Title: Gotta Count Stomata

Time Required:  Varies from 30 minute lessons, to year long activities.

Materials:

• Student set of clear nail polish (1 bottle per team)
• Student set of colorless, transparent tape (cheap, off-brand kind works best), (1 roll per team)
• Glass slides
• Facial tissues (1 box)
• Compound Light Microscopes (400 x)
• Plants (quack grass, dandelions, or leaves from various deciduous bushes or trees)
• (Optional, electronic CO₂ and pressure sensors and recorders)

Connections

Gotta Count Stomata can be used in ecology units to connect ideas about how different biotic (competition, species diversity, predation, human impact) and abiotic factors (altitude, sun exposure, wind, salination, humidity, soil compaction, pH, pollution, etc.) interact.  Additional topic connections include, water balance, respiration, transpiration, natural variation, evolution, and adaptation.

Lesson Plan Framework (Based on an Instructional Model for Contemporary Science Education¹)

1.  Engage  To get students interested and actively participating in the inquiry process, try to create a situation where the student can experience the phenomenon first hand, then brain storm with the students as to the possible causes of the phenomenon.  For the study of transpiration such engaging activities could include any of the following:  sharing a very stale snack (cookies, crackers, chips, dried fruit and vegetables etc.) with the students, then discuss why some students do not like the way this food tastes.  Have students place rubbing alcohol on their arms or fingers with cotton balls and record their observations.  Discuss the changes that occurred (evaporation, heat transfer, dehydration). Comparison between two plants, one wilted and one frequently watered.  Ask students what happened to the wilted plant.  Have students breath on a mirror.  Ask the students what makes the mirror foggy and where did it come from?

Once students have developed a working model of water flowing through living things, ask students to draw a diagram of how water flows through a plant.  Discuss student models and introduce the concept of stomata and how they functions to regulate the flow of water through a plant.  Demonstrate the movement of gases through a plant by using a potometer (Can Air Enter Through a Leaf?² ) or an electronic CO₂ or pressure sensor connected to a computer (Biology with Computers (or CBL) )³.  Discuss with students the costs (dehydration) and benefits (continual transport of water and minerals) of transpiration.

Demonstrate the technique for making an imprint of the epidermis to visualize the stomata present on the epidermis of a leaf.

• Lightly paint the epidermis of a leaf with colorless, transparent fingernail polish.  Coat only a small    area of the leaf blade (1 cm²) leaving a large portion of the leaf uncoated to create a nonsticky tab to peal the nail polish off the leaf.
• Allow nail polish to dry.
• Apply a strip of colorless, transparent tape on top of the nail polish.
• Gently peal off the tape with the nail polish imprint of the leaf attached.
• Stick tape to glass slide and gently smooth out the air bubbles using your fingers and a piece of tissue paper to avoid smearing oils from your skin on the slide.

2.  Explore  Students work together in small groups, collecting and observing stomata densities found on different plants in different locations. Students make sketches of their leaves, and record any important information about the environment in which the plant was growing (elevation, source of water, sun and wind exposure, competition, predation, human impacts, ect.).  Finally, students share their observations with the rest of the class.  (Teacher Hint:  By using a microscope connected to a T.V. monitor, students can display their findings directly for the entire class).

3.  Explain  Students are asked to develop a theory for stomata function, based on their direct observation, and intuition.  At this time the teacher may introduce students to the structure of a leaf and relevant terms such as guard cells, spongy mesophyll, stomate, and stomata.  Based on this common vocabulary, the teacher can consolidate the student's ideas into a class theory for stomata function.  The teacher should then ask the students if they have any evidence to support their theory?  If the students are unable to provide supporting evidence for any portion of their theory, they should be directed to design an experiment which would test the validity of their theory.

4.  Elaborate  Students write a hypothesis based on the class theory of stomata function, then design an experiment to tested their hypothesis.  For example, if the class theory states that greater densities of stomata will occur where plants are more photosynthetically active, then a test comparing stomata density in areas of partial and direct sunlight could be conducted.  This information could then be compared to measurements of CO₂ absorption to see if any correlations exist between these two tests. Students should write up formal experimental design, and data recording sheets that should be peer and teacher edited before they begin collecting their data.  Students should be encouraged to conduct multiple trials of their experiment and express their data in an appropriate statistical format (i.e. averages, standard deviations, chi square test, etc.).

5.  Evaluate  Students should formally present their finding in the formal lab write-up and a class presentation.  Students should constructively critique each of the other group's work, and to write a post presentation reflection on this activity which requires them to integrate the knowledge and skills gained throughout the activity and to apply this information to other areas of their lives.

Science Standards

The activities described here meet the following National Science Standards.

• Science as Inquiry [5-8, & 9-12]
• Life Science, Content Standard C.  Grades 5-8:  structure and function in living systems, regulation and behavior,  diversity and adaptations of organisms.  Grades 9-12:  the cell;  biological evolution;  the interdependence of organisms;  matter, energy, and organization of living systems;  behavior of organisms.

1.  Bybee, Roger, W.  1997.  Achieving Scientific Literacy, from Purposes to Practices.  Heineman, publishers a division of Reed Elsevier Inc., Portsmouth, NH.  ISBN  0-435-07134-3.

2.  Liem, Tik, L.  1987.  Invitations to science inquiry, 2nd Edition.  Science Inquiry Enterprises, publishers Chino Hills, CA.  ISBN  1-878106-21-X

3.  Biology with Computers or Biology with CBL.  Vernier Software & Technology, Beaverton, OR.  (503)277-2299.  http://www.vernier.com/cmat/BWC.html

Student Activity:

Some students may not need a handout.  Others will benefit from the use of a worksheet to remind them of the scientific process and explain the procedure.  Please click here for the student handout.