Download Pollination & Fertilization

Pollination &
Fertilization
Seeds, Fruits and Embryos
Section One
Flowers
Flowers
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Most people appreciate flowers for their appearance
or their fragrance.
Why do plants have flowers? Think about it!
Flowers are the reproductive organs of certain plants.
They are specialized to carry out sexual
reproduction and to begin the development of fruit
and seeds.
Let’s look closely at the structure of a typical flower.
Flower Structure
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The receptacle is the structure at
the tip of the twig. All the flower
parts are attached to the
receptacle.
The most visible parts of many
flowers are the petals.
All the petals together form the
corolla of the flower.
The petals usually are scented and
brightly colored. This helps
attract insects and animals, such as
butterflies, bees and birds.
Flower Structure
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The centrally located pistil is the
female organ of the flower.
The pistil consists of the following
parts:
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Stigma – The sticky top.
Style – The slender stalk that
supports the stigma.
Ovary – The swollen base that
contains the ovules (immature
seeds).
Flower Structure
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Each stamen consists of the
following parts:
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Anther – The sac-like structure
at the top of the stamen that
produces and stores pollen.
Filament – The slender stalk that
supports the anther.
Sepals are the outermost circle of
leaves that serve to protect the
other parts of the flower while it is
still a bud.
All the sepals together form the
calyx of the flower.
Sepals are usually green in color,
but they may be the same color as
the petals.
Information
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A complete flower contains these parts:
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Pistil
Stamens
Corolla (petals)
Calyx (sepals)
A flower that lacks any of these parts is an
incomplete flower.
An incomplete flower that lacks a pistil is a
staminate (male) flower.
An incomplete flower that lacks stamens is a
pistillate (female) flower.
Review
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In addition to a receptacle, complete flowers have these
structures:
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Pistil (female organ)
Stamens (male organs)
Corolla (petals)
Calyx (sepals)
An incomplete flower lacks one of the listed structures.
Staminate (male) flowers are incomplete because they lack
pistils.
Pistillate (female) flowers are incomplete because they lack
stamens.
Select The Best Matching Choice:
 Staminate:
Correct Answer: B
 Pistillate:
Correct Answer: D
 Stamen:
Correct Answer: E
 Pistil:
Correct Answer: A
 Calyx:
Correct Answer: F
 Corolla:
Correct Answer: C
A.
B.
C.
D.
E.
F.
G.
H.
Answer Column:
A female flower organ
Lacking pistils
Flower petals
Lacking stamens
A male flower organ
Flower sepals
Lacking a receptacle
Lacking sepals
Section Two
Gametophytes and Pollination
Information
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Flowering plants reproduce sexually through the
union of male and female gametophytes (gametes)
during fertilization.
The male gametophyte is in the pollen (located in
the anther).
The female gametophyte is the ovule (located in the
ovary).
Pollination includes the transfer of pollen from an
anther to a stigma. Before fertilization can take
place in the ovary, pollination must occur.
Anthers
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The anther produces
pollen.
The anther is located in
an exposed position,
making it easy for the
wind or visiting animals
to disperse the pollen.
Flowering Plant Gametophytes
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Each anther has four pollen
chambers, or sacs.
Within the pollen sac,
diploid cells develop
(change) into pollen grains.
A diploid cell contains 2N
chromosomes (N pairs).
The value of N is different
for almost every species.
Each diploid cell divides
twice by meiosis, forming
four haploid microspores.
Flowering Plant Gametophytes
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Haploid microspores
contain half the
chromosomes that the
diploid cell contained.
Therefore, each microspore
has 1N chromosomes.
Meiosis produces cells that
each have a haploid (N)
number of chromosomes.
Each microspore becomes a
pollen grain.
Flowering Plant Gametophytes
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A thick cell wall forms. This
protects the grain and prevents it
from drying out.
The nucleus divides by mitosis,
producing two nuclei within each
pollen grain.
One nucleus in the pollen grain is
the tube nucleus.
The other nucleus is the generative
nucleus.
Each pollen nucleus has 1N
chromosomes. Mitosis produces
two haploid (N) nuclei from the
original haploid nucleus.
Flowering Plant Gametophytes
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When the pollen sac matures
and splits open, it releases
thousands of pollen grains.
