Transpiration Lab

1. Describe the process of transpiration in vascular plants

There are many stomata in the epidermis of a leaf. Most of them are in the lower epidermis. This reduces the loss of water because the lower epidermis is exposed to less solar radiation than the upper epidermis. During photosynthesis, the stomata are open for carbon dioxide to enter. Meanwhile, water evaporates from stomata.

2. Describe any experimental controls used in the investigation.

In the experiment, for each plant, the type of plant is controlled for different conditions to be tested. The amount of time for the transpiration data is controlled--1 hour for all experiments.

3. What environmental factors that you tested increased the rate of transpiration? Was the rate of transpiration increased for all plants tested?

The amount of wind, the temperature, and the amount of light can cause the change in the rate of transpiration. For all plants, increased wind and higher temperature increase the transpiration rate. For some plants, the increase in light intensity and amount does not increase the rate of transpiration.

4. Did any of the environmental factors (heat, light, or wind) increase the transpiration rate more than the others? Why?

In general, the increasing amount of wind causes the greatest increase in transpiration rate. Wind increases the movement of water from the leaf surface when it reduces the boundary layer, because the path for water to reach the atmosphere is shorter. Higher temperature increases the rate because water will evaporate faster when the temperature is high. The increasing amount of energy causes the water molecules to move faster.

5. Which species of plants that you tested had the highest transpiration rates? Why do you think different species of plants transpire at different rates?

The species with highest transpiration rates are rubber plant, zebra plant, and dieffenbachia. Plants with higher transpiration rates tend to live in sub-tropical or tropical areas, where rainfall is abundant and the temperature is usually high. More water would evaporate from large amount of wind and solar radiation.

6. Suppose you coated the leaves of a plant with petroleum jelly. How would the plant's rate of transpiration be affected?

When the leaves are blocked by petroleum jelly, stomata are covered as well and light cannot penetrate through. The carbon dioxide would be trapped inside the stomata and water cannot evaporate from the leaves. Therefore, no transpiration would take place.

7. Of what value to a plant is the ability to lose water through transpiration?

Losing water is a crucial ability for plants because this is the way for them to operate their metabolism and keep homeostasis. By intaking new water, the plants are able to process photosynthesis and make products such as glucose and oxygen.

This graph is the percentage of each transpiration rate compared to the rate in normal condition.