2.6 Diffusion and Osmosis
Notes
Passive transport moves substances without using the cell's energy, from high concentration to low concentration.
- Diffusion: particles spread out until evenly mixed (equilibrium).
- Facilitated diffusion: particles move down their gradient through channel or carrier proteins.
- Osmosis: the diffusion of water across a membrane.
- In a hypotonic solution (less solute outside), water enters the cell; animal cells may burst.
- In a hypertonic solution (more solute outside), water leaves; cells shrink.
- In an isotonic solution, there is no net water movement.
Practice
A red blood cell is placed in pure distilled water. What happens?
Pure water is hypotonic to the cell, so water moves in by osmosis.
Salting a slug makes it shrivel. What kind of solution does the salt create on its skin?
Water leaves the slug's cells toward the higher solute concentration outside.
Glucose moves into a cell from high to low concentration through a carrier protein, without ATP. This is:
It goes down its gradient (passive) but needs a protein to cross.
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