Investigating plant pigments

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Investigating Plant Pigments

Abstract

Pigments are coloured molecules which absorb specific wavelengths of light within the visible spectrum. The colour of an object represents those wavelengths which are reflected or transmitted by the pigment. Leaves are green because their chloroplasts contain large amounts of chlorophyll, which absorbs the wavelengths blue and red and reflects the green wavelengths. These wavelengths can be plotted as an absorption spectrum. The array of the wavelengths absorbed by photosynthetic pigments situated in the thylakoids is further increased because the pigments are noncovalently linked with a mixture of different polypeptides. The pigments where separated by a process call paper chromatography. The separated pigments where analysed using a spectrophotometer.

Cheap University Papers on investigating plant pigments

This is a picture of an absorption spectrum for several photosynthetic pigments. As you can see chlorophyll a (yellow-green) absorbs mostly violet-blue and red wavelengths, chlorophyll b (green-blue) also absorbs blue and red wavelengths, while carotene (yellow-orange) absorbs mostly blue-green and green wavelengths. In my results pigment one chlorophyll a, absorbs mostly violent-blue. Pigment two chlorophyll b, absorbs mostly blue. Pigment three and four xanthophylls (a type of carotene) and carotene absorb mostly blue-green and green.

Aim

The aim of this experiment was to separate, analyse and identify the wavelengths which are absorbed by the pigments found in plants.

Hypothesis

I predict that chlorophyll a, will absorb mostly red because the colour that is reflected is yellow-green and red it at the other end of the spectrum. Chlorophyll b, will also absorb red because it reflects the colour blue-green and again red it at the other end of the spectrum. Carotene and xanthophylls will absorb mostly blue-violet because they reflect orange-yellow and blue-violet is at the other end of the spectrum.

Method

Extracting Pigments from Leaves

The extracting pigment from the leave section of the procedure was not preformed by us but by the science assistant.

Separating the Pigments by Paper Chromatography

•A strip of chromatography paper approximately 1-cm wide and 10-15cm long was obtained.

•A pencil line across the paper cm from the bottom was drawn.

•The toothpick was dipped into the pigment solution and placed in the middle of the pencil line on the paper.

•The spot was let dry and another spot in the same spot applied.

•This was repeated approximately 15 times.

•The chromatogram was placed on the glass stirring rod with sticky tape.

•The end of the chromatogram was placed in about 15mL of solvent in a jar and left for approximately 15mins

•The chromatogram was removed and the highest point of which the solvent reached was marked with a pencil and measured. And the different spots of pigment where circled.

•The pigment bands where cut out and placed in separate test tubes depending on how far up the chromatograms it was.

The separating of the pigments from the paper using acetone was not preformed by us but by the science assistant.

•The solution of the first pigment was places into the spectrophotometer tube and the spectrophotometer was set to 40nm. The process was repeated for the other pigments and the other wavelengths.

Results

Solvent .4cm

Pigment 1 cm

Pigment 6.cm

Pigment 4.7cm

Pigment 4 .5cm

Rf values for my pigments

Pigment 1 0.6

Pigment 0.66

Pigment 0.5

Pigment 4 0.7

Discussion

In this experiment four pigments where isolated from the spinach leaves.

The pencil was marked at the cm mark so that we knew where the pigment was placed and could accurately measure. The pigment which I believe was the strongest in spinach leaves was chlorophyll a and chlorophyll b, because spinach is a green colour and chlorophyll absorbs wavelengths blue and red and reflects green so the plant will appear green. The chlorophyll also travelled the furthest up the paper.

In my hypothesis I predicted that chlorophyll a, will absorb mostly red. In the 00 results chlorophyll a, absorbed mostly violet-blue. So my prediction would have been wrong, for chlorophyll a didn't absorb much red at all. In comparing the 00 results to the 00 results I found that chlorophyll a did absorb a of large amount red wavelengths, yet also absorbed a large amount of blue wavelengths. I predicted that Chlorophyll b, will also absorb red. In the result of 00 it absorbed mostly blue. so my prediction was wrong, because chlorophyll b didn't absorb much red if any. In comparing my results to the 00 results I found that chlorophyll b peaked in blue-violet and red-orange. Carotene and xanthophylls will absorb mostly blue-violet because they reflect orange-yellow. This prediction was not wrong as carotene and xanthophylls did peak in blue-violet and green. In comparing the 00 results to the 00 results I found that carotene and xanthophylls absorbed mostly blue and red. In comparing the two graphs to the abortion spectrum of many photosynthetic pigments I found that the results of 00 where more correct for chlorophyll a and chlorophyll b, yet when it came to carotene and xanthophylls the results of 00 where more accurate.

In this experiment four pigments where isolated from the spinach leaves.

The pigments absorb colour and also refect colour, the colours that they reflect will be the colour they appear to the human eye.

The data that we calculated was no the most accurate. Errors are expected when doing any experiment. Most of the errors obtained by the group would have come from experimental difficulties, equipment, and the loss of particular pigments.

Experimental difficulties Placing the right amount of pigment solution on the chromatograms. Not putting the chromatograms into the solution to far.

Equipment The spectrophotometer may have been faulty for particular wavelengths. eg. The 40 wavelength.

The experiment was overall done well by the class. We obtained information which contributed to our knowledge on photosynthetic pigments and photosynthesis.

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