(i) The respiration which needs oxygen or occurs in the presence of oxygen is called aerobic respiration. During this type of respiration, glucose is broken down into carbon dioxide and water with the release of considerable amount of energy. The energy is stored in the form of ATP.
It consists of two steps:
(a) Glycolysis: The conversion of glucose into pyruvate (or pyruvic acid) is called glycolysis. It occurs in the cytoplasm.
(b) Kreb's Cycle: It is the process of converting pyruvate into CO2 and H2O along with the release of considerable amount of energy. It occurs in the mitochondria. One molecule of glucose liberates 38 ATP of energy during aerobic respiration.
(ii)The respiration which takes place in the absence of oxygen is called anaerobic respiration. During this respiration glucose is broken down into ethyl alcohol and CO2 with the release of very small amount of energy. In anaerobic respiration, one molecule of oxygen produces only 2 ATP of energy. This type of respiration occurs in microscopic organisms like yeast, etc.
In human beings, the energy is obtained by aerobic respiration but sometimes anaerobic respiration occurs in muscles during vigorous exercise when oxygen gets consumed faster than its supply by the blood. During the anaerobic respiration in the muscles the glucose is converted into lactic acid with the release of 2 ATP of energy.
Anaerobic respiration in human beings:
