How does an ovule become 7-celled with 8 nuclei?

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.

👉 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:

1. One egg cell
2. 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

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Conclusion (Easy Line)

👉 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)