Question

Define imbibition.

Answer 1

Hint: Imbibition is a type of diffusion . Seeds exhibit imbibition.Imbibition is the initial step in seed germination. As dry seeds imbibe water, they expand and enzymes and food supplies become hydrated. By this enzymes become active and metabolism increases. The swelling of seed by imbibition is the reason for breaking of testa.

Complete answer:
Imbibition is the type of diffusion where the water is absorbed by a solid substance or colloid causing an enormous increase in volume of the substance. During this, water is tightly adsorbed on the surface of the compound without resulting in the formation of a solution. Imbibition is a type of diffusion because the liquid molecules are moving along a concentration gradient. The dry seeds don't have any water content hence they can absorb water easily.

Also imbibition is dominant in the initial stages of water absorption by roots. The hydrophilic compounds like cellulose and pectin compounds in root hair cells imbibe water from soil.
It's commonly observed that during the rainy season, wooden doors and windows swell and get stuck. This is also a result of imbibition of moisture by wood.
Water potential gradient between the solid substance and the liquid being imbibed is essential for this phenomenon to take place. The solid substances are referred to as imbibing and the liquid being imbibed is known as imbibate. The capacity of imbibition differs from substance to substance. Proteins have high imbibition capacity whereas cellulose and starch have very low imbibition capacity.

Note: Imbibition is affected by water potential gradient, force of attraction between imbibant and imbibe and temperature.
 Imbibition is a reversible process.