Module: | Pre-fertilization: Micro/Megasporogenesis
Q6: Consider the following statements regarding the nucleate stage and cell distribution of the embryo sac:
1. A typical mature angiosperm embryo sac is mathematically defined as 8-nucleate and 7-celled.
2. Three cells are grouped together at the micropylar end to constitute the egg apparatus.
3. The large central cell contains three polar nuclei which later fuse to form a triploid structure prior to fertilization.
Which of the above statements is/are correct?
2. Three cells are grouped together at the micropylar end to constitute the egg apparatus.
3. The large central cell contains three polar nuclei which later fuse to form a triploid structure prior to fertilization.
Which of the above statements is/are correct?
✅ Correct Answer: A
The correct option is A. Statements 1 and 2 are correct, while Statement 3 is strictly incorrect.
A mature female gametophyte (embryo sac) undergoes three sequential free-nuclear mitotic divisions to produce an 8-nucleate structure.
Structurally, cell wall formation follows, organizing these nuclei into seven distinct cells.
At the micropylar end, three cells form the egg apparatus (two synergids and one egg cell). At the chalazal end, three cells form the antipodals.
The remaining large central cell contains only two polar nuclei, not three.
The causal reasoning for this specific cellular architecture is the preparation for double fertilization: the egg cell awaits syngamy with one male gamete, while the two polar nuclei await fusion with the second male gamete to form the primary endosperm nucleus (PEN). Misidentifying the central cell as having three polar nuclei is a common distracter in historical exam patterns.
A mature female gametophyte (embryo sac) undergoes three sequential free-nuclear mitotic divisions to produce an 8-nucleate structure.
Structurally, cell wall formation follows, organizing these nuclei into seven distinct cells.
At the micropylar end, three cells form the egg apparatus (two synergids and one egg cell). At the chalazal end, three cells form the antipodals.
The remaining large central cell contains only two polar nuclei, not three.
The causal reasoning for this specific cellular architecture is the preparation for double fertilization: the egg cell awaits syngamy with one male gamete, while the two polar nuclei await fusion with the second male gamete to form the primary endosperm nucleus (PEN). Misidentifying the central cell as having three polar nuclei is a common distracter in historical exam patterns.