Transcript Document

SEXUAL REPRODUCTION IN ANGIOSPERMS
(FLOWERING PLANTS)
In contrast to gymnosperms, the reproductive
structures of the angiosperms are found within
structures called flowers, and the seeds, while
developing, are enclosed within a fruit.
STRUCTURE OF A FLOWER
Pedicel supports the plant and
connects it to the stem.
Receptacle is the part that
other flower parts are attached.
Sepals are leaflike structures
that form a ring around the
base of the flower.They may
be green or colored.
Pedicel
Petals are found above the
sepals and they are white or
colored. They surround the
reproductive organs of the
flower.
STRUCTURE OF A FLOWER
The stamen is male
reproductive organ. It is made
up of two parts;
filament and anther. Pollen
grains are produced within
anthers.
The pistil is usually called the
female reproductive organ. It is
made up of three parts;
Stigma: is enlarged area at the tip of the pistil that receives
pollen.
Style: supports the stigma.
Ovary: found at the base of the pistil and contains ovules.
The ovary develops into the fruit.
 Stamens and pistils are essential organs of the flower.
Corolla (complete circle of petals) and calyx (complete circle of
sepals) are the accessory organs.
 Plants that have flowers, which contain only pistils are
considered as female, and the plants that have flowers, which
contain only stamens are considered as male.
DEVELOPMENT OF GAMETES
Haploid spores are produced by meiosis within
the anthers of the stamen.
The spores undergo mitosis once, developing
into pollen grains. These pollen grains are the
young, male gametophytes.
Two haploid cells are found within the thick,
protective wall of each pollen grain.
One of the cells in the pollen grain is the
tube cell (nucleus), while the other is
generative cell (nucleus).
Once the pollen grains mature, anther bursts,
exposing pollen to air.
DEVELOPMENT OF GAMETES IN ANTHERS
microsporocyte (2n)
(anter ana hücresi)
meiosis
Microspores (n)
Each microspore undergoes mitosis
Vegetative nucleus
Generative nucleus
mitosis
Anthers
Generative nucleus
Sperm nucleus
Pollen tube nucleus
(Vegetative nucleus)
Pollen tube nucleus
POLLEN
DEVELOPMENT OF GAMETES IN OVARY
Every ovule within the
ovary of the pistil has a
small opening called
micropyle.
In each ovule, meiosis
of a single cell results in
four haploid spores.
Three of these spores
die, and the remaining
spore undergoes
mitosis three times.
DEVELOPMENT OF GAMETES IN OVARY
The resulting female
gametophyte, called an
embryo sac, has only
seven cells but eight
haploid nuclei.
Two of the nuclei, found
within a large central cell
are called polar nuclei.
The egg cell, which is near
the micropyle, is
surrounded by two cells
(synergids). Three other
cells are the other end of
the embryo sac. (antipodal
cells)
DEVELOPMENT OF GAMETES IN OVARY
megasporocyte (2n)
(Tohum taslağı ana hücresi)
meiosis
n
megaspore
Antipodal
cells
3 mitosis
synergids
Polar
nuclei
Embryo sac
egg
POLLINATION
In angiosperms, pollination is the
transfer of pollen from an anther to
stigma.
If pollen grain is transferred from an
anther to stigma on the same plant, it
is called self-pollination.
The transfer of pollen from the
anthers of one plant to the stigma of
another is called cross-pollination.
Artificial pollination occurs when
pollen is intentionally transferred by
humans from one plant to another.
FERTILIZATION
When a pollen grain
reaches the stigma of
a flower, it germinates.
A pollen tube grows
down through the
stigma and style and
into the ovary.
It then enters the ovule
through the
micropyle.
FERTILIZATION
The tube cell nucleus and
the generative cell nucleus
pass from the pollen grain
down the pollen tube.
As the generative nucleus
moves down, it divides to
form two haploid sperm
nuclei.
FERTILIZATION
The two sperm nuclei enter the embryo sac. One
fertilizes the egg cell to form a diploid zygote that
develops into the sporophyte embryo. The other fuses
with the two polar nuclei to form a triploid (3n)
endosperm cell.
FERTILIZATION
Because one sperm fertilizes the egg and the other fertilizes
the two polar nuclei, the process is called double fertilization.
