All plants exhibit alternation of generations .
In flowering plants, the female megaspore mother cell divides to produce several cells, one of which is the egg cell. Each pollen grain contains 4 microspores. Eventually, one sperm combines with the egg to produce a diploid zygote, which will divide mitotically to produce the sporophyte. Another sperm will fuse with other haploid nuclei of the female gametophyte to form a 3n or 5n nucleus. This tissue becomes the endosperm, which is utilized by the developing sporophyte.