After being released from the
anther, pollen is carried by the
wind or animals and can find
its way to the sticky stigma of
the same or another flower.
Flowering Plant Gametophytes
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The ovary produces ovules.
There can be several ovules within
an ovary.
Each ovule is attached to the wall
of the ovary by a short stalk.
Meiosis occurs twice in each ovule,
forming four haploid cells, three of
which disintegrate.
The haploid cell in the ovule has
1N chromosomes. Haploid cells
contain half the number of
chromosomes found in diploid
cells.
Flowering Plant Gametophytes
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The remaining haploid cell divides
several times by mitosis to produce the
embryo sac (female gametophyte).
The embryo sac contains seven cells,
one much larger than the others, and two
polar nuclei.
The polar nuclei can be fertilized by the
pollen to form the endosperm (food) in
the seed.
One of the smaller cells is the egg cell,
which can be fertilized by the pollen to
form a zygote.
Each nucleus in the embryo sac has 1N
chromosomes. Mitosis preserves the
chromosome number in each haploid
nucleus.
Pollination
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Pollination is the transfer of pollen from an anther to a
stigma.
Self-pollination is the transfer of pollen from the anther to
the stigma of the same flower or to the stigma of another
flower on the same plant. Self-pollination requires both male
(stamen) and female (pistil) parts on the same plant.
Only complete flowers, having both stamens and a pistil,
can pollinate themselves.
Incomplete flowers on the same plant can pollinate each
other only if one flower is pistillate and the other is
staminate.
Cross-pollination is the transfer of pollen from an anther on
one plant to a stigma on another plant of the same species.
Information
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Many plants can fertilize themselves through selfpollination, but this is not an effective means of
reshuffling genes within a species and increasing
variety.
Cross-pollination is most effective in creating new
combinations of genes within plants.
Cross-pollination is the transfer of pollen from an
another to a stigma on another plant.
Review
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The anthers of flowering plants produce male
gametophytes called pollen.
Each pollen grain contains one tube nucleus and
one generative nucleus. Both nuclei are haploid.
The ovary produces female gametophytes called
embryo sacs.
An embryo sac contains seven cells (including one
egg cell) and eight haploid nuclei.
Pollination is the transfer of pollen from an anther
to a stigma and is an essential step in sexual
reproduction among flowering plants.
Select The Letter Of The Correct
Answer From The List Below:
A. diploid
B. haploid
C. seven
D. pollination
E. ovary
F. pollen
1. The male gametophyte, ____________________, is formed in the anther.
2. The __________________ produces the female embryo sac.
3. Mature pollen and mature egg cells contain _________________ nuclei.
4. An essential step in sexual reproduction in flowering plants is
________________.
Answers:
pollen
1. The male gametophyte, ____________________,
is formed in the anther.
ovary
2. The __________________
produces the female embryo sac.
haploid
3. Mature pollen and mature egg cells contain _________________
nuclei.
4. An essential step in sexual reproduction in flowering plants is
pollination
________________.
Section Three
Fertilization and Embryos
What Happens After A Pollen Grain
Lands On The Surface Of A Stigma?
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What happens after a pollen grain lands on the
surface of a stigma?
Sticky fluid, hairs or rough projections often cover
the stigma and hold the pollen grain.
Chemicals from the pistil cause the pollen grain to
grow and form a pollen tube.
The generative nucleus divides by mitosis to form
two haploid sperm nuclei.
The haploid tube nucleus controls the growth of the
pollen tube.
What Happens After A Pollen Grain
Lands On The Surface Of A Stigma?
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The pollen tube continues to
grow down through the pistil for
several hours until it reaches the
embryo sac in the ovary.
When the pollen tube reaches the
ovule within the ovary, it digests
a hole in the embryo sac wall.
Then, the tube nucleus
disintegrates.
One sperm nucleus enters the
embryo sac and fuses (unites)
with the egg nucleus to form a
zygote (fertilized egg).
This process is called
fertilization.
What Happens After A Pollen Grain
Lands On The Surface Of A Stigma?
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The zygote is a diploid cell
containing 2N chromosomes; N
from the sperm and N from the
egg.
The two haploid polar nuclei
fuse to form a diploid fusion
nucleus which, in turn, fuses
with the other sperm nucleus.
