Photosynthesis

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DISCUSSION

In Tube 2, two readings were taken only in order to prevent and to minimise the reaction mix from exposing to light. The absorbance decreased from 0.821 to 0.776. Photosynthesis cannot occur due to lack of light, thus, the absorbance in Tube 2 should not decrease because the reaction mix was kept in the dark. The reason there was decrease in absorbance was because when DCPIP were being added into the test tube, the mixture of chloroplast was exposed to light, which then induced photosynthesis. In Tube 3 which was placed under the light, the absorbance decreased as predicted. However, the DCPIP did not turn completely colourless. The mixture may be needed to be left under the light for half a day in order to let the electron transport chain to produce sufficient electrons in order to reduce the DCPIP to get a colourless solution. As in Tube 4, the results of absorbance were not constant because experimental error occurred such as the test tube was not wiped cleanly and causes condensation occurred before inserting into the spectrophotometer. However, the results should remain constant because the chloroplasts were being boiled, thus it should be denatured completely and was not able to release electrons to reduce the DCPIP. In Tube 5, the absorbance decreased at first but slightly increased in the end. The absorbance should be decreasing because DCMU is an inhibitor for photosynthesis, which binds to photosystem II in the electron transport chain. The production of electrons was slowed down because of DCMU. The results were increases slightly at the end because of experimental error occurred. Experimental error occurred in such situation because there was possibility that the tube was being exposed to light when it was being transfer into the spectrophotometer or when taking out from the spectrophotometer to put into the large plastic tube that will be place on ice. This caused the readings of spectrophotometer fluctuated, thus the results were not constant. Whereas in Tube 6, which was being placed inside a large red plastic tube, the absorbance decreased more than other tubes. This happened because chloroplasts absorbed light with the wavelength which suited the colour red more actively, so the chloroplasts released more electrons and reduced the DCPIP faster. Lastly in Tube 7, it was being placed in a large green plastic tube. The absorbance decreased in a slower rate when exposed to green light because chloroplasts did not absorb the wavelength which suited green that actively, instead they reflected it. In conclusion, plants absorbed wavelength of green but not as much as wavelength of red, in fact the plants reflected wavelength of green. Chlorophyll will undergo photolysis of water and released electrons once absorbed light. However, once with inhibitors such as DCMU, the rate of photosynthesis will drop. Photosynthesis did not occur in the dark. Besides that, the chloroplasts were denatured when at exposed to high temperatures such as boiled therefore it did not undergo photosynthesis.

REFERENCE

Alexander P.H, Thomas B, Tobias W, Paolo P, Mathias P, Ute A, Dario L (2013) PGRL1 Is the Elusive Ferredoxin-Plastoquinone Reductase in Photosynthetic Cyclic Electron Flow. Molecular Cell 49, 511-523. doi: 10.1016/j.molcel.2012.11.030