**2. Physiological need for oxygen**

The requirement for oxygen is as important as a cell's need for biochemical energy, without which no cellular or biochemical process can occur. Of the various biochemical mediums for energy, ATP is the most crucial due to the inherently high energy stored within the bonds between phosphate groups. Additionally, these bonds are readily and quickly broken to yield energy stored due to their unstable nature [1]. While ATP can be produced by processes such as glycolysis and the Krebs cycle, the amount produced by oxidative phosphorylation during the reactions within the electron transport chain, an oxygen-dependent mechanism, is vastly greater than that which the other two processes can produce. Anaerobic metabolism is an important means by which tissues can continue to produce ATP in oxygen deprived states; however it does not yield enough energy to support the functional requirements of most tissues. Therefore, the need for adequate oxygenation and delivery of oxygen to tissues across the body is essential for normal physiology.
