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14.2 - 2015 June Q5

Gardeners use compost to fertilise their soil.
​The diagram shows a composter, where organic matter is broken down by aerobic bacteria to produce compost.
Picture
(a) (i) The bacteria that break down organic matter are non-pathogenic.
Non-pathogenic bacteria (1)
Picture
(ii) Explain why bacteria break down organic matter more quickly in summer than in winter. (2)

​(iii) This diagram shows a different type of composter. Every few days the gardener turns the handle to rotate the composter.
Picture
Suggest why rotating the composter helps to break down the organic matter more quickly. (3)

(iv) Once the organic matter in a composter has been broken down by the bacteria, the fertiliser produced can be spread over the soil. Suggest why fertiliser is useful to gardeners. (2)

​(b) This food web shows some of the organisms found in a composter.
Picture
(i) How many of the organisms in the food web are secondary consumers? (1)

(ii) Flatworms can also be found in compost heaps.
  • flatworms only eat the millipedes
  • flatworms are not eaten by any other organism in the food web
​Explain how the introduction of flatworms might affect the number of ground beetles and earwigs in the food web. (3)
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