The concept of water potential was introduced in 1960 by Slatyer and Taylor. Water potential is potential energy of water in a system compared to pure water when both temperature and pressure are kept the same. It is also a measure of how freely water molecules can move in a particular environment or system. Water potential is denoted by the Greek symbol \(\Psi \)(psi) and measured in Pascal (pa). At standard temperature, the water potential of pure water is zero.

Bennet-Clark's Protein-Lecithin Theory:
1. In 1956, Bennet-Clark proposed that the carrier could be a protein associated with the .phosphatide called as lecithin.
2. The carrier is amphoteric (the ability to act either as an acid or abase) and hence both cations and anions combine with it to form Lecithin-ion complex in the membrane. Inside the membrane, the Lecithin-ion complex is broken down into phosphatidic acid and choline along with the liberation of ions.

3. Lecithin again gets regenerated from phosphatidic acid and choline in the presence 8. of the enzyme choline acetylase, and choline esterase, ATP is required for regeneration of lecithin.

1. Plasmolysis plays an important role In preservation of meat, jellies and other food stuffs and prevents them from being destroyed by bacteria and fungi.
2. In salting of food stuffs to be preserved, Bacteria and fungi get plasmolysed and killed due to exosmosis.