Level 2: Herbivores eat plants/algae and are called primary consumers.

The idea

Trophic levels describe feeding positions in a food chain, and level 2 is the first consumer level. Producers such as grass, oak trees or phytoplankton occupy level 1 and make their own organic molecules by photosynthesis. Herbivores eat these plants or algae, so they obtain energy and matter from producers and are called primary consumers. For example, in the food chain phytoplankton → zooplankton → herring, the zooplankton is the primary consumer at level 2. A herbivore may be small, such as a caterpillar, or large, such as a cow, but its defining feature is a plant or algal diet. Ecologists identify level 2 by tracing the arrows, which show the direction of energy transfer, from a producer to the organism that eats it.

What earns the marks

• Level 1 contains producers, which are organisms such as plants and algae that make their own organic compounds by photosynthesis.
• Level 2 contains organisms that feed on producers, so they are the first consumers in the chain.
• Herbivores are animals that eat plants or algae, and in a food chain they occupy level 2 and are named primary consumers.
• The arrow in a food chain points from the organism being eaten to the organism that eats it, showing the direction of energy transfer.
• A named example such as grass → rabbit → fox correctly places the rabbit as the primary consumer at level 2.

Common mistakes and how to put them right

• Calling the producer a primary consumer.

  Put it right: The error is labelling level 1 as a consumer, and the correction is that producers make their own food while primary consumers eat producers.

• Reversing the arrow direction.

  Put it right: The error is drawing the arrow from consumer to producer, and the correction is that arrows show energy transfer from the eaten organism to the eater.

• Assuming all primary consumers are large grazing mammals.

  Put it right: The error is ignoring algae-eating aquatic animals, and the correction is that any herbivore feeding on plants or algae is a primary consumer.

Exam tips

• Trace the food chain from left to right and label each level before answering, so level 2 is identified from the producer rather than guessed.
• Use the exact terms herbivore and primary consumer together when explaining level 2, because both ideas are needed for a complete answer.
• If asked to complete a food chain, check that the arrow points away from the producer and towards the primary consumer.