Energy Flow Through Food Chains
- Plants are found at the start of almost every food chain
- This is because plants can convert light energy into usable forms which supports higher trophic levels in the food chain
- Chemical energy is stored in a plant’s biomass (after respiratory losses have been taken into account)
- This is the energy that is available to a plant for growth and reproduction
- This chemical energy also represents the energy that is available to organisms in higher trophic levels in the ecosystem
- Trophic levels describe the position of an organism in a food chain, web or pyramid
- Trophic levels can be represented by numbers or by the name of that trophic level eg. plants and algae are in trophic level 1, otherwise known as producers
- Further trophic levels are numbered subsequently according to how far the organism is along the food chain
- Like plants and other producers, these consumers store chemical energy in their biomass
Trophic levels table
Trophic level | Name of trophic level | Description of organisms in trophic level |
1 | Producers | Plants and algae produce their own biomass using inorganic nutrients and 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 |
Trophic Levels in a Simple Food Chain Diagram
Trophic levels for a simple food chain - the blue arrows show how the chemical energy originally produced by the primary producer (grass) is transferred to other organisms in the community
Decomposers
- Chemical energy stored in producers is also available to another group of organisms known as 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 (in the process gaining the chemical energy still stored in the dead matter)
- 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 and other producers
Exam Tip
Don’t forget – animals (known as consumers) can be at different levels within the same food web as they could be omnivores (animals that can eat both plants and animals) or could be predators that eat both primary, secondary and/or tertiary consumers!