3. Photosynthetic organisms produce about 300 x 1015 g of oxygen per year (Holland 1995. If this oxygen accumulated, the oxygen content of the atmosphere would double every 2000 years. Why does this not happen? Is the global system regulated? If so, how is this regulation accomplished? Solution Oxygen is considered as one of the most important gas in the atmosphere .it would have been impossible to imagine life without this gas. The contribution of oxygen to the atmosphere is mainly due to the photosynthetic activity of the plants apart from this the splitting of the hydrogen atoms from water vapor in the atmosphere due to photolysis also contributes to oxygen of the atmosphere to a negligible amount.the oxygen is left behind and the hydrogen escapes. The major contributor of atmospheric oxygen is the photosynthetic activity of the plants but this does not accumulate in the atmosphere as most of it is immediately used up by the respiration process. the maintenance of oxygen levels is one of the classic example of homeostasis . Of the amount of oxygen produced though all of it is immediately used in the respiratory process The net gain of oxygen comes from the burial of organic matter (plant and animal matter ) which reacts with the reducing substances of the earth like iron and is locked as the solid oxides over time. Eventually it would be all used up and equilibrium atmosphere would not contain more oxygen. The continuous photosynthesis and carbon burial keeps the level of oxygen as high as it is and thus homeostasis is maintained ,Where plant photosynthesis acts as the the pump and the rate of burial is equivqlent of the aperture between the reservoir halves..