The embryo sac, also known as the female gametophyte, is an oval structure found in flowering plants' ovules. It develops from a single megaspore nucleus splitting and contains two haploid nuclei and six haploid cells without cell walls. During fertilization, one male nucleus joins with the egg nucleus to form a zygote, while the other male nucleus fuses with the polar nuclei to form the endosperm nucleus. The embryo sac can take different forms depending on the number of megaspores involved in its development, including monosporic, bisporic, and tetrasporic types. The most common is the monosporic 8-nucleated polygonum type embryo sac.

1. Submitted to: Dr. Sanjay Kumar Kewat
Dr.Somanjana Khatua
Dr. Rikky Rai
Submitted by: Nandani Bhartiya
M.Sc. II sem

2. What is Embryosac?
The embryo sac, also known as the female
gametophyte, is an oval structure found in flowering
plants’ ovules.
When the haploid megaspore nucleus splits, an embryo
sac is said to develop. It has two haploid nuclei and six
haploid cells that are devoid of cell walls.
The haploid nuclei can sometimes merge to create a
single cell (endosperm motor cell). One male nucleus
and one egg nucleus join during fertilization to produce
a zygote, which leads to the development of the embryo.
The primary endosperm nucleus and the second male
nucleus fuse to produce the endosperm nucleus.

3. How to develop Embryo sac?
The functional megaspore represents the first cell of the female
gametophyte.
As the functional megaspore grows, many small vacuoles appear in
its cytoplasm, which later join together to form a large vacuole. The
nucleus undergo three mitotic divisions and form eight nuclei.
After first mitotic division, two nuclei are formed and due to
enlargement of vacuole one of the nucleus is pushed towards the
micropylar end and the other towards the chalazal end.
Both these nuclei towards their respective pole undergo two mitotic
division resulting the formation of four nuclei at each pole.

4. Continue
One nucleus from each pole migrates towards the centre. These
nuclei are called as polar nuclei. The three nuclei at the chalazal
end from the antipodal cell.
Of the three nuclei at the micropylar end, one nucleus forms the
egg or female gamete and the other two as synergids.
The entire structure, the two polar nuclei, three antipodal cell, one
egg and two synergids represent the mature female gametophyte
or embryo sac.
Since this type of embryo sac develop from single megaspore and
has 8-nuclei, it is called as monosporic 8-nucleate embryo sac or
polygonum type.
It is the most common type and found in 81% of angiospermic
plant.

6. Types of Embryosac
 Three different type of embryo sac have been reported on the basis of
number of megaspore involve in the developing of embryo sac
 a. Monosporic b. Bisporic c. Tetrasporic
 A monosporic embryo sac develops from a single megaspore and as such
all the nuclei present in this type of embryo sac are genetically alike.
 Monosporic embryo sacs are of the following two types.
 1. Monosporic 8-nucleate or polygonum type. This type of embryo sac
develops from the chalazal megaspore. Its nucleus divides thrice to form
eight nuclei. This type is generally referred to as normal type of embryo
sac. It is also called Polygonum type as it was first time described in
Polygonum divericatum by Stransburger (1879).
 2. Monosporic 4-nucleate or Oenothera type. This type of embryo sac
usually develops from the micropylar megaspore. The megaspore
nucleusdivides twice and forms only four nuclei; of these three organise
into egg apparatus and the fourth fuctions as polar nucleus. Thus
oenothera type of embryo sac does not have any antipodals. This type is
characteristic of the family Onagraceaes

8. Bisporic Embryo Sac
The bisporic embryo sac develops from one of the two dyads
formed as a result of the first meiotic division (meiosis I) of
megaspore mother cell. One of the dyads degenerates. Both the
nuclei of the functional dyad take part in the formation of embryo
sac.
Each nucleus undergoes two mitotic divisions and as such the
mature embryo sac is 8-nucleate. The eight nuclei are organised
into antipodals, egg apparatus and polar nuclei as in Polygonum
type of embryo sac.
In this type of embryo sac the 4-nuclei derived from one
megaspore nucleus are genetically different from the other four
derived from the second megaspore nucleus.
On the basis of the position of functional dyad the following two
types have been recognized in bisporic embryo sacs.
1. Allium type. This type develops from the chalazal dyad.
2. Endymion type. This type develops from the micropylar dyad.

9. Tetrasporic Embryo sac
Sometimes meiotic division of the megaspore mother cell
is not accompanied by cytokinesis and hence all the four
haploid nuclei lie in a single cell called coeno-megaspore.
 All the four nuclei of coeno-megaspore participate in the
formation of embryo sac. This type of embryo sac is called
tetrasporic and it is genetically more heterogeneous than
the bisporic type of embryo sac.
On the basis of (i) the position of haploid nuclei in the
coeno-megaspore, (ii) the number of times these nuclei
divide, and (iii) organisation of nuclei in the mature embryo
sac, the following types of tetrasporic embryo sacs have
been recognised.

10.  PLUMBAGO TYPE- 1.Haupt(1934) in
Plimbago capensis.The 4 megaspore
nuclei are arranged in a crosswise
fashion(1+1+1+1). 1st div. of spore
nuclei –> 8 nucleate stage; arranged
in four pairs, One nucleus of the
micropylar pair is now cut off to form
the lenticular egg cell ,of the
remaining 7 nuclei, 4(one from each
pair) increase in size, approach one
another and function as secondary
nuclei ,remaining 3 nuclei
degenerates at their original
places,syneigids are completely
absent.

11.  PENAEA TYPE• The four haploid nuclei of the coeno-megaspore
undergo two successive mitotic divisions forming 16 nuclei.• These
nuclei arrange themselves in four groups of four each, one at the
micropylar end, one at chalazal end and one each on the two lateral
sides.Now one nucleus from each groups migrtes to the centre, and
these four nuclei in the centre form polar nuclei.The three nuclei at the
micropylar end are cut off by membranes and form the egg
apparatus.The remaining three groups of nuclei (one chalazal and two
lateral) degenerate at maturity. Highly polyploid (5x) primary endosperm
nucleus is formed after double fertilization. Example – Family
Penaeaceae, Malpighiaceae and Euphorbiaceae.
 Peperomia type -Two nuclei at the micropylar end form egg and a
synergid, eight fuse in the centre of the cell to form a polar nucleus and
the remaining six at the chalazal end formed antipodals. Example-
Peperomia and Gunnera

13. DRUSA TYPE-the mature embryo sac three nuclei form egg
apparatus. Two act as polar nuclei and the remaining 11 nuclei are
cut off by membrane and form antipodal cells.Example – Drusa,
Rubia, Chrysanthemum, Ulmus etc.
FRITILLARIA TYPE- In mature embryo sac three haploid nuclei
organize into egg apparatus, three triploid into antipodal and
remaining one haploid and one triploid nuclei move to the centre
where they fuse to form a tetraploid polar nucleus.Example –
Fritillaria, Lilium, Piper and Gaillardia
PLUMBAGELLA TYPE- One triploid nuclei from chalazal end and one
haploid nucleus from the micropylar end fuse at the centre and form
tetraploid polar nucleus.One haploid nucleus at the micropylar end
forms the egg and one triploid nucleus at the chalazal end the single
antipodal. There is no synergids.

15. Embryo
sac is
the
female
gametop
hyte
give
rise to
endos
perm
on
antipoda
l cells.
polar
nuclei
consistin
g of egg
apparatu
s
eight
nucleat
ed
structur
e
Conclusion

16. Refrences
Book:
Angiosperms by
Singh,Pande.Jain
Biologydiscussio
n.com
Photos source-
Google

17. T H A N K S