Compared to anaerobic processes, what effect does oxygen availability have on ATP yield in respiration?

• A. Far more ATP per glucose
• B. The same amount of ATP
• C. Less ATP per glucose
• D. No ATP production

Answer: (A)

Oxygen enables oxidative phosphorylation to generate most of the ATP in respiration. With oxygen as the final electron acceptor, electrons flow through the electron transport chain, protons are pumped across the membrane, and ATP synthase makes a large amount of ATP. This step accounts for the bulk of ATP yield, giving about 30–38 ATP per glucose in many organisms. Without oxygen, cells can only rely on glycolysis (and often fermentation) to regenerate NAD+, producing only about 2 ATP per glucose. Some anaerobic respiration uses other electron acceptors, which can yield more ATP than fermentation but usually less than with oxygen. So, the presence of oxygen results in far more ATP per glucose.