Angiosperms are distinguished by double fertilization. In this process, two male gametes from a pollen tube fertilize two ovule components:
- A diploid zygote forms when one male gamete unites with the egg cell, subsequently developing into the embryo.
- A triploid primary endosperm nucleus forms when the second male gamete unites with two polar nuclei in the central cell. This nucleus develops into the endosperm, a nutrient-rich tissue supporting the developing embryo.
Alternative explanations are inaccurate:
- Seed coat: Originates from ovule integuments, independent of double fertilization.
- Pollen grain: The source of male gametes, not a fertilization outcome.
- Ovule: The seed-containing structure that matures post-fertilization, not a direct product.
Therefore, double fertilization yields the embryo and endosperm.