How does one megaspore become 8 nuclei but only 7 cells in the embryo sac? I keep losing marks counting
Vivek Mishra12th Sample
15 Sept 2026 · 1 min read
I study from NCERT and a few free videos, so I want to be sure of the basic logic. Megasporogenesis is giving me trouble.
What I know: ovule has nucellus, integuments, micropyle, funicle, chalaza. One cell in the nucellus near the micropyle becomes the megaspore mother cell (MMC), it is diploid. It does meiosis and gives four megaspores. Then in most flowering plants only one megaspore stays functional and the other three degenerate. The functional one makes the embryo sac.
Here is where I get confused. The book says the embryo sac finally has 8 nuclei but 7 cells. In a practice paper there was "how many mitotic divisions are needed to form the mature embryo sac from the functional megaspore" and I wrote 2, because I thought 2 divisions gives 4 and then 4 cells... then I realised 8 nuclei needs more. I don't understand how 8 nuclei turns into 7 cells, one cell is losing something?
Also, which end has the egg and which end has antipodals? And which of these cells are haploid? I think all, but I am not sure about the central cell. Please explain simply, my English is okay but simple words are better 🙏
8 answers & replies
Sign in to join the conversation.
[+][–]Tanvi Deshmukh12thSample· 1mo ago
Count it step by step!! 📝 Functional megaspore = 1 nucleus (n). Mitosis 1 → 2 nuclei (they go to opposite poles). Mitosis 2 → 4 nuclei (2 at each pole). Mitosis 3 → 8 nuclei (4 at each pole). So three mitotic divisions, and no more meiosis, the only meiosis was in the MMC. After that, cell walls form around 6 of the 8 nuclei and make 6 cells. The other 2 nuclei (one from each pole) move to the centre. That is why you wrote 2 and lost the mark, the answer is 3 mitoses from the megaspore.
[+][–]Vivek Mishra12thSample· 1mo agoAuthor
Thank you tanvi di, now it is very clear. 3 mitoses, not 2. I will redraw the diagram tonight.
[+][–]Pooja Iyer12thSample· 1mo ago
Layout of the embryo sac (this is the diagram you will be asked to label):
- Micropylar end: egg apparatus = 1 egg cell + 2 synergids. The synergids have a filiform apparatus (thickenings) that guide the pollen tube into the synergid.
- Chalazal end: 3 antipodal cells.
- Centre: one big central cell with 2 polar nuclei.
My silly trick: Egg at the Entrance (micropyle = the entry for the pollen tube). Antipodals are far away at the back, "anti" = opposite.
[+][–]Zoya Khan12thSample· 1mo ago
To answer "how 8 nuclei becomes 7 cells": it is because the two polar nuclei do not get their own cell walls. Both of them sit together in one large central cell. So you count cells like this: 3 (egg apparatus) + 3 (antipodals) + 1 (central cell) = 7 cells. And nuclei: 1 + 2 + 3 + 2 = 8, because the central cell has two. Nothing is lost, it is just that two nuclei share one cell.
About ploidy, all 8 nuclei came by mitosis from one haploid nucleus, so they are all haploid. The central cell is haploid too in the sense that each polar nucleus is n, but it will become triploid after it fuses with one male gamete, and that is a later chapter topic.
[+][–]Riya Singh12thSample· 1mo ago
the 8 nuclei → 7 cells thing took me a while too. I remember it as "8 nuclei, 6 corner cells, 1 middle cell with a double nucleus". 6 + 1 = 7. And I'd say the embryo sac has 8 cells because 3 mitoses → 2, 4, 8 cells, so the mature sac is 8-celled? Is that how the number comes?
[+][–]Rahul DubeyDropperSample· 1mo ago
Riya, careful. 2, 4, 8 is correct for nuclei in the sac, not cells. At the 8-nucleate stage the sac is one big cell with free nuclei, and only afterwards walls form around six of them. So "8-celled" is wrong, it is 7-celled, 8-nucleate. NCERT says exactly this and it is a popular NEET line.
Also for Vivek's other question: the MMC is 2n, the four megaspores are n, only one functional megaspore survives (monosporic development), and the embryo sac is the female gametophyte.
[+][–]Aarav Kulkarni11thSample· 1mo ago
I'm in class 11 so sorry if this is a dumb question, but why do three megaspores degenerate? Isn't it wasteful to make four and keep one?
[+][–]Zoya Khan12thSample· 1mo ago
Not dumb at all. Meiosis always gives four haploid products from one cell, there is no way around that. In the female side, the plant just uses one of them and the resources of the nucellus go to that one, so the embryo sac gets lots of nutrition. The other three are the leftover from the division, same idea as the polar bodies in human oogenesis, where only one egg is kept.
