constant). Adding more CO₂ doesn't increase rate because the Calvin cycle is now starved
of ATP and NADPH from the light-dependent reactions .
8. In the light-independent reaction, what is the role of ATP and NADPH?
A) They are used to fix CO₂ to RuBP
B) They provide energy and reducing power to convert GP to TP
C) They are produced during the Calvin cycle
D) They are used to regenerate RuBP
