Oxygen Cycle

Oxygen Cycle

We all know how important oxygen is for our sustenance, it is present in the air we breathe and the water we drink. With oxygen taking up 20.95% of dry air, it is the second most abundant gas on our planet.

What is Oxygen Cycle?

The oxygen cycle portrays how the flow of oxygen occurs through the several parts of our vast ecosystem. Oxygen is found in several parts of the ecosystem, from the air we breathe (Atmosphere), the water bodies on the planet (Hydrosphere), inside all the biological beings (Biosphere) and inside the earth’s crust (Lithosphere).

Oxygen Cycle


The biogeochemical cycle that describes the movement of oxygen in the atmosphere (air), the biological matter of the ecosystem biosphere (the global sum of all ecosystems) and the lithosphere (earth’s crust).

Oxygen Cycle Steps:

  • Atmosphere:
    Only a small percentage of the world’s oxygen is present in the atmosphere, only about 0.35 %. This exchange of gaseous oxygen happens through Photolysis.

    • Photolysis: This is the process by which molecules like atmospheric water and nitrous oxide are broken down by the ultraviolet radiation coming from the sun and release free oxygen.
  • Biosphere:
    The exchange of oxygen between the living beings on the planet, between the animal kingdom and the plant kingdom. The exchange of oxygen in the biosphere is codependent on the Carbon cycle and hydrogen cycle as well. It mainly occurs through 2 processes.

    • Photosynthesis:
      The process by which plants make energy by taking in carbon dioxide from the atmosphere and give out oxygen
    • Respiration:
      The process by which animals and humans take in oxygen from the atmosphere and use it to break down carbohydrates and give out carbon dioxide.
  • Lithosphere:
    The part of the planet containing the most of the oxygen content through biomass, organic content and mineral deposits. These deposits are formed when free radical elements were exposed to free oxygen and over time they form silicates and oxides. This trapped oxygen is released back due to several weathering processes. Also, animals and plants draw nutrient materials from the from the lithosphere and free some of the trapped oxygen.
  • Hydrosphere:
    Oxygen dissolved in water is responsible for the sustenance of the aquatic ecosystem present beneath the surface. The hydrosphere is 33% oxygen by volume present mainly as a component of water molecules with dissolved molecules including carbonic acids and free oxygen.
Oxygen Cycle

Co-dependence of Carbon Cycle, Hydrogen Cycle & Oxygen Cycle

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Practise This Question

Elemental oxygen is poisonous to which group of organisms?