The Carbon Cycle (Cambridge (CIE) AS Environmental Management): Revision Note

The Carbon Cycle

• Many different materials cycle through the abiotic and biotic components of an ecosystem

  • All materials in the living world are recycled to provide the building blocks for future organisms

• Elements such as carbon are not limitless resources

  • There is a finite amount of each element on the planet

  • Elements need to be recycled in order to allow new organisms to be made and grow

• Carbon is constantly being recycled around the biosphere so that the total amount of carbon in the biosphere is essentially constant

  • Carbon is transferred from one form to another by the various processes in the carbon cycle

• The main processes of the carbon cycle include the following:

  • Photosynthesis

  • Respiration

  • Feeding

  • Decomposition

  • Fossilisation

  • Combustion

Photosynthesis

• Producers such as plants and algae use the energy of sunlight to 'fix' carbon dioxide, turning its carbon into sugars and other organic molecules

  • This removes carbon from the atmosphere

• Terrestrial plants use gaseous CO₂ directly from the air

• Aquatic organisms use CO₂ dissolved in water

  • Just as much, if not more, CO₂ is fixed by ocean microorganisms, as by terrestrial plants

Respiration

• All life forms respire, including producers and microorganisms

• Respiration is the conversion of glucose and oxygen into carbon dioxide and water, releasing energy

  • Respiration puts carbon into the atmosphere in the form of CO₂

Feeding

• Carbon is passed from producers to consumers during feeding

• Carbon is also passed between consumers (e.g. from primary consumer to secondary consumer)

• Biomass transfer (feeding) always includes the transfer of carbon, the main element in living tissues

Decomposition

• Decomposition is the activity of microorganisms on dead matter and biological waste

  • Dead plants and animals are fed upon by detritivores and decayed by microorganisms such as bacteria and fungi

• Decomposers use dead organisms and waste as a source of nutrition and so release CO₂ when they respire

  • This releases carbon back into the atmosphere

Fossilisation

• If animals and plants die in conditions where decomposing microorganisms are not present, the carbon in their bodies can be converted, over millions of years and significant pressure, into fossil fuels such as peat and coal

• Aquatic organisms that die also form sediments on the sea bed

  • These can go on to form other fossil fuels like oil and gas

Combustion

• When fossil fuels are burned, the carbon locked within them combines with oxygen to form CO₂, which is released into the atmosphere

  • This process is known as combustion

• Increased use of fossil fuels is contributing to an artificial increase in the carbon content of the atmosphere

  • CO₂ is being returned to the atmosphere faster than it can be absorbed by plants and aquatic producers

  • The concentration of CO₂ in the atmosphere is approximately double that of 800,000 years ago

  • Warmer temperatures also mean that less CO₂ can be dissolved in the oceans, so this also increases CO₂ concentrations in the atmosphere

Carbon Stores

• Carbon is stored in short-term and long-term stores known as carbon stores (or carbon sinks)

• A carbon store is a natural (or sometimes artificial) store that absorbs carbon through one of the carbon cycle processes (such as photosynthesis)

• The main stores of carbon are located in, and transferred between the following:

  • Biosphere

  • Lithosphere

  • Pedosphere

  • Cryosphere

  • Atmosphere

  • Hydrosphere

Main Stores of the Carbon Cycle