I. Question and Hypothesis
In parts 1 and 2 of experiment I, the main goal was to prepare a cell homogenate from broccoli florets and determine which cell fraction had the most electron transport chain activity. Electron transport activity could be determined by the cell fraction with the largest number of chloroplast, which was indicated by the artificial electron acceptor called DCIP. This artificial acceptor can be read using a Spectronic 20 to measure the absorbance of a cell fraction.
To obtain cell fractions, differential centrifugation was, which separates organelles based on their sizes and densities. To perform differential centrifugation, a centrifuge is used, which is an instrument that spins cell homogenate at high speeds to push the larger or denser cell structures to the bottom of the tube. The densest and largest cell structures, such as the nucleus, form a solid pellet at the bottom of the tube, while the lighter cell structures, such as the chloroplast and mitochondria remain in the liquid part known as the supernatant (Leicht 42).
In our experiment, the first pellet, P1, was obtained by placing the cell homogenate into the centrifuge at 600 x g for 6 minutes. The supernatant was separated from the pellet at the bottom of the tube and then put back into the centrifuge at a higher speed for a longer period of time, 2,000 x g for 10 minutes. A higher g-force at a longer time allows the less dense cell structures to gravitate and form a second pellet, P2. After this, Pellet 2 and the remaining supernatant were then separated, and the supernatant was given the name S2.
Based on the prior knowledge from Wet Lab 1, it was known that P1 would contain the densest organelles, such as nuclei an...
... middle of paper ...
...ark sample does. This proves that our hypothesis was correct. Since both blue light and dark have relatively short wavelengths compared to the light apparatus, we expect that there would be less electron transport activity. One thing to note is that all of the samples in this experiment started with the same amount of chloroplast, so the actual number of chloroplast is not a factor, but activity is. The data collected shows that blue light did not have enough energy to activate a large amount of chloroplasts.
Since the data was conclusive, another experiment could be formed to further investigate how the wavelengths of different light sources affect the electron transport chain activity. An appropriate follow up experiment would be to test a variety of different light sources with varying wavelengths to determine the optimum light source for photosynthesis to occur.
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