4.3  Carbon Cycling

big ninja

Essential Idea:

Continued availability of carbon 

in ecosystems depends on carbon cycling


  • Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds
  • In aquatic ecosystems carbon is present as dissolved carbon dioxide and hydrogen carbonate ions
  • Carbon dioxide diffuses from the atmosphere or water into autotrophs
  • Carbon dioxide is produced by respiration and diffuses out of organisms into water or the atmosphere
  • Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans and some diffuses into the atmosphere or accumulates in the ground
  • Methane is oxidised to carbon dioxide and water in the atmosphere
  • Peat forms when organic matter is not fully decomposed because of acidic and/or anaerobic conditions in waterlogged soils
  • Partially decomposed organic matter from past geological eras was converted into either coal or into oil and gas that accumulates in porous rocks
  • Carbon dioxide is produced by the combustion of biomass and fossilised organic matter
  • Animals such as reef-building corals and mollusca have hard parts that are composed of calcium carbonate and can become fossilised in limestone


  • Estimation of carbon fluxes due to processes in the carbon cycle
  • Analysis of data from air monitoring stations to explain annual fluctuations


  • Construct a diagram of the carbon cycle