Counting Leaf Stomata
Plants and animals both have a layer of tissue called the epidermal layer. Plants have special pores called stomata to allow passage of material. The stomata pores are surrounded on both sides by jellybean shaped cells called guard cells. Unlike other plant epidermal cells, the guard cells contain chlorophyll to do photosynthesis. This allows the cells to expand/ contract to open or close the stomata. Guard cells also close when dehydrated. This keeps water in the plant from escaping. The opening or closing of guard cells can be viewed in a microscope by adding different water concentration to the leaf tissue.
Most stomata are on the lower epidermis of the leaves on plants (bottom of the leaf). The number of stomata on the epidermal surface can tell you a lot about a plant. Usually, a high concentration of stomata indicates fast growth and wet climate. Lower concentrations of stomata indicate lower rates of photosynthesis and growth or adaptations for dry weather.
To view and compare the stomata from the leaves of several species of plant
3 leaves (1 from 3 different species), compound light microscope, 3 microscope slides, clear nail polish, transparent tape
|Leaf 1||Leaf 2||Leaf 3|
|Name of Leaf|
(with several stomata)
|Stomata in field 1|
|Stomata in field 2|
|Stomata in field 3|
|Average Stomata in field|
1. Which leaf had the most stomata? Why do you think this was so?
2. Explain, in detail, how guard cells open and close stomata?
3. At what time of day would stomata be closed and why?
4. Why does the lower epidermis have more stomata than the upper epidermis of a leaf?
5. Define transpiration.
6. What two gases move in and out of the leaf stomata?
7. What does a larger number of leaf stomata indicate about the growing climate of that plant?
8. Would you expect CAM plants to have as many stomata? Why or why not?