Graduate Fellows in K-12 Education

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Raymond Ryan
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Graduate Fellows in K-12 Education Lesson Title: Stomatal Density Lab Discipline Focus: General Biology Grade level:10 th Grade Length of lesson: One 50 minute class period Stage 1 Desired Results

1.1 Explain how cell processes are affected by internal and external factors and how cells respond to their environment to maintain homeostasis 9.1.3.4.

1 Graduate Fellows in K-12 Education Lesson Title: Stomatal Density Lab Discipline Focus: General Biology Grade level:10 th Grade Length of lesson: One 50 minute class period Stage 1 Desired Results Content Standard(s): Minnesota Academic Standards in Science Explain how cell processes are affected by internal and external factors and how cells respond to their environment to maintain homeostasis Select and use appropriate graphical representation to communicate results Understanding (s)/goals Students will understand: 1. Plants must make tradeoffs to maintain water homeostasis. 2. Interaction between plants and different environmental conditions Essential Question(s): How do plants use stomata to regulate water homeostasis? Student objectives (outcomes): Students will be able to: Explain the basic structure and function of stomata and how plants use them to maintain water homeostasis (by placement of stomata on different leaf surfaces). Performance Task(s): Students will fill out a worksheet during the activity. They will conduct an experiment counting stomata on upper and lower leaf surfaces and collect data, analyze it, report results in a graph. Stage 2 Assessment Evidence Other Evidence: 1. Students will form a hypothesis based on their knowledge of stomata and a plant s need for water homeostasis and carbon dioxide for photosynthesis. 2. Students will be asked to explain whether or not their hypothesis was supported by results and why. 3. During follow up discussion students will be asked to verbally explain what they observed during the experiment and their conclusions related to their hypothesis. Stage 3 Learning Plan Learning Activities: Prior to beginning the lab, students should have some knowledge of stomata structure and function, photosynthesis, and transpiration. Students should be given a demonstration of how to make slides. Before the lab, a short video of stomata opening and closing was shown as well as a projection of a prepared slide with stomata so students can identify them. Students were also asked some questions before the lab to ensure that they understand stomata structure and function, and to get them thinking about the questions at the beginning of the lab.

2 Materials: clear nail polish, slides, clear tape, sharpies for labeling slides, leaves (ivy works particularly well, any plant with hairy leaves will be difficult to use with this procedure), calculators for calculating averages. Instructions for making slides (to be posted at lab tables or an overhead): 1. Select a leaf and tear it in two pieces. 2. On one piece, paint a thin, even coat of nail polish over a section of the upper side of the leaf of approximately 1 cm. 3. On the other piece, paint a section of nail polish on the lower side of the leaf. 4. Let the nail polish dry completely (approximately 5 minutes). 5. While waiting, label the top of the left side of your slide B for bottom and the right side T for top. 6. When the nail polish is completely dry, take a piece of clear tape no bigger than half of your slide and firmly press it on the nail polish on the bottom side of the leaf. 7. Carefully pull the tape off of the leaf, only lifting the nail polish from the leaf surface. 8. Place this tape on the left side of your slide labeled B. 9. Repeat steps 6 8 for the top section of leaf and place this piece of tape on the right side of the slide labeled T.

Stomata Counting Protocol 1. Place a stomata peel slide on the microscope stage and center the peel under the lowest power objective lens. 2. Focus on the peel from the bottom of your leaf. 3.

3 Stomata Counting Protocol 1. Place a stomata peel slide on the microscope stage and center the peel under the lowest power objective lens. 2. Focus on the peel from the bottom of your leaf. 3. Select the 10x objective lens. (Note: experiment with the leaves and microscopes you are using before the lab to determine appropriate magnification for the number of stomata students will likely be counting.) 4. If necessary, scan the peel until the entire field of view is filled with cells. 5. Draw what you see in this field of view in the figure provided on page 2 of your worksheet. 6. Count all stomata whose guard cells are more than half contained in the field of view. 7. Scan your field of view until it is completely filled with another section of cells from the same peel. 8. Repeat steps 5 and 6 for a total of three stomata counts from your peel. 9. Repeat steps 4 7 for the upper side of the leaf. 10. Find the average number of stomata from the three stomata counts from the upper side and lower side of the leaf. 11. Have fun!

4 Name: Hour: Stomata are openings or pores on leaf surfaces that allow plants to take in CO 2 from the atmosphere, which is necessary for photosynthesis. Plants also lose water through stomata by transpiration. One way that plants can minimize water loss (or maintain water homeostasis) while acquiring CO 2 is to regulate the number of stomata on the upper and lower surfaces of their leaves. In this lab you will compare stomatal densities on upper and lower leaf surfaces. 1. Form a hypothesis Answer the following questions based on the information presented before the lab. What tradeoff do plants have to address that may affect stomatal density on one side of a leaf vs. the other side? List at least one potential advantage or disadvantage of having more stomata on the upper and lower side of the leaf (hint: think of a hot, sunny day): Upper side of the leaf: Lower side of the leaf: Based on this knowledge, which leaf surface do you think will have more stomata? Why? Form a hypothesis answering these questions. 2. Make stomata peels and collect data Using the instructions provided, prepare a slide with a peel from the upper surface of a leaf and the lower surface of a leaf to fill in the table below. Table 1.1 Number of stomata on upper and lower leaf surfaces. Report your average number of stomata from the upper and lower leaf surfaces to your teacher. Plant Number of Stomata Upper Number of Stomata Lower Average:

5 Figure 1.1 Draw and label stomata and leaf cells of the lower leaf surface as you see them in your field of view. 3. Record results Use the results provided by your teacher for the entire class s data to fill in average number of stomata and then graph those results. Class averages for number of stomata: Upper leaf surface Lower leaf surface Figure 1.2 Graph the class averages for number of stomata on upper and lower leaf surfaces. 4. Conclusion Based on the class s data, was your hypothesis supported or rejected? Explain.

Figure 1. Basic structure of the leaf, with a close up of the leaf surface showing Stomata and Guard cells.

Figure 1. Basic structure of the leaf, with a close up of the leaf surface showing Stomata and Guard cells. BIOL100 Laboratory Assignment 3: Analysis of Stomata Name: Stomata (singular=stoma) are the respiratory control structures in plants (see Figure 1 below). They are essentially small holes in the surface