AQA GCSE Biology

Revision Notes

7.4.1 Trophic Levels

Trophic Levels

  • Trophic levels describe the position of an organism in a food chain, web or pyramid
  • Trophic levels can be represented by numbers, starting at level 1 with plants and algae. Further trophic levels are numbered subsequently according to how far the organism is along the food chain

Trophic levels table

Trophic levels, downloadable IGCSE & GCSE Biology revision notes

  • Energy flows from the Sun to the first trophic level (producers) in the form of light
  • Producers convert light energy into chemical energy
    • This occurs during photosynthesis, when producers convert carbon dioxide and water into glucose and oxygen
  • This chemical energy is then transferred to primary consumers as they consume (eat) producers
  • The chemical energy is then transferred from one consumer to the next as they eat one another
  • Apex predators are at the very top of the food chain – they are carnivores with no predators. The chemical energy stored within apex predators can be passed on to decomposers when apex predators die and are decomposed

Food chain showing trophic levels, downloadable IGCSE & GCSE Biology revision notes

Trophic levels for a simple food chain


Food web showing trophic levels, downloadable IGCSE & GCSE Biology revision notes

Trophic levels for a simple food web – note that some organisms can belong to more than one trophic level (such as the squirrel, fox and eagle in this food web)

The Importance of Decomposers

  • The two main groups of decomposers are bacteria and fungi
  • Decomposers carry out a very important function in ecosystems – they break down dead plant and animal material
  • They do this by:
    • Secreting digestive enzymes onto the surface of the dead organism
    • These enzymes break down the dead matter into small soluble food molecules
    • These molecules are then absorbed by the decomposers
  • This process of decomposition also helps to release organic nutrients back into the environment (eg. the soil) which are essential for the growth of plants (producers)

Exam Tip

Don’t forget – animals (known as consumers) can be at different levels within the same food web as they may be omnivores (animals that can eat both plants and animals) or may be predators that eat both primary, secondary and / or tertiary consumers!

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.

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