Leaf Pigments: A lab using chromatography to show how
leaf pigments assist in photosynthesis.
By:
Kyle McLaughlin
Introduction
In this lab researched how leaf pigments help in photosynthesis. In the lab that we
conducted we used chromatography to show leaf pigments that all plants contain. The reason leaf
pigments are so important to plants is because they allow the leaf to perform photosynthesis. The
main pigment is chlorophyll A. This is the pigment that absorbs sunlight. This pigment, when
extracted, is a yellow/green color. There are 3 other pigments that assist chlorophyll A in
photosynthesis. These include chlorophyll B, Carotenoids, and xanthophyll. All of these
pigments are embedded in the membrane of the chloroplasts. Chloroplasts are the same as solar
panels; they are sun collection devices for the plant to complete the process of photosynthesis.
Light and water are also required for the process of photosynthesis to take place. The equation
for photosynthesis is important for us to understand how it takes place. The elements that are
required for photosynthesis are carbon dioxide and water. Once the plant has these elements and
also acquires sunlight it then creates glucose which is the energy for the plant. The problem that
we are trying to solve in this lab is to prove that pigments exists, we will do this by conducting
an experiment that will cause the pigments to show up on a piece of coffee filter paper.
Methods
Our hypothesis is that; if we soak coffee filter paper in 70% isopropyl alcohol with plant
leaves in it then we will see the pigments of the plant leaf on the coffee filter paper.
Materials: In order to test our hypothesis we will need to gather the following supplies.
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Coffee filter paper
Aluminum foil
70% isopropyl alcohol
1-250 mL glass beaker
1 rubber band
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½ plant leaf
1 pair of scissors
1 piece of paper towel
1 magnifying glass
Stop watch
Procedure: The steps we followed to complete these short experiments were as follows.
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Cut your coffee filter into long strips that are about figure width.
Fill your glass beaker with 70% isopropyl alcohol. (Enough to cover the leaves)
Cut your ½ plant leaf into smallest pieces possible on the paper towel.
Place the pieces of the plant leaf into the beaker filled with 70% isopropyl alcohol.
Place aluminum foil on top of the beaker.
Secure the piece of aluminum foil on the beaker with a rubber band.
Let the beaker sit overnight. (24 hours)
Take the aluminum and rubber band off of the beaker.
Place the coffee filter paper you cut into strips in the beaker, with one end in the beaker
and on end out of it.
10. Let the coffee filter paper sit for 3 minutes in the beaker.
11. Then take the coffee filter paper out of the beaker and place them on the table. Let the
coffee filter paper dry.
12. Look for color on the coffee filter paper.
Results
In the results it displayed the color that was on the coffee filter paper when we took it out
of the solution. I also wrote down the coffee filter soak time and how long the cut up leaves
sat in the solution.
Test #1
3 minutes coffee filter paper soak
1 day leaf soak
Test #2
5 minutes coffee filter paper soak
9 day leaf soak
Test #3
10 minutes coffee filter paper soak
9 day leaf soak
Test #4
15 minutes coffee filter paper soak
11 day leaf soak
Test #5
20 minutes coffee filter paper soak
11 day leaf soak
Test #6
3 minutes coffee filter paper soak
11 day leaf soak
Conclusions and Discussion
In this experiment we put cut up plant leaves in a beaker filled with 70% isopropyl
alcohol and let it soak we will see the pigments in the leaf come out on to the filter paper. I ran
six tests for this experiment. The first test that we ran, the plant leaves soaked in the alcohol for 1
day. We then left the coffee filter paper in the beaker for 3 minutes. After 3 minutes we took it
out there was no color on the filter paper. Our group decided that we had done something wrong
and in our next tests we were going to change the time the filter paper sat in the alcohol because
we felt that that would have the biggest impact. The next time we ran tests was after the leaves
soaked in the alcohol for 9 days. When we ran more tests we put the coffee filter paper in for 5
minutes then 10 minutes. When we took the filter paper out there was a yellow/green color on it.
This proves that there is chlorophyll A on the filter paper. We thought that we had succeeded in
extracting chlorophyll A from the plant. However by doing this we changed two variables. We
changed the time the filter paper sat in the alcohol and how long the leaves soaked in the alcohol.
So then the next tests we ran we had the leaves soaking for 11 days. Then we ran the tests with
15 minute, 20 minute, and 3 minute filter paper soaks. The 15 minute and 20 minute soaks came
out with color on it. However once again we changed two variables. So I ran a test with 3
minutes again. When I finished the 3 minute test it had color on it. So my conclusion is that
changing how long the coffee filter soaks does not change the results as much as how long the
plant leaves soak in the alcohol.