Question

Define breathing .explain the mechanism of breathing in human being

Answer 1

The act of respiring; inhalation and exhalation of air; breathing. 2. Biology. the sum total of the physical and chemical processes in an organism by which oxygen is conveyed to tissues and cells, and the oxidation products, carbon dioxide and water, are given off.
When you breathe in, the intercostal muscles contract and the ribcage moves up and out. The diaphragm moves down, so the volume increases, meaning the pressure decreases, drawing air into the lungs. (vice versa for breathing out)

Answer 2

the process of taking air into and expelling it from the lungs is called breathing.
The action of breathing in and out is due to changes of pressure within the thorax, in comparison with the outside. This action is also known as external respiration. When we inhale the inter costal muscles (between the ribs) and diaphragm contract to expand the chest cavity.