Students should be able to:
A plant's need for water is dependent on the condition and type of plant, environmental stresses and the availability of the water at any given time. Water is used by the plant for maintenance and growth, and it moves through the plant via vascular tissues. These tissues are conductive and water is literally "pulled" up the plant. This lab will concentrate on the processes of transpiration and water absorption as it occurs in some common local plants.
Large amounts of water move through a plant on a daily basis. The plant looses water by two basic processes. These processes are transpiration, which is the evaporation of water from a plant's surface (stomata); and guttation, which is the loss of water at the leaf margins (hydathodes). In vascular plants, water enters the xylem tissue of the roots through extensions of the root epidermal cells. These extensions are called root hairs. The movement of water into the xylem occurs by osmosis and this movement creates what is termed root pressure. Root pressure can only force water up a short distance. Since a plant can be tall, the root pressure is not great enough to force water up to the leaves of the plant, therefore, another mechanism must be in play also. This mechanism is defined by the cohesion-tension model of xylem transport. If the water lost by a plant through transpiration and guttation is not replaced then the plant will wilt and eventually die.
In this laboratory exercise you will microscopically examine the vascular tissues of plants and perform an experiment designed to measure the effect of various environmental conditions on the transpiration rate.
Pre-Lab Activity #1 - Set-up for Lab
The Laboratory Activities and Data Collection
Lab Activity #1 - Transpiration in Vascular Plants
Let the set-up equilibrate for 10 to 12 minutes
At the end of the equilibration time, read the level of the water in the pipette and record it on your Data Collection Sheet. (time 0).
Continue to read and record the water level in the pipette every 10 minutes for 30 minutes.
Obtain data from the other lab groups.
Lab Activity #2 - Graphing the Transpiration Data
Post-lab Activities and Data Analysis
Results and Analysis