The mechanism of biodegradation of both yeast and mold is the same; i.e., the use of enzymes to convert organic matter into energy. Both molds and yeasts are heterotrophs, just like any other type of fungus. However, they work in different environmental conditions. Molds require humidity or dampness and degrade even tough biopolymers like wood and paper. Yeasts, on the other hand, are seen growing on surfaces of living organisms like the outer layer of certain fruits and skins of certain animals; therefore, even if the layer is tough, there is an internal source of water.