Oxygen cycle:

Oxygen cycle:

• Oxygen is an essential component of all biomolecules. It is also required as such by all organisms that respire aerobically.
• It is found in the elemental form is the atmosphere to the extent of 21%.it also occurs in combines forms as carbon dioxide, water and it the earth’s crust as oxides of metals, carbonates, sulphate etc.
• Oxygen from the atmosphere is used up in 3 processes namely combustion, respiration and in the formation of oxides of nitrogen.
• It return to the atmosphere by only one major process called photosynthesis.