Facts about Gynoecium, Ovule and Embryo Sac

Gynoecium

1. Gynoecium is the female reproductive part of a flower.
2. It may consist of:
   • One pistil → Monocarpellary
   • More than one pistil → Multicarpellary
3. Multicarpellary pistils may be:
   • Fused together → Syncarpous
   • Free from each other → Apocarpous
4. Each pistil has three parts:
   • Stigma – receives pollen grains
   • Style – slender stalk below stigma
   • Ovary – swollen basal part
5. Inside the ovary is the ovarian cavity (locule).
6. Placenta is present inside the ovary and bears ovules.

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Ovule (Megasporangium)

7. Ovules arise from the placenta.
8. Ovules are also called megasporangia.
9. Number of ovules may vary:
   • One ovule → wheat, paddy, mango
   • Many ovules → papaya, watermelon, orchids
10. Ovule is attached to placenta by a stalk called funicle.
11. The point where funicle joins ovule is called hilum.
12. Ovule has one or two protective layers called integuments.
13. Integuments leave a small opening called micropyle.
14. The opposite end of micropyle is called chalaza.
15. The central tissue inside ovule is called nucellus.
16. Nucellus stores reserve food material.
17. Female gametophyte or embryo sac is present inside nucellus.
18. Usually one embryo sac develops from one megaspore.

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Megasporogenesis

19. Formation of megaspores from megaspore mother cell is called megasporogenesis.
20. Megaspore mother cell undergoes meiosis to form megaspores.
21. Usually four megaspores are produced.
22. Generally only one megaspore remains functional.

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Embryo Sac Development

23. Functional megaspore develops into embryo sac.
24. Nucleus divides mitotically to form:

• 2-nucleate stage
• 4-nucleate stage
• 8-nucleate stage

25. Initial nuclear divisions are free nuclear divisions (without cell wall formation).
26. Later cell walls form and organise the embryo sac.
27. Typical angiosperm embryo sac is:

• 8-nucleate
• 7-celled

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Structure of Embryo Sac

28. Three cells at micropylar end form the egg apparatus.
29. Egg apparatus consists of:

• One egg cell
• Two synergids

30. Synergids possess filiform apparatus.
31. Filiform apparatus helps guide pollen tube.
32. Three cells at chalazal end are called antipodals.
33. Central cell contains two polar nuclei.
34. Polar nuclei later participate in double fertilisation.

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Important Terms

35. Micropyle → opening for pollen tube entry
36. Chalaza → basal region of ovule
37. Hilum → junction of ovule and funicle
38. Funicle → stalk attaching ovule to placenta
39. Nucellus → nutritive tissue of ovule
40. Embryo sac → female gametophyte of angiosperms

Important Structures from “The Pistil, Megasporangium (Ovule) and Embryo Sac”

(Class 12 Biology – CBSE Boards)

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1. Structure of Pistil (Most Basic Diagram)

Important Labels

• Stigma
• Style
• Ovary
• Ovule

Important Terms

• Monocarpellary
• Multicarpellary
• Syncarpous
• Apocarpous

Board Questions

• Draw labelled diagram of pistil.
• Differentiate syncarpous and apocarpous.

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2. Structure of Ovule (VERY IMPORTANT)

Most Important Labels

• Funicle
• Hilum
• Micropyle
• Chalaza
• Integuments
• Nucellus
• Embryo sac

Must Learn Definitions

• Funicle → stalk attaching ovule to placenta
• Hilum → junction of ovule and funicle
• Micropyle → opening in integuments
• Chalaza → basal end opposite micropyle
• Nucellus → nutritive tissue

Frequently Asked

• Draw labelled diagram of anatropous ovule.
• What is micropyle/hilum/chalaza?

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3. Megasporogenesis

Important Points

• Megaspore mother cell undergoes meiosis.
• Four megaspores formed.
• Usually one functional megaspore survives.

Important Terms

• MMC (Megaspore Mother Cell)
• Functional megaspore

Board Questions

• Define megasporogenesis.
• Why is embryo sac monosporic?

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4. Structure of Embryo Sac (MOST IMPORTANT)

Must Learn Labels

• Egg cell
• Synergids
• Filiform apparatus
• Polar nuclei
• Central cell
• Antipodals
• Micropylar end
• Chalazal end

Key Facts

• Embryo sac is:
  • 7-celled
  • 8-nucleate
• Egg apparatus consists of:
  • 1 egg cell
  • 2 synergids
• Central cell contains 2 polar nuclei.
• Antipodals present at chalazal end.

Most Important Board Questions

• Draw labelled diagram of mature embryo sac.
• Explain 7-celled 8-nucleate condition.
• What is filiform apparatus?

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Most Important Structures to Memorise for Boards

Structure	Importance
Pistil	Basic
Ovule	Very Important
Megasporogenesis	Important Process
Embryo Sac	MOST IMPORTANT

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One-Line Revision

• Micropyle → pollen tube entry
• Hilum → ovule-funicle junction
• Nucellus → food tissue
• Synergids → guide pollen tube
• Antipodals → chalazal cells
• Polar nuclei → triple fusion
• Embryo sac → female gametophyte