Transpiration is the loss of water from a plant, mainly through the stomata of leaves. Darkness, internal water deficit, and extremes of temperature tend to close stomata and decrease transpiration; illumination, ample water supply, and optimum temperature cause stomata to open and increase transpiration. Its exact significance is disputed; its roles in providing the energy to transport water in the plant and in aiding dissipation of the sun’s heat (by cooling through evaporation of water) have been challenged. Since stomatal openings are necessary for the exchange of gases, transpiration has been considered by some to be merely an unavoidable phenomenon that accompanies the real functions of the stomata. (“Transpiration”)
Hypothesis and Variables
If a plant is placed in a more humid location, there will be more water available to absorb, thus encouraging more transpiration within the plant. Independent variable: The amount of moisture residing in the air in the immediate vicinity of the plant. Dependent variable: The plant’s rate of transpiration.
Control: A plant placed in a standard indoor environment, with standard room temperature, relatively consistent CO2 and light, as well as level air pressure. Equipment/Materials
Experimental Design or Methods
Discussion of Results
The first graph represents the second column of Table 1. It displays the rate of water loss, over time, of the plant in the first run of the experiment. In this initial control run, the plant was placed in a standard indoor environment, with level air pressure, a standard room temperature, and relatively low humidity. In these conditions, the rate of water loss experienced was, on average, approximately 0.0021mL/min, as shown by the slope of the line of best fit. The rate of water loss occurred at a steady rate, without the presence of any outliers in the data.
The second graph represents the last column of Table 1. It displays the rate of water loss, over time, of the plant in the second run of the experiment. In this second experimental run, the plant was placed in a room with the exact same conditions, with the exception of a sealed plastic bag placed over the plant, the inside lightly misted with water. In these conditions, the rate of water loss experience was, on average, approximately 0.0005mL/min, as shown by the slope of the line of best fit. The rate of water loss occurs in a staircase manner, with the amount of water loss staying at one value for two intervals before moving onto the next interval.
From the data collected in this lab, it can be concluded that an environment that possesses more moisture in its atmosphere will impede the rate of water loss in plants, and, by extension, the rate of transpiration. As shown by the third graph, the rate of water loss in the second run of the experiment is noticeably lower than that of the initial control run. This can be deduced from the graphs mathematically as well, as the first trial’s line of best fit possesses a slope that is more than 4 times the slope of the line of best fit in the second trial. This is most likely due to the high concentration of water in the atmosphere, balancing the concentration of water within the plant and without, thus preventing water in the plant from dissipating into the atmosphere. “Low humidity promotes the diffusion of water vapor from the air passages inside the leaf into the outside air.” (“Transpiration”) Thus, high humidity reduces the diffusion of water vapor from the stomata into the air. Several problems were faced during the set-up, as well as the observation phases of this experiment.
Systematic errors were experienced due to the precision of the tools used. As mentioned above, the data produced by the second run of the experiment possessed somewhat of a stairway quality, with the amount of water loss staying at one value for two intervals before abruptly moving onto the next interval. This irregularity can most likely be accounted for with the precision of the tools used, as one could only estimate values lower than 0.01 mL. Another similar problem arose in timing, as the clock that was used displayed only hours and minutes, presenting potential fluctuation in the time span between measurements.
Random errors in our data were also possible. Since the measurements for the two different runs were taken on different days, the conditions the plants were placed in may have experienced slight fluctuations in temperature or availability of sunlight. These variables may have altered the actual amount of water loss in the second run in respect to the water loss the plant may have experienced during the first day of experimentation instead. During the set-up of the second run, the only practical manner of misting the plastic bag, which would be placed around the plant to simulate a humid atmosphere, was to spray the interior with a generic spray bottle. Because of this, it was impossible to record the amount of water that resided within the bag, as well as the extra water sprayed onto the plant. Though it is still possible to continue with the experiment without this information, figure would have allowed us to experiment with different levels of humidity, and its added effect on transpiration. This could be added to the lab in the future as an extension activity.
“transpiration.” Encyclopædia Britannica. 2009. Encyclopædia Britannica Online. 14 Jan. 2009 <http://www.britannica.com/EBchecked/topic/603040/transpiration>.
“Transpiration.” Columbia Encyclopedia. 14 Jan 2009 <http://www.answers.com/topic/transpiration>.