Question

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

Answer 1

The suction pressure is also known as diffusion pressure deficit or DPD which is the difference between the diffusion pressure of the solution and its solvents at particular atmospheric conditions.

Complete answer:
When a plant cell is put in a hypotonic solution, the water of the solution enters into a cell through the process of osmosis which causes an increase of turgor pressure in the cell which is in solution. The cell membrane gets stretched and the osmotic pressure of the cell becomes reduced. When a cell is fully inflated, its osmotic pressure is equal to turgor pressure, and the diffusion pressure deficit becomes zero. In a plant cells, the diffusion pressure deficit can be defined as the actual thirst of a cell for water and that is expressed as ${\text{DPD}} = {\rm O}{\text{P}} - {\rm T}{\text{P}}$ .
When DPD becomes zero, the water cannot enter the cell. Thus, it is the value of DPD that represents the water-absorbing ability of a cell which is also called suction force or suction pressure. Generally, DPD tends to equal suction pressure.
This DPD is directly proportional to the height of the plant. It is found to be regulated by two other important factors which are turgor pressure and osmotic pressure.
The term diffusion pressure deficit or DPD was first prescribed by B.S Meyer in 1938. It was described as suction pressure by Renner in 1915. He described DPD as a reduction in the diffusion pressure of water in solution or cell over its pure state due to the presence of solutes in it and forces opposing diffusion.
The concentration of the solution is directly proportional to DPD which decreases with a dilution of the solution. The actual pressure with which a cell absorbs water is known as suction pressure.

Hence, the correct answer is option (C).

Note: The difference between the diffusion pressure of the solution and its solvents occurring at a particular atmospheric conditions known as Diffusion Pressure Deficit or DPD. Suction pressure is the ability of a cell to absorb water. This suction pressure always tends to equal DPD. This DPD is directly proportional to the height of the plant and the concentration of the solution. This DPD is regulated by two major factors which are turgor pressure and osmotic pressure.