Question

Which of the following is the unit of measurement of water potential?
A. Watts
B. Joule
C. Pascal
D. Liter
E. Cubic centimeter

Answer 1

Hint: Water potential can be defined as the sum of the water potential of solution and water potential of pure water. Water potential of solution or solute potential or \[{\psi _S}\] is defined as the potency to dissolve the solute. Moreover, the water potential of pure water or \[{\psi _P}\] is defined as the pressure that is present inside any cell due to the entry of water.

Complete answer: Water potential is defined as the difference in the free energy of the water in its pure form and the free energy of water in solution. It is also defined as the sum of the solute potential and pure water potential. Free energy is the energy that is present in any system and is capable of doing work. Pure water has maximum free energy. Moreover, water always moves from higher free energy to lower free energy. The water potential is represented by the symbol of \[\psi \] and \[{\psi _W}\]. The water potential or \[{\psi _W}\] of pure water is 0. Therefore, the water potential of any solution or cell is always less than 0. Hence, it is negative. Water potential is equal to DPD or Diffusion Pressure Deficit in terms of the magnitude and opposite to it in terms of the sign. Since DPD is measured in the unit of pressure like pascals and atm as it is a type of pressure, so water potential is also measured in terms of pressure units like pascals and atmospheres. Thus, based on the above information we can conclude that pascal is the unit of measurement of water potential.
Hence, the correct answer is option (C).

Note: Diffusion pressure deficit or DPD is defined as the deficit in the diffusion pressure of water in the solution as compared to the diffusion pressure of water in its pure water. If the diffusion pressure decreases then the DPD increases and vice versa. Hence, when diffusion pressure is maximum the DPD is minimum. Moreover, water or solvent always moves from low DPD to high DPD.