Question

X and Y are two living cells adjacent to each other. The cell X has solute potential $\left({\Psi }_s\right)$ of -9 bars and pressure potential $\left({\Psi }_p\right)$ of 4 bars whereas cell Y has solute potential $\left({\Psi }_s\right)$ of -8 bars and pressure potential $\left({\Psi }_p\right)$ of 5 bars. What will be the direction of water movement between these cells?

• A. Cell X to cell Y
• B. Cell Y to cell X
• C. Does not move in any direction
• D. Moves in both directions

Answer 1

The correct option is B Cell Y to cell X

This question depicts Water Potential. Water potential is denoted by the Greek letter ψ (psi). It is the measure of the relative tendency of water to move from one area to another and are measured in the terms of bars. It is the difference between the free energy of water molecules in pure water and solution. Water potential can be measured using the formula, ψ = ψs + ψp where ψs = Solute Potential or Osmotic Potential and ψp = Pressure Potential or Turgor Potential. Here, the water movement across the concentration gradient will be higher water potential to lower water potential.

In the above question it is given as follows,

Cell X : ψs = -9 bars,

ψp = 4 bars and

ψ = ψs + ψp = -9 + 4 = -5 bars.

Cell Y : ψs = -8 bars,

ψp = 5 bars and

ψ = ψs + ψp = -8 + 5 = -3 bars.

Therefore, cell X Water Potential (ψ) = -5 bars,

cell Y Water Potential (ψ) = -3 bars,

In the case of water Potential (ψ), water movement will be higher water potential to lower water potential. i.e, from the cell Y to cell X.

So, the correct answer is option B.