Unit B: The Changing Environment

Why can termites digest cellulose?

1. Get Set to Explore


  • cellulose: A substance found in the cell walls of plants that most animals have difficulty digesting.
  • mutualism: A type of symbiotic relationship in which both species in the relationship benefit.
  • organism: A living thing.
  • symbiotic: Characteristic of a close relationship between two species.

Building Background

  • Ask students if they or anyone they know has had experience with termites. If necessary, explain that termites are considered pests because they eat wood. Guide students to realize that wood is difficult for most organisms to digest, but that the simulation shows how termites are able to gain nutrients from this tough substance.
  • Review the vocabulary words and go over the definitions.
  • Write the Discover! question on the board. Let students work in pairs to generate possible answers. After a few minutes, hold a class discussion to let students share ideas. Record their answers on the board to refer to later.

2. Guide the Exploration

  • Staying in pairs, students should launch the Discover! Simulation. Encourage them to first try to figure out the answer to the Discover! question. Explain that they can get clues about any organism by moving their cursor over the organism. They are trying to match organisms that help each other. If they think they've found a match, they should test the match by dragging the picture of the organism in the left column to the box next to the picture of the organism they've chosen in the right column. If the organisms don't have a symbiotic relationship, students will be prompted to listen to the clues.
  • When most students have found the termite's match, let students revisit their previous answers to the Discover! question. Through class discussion, let students revise or correct what is written on the board. Guide them to see that without the microorganism Trychonympha, termites would have to find a new food source. Challenge students to complete the simulation, correctly matching the other pairs.

3. Review/Assess

  • Ask a volunteer to read the first paragraph of Step 3's Wrap-up text aloud to the class. Invite students to share observations or ask questions. Clarify any concepts students find confusing or difficult to understand.
  • Have another volunteer read the second paragraph of the Wrap-up text aloud. Through class discussion, encourage students to talk about how each pair of organisms pictured in the simulation benefit from symbiotic relationships.
  • Challenge students to answer the Extension questions: Humans have symbiotic relationships with bacteria. How do bacteria help you? How can bacteria harm you? If necessary, refer students to Student Edition page B62. Guide them to realize the following:
    • Bacteria in human intestines produce vitamin K and other essential nutrients. This is an example of mutualism.
    • Bacteria cause respiratory and other infections. This is an example of parasitism.

If time permits, present students with the following questions:

  • Critical Thinking Classify Based on the Wrap-up text in Step 3, what kind of role do termites play in a natural ecosystem? Explain. Answer: Termites are decomposers because they digest wood from dead trees.
  • Inquiry Skill Infer Oxpeckers groom many animals besides rhinos. They also groom hippos, cattle, and oxen. Based on this, what inference can you make about the niche of the oxpecker? Answer: Oxpeckers have a fairly broad niche.

4. Reaching All Learners

English Language Learners

When you have students pair up to do the simulation, make sure to pair English Language Learners with native English speakers. After students complete the simulation, bring pairs together to form groups of four. Use the following Numbered Heads Together format to reinforce what students have learned about symbiosis, aid interaction among students, and let English Learners practice speaking in both a small- and large-group context. Have students number off, one to four, within their groups. Pose a question about the relationship between one of the pairs of animals in the simulation that requires a sentence or more of explanation. For instance, you might ask: What does the clownfish do that is beneficial to the anemone and vice versa? Give groups a few minutes to come up with an answer; all students in the group should understand, agree with, and be able to articulate the answer. Call out a number between one and four. When called on, students with that number should explain their group's answer. Continue the activity, asking three or four more questions about the other organisms in the simulation.