Bulldog News
Experiment promotes eco-awareness
Tuesday, November 17, 2009
A local “backyard experiment” at Hillside School has opened students’ eyes to the vital connection between trees and the world’s water resources.
Students in Sharon McKenna’s seventh grade science class didn’t have to travel far to conduct their experiment. Taking a short stroll into Hillside’s recently dedicated Weezie Courtyard, the students turned to the leafy trees that are a main feature of the courtyard landscape.
As explained by McKenna, the seventh graders were seeking to determine what role trees play in the global water cycle.
Familiar to many, this cycle involves the evaporation of water from Earth’s seas and surface into the atmosphere, which eventually becomes rain and then evaporates back into the sky to begin the process all over again.
To conduct their experiment, each of McKenna’s students first determined the mass of a plastic zip lock bag containing a pebble to the nearest tenth of a gram. “The pebble was necessary to weigh down the plastic bags so they wouldn’t blow away,” noted McKenna.
Next, the students ventured into the Weezie Courtyard to place their bags over the leaves of trees in this communal space. Twenty-four hours later, the boys discovered that the bags contained water condensation from the leaves. They then determined the mass of the bags again and, subtracting their original measurements from their latest findings, discovered the amount of water condensation within their bags.
As explained by McKenna: “In essence, this project enabled students to learn about water transpiration, a process in which plants give off water vapor through their leaves.”
However, the Hillside School science teacher asked her students to go further in their experiment to gain a broader perspective on their findings.
“I had the boys do some math. I told them a single birch tree may give off as much as 260 liters of water in a day during the summer,” recounted McKenna. “I asked them how much water would a grove of 1,000 birch trees return to the atmosphere in four months. Needless to say they were amazed.”
The class project eventually led to discussion about the importance of trees to our global eco-system including their role in retaining soil, removing carbon dioxide from the air and producing oxygen. As a result, the students gained deeper insight “into why a growing number of people are concerned about the destruction of forests around the world,” noted McKenna.
Matthew Chang '12 (left) and Justin De Valle '12 (right) cover leaves with zip lock bags as part of their water transpiration experiment.
