Why do raisins swell up in water but a cucumber shrivels into a pickle in brine?
It's osmosis, driven by the concentration difference across the cell membranes.
It's osmosis, driven by the concentration difference across the cell membranes. A raisin's inside is sugar-rich (concentrated), so water flows IN from the plain water and it swells. In salty brine the outside is more concentrated (hypertonic), so water flows OUT of the cucumber's cells and it shrivels. The same water-drawing effect is why salt and sugar preserve food — microbes lose water and can't grow.
Key point
Water moves across the membrane toward the more concentrated (saltier/sweeter) side.
Common mistake
thinking the salt or sugar itself moves into the cells.
Memory tip
hypotonic outside → cell swells; hypertonic outside → cell shrinks.
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