Lesson Plan

Ecosystem Interactions Among Organisms


In this lesson, students learn about organism interactions in lotic and lentic ecosystems. Students will:

  • describe the ecological roles of organisms in lotic and lentic ecosystems.
  • describe interactions among organisms in ecosystems.
  • explain the concept of trophic levels in an ecosystem.

Essential Questions


  • Consumer: Organism that does not make its own energy. Consumers can be plant eaters (herbivores), meat eaters (carnivores), plant and meat eaters (omnivores), or scavengers, which eat dead things or detritus (detritivores).
  • Decomposer: Bacteria or other organisms that break down dead organisms into nutrients that can return to the soil.
  • Energy Pyramid: Diagram that shows the amounts of energy as it is transferred through a food chain.
  • Food Web: A group of connected food chains that shows feeding relationships in an ecosystem.
  • Habitat: Place where a plant or animal lives.
  • Predator: An organism that captures, kills, and eats another organism.
  • Prey: An organism that is eaten by a predator.
  • Primary Consumer: Animal that eats producers (e.g., rabbit, cow).
  • Producer: Green plant or plant-like protist that makes its own food by photosynthesis.
  • Secondary Consumer: Animal that eats other secondary consumers and others below on the food chain (e.g., snake, fox).
  • Tertiary Consumer: Consumer that eats other tertiary consumers and others below on the food chain
  • Trophic Level: The feeding level of an organism in a food chain (e.g., producer, primary consumer, secondary consumer).


90 minutes/2 class periods

Prerequisite Skills

Prerequisite Skills haven't been entered into the lesson plan.


Related Unit and Lesson Plans

Related Materials & Resources

The possible inclusion of commercial websites below is not an implied endorsement of their products, which are not free, and are not required for this lesson plan.

Formative Assessment

  • View

    Day 1

    • Assess students’ understanding of concepts from their answers to the Otter Chaos questions, during the true/false activity, and during instruction on food chains and food pyramids. Circulate around the room during independent practice to check for understanding. Collect students’ food chains for individual assessment.

    Day 2

    • Assess the small groups’ food webs to check for understanding of ecosystem interactions among organisms and the flow of energy in an ecosystem. During the Critter Quest PA activity, circulate among the groups, observe their Pennsylvania maps, and assess their understanding of the concepts by asking relevant questions.

Suggested Instructional Supports

  • View
    Active Engagement, Modeling, Explicit Instruction
    W: This is a lesson on ecosystem interactions among organisms, with a focus on ecological roles and the flow of energy through food chains and food webs in lentic and lotic ecosystems.
    H: Students watch a short video on river otters to capture their attention. They answer questions about the river otter’s role in its ecosystem.
    E: The lesson includes direct instruction, group activities and discussion, independent work, and an online activity.
    R: Students revisit the concepts as they practice vocabulary during the true/false activity and as they do the Mixed-Up Food Chain activity independently. They review by writing sentences to describe energy flow in ecosystems at the beginning of Day 2. They practice their understanding of ecosystem interactions as they make a food web based on a reading selection.
    E: Students express their understanding during group activities, independent work on food chains, and during the concept review.
    T: This lesson can be tailored by modeling the food web and Critter Quest PA activities, and modifying the activities as needed. The food web activity can be extended by having students add more than ten organisms to the food web or by having them create a matrix of organisms in the ecosystem (see Extension section).
    O: The lesson begins with a video to engage students’ interest. After that, you provide direct instruction, and then there is guided practice in groups and individually.

Instructional Procedures

  • View

    In advance, view the Otter Chaos video clip and set up your computer with a projector so that you can show the video to students. Practice using the Critter Quest PA Web site, in order to become familiar with how to use the interactive map.

    Day 1

    Otter Chaos Video and Questions

    Give students the Otter Chaos Questions worksheet (S-7-5-2_Otter Chaos Questions and KEY.docx). Together with students, come up with a definition of habitat and have them write it in the blank on the worksheet. Tell students they will be watching a short video on river otters and read through the questions aloud. Show students the video and then have them answer the questions alone or in pairs. Go over the answers with students.

    Have students take notes as you present vocabulary terms and definitions for this lesson: trophic level, producer, primary consumer, secondary consumer, tertiary consumer, decomposer, predator, prey, carnivore, herbivore, and omnivore (see Vocabulary list). It is important that students understand the concept of trophic levels. On the board, write the following example of a food chain and the trophic levels represented in it:

    algae → fly → toad → snake → bacteria

    producer →primary consumer → secondary consumer → tertiary consumer → decomposer

    Ask students,

    • “Why do we need decomposers in ecosystems?” (Decomposers are important because they return nutrients to the ecosystem.)
    • “Must the decomposer always be at the end of the food chain?” (no)
    • “Where else could they fit?” (They can be placed anywhere on the food chain, since they break down dead organisms at all levels.)

