Biogeochemical cycles are repeated circulation of biogeochemical (water, nitrogen, oxygen etc) between abiotic and biotic components of the environment which result in their repeated withdrawal and replacement of their pool.
Water is an essential and a principle component of living beings and also vita for life processes. It forms 60% to 90% of self contained.
The whole process in which water evaporates and falls on the land as rain and later flows back into the sea by a river is known as water cycle.
All of the water that falls on the land does not immediately flows back into the sea. Some of it seeps into the soil and become part of the underground reservoir of fresh water.
Some of these underground water finds its way to the surface through springs or we bring it to the surface for our use through wells and tube wells.
Rain may fall directly into the ocean, some water flows into the river and return to the sea.
Water is also used by terrestrial animals and plants for various life processes.
Plants add water to the air as water vapors by transpiration. Animals return water to the air as vapors by respiration or to the soil as fluid by excretion.
So, there is a constant exchange of water between air, land, sea and between living organisms and their environment.
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.