Download Leaf Chromatography

Leaf Chromatography
Background Information:
Most plants are green because they contain the energy absorbing pigment, chlorophyll.
Chlorophyll appears green because it absorbs red and blue wavelengths, reflecting the green. Some
plants also contain other pigments. From red to violet, the entire color spectrum can be found in
plant materials. The three primary groups of plant pigments are anthocyanins, carotenoids, and
chlorophyll. Each of these absorbs light at different parts of the visible light spectrum and has a
different function in the plant.
Anthocyanins attract insects for pollination by absorbing light in the UV spectrum, serve as
a sunscreen to protect plants from sun damage, and provide protection against predators because of
their foul taste. Carotenoids and chlorophyll both serve as light-harvesting pigments in the
photosynthetic processes of plants.
You can separate these pigments from one another by the use of paper chromatography. In
this process, plant tissue is applied to filter paper and an organic solvent is allowed to move up the
filter paper. Some pigments have a higher affinity for the solvent than others and move at different
rates up the filter paper. Because of these differences, several color bands would be expected if
there is more than one pigment present. The order, from the top, should be carotenes (orange),
xanthophylls (yellow), chlorophyll a (yellow-green), chlorophyll b (blue-green), and
anthocyanin (red).
Purpose: Separate leaf pigments (colors) in a leaf using chromatography
Materials
Isopropyl alcohol
3 different leaves
Coffee filter strips
Coin
Beaker
Pencil
Tape
Procedure
1. Obtain 3 coffee filter strips for your group.
2. Draw a line about 2 cm above the bottom of the paper strip.
3. Firmly roll a coin over the leaf so that you have a colored band running across your strip.
Follow this procedure for the remaining 2 leaf samples. Be sure each leaf sample is on its
own labeled chromatography strip. DO NOT RUB THE LEAF ABOVE OR BELOW THE
LINE. RUB THE LEAF ON THE LINE ONLY.
4. Tape the top of the paper strip to a pencil so that the end of the strip with the green line
hangs down. The pencil should be able to sit across the top of the beaker with the bottom
of the paper strip just touching the bottom of the beaker.
5. Lay the pencil across the top of the beaker with the paper strip extending into the alcohol.
MAKE SURE THAT THE LEVEL OF THE ALCOHOL IS BELOW THE GREEN LINE
ON YOUR PAPER STRIP.
6. Observe how the alcohol gets absorbed and travels up the paper. This may take up to 30
minutes. WORK ON THE ANALYSIS QUESTIONS WHILE YOU ARE WAITING. Do
not touch your experiment during this time.
Questions
1.
2.
3.
4.
5.
6.
Why do most plants appear green?
Draw a chloroplast. Label the stroma, thylakoid, and granum.
Write a “word equation” for photosynthesis.
What are the two stages of photosynthesis?
What stage of photosynthesis is the chlorophyll needed for?
Did the leaf you tested contain different pigments? What were they called? Use your results
to support your answer.
7. Why do you think some pigments travelled further than others?
8. Why is it important for plants to have different pigments?
9. Based on what you have learned, explain why leaves tend to change color in the fall.
When you are finished, clean up your area, staple one of the strips to your paper and turn this
assignment in.