Osmosis: Water Across a Membrane
Watch what happens when two sugar solutions are separated by a thin wall that lets water through but not sugar. Water molecules cross in both directions, but more cross from the weaker solution to the stronger one, so the level on the stronger side rises until the rising level pushes back. Change the sugar on each side and the temperature to see how much and how fast. A second graph shows pieces of plant tissue left in sugar solutions: they gain mass in weak solutions, lose mass in strong ones, and stay the same where the solution matches the inside of their cells.
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What you can adjust
- Sugar on the left
- 0 – 1 mol/dm³
- Sugar on the right
- 0 – 1 mol/dm³
- Concentration inside the plant cells
- 0.1 – 0.6 mol/dm³
- Temperature
- 5 – 40 °C
How much sugar is dissolved on the left of the membrane. A bigger number is a more concentrated solution, with less water in the same space.
How much sugar is dissolved on the right of the membrane. Set both sides the same and the levels stay level.
The concentration of dissolved substances inside the cells of the plant tissue. A piece of tissue neither gains nor loses mass in a sugar solution of exactly this concentration.
Warmer water has faster-moving molecules, so more of them reach the membrane each second and the levels change faster. It does not change where they end up.
About this simulation
What it shows
A tank split by a thin wall with tiny holes: small water molecules pass through, bigger sugar particles cannot. The depth on each side and the water moved are shown as it runs. A second graph shows how plant tissue gains or loses mass in sugar solutions.
The key idea
Water moves from a weaker solution to a stronger one through a wall that only lets water through. The stronger side has less water in the same space, so more water crosses towards it than away from it. The rising level pushes some back, so the rise slows and levels off.
Try this
Set Sugar on the left and Sugar on the right to the same value and the levels stay level. Then set the left to 0 and the right to 1 and the right side rises much further.
A simple model: the molecules do not bump into each other, a handful of sugar particles stands for a whole solution, and the heights are scaled up so a 10 cm starting depth shows the effect. A real column of liquid would have to rise far higher to balance a strong solution. Temperature only changes how fast the water gets through. The tissue curve is a smooth model of how the mass changes, not a measured result.