DPD always has a positive value whereas water potential a negative value

Answer

**Step-by-Step Solution:**

1. **Understanding DPD (Diffusion Pressure Deficit):**
- DPD is defined as the difference between the diffusion pressure of pure water and the diffusion pressure of a solution.
- Pure water has a higher diffusion pressure compared to a solution because it contains no solutes that would lower its potential.

2. **Positive Value of DPD:**
- Since DPD measures how much lower the diffusion pressure of a solution is compared to pure water, it is always a positive value.
- This is because the diffusion pressure of pure water is always greater than that of any solution.

3. **Understanding Water Potential:**
- Water potential is a measure of the potential energy of water in a system and is influenced by solute concentration and pressure.
- The formula for water potential (Ψ) is given by:
\[ Ψ = Ψ_s + Ψ_p \]
where Ψ_s is the solute potential and Ψ_p is the pressure potential.

4. **Negative Value of Water Potential:**
- The solute potential (Ψ_s) is always negative because the addition of solutes to water reduces its potential energy.
- The pressure potential (Ψ_p) can be positive or zero, but when combined with the negative solute potential, the overall water potential (Ψ) often results in a negative value.

5. **Conclusion:**
- Therefore, it is true that DPD always has a positive value while water potential has a negative value. This is due to the intrinsic properties of solute concentrations and the definitions of these two concepts.

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