Falling
Leaves, Changing Colors ~ Why Does It Happen?
Read the story and
pay attention in the clues in yellow, then play the Fallen
Leaves, Fling Your Teacher Game below.
Trees have a
big job to do - they help to clean our air. They do this
with their leaves. In the summer, the shiny green leaves
provide shade to keep the ground temperature cooler, but
they also collect
carbon dioxide from the air. The carbon dioxide is
a gas that
living things exhale or breath out. Too much carbon
dioxide in the air is not good for living things. The
leaves on trees collect the carbon dioxide and mix it with
water their roots and leaves collect. The sunlight helps
this happen and it is called photosynthesis.
Photosynthesis
changes water and carbon dioxide into sugar for food for
trees. This sugar mixture, called
sap, is
carried down the
veins in leaves to the
trunk of
the tree and to the roots to feed the tree. As this
happens, the trees are cleaning the air so that living
things may breath
oxygen instead of carbon dioxide. At the same time,
the leaves are producing a substance called Chlorophyll.
Chlorophyll
is green, and that is the color you see in spring and
summer, or in evergreen trees.
Evergreen trees
never lose their leaves or change their leaf color. They
have needles
instead of regular leaves, and the needles are covered
with a thick waxy coating and the fluids inside the
needles have substances that resist freezing. Evergreen
trees are pines,
spruces, cedars,
firs--what we think of as
Christmas trees.
When fall or autumn comes, we get fewer hours of sunlight, which makes the temperature cooler. This happens as the Earth travels around the sun and some parts of the planet get fewer hours of sunlight than others. The days get shorter and the nights grow longer. As we get less sunlight, so do the trees. They can't produce as much chlorophyll as they do in summer, so the leaves can't be as green. Leaves have another substance in them all the time, called Carotenoid. This substance makes the tree leaves look shades of yellows and oranges. During the warmer months, the green or Chlorophyll cover up the yellows and oranges. But, when fall comes and the Chlorophyll or green starts to fade away, the yellows and oranges start to show through and the leaves start to change color.
As winter approaches and days get colder, the veins in the leaves begin to get smaller or shrink. Leaves are too tender to survive real cold and eventually the leaves will fall off. Before this happens, however, another substance called Anthocyanins is produced--and only in autumn. Anthocyanin makes the leaves turn to shades of red and purple while they help the trees recover nutrients in their leaves before they fall off. This helps the trees get ready for the next growing season.
Even in winter, the trees are working. As the leaves fall, they form a layer or blanket around the tree, helping to hold rainfall and to protect the trees roots from freezing. As the leaves slowly decompose or break down, they release nutrients back into the soil to help feed the tree.
If you read the story above and pay attention to the clues in yellow, you will do well when you play the game below. To play Fallen Leaves and Fling Your Teacher, click here.