Producers are eaten by primary consumers, which in turn may be eaten by…

The idea

Food chains show the direction of energy transfer between organisms. Producers, such as green plants and algae, make their own food by photosynthesis and form the first trophic level. Primary consumers are herbivores that eat producers; secondary consumers eat primary consumers; tertiary consumers eat secondary consumers. Each arrow points from the organism being eaten to the organism that eats it, showing the transfer of biomass and energy. For example, in a grassland chain: grass → rabbit → fox → eagle, grass is the producer, rabbit the primary consumer, fox the secondary consumer and eagle the tertiary consumer. Consumers may occupy more than one level in different chains, and a food web links overlapping chains.

What earns the marks

• Identify producers as organisms that make their own food by photosynthesis, such as grass, trees or algae.
• State that primary consumers are herbivores that feed directly on producers, for example rabbits eating grass.
• Describe secondary consumers as carnivores that eat primary consumers, and tertiary consumers as predators that eat secondary consumers.
• Use arrows correctly to show the direction of energy transfer from the eaten organism to the eater, not the reverse.
• Recognise that a consumer can be a secondary consumer in one food chain and a tertiary consumer in another, depending on what it eats.

Common mistakes and how to put them right

• Drawing arrows from the consumer to the food.

  Put it right: Arrows show energy flow from the organism being eaten to the organism that eats it.

• Calling a producer a primary consumer.

  Put it right: Producers make their own food, while primary consumers eat producers.

• Assuming every consumer occupies only one trophic level.

  Put it right: The same species can be a secondary consumer in one chain and a tertiary consumer in another.

Exam tips

• Always start a food chain with a producer and use arrows pointing in the direction of energy transfer.
• When asked to identify a consumer level, trace back along the chain and count the number of feeding steps from the producer.
• Use the terms producer, primary consumer, secondary consumer and tertiary consumer precisely rather than vague words such as 'eater'.