Question

Solution A has ${\Psi }_s=-30$ bars and ${\Psi }_p=5$ bars. Solution B has ${\Psi }_s=-10$ bars and ${\Psi }_p=0$ atm. The two are separated by semipermeable membrane. Flow of water will be

• A. B to A
• B. A to B
• C. Equal in both directions
• D. No flow of water

Answer 1

Answer: (A)

B to A

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,

Solution A : ψs = -30 bars,

ψp = 5 bars and

ψ = ψs + ψp = -30 + 5 = -25 bars.

Solution B : ψs = -10 bars,

ψp = 0 bars and

ψ = ψs + ψp = -10 + 0 = -10 bars.

Therefore, Solution A Water Potential (ψ) = -25 bars,

Solution B Water Potential (ψ) = -10 bars,

In the case of water Potential (ψ), water movement will be higher water potential to lower water potential. i.e, from the Solution B to Solution A.

So, the correct answer is option A.