The Carbon Cycle

This lesson covers the carbon cycle as required by the Edexcel GCSE Combined Science specification (1SC0). You need to describe how carbon is recycled through ecosystems, explain the roles of photosynthesis, respiration, combustion and decomposition in the carbon cycle, and understand the concept of carbon sinks.

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Why Carbon Is Important

Carbon is an essential element for life. It is found in:

• Carbohydrates (e.g. glucose, starch)
• Lipids (fats and oils)
• Proteins (made from amino acids)
• DNA and RNA (nucleic acids)

Carbon atoms are constantly being recycled between the living (biotic) world and the non-living (abiotic) environment. The carbon cycle shows how this happens.

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The Carbon Cycle — Overview

graph TD
    A["CO₂ in the atmosphere"] -->|"Photosynthesis"| B["Carbon in plants (glucose, starch)"]
    B -->|"Feeding"| C["Carbon in animals"]
    B -->|"Respiration"| A
    C -->|"Respiration"| A
    B -->|"Death"| D["Dead organic matter"]
    C -->|"Death / waste"| D
    D -->|"Decomposition (respiration by decomposers)"| A
    D -->|"Fossilisation over millions of years"| E["Fossil fuels (coal, oil, gas)"]
    E -->|"Combustion"| A
    A -->|"Dissolves in oceans"| F["CO₂ dissolved in water"]
    F -->|"Used by aquatic plants / algae"| B

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Processes That Remove CO₂ from the Atmosphere