This second fertilization results
in an endosperm nucleus.
The endosperm nucleus has
triploid (3N) chromosomes,
three times the chromosome
number of an egg or a sperm.
Information
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The ovules of flowering plants
undergo double fertilization:
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One sperm nucleus from the pollen grain
fertilizes the egg to form the zygote.
The other sperm nucleus fertilizes the
polar nuclei to form the endosperm
nucleus.
The zygote develops into an embryo,
and the endosperm nucleus becomes
the stored food that nourishes the
embryo.
A seed is a matured ovule consisting
of the embryo and its stored food.
Fertilization Summarized
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The sperm and the egg are haploid cells, each containing N
chromosomes.
Fusion occurs when the sperm and the egg nuclei combine to
form a zygote.
The zygote nucleus is diploid and contains 2N
chromosomes.
In flowering plants, a second fertilization takes place.
The two haploid polar nuclei (inside the embryo sac)
combine to form a fusion nucleus.
The fusion nucleus is diploid and contains 2N chromosomes.
The second sperm nucleus then fuses with the fusion
nucleus to form the endosperm nucleus.
The endosperm nucleus is triploid and contains 3N
chromosomes.
Cell Division
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The seed develops from the ovule as the zygote and
endosperm nucleus undergo many cell divisions
during the process of mitosis.
During mitosis, the nucleus divides and forms two
nuclei identical to the original.
After the nucleus divides, the entire cell divides and
two identical cells form.
What Happens To A Flower After
Fertilization?
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The flower’s job is done after fertilization. Much of the
plant’s energy is used to develop the ovary and the ovules.
In several weeks, the fertilized ovule ripens and becomes a
seed.
The ovary also ripens and becomes a fruit.
If an ovary contains several ovules, each ovule can form a
seed.
The petals and stamens of the flower are no longer
necessary, and they often wither.
In many plants, however, the receptacle and the calyx
become part of the fruit.
Review
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Under the control of the tube nucleus, the pollen tube grows
down through the pistil until it reaches the ovule. Then, the
two sperm nuclei enter the embryo sac.
Within the embryo sac, the haploid sperm nuclei carry out
two separate fertilizations. One forms a diploid zygote
(fertilized egg) and the other forms a triploid endosperm
nucleus.
The zygote develops into an embryo (immature plant). The
endosperm nucleus provides food (endosperm) for the
growing embryo.
A seed is a mature ovule made up of an embryo and an
endosperm.
Quiz: Fill In The Blanks…
After pollination, the tube nucleus directs the growth of
the _____________
pollen tube through the pistil to the ovule. The
two haploid ___________
sperm nuclei then enter the embryo
sac. There, one nucleus combines with the egg nucleus
to form the diploid ____________.
The other nucleus
zygote
combines with the fusion nucleus to form the triploid
_____________
endosperm nucleus. Eventually, the cells that
contain these nuclei, and the surrounding ovule,
become a seed.
Section Four
Seeds and Fruit
Fruits
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A fruit is a ripened ovary that can include other
parts of the flower, such as the calyx and the
receptacle.
Most fruits can be classified as either fleshy or dry.
Fleshy fruits are soft and pulpy at maturity.
Let’s learn more about these types of fleshy fruits:
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Apple
Grape
Peach
Apple
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An apple is a pome type
of fleshy fruit. Its outer
fleshy layer is derived
from the calyx and
receptacle of the flower
(blossom).
The soft core, formed from
the ovary, contains several
seeds.
A pear is another example
of a pome.
Grape
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A grape is a berry type of
fleshy fruit. The fleshy layer,
often juicy, is derived entirely
from the ovary and contains
numerous seeds.
Other examples of berry type
fleshy fruits include the
following:
 Watermelon
 Tomato
 Banana
Peach
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A peach is a drupe type of
fleshy fruit. It consists of an
outer fleshy layer and an inner
hard and stony layer.
Both layers are formed from the
ovary. The inner layer (pit)
contains one or more seeds.
Other examples of drupe type
of fleshy fruits include the
following:
 Plum
 Cherry
 Olive
Dry Fruit
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Dry fruits are another kind of fruit with which you
are probably familiar.
