Trophic Levels & Food Chains (Edexcel GCSE Biology): Revision Note

Trophic Levels & Food Chains

Trophic levels

• Trophic levels are used to describe the feeding relationships between organisms

• The Sun is the source of energy for nearly all life on Earth

• Energy flows from the Sun to the first trophic level (producers) in the form of light

• Producers then convert light energy into chemical energy and it flows in this form from one consumer to the next

  • For example, plants (one type of producers) convert a small percentage of the light energy that falls on them into glucose, some of which is used immediately in respiration and some of which is stored as biomass

  • When a primary consumer (e.g. a herbivore such as a rabbit) feeds on a plant, the chemical energy stored in the plant's biomass is passed on to the primary consumer

• Eventually, all energy is transferred to the environment – energy is passed on from one level to the next with some being used and lost at each stage

  • Energy is lost to the environment when heat energy is transferred from organisms to their surroundings

Trophic Levels Table

• Animals (known as consumers) can be at different trophic levels within the same food web as they may eat both primary, secondary and/or tertiary consumers

Food chains

• A simple way to illustrate the feeding interactions between the organisms in a community is with a food chain

• A food chain shows the transfer of energy from one organism to the next

• The source of all energy in a food chain is light energy from the sun

• The arrows in a food chain show the transfer of energy from one trophic level of the food chain to the next

An example of a food chain (the sun is not included in food chains as it is not a living organism)

• You need to know the terms given to each step in a food chain (the sun is not included in food chains as it is not a living organism):

1. Producer: food chains always begin with a producer

2. Primary consumer: producers are eaten by primary consumers (herbivores/omnivores)

3. Secondary consumer: primary consumers are eaten by secondary consumers (carnivores/omnivores)

4. Tertiary consumer: secondary consumers are eaten by tertiary consumers (carnivores/omnivores)

Trophic levels for a simple food chain