What happens to pyruvic acid in the absence of oxygen?

In the absence of oxygen, pyruvic acid undergoes fermentation, which is a metabolic process that allows cells to continue producing energy without the need for oxygen. During fermentation, pyruvic acid is converted into various byproducts, depending on the type of fermentation taking place. For instance, in lactic acid fermentation, pyruvic acid is converted to lactic acid, while in alcoholic fermentation, it is converted to ethanol and carbon dioxide. This process is crucial for cells, especially in anaerobic conditions, as it regenerates NAD+, which is necessary for glycolysis to continue functioning and producing ATP, the energy currency of the cell.

The other options do not apply in anaerobic conditions. For example, pyruvic acid does not enter the Krebs cycle without oxygen, as that requires the presence of oxygen for the complete oxidation of acetyl-CoA. Additionally, there's no conversion of pyruvic acid to glucose in anaerobic conditions, and contrary to the formation of energy, it does not get oxidized as that would typically occur in the Krebs cycle during aerobic respiration.