In terms of ATP yield, how does aerobic respiration compare to anaerobic respiration?

• A. Aerobic respiration yields less ATP per glucose than anaerobic respiration.
• B. Aerobic yields the same amount of ATP as anaerobic.
• C. Aerobic respiration yields more ATP per glucose than anaerobic respiration.
• D. Aerobic yields no ATP.

Answer: (C)

The main idea is how much energy (ATP) you get from glucose with or without oxygen. In aerobic respiration, glucose is fully oxidized through glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation. Glycolysis provides a small amount of ATP directly, but most of the energy comes from the electron transport chain and the ATP synthase that use the proton gradient created as electrons travel to oxygen, the final electron acceptor. Because of this, you typically end up with about 30–32 ATP per glucose, varying a bit by cell type.

In anaerobic respiration (fermentation), there’s no oxygen to accept electrons, so the electron transport chain doesn’t operate. Cells run glycolysis to produce 2 ATP, and NAD+ is regenerated by converting pyruvate to lactate (in animals) or to ethanol and CO2 (in yeast). Since oxidative phosphorylation isn’t used, there’s little to no additional ATP generated, so the total is around 2 ATP per glucose.

So, aerobic respiration yields more ATP per glucose than anaerobic respiration.