Anaerobic cellular respiration generates ATP when insufficient oxygen is available for aerobic respiration.

Anaerobic respiration takes place after glycolysis. This process differs among species, and in mammals it is called lactic acid fermentation. Lactic acid fermentation does not need oxygen to proceed, although it can occur in its presence. During lactic acid fermentation, pyruvate is converted into lactic acid and the NADH produced during glycolysis is recycled. The net release of energy comes from glycolysis in the form of 2 ATP molecules.

Diagram of the steps in anaerobic cellular respiration. First, glucose undergoes glycolysis to produce 2 molecules of pyruvate. During this step, 2 NAD are reduced to 2 NADH, and a total of 2 ATP are produced. The 2 pyruvate then go through lactic acid fermentation, which produces 2 lactic acid molecules. During this process, 2 NADH are oxidised to 2 NA Dplus.

Overview of anaerobic cellular respiration in mammals.