sentences:  Angiosperms have pollen grains comprising just three cells.One cell is responsible for drilling down through the integuments, and creating a conduit for the two sperm cells to flow down.The megagametophyte has just seven cells; of these, one fuses with a sperm cell, forming the nucleus of the egg itself, and another joins with the other sperm, and dedicates itself to forming a nutrient-rich endosperm.