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.

1. Osmosis (Latin: Osmos=impulse, urge) is a special type of diffusion.
2. It represents the movement of water or solvent molecules through a selectively permeable membrane from the place of its higher concentration (high water potential) to the place of its lower concentration (low water potential).

1. Reverse Osmosis follows the same principles of osmosis, but in the reverse direction, In this process movement of water is reversed by applying pressure to force the water against a concentration gradient of the solution
2. In reverse osmosis, the water molecules move from the lower concentration (salt water = hypertonic) to higher concentration (pure water = hypotonic) through a selectively permeable membrane.

3. Uses: Reverse osmosis is used for purification I of drinking water and desalination of seawater.

Phloem Loading:
The movement of photosynthates (products of photosynthesis) from mesophyll cells to phloem sieve elements of mature leaves is known as phloem loading. It consists of three steps.
1. Sieve tube conducts sucrose only. But the photosynthate in the chloroplast is mostly in the form of starch or trios-phosphate which has to be transported to the cytoplasm where it will be converted into sucrose for further translocation.
2. Sucrose moves from the mesophyll to nearby sieve elements by short-distance transport
3. From sieve tube to sink by long-distance transport.

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.

1. Pressure potential is a mechanical force for. working against the effect of solute potential Increased pressure potential will increase water potential and water enters the cell which becomes turgid. This positive hydrostatic pressure within the cell is called Turgor pressure.
2. In Turgor pressure (TP) the cell membrane exerts pressure towards the cell wall. The cell wall reacts to this Turgor pressure with equal and opposite force. The counter pressure exerted by the cell wall towards cell membrane is wall pressure.
3. Turgar pressure and wall pressure make the cell fully turgid. TP + WP = Turgid