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What is a Leaf?
Leaves
• Leaves come in many
shapes.
• There are two main
types: needle leaves
and broad leaves.
Conifers have Needles
• Many conifers have
needle leaves, which
are thin, pointed, and
very tough.
• They do not lose
much water to the air,
which helps conifers
survive in dry, cold
areas.
Deciduous Tree Leaves
• Many trees which
lose their leaves in
the winter have broad
leaves.
• Broad leaves are
wider and expose
more surface to the
sun.
Broad Leaves: Simple
• Broad leaves are
divided into two types:
simple and
compound.
• A simple leaf, just as
it sounds, is very
simple. There is one
main stalk and one
main blade.
Broad Leaves: Compound
• In compound leaves,
the leaf is divided into
leaflets, which are
attached to the
central stalk.
• It looks as if it has
many leaves, but it is
actually only one leaf.
Identifying Leaves
• At most times of the year, most
plants do not have flowers or
fruit, but they do have leaves.
• Therefore, when botanists
(scientists who study plants)
want to identify a plant, they
study its leaves. They look at
several things:
•
•
•
•
•
How the leaves are arranged
on the stem.
Whether the leaf is simple or
compound.
What the edges look like.
How the veins are arranged.
What the shapes of the
leaves are.
If they know these things and they
have a good plant guide, they
can usually tell exactly what
plant they are observing.
Leaves
• Ferns, conifers, and
flowering plants all have
leaves.
• Leaves perform an
important job because
they are the parts of the
plant where most of the
food is made.
• The outer surface of
some leaves has a waxy
coating called a cuticle,
which protects the leaf.
Parts of a Leaf
• Most leaves have
several main parts.
• There is a central
stalk (which is called
the "petiole"),
• a flat part of the blade
(the "lamina"),
• and veins, tubes
which carry water and
food in the leaf.
STALK
Parts of a Leaf
• Veins may run parallel to
the stalk or they may
branch out from it.
• On the underside of the
leaf there are tiny holes
or doors, microscopic in
size, called stomates.
• The stomates take in
water and air, and also
release air at night.
The stomates have been
magnified 750X in this picture.
Plants make their Own Food!
• Leaves are the site of the
food making process
called photosynthesis.
• Photosynthesis is unique
to green plants!
• Photosynthesis supplies
food for the plant and
oxygen for other forms of
life.
• A green plant helped
make the oxygen you are
breathing today.
http://www.urbanext.uiuc.edu/gpe/case1/c1facts2c.html
Some Leaves Look Different
• Many desert plants
have leaves that look
like spines.
• They have many
spines to shade the
surface of the plant
from the hot sun.
Some Leaves Look Different
• Some desert plants
have leaves that look
woolly.
• Some leaves look
silvery or glossy. This
helps them reflect the
sunlight during the
day.
Some Leaves Look Different
• Pine trees have
leaves called
‘needles’.
• The needles can be
long or short.
• They are in bundles
of 2-6.
• The needles can
persist for 1 ½ to 40
years.
A Review
STALK
VEIN
STOMATE
BLADE