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Exploring the Effect of Leaf Polish on Transpiration Rates and Stomatal Density in Plants, Lab Reports of Biology

Shippensburg University of Pennsylvania (SU)Biology

Instructions for a lab experiment investigating the impact of leaf polish on transpiration rates and stomatal density in plants. Students will learn about transpiration, use potometers to measure transpiration, test the hypothesis that leaf polish does not change transpiration rates, and determine the number of stomata per mm^2 on leaves. The document also includes instructions for data collection and analysis using a t-test.

Typology: Lab Reports

Pre 2010

Uploaded on 12/15/2009

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BIO 1
Section 3
Dr. Pablo Delis
Student Name
10/22/09
Plants 1- Does Leaf Polish Change Transpiration Rates?
Pre-Lab Library Research Assignment- Factors that influence opening and closing of
stomata:
•Large surface areas and high surface-to-volume ratios of leaves
•Number of stomata on a leaf
•Size of the pores of the stomata
•Stomatal density of a leaf determined by genetic and environmental control
•Changes in turgor pressure of guard cells (Campbell and Reece 277)
The objectives of this lab is to explore the factors that affect the transpiration rate of
plants. Students will learn how to explain what happens during transpiration, describe a
potometer and explain how it is used to measure transpiration, determine if leaf polish
changes transpiration, determine the number of stomata per mm^2 on leaves, and use
a t-test to compare means.
Transpiration is defined as the loss of water vapor from plants. It occurs mainly through
the stomata. In this lab, potometers are used to measure the effect of leaf polish on
transpiration rates. Stomata are pores in the surface of the leaf that open and close to
regulate the leaf's rates of water loss and carbon dioxide uptake. Open stomata allow
gas exchange of water vapor, oxygen and carbon dioxide. Leaf polish is used to give
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BIO 1

Section 3 Dr. Pablo Delis Student Name 10/22/

Plants 1- Does Leaf Polish Change Transpiration Rates?

Pre-Lab Library Research Assignment - Factors that influence opening and closing of stomata:

  • Large surface areas and high surface-to-volume ratios of leaves
  • Number of stomata on a leaf
  • Size of the pores of the stomata
  • Stomatal density of a leaf determined by genetic and environmental control
  • Changes in turgor pressure of guard cells (Campbell and Reece 277) The objectives of this lab is to explore the factors that affect the transpiration rate of plants. Students will learn how to explain what happens during transpiration, describe a potometer and explain how it is used to measure transpiration, determine if leaf polish changes transpiration, determine the number of stomata per mm^2 on leaves, and use a t-test to compare means. Transpiration is defined as the loss of water vapor from plants. It occurs mainly through the stomata. In this lab, potometers are used to measure the effect of leaf polish on transpiration rates. Stomata are pores in the surface of the leaf that open and close to regulate the leaf's rates of water loss and carbon dioxide uptake. Open stomata allow gas exchange of water vapor, oxygen and carbon dioxide. Leaf polish is used to give

the leaf surfaces of houseplants a glossy appearance. Leaf polish is not supposed to clog the stomata. The hypothesis being tested is that leaf polish will not change the rate of transpiration. I. Transpiration Rates Groups will be assigned two to a potometer. Each bench will have one group setting up a control with the other setting up the plant with leaf polish. The plants that will be used in this lab were cultivated in the SU greenhouse. The student must cut an aerial shoot at point where the diameter is slightly greater than that of the polyethylene tubing of the potometer. While the shoot is immersed in water, the student must trim the end of the shoot on an angle. The student must remove all bubbles from the potometer by squeezing water from a rubber pipette through the potometer. The student then inserts the shoot through the plastic collar of the potometer. Then, apply some petroleum jelly to seal the fit. Then, support then assembly with a ring stand. Make sure that no air enters the potometer. Make sure the leaf is dry before spraying it with the polish treatment. Coat each side of the leaf with polish until the polish runs off. Record the brand name and manufacturer of the leaf polish. Null Hypothesis: Leaf polish will not change the rate of transpiration Alternate Hypothesis: The leaf polish will decrease the rate of transpiration Collecting Data Record the ambient conditions in the lab manual. Allow the system to equilibrate for five minutes, then mark an initial position of the meniscus with a wax pencil (zero minutes). Take readings every five minutes by measuring the distance that the meniscus of the water column has moved up the capillary tube and record it in data Table 1. After 30

computed for your data with a value form a t-table. If the value from your data is larger than the value in the table the observed difference between the two means is significant and not due to chance alone. Most biologists want to be at least 95% sure their result is significant. Therefore, in this experiment, the P value must be less than 0.05 for you to consider a difference between the transpiration rates of the control and the experimental group to be statistically significant. II. Number of Stomata After removing a leaf form a plant, the student myst prepare casts of the leaves surfaces by painting the top surface of one leaf and the bottom surface of the same leaf with a thick coating of clear fingernail polish, coating an area about 1.5 times the size of a microscope cover slip. The nail polish must be applied to dry leaves or the replica will be cloudy and may not dry correctly. After allowing the nail polish to dry for 10 minutes, put an optional second coat on to make it easier to remove the cast from the leaf. Label microscope slides as either adaxial, or top of the leaf, or abaxial, bottom of the leaf while the nail polish dries. Cut a 1.5 cm piece of Scotch tape and fold the tape over itself leaving .5 cm of sticky surface exposed. Place the tape at the edge of the leaf so that it sticks to the nail polish cast. The remaining tape is used as a handle to carefully pull the nail polish cast from the leaf surface or use probes and forceps. The portion of the cast not covered by tape will be used to view stomata. Place the cast on the appropriately labeled slide and put a coverslip on the cast. Examine the slides under high power to determine whether both leaf surfaces have stomata and answer the correlating questions in the lab manual.