The Carbon Cycle (WJEC GCSE Biology)

The Carbon Cycle

• Elements, such as carbon, are not endless resources; they need to be recycled for ecosystems to function

  • Carbon is an essential part of the biological molecules from which cells are built, i.e. carbohydrates, proteins and fats

• Carbon stored in the tissues of organisms needs to be released into the atmosphere to be made available again for other organisms

Uptake of carbon by living organisms

• Carbon is taken out of the atmosphere in the form of carbon dioxide by plants during photosynthesis

  • The carbon is used to make glucose which can be turned into carbohydrates, fats and proteins within the biomass of plants

Transfer of carbon between living organisms

• This carbon is passed on to animals when they feed on plants

Release of carbon into the atmosphere

• Carbon is returned to the atmosphere in the form of carbon dioxide during respiration

  • Respiration occurs in plants and animals

  • Microorganisms, such as bacteria and fungi, use dead and waste material to fuel respiration, releasing CO₂ during decomposition

• If animals and plants die in conditions where decomposers are not present the carbon in their bodies can be converted into fossil fuels; these can be burned to release carbon dioxide into the atmosphere

  • The burning of fossil fuels is known as combustion

The carbon cycle diagram

Carbon is cycled between the atmosphere, the tissues of organisms and fossil fuels