Energy Flow in Ecosystems


Energy is defined as the ability to do work. The energy that is available to organisms in an ecosystem is trapped by plants during the process of photosynthesis. Photosynthesis converts and stores light energy from the sun in the form of a simple sugar called glucose. Glucose is used by the plant to carry out its life processes. The rest of the energy is stored as carbohydrates or lipids, which are used by other organisms as food. It is important to remember that all food chains start with a producer that serves as food for herbivores. Herbivores are then eaten by carnivores or omnivores. These organisms use some of the available energy for life processes, but most of the energy is lost as body heat.


  • Explain how energy flows through ecosystems.
  • The sun is the main source of energy in an ecosystem.
  • Compare and contrast a food chain and a food web.


  • Classify organisms in an ecosystem as producers, herbivores, carnivores, omnivores scavengers, or decomposers.
  • Draw a food web to show how food chains are interrelated or connected in an ecosystem.
  • Create an energy pyramid diagram of organisms in a specific ecosystem.
  • Produce a multimedia presentation using ClarisWorks Drawing and Slide Show.


  • Have each group choose an ecosystem to research. (ex. pond, Chesapeake Bay, ocean, freshwater, coral reef, Arctic or Antarctic )
  • Each group must research the ecosystem to determine the plants, animals and food chains that are present there.
  • The animals must be classified as producers, herbivores, carnivores, omnivores, scavengers, or decomposers.
  • An energy pyramid of these organisms is constructed.
  • Each group must plan a slide show using storyboard cards.

On the computer

  • Have students work in groups to create a slide show that utilize any of the following; clip art, scanned pictures, movie clips, video discs, or screen captures from CD-ROMs.
  • The slide show must contain at least these items; a title page, a fact page or pages about the ecosystem, an illustrated food web, and an energy pyramid diagram.
  • An option is to have students conduct research using the Internet and CD-ROMs.


  • Students will complete a self assessment of their project using a rubric.
  • Students will answer critical thinking questions based on their research about the flow of energy through an ecosystem. For example:

-What might happen if the producers suddenly disappeared?
-What might happen if there were no decomposers?
-What might happen if any one of the organismís population were to decrease or increase?
-Why arenít there more levels in an energy pyramid?
-Why do organisms need to eat?

Related resources

  • Glencoe Life Science textbook
  • CD-ROMs
  • Internet access
  • Related worksheets
  • ClarisWorks
  • Video discs