Download 06 Sexual Reproduction plants

Sexual Reproduction
In Plants
The Plant Kingdom
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Just as with animals,
there are many
different types of
plants.
Some reproduce
asexually, as we have
already seen.
Others reproduce
sexually.
Seeds
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In most plants sexual
reproduction takes
place in the seed.
It is a complete
package that contains
everything needed for
reproduction:
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An embryo
A food supply
A seed coat (keeps it
from drying out)
Seed Bearing Plants
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Seed bearing plants can be placed into
two groups:
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Angiosperms
Gymnosperms
Seed Bearing Plants - Angiosperms
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Angiosperms are
flowering plants.
The seeds, enclosed in
a case (like a pod),
form inside the
flowers.
Examples:
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Tulips
Sunflowers
Seed Bearing Plants - Gymnosperms
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Gymnosperms do not
bear flowers.
Most of them produce
seeds within cones
that have a coating on
them.
Example:
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Pine tree
Cycads
Sexual Reproduction in Angiosperms
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In angiosperms the
key to reproduction is
the flower.
All angiosperms
produce flowers, some
small and others
large.
The flowers contain
the plant’s
reproductive organs,
the pistil and the
stamen.
Time for an Art Break
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Please turn to p.62 in
your text.
At the top you will see
a drawing of the
reproductive system
of an angiosperm.
Please make a
detailed reproduction
of this drawing in your
notes.
Pollination and Fertilization in
Angiosperms
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Pollination occurs
when pollen grains
from the anthers
reach the stigma of
the pistil.
There are two types of
pollination:
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Self-pollination
Cross-pollination
Self-pollination
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In self-pollination both
male and female
gametes come from
the same plant.
Cross-pollination
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In cross-pollination
gametes from two
different plants (of the
same species) come
together.
Insects and wind are
the two most common
ways in which this
happens.
It creates a greater
variation.
Fertilization
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Even if pollination is
successful there is no
guarantee that
fertilization will occur.
The pollen grain
(which contains the
male gametes) must
now grow an
extension to reach the
ovule.
This extension is
called a pollen tube.
Seed Development
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As in animals, once
sperm reach an egg a
zygote is formed.
With a food source at
hand, called a
cotyledon, the zygote
undergoes mitotic
division developing a
leaf, stem and root.
Seed Dispersal in Angiosperms
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Before being
dispersed the
developing seed is
surrounded by the
walls of the ovary.
As the ovary matures
it forms a fruit.
Pea pods or berries
are examples.
Seed Dispersal
Dispersal means transporting seeds away
from the parent plant.
 Plants have devised many different ways
to do this.
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Plants that Launch Seeds
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Some plants are
capable of launching
seeds away from them
in order to disperse
their seeds.
The seed pod at right
will eventually
explode, sending
seeds a great distance
from the parent plant.
Hitching a Ride
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Berries that are eaten
by birds or other
animals will pass
through their digestive
system unscathed.
They will be deposited
in various locations
when the
animal…poops.
Hitching a Ride
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Other seeds will
actually attach
themselves to an
animal to be deposited
elsewhere.
Wind and Rain
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Wind will carry certain
types of seeds vast
distances.
Seeds that fall to the
ground can be swept
away by rainfall
runoff.
The Farther the Better
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It is important that
seeds get as far away
as possible from the
parent plant.
Why?
Competition. If the
seed stays close it
must compete with
the parent plant, a
contest it will probably
lose.
Seed Germination
Germination is the process in which a seed
begins to grow.
 Some seeds will stay dormant for years
before they begin to grow.
 As the seed grows it will eventually
mature and develop its own flowers,
repeating the cycle.
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Sexual Reproduction in Gymnosperms
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There are many
similarities between
reproduction in
angiosperms and
gymnosperms.
The difference is that
seeds in
gymnosperms are
contained in cones.
Sexual Reproduction in Gymnosperms
Sexual Reproduction in Plants Without
Seeds
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Many plants reproduce
without seeds.
Plants such as mosses
and ferns.
These plants
reproduce through
spores.
Sexual Reproduction in Plants Without
Seeds
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The big difference is
that plants without
seeds can develop
without being
fertilized.
Advantages
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Reproduction through spores carries with it some
distinct advantages.
First, spores are very light. This means that the
wind can carry them great distances to locations
that favour growth.
Advantages
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Secondly, spores can
remain dormant for
very long periods of
time.
This means that
periods of drought or
unfavourable
temperatures can be
survived.
Homework
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Please read section
2.3 which begins on
p.60.
Answer questions #15 on Page 71
Vocabulary:
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Pistil
Stamen
Pollination