Following fertilization, the endosperm nucleus divides by
mitosis to form the endosperm. Endosperm is the tissue that
stores food for the developing plant embryo.
Structures formed by the parts of the pistil after
pollination and fertilization;
OVARY
FRUIT
EGG CELL
EMBRYO
POLAR CELLS
ENDOSPERM
EMBRYO SAC
OUTER TISSUES OF
EMBRYO SAC
SEED
SEED COAT
FRUITS AND SEEDS
After fertilization, each ovule develops into a seed,
and the ovary develops into fruit.
In angiosperms, the seed is always found in fruit.
The parts of the flower are not involved in the
formation of fruit and die.
The ovary grows larger, and its wall thickens.
If a flower is not pollinated, a fruit usually does not
form, and the flowers falls away.
TYPES OF FRUITS
Fruits are classified according to their origin;
A fruit that develops from a single ovary is called
simple fruit. Ex: cherries and tomatoes
When several ovaries are found within one flower,
an aggregate fruit forms.
In some plants, such as the pineapple, the simple
fruits of many separate flowers fuse together to form
multiple fruit.
TYPES OF FRUITS
TYPES OF FRUITS
Only ovary (or
ovaries) is involved
during fruit formation
(REAL FRUIT)
Fruits that develop
from single ovary
(SIMPLE FRUIT)
Fruits that develop from more
than one ovaries
(AGGRAGATE FRUIT)
REAL – SIMPLE
FRUIT
Ex. Plum, peach,
cherry
REAL- AGGRAGATE
FRUIT
Ex: raspberry (ahududu),
blackberry (böğürtlen)
Ovary, sepals, petals
FALSE- SIMPLE
and receptacle are
FRUIT
involved during fruit Ex: apple, pear, fig,
formation
elma, mulberry (dut)
(FALSE FRUIT)
FALSE- AGGRAGATE
FRUIT
Ex: strawberry
FLESHY FRUITS
DRY FRUITS
STRUCTURE OF THE SEED
Seed is formed from the
embryo sac after
fertilization. It is formed
of three main parts;
1.Embryo: develops by
mitosis from the fertilized
egg
2. Endosperm: is food
storage tissue (stores
starch, protein, lipids or
cellulose for the developing
seedling)
3. Seed coat: protects
the seed from unfavorable
conditions
STRUCTURE OF THE SEED
In addition to one or two cotyledons, the plant
embryo has three parts:
*epicotyl
The part of the embryo above the
point of attachment of the
cotyledons, it gives rise to terminal
bud, leaves, upper stem
*hypocotyl
It is part of the embryo below the
point of attachment of the
cotyledons but above the radicle
*radicle
It is the lowermost part of the
embryo, the embryonic root
STRUCTURE OF THE SEED
MONOCOTS AND DICOTS
SEED GERMINATION
SEED GERMINATION IN DICOT PLANT
SEED GERMINATION IN MONOCOT PLANT
DORMANCY
• Seed dormancy is defined as a
state in which seeds are
prevented from germinating even
under environmental conditions
normally favorable for
germination.
• These conditions are a complex
combination of water, light,
temperature, gasses, seed coats,
and hormones.
• Living, non-dormant seeds
germinate when soil temperatures
and moisture conditions are suited
for cellular processes and division
• Legumes are typical examples of
physically dormant seeds; they
have low moisture content and
are prevented from intake of water
by the seed coat.
FACTORS AFFECTING SEED GERMINATION
The essential factors for seed germination are;
Water:
A dormant seed contains 10-15% of water and is generally dehydrated.
So the dormant seed has to absorb water to become active and exhibit
germination. Water makes the seed coat soft, causes it to rupture after
swelling and start germination. Water is also needed to bring in the
dissolved oxygen for use by the growing embryo.
Oxygen:
In the dormant condition the seeds respiratory rate is very low and so
oxygen is required in very small quantities. But for germination, oxygen is
needed in large quantities. The seeds obtain this oxygen from the air
contained in the soil.
Seeds placed deeply in soil, fail to germinate because of lack of oxygen.
FACTORS AFFECTING SEED GERMINATION
Temperature:
Germination can take place over a wide range of temperature
(5 - 400C), but the optimum for most of the crops is between 250 C to
300C.
Light:
Light has varied effects on germinating seeds of different plants. Some
seeds need light for germination, while in some seeds germination is
hindered by light.