With the help of a neat labelled diagram, explain, how does fertilization take place in flowering plants.

Explanation

The mature pollen grain contain two cells, the vegetative and the generative cell. The vegetative cell contains a large nucleus. The generative cell divides mitotically and form two male gametes. Pollen grains reach the stigma and begin to germinate. Pollen grain forms a small tube like structure called pollen tube, which emerges through the germ pore. The contents of the pollengrain move into the tube. Pollen tube grows through the tissues of the stigma and style and finally reaches the ovule through the micropyle. The vegetative cell degenerates and the generative cell divides to form two sperms or male gametes. Tip of pollen tube bursts and the two sperms enter the embryo sac. One sperm fuses with the egg and this process is called Syngamy and forms a diploid zygote. The other sperm fuses with the secondary nucleus, which is called the Triple fusion, to form the primary endosperm nucleus, which is triploid in nature.
Since two types of fusion syngamy and triple fusion take place in an embryo sac, the process is termed as double fertilization. After triple fusion, primary endosperm nucleus develops into an endosperm, which provides food to the developing embryo. Later the synergids and antipodal cells degenerate.