In aerobic cellular respiration, which process produces the greatest number of ATP molecules per molecule of glucose?

• A. Oxidative phosphorylation (electron transport chain coupled to chemiosmosis)
• B. Citric acid cycle (Krebs cycle)
• C. Fermentation
• D. Glycolysis

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the overall process of aerobic cellular respiration, which includes glycolysis, the citric acid cycle (Krebs cycle), and oxidative phosphorylation (electron transport chain coupled to chemiosmosis). Each stage contributes differently to ATP production.
2. Step 2: Recall that glycolysis breaks down one glucose molecule into two pyruvate molecules, producing a small net gain of ATP directly through substrate-level phosphorylation.
3. Step 3: Recognize that the citric acid cycle processes the products of glycolysis, generating electron carriers (NADH and FADH2) and a small amount of ATP directly through substrate-level phosphorylation.
4. Step 4: Understand that oxidative phosphorylation uses the NADH and FADH2 produced in earlier steps to drive the electron transport chain, creating a proton gradient that powers ATP synthase to produce a large amount of ATP through chemiosmosis.
5. Step 5: Compare the ATP yields from each process and conclude that oxidative phosphorylation produces the greatest number of ATP molecules per glucose molecule because it harnesses the energy stored in electron carriers most efficiently.