Short answers, pulled from the story.
A sporophyte is the diploid, multicellular phase in the life cycle of plants and algae. It develops from a zygote and produces haploid spores through meiosis; those spores grow into the gametophyte generation, which in turn produces gametes that fuse to restart the sporophyte phase. This recurring alternation is known as alternation of generations.
Sporophytes produce spores through meiosis, also called reduction division, which halves the chromosome count in each spore mother cell. The resulting meiospores are haploid and develop into gametophytes.
In mosses and other bryophytes, the gametophyte is the dominant visible organism and the sporophyte grows on it, depending on it for nutrition. In flowering plants (angiosperms), the sporophyte is the dominant, familiar green plant, while the gametophyte is extremely reduced, represented only by the germinated pollen grain and the embryo sac.
Heterospory is a condition in which a sporophyte produces two distinct spore sizes: larger female megaspores and smaller male microspores. Several plant groups evolved heterospory independently during the Devonian period, and it is considered one of the earliest steps toward the evolution of seeds in gymnosperms and angiosperms.
All land plants are called embryophytes because their embryo sporophyte develops while sheltered and nurtured inside the gametophyte's female sex organ, the archegonium. This embryo-nurturing feature is shared across every land plant group, from mosses to seed plants.
Meiosis in the diploid sporophyte provides a direct DNA repair capability in germline reproductive tissues, including repair of oxidative DNA damage. Because the sporophyte carries two sets of chromosomes, it has a built-in template for correcting errors before they are passed to the next generation.