Plants take carbon dioxide (CO 2) from the atmosphere through the photosynthesis process (involving the use of the energy provided by sunlight) incorporate some of the carbon they absorb. The rest of this element back into the atmosphere through respiration of plants. The CO 2 is incorporated into these organisms as carbohydrates, through different metabolic processes, give rise to other organic compounds. Herbivores, feeding, metabolize organic substances containing carbon, and, in turn, carnivores take a part of them by eating herbivores.
When, in nature, animals and plants die, their remains are degraded by microorganisms that release some of the carbon to the atmosphere as dioxide, and another is in their tissues, until they also disintegrate and are incorporated soil.
In astronomy, the carbon cycle, which has no relation with that given on earth, comprises a series of nuclear reactions that provide energy to the stars of first magnitude. It has a more significant role in high-mass stars than for lower mass. In the latter the energy comes from another series of reactions, called proton-proton chain.
The air CO 2 acts as a filter for long-wave radiation emitted by the Earth, along with other gases such as ozone, methane and chlorofluorocarbons.
The concentration of carbon dioxide in the atmosphere has increased due to human activity and, therefore, this gas layer has thickened and retains more of radiation, increasing the temperature on Earth. This phenomenon is known as "greenhouse effect."