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Tan Ying Xuan 29630770

Title An investigation of the impact of different treatments on photosynthetic electron transport in photosynthesis Introduction Photosynthesis is a process that takes place when light energy is converted into chemical energy in order to produce self-manufacture food for the green plants. It plays a vital role in maintaining the stability of atmospheric gases conducive to a balanced ecosystem. In photosynthesis, the light-dependent reactions occur in the thylakoid membranes and participate in the splitting of water into oxygen, protons and electrons (Johnson, M.P, 2016). Food is produced when carbon dioxide converts into sugars and oxygen by the green plants using light energy. Electrons which are supplied by organic food molecules get into the transport chain after obtaining light energy. Energy is used to pump the hydrogen ions across a membrane in the photosynthetic electron transportation. The importance of photosynthesis motivates people to investigate the factors that might contribute to affections on it. This experiment aims to examine the impact of different treatments on photosynthetic electron transport in photosynthesis. As the amount of DCPIP is a determinant to the rate of photosynthesis in this investigation, it is hypothesized that the faster the rate of photosynthesis, the faster the dye will turn colorless and the more rapid is the decrease in absorbance. Methods Seven spectrophotometer tubes were numbered and solutions A-D were added according to the volumes shown in Table 1. Tube 1 was capped and inverted several times. The spectrophotometer was calibrated using Tube 1, which contained chloroplasts and sucrose only, as the blank, to ensure that any changes in absorbance for the other treatments could be attributed to the reduction of the dye DCPIP. At time zero (mins), absorbance was recorded for all treatments immediately after addition of DCPIP and mixing of contents. Immediately following the time zero reading, all tubes (1-7) were placed in larger plastic tubes; tube 2 in a light-proof (black) tube, and tubes 6 and 7 in tubes covered in red and green cellophane respectively. All tubes were then placed horizontally on ice, under lights. At fifteen minute

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Tan Ying Xuan 29630770

intervals, readings of absorbance were taken for all treatments, except for the dark tube which was kept in the light-proof tube for 60 minutes, after which its absorbance was measured. Results Figure 1. Plot of absorbance vs. time for electron transport experiment

There was no decrease in absorbance where the reaction mix was kept in the dark (Tube 2) (Fig. 1). Meanwhile, absorbance of tube 3 to tube 7 were decreasing as the time passed. At the 60 minutes, the highest absorbance recorded is in tube 2 which was kept in the dark and the lowest absorbance recorded is in tube 3 which was kept under light.

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Tan Ying Xuan 29630770

ABSORBANCE Time (mins)

DARK Tube 2

LIGHT Tube 3

BOILED DCMU RED Tube 4 Tube 5 Tube 6 0 1.4 1.47 1.29 1.18 15 1.2 1.27 1.18 30 1.14 1.26 1.16 45 1.08 1.25 1.14 60 1.85 1.02 1.22 1.11 Table 2. Absorbance readings taken at 15 minute intervals for each treatment

1.26 1.22 1.19 1.17 1.14

GREEN Tube 7 1.31 1.32 1.28 1.25 1.22

As shown in Table 2, the absorbance of the treatments was decreasing except for tube 2 which was in the “dark” reaction mix. Discussions The result indicated the absorbance of dark reaction mix in tube 2 was the only one appeared as increasing while the other tubes’ absorbance was showed as decreasing. It has shown that light is essential for the process of photosynthesis as the rate of photosynthesis starts to rise when light is provided. Hence, this experiment proved the premise which proposed the faster the rate of photosynthesis, the faster the dye will turn colorless and the more rapid is the decrease in absorbance. According to evidence, tube 3 with light reaction mix had an obvious decrease in the rate of dye turning colorless which means it was in the process of photosynthesis. The boiled reaction mix in tube 4 was shown in a slower decrease as it was boiled to prevent photosynthesis from happening by leading protein to denature. Tube 5 which contained DCMU which acted as inhibitor of photosynthesis to block photosynthetic electron transport in photosystem II. (D. Nemie-Feyissa, A. Krolicka, N. Forland et al,2013) Hence, it still results in a decreasing rate of absorbance. In tube 7 which covered in green, it showed an increase in absorbance at first 15 minutes of the experiment where the error was obtained. In an opposite way, it should be decreasing. Red light which covered tube 6 was shown as more efficient than green light which covered tube 7 to carry out the photosynthesis. In short, this experiment contributes to agree with the effect of different treatments on photosynthetic electron transport in photosynthesis. 3

Tan Ying Xuan 29630770

References Johnson, M. P. (2016) ‘Photosynthesis’, Essays in Biochemistry, vol. 60(3), pp. 255-273. D. Nemie-Feyissa, A. Krolicka, N. Forland et al. (2013), ‘Post-translational control of nitrate reductase activity responding to light and photosynthesis evolved already in the early vascular plants’, Journal of Plant Physiology, vol. 170(7), pp. 662-667.

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