A plant cell with a ΨS of −0.65 MPa maintains a constant volume when bathed in a solution that has a ΨS of −0.30 MPa and is in an open container. The cell has a a. ΨP of +0.65 MPa. b. Ψ of −0.65 MPa. c. ΨP of +0.35 MPa. d. ΨP of 0 MPa.

Verified step by step guidance

1. Understand the concept of water potential (Ψ), which is the measure of the potential energy of water in a system compared to pure water. It is composed of solute potential (ΨS) and pressure potential (ΨP). The formula is Ψ = ΨS + ΨP.
2. Identify the given values: The solute potential of the plant cell (ΨS) is -0.65 MPa, and the solute potential of the solution is -0.30 MPa. The cell maintains a constant volume, indicating that the water potential inside the cell (Ψ) equals the water potential of the solution.
3. Since the solution is in an open container, its pressure potential (ΨP) is 0 MPa. Therefore, the water potential of the solution (Ψ) is equal to its solute potential, which is -0.30 MPa.
4. Set up the equation for the water potential of the plant cell using the formula Ψ = ΨS + ΨP. We know ΨS = -0.65 MPa and Ψ (total water potential of the cell) must equal -0.30 MPa because the cell's volume is constant and it is in equilibrium with the solution.
5. Solve for ΨP: -0.30 MPa = -0.65 MPa + ΨP. Rearrange to find ΨP = -0.30 MPa + 0.65 MPa = +0.35 MPa. Thus, the correct answer is c. ΨP of +0.35 MPa.

Key Concepts

Water Potential (Ψ)

Water potential (Ψ) is a measure of the potential energy in water, influencing the direction of water movement. It is composed of two components: solute potential (ΨS) and pressure potential (ΨP). Water moves from areas of higher water potential to lower water potential, affecting plant cell turgor and overall health.

Solute Potential (ΨS)

Solute potential (ΨS) quantifies the effect of solute concentration on the overall water potential of a solution. It is always negative or zero, as the presence of solutes lowers the water potential. In the context of the question, the plant cell's ΨS of -0.65 MPa indicates a relatively high concentration of solutes, which influences its ability to maintain turgor pressure.

Pressure Potential (ΨP)

Pressure potential (ΨP) is the physical pressure exerted by the fluid within the plant cell against the cell wall. It can be positive, negative, or zero, depending on the state of the cell. In this scenario, a ΨP of +0.65 MPa suggests that the cell is turgid, counteracting the effects of solute potential and maintaining cell volume despite being in a less concentrated solution.