Question

The accurate equation for presenting water potential is-
A. $\Psi w = \Psi s + \Psi p + \Psi m$
B. $\Psi s = \Psi w + \Psi p + \Psi m$
C. $\Psi w = \Psi s - \Psi p - \Psi m$
D. $\Psi w = - \Psi s - \Psi p - \Psi m$

Answer 1

Hint: Water potential is a very important term when it comes to understanding the movements of water. Water potential is measured as the potential energy of water per unit volume which is relative to pure water in certain conditions. It is denoted by the Greek letter ‘$\Psi $’ (psi) and has units of pressure such as Pa (pascal). There are several factors that determine water potential.

Complete answer: The molecules of water possess kinetic energy. When in a system the concentration of water increases then the kinetic energy or ‘water potential’ also increases. And so it is clear that the maximum water potential is of pure water. The two major components that determine the water potential of a system are solute potential and pressure potential.
Solute potential: It is the decrease in water potential due to the entry of solute in any system. It is denoted by ‘$\Psi s$’. The solute potential of a system is always negative. With increasing solute molecules, the solute potential becomes more and more negative.
Pressure potential: It is the increase in water potential due to the entry of water molecules. It is denoted as ‘$\Psi p$’. Generally, it is positive for a system. But, in plants, a tension or negative potential is seen in the water column of the xylem which plays an essential role in the transport of water up a stem.
Water potential is affected by both solute and pressure potential.
So, here the correct relation among these values is option A.

Note: There is another important factor that determines the water potential which is here in the above equation is denoted by ‘$\Psi m$’. This valve is of the matric potential. Matric potential is water that has bonds with particles of soil, cellulose, and proteins. The bond present there is a hydrogen bond. The value of matrix potential is from negative to zero. This potential also has a very important role in determining water potential.