Question

Where does triple fusion take place in a flowering plant? Why is it so called? Mention its significance.

Answer 1

Triple fusion is the process of fusion of sperm nucleus and the two polar nuclei which occurs in double fertilization. This results in formation of endosperm.

Complete answer: Triple fusion is the process occurring in embryo sac in the flowering plants known as the angiosperms. It is called triple fusion due to the presence of 3 nuclei one from the sperm nuclei and two nuclei of polar nuclei. The fusion involves the two polar nuclei and a sperm nucleus that occurs in double fertilization leads to formation of endosperm.
It is of very great significance because the endosperm formed as a result is necessary for the development of an embryo.
Endosperm is the result of triple fusion and hence triploid in nature. It means the presence of 3 nuclei (3n).
It provides all the basic nourishment and the nutrients to the embryo.
n + 2n - 3n.
-n here refers to the male gamete.
-2n here refers to the female gamete (polar nuclei).
-3n is the result i.e. endosperm.

Functions of endosperm:
-Supporting embryo sac in its early stage for growth and development.
-Providing nutrition.
-Acting as the barrier during seed development and germination.
-Nourishment and stored food supply.

Note: Triple fusion takes place in the embryo sac. It is called triple fusion because the vegetative cell of matured male gamete fuses to the polar nuclei.
This results in the formation of PEN: Primary Endosperm Nucleus having ploidy level 3n.