Trees have three main parts - the leaves, the trunk
and the roots. The upper part of the tree with the branches is called the crown.
Needles or leaves are the part of the tree that make sugar from air and
water. They do this by a chemical process called photosynthesis in which energy
from the sun, carbon dioxide from the air, and water recombine to form sugars and oxygen.
Stomates are tiny holes that control the amount of air that enters and leaves
the tree.
Chlorophyll is a chemical that makes leaves green. It is found inside the
plant's cells where chloroplasts absorb the sun's energy for photosynthesis.
The trunk has several layers.
The outer bark protects the tree from fire or insects and insulates it from
extreme heat and cold.
The phloem is the layer of cells that forms a pipeline to carry sugars from the
leaves to the rest of the tree. As these cells die, they become part of the outer bark.
The cambium is the growing part of the trunk. Each year the cambium produces new
phloem and sapwood. These cells grow more slowly in the winter and this slower growth
produces the tree's annual rings. These annual rings can help us find the age of a tree.
The oldest part of the tree is always on the inside.
The sapwood is the pipeline that carries water and nutrients from the roots up
to the leaves. As new layers develop, the inner layers die and become heartwood.
Heartwood is dead wood in the centre of the tree. It gives the tree its
strength.
Roots have two jobs - to anchor the tree to the earth and to absorb water and
nutrients from the soil.
Trees have fungi that live in and on the root cells and help them absorb water and
nutrients. In return, the fungi obtain food from the tree.
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