Question

Write two significance of double fertilization.

Answer 1

Hint:Double fertilization is an exclusive feature of flowering plants. It involves the fusion of one male gamete with the egg to form a zygote (syngamy) and another male gamete with two polar nuclei to form endosperm (triple fusion).

Complete answer:
Two significance of double fertilization are:
-The most important significance of double fertilization is energy conservation. The energy is stored inside the endosperm formed by the fusion of the two polar nuclei and sperm. It stores the nutrients for the growth of the embryo.
-Double fertilization also stimulates the plant to convert the ovary into fruit and ovules into the seed along with the degeneration of other floral parts.

Additional Information:
->Process of double fertilization: It begins when a pollen grain adheres to the stigma of the carpel, the female reproductive structure of a flower. The pollen grain then begins to germinate, forming a pollen tube that extends down toward the ovary through the style. The tip of the pollen tube carrying the male gametes (sperm) then penetrates through the micropyle opening in the ovule present inside the ovary. The two sperms are then released in the megagametophyte.

->There are eight cells present in an unfertilized ovule arranged in the form of 3+2+3. They are (from top to bottom) 3 antipodal cells, 2 polar central cells, 2 synergids & 1 egg cell. Out of two male gametes, one sperm fertilizes the egg cell and the other sperm combines with the two polar nuclei of the large central cell of the megagametophyte. This process of fertilization of a haploid sperm and haploid egg to form a zygote is called syngamy, while the other sperm and the two haploid polar nuclei of the large central cell of the megagametophyte form a megagametophyte triploid nucleus or the PEN (Primary Endosperm Nucleus). This is known as triple fusion.

Note:Exceptionally, Double fertilization also occurs in the sexual reproduction of an order of gymnosperms commonly known as Gnetales. It includes Ephedra and Gnetum.
-Double fertilization increases the viability of the seeds.
-PEN gradually develops into the endosperm.