How do lactic acid fermentation and aerobic respiration differ in ATP yield and final electron acceptor?

• A. Lactic acid fermentation yields 2 ATP per glucose and uses oxygen as final electron acceptor; aerobic yields up to 36–38 ATP
• B. Lactic acid fermentation yields 2 ATP per glucose and uses pyruvate as the terminal electron acceptor; aerobic yields up to 36–38 ATP using oxygen
• C. Lactic acid fermentation yields 36–38 ATP; aerobic yields 2 ATP
• D. Lactic acid fermentation yields nothing; aerobic yields 4 ATP

Answer: (B)

Energy yield and the final electron acceptor differ between lactic acid fermentation and aerobic respiration. In lactic acid fermentation, energy comes from glycolysis, giving 2 ATP per glucose. To keep glycolysis going without a full electron transport chain, NADH must be reoxidized to NAD+. Pyruvate serves as the terminal electron acceptor by accepting electrons to form lactate, so no oxygen is used and overall ATP yield stays at about 2 per glucose.

In aerobic respiration, pyruvate is fully oxidized through the mitochondria via the pyruvate dehydrogenase step, the citric acid cycle, and the electron transport chain. Oxygen acts as the final electron acceptor at the end of the chain, allowing a large number of ATP to be produced—commonly up to around 36–38 ATP per glucose, depending on the organism and cellular conditions.