How does pollination lead to fertilisation | STUDENT BABA



After learning about how pollination is related to fertilisation and knowing there is no difference between them one question arises is that, how does pollination lead to fertilisation ? To understand how pollination leads to fertilisation we will have to first understand the structure of flower, structure of anther and structure of ovule. 


How does pollination lead to fertilisation ?

After the transfer of pollen grains from anther to stigma the pollen grains germinate on the stigma and further the pollen tubes carry the motile male gametes to the egg apparatus

After the male gametes have reached the egg apparatus, the male gametes are fused with the stationary female gametes and this process is called as syngamy which further forms a diploid zygoteHence, it is said that fertilization has taken place. 

The zygote formed then undergoes meiosis to form haploid spores which grow into haploid individuals. The zygote is like a beginning of new life and it ensures the continuity of species

The zygote does not just form haploid individuals but also helps in the development of embryo and this process is called as embryogenesis. During this process the zygote undergoes mitosis (cell division) and cell differentiationCell division increases the number of the cells and cell differentiation helps that group cell to undergo modifications which further forms the end product. 

Structure of flower:

Flowers are the main part for sexual reproduction in angiosperms. Angiosperms are also called as flowering plants. The flower plays an important role is sexual reproduction because of it's colour, fragrance, nectar, etc. which attracts birds for pollination. It can also be called as a modified shoot specialized for reproduction.

 Structure of flower

Structure of flower

The thalamus of the flower is a shoot with denser internodes (a space between two nodes) which floral whorls like leafs, petals, stamens and carpels are produced. The stamen and the carpel are the female and male reproductive parts.

Structure of anther:

The anther is dithecous which means it is having two compartments or cells, it has two anther-lobes and is fertile part of a stamen. The filament and the anther are connected to each other by sterile connective.

Structure of anther
Structure of anther

The anther wall is made up of Epidermis, Endothecium, Middle layers and Tapetum.

  • Epidermis - This is the outermost wall of anther which functions as a protective layer.
  • Endothecium - It is internal to epidermis and is common for the four pollen sacs. It consists of single layers of cells
  • Middle layers - The layers of parenchyma cells surrounding each pollen sac is are called middle layers. They are internal to endothecium
  • Tapetum - The tapetum is the innermost wall which surrounds the sporogenous tissues.  
After studying the structure of anther it is also important to know the structure of pollen grains.

Structure of pollen grains:

Pollen grains are used for pollination which is seen on the anther of the flower. Each pollen grain is single-celled (having one cell), consist of single nucleus and has circular or oval haploid structure

Pollen grains
Pollen grains

The outermost layer of the pollen grain is called the exine which is thick. The exine can be smooth or rough (spiny). The sporopollenin provides resistance to a pollen grain from decomposition by physically and biologically

 Development of male gametophyte
Development of male gametophyte

Structure of ovule:

The ovule is the tough outer layer microsporangium of the seed bearing plant. The anatropous ovule is the is the most common type of ovule is angiosperms. It's axis is directing downwards which has an opening micropyle.

Structure of an ovule
Structure of an ovule

The ovule contains of stalk and body. The stalk of an ovule attaches with the placenta also known as the fertile tissue of the ovary. It supplies nutrients to the ovule by a vascular strand. The stalk is called funicle or funiculus.

The body of the ovule consists of - Nucellus, Chalaza, Integuments, Micropyle and Embryo sac
  • Nucellus - The nucellus contains many diploid (two complete sets of chromosomes) parenchyma cells. It forms the bulky part of the ovule which is at the centre
  • Chalaza - The chalaza is a part from where the integuments are developed. It is the basal part of the ovule. The end of an ovule is usually known as the chalazal end
  • Integuments - The integuments protect the nucellus. It surrounds the whole nucellus except for the small portion which is at the end known as micropyle
  • Micropyle - The narrow end left by the integuments at is called as micropyle. The end of the nucellus is known as micropylar end
  • Embryo sac - The oval shape haploid (having a single set of unpaired chromosome) structure shown by the nucellus at the micropylar end is called embryo sac or female gametophyte. It contains 7 cells and 8 nuclei

What are the end products after fertilisation ?

After fertilisation, the plant then starts to form a fruit or a seed.

Conclusion:

Who might have thought, the fruits or vegetables we eat go through this huge process and how the flower, the anther, the ovule and pollen grains play an immense role in this process. Pollen grains are like the hero which helps in carrying the male gametes and fusing it with the female gametes. 

The flower attracts the birds, the anther produce pollen grains which the birds carry, the pollen grains form into zygote and then haploid individuals also into embryo and the ovule without which this whole process won't even make sense. 

F.A.Q:

1. Which is the male reproductive floral whorl called ?
Ans: Androecium is the male reproductive floral whorl.

2. Which is the female reproductive floral whorl called ?
Ans: Gynoecium is the female reproductive floral whorl

3. What are the process of sexual reproduction in angiosperms ?
Ans: Formation of pollen grains (microsporogenesis), formation of megaspores (megasporogenesis), development of male and female gametophytes, pollination and fertilisation.

4. Where does formation of microspores take place ? 
Ans: Formation of microspores takes place in the pollen sacs of the anther. 

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