How does fermentation enable a cell to continue producing ATP in the absence of oxygen?

• A. By using oxygen as a final electron acceptor in the mitochondria
• B. By regenerating NAD\(^+\) needed for glycolysis to continue
• C. By directly producing large amounts of ATP through the electron transport chain
• D. By converting pyruvate into acetyl-CoA for the Krebs cycle

Answer: (B)

Verified step by step guidance

1. Understand the context: Fermentation occurs in anaerobic conditions, meaning there is no oxygen available for cellular respiration. This process allows cells to continue producing ATP despite the absence of oxygen.
2. Recall the role of glycolysis: Glycolysis is the first step in cellular respiration and does not require oxygen. It breaks down glucose into pyruvate, producing a small amount of ATP and NADH.
3. Identify the problem caused by the lack of oxygen: Without oxygen, the electron transport chain cannot function, and NADH cannot be oxidized back into NAD\(^+\). This creates a shortage of NAD\(^+\), which is essential for glycolysis to continue.
4. Explain how fermentation solves the problem: Fermentation regenerates NAD\(^+\) by converting pyruvate into other molecules, such as lactic acid (in animals) or ethanol and CO\(_2\) (in yeast). This allows glycolysis to continue producing ATP.
5. Clarify why fermentation does not produce large amounts of ATP: Fermentation does not involve the electron transport chain or the Krebs cycle, which are responsible for producing most of the ATP in aerobic respiration. Instead, it ensures that glycolysis can continue by replenishing NAD\(^+\).