An Investigate of Light-Dependent Electron Transport Using Dcpip

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ABSORBANCE

Time (mins) DARK

Tube 2 LIGHT

Tube 3 BOILED

Tube 4 DCMU

Tube 5 RED

Tube 6 GREEN

Tube7

0 0.859 0.908 0.855 0.953 0.993 0.870

15 - 0.862 0.853 0.952 0.870 0.862

30 - 0.777 0.857 0.970 0.868 0.864

45 - 0.770 0.944 0.975 0.864 0.867

60 0.850 0.766 0.868 0.955 0.853 0.878

Figure 1: Graph of time (minutes) versus absorbance.

The absorbance of tube 2 was slightly decrease as state in figure 1 after keeping in the dark for 1 hour. Tube 3 that exposed to light had a huge decrease in absorbance. Whereas, for tube 4 which filled with boiled chloroplast, there was a major increase in 30-45minutes and then decreased at 45-60minutes. Tube 5 which contained DCMU had increase until 45minutes and decrease in 45-60minutes. Tube 6 which was wrapped in red cellophane had a gradually decrease. The absorbance of tube 7 which was wrapped in green cellophane had a slightly decrease then it increased.

Conclusion:

Different treatments of the chloroplast can affect the electron transport chain and the rate of photosynthesis.

Discussion:

In this experiment, tube 1 which contained chloroplast and buffer sucrose was used as blank solution. Thus, the absorbance of tube 1 was set to zero.

The absorbance of tube 2 that was kept in the dark was slightly decrease which was different as predicted to have no changes in absorbance due to the chloroplast cannot harvest light energy as the light is absent. Thus, no electron can being transported to reduce DCPIP. The slightly decrease absorbance of tube 2 might happen because of the tube exposed to the light for few seconds before it wrapped with the aluminium foil.

The absorbance of tube 3 decrease gradually because it was exposed to light and the chloroplast could harvest the light to carry out photosynthesis. Therefore, the DCPIP reduced and its colour changed from blue to colourless.

The absorbance of tube 4 which filled with boiled chloroplast should not have a huge changes in this experiment because the high temperature had denatured the chloroplast. Thus, the chloroplast could not convert light energy to create an electron transport chain and the DCPIP would not have any changes. The results showed that the absorbance of tube 4 had a huge increase then a slightly decrease. It might be happened because of the fingerprint of the cuvette did not wiped properly and the temperature of the solution still have not drop to the room temperature.

Tube 5 had a major increase until 45minutes and after that it decrease. According to the theory, the absorbance of tube 5 should not have any huge changes due to the DCMU had the function to block the flow of the electrons in electron transport chain and no photosynthesis will be carry out. The changes of the absorbance of tube 5 might happened due to the DCMU which added were not enough to inhibit the chloroplast.

Tube 6 that was wrapped with a red cellophane had significant decrease. This result matched with the prediction. In chloroplasts, the photosynthetic pigments are mainly absorbing the red light to carry out photosynthesis. Red and violet-blue work the best for photosynthesis (Silverstein A et al. 2008). Hence, the transport in tube 6 was happening rapidly. The higher rate of photosynthesis causes the DCPIP lost colour and the absorbance decrease significantly.

Tube 7 that was wrapped with a green cellophane had slightly increase. This result was not matched with the theoretical data. There should not be any change in absorbance of tube 7 due to the wavelength of green will always reflected by chloroplast. This might be happened because of the improper way to wrap the tube with the green cellophane. The green cellophane did not cover the tube perfectly to cause the photosynthesis carried out.

Reference list:

Reece J.B, Urry L.A, Cain M.L, Wasserman S.A, Minorsky P.V & Jackson R.B, 2011, Photosynthesis, ‘Campbell Biology’, pp. 230-249, San Francisco: Pearson Benjamin Cummings

Silverstein A, Silverstein V, Nunn L.S, 2008, Photosynthesis, Lerner Publishing Group U.S.A.

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