Fermentation is an anaerobic
process that occurs in the cytoplasm of cells. In fermentation reactions,
pyruvic acid produced by glycolysis either serves as a final electron and
hydrogen acceptor from NAD forming lactic acid
(lactic acid fermentation), or is decarboxylated with the resulting acetaldehyde
to form alcohol (alcoholic fermentation).
Other products can be produced depending upon the species,
but all generate a net gain of only the two ATP molecules
formed during glycolysis.