The % of oxygen in air is 21%.
• The cyclic process by which oxygen element is circulated continuously through the living and non-living components of the biosphere constitutes oxygen cycle.
• Human beings and animals take oxygen from the atmosphere during the process of respiration.
The decomposition of dead organisms also takes in oxygen from the atmosphere.
Respiration and decay of dead organisms release CO2 and water.
• The carbon dioxide and water are used by the green plants during the process of photosynthesis.
• They give out oxygen during this process. This oxygen is again used by human beings and animals.
Thus, the oxygen cycle keeps repeating in nature.
