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Seperation of Chlorophyll pigments by paper chromatography

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Introduction

SEPERATION OF CHLOROPHYLL PIGMENTS BY PAPER CHROMATOGRAPHY Results of experiment Rf value for 1 = 2.6 / 7 = 0.37 Rf value for 2 = 3.2 / 7 = 0.45 Rf value for 3 = 5.6 / 7 = 0.80 Analysis From looking at the table of Rf values I have definitely found chlorophyll b and xanthophylls. But there were three different pigments with distinct colour differences, and from previous knowledge of the colours of photosynthetic pigments, I know that chlorophyll a is the other one. Chlorophyll a is the fundamental pigment in plants and without it they would not be able to photosynthesise. Paper chromatography separates the mixture of pigments (in liquid form) into its individual components. The technique is based on the fact that each substance in the mixture has a specific affinity for a solid surface and a specific solubility in different solvents. ...read more.

Middle

However, since each pigment reacts with only a narrow range of the spectrum, there is usually a need to produce several kinds of pigments, each of a different colour, to capture more of the sun's energy. Chlorophylls are greenish pigments, which contain a porphyrin ring with magnesium at the centre. This is a stable ring-shaped molecule around which electrons are free to migrate. It is linked to a long hydrocarbon chain, and because the electrons move freely, the ring has the potential to gain or lose electrons easily, and thus the potential to provide energized electrons to other molecules. This is the fundamental process by which chlorophyll "captures" the energy of sunlight. Chlorophyll absorbs two main colours from light quite well. These are blue and red. It reflects green light very well, however, the two different types of chlorophyll have their maximum absorption at different wavelengths of light. ...read more.

Conclusion

Along with chlorophyll b in transferring their energy produced to the chlorophyll a, two other pigments are found in plants. These are carotenes (orange) and xanthophylls (yellow), which can both come under the heading "carotenoids". Since chlorophyll is such a dominant pigment in green plants, this domination hides the colour of the carotenes and xanthophylls in the leaves. This causes most plant leaves to appear green most of the time. During the autumn, however, the chlorophyll starts to break down, causing the carotenes and xanthophylls to show their bright red, orange and yellow colours. Xanthophylls are yellowish pigments which include the compound carotene, which gives carrots their colour. They are composed of two small six-carbon rings connected by a chain of carbon atoms. As a result, they do not dissolve in water, and must be attached to membranes within the cell. They transfer all their energy to chlorophyll a. Nick Collinson - 1 - October 2002 ...read more.

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