The lesson: the diploid phase of a plant life cycle begins with a fertilized egg called a zygote.­ a zygote divides by meiosis and grows into a mature sporophyte.­ a sporophyte is a spore-producing plant.­ when it is mature, it will produce haploid spores through meiosis.­ a spore will divide by mitosis and grow into a mature gametophyte.­ a gametophyte is a gamete-producing plant.­­ when a sperm meets an egg, fertilization takes place and a new sporophyte is produced.­ this sporophyte starts the cycle all over again.