We know that oxygen is utilised by organisms to indirectly break down
nutrient molecules like glucose and to derive energy for performing
various activities. Carbon dioxide ,which is harmful is also released
during the abov catabolic reactions. It is evident that oxygen has to
continuously provided to the cells and carbondioxide 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 or
Respiration.
