Unit 1 - Energy Loss in Food Chains

This GCSE Biology quiz is all about food chains and the loss of both energy and biomass that occurs at each stage - from producers to primary and secondary consumers.

A food chain shows how the organisms in a particular habitat depend on each other as a source of food. At the start of any food chain is a producer which is normally a green plant. It is called a producer because it produces its own energy and food from raw materials it finds in its surroundings. Following on from the producer are the consumers, so called because they must eat something else. The first of these are called primary consumers and they are herbivores as all they eat are plants. Animals that feed on the primary consumers are called secondary consumers whilst tertiary consumers feed on the secondary consumers. Secondary consumers are carnivores or omnivores, as are the tertiary consumers. At the opposite end of a food chain to the producers is the top predator.

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Food chains are usually short, rarely containing more than 3 or 4 consumers. This is because there is a loss of both energy and biomass in each stage of the chain. The entire amount of energy and biomass for a food chain is contained in the producers - call that 100%. When this is eaten by the consumers, all of it is passed on. The primary consumer uses some of this energy for respiration in its cells which enables it to stay alive, move etc. The rest becomes part of the biomass of the primary consumer and is passed along the food chain; so less than the original 100% is available to the secondary consumers. This happens at each stage of the food chain and nothing hunts the top predator because it would take more energy than would be gained from eating it.

We can see the loss of biomass and energy by observing the numbers and sizes of organisms in food chains. The biomass of living organisms at each successive stage in a food chain can be represented using pyramids of numbers and/or pyramids of biomass.

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  1. Which of the following statements about algae in a food chain is true?
    Algae are found almost everywhere on Earth and are the producer for many marine and freshwater food chains. It is said that 70% of the oxygen in the atmosphere is produced by algae
  2. Energy for all food chains comes from what source?
    All energy for living things comes from the Sun. Plants trap this energy and use it to make food which provides energy for animals
  3. The producer is usually what type of organism?
    Chlorophyll in plant cells uses the energy from sunlight to convert carbon dioxide and water into glucose. This process, photosynthesis, also releases oxygen into the atmosphere
  4. Which of the following is not a way in which energy is lost from animals in a food chain?
    Photosynthesis occurs only in plants
  5. Which type of organism is usually found at the top of a pyramid of biomass?
    Predators are always found at the top of the energy pyramid and plants are always at the bottom
  6. How is most energy in food chains lost?
    The energy and biomass lost from a food chain by death and decay is recycled by the decomposers
  7. Which of the following statements about energy is true?
    This is the Conservation of Energy principle. All of the original energy of a food chain is still there but some of it has been spread out into the environment and is no longer available to the organisms of the food chain
  8. What happens to the biomass at each successive stage in a food chain?
    Not all of the biomass eaten as food remains in the consumer's body. Some is lost through excretion and respiration
  9. Energy in which form is lost to the surroundings in a food chain?
    Ultimately, all energy conversions result in heat
  10. Which process in green plants traps sunlight energy?
    This is done by the chlorophyll

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