Short answers, pulled from the story.
The sporophyte is a diploid multicellular organism that carries two full sets of chromosomes inherited from each parent. It emerges from a zygote formed when a haploid egg cell meets a haploid sperm to create a genetic foundation for robust DNA repair capabilities.
The sporophyte produces spores through a process called meiosis which is often referred to as reduction division. During this phase the number of chromosomes in each spore mother cell is cut in half to create haploid meiospores that carry only one set of genetic instructions.
During the Devonian period a pivotal shift occurred in plant evolution as several groups independently developed heterospory. This evolutionary leap led to the development of endospory where gametophytes develop in a miniaturized form inside the spore wall.
The embryo sporophyte develops by cell division of the zygote within the female sex organ known as the archegonium and remains nurtured by the gametophyte throughout its early development. This embryo-nurturing feature is so fundamental to all land plants that they are collectively known as embryophytes.
In the world of bryophytes which includes mosses liverworts and hornworts the gametophyte is the dominant generation while the sporophyte is a dependent stalk that grows from the tips of the gametophyte. The sporophyte in these plants consists of a sporangium that produces spores and remains nurtured by the gametophyte throughout its early development.