Biology / Carbon Cycle

Carbon Cycle

The carbon cycle begins when plants and other autotrophs absorb carbon dioxide from the atmosphere for use in photosynthesis.

In this process, carbon is returned to the medium at the same rate as it is synthesized by the producers, since carbon return occurs continuously through breathing during the life of beings.

In the biological cycle of carbon, we can have the total renewal of atmospheric carbon in up to twenty years.

This process occurs as plants absorb solar energy and CO 2 from the atmosphere. This generates oxygen and sugars, such as glucose, through the process known as photosynthesis , which is the foundation for plant growth.

In turn, animals and plants consume glucose during the breathing process, again emitting CO 2 .

With this, photosynthesis and organic decomposition through respiration renew the carbon of the atmosphere.
In terms of the chemical equation of these processes we have:

  • 6CO 2 + 6H 2 O + energy (sunlight) → C 6 H 12 O 6 + 6O 2 (photosynthesis)
  • C 6 H 12 O 6 (organic matter) + 6O 2 → 6CO 2 + 6 H 2 O + energy (Breathing)

With this, photosynthesis and respiration lead the carbon from its inorganic phase to the organic phase and back to the inorganic phase, completing the biogeochemical cycle .

Also part of the biological cycle is the removal of much of the carbon from the atmosphere beyond the limits of respiration when organic matter accumulates in sedimentary deposits that break down into fossil fuels.

Another way to further accelerate the rapid cycle and add CO 2 to the atmosphere is by natural fires. They consume biomass and organic matter, transferring more CO 2 at a faster rate than that which naturally removes carbon from its sedimentation.

This process causes atmospheric CO 2 concentrations to rise rapidly.

The Carbon and its Cycle

As the fifth most abundant element on the planet, carbon (C) necessarily has two forms, one organic , found in living and dead organisms, and another inorganic , present in rocks.

Thus, 99% of this carbon is in the lithosphere, mostly in inorganic form, stored in sedimentary rocks in fossil fuel deposits.

Carbon circulates through the oceans, the atmosphere and the interior of the earth in the long-term cycle defined as the "biogeochemical cycle". This process is divided into two types. The " slow " or geological cycle, where carbon is sedimented and compressed under the tectonic plates, and, for our interest, the " fast " or biological cycle.

Human Activities and the Carbon Cycle

Human actions influence the global carbon cycle, since they remove carbon stored in fossil deposits at a rate faster than carbon absorption by the cycle.

Thus, we are enhancing the increase in CO 2 concentrations in the atmosphere, especially considering the fact that these deposits are burned as fuels, further accelerating the process.

The concentration of carbon dioxide in the atmosphere has been growing at a rate of 0.4% per year. The extraction and burning of oil, gas and coal comes along with the destruction of forests and therefore we reduce absorption capacity while increasing carbon emissions.


  • Oceans are large deposits of carbon dioxide and constantly exchange carbon with the atmosphere.
  • The concentration of carbon in the atmosphere is the lowest, since most of it is in the oceans and the earth's crust.
  • Ocean life consumes large amounts of CO 2 , as low ocean temperatures increase atmospheric CO 2 absorption, while higher temperatures can cause CO 2 emissions.
  • The Greenhouse Effect is a symptom of the carbon cycle, a way the earth has to keep its temperature constant.