Unit 2 · Cell transport

Osmosis & diffusion lab

Set the solute concentration outside the cell and watch water move down its concentration gradient, from where it's more concentrated to where it's less concentrated.

Solution setup

The cell's internal solute concentration is fixed at 50% — drag the slider to change what's outside it.

External solute concentration: 50%0% (pure water)50% (matches inside)100% (very concentrated)

Outside

50%

Inside (fixed)

50%

Environment is

Isotonic

💡 Outcome: No net water movement — the cell stays its normal shape.

Why plants and animals respond differently

The rigid cell wall is the whole story.

Animal cells (no wall)

With nothing to push against, an animal cell in a strongly hypotonic solution keeps swelling until the membrane fails — lysis. In a hypertonic solution it just shrivels — crenation.

Plant cells (rigid wall)

The wall caps how far the membrane can expand, so a hypotonic solution just makes the cell turgid — firm, not burst. That turgor pressure is what holds a healthy plant upright. In a hypertonic solution, the membrane can still pull away from the wall — plasmolysis — which wilts the plant.