Diffusion and Osmosis – Membrane Model and Potato Strip Experiment
Integrated ScienceCells & OrganismsAges 12–13
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Sign in to playThree modes. Diffusion: solute particles move randomly through the pores of a partially permeable membrane from high to low concentration; change the temperature, the concentration gradient and the number of pores (surface area) to compare rates. Osmosis: water crosses the membrane but sugar cannot, so water moves into the sugar solution. Potato strips: six strips soak in sugar solutions from 0 to 1.0 mol/dm³; record the masses, plot the percentage change in mass and see whether the cells are turgid or plasmolysed.
Lesson: Diffusion, osmosis and water movement in plant cells: the potato strip experiment
What it shows
Particles in liquids and gases move randomly, so more of them cross from where they are concentrated to where they are dilute: this net movement is diffusion. A partially permeable membrane lets small molecules such as water through but holds back large ones such as sugar, so water moves by osmosis from a dilute solution into a more concentrated one. Plant cells gain water and become turgid in dilute solutions, and lose water and become plasmolysed in concentrated ones. The potato strip experiment measures this as a change in mass and finds the concentration that matches the cell sap.
How to use
In Diffusion across a membrane, change Starting particles or Membrane pores, or press Reset after changing Temperature, and compare the time to half-equilibrium with the dashed previous run. In Osmosis of water, raise Sugar molecules and watch the sugar side swell. In Potato strip experiment, let the strips soak, read the table and use the graph to find where the mass does not change. Tap a beaker to see its cells.
Parameters you can change
- Mode Diffusion across a membrane, Osmosis of water, Potato strip experiment
- Temperature 5–60 °C
- Starting solute particles on the left 20–150
- Number of membrane pores (surface area) 1–8
- Sugar molecules on the right (osmosis) 0–60
- Potato cell sap concentration 0.2–0.5 mol/dm³
- Width of the potato strip (square cross-section) 3–10 mm
Questions to explore
- Why do potato strips in pure water gain mass while strips in concentrated sugar solution lose mass?
- Why does raising the temperature or adding more membrane pores make diffusion faster?
- How can you use the graph to estimate the concentration of potato cell sap?
