Why do leaves change
color in the fall?
Plants need several things to live. They take water from the
ground through their roots. They also take a gas called carbon
dioxide from the air. Plants use sunlight to turn water and carbon
dioxide into glucose. Glucose is a kind of sugar which plants
use as food for energy and as building blocks for growing. The
way plants turn water and carbon dioxide into sugar is called
photosynthesis. A chemical called chlorophyll helps make photosynthesis
happen. Chlorophyll is what gives plants their green color. During
winter, there is not enough light or water for photosynthesis.
The trees will rest, and live off the food they stored during
the summer. They stop making food so the green chlorophyll disappears
from the leaves. As the bright green fades away, we begin to
see yellow and orange colors. Small amounts of these colors have
been in the leaves all along. We just can't see them in the summer,
because the green chlorophyll covers them up. This is the reason
leaves change color in the fall.
Since leaves do not have the materials they need to survive in
the winter and fall, their leaves die and lose the green color.
"Separate the colors of a green leaf using chromatography"
- leaves, small jars
- covers for jars or aluminum foil or plastic wrap
- rubbing alcohol,
paper (absorbent cellulose paper).
- shallow pan, hot tap water, tape, pen
- plastic knife or spoon, clock or timer.
- Collect 2-3 large leaves all from different trees. Cut the
leaves into very small pieces and put them into small jars labeled
with the name or location of the tree.
- Add enough rubbing alcohol to each jar to cover the leaves.
Using a plastic knife or spoon, carefully chop and grind the
leaves in the alcohol.
- Cover the jars very loosely with lids or plastic wrap or
aluminum foil. Place the jars carefully into a shallow tray containing
1 inch of hot tap water.
- Keep the jars in the water for at least a half-hour, longer
if needed, until the alcohol has become colored (the darker the
better). Twirl each jar gently about every five minutes. Replace
the hot water if it cools off.
- Cut a long thin strip of filter paper for each of
the jars and label it.
- Remove jars from water and uncover. Place a strip of filter
paper into each jar so that one end is in the alcohol. Bend the
other end over the top of the jar and secure it with tape.
- The alcohol will travel up the paper, bringing the colors
with it. After 30-90 minutes (or longer), the colors will travel
different distances up the paper as the alcohol evaporates. You
should be able to see different shades of green, and possibly
some yellow, orange or red, depending on the type of leaf.
- Remove the strips of paper, let them dry and then tape them
to a piece of plain paper.
- Make your final observation of the filter paper strips to draw a