Topics: Light, Electromagnetic radiation, Visible spectrum Pages: 6 (2078 words) Published: August 27, 2013
The effect of differing wavelengths of visible light on the photosynthetic activity of Beta vulgaris Introduction
Photosynthesis is a crucial biological process that occurs within the chloroplasts of plant cells where CO2 + H2O + Sunlight C6H12O6 + O2. The chloroplasts use light, an electromagnetic energy source, to produce food for the plant in the form of sugar molecules. During photosynthesis, the excited electrons from the light pass through proteins in the electron transport chain (ETC), where ATP and NADPH are produced. The CO2 absorbed by the plant are then fixed into carbohydrates by these two organic molecules (Hoober 1984; Halliwell 1984). It is currently known that plants do not use every colour of the visible light spectrum when undergoing photosynthesis, and that the different wavelengths of light are absorbed by the chlorophyll at different rates. In green land plants, the blue and red lights are most readily absorbed by the cells, whereas green light is not easily absorbed (Roberts and Ingram 2001). Photosynthesis is crucial to the survival of most species on the earth. It produces oxygen which is important for cellular respiration and glucose which provides the energy for living organisms in order to survive. If plants are not undergoing photosynthesis efficiently, or at all, then not enough oxygen and glucose are being produced. This can lead to detrimental effects on the entire world, including highly toxic levels of CO2 in the atmosphere and starvation (Endler 1993). The research being conducted in this practical aims to look at the differing wavelengths of visible light, and which range produces the most photosynthetic activity in green land plants. Since these plants absorb red and blue lights the most readily, and chlorophyll a absorbs blue light the most out of any other wavelength, it is hypothesised that in this practical the most activity will be seen under the blue light (Hoober 1984). In order to find the answer to the question above, a sample of spinach beet (Beta vulgaris) was centrifuged to isolate the chloroplasts. Four samples of the chloroplast isolate were then combined with DCPIP, a chemical that monitors the flow of electrons by changing colour from blue to colourless as it accepts electrons in the ETC, and placed under a red light, a blue light, a green light respectively. The fourth sample was placed in a no light environment as a control. Every two minutes for eight minutes the absorbance of each sample was recorded, and the experiment repeated using both the supernatant and isolate. Methods

A handful of spinach leaves were ground and then filtered to provide a thick green liquid, and then placed into a centrifuge to isolate the chloroplasts from the supernatant. The supernatant was placed on ice until further use. The isolated chloroplasts were then confirmed to be functional by adding 20µL of the isolate to 5mL of DCPIP, immediately measuring the absorbance at 605nm, and then placed in front of an unfiltered light source. At two minute intervals for eight minutes, the absorbance of the isolate was measured until it was decreasing at a rate of approximately 0.1nm.

Afterward, two students took a sample of both the isolate and supernatant and observed under the microscope. The number of the chloroplasts was counted and photos taken of each sample.

The remaining students then placed 5mL of DCPIP and 0.2mL of chloroplast isolate into four glass cuvettes, and the absorbance at 605nm was recorded for each one. The cuvettes were then placed under a red light, a blue light, and a green light, and no light respectively. At two minute intervals for eight minutes the absorbance for each cuvette was measured and again, placed under their respective light sources. Afterward, the same process for the experiment was conducted with the supernatant. The entire experiment was repeated two more times. All of the results were recorded, and the respective excel graphs were produced. Results...

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Halliwell, B. (1984) Structure, function, and isolation of chloroplasts. In: Chloroplast metabolism, revised edition (Ed.: B. Halliwell). Oxford University Press, Oxford, pages 1-30.
Hoober, J.K. (1984), The process of photosynthesis: the light reactions. In: Chloroplasts (ED.:J.K. Hoober). Plenum Press, New York, pages 79-110
Lee, D.W. (1987), The spectral distribution of radiation in two neotropical rainforests. Biotropica, 19, 161-166
Melis, A., Spangfort, M., Andersson, B. (1987), Light-absorption and electron-transport balance between photosystems II and photosystem I in spinach chloroplasts. Photochemsitry and Photobiology, 45, 129-136
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Tissue, D.T., Thomas, R.B., Strain, B.R. (1997), Atmospheric CO2 enrichment increases growth and photosynthesis of Pinus taeda: a 4 year experiment in the field. Plant, Cell and environment, 20, 1123-1134 light quantity and quality during
Turnbull, M.H. (1991) The effect of light quantity and quality during development on the photosynthetic characteristics of six Australian rainforest tree species. Oecologia, 87, 110-117.
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