Which statement best describes fermentation?

Which statement best describes fermentation?

• A. A process that regenerates NAD+ under anaerobic conditions; two common types are lactic acid fermentation and alcoholic fermentation
• B. A process that uses oxygen to generate ATP
• C. A pathway that produces energy only through Krebs cycle
• D. A process that occurs in the mitochondria during aerobic respiration

Answer: (A)

Fermentation is a way cells keep glycolysis going when oxygen isn’t available by regenerating NAD+. During glycolysis, NAD+ is reduced to NADH, and for glycolysis to continue, NAD+ must be replenished. In fermentation, pyruvate accepts electrons from NADH, converting NADH back to NAD+ so glycolysis can keep producing ATP, albeit only a small amount. Two common fermentation pathways are lactic acid fermentation, where pyruvate is reduced to lactate, and alcoholic fermentation, where pyruvate is decarboxylated to acetaldehyde and then reduced to ethanol. This whole process occurs in the cytoplasm and does not involve the mitochondrial electron transport chain or the Krebs cycle, and it does not produce large amounts of ATP. In contrast, using oxygen to generate ATP, or relying solely on the Krebs cycle, involves mitochondrial processes and aerobic respiration.

Fermentation is a way cells keep glycolysis going when oxygen isn’t available by regenerating NAD+. During glycolysis, NAD+ is reduced to NADH, and for glycolysis to continue, NAD+ must be replenished. In fermentation, pyruvate accepts electrons from NADH, converting NADH back to NAD+ so glycolysis can keep producing ATP, albeit only a small amount. Two common fermentation pathways are lactic acid fermentation, where pyruvate is reduced to lactate, and alcoholic fermentation, where pyruvate is decarboxylated to acetaldehyde and then reduced to ethanol. This whole process occurs in the cytoplasm and does not involve the mitochondrial electron transport chain or the Krebs cycle, and it does not produce large amounts of ATP. In contrast, using oxygen to generate ATP, or relying solely on the Krebs cycle, involves mitochondrial processes and aerobic respiration.