Saturday, October 6, 2012

Fall Leaf Experiment

Leaves have cells that have pigment-containing chloroplasts. They produce energy and their own food. The chloroplasts within a cell contain different pigments, which are what gives a leaf its color. Green chlorophyll is the most common type of pigment, but there are also xanthophylls (yellow), cartenoids (yellow, orange), and anthocyanins (red). The chlorophylls usually hide the other pigments, except when autumn comes along and chlorophyll begins to break down. This explains why leaves turn different colors in the fall.

Explore leaf pigments with your child in this fun experiment. My daughter and I just completed it and it was very fun. You are going to extract pigments from leaves. Collect several green leaves from different trees, a few from each one. Maples and others that have dramatic color changes in the fall will work best, but you can use any deciduous leaves (trees that lose their leaves in the winter).

Tear each set of leaves into several pieces and place them in a small drinking glass. Next, add just enough rubbing alcohol to cover them. You might want to cover the containers with foil or plastic wrap to keep the alcohol from evaporating into the air. Put the containers in a dish of hot tap water for about 30 minutes, until the alcohol turns green as the pigments from the leaves are absorbed into it.

Next, run a test to find out what colors are really in your leaves. You'll need coffee filters, filter paper, or chromatography paper for this part of the experiment. You can get chromatography at your local school supply store, or at least that’s where I got mine. Coffee filters are just fine.

Cut a strip out of the middle of a coffee filter, about one inch wide, for each of the leaf sets that you want to test. Tape one end of the paper to a pencil or stick, and suspend it across the container, with the other end just touching the alcohol and pigment mixture. A bit of the mixture will travel slowly up the paper. After about 30-90 minutes you should be able to see the "green" color break up into several different colors as the different pigments begin to separate. You'll see different shades of green, and perhaps other colors as well.

Which leaves had the most colorful pigments? Based on your experiment, which trees' leaves do you think will turn the brightest and least brightest colors this fall? Try the experiment again with evergreen leaves or needles to compare the results.

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