The following classroom activities were developed over two summers by Donna Schmidt as part of a teacher summer research experience funded by the National Science Foundation. They have been designed as an ongoing investigative experience that to some extent mimics the actual process of science as it occurs in a research facility.  Donna Schmidt is a high school biology teacher at Pattonville High School in St. Louis, MO.

Stomatal Peel Experiment
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Note: This experiment is not yet lab tested

Stomatal peels could be used to measure a plant's response to environmental conditions.  Using a microscope allows you to determine whether a stoma is opened or closed.  Counting the numbers of opened vs. closed stomata should indicate a plant's response to varying environmental conditions.

Since the stomas on corn are difficult to characterize as open or closed, this experiment will use broad bean, or Vicia fava, seeds.  You will alter one environmental condition and then measure the effect on opening of leaf stomata.

If a plant were kept in the dark for 24 hours, in what condition would you expect to see the majority of the stomata?  Opened/ Closed?

If the plant were then brought into the light, how do you predict the condition of the stomata would change over a period of one hour?

Procedure:

1. Label slides as follows: 1-T₀, 2-T₁₅, 3-T₃₀, 4-T₄₅, 5-T₆₀, 6-control

2. Obtain a plant kept in the light and paint the adaxial side of one leaf with polish.

3. While waiting for the first leaf to dry, obtain a plant from the dark cabinet and immediately paint the adaxial side of one leaf.  Be sure to note the times each leaf is painted so that the casts are not left to dry for more than 10 minutes.

4. As each cast dries, place it on the appropriate slide following the procedure used in the previous lab.

5. Continue making casts every 15 minutes for 60 minutes.

6. As slides are completed, bring them into focus under high power and count the number of open and closed stomata in three different fields of view on each slide.

7. Calculate an average and record it in the data table.

8. Make a graph to show the rate of change in stomatal opening. You should have two lines, one for opened and one for closed.

Data Table:

Analysis:

1. How were the numbers of stomata different on the control slide vs. the initial slide make from the plant kept in the dark?

2. Describe how the number of open stomata changed over the sixty minute time period.  Use data in your answer.

3. What were the conditions that were kept constant in this experiment?

4. What are some other variables that affect stomatal opening that could be tested using this method?

5. Compare your results to your hypothesis.  Did the experiment support your hypothesis?  If not, why do you think the results were different from what you expected?

6. Why would this information about what caused stomata to close be important to farmers?

Modified from: Brewer, C. A. 1992.  Responses by stomata on leaves to microenvironmental conditions. Pages 67-75, in Tested studies for laboratory teaching,.  Volume 13. (C. A. Goldman, Editor).  Proceedings of the 13th Workshop/Conference of the Association for Biology Laboratory Education (ABLE), 191 pages.

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