class 7 science textbook NCERT question what is breathing
Breathing consist of inhalation and exhalation. Inhalation means taking air in, to get oxygen and exhalation means expelling air out to release carbon dioxide. A breathe means one inhalation and one exhalation. It involves the movement of ribcage and diaphragm. Diaphragm is made up of muscles which form the floor of chest cavity, where lungs are situated.
Steps of breathing mechanism in humans:
i) Inhalation: During inhalation rib cage moves up and out and, diaphragm contracts and move down. This leads to increase in space of chest cavity and decrease in pressure of lungs. Then air goes into lung to fill the space with air.
ii) Exhalation: This is the reverse of inhalation. Rib cage moves down and inwards, whereas diaphragm relaxes and moves up. This reduces the size of chest cavity and increase in pressure, so air is pushed out of the lungs.