Sexual Reproduction in Flowering Plants — BIOLOGY STD 12 Science — Question

• On reaching synergid, pollen tube releases the two male gametes into cytoplasm of synergid.
• One of the male gamete fuses with egg nucleus to form a diploid cell called zygote. This event is called syngamy.
• Other male gamete fuses with polar nuclei at the centre to produce a triploid primary endosperm nucleus (PEN). This is termed as triple fusion. As syngamy and triple fusion take place simultaneously in the embryo sac, it is termed as double fertilisation.
• The central cell after triple fusion forms primary endosperm cell (PEC) which later develops into endosperm.
• The zygote later develops into an embryo.

Following are the post-fertilisation events:

1. Development of embryo: Embryo develops in fertilised ovule, from the zygote. The early stages of embryo development from a zygote is known as embryogeny. The formation of embryo starts only after certain amount of endosperm formation to assure the nutrition supply, for development and growth of embryo.
2. Development of seeds: Refer to Basic Concepts Point 10 (Embryogeny in Dicots). As a result of double fertilisation number of changes takes place in an ovule due to which ovule is converted into seeds.