Download Stomata

BIOLOGY – Activity
Stomata
Names _____________________
_____________________
_____________________
_____________________
_____________________
Period 1 2 3 4 5 6 7 8
Date: _____________
Station # _____
INTRODUCTION
The leaf is the main organ through which water is given off by a plant. As a plant
absorbs water through its roots, the water is carried through the stem to the leaves. Some of the
water is used in the leaves during photosynthesis. However, more water is taken in and
transported to the leaves than can be used during photosynthesis. The excess water evaporates
into the atmosphere through the stomata, or pores, in a process called transpiration.
Stomata are openings generally found on the underside of leaves. They are formed by
two specialized epidermal cells called guard cells. Guard cells regulate the passage of water
vapor, oxygen gas and carbon dioxide into and out of the leaf.
In this investigation, you will observe guard cells in a fresh leaf and estimate the total
number of stomata in the leaf.
OBJECTIVE
To observe and estimate the number of stomata in a leaf
MATERIALS
fresh leaf
wilted leaf
forceps
microscope
pipette
metric ruler
glass slides
cover slip
calculator
PROCEDURE
1. Place a couple drops of water in the center of a glass slide.
2. Use the forceps to carefully remove the thin layer of epidermis from the
underside of the fresh leaf and spread it out as smoothly as possible in the
drop of water on the slide. Cover the specimen with a cover slip.
Refer to the diagram in Figure 1.
Figure 1
3. Observe the leaf epidermis under low power. Don’t forget to adjust the diaphragm
for the best lighting. Notice the guard cells which are pairs of kidney-shaped cells
scattered among the irregular epidermal cells. The spaces between the guard cells
are the stomata.
4. Move the slide to center a guard cell pair in the field of view and switch to highest
power. In the observation section, draw a stoma guard cell unit as seen at the
highest power. Label the guard cells, the stoma and a chloroplast.
5. Save your fresh leaf slide and repeat the procedure using the wilted leaf.
6. Observe the fresh leaf again under low power. Count the number of stoma-guard
cell units seen in the field of view and record this number in data table 1.
7. Without moving the slide, switch to high power and count and record the
number of stoma-guard cell units seen.
8. Recall that the low power field of view diameter is 4.5 mm and the calculated high
power field of view diameter is 0.45 mm. Calculate and record the radius for
each field of view. Enter this in data table 2.
9. Calculate and record the area of each field of view using the formula :
area = π r2
10. Calculate and record for each field of view the number of stomata per square cm
using the formula:
stomata / cm2 = total number of stomata / area (cm2)
OBSERVATIONS
Magnification _______________
Magnification ________________
Data Table 1
Low Power
High Power
Low Power
High Power
Number of Stomata
Data Table 2
Measurement
Radius (mm)
Radius2 (mm2)
Area (mm2)
Area (cm2)
Stomata / cm2
ANALYSIS
1. How do the sizes of the stomata in fresh and wilted leaves compare?
__________________________________________________________
__________________________________________________________
2. Explain why the stomata in wilted leaves may be a different size from the
stomata in fresh leaves.
__________________________________________________________
__________________________________________________________
3. What is the function of the guard cells?
__________________________________________________________
_________________________________________________________
4. Why are the stomata of a leaf open during the day and closed at night?
_________________________________________________________
_________________________________________________________
5. Which plant leaf would you expect to have more stomata, that of a desert plant
or that of a water plant? Explain.
_________________________________________________________
_________________________________________________________
_________________________________________________________
6. On which side of the leaf would you expect to find the stomata of a
floating water lily? Explain.
__________________________________________________________
__________________________________________________________
__________________________________________________________