Grade 12 · Biology
Passive transport
Why it matters
Diffusion and osmosis.
Advanced20m readingPrerequisite: The fluid mosaic model
What is osmosis?
Short answer
Osmosis is the passive movement of water across a selectively permeable membrane from a region of lower solute concentration to one of higher solute concentration, until they are balanced. It requires no energy. Cells use osmosis to gain or lose water: a cell in a hypertonic solution loses water and shrinks, while one in a hypotonic solution swells.
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Frequently asked questions
- How is osmosis different from diffusion?
- Osmosis is specifically the diffusion of water across a selectively permeable membrane; diffusion is the general spreading of any particles.
- What happens to a cell in a hypotonic solution?
- Water moves in and the cell swells — and may burst if the membrane cannot withstand the pressure.