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What is osmosis?

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Quick answer

Osmosis is the movement of water across a semipermeable membrane from a region of lower solute concentration to higher concentration, balancing the two sides. It's how cells take in and lose water. Water moves toward the side with more dissolved solute, through a membrane that blocks the solute.

Key things to understand

  1. Water moves toward the side with more dissolved solute, through a membrane that blocks the solute.
  2. It continues until concentrations balance or pressure stops it.
  3. It's vital in biology: roots absorb water, cells stay hydrated, kidneys filter blood.
  4. It's a passive process — no energy is required.

People also ask

How is osmosis different from diffusion?
Diffusion is the spread of any particles; osmosis is specifically water moving across a semipermeable membrane.
Why do plant roots use osmosis?
Soil water has fewer solutes than root cells, so water flows into the roots by osmosis.
What happens to a cell in salty water?
Water leaves the cell by osmosis toward the saltier outside, and the cell shrinks.