Trophic Levels (AQA GCSE Biology): Revision Note
Exam code: 8461
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 level | Name of trophic level | Description of organisms in trophic level |
|---|---|---|
1 | Producers | Plants and algae – produce their own organic nutrients and biomass using energy from sunlight. |
2 | Primary consumers | Herbivores – feed on producers (plants and algae). |
3 | Secondary consumers | Predators – feed on primary consumers. |
4 | Tertiary consumers | Predators – feed on secondary consumers. |
5 | Quaternary consumers | Predators – feed on tertiary consumers. |
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
Diagram of trophic levels for a food chain
Diagram of a 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
which break down the dead matter into small soluble food molecules
and absorbing the resulting molecules
This process of decomposition also helps to release organic nutrients back into the environment (e.g. the soil) which are essential for the growth of plants (producers)
Examiner Tips and Tricks
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!
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