Anaerobic environment: Few structures of organisms can survive exclusively in the deficiency of oxygen (an aerobically). For Examples anaerobic organisms are found in microbes of the genus Clostridium, in parasitic protozoan-™s from the gastrointestinal tract of humans and additional vertebrates, and in ciliates connected with sulfide-containing sediments.

Organisms able of switching between aerobic and anaerobic existence are found in forms of fungi recognized as yeasts. The ability of an organism to function both in aerobic and anaerobic environment amplify the variety of sites in which it is able to exist and transmit some advantages over organisms with fewer adaptive prospective.