Why is lactic acid fermentation useful in living organisms?
Lactic acid fermentation is useful in anaerobic bacteria because they can convert glucose to two ATP molecules, which is the "energy currency"cells use to carry out their life processes. The waste product of fermentation is lactic acid. This is the substance that can turn milk into cheese or yogurt by bacterial action, or to turn cabbage into sauerkraut. A benefit of this process is the various food industries that rely on "aged" foods that are produced via fermentation. In humans and other animals, the muscles store excess glucose as glycogen until needed. During very strenuous activity, if aerobic respiration, which supplies 36 molecules of ATP for every glucose oxidized, cannot keep up, the stored glycogen in the muscles is converted back to glucose and fermentation occurs in the muscles. Although this process produces only 2 ATP per glucose, it supplies extra energy to muscles. However, the waste lactic acid can build up in the muscles, causing cramps. Therefore, it is important to not stop directly after exercising, rather, it is better to do a cool down or a walk, to give the lactic acid time to be transported to the liver where it is converted to pyruvate.
Lactic acid fermentation is a process used by organisms to extract energy from glucose in conditions where either the amount of oxygen available is severely restricted or when the organisms are unable to survive in an oxygen rich environment.
The glycolysis process of lactic acid fermentation produces lactate as a waste product and releases energy in the form of two molecules of NADH. Compared to aerobic respiration where 34 - 38 molecules of NADH are released, lactic acid fermentation is a very inefficient method of extracting energy. In muscular tissue it is only used to release energy for short durations of heavy exercise. When there is a drop in the load the lactic acid produced is converted to other molecules to complete the respiration process.