The Effect of the Environment on Transpiration
Purpose:
How is transpiration rate affected by different environmental conditions, namely sunlight, moisture, wind, and artificial light?
Hypothesis:
If a plant is exposed to sunlight, then its transpiration rate will increase because the surrounding air will need more water. If a plant is exposed to moisture in its environment, then its transpiration rate will decrease because the surrounding air will contain more water. If a plant is exposed to wind, then its transpiration rate will increase because the water in the surrounding air is being moved away. If a plant is exposed to artificial light, then its transpiration will increase because the surrounding air will require more water. The independent factor in each test of this experiment is time, and the dependent factor is mass, which shows changes in the transpiration rate and amount of water lost from the plant.
Materials:
Triple beam balance
15 snapdragon plants (in groups of 3)
3 small plastic bags
Spray bottle of water
Electrical fan
Large beaker
Strong artificial light
Procedure:
1.
Make five groups with three plants in each. Label the groups “Dark”, “Sunlight”,
“Moisture”, “Wind”, and “Artificial lighting.” Also number each plant within the group
(Dark 1, Dark 2, Dark 3, Moisture 1, Moisture 2, Moisture 3, etc.).
2.
Find the mass of each snapdragon. Record.
3.
Put the group labeled “Dark” in a cabinet. This is the control group used to measure how much water is evaporating from the soil.
4.
Put the group labeled “Sunlight” next to a window.
5.
Spray each plastic bag with three squirts of water. Place a plastic bag around each plant in the “Moisture” group.
6.
Put the group labeled “Wind” in front of the electrical fan and turn the fan on.
7.
Fill the large beaker up with water. Place this water bath in front of the strong artificial light and turn the light on. Put the group labeled “Artificial lighting” behind the water bath.
8.
After a day, measure the new mass of each plant and record accordingly. Do this for 2 more days so that there are a total of four mass measurements. Each day, be sure to respray the plastic bags with water.
9.
Within each group, find the average mass measurements of the three plants. Record.
10.
Find the amount of water lost in each group by subtracting each group’s average final mass from average initial mass. Record.
11.
To find the corrected difference, subtract the amount of water lost by the “Dark” group from the amount of water lost from the other groups. Record.
12.
Graph the corrected differences of each group.

13.
Use the data and graph to determine how different environmental factors affect transpiration rate.
Data & Results:
Table 1: Daily Measurements for Each Plant
Dark Sunlight Moisture Wind Artificial Light
Plant
#1 Mi: 98.6 g Mi: 116.2 g Mi: 113.1 g Mi: 101.9 g
Mf (day 2): 91.0 g Mf (day 2): 95.9 g Mf (day 2): 107.2 g Mf (day 2): 82.1
Mi: 105.3 g
Mf (day 2): 96.2 g
Plant
#2
Mf (day 3): 86.9 g Mf (day 3): 85.2 g Mf (day 3): 103.1 g Mf (day 3): 73.0 g Mf (day 3): 91.7 g
Mf (day 4): 82.3 Mf (day 4): 73.5 g Mf (day 4): 99.1 g Mf (day 4): 63.5 g Mf (day 4): 83.2 g
Plant
#3
Mi: 108.9 g Mi: 105.3 g Mi: 103.2 g Mi: 98.5 g Mi: 114.6 g
Mf (day 2): 100.5 g Mf (day 2): 90.0 g Mf (day 2): 95.7 g Mf (day 2): 83.1 g Mf (day 2): 104.6 g
Mf (day 3): 95.6 g Mf (day 3): 81.0 g Mf (day 3): 90.2 g Mf (day 3): 75.1 g Mf (day 3): 98.6 g
Mf (day 4): 89.9 g Mf (day 4): 69.9 g Mf (day 4): 85.3 g Mf (day 4): 67.9 g Mf (day 4): 90.2 g
Mi: 94.4 g Mi: 106.9 g Mi: 109.2 g Mi: 100.6 g Mi: 108.7 g
Mf (day 2): 87.5 g Mf (day 2): 90.7 g Mf (day 2): 100.0 g Mf (day 2): 80.0 g Mf (day 2): 99.3 g
Mf (day 3): 83.3 g Mf (day 3): 80.0 g Mf (day 3): 94.0 g Mf (day 3): 71.1 g Mf (day 3): 94.0 g
Mf (day 4): 78.1 g Mf (day 4): 66.8 g Mf (day 4): 88.6 g Mf (day 4): 63.6 g Mf (day 4): 86.4 g
As each day passed, the new mass of each plant was recorded in the appropriate box. It is clear that the measurements decrease each day, but the rate at which they change is different.
Table 2: Average Measurements and Differences
Dark
100.6 g
Sunlight
109.5 g
Moisture
108.5 g
Wind
100.3 g
Artificial Light
109.5 g Average Mi
Average Mf
(day 2)
Average Mf
(day 3)
Average Mf
(day 4)
Water Loss
93.0 g
88.6 g
83.4 g
17.2 g
92.2 g
82.1 g
70.1 g
39.4 g
101.0 g
95.8 g
91.0 g
17.5 g
81.7 g
73.1 g
65.0 g
35.3 g
100.0 g
94.8 g
86.6 g
22.9 g
Corrected Loss 0 g 22.2 g 0.3 g 18.1 g 5.7 g
The masses measured in Table 1 were averaged to fill in Table 2. Water loss was found by subtracting Average Mf (day 4) from Average Mi. For example, in the plants exposed to sunlight, water loss was found by 109.5 – 70.1 = 39.4. Because the plant started out with a mass of 109.5 g and had a mass of 70.1 g after four days, the plant lost 39.4 g. The corrected loss was found by subtracting water loss in the dark plants (17.2 g) from the water loss in the other groups.
For instance, the corrected loss of the wind group was found by 35.3 – 17.2 = 18.1. The water lost by the dark group is the amount of water that evaporated from the soil; this value must be subtracted from the other water loss measurements in order to find the amount of water lost by transpiration.

