Download What photosynthetic pigments exist in plants?

ESCOLA SECUNDÁRIA DE VIRIATO - 402977
Direcção Regional de Educação do Centro
Centro de Área Educativa de Viseu
10th year of schooling
Academic Year - 2008/2009
Biology and Geology
Name: _______________________________________________________ No. ___ Class B
Practical exercise:
What photosynthetic pigments exist in plants?
Introduction:
The photosynthesis is a photochemical process that occurs in green leaves, where the
light is captured by organic molecules - the pigments - found in thylakoid membranes of chloroplasts.
The separation of pigments contained in chloroplasts is of great interest because it allows studying the chemical and physical properties.
The chromatography is based on the principle of absorption. The pigments found in
chloroplast, when in the presence of a solvent, are absorbed differently by chromatography
paper. The solvent rises by capillary and drag the different pigments that are distributed from
the bottom to the top of the paper, in the following order: chlorophyll b (green / yellow), chlorophyll a (deep green), xanthophylls (yellow) and carotene (color orange).
Material:
Pestle and mortar
Fine Sand
Funnel
Beaker (50ml) (glasses cup or a glasses tube)
Test tubes and their support
Glass rod
Pipettes
Small Petri dishes
Filter paper
The role of cleanliness
Chromatography paper
Alcohol (90º) or acetone
Benzene
Distilled water
Green leaves (spinach, water cress, geranium (Pelargonium))
Procedure:
1. Put in a pestle 20 grams of fresh leaves of the plant selected and add a small amount of
fine sand.
2. Crush the leaves with the aid of mortar, gradually adding 50 ml of alcohol. Mix. Record the color of the solution.
Figure 1
3. Filter the mixture to a beaker, throwing away solid waste in order to obtain "crude
chlorophyll."
4. Place the filtrate of a Petri dish. Introduce a rectangular piece of folded chromatography paper, as shown in Figure 1.
Chromatography paper
“Crude cholorophyll”
Figure 2
5. Wait 15 minutes and observe.
6. Using colored pencils, make a diagram that depicts (describes) exactly what is shown
on the paper.
Topics for discussion:
1. Try to explain the reason for the following:
1.1 Why you crushed the leaves;
1.2 Why you have added alcohol.
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2. Why is it called "crude chlorophyll?"
3. Please observe carefully the filter paper used in the filtration of the solution.
3.1 Indicate the number of spots that are formed.
3.2 Establish the relationship between the colored spots and the photosynthetic pigments.
4. Why do leaves change colors in autumn?
5. What is the function of the chlorophylls in photosynthesis?
6. What are accessory pigments and what are their functions?
7. Make the report on your work (V Gowin).
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