With a neat, labelled diagram, describe the parts of a mature angiosperm embryo sac. Mention the role of synergids.

Explanation

Megaspore is the Mothercell for the development of female gametophyte (embryosac). The nucleus of the functional Megaspore divides mitotically to form two nuclei, which move to the opposite poles forming 2 nucleate embryosac. Two more Mitotic nuclear divisions occur in two nuclei results the formation of 8 nucleate embrayosoc. After this stage, cell walls are laid down leading to the organization of the typical female gametophyte or embryosac. Six of the eight nuclei are surroundectby cell walls and organised into cells. Three cells present towards the micropylar end grouped together constitute the egg apparatus. The egg apparatus, inturn consists of two synergids and one egg cell. The synergids have special cellular thickenings at the micropylar tip called filiform apparatus which play an importent role in guiding the pollen tubes into the synergid.
Three cells of the chalazal end are called the antipodals. The large central cell ts formed by the fusion of 2 polar nuclei. Thus a typical angiospermic embryosac, at maturity consists of 8 nuclei and 7 cells. This embryosac is formed from the single megaspore, so called Monosporic embryosac.