Stomata Lab

Question to Ponder

How do plants breathe?

Learning Target

• Students will observe evidence of plant structures that aid in the process of photosynthesis.

Success Criteria

• I have completed the stomata lab
• I can identify stomata
• I know how stomata aid in photosynthesis

The closing of the stomata help the plant by preventing dehydration due to loss of water vapor, and helps with maintaining the water necessary for photosynthesis and the homeostasis, or internal balance of the plant. It is also important to mention that this process is a crucial step in the Earth’s water cycle. Generally stomata are open during the day and close at night. Functioning of the stomata could be affected by light intensity, stress (disease, insects, etc.), climate, and/or latitude.

Stomata Lab

Guiding Questions

1. Where would you expect to find more stomata, on the top or underside of a leaf?
2. Will the number of stomata vary among different plant species? Why might this be the case?
3. Would you expect stomata to be the same size and shape in different plant species?
4. What environmental conditions might cause guard cells to open or close the stomata?

Materials

• Compound Microscope
• Microscope slides
• Clear tape (shiny, not translucent)
• Clear fingernail polish (not strengthener)
• Various leaf specimens- may be live, or dead (dried flat); pin oak is an excellent species for observation

Procedure

1. Select a leaf. Be sure it is dry. To prepare a cast of lower (abaxial) leaf surface, paint a small rectangular area of the underside of a leaf with nail polish (approximately 1 cm x 2cm). Allow the area to dry completely, usually at least 5 minutes. No longer than approximately 10-15 minutes should be allowed because the polish might be difficult to remove without damaging the leaf if the drying time is extended.
2. Repeat the same procedure from in step 1 with the upper (adaxial) surface of the same leaf.
3. Cut a piece of clear tape approximately 4.0 cm in length. Fold a 1-2 cm portion of the tape over onto itself to use as a “handle.” Once the polish is dry, place the sticky surface on the nail polish cast and press gently with your finger and rub back and forth about 5 seconds. Using the “handle,” carefully pull the nail polish cast from the leaf surface, taking care not to tear the leaf. You should observe some of the leaf epidermis (skin) on the tape.
4. Place the cast (sticky side down) in the central area of the slide. Press gently in place. The adhesive on the tape should mount the cast onto the slide. DO NOT REMOVE THE TAPE OR ADD A COVER SLIP.
5. Starting with the lowest objective (4x, bring the leaf epidermis into view and look for stomata. Next change to the 10x objective where stomata if present should be very visible. The stomata should look like round or oval circles with slits in the center (see photos at the top of the page). Try to observe if stomata appear open or closed.
6. Make a sketch of at least a few stomata and surrounding plant tissue at this magnification and try to count how many stomata you can observe in your field of view for the 10x objective. Write the total magnification of the observed cells in the space provided on the Data sheet. Finally, try to use the 40x objective to obtain a detailed view of the stomata.
7. Complete from step three with the top of the leaf. Remember you might not see any stomata on the upper side of the leaf, but will observe epidermal cells.
8. Complete from step three with the second leaf.

Learning Target

• Students will observe evidence of plant structures that aid in the process of photosynthesis.

Success Criteria

• I can identify stomata
• I know how stomata aid in photosynthesis
• I can use two column notes to arrange information from a written article.

Learning Target

• Students will construct a scientific explanation based on evidence for the role of photosynthesis in the cycling of matter and flow of energy into and out of organisms.

Success Criteria

• I can identify stomata
• I can demonstrate in writing how stomata aid in photosynthesis