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

Explanation

The nucleus of the formational megaspore divide mitotically, to form nuclei which move to the opposite poles, forming the 2-nucleate embryo sac. Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. After the 8-nucleate stage, cell walls are laid down leading to the organisation of the typical female gametophyte or embryo sac. six of the eight nuclei are surrounded by cell walls and are organised into cells, the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large centre cell. Three cells are grouped at the micropylar end and constitute the egg apparatus. the egg apparatus, in turn, consists of two synergids and one egg cell. The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergid. three cells are at the chalazal end are called the antipodals. Thus, a typical angiosperm embryo sac, at maturity, through 8-nucleate is 7-celled.