Q8. Explain the development and structure of seed.
Introduction
After fertilization in female gametophyte, zygote divides repeatedly by mitosis and develops into an embryo. At this stage, ovule changes into seed and this completes process of sexual reproduction in plants.
Structure of seed
It consists of three parts
1. Embryo formed from zygote.
2. Endosperm tissue formed from endosperm nucleus.
3. Seed coat developed from the wall of ovule.
Seed coat
It develops from the wall of ovule. It may be a thin or thick layer. Seed coat protects embryo from mechanical injury and from drying out.
Hilum
There is a scar on the seed coat called hilum. It is where the seed is attached to the ovary wall.
Micropyle
At one end of hilum, is micropyle. Seed uses this micropyle for absorption of water. ”
Development of seed
Emboryo is an immature plant. It consists of a radicle, a plumule and two cotyledons. The radicle of the embryo develops into new root while plumule develops into new shoot. The embryonic stem above the point of attachment of cotyledons is called epicotyl and embryonic stem below the point of attachment of cotyledon called hypocotyl. In angiosperms, the stored food is derived from the endosperm tissue.