There are many chemical equations for anaerobic fermentative reactions.
Anaerobic animals mostly use the lactic acid fermentation pathway:
Plants and fungi (e. g. yeasts) generally use alcohol (ethanol) fermentation when oxygen becomes limiting:
kJ per mol, which is conserved in regenerating two ATP from ADP per glucose.
Anaerobic bacteria and archaea use these and many other fermenative pathways, e. g. propionic acid fermentation, butyric acid fermentation, solvent fermentation, mixed acid fermentation, butanediol fermentation, Stickland fermentation, acetogenesis or methanogenesis.
Some anaerobic bacteria produce toxins (e. g. tetanus or botulinum toxins) that are highly dangerous to higher organisms, including humans.
See also: Aerobic organism, Fermentation