Oxygen is the second most abundant element in the earth’s atmosphere by volume after nitrogen. Oxygen forms about 21 percent of the atmospheric gases. It is an essential element for the building up of living organisms and its life processes such as respiration.
The Oxygen Reservoirs Are:
- Atmosphere –In terms of volume, 21 percent of Oxygen is present as free oxygen molecules, ozone, carbon dioxide, sulfur, water vapor, and nitrogen oxides.
- Biosphere – Oxygen is present at about 22 percent by volume as a compound of organic molecules and water molecules.
- Hydrosphere – Oxygen is present at about 33 percent by volume as a component of water molecules, free oxygen, and carbonic acids.
- Lithosphere– Oxygen is present at about 94 percent by volume mainly as silica minerals.
Oxygen cycle – The main steps of the oxygen cycle in nature are as given below:
- The living organisms like plants, animals, and decomposers take oxygen from the atmosphere or from water and utilize it for respiration. During respiration, oxygen is converted into carbon dioxide and water. The decay or decomposition of dead organisms like plants and animals by bacteria and fungi also utilize oxygen from the atmosphere and produces carbon dioxide and water. This carbon and water go into the surrounding atmosphere.
- The combustion of fuels such as wood, coal, natural gas, and petroleum in homes, transport, and industries also removes oxygen from the atmosphere for the combustion process. In this process carbon dioxide and water are produced and go to the surrounding atmosphere. Thus the plants, animals, decomposers, and fuels remove oxygen from the atmosphere and return carbon dioxide and water vapor to the atmosphere.
- The carbon dioxide and water vapor are produced during the respiration of living organisms, the decay of dead organisms and combustion of fuels are utilized by the green plants in the presence of sunlight and chlorophyll to prepare carbohydrates by photosynthesis. During the process of photosynthesis, oxygen is released to the atmosphere. In this way, the oxygen cycle in nature is completed.