The breathing or ventilation in humans takes place through the organs called lungs. The taking in of air rich in oxygen into the body during breathing is called 'inhalation' and giving out (or expelling) the air rich in carbon di-oxide is called 'exhalation'. Both, inhalation and exhalation take place regularly during breathing.

Respiration is the biological process in which glucose is broken down inside the cell to produce energy. Depending upon the availability of oxygen, there are two different types of respiration, and they are anaerobic and aerobic respiration.

The taking in of air rich in oxygen into the body during breathing is called 'inhalation'. When we breathe in, then two things happen at the same time: (i) the muscles between the ribs contract causing the rib cage to move upward and outward, and (ii) the diaphragm contracts and moves downward. The upward and outward movement of rib cage, as well as the downward movement of diaphragm, both increase the space in the chest cavity and make it larger. As the chest cavity becomes larger, air is sucked in from outside into the lungs. The lungs get filled up with air and expand.