In simple osmotic systems, at constant temperatures , the water potential results from the combined but opposite actions of

Options

A. Relative humidity & pressure potential
B. Pressure potential and saturation
C. Saturation vapour pressure and osmotic potential
D. Osmotic potential and pressure potential

Answer

To solve the question regarding the components that contribute to water potential in simple osmotic systems at constant temperatures, we need to understand the definitions and roles of various potentials involved.

### Step-by-Step Solution:

1. **Understanding Water Potential**: Water potential (Ψ) is a measure of the potential energy in water and is used to predict the direction in which water will flow. It is influenced by two main components: osmotic potential and pressure potential.

2. **Osmotic Potential (Ψs)**: This is the potential of water to move across a semipermeable membrane due to solute concentration. It is negative in value because the presence of solutes lowers the potential energy of water.

3. **Pressure Potential (Ψp)**: This is the physical pressure exerted on water in a plant cell. It can be positive (when the cell is turgid) or negative (when the cell is under tension, such as in xylem).

4. **Combined Effects**: In a simple osmotic system, water potential results from the combined effects of osmotic potential and pressure potential. They act in opposite directions: osmotic potential tends to draw water into the cell, while pressure potential tends to push water out.

5. **Conclusion**: Therefore, the correct answer to the question is that the water potential results from the combined but opposite actions of osmotic potential and pressure potential.

### Final Answer:
The water potential in simple osmotic systems at constant temperatures results from the combined but opposite actions of **osmotic potential and pressure potential**.

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