Osmosis & Water Potential Calculator
Calculate and visualize water potential (Ψ = Ψs + Ψp) across a plant cell membrane. Watch water movement and cell plasmolysis/turgidity based on hypertonic/hypotonic environments.
UNDERSTANDING WATER POTENTIAL
Water doesn't just move from high concentration to low concentration; it moves according to **Water Potential** (). Water potential is the measure of the relative tendency of water to move from one area to another. It is determined by two main factors: **Solute Potential** () and **Pressure Potential** ().
THE WATER POTENTIAL FORMULA
The total water potential of a system is the sum of its solute and pressure potentials: Psi = Psi_s + Psi_p 1. **Solute Potential ()**: Also called osmotic potential. Pure water has a solute potential of 0. Adding solutes *always* lowers the water potential (making it negative). 2. **Pressure Potential ()**: In plant cells, this is the turgor pressure exerted by the cell wall. It is usually positive.
HOW TO USE THIS VISUALIZATION
1. **Add Solute**: Watch how increasing the molarity () makes the solute potential () more negative. 2. **Change Temperature**: Note how higher temperatures decrease the solute potential. 3. **Simulate a Plant Cell**: Observe water entering a cell until the pressure potential () balances the solute potential, reaching equilibrium (). **Try This**: Set the external environment to have a lower (more negative) water potential than the cell. Watch the cell undergo **plasmolysis**. What happens to the pressure potential as the cell shrinks?
CORE FORMULAS
AP EXAM CONNECTION
Unit: Unit 2: Cell Structure and Function (Topic 2.8)
Learning Objective: ENE-2.H
COMMON MISCONCEPTIONS
- Thinking water potential is always positive.
- Confusing osmolarity with water potential (they are related, but not the same).
- Assuming water only moves toward the higher concentration of solute (it moves toward the lower water potential).
KEY TAKEAWAYS
- Water potential predicts the direction of osmosis.
- Solutes lower water potential.
- Pressure potential opposes solute potential in plants.
- Equilibrium is reached when total potentials are equal.
PRACTICE QUESTIONS
Q1 (QUANTITATIVE): A plant cell with a solute potential of -7 bars is placed in a solution with a solute potential of -3 bars. Which way will water move?
Show Answer & Explanation
Answer: Into the cell.
Explanation: Water moves from higher water potential (-3) to lower water potential (-7).
Q2 (QUANTITATIVE): What is the solute potential of pure water in an open beaker?
Show Answer & Explanation
Answer: 0 bars.
Explanation: By definition, pure water at standard pressure has a water potential of zero.
