The Carbon Cycle

The Carbon Cycle

• Nutrients such as carbon and nitrogen are not endless resources, and so, they need to be recycled in order to allow new organisms to be made and grow
  • Carbon is taken out of the atmosphere in the form of carbon dioxide by plants to be used for photosynthesis
  • It is passed on to animals (and microorganisms) by feeding
  • It is returned to the atmosphere in the form of carbon dioxide by plants, animals and microorganisms as a result of respiration
  • 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
  • When fossil fuels are burned (the process is known as combustion), the carbon combines with oxygen and carbon dioxide is released into the atmosphere
    • Increased use of fossil fuels is contributing to an increase in the carbon dioxide content of the atmosphere
  • In addition, mass deforestation is reducing the amount of producers available to take carbon dioxide out of the atmosphere by photosynthesis
    • This problem is exacerbated by the fact that in many areas of the world, deforestation is taking place for land rather than for the trees themselves, and as such they are burnt down, releasing yet more carbon dioxide into the atmosphere

The carbon cycle

The importance of the carbon cycle

• Carbon is a component of all organic molecules, many of which are essential for life on earth, such as glucose
• The Carbon cycle is a key process which allows the movement of carbon between global reservoirs including the
  • Atmosphere
  • Biomass
  • Ocean
  • Soil
• The balance of carbon between these reservoirs is fundamental due to the role that carbon plays in sustaining life
  • If the balance is disrupted, somewhere along the way organisms will suffer
  • Global warming is an large scale example of the effect which may be seen if the global carbon balance is disrupted

Exam Tip

The carbon cycle is simple:

• Carbon is taken out of the atmosphere by photosynthesis
• It is passed on to animals and decomposers by feeding
• It is returned by respiration; in plants, in animals and in decomposing
• microorganisms
• In addition, it is returned (in increasing amounts) by the combustion of fossil fuels

You should be able to identify what each arrow represents in any diagram of the carbon cycle.