Final answer:
The three major parts of a seed are the embryo, endosperm, and seed coat. The embryo is the young plant that develops from a fertilized egg, the seed coat protects the embryo, and the endosperm provides necessary nutrients.
Step-by-step explanation:
The three major portions of a seed are the embryo, the endosperm, and the seed coat. The embryo develops from a fertilized egg and later forms the cotyledon, stem (hypocotyl), and root (radicle) structures. The seed coat provides protection for the embryo, ensuring it does not dry out and can germinate in favorable conditions. The endosperm is a nutrient-rich tissue that provides food to the embryo until it's able to sustain itself through photosynthesis.