Question

Suction pressure of cell wall is
A. Equal to wall pressure
B. Equal to turgor pressure
C. Equal to D.P.D.
D. Osmotic pressure

Answer 1

Hint: The suction pressure of the cell is defined as the diffusion pressure deficit of the cell. It is the difference between diffusion pressure of solvent and solution at given atmospheric conditions. When suction pressure becomes zero no more water can enter the cell.

Complete answer:
The turgor pressure of the cell is defined as the pressure exerted by water entering the cell on its walls. When a cell is kept in a hypotonic solution, water from the surrounding cell enters inside the cells and applies turgor pressure on its walls. This occurs because of the osmosis process. Due to this the cell wall of the cell gets stretched and the osmotic pressure of the cell decreases. When a cell is filled its osmotic pressure (OP) becomes equal to turgor pressure (TP). This means that the diffusion pressure deficit becomes zero. So, diffusion pressure deficit (DPD) can be defined as the thirst of the cell for water. It is expressed as $DPD=OP-TP$. So, when DPD becomes zero, the cell needs no more water and this represents the water-absorbing capability of the cell which is referred to as suction pressure of the cell wall.
B. S. Meyer in 1983 first described the term DPD. In 1915 it was described as suction pressure by Renner. He explained DPD as a decrease in diffusion pressure of water in the cell over its pure state because of the presence of solutes in it. DPD is directly related to the concentration of the solution. DPD decreases with the dilution of the solution. Thus, suction pressure can be defined as the actual pressure with which water is absorbed by the cell.
So, from the above discussion, we can conclude that option C is the right answer.

Note: Suction pressure just like DPD can simply be stated as the ability of the cell to absorb water. Suction pressure is always equal to the diffusion pressure deficit. DPD is directly proportional to the concentration of the solution and plant height. Turgor pressure and osmotic pressure are also key factors that determine DPD.