IS PHOTOSYNTHESIS WAVELEGNTH DEPENDENT? THE EFFECT of different COLOR FILTERS ON The rate of photosynthesis in english ivy leaves author: Cherylle chapman
partners: sharif alston, ALEX SAFAVOV & EDuardo vie (Group 3) OBSERVATIONS & HYPOTHESIS
In the lab, we observed green plant leaves convert light energy into chemical energy by using photosynthesis. The species of green plant leaves that were used in this experiment were Hedera helix, commonly known as English Ivy. These plant leaves have both mitochondria and chloroplasts. The process of photosynthesis takes place in the chloroplasts and aerobic respiration is carried out in the mitochondria, these reactions may occur simultaneously. To determine the rate of photosynthesis, we estimate the changes in the amount of oxygen produced in leaf disks. To do this, we first vacuum infiltrate the leaf disks to displace oxygen with water, this will make the leaf disks sink. Then, when we were ready to let photosynthesis begin, we exposed the leaf disks to light and they began to float, because the production of oxygen displaced the liquid. There is an inverse relationship between the time it takes the disks to float and the rate of photosynthesis; a slow rate of photosynthesis means leaf disks will float less quick. When we did this first experiment, we observed that light is needed for photosynthesis to occur, and in the presence of light leaf disks floats because of photosynthesis. This supports the fact that photosynthesis is light dependent. To take this experiment a step further, we wanted to test the effect of different color filters (red and blue) on the rate of photosynthesis in English Ivy leaves. Since we already know that photosynthesis is light dependent, we wanted to see what would happen at different light waves. The justification for this comes from the fact that photosynthesis depends on the absorption of light by the pigments in plant leaves, called chlorophylls. We know that chlorophyll absorbs the most light at blue. Red is the second most optimal color of absorption, and yellow is the poorest color for light absorption. Chlorophyll also doesn’t absorb green light but it reflects green, which is why plants appear green. You can see this information represented in Figure 1. Since blue light is well absorbed by chlorophyll, we hypothesized that the plant leaves that are exposed to the blue filter will have a higher rate of photosynthesis than plants exposed to the red filter. The null hypothesis would be that blue and red color filters have no effect on the rate of photosynthesis. If we vacuum infiltrate English Ivy leaf disks by removing the air from the intercellular spaces and fill it with bicarbonate solution it will cause the leaves will sink, then when we expose the leaf disks to blue light and red light photosynthesis will begin and produce oxygen making the disks float, we will observe the leaf disks that were exposed to the blue light will have a higher percentage of floatation than the leaves that were exposed to the red light. Figure 1: The absorption spectra of chlorophylls a and b
Caption: Figure 1 shows the graph of the amount of light that is absorbed at different wavelengths for chlorophylls a and b.
Source: Biology: The Dynamic Science, 3rd Edition Figure 9.7
In this experiment, we investigated whether blue light has more of an effect on the rate of photosynthesis than red light. The independent variables are the variables that we manipulated –which is exposure to a blue filter, a red filter or a clear filter (for the control). The dependent variable is the percentage of leaf disks floating we observed over time, as an indicator of the rate of photosynthesis. Variables that were standardized in this experiment were the use of English Ivy leaf disks, the size of the leaf disks, same light source, and the leaves were placed in 50 mL bicarbonate solution.
Table 1: Elements of the experiment.
Cited: Correa-Reyes, G., Figueroa, F., Lubian, L., Mercado, J. M., Montero, J.C., Sanchez, M. 2004. Blue light effect on growth, light absorption characteristics and photosynthesis of five benthic diatom strains. Aquatic Botany 78: 265-277.
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Hertz, P. E., Russell, P. J., McMillan, B. 2013. Biology: The Dynamic Science. Third Edition. Cengage Learning, Inc., Belmont, KY.
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