Question

A flower of a tomato plant following the process of sexual reproduction produces 240 viable seeds. Answer the following questions giving reasons:
(i) What is the minimum number of pollen grains that must have been involved in the pollination of its pistil?
(ii) What would have been the minimum number of ovules present in the ovary?
(iii) How many megaspore mother cells were involved?
(iv) What is the minimum number of microspore mother cells involved in the above case?
(v) How many male gametes were involved in this case?

Answer 1

Hint: Double fertilization is a characteristic phenomenon feature that is exclusive to the angiosperms in the plant kingdom. The seed is fertilized ovule. Products of double fertilization are zygote and endosperm. The zygote develops in the embryo while the endosperm provides nutrition to the developing embryo.

Complete answer:
A microspore is defined as the spore produced by sporophytes which are haploid and give rise to a male gametophyte. The megaspore, on the other hand, develops into a haploid female gametophyte.
(i) What is the minimum number of pollen grains that must have been involved in the pollination of its pistil?
The minimum number of pollen grains that might be involved are 240, as 240 viable seeds are formed. This is because each pollen grain contains 2 male gametes, out of which one fuses with egg forming zygote that gives rise to seeds.
(ii) What would have been the minimum number of ovules present in the ovary?
The minimum number of ovules would also have been 240, as 240 viable seeds are formed. After fertilization, the ovule turns into seeds.
(iii) How many megaspore mother cells were involved?
240 megaspore mother cells were involved. They undergo meiotic division to form 4 haploid megaspores. Out of them, only 1 becomes a functional megaspore and the rest 3 degenerate.
(iv) What is the minimum number of microspore mother cells involved in the above case?
The minimum number of microspore mother cells in the above ease would be 60. This is because each microscope mother cell gives rise to 4 microspores. Thus, to obtain 240 microspores, 60 microspore mother cells are required.
(v) How many male gametes were involved in this case?
The number of male gametes involved would be 240. Each male gamete fuses with one egg nuclei to form a zygote that gives rise to seed.

Additional information:
Microspores and pollen grain are different structures. Initially, the diploid microspore mother cell divides by meiosis to form four haploid microspores which are arranged in tetrads. This structure is regarded as a young male gametophyte and called a pollen grain. Pollination takes place at this two-celled stage.

Note:
60 microspore mother cells are involved in providing 240 pollen grains. Because each microspore mother cell undergoes meiosis producing four pollen grains (i.e. 60 × 4 = 240). Each pollen grain produces two male gametes of which one undergoes true fertilization of ovule producing seeds. Other male gametes participate in double fertilization.