1. What is Water Potential?

Water potential (Ψ) is the potential energy of water per unit volume relative to pure water in reference conditions. It measures the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, and matrix effects.

2. How Does the Calculator Work?

The calculator uses the water potential equation:

Where:

• \( Ψ \) — Total water potential (MPa)
• \( Ψ_π \) — Osmotic (solute) potential (MPa)
• \( Ψ_p \) — Pressure potential (MPa)

Explanation: The total water potential is the sum of its components, with osmotic potential typically being negative and pressure potential typically being positive in plant cells.

3. Importance of Water Potential

Details: Water potential determines the direction of water movement in plants, soils, and across membranes. It's crucial for understanding plant water relations, transpiration, and cell turgor.

4. Using the Calculator

Tips: Enter both osmotic potential (Ψ_π) and pressure potential (Ψ_p) in MPa (megapascals). The calculator will sum them to give total water potential.

5. Frequently Asked Questions (FAQ)

Q1: What are typical water potential values?
A: In plant cells, Ψ typically ranges from -0.5 to -3.0 MPa. Soil water potential ranges from 0 (saturated) to below -1.5 MPa (dry).

Q2: What other components affect water potential?
A: In some systems, matric potential (Ψ_m) and gravitational potential (Ψ_g) may also be significant components.

Q3: Why is osmotic potential usually negative?
A: Solutes reduce the free energy of water, making Ψ_π negative relative to pure water (which has Ψ = 0 by definition).

Q4: How does this relate to plant turgor pressure?
A: When Ψ_p equals the absolute value of Ψ_π, the cell is fully turgid (Ψ = 0, no net water movement).

Q5: What units are used for water potential?
A: The SI unit is MPa (megapascal), though bars (1 bar = 0.1 MPa) are sometimes used in older literature.