Question

Plz explain polygonal type of embryosac

Answer 1

In Angiosperms the female gametophyte is called Embryo sac.

i) The most common type of embryo sac in

angiosperms is seven celled and eight nucleated Polygonum type.

ii) In majority of flowering plants, one of the

megaspores is functional and acts as a mother cell for the development of female gametophyte(embryo sac), the other three degenerate.

iii) The method of embryo formation from a single functional megaspore is termed megaspore development.

iv) Polygonum type of embryo sac was shows three main parts. They are

1) Egg apparatus 2) Central cell 3) Antipodals

1. Egg apparatus : Three cells are grouped

together at the micropylar end and constitute

the egg apparatus. They are one egg cell and

one egg cell andtwo synergids.

i) The synergids have special cellular thickenings at the micropylar tip called filiform apparatus.

ii The middle largest cell in the egg apparatus is

called oospore or egg.

Role of Synergids:

a) They nourish female gametophyte by absorbing

nutrients from surrounding nucellus.

b) The filiform apparatus of synergids secrete

chemical substances which help in guiding the

pollen tubes into the synergid.

2. Central cell: It is the largest cell of embryo sac.

In has two polar nuclei which fuse to form a

single diploid secondary nucleus.

3. Antipodals : Three cells present at the chalazal

end of embryo sac are called antipodals

i) These cells are ephemeral, smallest cells of

embryo sac and degenerate before or after

fertilisation.

ii) They are considered as vegetative cells of

embryo sac.