Plant Transpiration Activity, Lab, and Questions

The Online Lab Setup 

In class we have been learning about plant evolution, photosynthesis, and now transpiration. For homework, we did an online lab that tested the different amounts of transpirations in 9 different plants. The transpiration levels were tested using a heater, fan, and light as possible factors of influence. All of these environmental factors effected each of the plants by increasing their rate of transpiration.


The picture below is what was used in the lab to help determine the mL of water. 

The results of the 9 different plants are posted down below in the table.

Table of Data for Plant Transpiration Lab 

After completing the lab, the website offers more information regarding plant transpiration:

"What factors affect the transpiration rate in plants?

In vascular plants, water is absorbed through the roots and carried upward through the stem to the leaves. The force behind this upward movement is called capillary action, a force of attraction between molecules that causes liquids to move up narrow tubes, such as those inside a plant's stem. 

Some of the water absorbed by a plant's roots is used for photosynthesis, but much is lost to the environment through a process called transpiration. During photosynthesis, tiny pores on the surface of the leaves, called stomata, open to permit the intake of carbon dioxide and the release of oxygen. Because the stomata must remain open for the exchange of gases, large amounts of water are lost to the environment through evaporation. 

Water that evaporates from the leaves is continually replaced with water that is absorbed through the roots. Therefore a plant's rate of transpiration can be measured by observing the amount of water taken up through a plant's roots over a period of time. The transpiration rate can be approximated by measuring the amount of water taken up in a short time through the plant's stem. 

In a laboratory, a plant's transpiration rate can be measured using a potometer. A potometer can be assembled from standard laboratory materials including: a ring stand, clamps, a 10mL pipette, a 100mL burette, a T-tube, glass tubing, and rubber tubing. 

To measure transpiration rate, a plant sprig is mounted on the potometer and the burette and pipette are filled with water. Over time the plant will transpire and absorb water through its stem. The potometer is constructed in such a way that the plant's water source is the pipette, therefore the amount of water transpired over time can be determined by reading the water level in the pipette after time has passed. The water supply in the pipette can be replenished from the water supply in the burette by releasing the pinch clamp." (Information Source)

Lastly, we were asked to complete the journal questions that followed up the lab.

Journal Questions:

1.) Describe the process of transpiration in vascular plants.

Transpiration is the release of water from a plant, as the water evaporates into the atmosphere from the leaves and stems of plants. In transpiration, water travels from the soil into the roots of plants, and up to the underside of plant leaves, where it is released into the air. This evaporation of water from plants into the atmosphere happens due to the small pores in the leaves called stomates. Stomates are small openings underside leaves that are connected to tissues of a vascular plant. 

2.) Describe any experimental controls used in the investigation.

The controls for the plants were by testing the normal amounts of transpiration in the plant without the influence of any environmental factors. 

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

All of the factors that were tested (heat, wind, light) influenced the rate of transpiration by increasing it. In the data, all of the plants showed the same increase with these factors.

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


The heat increased the rate of transpiration in the plants the most. This is because the heat acted as a type of  "catalyst" to speed of the rate in which the plant transpires. 

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?

Based on the data collected, the rubber plant had the highest rate of transpiration. Different amounts of water found in soil can influence this, as well as the plant's own metabolic rate. 

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

The jelly would impact the plant's rate of transpiration by slowing it down significantly. This would occur because the jelly would block the plant's stomata on its underside, and now allow the water in the plant to evaporate. 

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

Because water has cohesion between its molecules, the water is "pulled up" through the xylem. When the water evaporates, this creates the transpiration flow through the xylem and carries any dissolved nutrients with the water itself. For plants, having the ability to draw water and nutrients upwards to branching leaves allows plants to spread its leaves to receive more necessary sunlight.