Trophic Levels (AQA GCSE Biology): Revision Note
Exam code: 8461
Trophic levels
An organism's trophic level is its position in a food chain, web or pyramid
Trophic levels start at level 1 with producers, e.g. plants and algae
Further trophic levels are numbered according to how far the organism is up the food chain
Trophic level | Name of trophic level | Description of organisms |
|---|---|---|
1 | Producers | Plants and algae – produce their own food |
2 | Primary consumers | Herbivores – feed on producers (plants and algae) |
3 | Secondary consumers | Carnivores – feed on primary consumers |
4 | Tertiary consumers | Carnivores – feed on secondary consumers |
5 | Quaternary consumers | Carnivores – feed on tertiary consumers |
Energy is transferred to the first trophic level when light energy is converted to chemical energy in the biomass of producers
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 the producers
The chemical energy is then transferred from one consumer to the next, until it reaches the tissues of the apex predator
Apex predators are carnivores with no predators
The chemical energy stored within predators at the top of the food chain can be released during the process of decomposition
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 releases mineral ions (e.g. nitrate) back into the soil, which plants (producers) need for growth, and the decomposers' respiration returns carbon dioxide to the air
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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