Explain the mechanism of breathing with | Class 11 Biology Chapter Breathing and Exchange of Gasses, Breathing and Exchange of Gasses NCERT Solutions

Breathing is brought about by alternate expansion and contraction of the thoracic cavity wherein the lungs lie. This leads to the intake of fresh air called inspiration (inhalation, breathing in) and elimination of the foul or contaminated air is called expiration (exhalation, breathing out). These both inspiration and expiration together referred as respiratory movements.

Inspiration: It is an active process which is brought about by diaphragm muscles and external intercostal muscles which are referred as Inspiratory muscles. Movement of the diaphragm and the thorax is shown in the diagram.  

Expiration: It is normally a passive process as it simply involves relaxation of the inspiratory muscles, peripheral muscles of diaphragm and external intercostal muscles. Movement of the diaphragm and the thorax is shown in the diagram.