Fermentation
If there is no oxygen, then an organism must find a new electron acceptor. This
can occur through Fermentation. A common form of fermentation is
converting sugar to ethanol or acid. This reaction, however, is not as
efficient as oxidation. Only a fraction of the organic carbon is oxidized to CO2
(the rest remains in the alcohol/acid by-product):
2) What are some examples of fermentation that result in alcohol (ethanol) or acid (acetic or lactic acid)?
Heterotrophs
(different-feeding) are organisms that obtain their
carbon from previously produced organic molecules. All animals, fungi, and many
bacteria are heterotrophs.
3) Where does this organic carbon ultimately come from?
Autotrophs
(self-feeding) obtain their carbon from inorganic CO2.