AP biology exam with 200 practice questions and answers with rationales
Monday, May 4, 2026
Section I: Multiple Choice (Sample of 50 Questions)
Questions 1–50
1. Which of the following best describes the role of oxygen in aerobic respiration?
A) Final electron acceptor in the electron transport chain
B) Initial substrate for glycolysis
C) Direct phosphorylator of ADP to ATP
D) Catalyst for the Krebs cycle
Answer: A
Rationale: Oxygen is the final electron acceptor at the end of the electron
transport chain, combining with electrons and protons to form water. This allows
the chain to continue pumping protons, driving ATP synthesis.
2. In a population of rabbits, brown fur (B) is dominant to white fur (b). If the
frequency of the bb genotype is 0.09, what is the frequency of the B allele?
A) 0.3
,B) 0.7
C) 0.09
D) 0.49
Answer: B
Rationale: q² = 0.09 → q = 0.3 (b frequency). p = 1 – 0.3 = 0.7 (B frequency).
Hardy-Weinberg equilibrium assumed.
3. Which of the following best explains why the rate of photosynthesis decreases
at very high light intensities?
A) Stomata close to conserve water
B) Photorespiration increases due to RuBisCO oxygenase activity
C) Chlorophyll molecules become denatured
D) NADPH accumulates, inhibiting the Calvin cycle
Answer: B
Rationale: High light can cause excess O₂ production, leading RuBisCO to fix O₂
instead of CO₂ (photorespiration), reducing photosynthetic efficiency.
,4. A mutation inactivates the lac repressor protein in E. coli. Which of the
following will occur?
A) The lac operon will be permanently repressed
B) β-galactosidase will be produced only when glucose is absent
C) β-galactosidase will be produced constitutively
D) The operon will not be transcribed due to allolactose binding
Answer: C
Rationale: Without a functional repressor, the lac operon is always “on”
(constitutive expression), regardless of lactose presence.
5. Which of the following cellular processes is most directly driven by ATP
hydrolysis?
A) Diffusion of O₂ across a membrane
B) Transport of Na⁺ out of a cell against its concentration gradient
C) Movement of water through aquaporins
D) Facilitated diffusion of glucose
Answer: B
, Rationale: Active transport (Na⁺/K⁺ ATPase) requires ATP hydrolysis. The others
are passive transport.
6–8 refer to the following experiment:
Enzyme activity (product formation/min) was measured at pH 5, 7, and 9. Data:
pH 5 → 20 units, pH 7 → 95 units, pH 9 → 15 units.
6. The optimal pH for this enzyme is closest to:
A) 5
B) 7
C) 9
D) Cannot be determined
Answer: B
Rationale: Highest activity at pH 7.
7. What likely causes the low activity at pH 9?
A) Enzyme denaturation affecting tertiary structure
B) Substrate depletion
C) Competitive inhibition
Monday, May 4, 2026
Section I: Multiple Choice (Sample of 50 Questions)
Questions 1–50
1. Which of the following best describes the role of oxygen in aerobic respiration?
A) Final electron acceptor in the electron transport chain
B) Initial substrate for glycolysis
C) Direct phosphorylator of ADP to ATP
D) Catalyst for the Krebs cycle
Answer: A
Rationale: Oxygen is the final electron acceptor at the end of the electron
transport chain, combining with electrons and protons to form water. This allows
the chain to continue pumping protons, driving ATP synthesis.
2. In a population of rabbits, brown fur (B) is dominant to white fur (b). If the
frequency of the bb genotype is 0.09, what is the frequency of the B allele?
A) 0.3
,B) 0.7
C) 0.09
D) 0.49
Answer: B
Rationale: q² = 0.09 → q = 0.3 (b frequency). p = 1 – 0.3 = 0.7 (B frequency).
Hardy-Weinberg equilibrium assumed.
3. Which of the following best explains why the rate of photosynthesis decreases
at very high light intensities?
A) Stomata close to conserve water
B) Photorespiration increases due to RuBisCO oxygenase activity
C) Chlorophyll molecules become denatured
D) NADPH accumulates, inhibiting the Calvin cycle
Answer: B
Rationale: High light can cause excess O₂ production, leading RuBisCO to fix O₂
instead of CO₂ (photorespiration), reducing photosynthetic efficiency.
,4. A mutation inactivates the lac repressor protein in E. coli. Which of the
following will occur?
A) The lac operon will be permanently repressed
B) β-galactosidase will be produced only when glucose is absent
C) β-galactosidase will be produced constitutively
D) The operon will not be transcribed due to allolactose binding
Answer: C
Rationale: Without a functional repressor, the lac operon is always “on”
(constitutive expression), regardless of lactose presence.
5. Which of the following cellular processes is most directly driven by ATP
hydrolysis?
A) Diffusion of O₂ across a membrane
B) Transport of Na⁺ out of a cell against its concentration gradient
C) Movement of water through aquaporins
D) Facilitated diffusion of glucose
Answer: B
, Rationale: Active transport (Na⁺/K⁺ ATPase) requires ATP hydrolysis. The others
are passive transport.
6–8 refer to the following experiment:
Enzyme activity (product formation/min) was measured at pH 5, 7, and 9. Data:
pH 5 → 20 units, pH 7 → 95 units, pH 9 → 15 units.
6. The optimal pH for this enzyme is closest to:
A) 5
B) 7
C) 9
D) Cannot be determined
Answer: B
Rationale: Highest activity at pH 7.
7. What likely causes the low activity at pH 9?
A) Enzyme denaturation affecting tertiary structure
B) Substrate depletion
C) Competitive inhibition
