Sometimes cells need to obtain energy from sugar, but there is no oxygen present to complete cellular respiration. In this situation, cellular respiration can be anaerobic, occurring in the absence of oxygen called Fermentation.
Yeast (single-celled eukaryotic organisms) perform alcoholic fermentation in the absence of oxygen. The products of alcoholic fermentation are ethyl alcohol (drinking alcohol) and carbon dioxide gas. This process is used to make common food and drinks.
Animals and some bacteria and fungi carry out lactic acid fermentation. Lactic acid is a waste product of this process.
Fermentation happens in the absence of oxygen.
Only the two ATP from glycolysis are produced under anaerobic conditions.
Alcoholic fermentation and lactic acid fermentation are the two types of fermentation.