The embryo sac in female gametophyte is seven-celled and eight nucleated structure. Justify the statement with the help of a labelled diagram.

OR

List the changes that occur when an ovule matures into the seed.

A matured embryo sac contains an egg apparatus, antipodal cells and central cell.

Egg apparatus

• located in the micropylar end

• Constitute three cells which are grouped together.

• They are two synergids and one egg cell.

• Synergids guide the entry of pollen tube. It has a special cellular thickening at the micropylar tip called filiform apparatus.

• An egg cell has the female gamete.

Antipodal cells

• Three cells in the chalazal end are the antipodal cells.

Central cell

• It is a large cell

• Central cell constitutes two polar nuclei.

Hence a total of 7 celled (3 antipodal cells, one central cell, 2 synergids, 1 egg cell) and 8 nucleate (3 antipodal nuclei, 2 polar nuclei, 2 synergids nuclei, 1 female gamete nuclei) makes the nature of female gametophyte.

OR

In angiosperms, the seed is the final product of sexual reproduction. It is often described as a fertilized ovule.

Steps involved in the maturation of an ovule into a seed:

• Integuments of the ovule harden as tough to produce protective seed coats.

• Micropyle remains as a small pore in the seed coat. It facilitates the entry of oxygen and water into seed during germination.

• As seed matures, the water content is reduced and become relatively dry.

• The metabolic activities of the embryo slow down.

• Embry enters into a state of inactivity called dormancy.

• Germination on availability of favourable conditions (adequate moisture, oxygen and suitable temperature).