Question

[A] The given figure shows the L.S. of an ovary at the time of fertilisation. Study the figure and answer the questions based on it.

(i) Label parts 1-10.
(ii) Define triple fusion.
(iii)What happens to part 6 and 7?
[B]
(i) What are the disadvantages of self-pollination?
(ii) Why is the fertilisation process in Angiosperms known as double fertilization?

Answer 1

(i) 1: Pollen grains; 2: Stigma; 3: Style; 4: Pollen tube; 5: Male gametes; 6: Egg cell; 7: Polar nuclei; 8: Antipodals; 9: Embryo sac; 10: Synergids
(ii) The fusion of one male gamete and two polar nuclei is called triple fusion.
(iii)Part 6 changes into the zygote and later into an embryo. Part 7 changes into an endosperm nucleus and later into an endosperm.
[B]
(i) Disadvantages of self-pollination:
i. Continued self pollination, generation after generation, may lead to the weakening of the variety or the species.
ii. The weaker or defective characters of the variety or breed cannot be eliminated. iii. It does not yield new varieties.
(ii) In angiosperms, the process of fertilisation occurs twice. Firstly, one male nucleus (sperm nucleus) fuses with the polar nuclei to form the endosperm. Secondly, the other male nucleus fuses with the egg nucleus to form an embryo. This is why, it is called double fertilisation.