In aerobic cellular respiration, which process directly yields the greatest number of ATP molecules per molecule of glucose in eukaryotic cells?

• A. Oxidative phosphorylation (electron transport chain coupled to ATP synthase)
• B. Citric acid cycle (Krebs cycle) substrate-level phosphorylation
• C. Glycolysis
• D. Fermentation (lactate or ethanol production)

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 ATP synthase). Each stage contributes differently to ATP production.
2. Step 2: Recall that glycolysis produces a small amount of ATP directly through substrate-level phosphorylation, yielding 2 ATP molecules per glucose molecule.
3. Step 3: Recognize that the citric acid cycle also produces ATP (or GTP) directly via substrate-level phosphorylation, but the amount is relatively small (1 ATP per cycle, and since each glucose produces two cycles, this totals 2 ATP).
4. Step 4: Understand that oxidative phosphorylation involves the electron transport chain creating a proton gradient that drives ATP synthase to produce ATP. This process yields the majority of ATP molecules per glucose, typically around 26 to 28 ATP molecules.
5. Step 5: Conclude that among the listed processes, oxidative phosphorylation directly yields the greatest number of ATP molecules per glucose in eukaryotic cells.