Here are NEET/JEE-ready notes from the given passage, with the most important facts highlighted.

Gynoecium — Female Reproductive Part

• Gynoecium = female reproductive part of a flower.
• It may be:
  • Monocarpellary → one pistil
  • Multicarpellary → more than one pistil
• Multicarpellary pistils may be:
  • Syncarpous → carpels fused
  • Apocarpous → carpels free

Parts of a Pistil

Stigma → Style → Ovary

Part	Function
Stigma	Landing platform for pollen grains
Style	Slender elongated part below stigma
Ovary	Basal swollen part containing ovules

Inside the ovary:

• Ovarian cavity = Locule
• Placenta is present inside the locule.
• Ovules (megasporangia) arise from the placenta.

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Structure of Ovule

An ovule is attached to the placenta by a stalk called the funicle.

Important terms

Funicle → stalk attaching ovule to placenta
Hilum → junction between ovule and funicle
Integuments → protective coverings around nucellus
Micropyle → small opening in integuments
Chalaza → basal region opposite micropyle
Nucellus → mass of cells enclosed by integuments
Embryo sac → female gametophyte present inside nucellus

Simple arrangement

Micropyle → Nucellus + Embryo sac → Chalaza

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Megasporogenesis

Megasporogenesis = formation of megaspores from Megaspore Mother Cell (MMC).

Sequence

Megaspore Mother Cell (MMC)
↓ Meiosis
4 megaspores
↓
1 functional megaspore + 3 degenerate

In most angiosperms:

Only ONE megaspore remains functional.

The development of embryo sac from a single functional megaspore is called:

Monosporic development

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Ploidy — Very Important

Structure	Ploidy
Nucellus	2n
Megaspore Mother Cell (MMC)	2n
Megaspores	n
Functional megaspore	n
Embryo sac	n
Egg	n
Synergids	n
Antipodals	n
Polar nuclei	n + n

Why does MMC undergo meiosis?

Because:

2n MMC → meiosis → four n megaspores

Thus, meiosis reduces chromosome number from diploid (2n) to haploid (n).

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Formation of Embryo Sac

The functional megaspore undergoes three successive mitotic divisions.

Nuclear stages:

1 nucleus
↓ mitosis
2 nuclei
↓ mitosis
4 nuclei
↓ mitosis
8 nuclei

These divisions are free-nuclear divisions because:

Nuclear division occurs without immediate cell-wall formation.

After the 8-nucleate stage, cell walls are formed.

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Mature Embryo Sac

A typical angiosperm embryo sac is:

8-nucleate but 7-celled

This is one of the most important NEET facts.

Arrangement

Micropylar end:

• 2 Synergids
• 1 Egg

Together = Egg apparatus

Chalazal end:

• 3 Antipodals

Central cell:

• 2 Polar nuclei

Therefore:

3 cells + 3 cells + 1 central cell = 7 cells

But nuclei:

3 + 3 + 2 polar nuclei = 8 nuclei

Hence:

Embryo sac = 7-celled and 8-nucleate

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Egg Apparatus

The egg apparatus consists of:

2 Synergids + 1 Egg cell

Synergids have:

Filiform apparatus

Function:

Guides the pollen tube into the synergid.

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One-Line NEET Revision

Gynoecium → Pistil → Stigma + Style + Ovary

Ovary → Locule → Placenta → Ovules

Ovule → Funicle + Hilum + Integuments + Micropyle + Nucellus + Embryo sac

MMC (2n) → meiosis → 4 megaspores (n) → 1 functional megaspore → 3 mitotic divisions → 8 nuclei → 7-celled, 8-nucleate embryo sac

Embryo sac formula:

Micropylar: 2 Synergids + 1 Egg
Central: 2 Polar nuclei
Chalazal: 3 Antipodals

Total = 7 cells + 8 nuclei 🌟