Oxygen forms 21% of the atmosphere.
It is also present in the hydrosphere and lithosphere.
Circulation and recycling of oxygen within the biosphere is called the oxygen cycle.
This cycle, includes both the biotic and abiotic components.
Oxygen is continuously produced as well as used up in the atmosphere.
Oxygen is highly reactive and it readily reacts with other elements and compounds.
As oxygen is found in various forms like molecular oxygen (Oz), water (H,0), carbon dioxide (C02), inorganic compounds etc, the oxygen cycle of the biosphere is extremely complex.
Oxygen is released in the process of photosynthesis, whereas it is used up in processes like respiration, combustion, decomposition, corrosion, rusting, etc.
