Our body also requires energy for performing various functions. This energy mainly comes from carbohydrates and fats that we take as food. Carbohydrates are decomposed into glucose or its derivatives in the stomach. Glucose is soluble in blood. It is transported by the blood cells to various parts of the body where it reacts with oxygen in a series of steps producing carbon dioxide (CO2), water (H2O) and energy.
C6H12O6 +6O2 ------------6CO2 +6H2O +Energy
This process is very much similar to the process of burning. However, this process takes place inside our body quite slowly and at the much lower temperature. This slow combustion of food material takes place at the body temperature because of the catalytic action of enzymes. This slow combustion of food in the cells resulting in the release of energy is called respiration. Carbon dioxide and water, which are formed during respiration, are expelled through various organs of the body. The energy released in respiration fulfils the energy needs of the body.
Although respiration is similar to combustion in respect of the products formed and the energy released yet it differs from it in many respects.