Define breathing. Explain the mechanism of breathing in human beings.

Explanation

A physical process by which oxygen is taken in and carbon dioxide is given out is called breathing.
Breathing in humans involves three steps :
(i) Inspiration : When we breathe in, ribs move up and flatten the diaphram due to which the chest cavity becomes larger. As a result air is sucked into the lungs and fills the expanded alveoli.
(ii) Gaseous exchange : Haemoglobin binds with the oxygen and carries it along the blood in the body. As blood passes through the tissues of the body, oxygen from the blood diffuses into the cell, whereas carbon dioxide which is produced during respiration diffuses into the blood and is carried to the lungs for expiration.
(iii) Expiration : Ribs move down and diaphragm becomes domw - shaped decreasing the chest cavity. Thus, pushing the air out from lungs.