Date: May 1994

Grade Level(s): 5, 6, 7, 8

Subject(s):

• Science/ Earth Science

Many diagrams have been utilized to illustrate the working of the HYDROLOGIC CYCLE. The following activity demonstrates the part that transpiration has in this critical dynamic system. The students should come away with a better understanding of the important role that plants play in maintaining a stable environmental condition on this the "Water Planet".

PURPOSE:

To show how plants act to help maintain the HYDROLOGIC CYCLE.

OBJECTIVES:

To explain the functioning and the major components of hydrologic cycle. To demonstrate how transpiration rates can be experimentally manipulated. To increase the students' awareness of how important all components of an ecosystem are in the proper maintenance of our atmosphere.

RESOURCES/MATERIALS:

1. A container (flask, jar, test tube, bottle, etc.) with a neck size capable of holding a two-hole stopper with a volume of at least 25 ml.
2. Stopper (cork or rubber) with two holes, one to hold a plant stem and the other to hold an L-shaped piece of glass tubing (legs 7.5 cm.)
3. Stopper with one hole for control.
4. Plastic or rubber tubing (l5 cm.)
5. Pipette or syringe to which the rubber tubing can be attached at the delivery end.
6. Ring stand with clamp.
7. Pipette bulb or syringe.
8. Plastic bag and rubber band.

ACTIVITIES AND PROCEDURES:

Connect the tubing to the delivery end of the pipette. Push the other end onto one leg of the L-shaped glass tube. Carefully push the other end of the glass tube into one hole of the two -hole stopper, the end must extend at least 2 cm. through the stopper. Put the stopper into the large container top. Connect the pipette to the ring stand and fill the system with water through the top of the pipette using the bulb or the syringe. When the system is full, place a plant stem into the open hole of the stopper so that it extends at least 2 cm. past the stopper. (Set up a duplicate system using the one-hole stopper to act as a control.)

At different times, the system can be located close to a heat lamp, a fan, a mister, or any other variables you can think of. (Dust the leaves with chalkdust, cut the leaves in half, remove all the leaves, submit the leaves to a flame, etc.) The results should all be compared to the control. Measurements in the pipette should be taken every two minutes for twelve minutes. Record the water transpired at every two-minute period and the total water loss from each test.

TIE IT ALL TOGETHER:

Relate the experimental findings to various weather conditions or ecosystem types. The surface area of the leaves can be measured and this number can then be extrapolated to a whole tree or a whole forest.

May 1994

These lesson plans are the result of the work of the teachers who have attended the Columbia Education Center's Summer Workshop. CEC is a consortium of teacher from 14 western states dedicated to improving the quality of education in the rural, western, United States, and particularly the quality of math and science Education. CEC uses Big Sky Telegraph as the hub of their telecommunications network that allows the participating teachers to stay in contact with their trainers and peers that they have met at the Workshops.