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Plant Structure
plant organs
1.
2.
3.
4.
Roots,
Stems,
Leave,
Flowers
BIOLOGI TEAM - SMAMDA
Roots:
A root is an organ that
attaches a plant to the
ground and collects water
and minerals from the soil.
Most roots are important
food storage organs too.
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Types Of Root
Food crops such
as wheat, barley,
and beans have
fibrous roots
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A single large
root that
grows straight
down into the
ground is
called a
taproot.
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The taproots of
many plants store
large quantities of
food. Beets and
turnips are two
examples. Can you
think of others?
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Root Structure
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Vascular tissue is
made of two kinds of
cells. One kind of cell,
called phloem, carries
food from one part of a
plant to another..
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Food produced in
the leaves of the
plant travels down
to the root through
phloem
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Xylem carries
water and
dissolved minerals
upward from the
roots to the stem
and leaves.
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Root Growth
A root grows longer at its
tip. The root cap protects
the growing tip as it
pushes through the soil.
Dividing cells behind the
root cap produce new
cells
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Stems
The tree trunk is actually a
stem, an organ that
transports food, water, and
minerals between the roots
and leaves of a plant. A
stem also supports the
leaves and holds them up
to the light.
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Many stems
store water and
produce food.
Saguaro cactus
ran store
enough water to
last the cactus
two years.
How would you tell if a stem carries
BIOLOGI TEAM - SMAMDA
on photosynthesis?
Stem Structure
Two are types Stem
herbaceous stem is
soft, green, and flexible.
Plants with herbaceous
stems usually live one
or two years.
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Grasses, bean
plants, and many
wildflowers have
herbaceous stems.
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A woody stem is hard,
strong, and rigid Plants.
They live for many
years. Each year their
stems grow wider.
Most trees and shrubs
have woody stems.
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Herbaceous stems may carry on
photosynthesis. The woody stem becomes
thicker and covered during the first year of
growth.
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Stem Growth
The cambium of woody stems
causes the stem to grow
wider.
Each year the cambium
produces a new layer of
phloem cells. The new phloem
cells push older phloem cells
toward the outside surface of
the stem.
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The cambium also
produces a new layer
of xylem cells each
year. The new xylem
cells are produced
toward the inside of
the stem.
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Together the growth
rings form a tree's wood.
The wood strengthens
and supports the tree.
What can you tell by
counting a tree's growth
rings?
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As the stem grows wider,
cells of the epidermis
become filled with a fatty
material. These cells are
soon changed into a new
tissue called bark.
Bark is the tough protective
covering of a woody stem.
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A woody stem grows
longer by adding new
cells to areas called
buds. A bud is
covered with scales
that protect growing
tissues from hungry
animals and extreme
temperatures.
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BIOLOGI TEAM - SMAMDA
The tip of the stem and several
young leaves are underneath
the scales. In early spring, cells
in the tip of the stem divide
and grow longer. As the stem
lengthens, the bud scales fall
off, leaving a scar on the stem.
Each year new buds form.
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Leaves
A leaf is an organ that
produces food for a plant.
It takes many leaves to
make enough food for a
large tree to live.
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There are two
common leaves
types :
broad leaves and
needlelike leaves.
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Leaf Structure
Look closely at the leaf in
Figure The upper and lower
epidermises enclose the green
part of the leaf.
A leaf's epidermis is covered
by a waxy cuticle that keeps
the leaf from drying out.
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Mesophyll
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Notice that the leaf has many
openings, or stomates, on its
lower surface. Gases such as
carbon dioxide, oxygen, and
water vapor pass in and out of
the leaf through these
openings. Two bean-shaped
cells open and close each
stomate.
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Between the two layers of
epidermis is the middle part of
the leaf called the mesophyll.
The mesophyll of many leaves
is arranged in two layers. The
top layer contains long, narrow
cells, while the bottom layer
contains irregularly shaped
cells and many air spaces.
