NCERT Solutions for Class 11 Biology Chapter 17 Breathing and Exchange of Gases

The process of exchange of O2 from the atmosphere with CO2 produced by the cell is called breathing. It occurs in two stages of inspiration and expiration. During inspiration, air enters the lungs from the atmosphere and during expiration air leaves the lungs. Oxygen is utilised by the organisms to indirectly break down simple molecules like glucose, amino acids, fatty acids, etc., to derive energy to perform various activities. Carbon dioxide, which is harmful, is also released during the above catabolic reactions. It is, therefore, evident that oxygen has to be continuously provided to the cells and carbon dioxide produced by the cells have to be released out. This process of exchange of oxygen from the atmosphere with carbon dioxide produced by the cells is termed as breathing. It is also known as respiration.