Cactus Adaptations

Science, Language Arts (Extension of the Previous Lesson)

Grade Level: Third - March
Teacher of Lesson: Stacey Perri
Approximate Time: Thirty Minutes

PREINSTRUCTIONAL

Objectives:

Materials:

DURING INSTRUCTION

Procedures:

  1. As a class, brainstorm ways that the cactus might be adapted to survive the heat (sun) of the desert, and record these on the board. Ask the class to take their journals out.
  2. Give the students instructions as to handle the plants and the flashlights.
  3. Turn out the lights, and have the students shine their flashlights onto their woodland plants from above. Ask the students how much of the sunlight the plant is receiving (the leaves catch a lot of the sunlight). Have the students sketch the experiment in their journals.
  4. Give each group a cactus. Have the students shine their flashlights on the cactuses from above. Do they notice a difference? How do they account for this difference? How does this help the plant? (the more flattened or barrel-shaped a cactus is, the less sunlight it will receive from overhead. A plant that is shaped like a cylinder in the desert receives the least amount of sunlight when the sun is directly overhead-the hottest time).
  5. Now allow the students to experiment with the angles that they shine the light onto the plant. Ask them where the shadow falls (They should see that the spines cast shadows on the trunk).
  6. Discuss how the shadow from the spines is important (the spines shade the plant to keep it from being scorched in the hot desert).
  7. Discuss how each adaptation is important to the cactus.
  8. Have the students record what they think in their journals.
POSTINSTRUCTIONAL

Evaluation:

  1. Did the students observe a difference between the cactus and the woodland plant in terms of how much sun each received?
  2. Did the students name two ways in which the sun reaching the cactus is reduced?
  3. Do the student journals have accurate sketches of the phenomena? Accurate reactions?

Reteaching:


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