Breathing

Breathing is the act of moving air in and out of the lungs. The first step is inhalation - bringing air into the lungs. Inhalation is accomplished by flexing the diaphragm with assistance from other muscles. Exhalation is expelling air from the lungs, which is done by relaxing the diaphragm.

Breathing is necessary for several reasons: exchanging gasses, water, and heat, and for speaking or singing.

Gas exchange
The primary function of breathing is to bring oxygen gas into the body and expel carbon dioxide.