When oxygen is not available, converting pyruvate to lactate (a process known as lactic acid fermentation) allows glycolysis to continue. This is crucial because glycolysis is the primary means of producing ATP in the absence of oxygen.
The correct answer is a) it allows the electron transport chain to continue. However, this statement can be misleading in this context because during anaerobic conditions, the electron transport chain does not operate efficiently due to the lack of oxygen, which is the final electron acceptor in oxidative phosphorylation.
Instead, what really happens is that the conversion of pyruvate to lactate regenerates NAD+. Glycolysis requires NAD+ to proceed, and when oxygen is scarce, the cell needs to ensure that this coenzyme is available. By reducing pyruvate to lactate, cells are able to harvest energy from glucose, albeit less efficiently than aerobic respiration. Thus, while the electron transport chain itself isn’t functioning properly in anaerobic conditions, the process ensures that ATP can still be generated through glycolysis.
In summary, the conversion of pyruvate to lactate under anaerobic conditions is vital for sustaining ATP production by enabling glycolysis through the regeneration of NAD+.