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Fermentation is a chemical reaction that takes place in the cytoplasm and occurs when oxygen is low or absent. Byproducts of fermentation may include lactic acid or ethanol. Fermentation yields less ATP than the electron transport chain.

Explanation:

Fermentation is a chemical reaction that occurs under anaerobic or low-oxygen condition whereby the NADH produced during glycolysis is oxidized to NAD⁺ with the production of lactic acid as well as other products such as ethanol.

Since oxygen is lacking, pyruvate and NADH produced in glycolysis cannot be oxidized. In order to produce energy in the form of ATP for the cells and tissues,the NAD⁺ is regenerated from NADH by the reduction of pyruvate to lactic acid by the enzyme lactate dehydrogenase. In some other organisms such as yeast and microorganisms, pyruvate is converted to ethanol and carbon dioxide.

The  net production of ATP in fermentation process is 2 molecules of ATp much lesser than that produced in aerobic respiration.