Dry fruits are dry and hard or papery at maturity.
Let’s learn more about these types of dry fruits:
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Bean pod
Corn kernel
Acorn
Bean Pod
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A lima bean plant produces a pod
type of dry fruit. The fruit consists
of a single chamber (pod)
containing many seeds.
The pod splits when ripe and
releases the seeds (beans).
Other examples of plants that
produce pod type dry fruits include:
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Pea plant
Milkweed plant
Lily plant
Corn Kernel
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A corn kernel is a grain type of
dry fruit. Each kernel (grain) of
corn is a complete fruit.
A corn kernel contains one seed.
The seed coat is permanently
attached to the ovary wall.
Other examples of plants that
produce grain type dry fruits
include:
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Wheat
Oat
Barley
Acorn
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An acorn is a nut type of
dry fruit. It consists of
one seed surrounded by a
hard ovary wall.
Other examples of nut
type dry fruits include the
following:
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Hazelnut
Pecan
Chestnut
Information
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A seed is the mature ovule of a flower, consisting of the
following parts:
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Seed coat
Embryo
Endosperm
The seed coat (outer layer) develops from the wall of the
ovule and protects the embryo against injury, parasites and
dehydration.
The embryo is a tiny plant that develops from the zygote.
The endosperm develops from the endosperm nucleus of
the embryo sac. It provides the embryo with nutrients.
Monocot Seed Structure
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A kernel of corn is a complete fruit.
Let’s examine the following parts of a corn kernel:
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Cotyledon
Hypocotyl
Epicotyl
Endosperm
Monocot Seed Structure
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Corn is a monocot plant. Each
kernel has one cotyledon that
contains stored nutrients (starch
and sugar).
The cotyledon absorbs food from
the endosperm when the kernel
germinates.
The hypocotyl is the embryonic
stem and root of the corn plant.
The rolled-up leaves of the
epicotyl are true leaves that
become permanent leaves in the
adult plant.
Monocot Seed Structure
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The endosperm fills most of the
corn grain and contains starch
and sugar.
The plant uses the endosperm as
a source of food for growth.
Dicot Seed Structure
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Each lima bean is a separate seed.
Let’s examine the following parts of the bean seed
embryo:
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Cotyledons
Hypocotyl
Epicotyl
Dicot Seed Structure
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The bean is a dicot plant. Bean seeds
have two cotyledons.
The cotyledons completely digest and
absorb the endosperm and make up
most of the bean structure.
The cotyledons store a large amount
of protein and starch. This provides
food for the growing embryo as well
as for humans and other animals that
eat the bean.
The hypocotyl is the embryonic stem
and root of the plant.
The epicotyl consists of two tiny
leaves that grow quickly when the
seed germinates (sprouts).
The leaves of the epicotyl are true
leaves that become permanent leaves
in the adult plant.
Information
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Seeds can be dispersed by the following means:
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Mechanical
Wind
Animals
Water
Each plant’s seeds are specialized to take advantage
of one method of seed dispersal.
Information
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Mechanical dispersal occurs when a pod dries out
and bursts. Seeds within the pod can be thrown
several feet.
The wind carries dandelion and maple seeds, which
contain wisps of hair or wings.
Animals help disperse seeds by eating fleshy fruits
and eliminating the seeds in their feces. Seeds with
burrs can stick to animal fur and be carried several
miles.
Water helps disperse floating seeds or fruit, such as
the coconut.
Seed Germination
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Under favorable conditions, a seed can germinate
(sprout) and form a new plant.
Let’s compare the germination of a monocot grain
of corn and a dicot bean seed.
Monocot (Corn) Seed Germination
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The embryo absorbs water, and the root pushes through the
softened fruit to form a temporary primary root.
Growth occurs as cells divide mitotically in the embryo’s
meristematic tissue.
The tightly rolled leaves of the epicotyl push through the soil
and secondary branch roots develop.
Meristematic tissue continues to produce cells that become
roots, stems and leaves.
Once above ground, the leaves unroll and the stem grows to
form the cornstalk.
The hypocotyl and cotyledon of the corn grain never appear
above ground.
Dicot (Bean) Seed Germination
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Water softens the seed coat, and the hypocotyl grows out.
