What is the fate of pyruvate when oxygen is absent?

When oxygen is absent, pyruvate undergoes anaerobic fermentation to regenerate NAD+ for glycolysis to continue. In muscle cells, pyruvate is converted into lactate through lactic acid fermentation. In yeast and some bacteria, pyruvate is converted into ethanol and carbon dioxide via alcoholic fermentation. These anaerobic pathways allow for continued ATP production through glycolysis in the absence of oxygen, although less ATP is produced compared to aerobic respiration.