Question

When a plant cell is placed in a hypotonic solution, which of the following will not apply?
A. Wall pressure is decreased
B. The cell becomes turgid
C. The suction pressure of the cell sap will decrease
D. Water potential of the cell sap will increase

Answer 1

The hypotonic solution is a diluted solution having very less amount of solute in it. It causes the cell to undergo endosmosis. During this process, low solute content in solution causes water to move inside the cell.

Complete step by step answer: A hypotonic solution is the one that has less solute (dissolved solids in water or any other solvent) concentration in it. Thus, to balance the concentration gradients, the water molecules from the hypotonic solution will move inside the cell making it swell. The movement of water molecules from the hypotonic solution makes it less diluted and the concentration gradients get restored.
Now, let us see which of the given situations does not apply to the above-given explanation.
-Option A is that the wall pressure is decreased when the cell is placed in a hypotonic solution. This is incorrect because, in a hypotonic solution, the cell sucks water inside it and swells thus, pushing the plasma membrane on outer edges. This means that the wall pressure increases not decreases.
-Option B is that the cell becomes turgid. Turgid cells mean swelled up cells. So, it is true as the water rushes inside the cell and makes it swollen.
-Option C is that the suction pressure of the cell sap will decrease. The suction pressure of the cell is the measure of the thirst for the water of the cell. As the cell fills up completely with water, eventually its thirst decreases. Thus, the suction pressure decreases.
-Option D is that the water potential of the cell sap will increase. The water potential of a cell is always equal to the suction pressure of the cell but is opposite in sign. Thus, when the cell swells with water, the suction pressure decreases, and inversely proportional to it, the water potential increases.
Therefore, the right answer is option A.

Note: The cells do not have any systems to regulate water contents inside them. Thus, the body acts as a regulator for the water contents in and out of the cells. The extracellular and intracellular solute concentrations are kept constant with the help of kidneys, adrenal glands, and hypothalamus that commands our thirst for water.