Breathing

Breathing is a physiological process of gas exchange that is remains one of the primary qualifiers that describe a living organism.

While observing the giant space amoeba discovered in 2268, Doctor Leonard McCoy described it as a very simple form of life capable of displaying almost all the functions living organisms perform, including the ability to breathe, eat and reproduce. 

For most humanoids breathing involves the intake of oxygen (respiration) and the exhale of carbon dioxide, to and from the lungs. The inability to breathe is known as suffocation. The predecessors of the Aquans, known to their descendants as 'air-breathers' developed technology, a surgo-op process, that allowed their species to mutate into 'water-breathers'. 

Not all humanoids breathe the same, for example:
 * The Axanar breathe nitrogen-methane.
 * Benzites wore a respiration device in order to breathe in an oxygen-nitrogen environment.
 * Lorillians, prior to the age of four, were only able to breathe methyl oxide.
 * Yalosians breathe a corrosive mixture of 60% nitrogen, 10% benzene, and 30% hydrogen fluoride.
 * Zaranites breathe fluorine and cannot survive in oxygen, requiring them to wear breathing masks in class M environments.