Trophic Levels (AQA GCSE Biology)

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

• 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

Trophic levels for a simple food chain

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)