Graph 1:
Average Mass of Plants
120
100
80
60
40
20
Dark
Sunlight
Moisture
Wind
Artificial Light
0
1 2 3 4
Day
In the graph, the mass of the snapdragon flower depends on time. The graph represents data from Table 2. All the lines are decreasing, meaning all of the plants are decreasing in mass as the days pass; mass decreases whenever a plant loses water by transpiration. These lines, however, are decreasing at different rates; some are steeper than others, meaning they are losing mass faster.
Graph 2:
Water Lost by Transpiration
25
20
15
10
5
0
1 2 3 4
Group 1: Sunlight, Group 2: Moisture, Group 3: Wind,
Group 4: Artificial Light

This graph shows the amount of water lost by transpiration for each of the four groups. Clearly, some groups lost much more water than others. The most transpiration occurred in Group1, the group of plants exposed to sunlight. The least transpiration occurred in the Moisture group.
Conclusion:
I accepted my hypothesis. As shown in the data, transpiration rate was faster in the sunlight, wind, and artificial light groups because there was less water in the surrounding air. Since water moves from higher potential to lower potential, the water from the plants of these groups was released at a faster rate into the air. In contrast, transpiration rate was slowest in the moisture group, since there was already water in the surrounding air; therefore, the water potential was much higher than that of the other groups. As each day passed, water was lost in all of the plants from transpiration. After four days, however, the sunlight group lost the most water.
Transpiration occurred, from fastest rate to slowest rate, in the sunlight group, wind group, artificial light group, and moisture group.
Overall, this lab worked very well and there were few errors. Both the graph and data proved my hypothesis to be correct. If I were to redo this experiment in the future, I would make sure that all the environmental conditions stayed consistent within each group from day to day. In addition, it would help to measure mass using a more precise triple balance beam. Both of these changes would improve the accuracy of the results of the experiment.
This lab really helped me understand how different environmental factors affected transpiration.
Plants exposed to sunlight transpire much more than those living in moist environments. In addition, this lab helped reinforce the idea of water moving from areas of higher water potential to those of lower water potential. It allowed me to see how water potential affects living organisms.
The completion of this lab made me wonder about how the transpiration rate would change had we continued measuring for a few more weeks. Would water continue to be lost at the same rate, or would it slow down? What would happen when there was no water left to be lost? How would other environmental factors affect transpiration rate? It would be interesting to further this experiment and find out.