Leaves actually have several different colors
in them. We call them pigments. The green
pigment is called chlorophyll. It allows
plants to turn the sun's energy into a type of
energy they can use. Other pigments can do this
too, but chlorophyll is the main one.
Chlorophyll is extremely important to a
tree, but it is also very expensive (in terms of
energy) for the tree to make. So when the
tree is about to drop its leaves, it stops making
new chlorophyll. As the old chlorophyll is broken
down, the green fades. Other pigments are left in
the leaves. Of course in Santa Barbara, not all
plants lose their leaves in the Fall. Even here
in Wisconsin, pines, firs, and other "evergreens"
Does this tell you why there are pine trees
high up on mountains where you would never see a
eucalyptus or an oak? For some great pictures
of Autumn colors here in Wisconsin, check out this
site. This site also explains the chemistry of
changing leaf color.
Do you know what makes leaves green? What makes
them yellow or red? What makes paint or clothing
green or yellow or red?
I wonder what you would
find if you weighed 10 green leaves, one at a
time, and 10 yellow or red leaves and 10 brown
leaves from the same tree. If you calculated the
average weight of a green leaf, a red or yellow
leaf, and a brown leaf, do you think they would be
the same? If I were doing it, I'd want to try to
find 30 leaves (10 of each color) that were all
about the same size. Or, I guess, I could try to
find 3 leaves, 1 of each color, where all 3 leaves
were the same size, and weigh each one, and then
find 3 more leaves and so on, and see which color
leaf was the heaviest and the lightest for each
group of three. That would make a nice
I've heard that leaves turn
yellow or red when their green pigment disappears
- so they always have red and yellow pigments, but
it's just hidden by the green. I don't know if
that's true. Trees must have evolved to lose
their leaves in winter because then they were able
to live through the cold weather without having
their delicate leaves freeze. And the water in
the tree moves down towards the trunk and roots to
protect the small branches from freezing, too.
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