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.

Zoom in on a Leaf
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Zoom in on a Leaf

Plants can respond to changes in their environment by reducing the amount of water that is lost through transpiration and evaporation from the stomata on the leaves.  Can we see these openings?  In this activity you will make a cast of a corn leaf surface that can be viewed with a microscope.  We will first compare the top side, or abaxial part of the leaf with the under side, or adaxial part of the leaf to see which one, on average, contains more stomata.  If the cast is accurate, then you should be able to see stomata well enough to count how many there are in a given field of view.  Make a prediction below whether the abaxial or adaxial side will have more stomata.

Hypothesis:

Materials:

Procedure:

1. Label two microscope slides, abaxial and adaxial

2. On the third leaf, apply a coating of the clear nail polish to a section about 2 cm in length in the center of the abaxial side of the leaf.  Immediately cap the polish afterwards to minimize fumes.  Allow polish to dry for 10 minutes.

3. While waiting for the polish to dry, cut a piece of Scotch tape approximately 1.5 cm in length.  Fold the tape over on itself leaving 0.5 cm of sticky surface exposed.

4. Once the polish has dried, place the sticky tab of the tape on the leaf so that it sticks to the edge of the nail polish cast.  Grasp the remaining tape and pull the nail polish cast from the leaf surface.

5. Place the cast on its labeled slide and place a cover slip over the cast.  You may want to cut the tape off at the edge of the cover slip using the razor blade.

6. Follow steps 2-5 using the adaxial side of the leaf.

7. While viewing the abaxial slide under high power, count the number of stomata in the field of view.  Record this number in the data table.  Move the slide until you have a different section of the cast in view and again count the number of stomata.  Do this one more time and then calculate an average and record it in your data table.

8. Repeat step 7 for the adaxial slide.

9. Compare the results to your hypothesis and answer the following questions.

Analysis Questions:

1. Was your hypothesis supported by the experiment? ________ Use data to justify your answer.

2. On average, which side of the corn leaf has more stomata? _________Do you think this is true for all plant species? _____ Why or why not?

3. Thinking about the environmental conditions that are known to cause stomata to close, why would having more stomata on this side be an advantage to the plant?

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.