Carbon Cycle

Carbon is required for the building of all
organic compounds. Carbon in the form of
carbon dioxide (CO2) is obtained from the atmosphere and transformed into a usable
organic form by organisms. The reservoirs for
the carbon cycle are the atmosphere, where
carbon dioxide exists as a free gas, fossil organic
deposits (such as oil and coal), and durable
organic materials like cellulose. Mineral
carbonates, such as limestone, are a significant
geological sink for carbon. During the process
of carbon fixation, carbon dioxide is taken up
from the atmospheric reservoir (or from biocarbonates
dissolved in water) by plants,
photosynthetic bacteria, and algae and is “fixed”
into organic substances. Animals obtain their
requirements for carbon (as carbon-based
molecules) by eating plants or other animals. For
the biological links, the carbon cycle comes full
cycle when carbon is released by either plants
or animals as they respire or after life as they
decompose. Organisms respire carbon dioxide
as a waste product from the breakdown of
organic molecules as their cells derive energy
from oxidizing the molecules containing “fixed”
carbon. The burning of organic material such as
wood or fuels also results in the release of carbon
dioxide from organic carbon.
CO2 is a trace gas and has huge effects on
Earth’s heat balance by absorbing infrared
radiation. During the growing season or
summer, there is a decrease in atmospheric CO2
because increased sunlight and temperature
helps plants increase their carbon dioxide uptake
and growth. In the winter time, more CO2 enters
the atmosphere than can be removed by plants.
This happens because plant respiration and the
death of plants happens faster than
photosynthesis.