Leaves are like little factories. They make food for the plant through photosynthesis. "Photo" means light, and "synthesis" means "to put together." Leaves use sunlight, carbon dioxide from the air, and water brought up from the roots. They put those ingredients together to make glucose, a kind of sugar that feeds the tree, and oxygen. Plants don't need the oxygen, so they release it into the air.
The sun's energy is absorbed by chlorophyll (KLOR-uh-fill), a green pigment contained in special foodmaking cells in the leaves. Green chlorophyll makes leaves green.
When the weather gets cold and the days get shorter, trees stop growing. The leaves don't need to make food, so they stop making chlorophyll. When the green chlorophyll is gone, we see the other colors of the leaves - the reds, yellows, and oranges. The leaves would be these colors all the time, if it weren't for chlorophyll.
(c) Copyright 1999. The Christian Science Publishing Society