Final answer:
Double fertilization is a reproductive process unique to angiosperms, involving two separate fertilization events that result in the formation of an embryo and endosperm.
Step-by-step explanation:
Double fertilization is a reproductive process unique to angiosperms, or flowering plants. It involves two separate fertilization events occurring within the ovule of the flower. One sperm fertilizes the egg cell to form a diploid zygote, which develops into the embryo.
The other sperm fuses with the polar nuclei to form a triploid endosperm, which serves as a nutrient-rich tissue for the developing embryo. This process ensures the successful development of both the embryo and the endosperm in angiosperms.