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
Examiner Tip
The two main pitfalls to avoid when describing the carbon cycle are as follows:
- Don't forget that plants respire as well as animals
- When bacteria break down dead and waste material the carbon released enters the atmosphere in the form of carbon dioxide; it does not enter the soil!
