Carbon Cycle in an Ecosystem (Cambridge (CIE) IGCSE Environmental Management): Revision Note

Carbon cycle in an ecosystem

• The carbon cycle is the continuous movement of carbon between the atmosphere, living organisms, oceans, and the Earth’s crust

• Carbon is stored in:

  • the atmosphere as carbon dioxide

  • plants and animals as biomass

  • fossil fuels underground

  • oceans and marine life

  • soils and decaying matter

• The cycle ensures carbon is always recycled, which keeps:

  • ecosystems supplied with the carbon plants need

  • the climate stable

  • nutrients flowing between organisms

• Without the carbon cycle, life would quickly run out of the carbon needed to build cells and release energy

Key processes in the carbon cycle

1. Photosynthesis

• Plants remove carbon dioxide from the air

• They use it to make glucose during photosynthesis

• This locks carbon into plant tissues such as leaves, stems and roots

2. Feeding

• When animals eat plants or other animals, the carbon in their food moves into their bodies

• This passes carbon along food chains and food webs

3. Respiration

• Plants, animals and microorganisms release carbon dioxide back into the atmosphere when they respire

• This happens day and night

• Respiration is a major way carbon returns to the air

4. Decomposition

• When organisms die, decomposers such as fungi and bacteria break them down

• Carbon from dead bodies is released back into:

  • the soil

  • the atmosphere

  • the ocean

• Decomposition keeps nutrients flowing and prevents dead matter from building up

5. Formation of fossil fuels

• Over millions of years, buried dead organisms can turn into:

  • coal

  • oil

  • natural gas

• This traps large amounts of carbon underground

6. Combustion

• Burning fossil fuels or wood releases stored carbon dioxide into the atmosphere

• This speeds up the carbon cycle dramatically and adds extra carbon to the air

How human actions affect the carbon cycle

• Humans are changing the carbon cycle faster than nature can cope with

• Key impacts include:

  • Deforestation reduces the amount of carbon removed by photosynthesis

  • Burning fossil fuels releases carbon dioxide more quickly than it is absorbed

  • Agriculture adds carbon through soil disturbance and methane release

  • Climate change increases the amount of carbon released from melting permafrost

• These changes strengthen the enhanced greenhouse effect and contribute to global warming

Why the carbon cycle matters for ecosystems

• The carbon cycle:

  • Provides plants with carbon for photosynthesis

  • Keeps atmospheric carbon dioxide at stable levels

  • Supports food chains and energy transfers

  • Allows decomposers to recycle nutrients

  • Links photosynthesis and respiration into one continuous loop

• Disrupting the carbon cycle can damage ecosystems and reduce biodiversity