Question

A typical angiosperm embryo sac has _________.

• A. Seven nuclei and eight cells
• B. Eight nuclei and eight cells
• C. Seven nuclei and seven cells
• D. Eight nuclei and seven cells

Hint:

Standard Polygonum Embryo Sac:
$\text{Structure} = \mathbf{7\text{ Cells, } 8\text{ Nuclei}}$.
Egg apparatus (3 cells, 3 nuclei) + Antipodals (3 cells, 3 nuclei) + Central cell (1 cell, 2 nuclei).

Answer 1

The Correct Option is D

Concept:
The female gametophyte of flowering plants (angiosperms) is enclosed inside the nucellus of the ovule and is known as the embryo sac.
In the vast majority of angiosperms, it follows the Polygonum-type monosporic development, originating from a single functional megaspore.
The developmental sequence involves free-nuclear mitotic divisions followed by precise cellular organization.

Step 1: Nuclear Divisions During Megagametogenesis:
A single functional haploid megaspore undergoes three consecutive rounds of free-nuclear mitotic divisions.
1. The first mitosis produces 2 nuclei.
2. The second mitosis produces 4 nuclei.
3. The third mitosis produces 8 nuclei.
At this stage, the embryo sac is an 8-nucleate structure before cell wall formation begins.

Step 2: Cellular Compartmentalization and Spatial Distribution:
The 8 nuclei are distributed and walled off into distinct cells:
- Micropylar end (3 cells): 1 central Egg cell flanked by 2 Synergids (collectively forming the egg apparatus).
- Chalazal end (3 cells): 3 Antipodal cells.
- Central region (1 cell): The remaining 2 nuclei migrate to the large Central Cell and remain together as polar nuclei.

Step 3: Calculating Total Cells and Nuclei:
Summing the individual compartments gives:
- Total cells $= 3 \text{ (egg apparatus)} + 3 \text{ (antipodals)} + 1 \text{ (central cell)} = 7\text{ cells}$.
- Total nuclei $= 3 + 3 + 2 \text{ (polar nuclei in central cell)} = 8\text{ nuclei}$.
Thus, a mature embryo sac is characteristically 7-celled and 8-nucleate.

Step 4: Final Answer:
Therefore, a typical angiosperm embryo sac has eight nuclei and seven cells, matching option (D).