BIOLOGY [5 Mark Question Answer]

Apparatus required for three beans experiment are beaker, bean seeds, and wooden piece.
The air-dried seeds are attached to a piece of wood, one at each end and one in the middle. This is then placed in a beaker and water is poured into it till the middle seed is half immersed in it. The beaker is then left in a warm place for a couple of days. From time to time, water is added to maintain the original level.
It is observed that after a couple of days that the bean in the middle germinates normally since it has sufficient water, oxygen, and temperature. The bottom seed gets sufficient water and temperature but not oxygen hence it may develop a radicle but doesn't grow further. The upper seed gets oxygen and temperature but not water and hence fails to germinate.
This experiment shows that water, temperature, and oxygen are essential for seed germination and that germination will not occur if any one of these factors are absent.

The factors necessary for germination are:

1. Water-Water is essential for seed germination since protoplasm becomes active only when saturated with water. Water facilitates the necessary chemical changes in food material. Also enzymatic reaction occurs only in the water medium. Water when imbibed by the seed coat makes it soft and swollen. Then the seed coat bursts open, helping the embryo come out easily.
2. Temperature - A suitable temperature is essential for seed germination since many physiological processes occur within the seed during germination. Seeds fail to germinate below 0°C or above 45°C. The optimum temperature for seed germination is 15-30°C.
3. Oxygen - During germination, embryo resumes growth and for this energy is required. This energy comes from the oxidation of food material stored in the endosperm or cotyledons. This process requires oxygen.

A typical seed consists of the following parts:
(i) Seed coat - It is the outer covering of the seed and develops from the integument of the ovule. Its outer layer is called testa and the inner layer is called tegmen. A seed coat protects the inner parts of the seed.
(ii) Micropyle - It is a small pore present near the hilum which allows entry of water into the embryo.
(iii) Embryo - It is the miniature plant present inside the seed coat. It develops from the fertilized egg. The embryo of a mature seed consists of cotyledons (or seed leaves), plumule, Hypocotyl, and radicle. Dicots have two cotyledons joined by a stalk whereas monocots have one cotyledon joined to the embryo. Cotyledons store food material for the embryo.
(iv) Endosperm - It is a food reserve present in certain seeds. Such seeds are called endospermic seeds.