Growth and Development in Plants
In plants, growth and development starts with the germination of the mature seed.
There are two kinds of seeds based on the number of cotyledons (embryo leaves).
Structure of the Seed
|
Part |
Function |
|
Seed coat/testa |
Protect the inner delicate tissues |
|
Plumule |
Develop into young shoot |
|
Radicle |
Develop into young root |
|
Cotyledon |
Store food Protect the embryo Photosynthesis, when exposed |
|
Micropyle |
Allow movement of water and air into the seed |
|
Scar |
Point of attachment to the placenta |
|
Endosperm |
Store food |
|
Coleoptile |
Protect the plumule |
|
Coleorhiza |
Protect the radicle |
(a) Monocot seed (maize)
(b) Dicot seed (bean)
A typical seed consists of;
Seed coat
The seed coat is the outer covering encloses an embryo.
It is made up of an outer layer testa and an inner layer tegmen.
The testa is thick while tegmen is a transparent membranous tissue. The seed coat protect the seed from damage by bacteria, fungi and other organism.
Scar (hilum)
It is the point of attachment to the seed stalk or funicle.
Near one end of the hilum is a tiny pore, the micropyle.
Micropyle
It is the pore that allows water and air into the embryo.
Embryo
It is made up of plumule (embryonic shoot), radicle (embryonic root) and 1 or 2 cotyledons (seed leaves).
The tip of the radicle is opposite the micropyle.
In some seeds, cotyledons may be swollen when they contain stored food for growing radicle and plumule. Such seeds are called non-endospermic seeds.
Some seeds have their food stored in the endosperm. Hence are called endospermic seeds.
Monocotyledonous seeds have one cotyledon, hence belong to class Monocotyledonae.
Dicotyledonous seeds have two cotyledons, hence belong to class Dicotyledonae.
