Question

Water potential of a flaccid cell will be:
A) Ψw = Ψs
B) Ψs = Ψp
C) Ψw = 0
D) Ψw = Ψs - Ψp

Answer 1

Hint: Water potential of a plant cell is what causes water to be transported throughout the plants. It depends on the potential difference between that of pure water and the potential in the plant cell.

Complete answer:
The total water potential of the system in a plant cell is given by the equation Ψsystem = Ψs + Ψp + Ψg + Ψm. The solute potential or Ψs of a plant cell is always negative in relation to pure water, because of the osmotic pressure created by solute particles. This helps the movement of water from the soil to the roots.

In a flaccid cell which has undergone plasmolysis, there is absolutely no turgor pressure experienced. The solute potential will also be very negative as both the cytoplasm and vacuole have shrunk in size increasing solute concentration. The pressure potential of that cell will be equal to zero, and the solute potential will be negative. The water potential of that cell will be dependent only on the solute potential, and therefore option A is the correct answer.

Option B is not correct as the pressure potential will be zero, but the solute potential will be very negative in a flaccid cell, allowing water to be easily pushed into the cell from the surrounding environment.

The water potential of pure water is equal to zero, and therefore option C is incorrect.
In any cell, the water potential is the sum of solute and pressure potentials. Option D is incorrect as it states that water potential is equal to solute potential minus pressure potential.

Hence, the correct answer is option (A)

Note: Adding solutes to a cell causes water to flow into the cell from the outside. The movement of water is dependent on capillary forces, gravity, and the osmotic pressures experienced by the differences in solute concentration within the plant cells.