Plant Transpiration Lab

Plant Transpiration Lab 

           

         In this online lab, I compared the rates of transpiration on nine different plant species undergoing varying environmental conditions. We used a potometer to determine the mL of water of each plant in the experiment. I tested and recorded data, observing the effect of environmental factors (wind, heat and light) on the plants transpiration rate for an hour. My control was the plants transpiration rate without any environmental factors interfering. All of these influences and environmental factors increased the transpiration rate of the plants.  

Here are my results of the nine plants in the lab

Amount of water transpired in 1 hour (mL)

   Plant                         Control                     Fan                           Heat                         Light

Arrowhead	3.6	7.5	6.6	4.0
Coleus	0.9	6.0	3.9	3.0
Devil’s Ivy	2.9	4.4	4.1	3.6
Dieffenbachia	4.1	7.7	6.0	3.9
English Ivy	1.8	5.1	3.2	2.1
Geranium	1.2	4.7	5.8	2.4
Rubber Plant	4.9	8.4	6.8	4.3
Weeping fig	3.3	6.1	4.9	2.5
Zebra Plant	4.2	7.6	6.1	3.2

About 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." (Online Plant Transpiration Lab )

Journal Questions

1. Describe the process of transpiration in vascular plants

    Transpiration is a process like sweating for plants. Leaf and stem surfaces are dotted with stomata (small openings like pores) that are more numerous on the underside of the leaf. The purpose of transpiration is to cool the plant and enable the flow of minerals and nutrients from the root to shoot. All plants continuously absorb water through their roots. This water is conducted upward through the stem and is distributed to all the aerial parts including the leaves. Only a small quantity of this water (about 2%) is used by the plant in photosynthesis and other activities. The rest of it is almost lost to the atmosphere as water vapor. Transpiration is a very useful process for the plants for two reasons: first, to get rid of the excess water absorbed and second, for cooling the plant in hot weather. 

2. Describe any experimental controls used in the investigation.

    The control for this experiment was recording each plants rate of transpiration without any environmental factors influencing the test.

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

    All the factors that were used (wind, heat, light) influenced the rate of transpiration by increasing it. The data table shows that all plants had an increase in their rate of transpiration with every factor tested. 

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

    Yes. Plants transpire in light with a more rapid rate than in the dark. This is a legal factor because in the light the stimulation of opening of the stomata is larger than in the dark. Due to light, the cells vibrate against each other, warming the leaf making the temperature increase, speeding up the process. Heat and the rate of the temperature also affect the rate of transpiration. They transpire more rapidly when the temperature is high because at high temperature water evaporates more rapidly. 

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?

    According to the data collected, the rubber plant had the highest transpiration rates. There are a number of reasons why different species of plants transpire at different rates. For example, the origin of the plant - plants originally from sub-tropical or tropical areas will transpire at a higher rate than those originally from arid or semi-arid areas. The size of the plant (larger leaf surface area = more transpiration). The metabolic rate of the plant = plants with a higher metabolism have a higher transpiration rate. The amount of water in the soil - plants that have access to more soil water will transpire at a higher rate than those which don't. Availability of nutrients - plants which have adequate nutrient supplies have higher metabolic rates than those which don't, and therefore transpire at a higher rate.


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

    If I coated the leaves of the plant with petroleum jelly, the act of transpiration would completely stop. By covering the entire leaf with petroleum jelly the plants gard cell would be unable to obtain co2 from the atmosphere thus making the rate of photosynthesis stop and if photosynthesis stops the plant will not be able to produce glucose and in doubt will not be able to produce ATP and will die. 


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

    Because water has cohesion between molecules it is drawn up through the xylem when the water evaporates from the top of the column. This creates the transpiration flow through the xylem and carries any dissolved nutrients upwards with the water. Having the ability to draw water and nutrients upwards to a branching leaf canopy allows plants to spread the leaves to intercept more sunlight. Transpiration raises the air humidity and moderates the daily change in temperature. Evaporation cools the leaves just as sweat evaporating from skin is cooling.