Which process allows ATP production to continue in the absence of oxygen by enabling glycolysis to proceed?

Which process allows ATP production to continue in the absence of oxygen by enabling glycolysis to proceed?

• A. Fermentation
• B. Krebs Cycle
• C. Electron Transport Chain
• D. Glycolysis

Answer: (A)

When oxygen isn’t available, cells still need ATP and glycolysis can run, but it requires a steady supply of NAD+. Normally, NADH produced in glycolysis must be reoxidized to NAD+ to keep glycolysis going, and that reoxidation is usually handled by the electron transport chain with oxygen as the final electron acceptor. In anaerobic conditions, that chain can’t operate, so another pathway must regenerate NAD+. Fermentation does exactly that. It uses the product of glycolysis (pyruvate) as an electron acceptor to convert NADH back to NAD+. This restoration of NAD+ allows glycolysis to continue producing ATP by substrate-level phosphorylation, even without oxygen. In animals, pyruvate is reduced to lactate; in yeast, it’s converted to ethanol and CO2. So fermentation is the process that enables continued ATP production via glycolysis in the absence of oxygen. The Krebs cycle and the electron transport chain depend on oxygen to function, and glycolysis without NAD+ regeneration would stall, though glycolysis can occur briefly by itself without oxygen.

When oxygen isn’t available, cells still need ATP and glycolysis can run, but it requires a steady supply of NAD+. Normally, NADH produced in glycolysis must be reoxidized to NAD+ to keep glycolysis going, and that reoxidation is usually handled by the electron transport chain with oxygen as the final electron acceptor. In anaerobic conditions, that chain can’t operate, so another pathway must regenerate NAD+.

Fermentation does exactly that. It uses the product of glycolysis (pyruvate) as an electron acceptor to convert NADH back to NAD+. This restoration of NAD+ allows glycolysis to continue producing ATP by substrate-level phosphorylation, even without oxygen. In animals, pyruvate is reduced to lactate; in yeast, it’s converted to ethanol and CO2.

So fermentation is the process that enables continued ATP production via glycolysis in the absence of oxygen. The Krebs cycle and the electron transport chain depend on oxygen to function, and glycolysis without NAD+ regeneration would stall, though glycolysis can occur briefly by itself without oxygen.