in the form of heat. It is called heat of wetting or heat of hydration. The heat of wetting can be experienced during
the kneading of wheat flour, where the starch and cellulose molecules imbibe water. The swelling imbibant also develops
a pressure called imbibition pressure or matric potential. air dried pea seeds, on coming in contact with water, can
develop an imbibition pressure of upto 1000 bars (100 MPa).
Imbibition pressure is tested by placing dry seeds in a tin, adding water upto their upper level, and then tightly putting
the lid over it. Within an hour, the lid will be blown off. alternately, fill a gas jar 3/4 with dry seeds. Pour water upto
the brim. Cover the cylinder with a lid, and place a weight over the lid. Within a couple of hours the lid, alongwith
weight, is lifted.Proteins are powerful imbibants as compared to polysaccharides like starch, cellulose or lignin. Pure gelatin adsorbs
water more quickly, than cellulose or lignin.
Factors influencing imbibition
● Looseness of texture of imbibant shows more imbibition, while compactness of texture shows less imbibition.
● Imbibition rises with rise in temperature.
● It decreases with rise in pressure.
● Imbibition either decreases or increases, depending upon the charge of imbibant.
Consequences of imbibition
(i) Imbibition plays an important role in absorbing and retaining water.
(ii) absorption of water by young cell is mostly through imbibition.
(iii) Water is absorbed by the germinating seeds through imbibition.
(iv) Breaking of the seed coat in germinating seeds is due to greater imbibitional swelling of the seed kernel (starch and
protein), as compared to seed coverings (cellulose).
(v) Seedling is able to come out of soil due to development of imbibition pressure.
(vi) Imbibition pressure developed during germination of seeds and spores can break asphalt roads and concrete
pavements.
(vii) Jamming of wooden frames, during rains is caused by swelling of wood due to imbibition. In older times, it was used in
breaking the rocks and stones.
(viii)fruits of many plants come to develop matric potential, in addition to their osmotic potential. This helps to maintain
inflow of water, even under conditions of water scarcity.
(ix) Imbibition is dominant in the initial stage of water absorption by roots.
(x) Since the imbibition is not dependent on metabolic activity of cell, it can occur under anaerobic conditions.
(xi) The water moves into ovules, ripening into seeds, by the process of imbibition.
water Potential (yw)
Water potential is the fundamental concept for understanding movement of water. Water molecules possess kinetic
energy. In liquid and gaseous form, water molecules are in random motion that is both rapid and constant. The difference
between the free energy of water molecules in pure water, and the energy of water in any other system (e.g., water in
a solution or in a plant cell or tissue) is termed the water potential. It is represented by Greek letter y (psi) or more
accurately yw. The value of yw is measured in bars, pascals or atmospheres.
Water always moves from the area of high water potential or high energy to the area of low water potential or low energy.
The water potential of a solution can be determined using pure water as the standard of reference.
The pure water, at normal temperature and pressure has a water potential of zero (0). The presence of solute particles
reduces the free energy of water, and thus decreases the water potential (negative value). Therefore, the water potential