Explain with reasons.

Upward and downward movement of diaphragm occurs consecutively.

Diaphragm is a muscular partition which is present between the thoracic cavity and abdominal cavity. During the process of breathing, the upward and downward movement of diaphragm occurs simultaneously.

A. Inspiration / Inhalation: Air is taken in through nose and sent towards the lungs through trachea (wind pipe). When we inhale, the ribs rise up while the diaphragm lowers down simultaneously causing a decrease in pressure on lungs. This results in the moving of air into lungs through nose.

B. Expiration / Exhalation: Oxygen from the inspired air goes into blood. Blood carries the CO₂ from various parts of body towards lungs. This air is given out by exhalation. As the ribs return to their original position, diaphragm rises up leading to the increase in pressure inside the lungs. This results in moving of the air outside the nose.