Question

Tetrad of megaspore is generally
A) Tetrahedral
B) Linear
C) Decussate
D) Isobilateral

Answer 1

Hint: The megaspores are mostly seen in the gymnosperms and land plants. Megaspores are the large spores which germinate into female gametophyte also known as female spores and produce egg cells. The megaspores are formed as a result of meiosis of megasporocyte nucleus. This results in four haploid megaspores.

Complete answer:
The megaspores are found in the gymnosperms and flowering plants. The megaspores are produced inside the nucellus of the ovule. The megaspores are produced by the process of megasporogenesis. During this process, the precursor cells which are diploid in nature undergo meiosis to produce four haploid cells. These cells or the megaspores arrange themselves in the linear fashion to form tetrad.

The first meiotic division results in the formation of a dyad. The two dyads arrange themselves forming a linear tetrad. Out of the 4 megaspores, three degenerate and only one is functional and can take part in the reproductive process. The functional megaspore enlarges and forms eggs.

The tetrads which are tetrahedral, decussate or isobilateral are formed as a result of microsporogenesis. The microspores are the spores which form the male gametophyte. This male gametophyte is used for the fertilisation of the egg to form a zygote. These are formed from the mother cells inside the anther.

Thus, the correct answer is option (B), Tetrad of megaspore is generally linear.

Note: The megaspores develop into female gametophyte whereas the microspores develop into sperm cells. The megaspores are larger in size as compared to microspores. This condition is known as heterospory. The megaspores have a giant vacuole.