19.2 Food chains and food webs

2026 Syllabus Objectives

  1. Describe a food chain as showing the transfer of energy from one organism to the next, beginning with a producer
  2. Construct and interpret simple food chains
  3. Describe a food web as a network of interconnected food chains and interpret food webs
  4. Describe a producer as an organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis
  5. Describe a consumer as an organism that gets its energy by feeding on other organisms
  6. State that consumers may be classed as primary, secondary, tertiary and quaternary according to their position in a food chain
  7. Describe a herbivore as an animal that gets its energy by eating plants
  8. Describe a carnivore as an animal that gets its energy by eating other animals
  9. Describe a decomposer as an organism that gets its energy from dead or waste organic material
  10. Use food chains and food webs to describe the impact humans have through overharvesting of food species and through introducing foreign species to a habitat
  11. Draw, describe and interpret pyramids of numbers and pyramids of biomass
  12. Discuss the advantages of using a pyramid of biomass rather than a pyramid of numbers to represent a food chain
  13. Describe a trophic level as the position of an organism in a food chain, food web or ecological pyramid
  14. Identify the following as the trophic levels in food webs, food chains and ecological pyramids: producers, primary consumers, secondary consumers, tertiary consumers and quaternary consumers
  15. Draw, describe and interpret pyramids of energy
  16. Discuss the advantages of using a pyramid of energy rather than pyramids of numbers or biomass to represent a food chain
  17. Explain why the transfer of energy from one trophic level to another is often not efficient
  18. Explain, in terms of energy loss, why food chains usually have fewer than five trophic levels
  19. Explain why it is more energy efficient for humans to eat crop plants than to eat livestock that have been fed on crop plants

🌍 Ecology and Ecosystems

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Key Ecological Terms 🔑

Understanding how organisms interact with their environment requires knowledge of several important terms:

Ecology is the study of organisms in their environment. It examines how living things interact with each other and with their surroundings.

Habitat refers to the place where an organism lives. For example, a tadpole's habitat might be a pond.

Population is a group of organisms of the same species, living in the same area at the same time. All the tadpoles living in a pond form a population of tadpoles.

Community consists of all the organisms, of all the different species, living in the same habitat. A pond community includes tadpoles, fish, water plants, insects, and many other species.

Ecosystem is a unit containing all of the organisms in a community and their environment, interacting together. The interactions between the living organisms in the pond, the water, the stones, and the mud at the bottom make up the pond ecosystem.

Niche describes the role of an organism in its natural environment and the way in which it interacts with other organisms and with the non-living parts of the environment.

Example: The niche of a tadpole includes eating algae and other weeds in the pond, disturbing pebbles and mud at the bottom of shallow areas, excreting ammonia into the water, and breathing in oxygen from the water while breathing out carbon dioxide.

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