Comparison of Opening or Closing of Stomata under Selected Conditions

Activity 2: Pre-Assessment

1. What environmental conditions could be applied to a plant that would cause it to open more of its stomata?
2. Do you think there is a condition that would result in mostly closed stomata?
3. Discuss the answers to questions 1 and 2 with the class.

Activity 2: Comparison of Opening or Closing of Stomata under Selected Conditions

Plants will open or close stomata based on many factors. Stomata help regulate the water needs of the plant and exchange gases with the environment. If there is too much water inside the cells, stomata will open to release the pressure. If water pressure is low, stomata will remain closed to retain moisture. However, to keep water moving up from the roots and into the leaves, some stomata do need to open to build the negative pressure that allows roots to draw up water. Special cells, called guard cells, act like doors to open or close stomata.

Safety Precautions

• Avoid directly inhaling nail polish fumes.
• Handle the microscope carefully and always carry it with two hands.

For this activity, you will need the following:

• Scissors
• Clear nail polish
• Empty microscope slides
• Microscope
• Leaves
• Clear cellophane tape
• Forceps

For this activity, you will work in pairs.

Structured Inquiry

Step 1: Prepare slides of leaf samples at normal room conditions. To do this, you will cut a sample of a leaf and coat both sides of the leaf with clear nail polish. Allow it to dry completely by holding the sample and waving it gently in the air.

Then, create wet mounts of the leaf samples and observe them under the microscope.

Step 2: Hypothesize/Predict: What percentage of open to closed stomata do you expect to find? Record your hypothesis in your notebook.

Step 3: Student-Led Planning: Prepare a data table to count the stomata. Then, place the slide under the microscope and count the number of stomata. Record your data in your table. If there is time, consider making more than one sample.

Draw sketches of the samples.

Step 4: Critical Analysis: Is it simple or complicated to count the stomata? Is it possible to count the same ones more than once? How did you ensure this did not happen? What did the results show when the leaves from the two different trials were compared?

Guided Inquiry

Step 1: Hypothesize/Predict: Choose a condition to which you will expose a leaf sample for 20 minutes. How do you think the altered condition will affect the stomata? Record your ideas in your notebook.

Step 2: Student-Led Planning: Prepare a slide of the leaf sample by cutting a leaf and coating both sides with clear nail polish. Allow the leaf sample to fully dry before placing it on the microscope slide. Prepare a data table and count the number of closed and open stomata. Draw sketches of the samples.

Step 3: Critical Analysis: Compare your results to the results from the Structured Inquiry. What conclusion can you draw from the data? Write your answer in your notebook.

Assessments

1. In a certain habitat, the plants can keep their stomata open for most of the day. What does this suggest about the characteristics of the habitat?
2. Could a researcher estimate how many plants in an enclosed area have their stomata open using the concentration of carbon dioxide in the air? Explain your answer.
3. How could a research scientist use the methods in this lab to determine how to care for a given species of plant?