Name: Date: Period: Lab#:

LEAF STOMATA

Background: The bottom surface of plants have specialized pores called stomata. Gas exchange in plants, including the movement of O2, CO2 and water vapor, occurs primarily through the stomata. Note that “stomata” is plural, used when referring to more than one pore; “stoma” is singular and is used when referring to just one pore. For more information, see handout "What are the Stomata?"

Purpose: to test whether the percentage of open stomata is affected by different light conditions

Hypothesis: When coming up with your hypothesis, think about what you know about metabolism in plants and what conditions you predict would lead to open or closed stomata and why.

Materials: Light microscope, clear nail polish, microscope slides, clear scotch tape, leaf samples

Procedure:

1. Prepare slides containing samples of leaves from two different light conditions (sun and shade), and identifying open and closed stomata.

2. Next, count stomata that are open and closed.

3. Finally, calculate the percentage of stomata that are open under each condition (sun and shade).

Details of preparing slides for stomata observation:

1. Pick two leaves from the same plant from the “sun”. Label one leaf “#1” and the other leaf “#2”.

2. Pick two leaves (from the same species of plant as step 1) from the “shade”. Label one leaf “#3” and the other leaf “#4”.

3. Apply a thin layer of nail polish to the underside of each leaf and let it dry.

4. Apply a small strip of clear tape over the nail polish on leaf #1.

5. Slowly remove the tape from leaf #1 and stick the tape with the nail polish impression onto the right half of a microscope slide. Label the bottom-right corner of the slide #1.

6. Apply tape to polish on leaf #2, remove tape, and apply it to the left half of the above slide. Label the bottom-left corner of the slide #2.

7. Repeat steps 4 through 6 for leaves #3 and #4; label the slide #3 and #4.

8. Examine the slides under a microscope at 40x, 100x and 400x. Identify stomata, and determine what stomata look like when they are open and closed.

Data/Observations and Calculations/Results:

Microscope observations

1. On your own paper, make four circles with a Petri dish representing four views through a microscope.

2. Make a drawing of each leaf sample under the magnification of your choosing, but be sure to record the magnification used under each drawing.

3. Be sure to label at least one open stomata and at least one closed stomata.

Record information about stomata in the following data table, to be created on your own paper:

Leaf #

/ # of open stomata / TOTAL # of stomata, (opened and closed) / Percentage of open stomata

1. Observe leaf #1 under high magnification and count the number of open stomata. Record this number on your data table.

2. Without moving the slide, count the total number of stomata. Record this number on your data table.

3. Repeat steps 1 and 2 for leaves #2, #3 and #4, making sure to record all data in your table.

4. To calculate the percentage of open stomata, divide the number of open stomata by the total number of stomata. Record this percentage in your data table.

Conclusions: Complete the conclusions for the lab that are provided on your Lab Format sheet.

Questions (to answer if full sentences on an attached sheet of paper):

1. Under what magnification do you think it will be easiest to count stomata? Why?

2. Under what magnification do you think it will be easiest to determine whether stomata are open or closed? Why?

3. Why do you think we looked at a nail polish impression of a leaf, rather than directly at the leaf itself?

4. Describe what method you used for counting the stomata.

5. Did you get the same percentages for leaves from sunlight and leaves from the shade? If not, why do you think these percentages were different?