Feeding relationships within a community can be represented by food…

The idea

A community is the interacting populations of different species in a habitat. The feeding relationships between these organisms can be shown as food chains, in which arrows represent the transfer of energy and biomass from one organism to the next. Every food chain begins with a producer because producers synthesise their own organic molecules from inorganic raw materials. In most ecosystems the producer is a green plant or an alga, which makes glucose by photosynthesis using carbon dioxide and water. For example, in a pond food chain, algae → water flea → small fish → heron, the algae are the producer. Consumers cannot synthesise their own organic molecules in this way, so they depend on the molecules made by producers. Food chains therefore show the direction of energy flow and the feeding relationships within a community.

What earns the marks

• A community consists of the populations of different species living and interacting in a habitat.
• Food chains represent feeding relationships and show the direction of energy transfer between organisms.
• Arrows in a food chain point from the organism being eaten to the organism that eats it, indicating the direction of energy flow.
• All food chains begin with a producer because producers synthesise organic molecules from inorganic raw materials.
• Producers are usually green plants or algae, which make glucose by photosynthesis.
• Consumers obtain their organic molecules by feeding on other organisms, so they depend on producers.
• A food chain is a simplified representation; interconnected food chains form a food web.

Common mistakes and how to put them right

• Drawing arrows that point from the consumer to the food it eats.

  Put it right: Arrows must point from the organism being eaten to the organism that eats it, showing the direction of energy transfer.

• Starting a food chain with a consumer such as a rabbit or a fox.

  Put it right: Every food chain must begin with a producer, such as a green plant or alga.

• Saying that producers 'make energy'.

  Put it right: Producers transfer light energy into chemical energy stored in glucose; energy is not created.

• Treating a food chain as a complete description of all feeding relationships.

  Put it right: Food chains are simplified; a food web shows the interconnected feeding relationships in a community.

Exam tips

• When constructing a food chain, always start with a producer and use arrows correctly; check the direction of each arrow before moving on.
• If asked to explain why a food chain starts with a producer, refer to the synthesis of glucose by photosynthesis and the production of biomass.
• Use the term 'community' accurately: it refers to all the populations of different species in a habitat, not just the plants.
• Practise converting a written feeding description into a food chain, and identify the producer, primary consumer and secondary consumer.