Question

A flower of the tomato plant following the process of sexual reproduction produces 240 seeds. Answer the following question giving reasons. How many megaspore mother cells were involved?

Answer 1

Hint:As the megaspore mother cell undergoes meiosis, the cell walls are laid down transversely. So first a dyad is formed, and then a tetrad. The arrangement of these cells, due to the transverse cell wall, is linear.

Complete answer:
Each pollen grain in the tomato plant contains two male gametes. During sexual reproduction, these gametes fuse with (a) the polar nuclei to give rise to endosperm, and (b) with the egg cell to form a seed. Similarly, the number of ovules would also be 240, as each ovule would correspond to one seed.

In every ovule, a megaspore mother cell will undergo meiotic division to form a set of 4 cells known as a tetrad. Of these four cells, only one ultimately forms the seed. From each tetrad, one megaspore ultimately forms the female gametophyte which fuses with the male gamete to form the seed. Going backwards, each of these comes from one megaspore mother cell. There, to form 240 seeds, 240 megaspore mother cells are produced.

The remaining megaspore cells undergo degeneration via a process known as programmed cell death. The term megaspore and microspore is used to differentiate between the male and female spores which gave rise to male and female gametes in heterosporous plants.

Note:However, if the microspore cells are examined, one microspore mother cell gives rise to four microspore cells, all of which are functional. Therefore to obtain 240 microspore cells, only sixty microspore mother cells would be needed.