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This 7 page Class Notes was uploaded by james gruver on Monday January 11, 2016. The Class Notes belongs to EXPH 1490 at Ohio University taught by Marcus Barr in Winter 2016. Since its upload, it has received 20 views. For similar materials see Intro to Exercise Science in General Science at Ohio University.
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Date Created: 01/11/16
The effect of Light Intensity and Wavelength on the Rate of Photosynthesis James Gruver (Partner: Rob Cooper) 24 March 24, 2015 Objectives/ Hypothesis: The purpose of our experiment was to see if photosynthesis is an on/off type of phenomenon in which the reaction proceeds at a fixed rate regardless the intensity or amount of light, or does the rate of reaction vary with the intensity of light. So with this experiment we are going to determine where light intensity has an effect on the rate of photosynthesis. Since oxygen is a byproduct of the reaction we can measure the rate of the reaction by measuring the production of oxygen. Our hypothesis going into the experiment is that the rate of photosynthesis increases with light intensity evidenced by the increased production of oxygen. Our null hypothesis was the rate of photosynthesis does not change with the light intensity. These two hypotheses lead us into our prediction which state “ If we increase the light intensity that is shown onto the spinach leaves, then the rate of photosynthesis should increase which will be shown by the increased production of oxygen which is seen by the sunken spinach leaves floating again. For experiment two the purpose of our experiment was to see what wavelength plants utilized in photosynthesis. We see that in the fall leaves are yellow, orange, red, and green, which could mean that they do not use these colors. That leaves only blue wavelength left and we wanted to know if that is the wavelength that plants use to power photosynthesis. Our hypothesis going into this experiment was that plants use only the blue wavelengths of the visible spectrum to power photosynthesis. With this hypothesis came our null hypothesis which stated plants use other wavelength of the visible spectrum to power photosynthesis. Using this hypothesis and null hypothesis we created a prediction that state “ If no leaves float to the top with any other color besides blue, then blue is the only wavelength to power photosynthesis. Methods (Experimental Protocol): We began our first experiment by cutting out 30 circular spinach leave pieces. We then placed the spinach leave pieces into a syringe filled with a bicarbonate solution. By creating a vacuum with our finger we sucked out all the oxygen that was present in the spinach leaves and they sunk to the bottom of the syringe. We then placed the de- oxygenated spinach leaves into a petri dish full of bicarbonate solution and placed that dish under various light intensities ranging from 15-80 watts. I believe that one group had no light on their dish, this served as the control group. The independent and dependent variables were the light intensity and the percent discs floats at the end of trial; respectively. The control variables were the number of spinach discs and petri dishes the leaves were in when under different light intensities. In order to find out the percent of floating discs we used the mathematical equation ((mean/30)*100). In our second experiment dealing with wavelength, we started by again cutting out 30 circular pieces of spinach leaves. We did the same de-oxygenation of the leaves as was done in experiment 1. But in experiment 2 all groups used the same watt light bulbs but had different color caps on the petri dishes. Those colors were red, blue, green, white, and black (this was our control that allowed no light or wavelength into the petri dish). In this second experiment our independent variables were the color of the caps on the petri dishes (which correlated with different wavelengths) and our dependent variable was the percentage of leaves that floated to the top of the petri dish after the trial was run. In this experiment the control variables were the number of disc leaves in each group and the light intensity, which was the same for all groups. This mathematical calculation was done the same as in experiment 1. Results: Percentage vs Light Intensity 61.94 45.00 25.56 16.11 1.11 7.78 Figure 1:Light intensity vs Percentage of floating discs Figure 2: Wavelength vs. Percentage of floating discs Figure 3: the top chart shows the data collected in experiment 1 and the mean used to calculate percentage of discs floating. The bottom chart shows the data collected in experiment 2 and the calculated means. Example calculation for mean, percentage of floating discs, and standard deviation using red wavelength data. o Mean: (4+4+3+6+5+5+4+3+4+2+5+5)/12 = 4.16 o Percentage of floating disc: (4.16/30)*100= 13.89% o Standard deviation: ((4-4.16)^2)+(4-4.16)^2+((3- 4.16)^2)+…. )/ 12= 1.11 Waveleng Standar Standar th d Deviati d on Deviati on Dark .98 Red 1.11 Green .79 Blue 1.0 White 1.27 In experiment one we found the mean Light number of disc intensit leaves that floated to the top increased as the y light intensity increased also. This correlates 0 .65 to Figure 1, which shows the percentage of disc leaves that floated to increase as the light 15 1.07 intensity increased from no light all the way to 27 .93 80 KW. The exact 45 1.37 percentages can be 60 1.45 found along the top of each bar in Figure 1. As 80 1.83 stated in our methods used in order to find the percentage used in our graph for each light intensity we took our mean value divided it by 30 then multiplied that number by 100. In experiment two we found the mean number of disc leaves that floated to the top fluctuated from wavelength to wavelength. There is no steady increase or decrease in the means as you changed the wavelength. As seen in figure 2 the percentage of discs that floated to the top also did not have a pattern. The percentages fluctuated from 2% to 13% back down to 4% and then up again to about 16%. Like in experiment 1 in order to find our percentage of discs that floated to the top we took our mean and divided it by 30 then multiplied that number by 100. Discussion/ Conclusion: For experiment 1 we can see that as light intensity increased the percentage of discs that floated to the top also increased. This means that the amount of oxygen produced increased along with the light intensity because they discs floated to the top, which means they gained oxygen. This increase of oxygen means that photosynthesis increased its production as light intensity increased. This is follows our hypothesis which stated that the rate of photosynthesis increases with light intensity evidenced by the increased production of oxygen. These results were expected because we know that when you increase the amount of light into photosynthesis you increase the amount electrons that ultimately are added into the electron transport chain. Increases this means increased production of oxygen, hence our prediction. Our results compare very similar to experiments we heard about in class and lectures. This experiment was fairly simple and I see no other new hypotheses that could be created nor do I have any concerning questions for future studies. For experiment 2 we can see that there is no clear sign of a trend in the different colors and the percentage of discs floating. As a matter of fact our hypothesis stated that plants use only the blue wavelengths of the visible spectrum to power photosynthesis. As you can see from the results this is false because not only did other wavelengths produce floating leaves, which meant they were used to power photosynthesis, but the blue wavelength did not produce the most floating discs. We actually proved our null hypothesis with this experiment saying that plants use other wavelength of the visible spectrum to power photosynthesis. As you can tell our results where not what we expected. We hoped to see a large percentage of discs floating with the blue wavelength and little to none with the other wavelengths. Looking at an experiment similar to our by Alison Lederer, student at College of DuPage, I found that her results were very similar tours. She found that different wavelengths produced different amounts of oxygen but blue was not the only one like we thought. From lederer’s experiment I concluded that the varying percentages of floating discs could be because of different pigments in the spinach leaves that react with different wavelengths. So that’s why we see different percentages because we could have disc samples that have certain pigments that react well with certain colors better than others. A new hypothesis that could be tested is which wavelengths, colors, react best with what pigments in spinach leaves. This experiment could show us what wavelength powers photosynthesis the best. If we did this experiment we could find which color produced the most floating discs. Lederer, Alison (2007) "Investigation of Photosynthetic Properties In Spinach and Geranium: Pigments, Starch Production, and Light Wavelength Absorbance," ESSAI: Vol. 5, Article 29
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