Compare aerobic and anaerobic respiration in terms of oxygen use and ATP yield.

• A. Aerobic uses no oxygen and yields more ATP; anaerobic does not require oxygen and yields less ATP.
• B. Anaerobic uses oxygen and yields less ATP.
• C. Aerobic uses oxygen and yields more ATP; anaerobic does not require oxygen and yields less ATP.
• D. Both require oxygen but only one yields ATP.

Answer: (C)

Energy yield from glucose depends on whether oxygen is present to accept electrons at the end of the electron transport chain. In aerobic respiration, oxygen serves as the final electron acceptor in the mitochondria, allowing the full oxidative phosphorylation process to run and produce a large amount of ATP. In contrast, anaerobic pathways operate without oxygen, so cells rely on glycolysis and fermentation to regenerate NAD+, yielding only a small amount of ATP (about 2 ATP per glucose) compared with aerobic respiration. That’s why the statement that aerobic uses oxygen and yields more ATP, while anaerobic does not require oxygen and yields less ATP, is the best description.