Explain carbon cycle.

Hint: The nutrients move from soil to organism and then back to the soil showing recycling. The nutrient elements move through the various components of an ecosystem called nutrient cycling or biogeochemical cycles. Nutrient cycles are of two kinds : (i) gaseous and (ii) sedimentary.

Complete answer:
1.In living organisms, carbon constitutes 49% of dry weight of organisms and is next only to water.
2.The global quantity of carbon is 71 % which is found dissolved in oceans.
3.The oceanic reservoir regulates the amount of CO2 in the atmosphere.
4.The carbon is found in the abiotic environment in various forms like carbon dioxide, carbonates, bicarbonates, coal, petroleum and natural gas.
5.About 60 billion (60 x10') metric tons of carbon is annually assimilated or converted into 150 billion tons of organic matter through the process of photosynthesis.
6.The organic carbon passes as food inside the biosphere through food chains.
7.Even though large quantity of inorganic carbon is withdrawn from the abiotic environment for photosynthesis, the atmosphere and hydrosphere do not get depleted of their carbon content because of its return through the following:

a.Respiration of living organisms,
b.Decomposition of organic matter,
c.Burning of fossil fuels,
d.Volcanic eruptions and hot springs,
e.Weathering of rocks.

The carbon cycle is disturbed by the deforestation activity of men as the $CO_{2}$ is mainly used by green plants in photosynthesis.
If the concentration of $CO$ is relatively much more than the normal concentration, it acts as a pollutant causing greenhouse effect.

Note: Nutrient cycles are of two types : (a) gaseous and (b) sedimentary. The reservoir of gaseous type of nutrient cycle (e.g., carbon cycle, nitrogen cycle) exists in the atmosphere and for the sedimentary cycle (e.g., sulphur and phosphorus cycles), the reservoir is located in earth's crust.