The Carbon Cycle (OCR GCSE Combined Science A (Gateway))
Revision Note
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) via 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
This problem is exacerbated by the fact that in many areas of the world, deforestation is taking place for land (for livestock grazing) rather than for the trees themselves
As such, trees are burnt down, releasing yet more carbon dioxide into the atmosphere
In addition, mass deforestation is reducing the amount of producers available to take carbon dioxide out of the atmosphere by photosynthesis
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
Oceans
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 a large scale example of the effect which may be seen if the global carbon balance is disrupted
Examiner Tips and Tricks
The carbon cycle is quite straightforward if you think about the story of a single carbon atom since the beginning of the universe:
For billions of years the carbon atom would have been combined with oxygen as CO2
At the beginning of life, it might have found itself part of a sugar molecule by photosynthesis
An organism would have returned the carbon atom to the atmosphere as CO2 by respiration
This cycle would have repeated thousands of times
The carbon may have become locked away as coal as a tree decomposed
Millions of years later, it is returned by the combustion of the coal
....and the process repeats again...and again...
You should be able to identify which process each arrow represents in any diagram of the carbon cycle.
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