    Check students’ understanding of vocabulary concepts by having them vote True or False on the following statements:

    • “A carnivore can be a producer.” (False)
    • “An omnivore can also be a primary consumer.” (True)
      • “A secondary consumer makes its own food.” (False)
      • “Most humans are omnivores.” (True)
      • “An animal can be both an herbivore and a primary consumer.” (True)

    Add more statements to those above, if needed, to provide students with extra practice and reinforce the concepts.

    Food Chain Trophic Levels and Energy Flow

    Show students the Stream Food Chain and Pyramid (S-7-5-2_Stream Food Chain and Pyramid.docx). Ask, “Does this food chain depict a lentic or lotic ecosystem?” (lotic) Have them identify the trophic levels of each organism. (algae–producer; black fly larvae–primary consumer; trout–secondary consumer; kingfisher–tertiary consumer) Also, ask students,

    • “What is the original source of energy in this food chain?” (the Sun)
    • “When a kingfisher eats a trout, in which direction does energy flow?” (from the trout to the kingfisher)

    Show students the stream food pyramid on the Stream Food Chain sheet. Explain that the size of each level of the pyramid shows how much energy is available at that trophic level. Tell students, “Only about 10% of the energy at each trophic level is passed up to the next level. For example, if the algae have 50,000 kilocalories (kCal) of energy, the black fly larvae only receive 5,000 kCal, and the herons receive 500 kCal. How much energy is available for the kingfishers?” (50 kCal) “The rest of the energy is used up by organisms for life processes like movement and given off as heat.”

    Mixed-Up Food Chain

    Write the following mixed-up food chain for a pond ecosystem on the board:

    wood frog tadpole → great blue heron → green algae → sunfish

    Have students work alone to write the food chain in the correct order and label the trophic level of each organism. Then, have them add a decomposer (at any trophic level) and the Sun to the food chain, and write a sentence describing how energy is transformed as it flows through the food chain. Have them identify this pond food chain as a lentic or lotic ecosystem. (It is lentic.) Remind students to use arrows in the food chain to show the direction of energy flow.

    Sun→ green algae → wood frog tadpole → sunfish → great blue heron

    producer → primary consumer → secondary consumer → tertiary consumer

    Day 2

    Students will need computers with Internet access for the Critter Quest PA activity. If this is not possible, you can do the activity as a demonstration using your computer and a projector.

    Have students write one or two sentences explaining how energy is transformed as it flows through an ecosystem. (Producers change the Sun’s energy into chemical energy, stored as food that consumers take in. The chemical energy is changed into heat energy and used for movement as it flows through the trophic levels.) Have several students share their sentences and correct any misunderstandings.

    Create a Food Web

    Have students read the Wetlands Food Web Story (S-7-5-2_Food Web Story.docx).

    In small groups, have students create a food web that includes any ten of the organisms from the story. Food webs will vary, but they should include arrows to show the direction of energy flow, and should accurately depict interactions among organisms from the story.

    Critter Quest PA

    Move student groups to computer stations and give each group a copy of Critter Quest PA (S-7-5-2_Critter Quest PA.docx). Read through the instructions with students and answer any questions that arise. Allow about 15–20 minutes for students to do the activity. Circulate among the groups, observe their Pennsylvania maps, and assess their understanding of the concepts.

    To conclude the lesson, have each group present one fact that they learned about a Pennsylvania species during the Critter Quest PA activity.


    • Students who need an opportunity for additional learning can color-code the organisms in the food web story as they read to show their ecological roles. Limit the number of organisms they should include in the food web and model the activity by starting the food web with a few organisms. Provide extra practice by having them use vocabulary terms to describe the organisms in the food web and explain the transfer of energy among organisms.
    • During the Critter Quest PA activity, model the activity first, and then do it step-by-step with students until they are familiar with how to use the Web site.
    • Students going beyond the standards can create a matrix of organisms from the food web. The matrix should list ecological roles (e.g., producer, consumer, omnivore, decomposer, etc.) across the top and the organisms’ names down the left side. For each organism, have them check all the boxes that describe it. Then have them judge which relationship in the food web they think is most important to the balance of the ecosystem, and which one is least important.

Related Instructional Videos

Note: Video playback may not work on all devices.
Instructional videos haven't been assigned to the lesson plan.
DRAFT 05/12/2011
Please wait...