What type of cellular respiration occurs in the absence of oxygen?

The type of cellular respiration that occurs in the absence of oxygen is fermentation. This process allows organisms to produce energy when oxygen is not available. Fermentation occurs in the cytoplasm of cells and begins with glycolysis, where glucose is partially broken down to produce a small amount of ATP. The end products of fermentation can vary depending on the organism and the type of fermentation. For example, in yeast, the end products include ethanol and carbon dioxide, while in certain bacteria and animal cells (like muscle cells under strenuous activity), lactic acid is produced.

In contrast, aerobic respiration requires oxygen and is typically more efficient, allowing for greater ATP yield from glucose than fermentation. Oxidative phosphorylation is a specific stage within aerobic respiration that occurs in the presence of oxygen, making it irrelevant in anaerobic conditions. Thus, fermentation is the correct answer as it specifically describes a metabolic pathway that sustains energy production in the absence of oxygen.