|Why Plants have Leaves
Leaf answers and information
The main job of a leaf is to make food (see left navigation for a separate page about this) for
a plant. Leaves do this by using sunlight for energy to take apart
water from the ground and carbon dioxide from the air. Leaves use parts
of water and carbon dioxide to make sugar. This food making is called
photosynthesis, a large word which means making something new
(synthesis) using light (photo).
Water gets to the leaf through a set of pipes inside the tree which goes all the way down to the roots. Roots
take water in from the soil so that it can be used by the tree. There
are also chemicals in the water which help the plant stay healthy, a lot
like vitamins help people stay healthy. In winter, the ground freezes.
This makes it hard for water to get into the soil. Roots can't get as
much water from the soil in winter as in the warm seasons of the year.
dioxide mixed in the air comes into the leaf through small openings on
the bottom side of the leaf. These small openings also let air back out,
air which has a little extra oxygen in it from the leaf's using carbon
dioxide and water to make food. The small openings also let moisture get
out of the leaf. This can make problems for the plant in winter when
water is not as easy to get. Many trees in New York State get rid of
their leaves before the ground freezes. This helps protect them from
losing too much water during the winter.
leaves are making food, they use the chemical chlorophyll to get energy
from sunlight. Chlorophyll is green. When the leaf is ready to stop
making food in the fall, it stops making chlorophyll. Without
chlorophyll, the other chemicals that are in leaves can be seen. These
chemicals show up as different colors. For a more complete explanation,
visit the Web site Chemistry of Fall Colors.