Lesson 30: Food Chains and Energy Flow

Food chains and webs represent feeding relationships and the transfer of energy through ecosystems. The lesson covers producers, consumers, and the effects that changes in one population can have on others.

Key Ideas

  • Most food webs begin with producers using sunlight to make food. Some begin with microbes that use chemical energy.
  • A food chain shows one path that food energy takes. A food web shows many connected feeding paths.
  • Less energy is passed on at each step in a food chain. Living things use energy for life activities, and much spreads into the surroundings as heat.
  • The number of living things in a place can change as food, predators, disease, shelter, and other conditions change.
  • Changing one part of a food web can affect many others. Losing an important species or adding a harmful new one can change the whole community.

Vocabulary

  • Food Chain / Food Web: A food chain shows one feeding path. A food web shows many connected feeding paths.
  • Producer / Consumer: A producer makes its own food. A consumer gets food from other living things or things they produce.
  • Energy pyramid: A diagram showing how less energy is available at each feeding step in a food chain.
  • Ecosystem: The living things in a place and the nonliving things, such as water and soil, that they interact with.
  • Invasive species: A species living outside its native range that causes harm to the new ecosystem.
  • Keystone species: A species that has an unusually large effect on its ecosystem.

Discussion Questions

  1. Where do producers in familiar food webs obtain energy? How can photosynthesis-based and chemical-energy-based food webs differ?
  2. Why does energy available through successive trophic transfers decrease? Why does an energy pyramid not necessarily predict the number of organisms at each level?
  3. Why are real ecosystems better described as food webs instead of simple food chains? Can you think of an animal that eats more than one kind of food?
  4. What do you think would happen to a food web if one important predator suddenly disappeared? What other populations might be affected?
  5. Why can an invasive species cause problems even if it doesn't directly harm or eat another species? What might happen when it competes for the same food or space?

Slideshow

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Wordwalls

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