The carbon cycle

Overview

Why materials must be recycled, the biotic and abiotic parts of material cycles, decomposers, and the carbon cycle, with photosynthesis removing carbon dioxide, respiration and combustion returning it, carbon passing along food chains, and the effects of burning fossil fuels and clearing forests.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Explain why materials must be recycled within an ecosystem.

   Model answer

   The supply of each element on Earth is fixed, so the materials locked in dead organisms must be released for living things to reuse.

2. 2

   Name three elements that cycle between the living and non-living parts of an ecosystem.

   Model answer

   Carbon, nitrogen and oxygen.

3. 3

   Describe the general path a material follows as it cycles through an ecosystem.

   Model answer

   Producers take it from the environment, it passes along the food chain, and respiration, excretion and decay return it to the environment.

4. 4

   Distinguish between the biotic and abiotic parts of a material cycle.

   Model answer

   The biotic parts are the living organisms holding the material, and the abiotic parts are stores such as the air, water and soil.

5. 5

   What part do decomposers play in the cycling of materials?

   Model answer

   They break down dead organisms and waste, releasing the elements they contain back into the soil and the air.

6. 6

   Explain why an ecosystem without decomposers would eventually stop producing new growth.

   Model answer

   Nutrients would stay locked inside dead material, so plants could not take them up to build new tissue.

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