Question

Why is the embryo sac called the female gametophyte?

Answer 1

The embryo sac is also known as the female gametophyte or megagametophyte. In the angiosperm the ovule contains a reduced sac like structure known as the embryo sac which is embedded in the sporophytic tissue.

Answer 2

Any plant has two components a gametophyte (haploid) and a sporophyte (diploid).As we move from lower plants like bryophytes ,where main plant body is gametophyte and sporophyte is dependant on gametophyte , to higher plants like angiosperms where main plant body is sporophyte and gametophyte(pollen grain in male flower and embryo sac in female flower) is dependant on the  sporophyte ;that is the whole plant ,the size of gametophyte gets reduced and the gametophyte becomes dependant on the sporophyte.thus the embryo sac(present in female flower ) which is haploid is called as female gametophye.