Question

In the development of the female gametophyte, the lower megaspore toward the centre of the nucellus remains functional. This functional megaspore undergoes successive mitotic divisions. This entire method of embryo sac development is called:

• A. Tetrasporic
• B. Monosporic
• C. Bisporic
• D. Diplosporic

Hint:

Key Exam Tip:
The term 'monosporic' indicates that the embryo sac develops from a single megaspore. Other types are bisporic (two megaspores) and tetrasporic (four megaspores). Diplospory is a related but distinct process where the megaspore mother cell directly forms a diploid embryo sac.

Answer 1

The Correct Option is B

The development of the female gametophyte (embryo sac) from a single functional megaspore is termed monosporic development. After meiosis of the megaspore mother cell (MMC), four haploid megaspores are formed. In monosporic development, typically three of these megaspores degenerate, while one, usually the one closest to the center of the nucellus, remains functional. This functional megaspore then undergoes three successive mitotic divisions to form the typical 8-nucleate, 7-celled embryo sac (e.g., Polygonum type). The description in the question perfectly matches this process. Let's briefly consider the other options: Tetrasporic: All four megaspores contribute to the embryo sac development. Bisporic: Two megaspores contribute to the embryo sac development. Diplosporic: The embryo sac develops directly from the megaspore mother cell (or other sporophytic cells) via a modified division process, often resulting in a diploid embryo sac, bypassing the formation of distinct, functional megaspores in the typical way. Since the question specifies that *one* megaspore remains functional and develops, it is monosporic development. Final Answer: \(\boxed{B}\)