Carbon Cycle in an Ecosystem (Cambridge International IGCSE Environmental Management)

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

A simplified carbon cycle diagram showing some of the key carbon sources and carbon sinks

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

Exam Hint Always link photosynthesis, feeding, respiration and decomposition.

Use simple arrows to show the cycle when explaining it.

Mention human impacts such as combustion and deforestation in higher-mark answers.

Remember that carbon never disappears; it just moves between stores.

Think of the carbon cycle as the glue that holds the atmosphere and ecosystems together.