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Climate clues: a student investigates plant leaves to learn about Earth's changing climate.

Most experts agree that over the past century, the average temperature of Earth's atmosphere has risen. This warning has had an effect on weather patterns, wildlife, and plant life. The recent climate change is believed to be largely due to a steady increase in greenhouse gases like carbon dioxide (C[O.sub.2]) in the air--a by-product of the burning of fossil fuels by power plants, factories, automobiles, and other sources.

When faced with choosing a science project in school, Marlene Bond, an eighth-grader from Fairbanks, Alaska, decided to investigate how rising C[O.sub.2] levels have affected plants.




Through background research, Marlene learned that plant leaves have small openings on their undersides called stomata that take in C[O.sub.2] and release water and oxygen during photosynthesis (see Structure of a Leaf, right). The number of stomata in each square millimeter, called the stomatal density, depends on the plant species and its environment. Previous scientific studies have shown that some plants have responded to the rise in C[O.sub.2] levels with a decrease in stomatal density. None of those studies, however, were done on plants growing in the far north. Marlene's hypothesis was that Arctic plants would show a response to climate change similar to that of plants from other regions.

Marlene's mother is the curator of the herbarium at the University of Alaska Museum of the North, which contains the world's largest collection of preserved Alaskan plants. The museum makes its specimens available to researchers, so it was the perfect place for Marlene to begin her investigation.


She chose the dwarf arctic birch (Betula nana) for her study because the herbarium has specimens of this plant spanning more than 100 years. She removed a leaf from each of four specimens collected between 1898 and 2004. Following a procedure similar to past researchers', she applied glue used for dental impressions to the underside of each leaf. When dried and removed, the glue held negative molds of the leaves' surfaces. Then she coated the molds with Clear nail polish, allowed them to dry, and peeled off the polish. The resulting strips of polish created thin, positive impressions of the leaves' epidermis, or outermost layer of cells.


Marlene placed the impressions on slides and studied them under a microscope fitted with a digital camera. The stomata appeared as banana-shaped cells. She photographed each enlarged image and then counted the number of stomata within various square-millimeter areas. She compiled her data on a spreadsheet, calculated the average stomatal density of each leaf, and plotted the results on a graph.


Marlene found that the oldest specimen had significantly more stomata than the most recent. The study supported her hypothesis that arctic plants have experienced a decrease in stomatal density over time.

Competing in the Interior Alaska Science Fair, Marlene won awards from the Association of Women in Science and the Fairbanks Memorial Hospital. Now the budding researcher has an idea for future studies. "One really cool experiment would be to grow the dwarf arctic birch in [a] greenhouse under set C[O.sub.2] concentrations to see if one could imitate the conditions found in nature and get the same results."

Her wish for the future: "I hope we can all make a better effort to save energy and produce less carbon dioxide."


Stomata are invisible to the naked eye. To count them, Merlene had to view each leaf under a microscope that magnified it 200 times. To keep track of which stomate she had already counted, she used a computer with a photo-editing program and "painted" each stoma red.

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Title Annotation:INQUIRY: SCIENTIFIC METHOD; Marlene Bond
Author:Burk, Rachelle
Publication:Science World
Geographic Code:1USA
Date:Oct 17, 2011
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