Water Potential Calculator
Calculate water potential in plants and biological systems using multiple components
Calculate Water Potential
Usually negative (cannot be positive)
Hydrostatic pressure (can be positive or negative)
Effect of gravity on water movement
Water Potential Results
Component Breakdown
Water Flow Direction
Moderate water flow
Plant Status
Normal plant condition
Unit Conversions
Water Potential Equation
Example: Plant Cell Water Potential
Given Parameters
Osmotic potential: -0.5 MPa (concentrated cell sap)
Pressure potential: +0.3 MPa (turgor pressure)
Gravitational potential: 0 MPa (reference level)
Calculation
Ψ = Ψo + Ψp + Ψg
Ψ = (-0.5) + (+0.3) + (0) MPa
Ψ = -0.2 MPa
Result: Moderate water potential, normal plant condition
Water Potential Ranges
Component Guide
Water Potential Tips
Water flows from higher to lower potential
Pure water at atmospheric pressure = 0 MPa
Most biological potentials are negative
Osmotic potential cannot be positive
Consider all relevant components for accuracy
Understanding Water Potential
What is Water Potential?
Water potential is a measure of the tendency of water to move from one area to another. It represents the chemical potential of water in a system compared to pure water at atmospheric pressure.
Key Principles:
- • Water moves from high to low potential
- • Pure water at standard conditions = 0 MPa
- • Most biological systems have negative potential
- • Sum of all component potentials
- • Measured in pressure units (Pa, MPa, bar)
Biological Significance
Plant Water Transport
Explains how trees move water from roots to leaves, sometimes over 100 meters high.
Cell Turgidity
Determines cell volume, plant structure, and stomatal function.
Soil Water Availability
Indicates how easily plants can extract water from soil.
Water Potential Components Explained
Osmotic Potential (Ψo)
Also called solute potential:
- • Always negative or zero
- • Depends on solute concentration
- • Lower with more dissolved substances
- • Calculated using van't Hoff equation
Pressure Potential (Ψp)
Physical pressure component:
- • Can be positive or negative
- • Positive = turgor pressure in cells
- • Negative = tension in xylem
- • Related to cell wall elasticity
Gravitational Potential (Ψg)
Height-dependent component:
- • Always opposes upward movement
- • ~0.01 MPa per meter height
- • Important in tall trees
- • Often negligible in small systems
Applications and Examples
Tree Hydraulics
A 100-meter tall tree creates a water potential gradient:
• Soil: -0.1 MPa (moist conditions)
• Root cells: -0.5 MPa (osmotic effect)
• Leaf xylem: -1.2 MPa (tension)
• Atmosphere: -100 MPa (dry air)
Seed Germination
Seeds have extremely low water potential:
• Dry seeds: -50 to -350 MPa
• Imbibition begins: -10 MPa
• Germinating seed: -1 MPa
• Young seedling: -0.3 MPa