Variations of the Photosynthetic Rate of Chloroplasts Extracted from Spinach Leaves Under Different Conditions is Displayed through the Hill Reaction Carla Merveille, Sana Jabeen, Lauren Jones, Juan Martell, and Bera Koskulu March 22, 2018 Abstract Chloroplasts from spinach leaves were extracted and made into a suspension in order to study the changes occurring in the electron transport chain of Photosynthesis under differing conditions. To do so, their photosynthetic rate was calculated via the changes in absorbance measured by spectrophotometry during the Hill reaction. The results show that herbicide, non-exposure to light, and protein denaturation impact the electron chain reaction, stopping the Hill reaction altogether. On the other hand, …show more content…
To blank the apparatus, 3mL of the solution in test tube 1 pipetted in a 100 x 13 mm test tube was used. Then, 3mL of the solution in test tube 5 was put in a similar test tube, and its absorbance was recorded. This test tube was immediately wrapped in aluminum foil and put on ice to prevent light exposure. Similarly, the absorbance of 3mL of the solution in test tube 2 was recorded. The tube was then placed 20 centimeters under a high intensity lamp for 30 seconds, then its absorbance was measured and recorded. The previous step was repeated until the reaction went to completion or until the absorbance did not change for two minutes. The same procedure was effectuated for test tube 3 and 4. Finally, the absorbance of test tube 5 that was kept on ice and wrapped in aluminum foil was recorded a second time, then the same steps used for test tube 2 were …show more content…
For both Tube 3 which contained boiled chloroplasts, and was exposed under a high-intensity lamp, the absorbance reading stayed constant at 2.50 (Table 1) from the first reading until the last after two minutes of light exposure. The photosynthetic activity under these conditions was consequently of 0 min-1 (Table 2). Tube 4 which contained the pre-herbicide DCMU also had an initial absorbance of 2.50 and stayed constant in spite of the light exposure (Table 1). In these conditions, the photosynthetic activity was then also of 0 min-1. Tube 5 which was initially kept away from light exposure with aluminum foil, then exposed under the high-intensity lamp, saw its initial absorbance reading decrease from its constant 2.50 when not exposed for several minutes, to 0.07. The photosynthetic activity rate of under these conditions was of -0.972 min-1. Table 1: Absorbance of the solution of 1:5 dilution of the suspension of chloroplasts’ stock measured at different time