Diffusion and Osmosis Simulator
How to use the diffusion and osmosis simulator
- Red solute particles and small blue water particles jostle randomly on either side of a membrane. Set more solute on one side than the other.
- With a permeable membrane, everything crosses and both sides end up with the same concentration: diffusion.
- With a semipermeable membrane only water crosses, and more of it moves toward the saltier side than back: osmosis. Watch the water counts drift apart.
Frequently asked questions
What is diffusion?
The net movement of particles from where they are concentrated to where they are not, driven by nothing more than their random motion: more particles happen to wander out of a crowded region than into it. It stops when the concentration is even, although the particles keep moving.
What is osmosis?
The net movement of water across a membrane that lets water through but not the solute, from the side with less solute to the side with more. In the simulation, solute particles crowding the membrane on their side block pores, so fewer water molecules get across from the saltier side, which is a simple version of the real mechanism.
Why does this matter for cells?
Cell membranes are semipermeable. A cell in pure water takes in water and can burst; in strong salt water it loses water and shrinks. Isotonic solutions such as saline (0.9% NaCl) have the same solute concentration as the cell, so there is no net flow. The dilution guide and Concentration Converter deal with the concentrations themselves.
It says WebGL is turned off.
The 3D view needs WebGL, which every current browser has. It can be switched off by hardware acceleration being disabled in the browser settings, or by a very old graphics driver. Turn hardware acceleration on, or try another browser.
Is anything uploaded?
No. The simulation is drawn by your own browser with WebGL; nothing is sent anywhere, and it keeps working offline once the page has loaded.