Water potential is -

Options

A. Equal to solute potential
B. Equal to pressure potential
C. Equal to O.P.
D. A tendency of a solution to take up water from another solution across a membrane.

Answer

### Step-by-Step Solution:

1. **Understanding Water Potential**:
Water potential (Ψw) is a measure of the potential energy in water and is used to predict the direction in which water will flow. It is represented by the Greek letter psi (Ψ).

2. **Components of Water Potential**:
Water potential is composed of two main components:
- **Solute Potential (Ψs)**: This is the potential of water to move by osmosis, influenced by the concentration of solutes in the solution.
- **Pressure Potential (Ψp)**: This is the physical pressure on a solution, which can either increase or decrease the water potential depending on whether the pressure is positive or negative.

Therefore, the formula for water potential is:
\[ Ψw = Ψs + Ψp \]

3. **Analyzing the Options**:
- **Option 1**: "Equal to solute potential" - This is incorrect because water potential includes both solute and pressure potential.
- **Option 2**: "Equal to pressure potential" - This is also incorrect for the same reason as above.
- **Option 3**: "Equal to osmotic pressure" - This is incorrect as osmotic pressure is related to solute potential but is not the same as water potential.
- **Option 4**: "A tendency of solution to take up water from another solution across a membrane" - This is correct. Water potential describes the tendency of water to move from areas of higher water potential to areas of lower water potential.

4. **Conclusion**:
The correct answer is that water potential is best described as the tendency of a solution to take up water from another solution across a membrane.

### Final Answer:
Water potential is the tendency of a solution to take up water from another solution across a membrane.

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