Question

Fertilization of angiosperms involves a mechanism so-called 'double fertilization'. Explain this process using the following key words:

Egg cell, pollen tube, sperm cell(s), central cell, endosperm, embryo

Answer 1

Double fertilization in Angiosperms

Double fertilization is a major characteristic of flowering plants (Angiosperms). In this process, two male gametes fuse with one female gamete wherein one male gamete fertilizes the egg to form a zygote, whereas the other fuses with two polar nuclei to form an endosperm.Double fertilization gives stimulus to the plant that results in the development of the ovary into fruit and ovules into seed. The fusion of haploid male and female gametes restores the diploid condition of the plant.

Angiosperms are flower-bearing plants and are the most diverse group of terrestrial plants. The flowers form the reproductive part of angiosperms with separate male and female reproductive organs. Each contains gametes – sperm and egg cells respectively.

Pollination helps the pollen grains to reach stigma via style. The two sperm cells enter the ovule-synergid cell. This proceeds to fertilization.

In angiosperms, fertilization results in two structures, namely, zygote and endosperm, hence named, double fertilization.

Double fertilization is a complex process where out of two sperm cells, one fuses with the egg cell and the other fuses with two polar nuclei which result in a diploid (2n) zygote and a triploid (3n) primary endosperm nucleus (PEN) respectively.

Since endosperm is a product of the fusion of three haploid nuclei, it is called triple fusion. Eventually, the primary endosperm nucleus develops into the primary endosperm cell (PEC) and then into the endosperm.

The zygote becomes an embryo after numerous cell divisions.