Breathing is the process by which organisms takes oxygen from the air and releases carbon dioxide. It is a simple process which is controlled by the diaphragm and the intercostal muscles. Breathing in human has two phases- Inhalation and exhalation.

During inhalation, the diaphragm contracts and flattened and the intercostal muscles contracts to pull the ribs up and out. Thus, the lungs expand and air is inhaled.

During exhalation, diaphragm relaxes and moves up, the lungs contract and air is exhaled.