A group of students designed an experiment to measure transpiration rates in a particular species of herbaceous plant. Plants were divided into groups and were exposed to the following conditions. Group I - Room conditions (light, low humidity, 200 C, and little air movement)
Group II - Room conditions with increased humidity
Group III - Room conditions with increased air movement (fan)
Group IV - Room conditions with additional light
The cumulative water loss due to transpiration of water from each plant was measured at 10-minute intervals for 30 minutes. Water loss was expressed as milliliters of water per square centimeter of leaf surface area. The data for all plants in Group I (room conditions) were averaged. The average cumulative water loss by the plants in Group I is presented in the table below.
Average Cumulative Water Loss by the Plants in Group I
Time (minutes) Average Cumulative Water Loss
(milliliters H2O/centimeter2)
10 3.5 x 10-4
20 7.7 x 10-4
30 10.6 x 10-4
a. Construct and label a graph using the data for Group I. Using the same set of axes, draw and label three additional lines representing the results that you would predict for Groups II, III, and IV.
b. Explain how biological and physical processes are responsible for the differences between each of your predictions and the data for Group I.
c. Explain how the concept of water potential is used to account for the movement of water from the plant stem to the atmosphere during transpiration.