This happens during the formation of the embryo sac inside the ovule.
The embryo sac is the female gametophyte of flowering plants. Step-by-step Process (Very Simple)
Step 1: Formation of Megaspore
- Inside the ovule, there is a Megaspore Mother Cell (MMC).
- MMC divides by meiosis.
- It forms 4 megaspores.
đ Out of 4 megaspores:
- 3 degenerate (die)
- Only 1 megaspore remains functional
Step 2: Functional Megaspore divides
The functional megaspore has 1 nucleus.
Now it divides by mitosis (normal division).
First mitotic division:
- 1 nucleus → 2 nuclei
Second mitotic division:
- 2 nuclei → 4 nuclei
Third mitotic division:
- 4 nuclei → 8 nuclei
✅ So finally, embryo sac has 8 nuclei.
Step 3: Arrangement of nuclei
These 8 nuclei move to different positions:
At Micropylar end (top):
- 3 nuclei form 3 cells:
- One egg cell
- Two synergids
➡️ Together called egg apparatus
At Chalazal end (bottom):
-
3 nuclei form 3 cells called:
-
Antipodal cells
In the centre:
- Remaining 2 nuclei stay in the middle.
- They are called polar nuclei.
These two polar nuclei join to form one central cell.
Final Structure: 7 Cells with 8 Nuclei
| Cells in embryo sac | Number |
|---|---|
| Egg cell | 1 |
| Synergids | 2 |
| Antipodal cells | 3 |
| Central cell | 1 |
| Total cells | 7 |
Nuclei Count
- Egg cell = 1 nucleus
- 2 synergids = 2 nuclei
- 3 antipodals = 3 nuclei
- Central cell = 2 polar nuclei
Total nuclei = 8 nuclei
Conclusion (Easy Line)
đ Embryo sac becomes 7-celled and 8-nucleate because:
- One megaspore divides 3 times
- Producing 8 nuclei
- Which arrange into 7 cells (central cell has 2 nuclei)







