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The Oxygen Cycle

Oxygen is present in the atmosphere as a gas and constitutes about 21% of the atmosphere. Also molecular oxygen - O2, is dissolved to a small extent in water. The freely available oxygen in air and water makes it possible for terrestrial and aquatic life to continue. Oxygen is also available in the form of a large variety of oxide compounds. Two familiar examples are H2O and CO2.




Besides these, oxides of iron, sulphur, and nitrogen are abundantly present in nature. Withdrawal of oxygen from the atmosphere is primarily through respiration and combustion of wood, coal, etc. Oxygen is returned to the atmosphere by photosynthesis. Photosynthesis and respiration are among the important balancing mechanisms in nature. They are interdependent and together make the biosphere self-supporting with respect to two important resources i.e. oxygen and carbon dioxide.



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