Photosynthesis

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According to Table 2, the absorbance of Dark Tube 2 has decreased across the time; whereas the absorbance of Light Tube 3, Boiled Tube 4, DCMU Tube 5, Red Tube 6 and Green Tube 7 have increased by time.

[pic 1]

Figure 1. Graph of absorbance against the time for the light-dependent photosynthetic reaction under different treatments.

Absorbance reading in tube 2 is slightly increased while Tube 3 that receives light treatment shows a gradual decrease. In Tube 4, the readings is slightly decreasing. For Tube 5, it is constant for 30 minutes then it decreases sharply. Absorbance of Tube 6 is constantly decreasing and tube 7 has a tremendous decrease in absorbance.

Discussion

Tube 1 was served to be a reference for the spectrometer. It is used as a reference because it contains everything that can be found in the sample except the components which are trying to be found.

Absorbance of Tube 2 has increased because it was wrapped with aluminum foil, so no light can penetrate into the tube. There is no light reaction, the dye does not decolourise, therefore the absorbance increases by time.

In tube 3, the readings of absorbance decreases because tube 3 was completely exposed to light and photosynthesis is occurred. DCPIP was decolourised as the electrons are donated, hence the absorbance reading is decreased.

In Tube 4, the absorbance has slightly decreased but theoretically the light reaction would not occur for denatured chloroplast. Yet, absorbance readings for tube 4 have decreased gradually due to some chloroplast is not denatured. Therefore, there is a low rate of photosynthesis, and decrease in absorbance readings.

DCMU is an inhibitor for photosynthesis, it inhibits electron transport and photosystem II in chloroplast Suggett, Prášil and Borowitzka, 2010). But, the absorbance readings for Tube 5 are decreasing because the concentration of DCMU is not sufficient to inhibit the reaction completely. Hence, photosynthesis will still occur.

In Tube 6, the absorbance reading is lower than the green tube but higher than in the red tube and light tube. By prediction, the highest rate of photosynthesis should have occurred when red colour wavelength is absorbed and green colour wavelength is reflected. However, low intensity of light penetrating through the tube might cause the absorbance to be decreased as the rate of photosynthesis is low.

The absorbance reading for Tube 7 is decreasing because the rate of photosynthesis is low. Also, the chloroplast reflects green light more than absorbing it.

Conclusion

The hypothesis does not match completely with the results obtained in the end of this experiment as there might be some experimental errors occurred during the experiment. Yet, there are some treatments are following the hypothesis.

References

Reece, J., Urry, L., Cain, M., Wasserman, S., Minorsky, P., Jackson, R. and Campbell, N. (n.d.).Campbell biology.

Silverstein, A., Silverstein, V. and Nunn, L. (1998). Photosynthesis. Brookfield, Conn.: Twenty-First Century Books.

Suggett, D., Prášil, O. and Borowitzka, M. (2010). Chlorophyll a fluorescence in aquatic sciences. Dordrecht: Springer.