Question

Define the term water potential. What are its components? Explain.

Answer 1

Hint: Water potential defined as the potential energy of water per unit volume with respect to pure water. Plants use water potential phenomenon for the transportation of water from roots to all the parts. It is denoted by Psi (Ψ).

Complete Answer:
Water potential is given by the equation;
    Ψ = Ψs + Ψp + Ψm.

The important components of water potential are
1. Solute potential(Ψs): It is also called as osmotic potential. It is the pressure applied on the solution to avoid the inward flow of water through a semipermeable membrane.

2. Matrix potential(Ψm): The potential determined by the attraction between water and the hydrated colloidal molecules, cell wall etc. the water attracted by the matrix of the soil has a lower energy with respect to pure water.hence the matrix potential is always negative.

3. Pressure potential(Ψp): It is one of the most important components. The cell wall applies a pressure on the cell component. By the virtue of solute content, the cell membrane also applies pressure on the cell. Plants maintain turgor, which inturn keeps the rigid by creating pressure potential. Usually plants have positive pressure potential.it is almost zero in plasmolysed cells. Pressure potential is negative when water is pulled through the xylem vessel of the plant.

Note: Water always moves from the higher potential system to the lower potential system. With increase in the concentration solute, the solute potential decreases and hence the total water potential decreases.