Explain the post-fertilisation process in plants.(formation of seed, parts of seed, formation of fruit, germination)
After fertilization, the zygote undergoes a number of mitotic divisions and forms a multi-cellular embryo. The primary endosperm nucleus also passes through a series of mitotic divisions and forms a mass of endosperm cells which provide nourishment to the developing embryo. Endosperm may either be completely consumed by the developing embryo before seed maturation or it may persist in the mature seed and be used up during seed germination.
The zygote undergoes a regular sequence of divisions to give rise to the proembryo and subsequently to the mature embryo. A typical dicotyledonous embryo consists of an embryonal axis and two cotyledons. The portion of embryonal axis above the level of cotyledons is the epicotyl, which terminates with the plumule or stem tip. The cylindrical portion below the level of cotyledons is hypocotyl that terminates at its lower end in the radical or root tip. The root tip is covered with a root cap. In monocots only one cotyledon develops.
In angiosperms, the seed is the final product of sexual reproduction. Seeds are formed inside fruits. A seed typically consists of seed coat, cotyledon and an embryo axis. The cotyledons of the embryo are simple structures, generally thick and swollen due to storage of food reserves.
Integuments of ovules harden as tough protective seed coats. The micropyle remains as a small pore in the seed coat. This facilitates entry of oxygen and water into the seed during germination. As the seed matures, its water content is reduced and seeds become relatively dry. The general metabolic activity of the embryo slows down. The embryo may enter into dormancy (a state of inactivity), or if favourable conditions are available they germinate.
As ovules mature into seeds, the ovary develops into a fruit. The wall of the ovary develops into the wall of fruit called pericarp.