Biologycalendar_todayLast updated: Apr 2026
What is Osmosis?
/ɒzˈməʊsɪs/
Osmosis is the movement of water molecules through a semi-permeable membrane from a region of low solute concentration to a region of high solute concentration, until equilibrium is reached.
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Everyday Example
When you soak a raisin in water, it swells because water molecules pass through its skin into the more concentrated grape-sugar interior — that is osmosis.
publicReal-World Application
“Our kidneys use osmosis to control water balance in the body. Dialysis machines for kidney patients work by exploiting the same principle to filter waste from blood.”
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Did you know?
Osmosis was first described in 1748 by French physicist Jean-Antoine Nollet, who noticed that wine diluted faster when separated from water by a pig bladder membrane.
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Key Insight
Osmosis does not require energy — water moves passively down its concentration gradient. Active transport, by contrast, requires the cell to spend energy to move substances against the gradient.
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