This is a part of the online class for the Botany undergraduate students, Government First Grade College, Yelahanka, Bangalore

1. THE EMBRYO SAC STRUCTURE
IN
ANGIOSPERMS
By
P B MALLIKHARJUNA
GFGC YB
17.04.2020

2.  A typical mature embryo sac or the female
Gametophyte is usually a 7-celled, 8-nucleated sac
like structure present in the nucellus of the ovule.
 It is derived from a megaspore due to
megagametogenesis (multiple mitotic divisions)
 The functional mature Embryo sac may be a sac-
like, haploid, short-lived and heterotrophic structure.
 It usually possesses, viz.,
1) The Egg Apparatus
2) Antipodals, and
3) The Central cell.

3. An Embryo sac structure

4. 1.Egg Apparatus:
a) It is a 3-celled structure always present in
the central cell towards the micropylar end.
b) It possesses a pair of synergids and the egg
cell.
c) All three cells are intactly present as a
triangular structure.
d) Their protoplasts are highly polarized
differentially.

5. a) Synergids: These are elongated cells with a
pointed or hooked end towards the micropylar
end.
 The walls of synergids are incomplete.
 They possess a mass of finger-like projections
of the wall into the cytoplasm called Filiform
Apparatus. It is a wedge or spheroidal
structure made up of the cellulosic
microfibrills.
 They play a role in the absorption of nutrients,
attracting the pollen tube due to the
chemotropic nature or maybe involved as the
target site for the pollen tube entry.
 They may degenerate soon after fertilization.
The ultrastructure of a synergid cell

6. B) The Egg cell: It is a highly specialized and haploid
structure with the polarized protoplast.
 It is sharing the wall with the antipodals and the central
cell towards the micropylar end. While, the distal
portion has a thin wall.
 It contains the vacuolated cytoplasm with more plastids
towards the micropylar end and with a large nucleus
towards the distal end.
 Its nucleus or the female gamete results a Zygote due to
the Syngamy (Fertilization) with the fusion of a male
gamete

7. 2. Antipodals:
a) Antipodals are usually present in the
central cell towards the chalazal end.
b) There are three antipodal cells with a
variable nuclear condition (haploid –
polyploid).
c) They may be persistent or ephemeral and
proliferate in number, and also sometimes
become haustorial.
d) They help in the nourishment of Embryo
sac intially and the embryo later on.

8. 3. The Central Cell:
a) The central cell is the largest cell of the Embryo sac.
b) It is the mother cell of the endosperm after fertilization.
c) It encompasses the egg apparatus towards the micropylar
end and the antipodals towards the chalazal end.
d) It is also a polarized cell with a large central vacuole with the
scanty but organelle-nutrient rich peripheral cytoplasm.
e) A paired or fused polar nuclei are present just below the egg
apparatus. It is usually diploid but often exists with a
polyploidy condition.
f) The polar nuclei may be fused and resulting the Primary
Endosperm Nucleus (PEN) which later on fuses with the
nucleus of another male gamete (Triple fusion) and
develops into endosperm.

9. Conclusion: The mature embryo sac metamorphoses
into the embryonic and the endospermic structure in the
ovule soon after double fertilization.
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