Pollination & Fertilization

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Transcript Pollination & Fertilization

Pollination & Fertilization

Seeds, Fruits and Embryos

Section One

Flowers

    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

    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

  The centrally located

pistil

is the

female

organ of the flower.

The pistil consists of the following parts:   

Stigma

– The sticky top.

Style

– The slender stalk that supports the stigma.

Ovary

– The swollen base that contains the

ovules

(immature seeds).

   

Flower Structure

Each stamen consists of the following parts: 

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

    A

complete flower

contains these parts: 

Pistil

  

Stamens Corolla

(petals)

Calyx

(sepals) A flower that lacks any of these parts is an

incomplete flower

incomplete flower staminate

(

male

that lacks a pistil is a ) flower.

incomplete flower pistillate

(

female

that lacks stamens is a ) flower.

Review

    In addition to a receptacle,

complete flowers

have these structures:    

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

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

    Flowering plants reproduce sexually through the union of male and female during

fertilization

gametophytes

(gametes) The

male gametophyte

the anther).

is in the

pollen

(located in The

female gametophyte

ovary).

is the

ovule

(located in the

Pollination anther

to a includes the transfer of pollen from an

stigma

. Before fertilization can take place in the ovary, pollination must occur.

Anthers

  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

    Each anther has four

pollen chambers

, or sacs.

Within the pollen sac,

diploid

cells develop (change) into

pollen grains

A diploid cell contains

chromosomes (

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

    Haploid microspores contain

half

the chromosomes that the diploid cell contained.

Therefore, each microspore has

chromosomes.

Meiosis produces cells that each have a

haploid

(

) number of chromosomes.

Each microspore becomes a

pollen grain

Flowering Plant Gametophytes

     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

chromosomes. Mitosis produces two

haploid

(

) nuclei from the original

haploid

nucleus.

Flowering Plant Gametophytes

  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

animals

and can find its way to the sticky stigma of the same or another flower.

Flowering Plant Gametophytes

     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

which disintegrate.

cells, three of The

haploid 1N

cell in the ovule has chromosomes.

Haploid

cells contain

half

the number of chromosomes found in diploid cells.

Flowering Plant Gametophytes

     The remaining

haploid

several times by

mitosis

cell divides 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

chromosomes. Mitosis preserves the chromosome number in each

haploid

nucleus.

    

Pollination

Pollination stigma

is the transfer of pollen from an

anther

to a

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

can pollinate themselves.

and a

pistil

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

   Many plants can fertilize themselves through self pollination, 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

     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 embryo sacs

called An embryo sac contains seven cells (including one egg cell) and eight

haploid

nuclei.

Pollination

to a

stigma

is the transfer of pollen from an and is an essential step in sexual

anther

reproduction among flowering plants.

Select The Letter Of The Correct Answer From The List Below:

A. diploid D. pollination B. haploid E. ovary C. seven 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:

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?

     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?

     The

pollen tube embryo sac

continues to grow down through the

pistil

for several hours until it reaches the in the ovary.

When the

pollen tube ovule

reaches the 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 zygote

to form a (fertilized egg).

This process is called

fertilization

What Happens After A Pollen Grain Lands On The Surface Of A Stigma?

    The

zygote

is a

diploid

containing

cell chromosomes;

from the sperm and egg.

from the The two

haploid polar nuclei

fuse to form a

diploid fusion nucleus

which, in turn, fuses with the other sperm nucleus.

This second

fertilization

in an

endosperm nucleus

results The

endosperm nucleus

has triploid (

) chromosomes, three times the chromosome number of an egg or a sperm.

Information

   The ovules of flowering plants undergo

double fertilization

:   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.

seed

is a

matured ovule

consisting of the embryo and its stored food.

       

Fertilization Summarized

The sperm and the egg are

haploid

chromosomes.

cells, each containing

N Fusion

occurs when the sperm and the egg nuclei combine to form a

zygote

The

zygote nucleus

chromosomes.

diploid

and contains

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

diploid

and contains

chromosomes.

The second

sperm nucleus nucleus

then

fuses

with the to form the endosperm nucleus.

fusion

The

endosperm nucleus

chromosomes.

triploid

and contains

Cell Division

   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?

      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

    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.

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 sac. There, one nucleus combines with the egg nucleus combines with the fusion nucleus to form the triploid contain these nuclei, and the surrounding ovule, become a seed.

Section Four

Seeds and Fruit

Fruits

    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

dry

Fleshy

fruits are

soft

and

pulpy

at maturity.

Let’s learn more about these types of

fleshy fruits

:  Apple   Grape Peach

Apple

   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.

pear

is another example of a

pome

Grape

  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

   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

of fleshy fruits include the type following:  Plum   Cherry Olive

Dry Fruit

  

Dry fruits

are another kind of fruit with which you are probably familiar.

Dry

fruits are

dry

and

hard

papery

at maturity.

Let’s learn more about these types of

dry fruits

:  Bean pod   Corn kernel Acorn

Bean Pod

   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:    Pea plant Milkweed plant Lily plant

Corn Kernel

   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:   Wheat Oat  Barley

Acorn

  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:  Hazelnut   Pecan Chestnut

Information

    A

seed

is the

mature ovule

of a flower, consisting of the following parts:    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

  A kernel of

corn

is a complete fruit.

Let’s examine the following parts of a corn kernel:     Cotyledon Hypocotyl Epicotyl Endosperm

Monocot Seed Structure

    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

  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

  Each

lima bean

is a separate seed.

Let’s examine the following parts of the

bean seed embryo

:    Cotyledons Hypocotyl Epicotyl

     

Dicot Seed Structure

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

and

root

is the of the plant.

embryonic stem

The leaves that grow quickly when the seed

epicotyl

consists of two tiny

germinates

(sprouts).

The leaves of the epicotyl are true leaves that become permanent leaves in the adult plant.

Information

  Seeds can be

dispersed

by the following means:    Mechanical Wind Animals  Water Each plant’s seeds are specialized to take advantage of one method of seed dispersal.

Information

   

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

  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

      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

    

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

monocot’s

hypocotyl

and

cotyledon

appear above ground. A remain below ground.

Information

    Several factors influence the

germination

of seeds:  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

    A

fruit

seeds.

is a mature (ripened) ovary that contains one or more A

seed

is a mature ovule consisting of the following parts:   

Seed coat

(for protection)

Embryo

(immature plant)

Endosperm

(for food) An

embryo

can consist of the following parts:     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 hypocotyl and one or more cotyledons. Monocot seeds, seeds, such as beans, have two cotyledons. The two most important factors that affect seed germination are

Section Five

Testing Your Knowledge

This Is A Test of What You Have Learned…

 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.



Germinate: 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.

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.



Ovule: Correct Answer: A

An ovule is the immature seed of a plant that develops from the embryo sac within the ovary.

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: seed

ovule

 A

fruit

is to a

flower ovary

A. sepal B. seed C. calyx D. gamete E. 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: ovary

pistil

 An

anther

is to a

stamen

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 allow them to reproduce sexually. During the process to form a zygote. The ovary matures into a structure mature into seeds. Seeds are dispersed by several form new plants.