Question

How does the process of fertilization take place in flowers?​

Answer 1

Answer:

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Pre-fertilization events in a flower

Events that take place before fertilization are termed as Pre-fertilization events. Following events would occur before actual fertilization takes place in a plant:

Gametogenesis

Development of male & female reproductive structures

Formation of male & female gametes

Gamete transfer

Bringing together male & female gamete

Pollination occurs in plants to facilitate gamete transfer

We will now understand the formation of male & female gametes in a plant. It is important to understand the structure of male & female reproductive parts in detail.

 

Male reproductive structure in a Flower : Stamen

Stamens are the male reproductive structures in a plant. The structure of a stamen consists of 3 important parts:

Filament

Stalk that bears anthers

Anther

Bilobed, dithecous structure at the tip of filament

Each lobe has 2 pollen sacs/ microsporangia

A total of 4 microsporangia are present in a anther

Each microsporangia produce spores, which later develop into pollen grains

Connective

Part attached to the back of anther

 

 Detailed structure of Microsporangium

 If the transverse section of a microsporangium is observed carefully, it is seen that there are 4 layers surrounding the microsporangia:

Epidermis

Endothecium

Middle layers

Tapetum

The first three ensure protection of the microsporangium, while the innermost layer, Tapetum provides nourishment to the pollen grains.

Sporogenous tissue is present at the centre of each microsporangium.

 

 

Microsporogenesis

 

Formation of microspores is termed as Microsporogenesis. Microspores are formed inside microsporangium.

Sporogenous cells differentiate to form meiocytes

Meiocytes under meiosis

4 haploid microspores are formed (Microspore tetrad)

Microspores dissociate & develop to form Pollen grains

Pollen grains are male gametophyte

 

 

 

 Pollen grains

 Each pollen grain is a tiny spherical structure, surrounded by 2 layers:



Exine

Hard, outer layer

Composed of sporopollenin

Highly resistant

Intine

Thin inner layer

Composed of cellulose & pectin

 

Formation of a pollen grain from microspore involves the following changes:

Expansion of the microspore

Formation of a large vacuole

Microspore nucleus displaced to an eccentric position against microspore wall

Nucleus undergoes first pollen mitosis

A large vegetative cell & a small generative cell are formed. This is the 2-cell stage. In many plants, pollen grains are released at this 2-celled stage. However, in some others, they are released at a 3-celled stage.

Generative cell detaches from pollen grain wall

Generative cell is engulfed by the vegetative cell

Answer 2

Question :-

How does the process of fertilization take place in flowers​.

Answer :-

❥・ 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.

❥・ It is a physicochemical process which  occurs after the pollination of the  carpel.

❥・ The complete series of this process  takes place in the zygote to develop  into a seed.