Does a plantŐs ambient environment alter its physiology?

Brittany Abel, Karoline Borgnes, and Corey Anderson

CU Boulder, Fall 2007

            We tested whether or not a plantŐs ambient environment will alter its physiology. Plants absorb sunlight in the thylakoid membrane of the chloroplast to split water and makes ATP for energy. CO2 is absorbed by the plant and combined with the ATP to produce glucose. This reaction requires light, and the amount of sunlight the plant is exposed to directly relates to the rate of photosynthesis. Since photosynthesis occurs mainly in sunlight, this led us to hypothesize that plants have the ability to adapt to their environment. We hypothesize that a plant grown in the sunlight will have a higher rate of photosynthesis, since there is more light energy available, as opposed to the plant grown in the shade.

            In order to test this hypothesis, we collected Juniper samples from both sunny and shady areas. We determined the mass of each sample, and placed each one in a gas chamber connected to a probe that measures the concentration of CO2 . We shined light through a container of water directly onto the plant for five minutes. Then we covered the plant for five minutes, ensuring that no more light energy was available. We then measured the rate of change in CO2 for each set of five minutes. For the first five minutes, the slope of the change in CO2 includes the CO2 used by the plant during photosynthesis and cellular respiration, while the slope of the change in CO2 for the second five minutes describes only the change in CO2 during cellular respiration. To account for cellular respiration, the rate of photosynthesis is the difference between the two slopes.

            We collected data from two trials of both types of plants. Our results indicated that the rate of photosynthesis for plants grown in the sun (mean= -7.881 ppm CO2 /min/g) was not significantly higher than the rate for plants grown in the shade (mean= -4.548 ppm CO2 /min/g; T= -0.969, P= 0.435, which is >0.05).

            Our results were not consistent with the predictions we created from our hypothesis. However, there was a visual difference between the means. One problem we encountered was the time restraint. Our CO2 sensor was not functioning properly and decreased the amount of trials we could run, allowing for more variation. We feel that if we could eliminate this source of error and run more trials, our results would become more consistent with our predictions. Perhaps, with more trials, we could conclude a significant difference in the rate of photosynthesis between the plants grown in different areas.