Draw a neat and labelled diagram of the 'Experimental set-up of three-bean seed experiment' and mention the necessity of each condition for the germination of seeds.

Experimental set-up of three-bean seed experiment is shown in the diagram below:

The observations of the three-bean seed experiment are as follows:

1. The middle seed germinates. It gets both oxygen and water.
2. The top seed does not germinate at all. It gets only oxygen but no water.
3. The bottom seed does not germinate or stops germinating after the emergence of a small radicle. It gets water but very little oxygen (from the air dissolved in water).

Water, suitable temperature and air (oxygen) are necessary for germination.

1. Water — Water is necessary because:
2. By absorbing water, the seed swells and consequently the seed coat ruptures allowing the elongating radicle to come out and form the root system.
3. Water is essential for chemical reactions and enzyme action on stored food in cotyledons or endosperm, converting it into a diffusable (dissolved) form for the developing embryo.
4. Suitable temperature — A moderately warm temperature (25°C to 35°C) is usually favourable for germination which is also called optimum temperature. A very low temperature inhibits the growth of the embryo and a very high temperature destroys its delicate tissues.
5. Oxygen — Oxygen is needed for respiration that provides energy for the rapid cell division and cell growth during germination.