Osmosis & Tonicity 3D

Osmosis & Tonicity 3D compares how animal and plant cells respond to extracellular solute concentration and water potential. On the left floats a flexible biconcave red blood cell; on the right sits a plant cell enclosed in a rigid cellulose wall with a large central water vacuole and chloroplasts. Students drag the golden solute handle or adjust the molarity slider from 0.00 M pure water through 0.15 M isotonic saline up to 0.80 M hypertonic brine. Animated water molecules stream inward or outward while live readouts display solution tonicity, net water movement, red blood cell state, and plant cell state.

• Set External solute concentration to 0.15 M and observe dynamic equilibrium where water enters and leaves both cells at equal rates.
• Drag the solute handle down to 0.00 M (hypotonic pure water) and watch the red blood cell swell and haemolyse while the plant cell becomes turgid.
• Raise External solute concentration to 0.65 M (hypertonic) to see the red blood cell shrivel with crenated spikes and the plant vacuole shrink in plasmolysis.
• Adjust Aquaporin permeability to see how membrane water channels change the speed of osmotic equilibration.

1. 1Define osmosis in terms of solute concentration, selectively permeable membranes, and water potential.
2. 2Compare the behaviour of an animal cell without a cell wall and a plant cell with a rigid cellulose wall in hypotonic, isotonic, and hypertonic solutions.
3. 3Explain why 0.15 M saline is used for intravenous drips whereas pure water causes haemolysis of red blood cells.
4. 4Describe how turgor pressure inside the central vacuole supports non-woody plant tissues.

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