Mitotic division of the cells making up the embryo’s
meristematic tissue provide new cells for growth.
The root grows downward and the hypocotyl forms an arch
that pushes up through the soil.
Above ground, the hypocotyl straightens and lifts up the two
cotyledons and becomes the shoot.
The tiny leaves of the epicotyl unfold and grow into adult
plant leaves.
A dicot’s hypocotyl and cotyledon appear above ground. A
monocot’s hypocotyl and cotyledon remain below ground.
Information
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Several factors influence the germination of seeds:
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Water
Air
Temperature
Light
Water is needed to soften the seed coat (allowing the embryo
to grow) and aid in the life processes during growth. Too
much water can cause rotting.
Seeds must have oxygen to convert food into the energy
required for rapid cell division and growth.
The two most important factors that affect seed germination
are moisture and warmth.
Review
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A fruit is a mature (ripened) ovary that contains one or more
seeds.
A seed is a mature ovule consisting of the following parts:
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An embryo can consist of the following parts:
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Seed coat (for protection)
Embryo (immature plant)
Endosperm (for food)
One cotyledon (monocot plants)
Two cotyledons (dicot plants)
Epicotyl that forms leaves
Hypocotyl that forms stem and root
Seeds can germinate (sprout) under favorable conditions, the
most important of which are warmth and moisture.
Quiz: Fill In The Blanks…
After an ovule is fertilized, it develops into a seed. The
ovary, meanwhile, becomes the ____________.
The
fruit
____________
embryo within a seed consists of an epicotyl, a
hypocotyl and one or more cotyledons. Monocot seeds,
such as corn, have one cotyledon, and _____________
dicot
seeds, such as beans, have two cotyledons. The two
most important factors that affect seed germination are
moisture and ____________.
warmth
Section Five
Testing Your Knowledge
This Is A Test of What You Have
Learned…
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There are 10 questions on this test.
Try to correctly answer all of the questions.
If you miss a question, watch the screen for an
explanation of the correct answer.
Select The Best Matching Choice:
 Cotyledon:
Correct Answer: G
The cotyledon is the part of a plant embryo that
often provides food during germination.
Monocot plant embryos have one cotyledon, and
dicot plant embryos have two cotyledons.
A.
B.
C.
 Germinate:
D.
Correct Answer: C
When a seed germinates, it sprouts roots and
a stem. Germination occurs under various
conditions that depend on the type of seed.
E.
F.
G.
H.
Answer Column:
Immature seed
Spread far and wide
Sprout stem and roots
Immature fruit
Diploid cell
Male plant gamete
Plant embryo part
True plant leaf
Select The Best Matching Choice:
 Pollen:
Correct Answer: F
Pollen is the male gamete of plants produced in
the anthers of plants that have stamens. Female
plants that lack stamens cannot produce pollen.
A.
B.
C.
 Ovule:
D.
Correct Answer: A
An ovule is the immature seed of a plant that
develops from the embryo sac within the
ovary.
E.
F.
G.
H.
Answer Column:
Immature seed
Spread far and wide
Sprout stem and roots
Immature fruit
Diploid cell
Male plant gamete
Plant embryo part
True plant leaf
Select The Best Choice To Complete
Each Analogy:

A fruit is to a flower ovary as a(n) ________
seed is to an ovule.
A.
B.
C.
D.
E.
sepal
seed
calyx
gamete
pistil
Since a fruit is a ripened flower ovary, it is most like a seed,
which is a ripened flower ovule.
Select The Best Choice To Complete
Each Analogy:

An anther is to a stamen as a(n) ______________
ovary is to a pistil.
A. ovule
B. style
C. filament
D. ovary
E. petal
Since the anther is the gamete producing structure of a stamen,
it is most like the ovary, which is the gamete producing structure
of a pistil.
Fill In The Blanks…
Many higher plants are equipped with specialized
reproductive structures, called ______________,
which
flowers
allow them to reproduce sexually. During the process
fertilization male and female gametes combine
of ______________,
to form a zygote. The ovary matures into a structure
called a(n) ______________,
and the ovules within it
fruit
mature into seeds. Seeds are dispersed by several
means and can ______________
germinate (begin to grow) to
form new plants.
Pollination & Fertilization
~Seeds, Fruits and Embryos~