In cellular respiration, the final electron acceptor is oxygen. During fermentation, energy stored in pyruvate is unavailable to the cell. Cellular respiration yields 18 times more ATP per glucose molecule than does fermentation. The higher energy yield is a consequence of the Krebs cycle which completes the oxidation of glucose and thus taps the chemical bond energy still stored in pyruvate at the end of glycolysis. Fermentation does not require oxygen.
Cellular respiration occurs only in the presence of oxygen.
Organisms can be classified based upon the effect oxygen has on growth and metabolism. Organisms that require oxygen for growth and as the final electron acceptor for aerobic respiration. Microorganisms that only grow in the absence oxygen and are, in fact, poisoned by it. Yeasts, many bacteria, and mammalian muscle cells are facultative anaerobes. Can make ATP by fermentation in the absence of oxygen or by respiration in the presence of oxygen.