Final answer:
A spore grows into a mature plant during the process of sporophyte development.
Step-by-step explanation:
In the life cycle of plants, particularly in those with an alternation of generations, there are two main stages: the gametophyte stage and the sporophyte stage. The spore is a reproductive cell that is typically produced by the sporophyte through the process of sporogenesis. When the spore undergoes germination, it gives rise to a multicellular structure called the gametophyte. The gametophyte is a haploid plant body that produces gametes—sperm cells and egg cells—through mitosis.
Fertilization occurs when the sperm from the gametophyte combines with the egg, forming a diploid zygote. This zygote then develops into a mature, multicellular structure known as the sporophyte. The sporophyte is the dominant, multicellular, diploid phase in the life cycle of plants. It produces spores through the process of sporogenesis, completing the life cycle.