The oxygen cycle components

A major component of the oxygen cycle is the interaction between plant and animal life and the atmosphere. Most of the oxygen of the atmosphere comes from the photosynthesis of plants. In fact all living things require oxygen. During the very important process of photosynthesis plants use the energy from the sun to combine water and carbon dioxide from the air to make sugar. As part of this process oxygen is produced which transfers into the air:

Sunlight energy + 6 CO₂ + H₂O => C₆H₁₂O₆ + 6O₂Thus plants pass back oxygen to the atmosphere as part of their process of growth. If there were no photosynthesis, then oxygen stocks in the atmosphere would decrease and be depleted within a few thousand years. Water-based plants, such as phytoplankton, also photosynthesise and thus pass oxygen back to the atmosphere.

In the case of animals and man, the process goes in the other direction.

C₆H₁₂O₆ (organic matter) + 6O₂ => 6CO₂ + 6H₂O + energyThere is intake of oxygen from the atmosphere to create energy by the process of respiration. Humans and animals breathe in air containing oxygen. Oxygen can also be dissolved where there is contact between the atmosphere and the various moving water bodies such as oceans and rivers. The dissolved oxygen supports aquatic life. Like the land-based animals, marine and freshwater organisms respire thus giving out oxygen. The two processes, photosynthesis by which plants return oxygen to the atmosphere, and respiration by animals in which oxygen is taken in from the atmosphere, are the major parts of the oxygen cycle.

Other significant components of the oxygen cycle include losses from the atmosphere, due to the combustion of fossil fuel, microbial oxidation, and small amounts from fixation by lightning and by oxidation of volcanic gases.