Which statement about fermentation is true?

• A. It regenerates NAD+ to allow glycolysis to continue in absence of oxygen
• B. It yields more ATP per glucose than aerobic respiration
• C. It occurs in mitochondria of animal cells
• D. It uses oxygen as the final electron acceptor

Answer: (A)

Fermentation is the way cells keep glycolysis going when oxygen is scarce by restoring NAD+ for continued ATP production. In glycolysis, NAD+ is reduced to NADH, and for glycolysis to keep producing ATP, NAD+ must be reoxidized. Fermentation accomplishes this by transferring electrons from NADH to an organic molecule: in lactic acid fermentation, pyruvate becomes lactate, regenerating NAD+; in alcoholic fermentation, pyruvate is converted to acetaldehyde and CO2, and acetaldehyde accepts the electrons to form ethanol, also regenerating NAD+. This lets glycolysis continue in the absence of oxygen, yielding only about 2 ATP per glucose, much less than aerobic respiration, which uses oxygen to drive the TCA cycle and oxidative phosphorylation and produces roughly 30–32 ATP per glucose. Fermentation occurs in the cytosol and does not use oxygen as the final electron acceptor.