In aerobic cellular respiration, which process generates the most ATP per molecule of glucose?

• A. Citric acid (TCA) cycle via substrate-level phosphorylation
• B. Fermentation (lactate or ethanol formation)
• C. Oxidative phosphorylation (electron transport chain coupled to chemiosmosis)
• D. Glycolysis

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the main stages of aerobic cellular respiration: glycolysis, the citric acid (TCA) cycle, and oxidative phosphorylation (electron transport chain coupled to chemiosmosis). Each stage contributes differently to ATP production.
2. Step 2: Recall that glycolysis produces a small amount of ATP directly through substrate-level phosphorylation, generating 2 ATP molecules per glucose molecule.
3. Step 3: Recognize that the citric acid cycle also produces ATP via substrate-level phosphorylation, but only a small amount (1 ATP per cycle turn, and since one glucose produces two turns, this totals 2 ATP).
4. Step 4: Understand that fermentation (lactate or ethanol formation) occurs under anaerobic conditions and produces ATP only through glycolysis, so it yields much less ATP compared to aerobic respiration.
5. Step 5: Identify that oxidative phosphorylation, which includes the electron transport chain and chemiosmosis, generates the majority of ATP by using the high-energy electrons from NADH and FADH2 to drive ATP synthase, producing approximately 26-28 ATP molecules per glucose.