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Osmosis and Water Potential Simulator

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About This MicroSim

This MicroSim models two fluid chambers separated by a semipermeable membrane so students can see how solute potential (Ψs), pressure potential (Ψp), and temperature determine the direction of osmotic water flow. Animated water molecules drift between the cell interior and the external solution, a bold blue arrow shows net flow, and plant mode adds a rigid cell wall plus turgor gauge to depict pressure buildup.

Key visual elements

  • Dynamic cell cartoon that swells, shrinks, or plasmolyzes based on tonicity.
  • Water and solute particles with densities proportional to the selected concentrations.
  • Ψ calculations (Ψs, Ψp, Ψcell, Ψexternal) rendered live in Stage 2 and Stage 3.
  • A Stage 1–4 info rail that documents concentrations, calculated potentials, net ΔΨ, and the equilibrium preview triggered by the Equilibrate button.

How to Use

  1. Set concentrations – Use the Internal and External solute concentration sliders (0–1.0 mol L⁻¹) to create hypotonic, isotonic, or hypertonic conditions.
  2. Adjust temperature – Use the temperature slider (273–313 K) to see how higher thermal energy decreases the magnitude of Ψs (−iCRT).
  3. Toggle cell type – Switch between Animal cell and Plant cell to reveal the cell wall and turgor pressure gauge; plasmolysis appears automatically when the external medium is strongly hypertonic.
  4. Control animation – Pause/resume the stochastic motion of the molecules at any time; Equilibrate gradually balances the two solutions and activates the Stage 4 explanation block.
  5. Interpret the Stage rail – Stage 1 lists concentrations, Stage 2 displays Ψs, Stage 3 reports Ψcell, Ψexternal, ΔΨ, and Stage 4 either prompts equilibration or confirms when ΔΨ ≈ 0 MPa.

Iframe Embed Code

You can add this MicroSim to any web page by adding this to your HTML:

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<iframe src="https://dmccreary.github.io/biology/sims/osmosis-simulator/main.html"
        height="610px"
        width="100%"
        scrolling="no"></iframe>

Lesson Plan

Grade Level

High School Biology (Grades 9–12)

Duration

12–15 minutes

Prerequisites

  • Familiarity with diffusion and osmosis vocabulary.
  • Ability to interpret positive vs. negative water potential values.
  • Awareness that temperature is measured in Kelvin when using the Ψs equation.

Learning Objectives

  • Students will calculate Ψs, Ψp, and overall Ψ for given concentrations and temperatures.
  • Students will classify solutions as hypotonic, isotonic, or hypertonic relative to the cell interior.
  • Students will predict which direction water will move and describe how that movement affects animal vs. plant cells.

Activities

  1. Explore Baseline (4 min) – Set both concentrations to 0.30 mol L⁻¹, note the missing arrow, and explain why water exchange is balanced.
  2. Compare Tonicities (5 min) – Create a hypotonic scenario (internal = 0.5, external = 0.1) and then a hypertonic scenario (internal = 0.2, external = 0.65); have students record the Stage 3 ΔΨ values and direction statements.
  3. Plant vs. Animal Focus (3 min) – Toggle to plant mode, press Equilibrate, and discuss why turgor pressure appears while animal cells risk lysis when ΔΨ is highly negative.
  4. What-if Challenge (3 min) – Students set a temperature, cell type, and concentration pair that makes ΔΨ ≈ 0 MPa and justify their configuration verbally or in writing.

Assessment

  • Ask students to capture a screenshot (or reading) of the Stage rail that demonstrates each tonicity and annotate which control values produced it.
  • Provide ΔΨ targets (e.g., +0.30, −0.15 MPa) and have learners reproduce them within ±0.02 MPa, explaining how they tuned both concentration and temperature.

References

  1. Campbell, N. A. & Reece, J. B. Campbell Biology (12th ed.). Pearson, 2020.
  2. Raven, P. H. et al. Biology of Plants (8th ed.). W. H. Freeman, 2012.