Light Intensity And Wavelength On Photosynthesis Of Spinach Leaves

Claire Graham
BSC 2010L
November 4th, 2015
Effects of Light Intensity and Wavelength on Photosynthesis of Spinach Leaves
By replacing the air pockets in spinach leaf disks with a bicarbonate solution and allowing the disks to sit in the solution while being exposed to different light conditions, we were able to observe the effects of various light intensities as well as colors on the rate of photosynthesis. As the spinach leaves photosynthesized, oxygen pushed out the solution and filled the intercellular spaces, decreasing the density of the leaves. This causes the disks to float to the top of the solution, which we can then count and use as a measurement for the rate of photosynthesis. We hypothesized that higher intensity light would cause
The reactants of photosynthesis are carbon dioxide and water, and the resulting products are glucose, water, and oxygen. Leaf tissues normally contain spaces filled with gas, making them less dense. This causes the leaf tissues to float to the top when they are placed in a solution. For this experiment, the leaf tissues were exposed to a vacuum, pulling the gas out of the air pockets and filling them with the bicarbonate solution. They thus become more dense and sink when placed in a bicarbonate solution. When these leaf discs photosynthesize, the oxygen produced replaces the liquid in the intercellular places, causing the leaf to float. Leaves that are photosynthesizing will float, and those that aren’t will remain at the bottom of the solution (David, 2015).This is how we will be measuring photosynthesis. In the first experiment, we hypothesized that the increase in light intensity will increase the number of discs floating in the water, which depicts an increase in the rate of photosynthesis. In our second experiment, we hypothesized that adding red coloring to the heat shield will cause an increase in photosynthesis, and adding blue coloring to the heat shield will also increase the rate of photosynthesis. The independent variable for the first experiment is the light intensity, and in the second experiment it is the coloring of the heat shield. The dependent
We also hypothesized that adding blue to the petri dish heat shield and red to another heat shield would cause an increase of floating disks compared to the control, which had a heat shield containing only water. The results of the first experiment supported our hypothesis, as the spinach leaves exposed to the highest intensity light, the lamp, had the greatest number of floating disks. Since the disks float due to the liquid in the tissue’s intercellular spaces being pushed out by oxygen produced through photosynthesis, we can determine that the high intensity light caused an increase in the rate of photosynthesis (David, 2015). The results of our second experiment did not support our hypothesis that the wavelengths from the blue and red light waves would cause an increase in photosynthesis when compared to the wavelengths of the light that did not have coloring added. The control petri dish had the highest number or floating disks, telling us that the spinach plant best absorbs the wavelengths of white light, as opposed to blue or red light. Our experiments were limited by the small sample of 10 spinach leaves in each dish and because we only tested each varying condition once. Sources of error for our experiments include the possibility that the disks were