Question

Identify the correct statement.

• A. Only one megaspore present towards chalazal end remains functional.
• B. 3 megaspore present towards chalazal end degenerate gradually.
• C. Each megaspore mother cell, directly develops into a megaspore.
• D. Each female gameophyte is 7-celled & 7-nucleated structure.

Answer 1

The Correct Option is A

Let's analyze each statement regarding megasporogenesis and female gametophyte development in angiosperms:

"Only one megaspore present towards chalazal end remains functional."

• During megasporogenesis, the diploid megaspore mother cell (MMC) undergoes meiosis to produce four haploid megaspores, usually arranged in a linear tetrad.
• In the most common type of embryo sac development (Polygonum type), three of these megaspores, typically those towards the micropylar end, degenerate.
• The single megaspore located at the chalazal end remains functional and develops into the female gametophyte (embryo sac).
• This statement is correct.

"3 megaspore present towards chalazal end degenerate gradually." 

• As explained above, usually only one megaspore is present at the chalazal end, and it is the functional one. The three megaspores that degenerate are typically located towards the micropylar end.
• This statement is incorrect.

"Each megaspore mother cell, directly develops into a megaspore."

• The megaspore mother cell (MMC) is diploid (\(2n\)). It undergoes meiosis (a reductional division) to produce four haploid (\(n\)) megaspores.
• It does not directly develop into a single megaspore; it divides to form four.
• This statement is incorrect.

"Each female gametophyte is 7-celled & 7-nucleated structure."

• The typical mature female gametophyte (embryo sac) in angiosperms develops from the functional megaspore through mitotic divisions.
• It consists of an egg apparatus (one egg cell and two synergids) at the micropylar end, three antipodal cells at the chalazal end, and a large central cell containing two polar nuclei.
• Counting the cells: 1 egg + 2 synergids + 3 antipodals + 1 central cell = 7 cells.
• Counting the nuclei: 1 (egg) + 2 (synergids) + 3 (antipodals) + 2 (polar nuclei in central cell) = 8 nuclei.
• Therefore, the typical structure is 7-celled and 8-nucleated.
• This statement is incorrect.

The only correct statement among the given options is: Only one megaspore present towards chalazal end remains functional.

Answer 2

In a typical angiosperm ovule, a single megaspore mother cell (MMC) undergoes meiosis to produce four megaspores arranged in a linear tetrad.
Out of these four, only the megaspore towards the chalazal end remains functional, while the other three degenerate.
This functional megaspore develops into the female gametophyte (embryo sac), which is typically a 7-celled and 8-nucleated structure — not 7-nucleated.

Therefore, the correct statement is: (A) Only one megaspore present towards chalazal end remains functional.