Name ______LAB 9
Homeostasis in Stomates
Introduction:
Stomates are special openings on the underside of leaves that allow for the exchange of carbon dioxide and oxygen between the tissue inside the leave and the environment. Water vapor also passes out of the leaf through the Stomates. The Stomates are not open all the time. Instead, they open and close according to the needs of the leaf. This is an example of homeostasis. Each stomate is surrounded by a pair of specialized epidermal cells called guard cells. The kidney shaped guard cells regulate the opening and closing of the Stomates. Stomates allow for the process of transpiration to occur with in a plant. Transpiration is the evaporation of water vapor from plant surfaces.
Materials:
Crisp spinach leafDropper
ForcepsMicroscope slide
Microscope cover slipCompound light microscope
Procedure:
1.Soak spinach in water.
2.Take on leaf and tear it gently, crosswise.
3.With forceps, carefully remove a thin layer of lower epidermis from the piece of spinach, (it should be transparent)
4.Place it on a microscope slide and add a drop of water. If the spinach epidermis becomes folded on the slide, use a probe to gently unfold and flatten it. Add a cover slip.
5.Observe the epidermis under low power of the microscope. HINT: you may need to adjust the amount of light entering through the diaphragm in order to see the cells clearly.
6.Switch to high power and identify the guard cells which are half circle-shaped cells and the Stomates whichare the small spaces or openings between the guard cells.
Record the number of Stomates in your field of view:______
Make a drawing of the high power field of view. Include the epidermal cells, guard cells, stomates, and chloroplasts.
7. Lift up the cover slip and place a drop of 4% salt solution on the spinach epidermis. How has the stomate opening changed in comparison to your first observation? ______
When plant cells are placed in a 4% salt solution, does water move into or out of the cells? ______
As water is lost from guard cells they tend to collapse. Based on your observations, does this cause the stomates to open or close? ______
As water is gained by guard cells, they tend to swell. Based on your observations, does this cause the stomates to open or close? ______
Analysis and Observations
1. What is the function of the chloroplasts in the guard cells? ______
2. While guard cells are performing photosynthesis, what happens to their sugar concentrations? Their water concentration?
______
3. What part of the 24 hour day are stomates opened, closed? ______
4. How does the shape of a leaf help it use sunlight efficiently? ______
5. Explain the function of the cuticle. ______
Part B
Construct a line graph based on the information in the table, which shows the hourly rate of transpiration in a plant over a 16-hour period. Plot time on the x-axis and transpiration rate on the y-axis.
Time (h) / Transpiration rate (g/h) / Time (h) / Transpiration rate (g/h)8 am / 190 / 4 pm / 227
9 am / 200 / 5 pm / 220
10 am / 209 / 6 pm / 213
11 am / 215 / 7 pm / 208
12 noon / 221 / 8 pm / 190
1 pm / 227 / 9 pm / 120
2 pm / 233 / 10 pm / 100
3 pm / 230 / 11 pm / 98
After completing the graph, answer the following questions
1. At what times are the rates the highest? ______
2. At what times are the rates the lowest? ______
3. How do you account for this? ______
4. What is the independent variable? ______
5. What is the dependent variable? ______
6. What is the transpiration rate at 8:30 pm? ______
Part C
1. What typical plant cell organelle would a root cell have less of than a leaf? Explain.
______
2. If the atmosphere was contaminated and only green light was able to pass through the ground, what would surviving plants look like in a thousand years?
______
3. What factors regulate the opening and closing of stomates?
______
4. Explain how your answer to question 3 is an example of homeostasis?
______
5. What effect would a drought have on a plant regarding stomates?
______
6. On which leaf surface of a water lily plant would you expect to find the stomates (top or bottom)? Explain your answer.
______
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