PREINSTRUCTIONAL

Objectives:

• Students will be able to observe the difference between a cactus and a woodland plant in terms of how much sunlight each receives by holding a flashlight above each plant.
• Students will be able to name two ways in which the amount of sun that reaches a cactus is reduced.
• Students will record their observations in their journals.

Materials:

• Cactuses (one per group)
• Newspaper (for handling plants)
• Flashlights (one per group)
• Woodland Plants (one per group)

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.
   • The flashlight is the "sun"
   • They will hold the flashlight directly above the plant, and record how much light the plant receives. (Remind students that the sun is hottest when it is directly overhead) The amount of sunlight that the plant receives can be determined by the size of the shadow. The larger the shadow, the more light it is "catching".
   • They will hold the flashlight to the side of the plant, and record any shadows seen.
   • Hand out one woodland plant and one flashlight to each group.
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.

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:

• If there are not enough cactuses available, this activity can be done in centers during center time using one or two cactuses. It can also be done as a whole class in an intimate setting, such as on the floor.
• If a student is having difficulty understanding, work with him or her during study hall that afternoon (immediately following the lesson), pointing out several student's sketches of the phenomena.