Sorry I did not respond to Michael's question, but fermentation is way different that cellular respiration. It occurs when oxygen is not available, because oxygen is the final electron acceptor, at the end of the electron transport chain proteins in the cristae. So, after glycolysis occurs in the cytoplasm (giving 2 ATP), the cell takes the 2 new pyruvate and breaks them down into 2 lactate, coupled with NADH turning into NAD+, which can be used for glycolysis again. This form of fermentation happens in most cells, like muscle cells, but in yeast cells, the pyruvate is turned into ethyl alcohol and carbond dioxide.