1. THE CARBON CYCLE

2. Carbohydrates Fats Proteins Vitamins DNA
Carbon is an important element for living organisms as it present in many of the essential molecules that are necessary for life:
Carbohydrates
Fats
Proteins
Vitamins
DNA
In much the same way that nitrogen is transformed throughout the biosphere, carbon too follows a similar cycle.

4. Photosynthesis 6CO2 + 6H2O C6H12O6 + 6O2
Carbon exists in our atmosphere as carbon dioxide CO2
The proportion of carbon dioxide is around 0.04%.
Photosynthesis
The carbon in the atmosphere is absorbed by plants through the process of photosynthesis:
6CO2 + 6H2O C6H12O6 + 6O2
light
sugar
These sugars are then used in the formation of organic material and compounds within the plant.

5. Respiration C6H12O6 + 6O2 6CO2 + 6H2O
Sugars are also the source of energy for plants and animals, extracted through the process of respiration
C6H12O6 + 6O CO2 + 6H2O
As a result of this process, the carbon is released back into the atmosphere as carbon dioxide.

6. Decomposition
When plants and animals die, their remains are broken down by bacteria and other organisms which feed on this organic material.
These organisms in turn respire releasing some of this carbon back into the atmosphere.

7. Ocean respiration
CO2 is continually exchanged between the atmosphere and the upper layers of the ocean.
Phytoplankton and other organisms photosynthesise the CO2 into
organic compounds.
Organisms in the ocean respire releasing CO2 back into the ocean.
Some CO2 is absorbed by organisms to form exoskeletons in the form of CaCO3, such as shell fish and corals.
Large amounts of carbon move down into the deep ocean where it can remain for hundreds of years or more.

8. Fossil stores
Organic material that is buried under layers of other organic material, or sediments that collect at the bottom of the ocean, swamps lakes can over the course of millions of years undergo process of fossilisation.
Plant matter and organic matter becomes coal, oil and gas.
Coral and shellfish, etc. become limestone.
Burning fossil fuels (coal, oil and gas) releases this carbon back into the atmosphere as CO2.

9. Activity: What proportions of carbon exist where?
How much carbon is in a tree?

10. What proportions of carbon exist where?