Question

Name the two end products of double fertilization in angiosperms. How are they formed? Write their fate during the development of seed.

Answer 1

Hint: The process of sexual reproduction in angiosperms occur through production of male and female gametes. The male gametes are transferred to the female part of the flower through pollination. A unique feature of fertilization in angiosperms is that it occurs twice in the ovary and is known as double fertilization.

Complete answer:
Double fertilization is the phenomenon where the female gametophyte fertilizes with two male gametes. It exclusively occurs in flowering plants.
The microspore mother cell in the anther divides twice to form four pollen grains. Each mature pollen grain has two cells – a generative cell and a pollen tube cell. The tube cell grows into the style and reaches the ovary. Just before its entry into the ovary, the generative cell divides to form to male gametes. The male gametes are haploid cells. The female gametes are formed within the megasporangium. The female gamete or the megagametophyte is a seven celled structure, but with eight nuclei. The megagametophyte is also known as the embryo sac. It has got a minute opening called the micropyle through which the pollen tube enters. The micropylar end of the embryo sac has three cells – the egg cell in the middle and two synergids on the sides. The end opposite to the micropylar end is known as the chalazal end and has three antipodal cells. In the centre of the sac, a diploid cell is present. Once the pollen tube enters through the micropyle, the microspores are inserted into the embryo sac. Out of the two sperm cells, one fuses with the central diploid cell resulting in a triploid cell and the other sperm cell fuses with the egg cell forming a diploid zygote. Therefore, the end products of double fertilization are the triploid endosperm nucleus and a diploid zygote. The triploid cell forms the endosperm and the diploid zygote develops into the embryo. The endosperm functions to provide the embryo with nutrition, while the zygote develops into the embryo or an immature plant.

Note: The fertilization in angiosperms occurs twice in the embryo sac and is known as double fertilization. It is a means of sexual reproduction in angiosperms. The resulting embryo develops into a miniature plant capable of growth and development into a viable plant. Gymnosperms do not undergo double fertilization.