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Stomatal Peel Experiment

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									Stomatal Peel Experiment
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?


Hypothesis:
You will first make a control slide from a plant that has been kept in the light and then compare it to slides
you make from a plant kept in the dark for 24 hours. You will make an initial slide from the dark plant and
then four more slides 15 minutes apart to determine how quickly the stomata reopen.

Materials:
                                                                        6 microscope slides w/ cover
Broad bean plant kept in light       Broad bean plant kept in dark
                                                                        slips
labeling tape and Sharpee            microscope                         clear nail polish
Scotch tape                          razor blade


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:
Time        Stomatal condition, number of open and closed
            Field 1    Field 2     Field 3    Ave.        Field 1                    Field 2       Field 3       Ave.
            open       open        open       open        closed                     closed        closed        closed
Control

T0

T15

T30

T45

T60



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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