Final answer:
A cell must lack oxygen to engage in aerobic fermentation, typically resulting in lactic acid fermentation in animal cells, which allows for ATP production and continuation of glycolysis without oxygen.
Step-by-step explanation:
The condition that must exist in a cell for it to engage in aerobic fermentation is an absence of oxygen. When oxygen is not present, cells must undergo a process known as fermentation to regenerate the electron carrier NAD+, which is necessary for glycolysis to continue. In animal cells, including human muscle cells, the type of fermentation that readily occurs is lactic acid fermentation. This process initiates when cells lack oxygen and need to continue producing ATP without aerobic respiration.
Under these conditions, pyruvate from glycolysis is reduced to form lactate. Lactic acid fermentation allows for the production of ATP albeit in much smaller quantities - only two molecules of ATP per molecule of glucose. It does so by ensuring the continuation of glycolysis even in the absence of oxygen, which is crucial for a cell's survival.