Osmosis
Definition
Osmosis is the movement of water molecules from a region of lower solute concentration to a region of higher solute concentration through a semipermeable membrane. It is a special type of diffusion that only involves water and continues until equilibrium is reached or opposed by other forces.
Key Points for NEET
- 1Water moves from hypotonic to hypertonic solution
- 2Requires a semipermeable membrane
- 3Isotonic solutions have no net water movement
- 4Creates osmotic pressure
- 5Important for plant turgor and cell function
Example
Plant roots absorbing water from soil, or red blood cells swelling in pure water
Asked in NEET
Common Mistakes to Avoid
- ✗Confusing osmosis with diffusion — osmosis is specifically water movement through a semipermeable membrane
- ✗Mixing up hypertonic (cell shrinks/plasmolysis) and hypotonic (cell swells/turgid) solutions
- ✗Thinking osmosis requires energy — it is a passive process driven by water potential gradient
Quick Revision Notes
- ⚡Water potential (Ψ) = Solute potential (Ψs) + Pressure potential (Ψp); water moves high Ψ → low Ψ
- ⚡Plant cell in hypotonic: turgid (wall pressure prevents lysis); Animal cell in hypotonic: lysis (no cell wall)
- ⚡Plasmolysis: cell membrane pulls away from cell wall in hypertonic solution — reversible (deplasmolysis)
- ⚡RBC in water: swells and bursts (hemolysis); in salt solution: shrinks (crenation)
Related Terms
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