Explain the Oxygen Cycle of biosphere

The oxygen is very essential component for survival. It forms many organic compounds. It is required by the organisms that respire aerobically. It can occur in the form of gas or in combined form. The gaseous form constitutes 20 percent of the total content. In the combined form it occurs as a carbon dioxide and water. The requirement of organisms for oxygen is met from the atmosphere. The aquatic animals meet their requirement of oxygen from the water where the oxygen is present in the diffused form. Some of them may come to the surface to obtain oxygen. The process of respiration involves the oxidation in which carbon dioxide and water is formed. The burning of fossil fuels lead to the emission of number of gases like the carbon dioxide, sulphur dioxide etc. The oxides can be reduced chemically as well as biologically. They release oxygen. Main process which is concerned with the liberation of oxygen is photosynthesis. The photolysis breaks the water. So, the oxygen content of the atmosphere has remained static for long decades. In the early time when the earth evolved the oxygen was present in the combined form.