1
BIOD 171 MODULE 3 EXAM Actual Exam
2026/2027 Complete Questions and Verified
Answers with Detailed Rationales Essential
Microbiology Portage Learning Pass
Guaranteed - A+ Graded
Q1: Which coenzyme serves as the primary electron carrier in glycolysis and the Krebs cycle,
accepting electrons and hydrogen atoms to become reduced?
A. FAD
B. NAD⁺ [CORRECT]
C. Coenzyme A
D. ATP
Correct Answer: B
Rationale: NAD⁺ (nicotinamide adenine dinucleotide) functions as the principal electron carrier
in glycolysis and the Krebs cycle, accepting two electrons and one proton to form NADH, which
then delivers electrons to the electron transport chain.
Q2: In the glycolytic pathway, what is the net ATP yield per molecule of glucose through
substrate-level phosphorylation?
A. 1 ATP
B. 2 ATP [CORRECT]
C. 4 ATP
D. 36 ATP
Correct Answer: B
Rationale: Glycolysis produces 4 ATP through substrate-level phosphorylation but consumes 2
ATP during the energy investment phase, resulting in a net gain of 2 ATP per glucose molecule.
Q3: Which enzyme catalyzes the irreversible, committed step of glycolysis by phosphorylating
glucose to glucose-6-phosphate?
A. Phosphofructokinase
B. Hexokinase [CORRECT]
,2
C. Pyruvate kinase
D. Enolase
Correct Answer: B
Rationale: Hexokinase catalyzes the first phosphorylation of glucose using ATP, trapping
glucose inside the cell as glucose-6-phosphate; this is the first committed step of glycolysis and
is physiologically irreversible.
Q4: What is the primary function of the electron transport chain in aerobic respiration?
A. Direct synthesis of glucose
B. Generation of a proton gradient for ATP synthesis [CORRECT]
C. Conversion of pyruvate to acetyl-CoA
D. Breakdown of fatty acids
Correct Answer: B
Rationale: The electron transport chain transfers electrons through protein complexes, pumping
protons across the membrane to create an electrochemical gradient (proton-motive force) that
drives ATP synthesis through chemiosmosis.
Q5: In the Krebs cycle (citric acid cycle), how many molecules of CO₂ are released per acetyl-
CoA entering the cycle?
A. 1
B. 2 [CORRECT]
C. 3
D. 4
Correct Answer: B
Rationale: Each acetyl-CoA (2 carbons) entering the Krebs cycle undergoes two
decarboxylation reactions: isocitrate → α-ketoglutarate and α-ketoglutarate → succinyl-CoA,
releasing 2 CO₂ molecules per turn of the cycle.
Q6: Which metabolic pathway occurs in the cytoplasm of both prokaryotic and eukaryotic cells
and does not require oxygen?
A. Krebs cycle
B. Glycolysis [CORRECT]
C. Electron transport chain
D. Oxidative phosphorylation
Correct Answer: B
, 3
Rationale: Glycolysis is an ancient, universal pathway occurring in the cytoplasm of all cells; it
is anaerobic, requiring no oxygen and producing pyruvate regardless of oxygen availability.
Q7: What is the final electron acceptor in the electron transport chain of aerobic bacteria?
A. Nitrate
B. Sulfate
C. Molecular oxygen [CORRECT]
D. Carbon dioxide
Correct Answer: C
Rationale: In aerobic respiration, molecular oxygen serves as the terminal electron acceptor,
combining with electrons and protons to form water; this maximizes energy yield from glucose
oxidation.
Q8: Which fermentation pathway converts pyruvate to lactic acid to regenerate NAD⁺ from
NADH?
A. Alcoholic fermentation
B. Lactic acid fermentation [CORRECT]
C. Mixed acid fermentation
D. Propionic acid fermentation
Correct Answer: B
Rationale: Lactic acid fermentation reduces pyruvate directly to lactic acid using NADH,
oxidizing NADH back to NAD⁺ to allow glycolysis to continue producing ATP under anaerobic
conditions.
Q9: In chemiosmosis, what protein complex utilizes the proton gradient to synthesize ATP?
A. NADH dehydrogenase
B. Cytochrome c oxidase
C. ATP synthase [CORRECT]
D. Succinate dehydrogenase
Correct Answer: C
Rationale: ATP synthase is a rotary enzyme complex that uses the energy of protons flowing
down their electrochemical gradient to phosphorylate ADP to ATP, coupling proton motive force
to chemical bond formation.
