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Ecology

How materials are cycled

  • 3 things to know
  • Biology Paper 2

Overview

Why materials must be recycled, the carbon cycle through photosynthesis, respiration, combustion and decomposers, the water cycle through evaporation, condensation and precipitation, and the role of microorganisms in returning carbon dioxide and mineral ions.

What you need to know

Answer each one before you reveal it.

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Key term

Why must the materials in the living world be recycled?

Process

Which process removes carbon dioxide from the atmosphere, and which two processes return it?

Key term

Describe how the carbon in a dead leaf is returned to the atmosphere.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Why must the materials in the living world be recycled?

    Model answer

    The supply on Earth is limited, so the same materials must be used again as the building blocks of future organisms.

  2. 2

    What is meant by saying that materials are cycled through an ecosystem?

    Model answer

    They pass repeatedly between the living organisms and the non-living parts of the environment.

  3. 3

    Why is the carbon cycle important to plants?

    Model answer

    It returns carbon dioxide to the atmosphere so that plants can continue to photosynthesise.

  4. 4

    Why is the water cycle important to organisms living on land?

    Model answer

    It supplies them with a continuous supply of fresh water.

  5. 5

    Which process removes carbon dioxide from the atmosphere, and which two processes return it?

    Model answer

    Photosynthesis removes it, while respiration and combustion return it.

  6. 6

    Describe how the carbon in a dead leaf is returned to the atmosphere.

    Model answer

    Decomposers feed on the leaf and respire, releasing the carbon as carbon dioxide.

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