Is Nucellus Embryo Sac?

In angiosperms, the nucellus contains the embryo sac and is surrounded by the integuments.

Is nucellus and embryo sac same?

It consists of three parts: the integument, forming its outer layer, the nucellus (or remnant of the megasporangium), and the female gametophyte (formed from a haploid megaspore) in its center. The female gametophyte — specifically termed a megagametophyte— is also called the embryo sac in angiosperms.

Is nucellus involved in embryo sac formation?

The embryo sac develops within the ovule surrounded by the nucellus, which is in turn surrounded by the integuments. One cell of the nucellus undergoes meiosis to produce four megaspores.