Question

A flower of brinjal plant following the process of sexual reproduction produces 360 viable seeds.

Answer the following questions, giving reasons:

1. How many ovules are minimally involved?
2. How many megaspore mother cells are involved?
3. What is the minimum number of pollen grains that must land on the stigma for pollination?
4. How many male gametes are involved in the above case?
5. How many microspore mother cells must have undergone reduction division prior to dehiscence of the anther in the above case?

Answer 1

The number of viable seeds produced by the brinjal plant through sexual reproduction = 360

(a) The number of ovules minimally involved in this process would be 360, as the number of viable seeds is 360. After fertilisation, the ovary turns into fruit and the ovules turn into seeds. Therefore, the number of ovules corresponds to the number of seeds formed.

(b) During the process of gametogenesis, 360 megaspore mother cells are involved, as only one megaspore of the tetrad becomes functional and develops further and the other three megaspores get degenerated.

(c) The minimum number of pollen grains that must land on the stigma for pollination is 360 because each pollen grain contains two male gametes. Out of these two gametes, one fuses with polar nuclei and forms endosperm, while the other male gamete fuses with the egg cell to form the zygote that eventually gives rise to seeds. Therefore, in order to obtain 360 seeds, the number of pollen grains needed would be 360.

(d) Each pollen grain releases two male gametes in an embryo sac. One male gamete fuses with the egg to form a zygote, and another male gamete fuses with polar nuclei to form an endosperm nucleus. Hence, the number of male gametes involved is 360 × 2 = 720.

(e) In the above case, 90 microspore mother cells must have undergone reduction division prior to dehiscence of the anther, as each microspore mother cell would give rise to 4 microspores. Since 1 microspore mother cell would produce 4 microspores, therefore, to obtain 360 microspores, there must be 90 microspore mother cells.