High Quality Content by WIKIPEDIA articles! Alternation of generations (also known as alternation of phases or metagenesis) is a term primarily used to describe the life cycle of plants (taken here to mean the Archaeplastida). A multicellular sporophyte, which is diploid with 2N paired chromosomes (i.e. N pairs), alternates with a multicellular gametophyte, which is haploid with N unpaired chromosomes. A mature sporophyte produces spores by meiosis, a process which results in a reduction of the number of chromosomes by a half. Spores germinate and grow into a gametophyte. At maturity, the gametophyte produces gametes by mitosis, which does not alter the number of chromosomes. Two gametes (originating from different organisms of the same species or from the same organism) fuse to produce a zygote, which develops into a diploid sporophyte. This cycle, from sporophyte to sporophyte (or equally from gametophyte to gametophyte), is the way in which all land plants and many algae undergo sexual reproduction.