As you have read earlier, oxygen (O2) is utilised by the organisms to indirectly break down nutrient molecules like glucose and to derive energy for performing various activities.
Carbon dioxide (CO2) which is harmful is also released during the above catabolic reactions.
It is, therefore, evident that O2 has to be continuously provided to the cells and CO2 produced by the cells have to be released out.
This process of exchange of O2 from the atmosphere with CO2 produced by the cells is called breathing, commonly known as respiration. Place your hands on your chest; you can feel the chest moving up and down. You know that it is due to breathing. How do we breathe?
The respiratory organs and the mechanism of breathing are described in the following sections of this chapter.