Under which conditions would a cell begin lactic acid fermentation?

• A. When the cell has excess ATP and low NADH
• B. When oxygen is unavailable for cellular respiration
• C. When the electron transport chain is highly active
• D. When glucose is completely oxidized in the presence of oxygen

Answer: (B)

Verified step by step guidance

1. Understand that lactic acid fermentation is an anaerobic process, meaning it occurs when oxygen is not available to the cell.
2. Recall that under normal aerobic conditions, cells use oxygen as the final electron acceptor in the electron transport chain to produce ATP efficiently.
3. Recognize that when oxygen is unavailable, the electron transport chain cannot operate, causing a buildup of NADH and a shortage of NAD+, which is needed for glycolysis to continue.
4. Know that lactic acid fermentation regenerates NAD+ by converting pyruvate into lactic acid, allowing glycolysis to proceed and produce ATP in the absence of oxygen.
5. Therefore, the condition that triggers lactic acid fermentation is the lack of oxygen, which prevents aerobic respiration and forces the cell to rely on fermentation to meet its energy needs.