Collecting Photosynthetic Rates in Spinach (Spinacia oleracea) Introduction: The purpose of this study was to see which light color would cause the spinach sample to photosynthesize the most within the given time. In order to understand photosynthesis, we need to know that chloroplasts absorb light energy from the sun, the plant then takes that energy along with water and carbon dioxide and changes it to sugar and oxygen. This happens in order for the plants to grow. But, light energy comes in a spectrum of colors called visible light.
When visible light is absorbed it is also reflected, such as the green and yellow range. Photosynthetic pigments also protect plants from UV rays. Carotenoids absorb light in the blue range which gives them the vibrant colors they possess in fruits and flowers. Phycobilins absorb light in the green and orange range to allow photosynthesis in plants found under water. We hypothesized that the red and violet lights would work best with the spinach leaves because plants have been shown to absorb colors in these ranges more often than colors in the green and yellow ranges.
Chlorophyll a absorbs its energy from the Violet-Blue and Reddish orange-Red wavelengths, and little from the intermediate (Green-Yellow-Orange) wavelengths” (Farabee, 2007). Materials and Methods: An O2 gas sensor was connected to a laptop with the Vernier Lab Pro software suite to record the amount of O2 produced in photosynthesis. We set the duration to 15 minutes, for 60 samples per minute in ppm. Ten grams of spinach was weighed and placed into the respiration chamber, and the lamp was adjusted to 7 centimeters from the table.
The O2 sensor was then placed into the chamber and put on its side. We waited 5 minutes before collecting data, then O2 production was measured for 15 minutes, while the light color of interest was shone on the chamber. Next, aluminum foil was wrapped around the chamber to occlude light and placed under the lamp, waiting another 5 minutes. The same experimental procedure was repeated in the “dark” condition. We repeated these two treatments for each color of interest (blue, green, red, etc. ).
Next, we weighed out 4 grams of spinach and placed it into a 250 milliliter glass beaker. We poured in 50 milliliters of 95% ethanol alcohol. We placed it on a hot plate and manually stirred the leaves in the solution. We stirred the solution at 145 degrees celsius until it came to a boil. While stirring the solution, we folded filter paper into quarters and placed a few drops of ethanol to moisten the filter paper. When the filter paper was in a funnel in a beaker they took the spinach and ethanol and poured the solution into the filter funnel.
We then pipetted a sample of this pigment into the cuvette after blanking the spectrophotometer with the ethanol alcohol but it didn’t work. We then decided to dilute the sample with 50% alcohol and 50% pigment. After blanking it with the alcohol they placed the dilution into the machine. Absorbance for the solution was then read at increments of 20nm, from 380nm to 720nm. Results: The white light worked best for photosynthesis. The spinach sample in the white light photosynthesized best in the light and overall night and day. However it didn’t do that well in the dark.
None of the plants photosynthesized in the dark but the blue light samples conserved oxygen the most in the dark. Figure 1. Respiration rate (rates in the dark). The plants experimented with the blue light had the worst reaction towards the lack of energy with an average of -129. 03. The orange light had the better reaction, the respiration rate was higher for the orange light with an average of -100. 50. Figure 2. Photosynthetic rates in the light. The plants experimented with the white light were able to convert the light into glucose and oxygen best with an average rate of 335. 5.
The green light was the worst light to use for photosynthetic rates with an average of 141. 87. Figure 3. Gross photosynthetic rates. The white light had the best gross rate with an average of 465. 12. The green light had the worst gross rate with an average of 268. 05. Figure 4. The average of the absorbance data for each wavelength of light absorbed by plants. All the plants were able to photosynthesize with the lights due to the fact that there was light fueling the source of energy to be converted into glucose and oxygen.
Based off the oxygen emittance we were able to determine the white light as the light that allowed the spinach samples to photosynthesize best, as seen in figure 2. In figure 1, we can see that none of the plants were able to photosynthesize. Respiration rates happen during the night when there is no sun or light to fuel the plants energy source. We can also see that the blue light didn’t do to well and started conserving it’s energy and oxygen. In figure 3, we get the gross data which is the sum of the absolute value of photosynthesis in the light and respiration in the dark.
We are able to see that the white light did far better than the others. Discussion: The lab didn’t support the hypothesis, the red light did not cause the most photosynthetic rates. The red light didn’t photosynthesize as well as the white light did and had low photosynthetic rates compared to some of the other visible lights. I think this may have happened because the lights have a color coating, so the red light wasn’t a pure red light and may have filtered out the light. In figure 2, white light almost doubles the results of the red light.
Even in figure 3, the gross rate, the white and blue light were able to photosynthesize more than the red light. I think this happens because plants are able to photosynthesize based on the color of natural light, such as the sun and moon, white light. “White light is composed of all the visible colors in the electromagnetic spectrum…As light passes through a prism, it is bent, or refracted, by the angles and plane faces of the prism and each wavelength of light is refracted by a slightly different amount” (Davidson, 2015).
This means white light is every visible light, meaning white light would best be absorbed by plants. You could test this by conducting an experiment with several plants, all of the same height and breed, leaving half in the sunlight and moonlight and the other half under lights that aren’t white, blue, or yellow to see which light would have the best photosynthetic rates. Another topic that may get brought up is excessive light.
Even though the spinach samples were only under the light for 15 minutes the length of time could have played a huge role to the spinach. For example, they could have been hidden in the shade or not properly left out to collect light energy when growing, so the sudden exchange of light so close up could have given the spinach excessive light. “Too much light can lead to increased production of damaging reactive oxygen species as byproducts of photosynthesis” (Muller, Li, Niyogi, 2000).
If any of the spinach samples we experimented on were to get excessive light they could have caused an excess amount of oxygen to be produced, adding extra oxygen to the data. We can test this by leaving out spinach plants in the sunlight for a certain amount of time and leaving another batch in a shaded region of a room where it gets limited sunlight and placing it in the sun or under the lights for the full amount of time after.
