What is the fate of glucose in the absence of oxygen?

In the absence of oxygen, the fate of glucose primarily involves a process known as fermentation. In animals, glucose is converted into lactic acid through lactic acid fermentation. This process allows for the rapid production of ATP when oxygen levels are low, as in intense exercise. In yeast and some bacteria, glucose undergoes alcoholic fermentation, producing ethanol and carbon dioxide.

This anaerobic pathway is essential for cells to continue generating energy in situations where oxygen is not available. While glycogen storage is an important aspect of glucose metabolism, it does not directly relate to the fate of glucose under anaerobic conditions, where immediate energy production is prioritized. Similarly, oxidizing glucose to carbon dioxide and water occurs during aerobic respiration, which requires oxygen, and entering the Krebs cycle also necessitates oxygen as it is part of the aerobic respiratory pathway. Thus, the conversion of glucose to lactic acid or ethanol represents the key outcome of glucose metabolism in the absence of oxygen.