question_answer 69)

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

Answer:

                  After the 8-nucleate stage, cell walls are laid down leading to the organization of the typical female gametophyte or embryo sac.   Six of the eight nuclei are surrounded by cell walls and organized into cells. Three cellspresent towards the micropylar end grouped together, constitute the egg apparatus. Theegg apparatus, in turn consists of two synergids and one egg cell.Three cells of the chalazal end are called the antipodals. The large central cell is formed bythe fusion of 2-polar nuclei. Thus, a typical angiospermic embryo sac at maturity consists ofeight nuclei and seven cells. This embryo sac is formed from, the single megaspore, so it iscalled 'monosporic embryo sac. Role of Synergids The synergids have special cellular thickenings at the micropylar tip called filiformapparatus, which play an important role in guiding the pollen tubes into the synergid.