Boxi Learn › Biology › Stage 3 · Structure and Evidence
Why does a potato shrink in salt water?
BIO-1 Cells are the units of lifeBIO-2 Structure fits functionX-1 Guess, then check
What many people think
Once the concentrations are equal on both sides, the particles stop moving.
The idea
Particles never stop moving; water crosses a cell membrane both ways, and the net flow is towards the side where water is scarcer, the saltier side.
Explain it
A friend says that once both sides are equal, the water stops moving. Use the crossing counters to explain what really happens, and why a potato strip in salt water loses mass.
Try at home
Cut two equal potato sticks. Put one in plain water and one in water with 2 big spoons of salt. After an hour, bend them: which is floppy? Weigh them if you have a kitchen scale.