CBSE Class 10 Answered

Double fertilisation is a characteristic of angiosperms. Here two sperm nuclei from each pollen tube fertilise two cells in an ovary. One sperm fertilizes the egg cell, forming a diploid (2n) zygote from which the embryo develops.  This fusion is called syngamy or fertilization.

The other sperm cell fuses with two haploid polar nuclei (contained in the central cell) of the megagametophyte. The resulting cell is triploid (3n). This fusion is called triple fusion because three nuclei takes part in this fusion. This triploid cell divides through mitosis and forms the endosperm, a nutrient-rich tissue, inside the seed.  The ovary, surrounding the ovules, develops into the fruit, which protects the seeds and may function to disperse them.