Respiration is defined as the metabolic process wherein the living cells of an organism obtains energy. Three stages occur in the entire process of respiration.
1. Breathing
2. Exchange of gasses
3. Cellular respiration
Breathing is the physical process of inhaling oxygen and exhaling carbon dioxide.
During exchange of gases, oxygen passes from the blood to tissue fluid and carbon dioxide from tissue fluid into the blood. It occurs primarily through the process of diffusion.
Cellular respiration is a set of metabolic reactions occurring inside the cells to convert biochemical energy obtained from the food into ATP.