Question

What would enhance water uptake by a plant cell?

(A) decreasing the Ψ of the surrounding solution

(B) positive pressure on the surrounding solution

(C) the loss of solutes from the cell

(D) increasing the Ψ of the cytoplasm

Short answer

(A) The statement "decreasing the Ψ of the surrounding solution" is false.

(B) The statement "positive pressure on the surrounding solution" is true.

(C) The statement "the loss of solutes from the cell" is false.

(D) The statement "increasing the Ψ of the cytoplasm" is false.

Step-by-step solution

Water potential

Osmosis is the diffusion of free water—water that is not bound to solutes or surfaces—across a membrane that allows a cell to absorb or lose water.

Water potential, which contains the impacts of concentration of solutes and physical pressure, is the physical property that estimates the direction wherein water will move.

Explanation for option '(A)'

A decrease in the surrounding solution's water potential leads to the overall negative pressure potential than the pure water, so water flows from low to high concentration.

Thus, the uptake of water will decrease in the plant cells.

Therefore, the given statement is false.

Explanation for option '(B)'

The water in living cells is usually under positive pressure due to the osmotic uptake of water. Loading sugar into the sieve tube at the source (in this example, a mesophyll cell in a leaf) reduces water potential inside the sieve-tube elements.

This causes the tube to take up water by osmosis. This uptake of water generates a positive pressure that forces the sap to flow along the tube. The pressure is relieved by the unloading of sugar and the consequent loss of water at the sink.

Thus, it leads to increasing the pressure potential in the surrounding cells.

Therefore, the given statement is true.

Explanation for option '(C)'

Loss of solute leads to the plasmolysis of cells because the outer solution has a lower (more negative) water potential. Water will diffuse out from the cell and the solutes will remain, due to which plasmolysis occurs in the protoplasm.

Thus, the cell will shrink and pull opposite ends of the cell wall that does not enhance water uptake.

Therefore, the given statement is false.

Explanation for option '(D)'

Increasing the Ψ of the cytoplasm leads to an increase in the water potential outside of the cell compared to the inside of the cells. A flaccid cell is a walled cell with a higher solute concentration than its surroundings and is turgid or very firm.

The stiffening of a non-woody tissue occurs when turgid cells push against each other.

Thus, turgor loss is visible during wilting, when leaves and stems droop due to cells losing water.

Therefore, the given statement is false.