Question

At maturity, a typical angiosperm embryo sac is:

• A. 6-nucleate and 8-celled
• B. 7-nucleate and 7-celled
• C. 7-nucleate and 8-celled
• D. 8-nucleate and 7-celled

Hint:

Mature Embryo Sac (Polygonum type):
$\bullet$ 7 Cells: 3 antipodals + 1 central cell + 2 synergids + 1 egg cell.
$\bullet$ 8 Nuclei: 3 in antipodals + 2 polar nuclei in central cell + 3 in egg apparatus.
Structure = 8-nucleate, 7-celled.

Answer 1

The Correct Option is D

Concept:
In angiosperms, monosporic female gametophyte development (Polygonum type) involves three consecutive mitotic nuclear divisions of the functional megaspore, followed by cellular organization into an embryo sac.

Step 1: Cellular and Nuclear Organization of Mature Embryo Sac:
The functional megaspore undergoes three free-nuclear mitotic divisions, producing 8 nuclei.
Subsequent cytokinesis and cell wall formation result in the following organization:
1. Egg Apparatus (Micropylar end): Composed of 3 cells---one central egg cell and two flanking synergids (total = 3 cells, 3 nuclei).
2. Antipodal Cells (Chalazal end): Composed of 3 distinct cells that degenerate after fertilization (total = 3 cells, 3 nuclei).
3. Central Cell: A large single cell located in the middle containing two free polar nuclei (total = 1 cell, 2 nuclei).

Step 2: Counting Nuclei and Cells:
- Total number of cells = $3 \text{ (egg apparatus)} + 3 \text{ (antipodals)} + 1 \text{ (central cell)} = 7\text{ cells}$.
- Total number of nuclei = $3 \text{ (egg apparatus)} + 3 \text{ (antipodals)} + 2 \text{ (polar nuclei)} = 8\text{ nuclei}$.
Therefore, a typical mature female gametophyte (embryo sac) is 8-nucleate and 7-celled.

Step 3: Final Answer:
Hence, the correct option is (D).