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Cells in both layers are
green because they
contain chloroplasts.
chloroplasts contain
chlorophyll, the green
pigment needed for
photosynthesis.
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Look at the leaf blade
in Figure. Notice the
larger veins branch into
smaller and smaller
veins. A vein is
actually a bundle of
phloem and xylem in a
leaf
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BIOLOGI TEAM - SMAMDA
Lesson Review
1. What are the main
functions of roots, stems,
and leaves?
2. What path does water
follow when it travels from
the soil into the xylem of a
root?
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3. Explain how growth
rings are formed in a
woody stem.
4. Give the function of the
mesophyll, epidermis,
and stomates of a leaf.
5. Explain how a Venus'sflytrap catches an insect.
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Interpret and Apply
12. How could you tell
the difference between
herbaceous and woody
stems by looking at
their vascular tissue?
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Flower
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Flower Structure and
Function
The leaflike structures at
the base of a flower are
sepals. Sepals are usually
green but can be other
bright colors. The sepals
enclose a flower before it
opens.
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Inside the sepals, leaflike
structure are called
petals. The petals, often
white or brightly colored,
surround and protect the
reproductive parts of a
flower. They also attract
insects to the flower.
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Stamen is the male
reproductive part of a flower.
Each stamen has a long thin
stalk called a filament. The
filament supports the
anther. The anther is a sac
at the end of a stamen that
produces pollen,
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Pistil is the female
reproductive part of a flower.
The enlarged base of a pistil,
called an ovary, contains
ovules. Ovules produce eggs.
The slender stalk of the pistil
is called a style. The style
supports the stigma, the sticky
end of a pistil that collects
pollen.
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Not all flowers have sepals,
petals, stamens, and pistils.
Grass flowers, for example, do
not have sepals or petals.
Corn plants produce flowers
that contain only male or
female reproductive parts.
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Pollination
Before an angiosperm can
sexually reproduce,
pollination must occur.
Pollination in angiosperms
occurs when pollen from the
male structure, or anther, is
transferred to the female
structure, or stigma.
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The transfer of pollen
within the same plant is
called self-pollination. In
garden peas, pollen is
transferred from an anther
to a stigma in the same
flower.
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The transfer of pollen from
one plant to another is
called cross-pollination.
In willows, pollen from an
anther on one tree is
carried to a stigma on a
different tree.
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Pollen grains
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Pollination and pollinator
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Fertilization
Pollination is an important
step in angiosperm
reproduction. But it is not
the final step. Sperm cells
in the pollen must get to
the egg in the ovule for
fertilization to occur.
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Figure: The egg in each ovule is fertilized
by sperm from a single pollen grain.
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After a pollen grain reaches
the stigma of a flower,
chemicals on the stigma
cause the pollen grain to
form a tube As seen in
Figure, the pollen tube
grows down through the
style and ovary to an ovule.
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Sperm produced by the
pollen grain then travel
through the pollen tube
into the ovule. A sperm
fertilizes an egg inside the
ovule. The fertilized egg, or
zygote, is the beginning of
a new angiosperm.
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Fruits and Seeds
As you know, fertilization
occurs inside an ovule in
the ovary of a flower.
After fertilization, three
changes take place in the
flower. These changes are
shown in
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Figure : Once pollination and fertilization
are completed, fruit development begins.
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First, by the process of
mitosis, the zygote grows
into an embryo. Second,
the ovule develops into a
seed. Third, the ovary may
enlarge or change color. As
the ovary changes, it
becomes a fruit.
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Seed Germination
After a seed goes through
dormancy, favorable
conditions may cause it to
germinate. Germination
begins when water enters
the seed.
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The root of the embryo pushes through the seed coat first. Root hairs
soon develop and absorb water from the soil. Meanwhile the stem
pushes the cotyledons above the ground. The embryo's two tiny leaves
then start to grow. Once exposed to sunlight, the leaves turn green and
begin the process of photosynthesis. Now that the young plant can
make its own food, the cotyledons shrivel up.
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