Labs / Biology
Osmosis & Tonicity
A single cell floats in a bath of salty water. Move the solute slider and water will cross the semi-permeable membrane on its own, chasing the concentration gradient — swelling the cell, holding it firm, or shrinking it. Add a rigid plant cell wall to see how it changes the ending.
in 300 mMflux balancedvol 100 %cell at rest
What to try
- Drop the bath to pure water (0 mM). Which way does the water rush, and what happens to an animal cell with no wall?
- Turn the plant cell wall on and go hypotonic again. Why does the cell stop swelling instead of bursting?
- Can you find the bath concentration where the net flux reads "balanced"? How does it compare to the cell's inside concentration?
- Crank the bath up to 600 mM. Why does the inside concentration climb as the cell shrinks, even though no solute crossed the membrane?
- In a hypertonic bath, how does a walled cell's fate differ from a naked one's — plasmolysis versus crenation?