When yeast cells metabolize glucose in the absence of oxygen, which of the following statements is true?

• A. The electron transport chain operates at maximum efficiency.
• B. Ethanol and carbon dioxide are produced through fermentation.
• C. ATP yield is higher than during aerobic respiration.
• D. Oxygen acts as the final electron acceptor.

Answer: (B)

Verified step by step guidance

1. Understand that yeast cells can metabolize glucose both aerobically (with oxygen) and anaerobically (without oxygen). The problem specifies metabolism in the absence of oxygen, which means anaerobic conditions.
2. Recall that under anaerobic conditions, yeast perform fermentation rather than aerobic respiration. Fermentation is a process that allows ATP production without the electron transport chain functioning fully.
3. Recognize that during fermentation in yeast, glucose is converted into ethanol and carbon dioxide. This is a key characteristic of yeast metabolism in the absence of oxygen.
4. Note that the electron transport chain does not operate at maximum efficiency without oxygen because oxygen is the final electron acceptor in aerobic respiration. Without oxygen, the chain cannot function properly.
5. Understand that ATP yield during fermentation is lower than during aerobic respiration because fermentation produces ATP only through glycolysis, whereas aerobic respiration produces much more ATP via the electron transport chain.