Most of the cells that comprise a plant are somatic cells , which by mitotic division allow the organism to grow, differentiate and repair itself. A few select cells are specialized germ cells that undergo reduction division during meiosis, reducing the chromosome number by half. Subsequent sexual reproduction restores the full chromosomal complement when the zygote forms during fertilization. This life cycle is typical of many algae and fungi. Gametes fuse to form a zygote that develops via mitosis into a diploid adult.
Most animals exhibit gametic meiosis.
Here, a diploid individual, or sporophyte , produces haploid spores via meiosis. These undergo mitosis to produce a multicellular haploid individual, or gametophyte . Eventually the gametophyte produces gametes that fuse to create a diploid zygote that grows via mitosis into an adult. This type of life cycle, where a multicellular haploid stage gives rise to a multicellular diploid stage, is commonly referred to as an alternation of generations and is one of the defining characteristics of the Plantae. Plants differ from green algae in that the diploid sporophyte begins development within the haploid gametophyte.