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8.11.1. Carbon cycle

The carbon cycle

The carbon is one of the main constituents of living matter, the base of the structure of the organic matter ( carbohydrateslipidsproteinsnucleic acids ).

Carbon is in different deposits in nature:

Ciclo biogeoquímico del carbono

By Carbon_cycle-cute_diagram.jpeg: User Kevin Saff on en.wikipediaDerivative work: FischXTraducción: Tomás Clarke [Public domain], via Wikimedia Commons

The carbon cycle can be summarized in these steps:
  • Organisms producers, land and water, capture the carbon as CO2 from the atmosphere and, through photosynthesis, incorporate it into organic molecules.
  • Consuming organisms incorporate carbon through food.
  • Producing, consuming and decomposing organisms, through cellular respiration, oxidize organic molecules to obtain energy, releasing CO2 into the atmosphere.
  • Some organic remains are buried with sediments and can be transformed into carbonate rocks (skeletons and shells) or into coal and oil (organic remains).
  • The carbon can be stored in the form of fossil fuels for many years but, if man burns for energy, or produced forest fires, or produced volcanic eruptions, this carbon was retained in the geosphere pass to the atmosphere, contributing to the air pollution.


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Biology and Geology teaching materials for Compulsory Secondary Education (ESO) and Baccalaureate students.