Unit 1.
6
Fertilization
• In plants, fertilization is a process of sexual
reproduction, which occurs after pollination and
germination.
• Fertilization can be defined as the fusion of the
male gametes (pollen) with the female gametes
(ovum) to form a diploid zygote.
• The complete series of this process takes place
• In sexual reproduction, the nucleus of a male
gamete and the nucleus of a female gamete
join together.
• This is called fertilisation.
• When the nuclei of the two gametes have
joined together, they form a new cell.
• This cell is called a zygote.
Pollination and Fertilization
• Pollen contains TWO nuclei: a sperm nucleus and tube nucleus
• Sperm nucleus is protected in gametophyte tissue (pollen can travel in the
air)
The ovule is the inner part of the ovary
Parts of a mature ovule
Integuments
Two layers of protective coating
Micropyle
Minute pore or opening through which the pollen tube enters.
Nucellus
Nutritive tissue lining the interior of the ovule.
Embryo sac
In the center of the nucellus, it contains seven cells-
Three cells at the micropylar end one egg cell and two synergids.
Three cells at opposite ends, are called antipodal cells.
One large central cell. The central cell is different containing two
nuclei called polar nuclei.
12
The pollen grain on reaching to the stigma absorb nutrients
secreted by the stigma and the pollen tube begins to grow.
The tube nucleus remains close to the growing tip of the
pollen tube and eventually disintegrates.
Meanwhile, the generative nucleus divides into two male
gametes or nuclei which move to the tip of the tube and lie
in the mass of cytoplasm.
The pollen tube reaches the embryo sac, close to the egg
cell.
After pollen tube penetrates into the embryo sac, the tip of
One male gamete fuses with the egg cell and forms the
fertilized egg or the zygote.
The second male gamete fuses with the secondary nucleus,
i.e., the nucleus formed by the fusion of the polar nuclei
and forms the endosperm nucleus.
The fusion of male gamete with the two polar nuclei is
often termed as triple fusion.
The zygote develops into the embryo, while the endosperm
nucleus develops into endosperm of the seed.
Double fertilization involves two sperm cells; one fertilizes the
egg cell to form the zygote, while the other fuses with the two
polar nuclei that form the endosperm.
Seed formation
When the male nucleus fuses with the female nucleus inside an ovule, it
produces a zygote.
The zygote starts to divide.
It produces a little group of cells called an embryo.
This embryo will eventually grow into a new plant.
The ovule also begins to change.
It gradually grows into a seed.
Structure of bean seed
The testa is the tough outer coat of the seed.
The micropyle is a tiny hole where the pollen tube grew into the ovule.
Peel the testa away from the seed.
Inside, you should find two creamy-coloured structures.
These are called cotyledons.
They contain food stores for the embryo to use when it starts to grow.
Stigma
Style
Ovary
Stigma
Style
Ovary
Embryo Sac
Polar nuclei
Egg Cell
Pollen Grain
Pollen Tube
Generative Nucleus
Tube Nucleus
Mitotic division of
generative
nucleus to form 2
male gametes
Tube nucleus
disintegrates
1 Male gamete fuses
with the 2 polar nuclei
to form the triploid
1 male gamete fuses
endosperm nucleus
with the egg nucleus
to form the diploid
zygote
3N endosperm
nucleus
Double
fertilisation
2N Zygote
Every part of the flower sheds off except the ovary.
The ovary of the flower develops into the fruit while ovules develop into
seeds.
Fruit
https://youtu.be/4SCmfRZuj0A?si=Mur5BApTPQ6_5qX8