BIOD 171 MODULE 3 EXAM Actual Exam
2026/2027 Complete Questions and Verified
Answers with Detailed Rationales Essential
Microbiology Portage Learning Pass
Guaranteed - A+ Graded
Q1: Which coenzyme serves as the primary electron carrier in glycolysis and the Krebs cycle,
accepting electrons and hydrogen atoms to become reduced?
A. FAD
B. NAD⁺ [CORRECT]
C. Coenzyme A
D. ATP
Correct Answer: B
Rationale: NAD⁺ (nicotinamide adenine dinucleotide) functions as the principal electron carrier
in glycolysis and the Krebs cycle, accepting two electrons and one proton to form NADH, which
then delivers electrons to the electron transport chain.
Q2: In the glycolytic pathway, what is the net ATP yield per molecule of glucose through
substrate-level phosphorylation?
A. 1 ATP
B. 2 ATP [CORRECT]
C. 4 ATP
D. 36 ATP
Correct Answer: B
Rationale: Glycolysis produces 4 ATP through substrate-level phosphorylation but consumes 2
ATP during the energy investment phase, resulting in a net gain of 2 ATP per glucose molecule.
Q3: Which enzyme catalyzes the irreversible, committed step of glycolysis by phosphorylating
glucose to glucose-6-phosphate?
A. Phosphofructokinase
B. Hexokinase [CORRECT]
,2
C. Pyruvate kinase
D. Enolase
Correct Answer: B
Rationale: Hexokinase catalyzes the first phosphorylation of glucose using ATP, trapping
glucose inside the cell as glucose-6-phosphate; this is the first committed step of glycolysis and
is physiologically irreversible.
Q4: What is the primary function of the electron transport chain in aerobic respiration?
A. Direct synthesis of glucose
B. Generation of a proton gradient for ATP synthesis [CORRECT]
C. Conversion of pyruvate to acetyl-CoA
D. Breakdown of fatty acids
Correct Answer: B
Rationale: The electron transport chain transfers electrons through protein complexes, pumping
protons across the membrane to create an electrochemical gradient (proton-motive force) that
drives ATP synthesis through chemiosmosis.
Q5: In the Krebs cycle (citric acid cycle), how many molecules of CO₂ are released per acetyl-
CoA entering the cycle?
A. 1
B. 2 [CORRECT]
C. 3
D. 4
Correct Answer: B
Rationale: Each acetyl-CoA (2 carbons) entering the Krebs cycle undergoes two
decarboxylation reactions: isocitrate → α-ketoglutarate and α-ketoglutarate → succinyl-CoA,
releasing 2 CO₂ molecules per turn of the cycle.
Q6: Which metabolic pathway occurs in the cytoplasm of both prokaryotic and eukaryotic cells
and does not require oxygen?
A. Krebs cycle
B. Glycolysis [CORRECT]
C. Electron transport chain
D. Oxidative phosphorylation
Correct Answer: B
, 3
Rationale: Glycolysis is an ancient, universal pathway occurring in the cytoplasm of all cells; it
is anaerobic, requiring no oxygen and producing pyruvate regardless of oxygen availability.
Q7: What is the final electron acceptor in the electron transport chain of aerobic bacteria?
A. Nitrate
B. Sulfate
C. Molecular oxygen [CORRECT]
D. Carbon dioxide
Correct Answer: C
Rationale: In aerobic respiration, molecular oxygen serves as the terminal electron acceptor,
combining with electrons and protons to form water; this maximizes energy yield from glucose
oxidation.
Q8: Which fermentation pathway converts pyruvate to lactic acid to regenerate NAD⁺ from
NADH?
A. Alcoholic fermentation
B. Lactic acid fermentation [CORRECT]
C. Mixed acid fermentation
D. Propionic acid fermentation
Correct Answer: B
Rationale: Lactic acid fermentation reduces pyruvate directly to lactic acid using NADH,
oxidizing NADH back to NAD⁺ to allow glycolysis to continue producing ATP under anaerobic
conditions.
Q9: In chemiosmosis, what protein complex utilizes the proton gradient to synthesize ATP?
A. NADH dehydrogenase
B. Cytochrome c oxidase
C. ATP synthase [CORRECT]
D. Succinate dehydrogenase
Correct Answer: C
Rationale: ATP synthase is a rotary enzyme complex that uses the energy of protons flowing
down their electrochemical gradient to phosphorylate ADP to ATP, coupling proton motive force
to chemical bond formation.
