Transpiration (Lab 9)

Some Key Review Concepts

Movement of Water in Plants

Water enters a plant through the root hairs, passes through the tissues of the root into the xylem, and travels up through the xylem vessels into the leaves. Transpiration, the evaporation of water from the leaves, is the major factor that pulls the water up through the plant.   It is important to recognize that this upward conducting tissue is continuous through vascular or tracheophyte plants, starting at the roots and continuing upward through the plant to the leaves.

Transpiration

There are hundreds of stomata in the epidermis of a leaf. Most are located in the lower epidermis. This reduces water loss because the lower surface receives less solar radiation than the upper surface. Each stoma allows the carbon dioxide necessary for photosynthesis to enter, while water evaporates through each one in transpiration.

Guard Cells

Guard cells are cells surrounding each stoma. They help to regulate the rate of transpiration by opening and closing the stomata.

Lab Design

In this lab, you use a potometer. A potometer is a device that measures the rate at which a plant draws up water. Since the plant draws up water as it loses it by transpiration, you are able to measure the rate of transpiration.  

Set up four potometers to measure the rate of transpiration of four different scenarios. The four different situations are room temperature (control), mist, wind, bright light.

Measure the water loss in each of the potometers every three minutes for thirty minutes.

You will also need to measure the surface of the leaf.

In the other part of the lab you will need to be able to recognize the following plant structures: xylem, phloem, parenchyma, and epidermis.

Analysis of Results