Embryo Sac Development — Meiosis Plus Three Free-Nuclear Mitoses to 8-Nucleate
✅ Asked in NEET 2025How many meiotic and mitotic divisions need to occur for the development of a mature female gametophyte from the megaspore mother cell in an angiosperm plant?
How many meiotic and mitotic divisions need to occur for the development of a mature female gametophyte from the megaspore mother cell in an angiosperm plant?
In angiosperms, the correct sequence of events leading to the formation of female gametophyte in the ovule is: (NEET 2023) A. 3 successive free nuclear divisions in functional megaspore. B. Degeneration of 3 megaspores. C. Meiotic division in megaspore mother cell. D. Migration of 3 nuclei towards each pole. E. Formation of a wall resulting in seven-celled embryo sac.
Answer & NCERT explanation
Correct answer: A — 1 Meiosis and 3 Mitosis
Megaspore mother cell undergoes 1 meiotic division producing 4 megaspores. One functional megaspore survives while 3 degenerate. The functional megaspore then undergoes 3 successive mitotic divisions to form the 8-nucleate embryo sac. This is the standard pattern in angiosperm female gametophyte development.
Read more NCERT concept on the PYQ
Let us study about the formation of the embryo sac in detail.. The nucleus of the functional megaspore divides mitotically to form two nuclei which move to the opposite poles, forming the 2-nucleate embryo sac. Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. It is of interest to note that these mitotic divisions are strictly free nuclear, that is, nuclear divisions are not followed immediately by cell wall formation. After the 8-nucleate stage, cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac. Observe the distribution of cells inside the embryo sac. Six of the eight nuclei are surrounded by cell walls and organised into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell.
Female gametophyte (embryo sac) development in angiosperms begins with the megaspore mother cell (MMC) undergoing ONE MEIOTIC division to produce 4 megaspores. Three megaspores DEGENERATE; only ONE FUNCTIONAL megaspore survives. The functional megaspore then undergoes THREE successive MITOTIC divisions: first mitosis gives the 2-nucleate stage; second mitosis gives the 4-nucleate stage; third mitosis gives the 8-NUCLEATE stage. These mitotic divisions are strictly FREE NUCLEAR — nuclei divide without immediate cell wall formation. After the 8-nucleate stage, cell walls are laid down to organise the typical 7-CELLED embryo sac: six nuclei become walled cells (3 antipodals + 2 synergids + 1 egg = egg apparatus), and the remaining two POLAR NUCLEI sit in the large central cell.
NEET 2025 asked: 'How many meiotic and mitotic divisions for a mature female gametophyte from MMC?' Answer: 1 meiosis + 3 mitoses. NEET 2023 tested the SEQUENCE: meiosis → 3 megaspores degenerate → 3 mitoses → nuclear migration to poles → wall formation → 7-celled sac. The '8-nucleate but 7-celled' paradox: 8 nuclei initially, but 2 polar nuclei share ONE central cell, so 6 walled cells + 1 central = 7 total.
The embryo sac forms from the megaspore mother cell through 2 meioses and 3 mitoses producing an 8-nucleate, 8-celled structure.
1 MEIOSIS in MMC + 3 MITOSES in the functional megaspore → 8 NUCLEI in 7 CELLS (2 polar nuclei share the large central cell).
1 meiosis (MMC) + 3 mitoses (functional megaspore) = 8 nuclei in 7 cells. Egg apparatus = 1 egg + 2 synergids.
- MMC (2n) → 1 meiosis → 4 megaspores; 3 degenerate, 1 functional.
- Functional megaspore → 3 successive mitoses → 2-nucleate → 4-nucleate → 8-nucleate.
- Mitotic divisions are strictly FREE NUCLEAR — no cell walls form until after the 8-nucleate stage.
- Mature embryo sac: 7 cells, 8 nuclei | 3 antipodals + 2 synergids + 1 egg + 1 central cell (with 2 polar nuclei).
Consider the following statements about embryo sac (female gametophyte) development in angiosperms: S1: The megaspore mother cell undergoes one meiotic division to produce 4 megaspores. S2: All four megaspores survive and contribute to the mature embryo sac. S3: The functional megaspore undergoes three successive mitotic divisions to produce an 8-nucleate stage. S4: The mitotic divisions in embryo sac formation are strictly free nuclear (no cell wall after each division). S5: The mature embryo sac is 8-nucleate but only 7-celled because two polar nuclei share the large central cell.
View bonus solution & explanation
Correct answer: B — S1, S3, S4 and S5
S1 CORRECT: MMC → 1 meiosis → 4 megaspores. S2 WRONG: 3 megaspores DEGENERATE; only ONE survives as functional megaspore. S3 CORRECT: 3 successive mitoses → 2-nucleate → 4-nucleate → 8-nucleate (NEET 2025 answer: 1 meiosis + 3 mitoses). S4 CORRECT: Free nuclear divisions — cell walls only form after the 8-nucleate stage. S5 CORRECT: 8 nuclei but 7 cells (the 2 polar nuclei share the single large central cell).
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