Cellular respiration is divided into two categories: aerobic and anaerobic respiration. Aerobic requires oxygen; anaerobic does not. These energy-producing biochemical processes serve different functions. Anaerobic respiration provides energy quickly when it is needed on short notice for short periods of time. Aerobic respiration provides energy evenly to provide a constant source of energy. Despite these significant differences, they nevertheless have some important features in common.
When cells transfer chemical energy from a fuel source such as glucose to molecules of adenosine triphosphate, the cells are conducting a basic metabolic process called cellular respiration. The ATP produced as a result of this biochemical process is tapped by the cell for energy when needed. The energy is released when ATP loses a phosphate group to become adenosine diphosphate.
Glucose and oxygen interact to release energy with carbon dioxide and water as byproducts. It is so efficient that 38 molecules of ATP may be produced per glucose molecule. The chemical stages of aerobic respiration occur in 1. the cytosol: glycolysis, and 2. the mitochondria: the Krebs Cycle -- in which pyruvate serves as one substrate in the pathway -- and electron transport. Aerobic respiration provides energy for prolonged, less intense workouts when the body is able to take in and deliver enough oxygen to cells to support this more efficient means of generating ATP.
In the absence of oxygen, glycolysis takes place during anaerobic respiration as it does during aerobic respiration. The next stages, however, differ significantly, and no more ATP beyond the two molecules produced during glycolysis is generated. In humans and other animals, pyruvate is then converted in the cytosol into lactic acid and water. A byproduct of anaerobic respiration, lactic acid, contributes to muscle fatigue and discomfort. When you pant or “catch your breath” after exercising, your body is trying to take in enough oxygen to reestablish a chemical state capable of cleaning up unwanted byproducts such as lactic acid that build up when oxygen is in short supply.
Both aerobic and anaerobic respirations are types of cellular respiration. It is clear both use glycolysis to produce ATP. Both generate energy by breaking down glucose, produce byproducts and depend on chemical reactions that are localized in the cytosol. Both use pyruvate as a substrate, and of course, both processes depend on enzymes to catalyze their respective chemical reactions.
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