Abstract
The purpose of this experiment was to determine the differences in transpiration rates among experimental stimuli. Transpiration occurs when the stomata of a plant loses water in the process of exchanging CO2 gas. The experimental stimuli tested in this experiment are the control, light, and wind. One tomato plant was placed under a light and another across from a fan in order to determine the differences when compared to a control. All three plants were attached to a transpirometer in order to supply the water needed for this experiment. The differences of the light and wind reaction were measures with a ruler and recorded. The results of this experiment show that the addition of light and wind increase the rate of transpiration.
Introduction
To survive and reproduce, land plants must cope with many environmental challenges. Among the biggest of these problems are obtaining water and avoiding desiccation (water loss) (Vodopich, Moore 219). One unique way plants have learned to adapt is through transpiration. Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. This process usually occurs due to a higher water potential inside the cells of a plants rather than the atmosphere. If there is enough water in a plant, the guard cells will become turgid as their vacuoles become filled with water. The opening or closing of stomata is determined by the water status which also affects the exchange of CO2 gas in the plant.
The plant used in this experiment is known as the BigBoy tomato plant. According to the University of Arkansas Division of Agriculture, the Big Boy plant prefers a moist, warm, and sunny environment (Anderson). All of these factors can possibly influence the rate of transpiration among the tomato plant. However, transpiration rates vary among all plants depending on their diverse environmental conditions.
The experimental stimuli tested in this experiment are the control, light, and wind. The dependent variables include the light and the wind which will be tested against the control for differences in the rate of transpiration. My hypothesis based on the light reaction is that the excess light will cause the transpiration rate to increase compared to the control. Because excess light is being applied, photosynthesis will be promoted, requiring the intake of CO2 and the release of water through the stomata. My hypothesis based on the wind reaction is that the flow of wind will also increase the rate of transpiration. Because the wind causes the removal of humidity in the atmosphere, the water moving up the plant will have more potential to leave the stomata into the dry air around the plant. The temperature of the room was kept within a local range in the three experiments in order to have no effect on the transpiration rate.
Methods
To prepare the plant before transpiration, acquire a section of the tomato plant stem, BigBoy Hybrid, ensuring that the diameter of the stem is larger than the tan rubber tubing that is attached to the pipette tip. Below the slightly larger diameter, cut the stem of the plant at its base and submerge in a water filled pan. To remove air bubbles, insert the pipette into a piece of rubber tubing attached in the pan of water. With the stem of the plant emerged in water, cut the plant again at a point where the stem is slightly larger than the rubber tubing. The stem must remain under water at all times to ensure that no excess air will cause errors. After fitting the tubing over the cut stem, hold the plant and tubing out of the water to check for any leaks. An indication of a leak will be showed by visible air gathering in the pipette tip. If this occurs, resubmerge and slide the tube further onto the stem. When preparing the apparatus, open the screw valve below the reservoir to flush out the system. Clear the micropipette of bubbles then clamp off using a spring clamp. Until no bubbles are present in the course of where the plant will be inserted, continue to flush the system. Next place the plant and pipette into the tube, wrap a paper towel around the plant’s stem, and place the plant into the open clamp. Close the clamp so that the plant is upright. On the line leading to the micropipette, open the spring clamp. In order to remove extra air, open the screw valve on the reservoir for water to drip, then blot the drop from the tip of the pipette. Blot the leaves of the plant if they are very wet. Within a few minutes, water should be drawn from the micropipette and transpiration should be visible. Record the data and observations every five minutes for fifteen minutes total. Repeat the experiment for the wind reaction with a fan that is placed 150 mm away. Repeat experiment again for the light reaction with a lamp that is places 150 mm away.
Results
In order to measure the rate of transpiration, the difference in water traveled was measured using a ruler. For each trial, the distance traveled was recorded every five minutes for fifteen minutes. The control experiment resulted in a traveled distance of 7 mm, the light experiment 10 mm, and the wind experiment 8 mm. The rates can initially be expressed in the unit mm/min resulting in the rate of the control as 0.47 mm/min, the light as 1.00 mm/min, and the wind as 0.53 mm/min. To convert mm into L, 1 mm traveled in distance is equivalent to 1.138 L in volume. Using this conversion, express the rate of transpiration in L. The alternate expression of the rate of the control is 0.53 L/min, of the light is 1.138 L, and the wind is 0.6 L. The surface area of the leaves on each plant of each trial were measured. The surface area of the control is 2996 mm^2, of the light is 5175 mm^2, and of the wind is 3860 mm^2. To find the transpiration rate by surface area, take the rate ( L/min) of each trial and divide it by the surface area (mm^2). The transpiration by surface area for the control is 0.000177 L/min/ mm^2, for the light is 0.0002199 L/min/ mm^2, and for the wind is 0.000196 L/min/ mm^2. The difference was calculated by subtracting the transpiration rates by surface area of the different (light and wind reactions) by the control. The difference of the light reaction is 0.0000429 L/min/ mm^2 and of the wind reaction is 0.000019 L/min/ mm^2. To calculate the percent difference, divide the difference of the independent variables by 100. The percent difference for the light reaction is 0.43% and of the wind reaction is 0.19%.
Transpiration Experiment with Tomato Plants
Time (min)
0 5 10 7 Avg. temp (°C) Surface area (mm^2) Rate (mm/min) rate ( L/min) Transpiration rate by surface area ( L/min/ mm^2) Difference (T-C) % difference
Control 0 3 5 7 23.0 2996 0.47 0.53 0.000177
Light 0 5 10 15 27.5 5175 1.00 1.138 0.0002199 0.000019 0.43%
Wind 0 3 6 8 24.0 3860 0.53 0.6 0.000196 0.000019 0.19%
Discussion
After completing the three trials of possible plant transpiration stimuli, the results reflect the validity of the previously stated hypothesis. As the data in the table displays the positive percent difference for the light and wind, it is understandable that the hypothesis stated is supporting this data. The light reaction has the higher percent difference compared to the wind reaction. Because of the photosynthesis that occurred, it permitted more water to escape as the exchange of CO2 occurred. The wind reaction only dehumidified the surrounding air, not requiring any reactions to occur, but only a minimum transpiration rate because of the emission of water. Therefore, the hypothesis stated is supporting the experimental results.
In order to better the results, more trials of each reaction could have taken place. Some errors that could have occurred could be that some air bubbles in the tubing could have become trapped causing marginal error in the distance of the traveled water. The transpirometer used for this specific lab was very complicated and could have caused error as well. However, the more experiments performed for each experimental stimulus, the more accurate the results. Based on the overall class data, the hypothesis was proven successful and the averages of our data support our estimations.
Literature Cited
Anderson, Craig R. “Home Gardening Tomatoes Series.” University of Arkansas Division of Agriculture Cooperative Extension Service, www.uaex.edu/publications/pdf/FSA-6017.com.
Vodopich, Darrell S., and Randy Moore. Biology Laboratory Manual. McGraw-Hill, 2017.