The process of oxidation of food into carbon dioxide and water to produce energy is called respiration. On the basis of presence of oxygen respiration is of two types :
(a)     Aerobic respiration : When break-down of glucose occurs with the use of O2 , it is called aerobic respiration. In this process there is complete breakdown of food, so maximum production of energy.



(b)     Anaerobic respiration : When breakdown of glucose occurs in lack or limited supply of O2 is called anaerobic respiration.

During heavy exercise, when the supply of oxygen to our muscle cell is insufficient, food breakdown occurs by anaerobic respiration.

       There are two types of respiration – aerobic and anaerobic respiration.
1.    Aerobic Respiration :     When the breakdown of food substances (like glucose) takes place in the presence of oxygen with the release of a large amount of energy, it is called aerobic respiration. In this process, carbon dioxide and water are released          as waste products.
     The overall equation for aerobic respiration is:

Most animals including humans and green plants respire aerobically.

2.    Anaerobic Respiration : Anaerobic respiration is the breakdown of food substances with the release of a small amount of energy in the absence of oxygen. It occurs in certain organisms like yeast and some bacteria. These organisms are called                    anaerobes.

     In th absence of oxygen, glucose breaks down into alcohol and carbon dioxide with the release of comparatively less energy.
    The equation for anaerobic respiration is: