Fermentation is essentially glycolysis plus an extra step in which pyruvate is reduced to form lactate or alcohol and carbon dioxide. This last step __________.

• A. removes poisonous oxygen from the environment
• B. extracts a bit more energy from glucose
• C. prevents pyruvate from accumulating
• D. enables the cell to make pyruvate into substances it can use
• E. enables the cell to recycle the reduced NADH to oxidized NAD⁺

Answer: (E)

Verified step by step guidance

1. Understand the process of glycolysis: Glycolysis is the first step in cellular respiration where glucose is broken down into two molecules of pyruvate, producing a net gain of 2 ATP and 2 NADH molecules.
2. Recognize the role of fermentation: In the absence of oxygen, cells undergo fermentation to continue producing ATP. Fermentation allows glycolysis to continue by regenerating NAD+ from NADH.
3. Identify the extra step in fermentation: This step involves the reduction of pyruvate to either lactate (in lactic acid fermentation) or ethanol and carbon dioxide (in alcoholic fermentation).
4. Connect the extra step to NAD+ regeneration: The reduction of pyruvate to lactate or ethanol allows NADH to be oxidized back to NAD+, which is essential for glycolysis to continue.
5. Conclude the purpose of the extra step: The primary function of this step is to recycle NADH to NAD+, enabling the cell to maintain glycolysis and continue producing ATP in anaerobic conditions.