Spinach Lab Report

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I) Introduction
In this lab, a test was conducted to determine how the relative redox activity of chloroplasts from spinach leaves, which were performing photosynthesis, would change when in the presence or absence of light. To observe these changes in redox activity, the chloroplasts were exposed to DCPIP, a chemical that changes color according to such activity. By determining the redox activity of the chloroplasts, it could then be inferred which chloroplasts were photosynthesizing more actively than others. Redox activity, otherwise known as oxidation-reduction reactions, is the loss or gain of electrons. These two reactions, where electrons are lost through oxidation and gained as a result of reduction, are always coupled together.
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More specifically, however, this experiment focused on the photo part of photosynthesis, or the light dependent reactions in chloroplasts. Light dependent reactions require the presence of light to function, so that this light can be taken to create ATP and to reduce NADP+ to NADPH. Consequently, light dependent reactions shut down in the absence of light, thereby stopping the production of ATP and NADPH (Sadava et al. 2012). With this information, an experimental hypothesis can be formed that the presence of light will cause the redox activity of the spinach chloroplasts to increase, while the absence of light will cause this activity to decrease. One possible null hypothesis could be that there will be no significant difference in redox activity between spinach chloroplasts that are under light and in the dark. Therefore, the alternative hypothesis must be that there will be a difference in this activity between the two groups of chloroplasts. To test these hypotheses, chloroplasts were extracted from spinach leaves in order to create enriched chloroplasts, which were a vital …show more content…
Each test tube, except for the blank, had 1.5 mL of water serologically pipetted into them. In addition to the water, those same test tubes had 500 µL of both the DCPIP and reaction buffer added to them with a micropipette. Next came the blank, which only had 2 mL of water and 500 µL of the reaction buffer pipetted into it. Once the addition of these substances was completed, 25 µL of the enriched chloroplast was added to just the blank, as well as test tubes 4-9. Each test tube with the added chloroplast was then placed onto the vortex, one by one, to ensure the substances thoroughly combined. Once the mixing was finished, the blank, test tubes 1-3 and 7-9 were all placed in a tube rack beneath the light source. Tubes 4-6, which contained no enriched chloroplast, were put into a separate tube rack, which was situated in a closed drawer so that no light made contact with those samples. As soon as both racks were placed in their respective locations, a 5 minute timer was started. Once these 5 minutes passed, both racks were taken and placed next to the spectrometer. Test tube 0 was used to then blank the spectrometer, after which each tube had their absorbance read at 600 nm by the spectrometer. After each tube had its absorbance read and recorded, they were placed back where they came from, either under the light source or in the dark. This process of placing the

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