(N/A) The process of breathing in humans involves two main phases: inhalation and exhalation.
$1.$ Inhalation: The diaphragm contracts and moves downward,and the rib muscles contract,lifting the ribs upward and outward. This increases the volume of the thoracic cavity,decreasing the air pressure inside the lungs. Consequently,air from the atmosphere rushes into the lungs through the respiratory tract.
$2.$ Exhalation: The diaphragm relaxes and moves upward,and the rib muscles relax,causing the ribs to move downward and inward. This decreases the volume of the thoracic cavity,increasing the air pressure inside the lungs. Consequently,air is pushed out of the lungs into the atmosphere.
$3.$ Gaseous Exchange: This occurs in the alveoli. Oxygen from the inhaled air diffuses into the blood,while carbon dioxide from the blood diffuses into the alveoli to be exhaled.