Which of the following describes a primary function of both lactic acid fermentation and alcohol fermentation?

• A. Reduction of NAD⁺ to NADH.
• B. Oxidation of NADH to NAD⁺.
• C. Reduction of FAD to FADH₂.
• D. Hydrolysis of ATP to ADP.

Answer: (B)

Verified step by step guidance

1. Understand the context of fermentation: Fermentation is a metabolic process that occurs in the absence of oxygen, allowing cells to regenerate NAD+ from NADH, which is crucial for glycolysis to continue producing ATP.
2. Identify the role of NAD+ and NADH: During glycolysis, NAD+ is reduced to NADH. For glycolysis to continue, NADH must be oxidized back to NAD+.
3. Recognize the primary function of fermentation: Both lactic acid fermentation and alcohol fermentation serve to oxidize NADH to NAD+, ensuring a continuous supply of NAD+ for glycolysis.
4. Differentiate between the types of fermentation: Lactic acid fermentation converts pyruvate into lactic acid, while alcohol fermentation converts pyruvate into ethanol and carbon dioxide, both processes oxidizing NADH to NAD+.
5. Conclude the primary function: The key function of both types of fermentation is the oxidation of NADH to NAD+, which is essential for the continuation of ATP production via glycolysis.