What do you mean by double fertilization (2 marks)

In angiosperms, fertilization results in two structures namely zygote and endosperm; thus fertilization is known as double fertilization. By definition, double fertilization is a complex fertilization method where out of two sperm cells, one fuse with the egg cell and other fuses with two polar nuclei which results in diploid (2n) zygote and triploid (3n) primary endosperm nucleus (PEN) respectively. Since endosperm is a product of fusion of three haploid nuclei, it is called as triple fusion. Eventually, the primary endosperm nucleus develops into primary endosperm cell (PEC) and then into endosperm. Zygote becomes an embryo after numerous cell divisions.