Water Potential

To study the process of movement of water, the concept of water potential is considered as fundamental. Two other components that actually determine the water potential are pressure potential and solute potential. The molecules of water consist of kinetic energy. The molecules of the gases and liquid move randomly which is represented as constant and rapid motion. If a system has a higher concentration of water in it, then it has higher water potential. Therefore, we can understand that highest water potential can be seen in the pure water. The system with higher water potential is also known to have higher kinetic energy.

If two liquids are in contact with each other, the water molecules move randomly from one system to the other. The net movement of water molecules will happen from the system that has the higher kinetic energy to the system with lower kinetic energy. The movement of water will happen from the system that has higher water potential into the system with lower water potential. The movement of the substance from higher solute concentration into the lower solute concentration region is called as diffusion. The water potential is identified with the Greek symbol known as Psi or ᵠ. The units of measurement used for water potential are Pascals also known as pressure units. The water potential of pure water at standard temperature and no pressure is measured as zero.
If pure water is mixed with any substance, the concentration of water reduces and the water potential in it decreases. Any solution will have water potential lower than that of pure water. The evaluation of reduced water potential with the addition of solute in pure water can be done with solute potential. The solute potential is represented by ᵠs which have negative value every time. If the solute molecules are more in pure water, then the solute potential value will be less measured as a more negative value. The pure water that is applied with a pressure which is higher than the atmospheric pressure will enhance its water potential. The water potential will trigger the movement of water from one side to another. The plant system will develop pressure inside the cell when the water moves into the cell by diffusion. The pressure will develop inside the cell against the cell wall and the cell is said to be turgid. The turgidity increases the pressure potential. The pressure potential created by the water column in plant xylem is a negative potential while normally pressure potential is positive. The pressure potential exists in xylem during the transport of water into the stem from the soil. The symbol used for denoting pressure potential is ᵠp. The cellular water potential is the combination of pressure and solute potential. The relation among them is given as ᵠw = ᵠp ¬¬+ ᵠs