The force generated by the imbibants ss termed as matric potential and replaces the old term imbibition pressure. The matric potential is analogous to solute potential. In the plant cells the imbibition refers to the absorption and adsorption of water by insoluble, solid, hydrophilic protoplasmic, and cell wall constituents.
MATRIC POTENTIAL (q M)
If dry plant material such as dry wood is placed in water it swells and there is a noticeable increase in its volume as we. Similarly when air-dried pea seeds are placed in water, this swell. Lite direction of water movement is from a region of higher water -potential to one of lower water potential. The force responsible for binding adsorption of water molecules to the hydrophilic surfaces protein pea seeds is arfect bonding.
A tremendous amount of pressure imbibition pressure can develop if the imbibant is confined and then allowed to imbibe water. A common example of imbibition is that of a sticking timoden door or window frame during humid weather or rainy season. The hydrophilic surfaces, for example, those of colloids such as proteins, starch, and clay adsorb water and tenacity the force with which the molecules stick or cling to an object with which the water molecules are adsorbed depends not only upon the nature of the surface but also of the distance facyors the surface and adsorbed water molecules. Those molecules that are present directly on the adsorbing surface are held extremely tightly and those which are at a distance from the adsorbing surface are held less tightly.
The matric potential is osomtic measure of the tendency for a matrix to absorb additional water molecules. This tendency is equivalent to the average tenacity with which the least tightly held more distant layer of water molecules is adsorbed. Matric potential is expressed in units of water potential. A dry- colloid or hydrophilic surface such as filter paper, wood, soil, or gelatin often has negative matric potential, while the same colloid in a large volume of pure water has a matric potential of zero since it is saturated and therefore in equilibrium with the water.
In general, when any colloid at atmospheric pressure is in equilibrium with its surroundings, the least tightly held water molecules have the same free energy as the water molecules in the surroundings, so the matric potential of the colloid is equal to the water potential of the colloid s equal to the water potential of the surroundings. The matric potential is analogous to the solute potential osmotic potential in that it represents the potential maximum pressure that an adsorbent will develop if submerged in pure water.
En a complex system such as a cell that contains molecules of colloidal protein and other hydrophilic surfaces, as well as simple solute ions and molecules, the final water potential will be determined not only by the solute particles and the pressine but also by the matric effects of the proteins and other surfaces because these surface bind water molecules and result in a decrease in water potential.
A water potential gradient must exist between the surface of the imbibant and the liquid imbibed. Very negative water potentials exist in dry plant materials, e. Therefore, when the osmoyic seeds are placed in pure water, the water moves rapidly to the surface of the imbibant due to the presence of a steep water potential gradient.]