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Passive Transport
Quick revise
Transport of substances across a membrane by a trans-membrane protein molecule
Transport proteins are often specific to one molecule
No energy is involved
Substances move down concentration gradient
Channel proteins
- form channel in membrane which is filled with water
- ions diffuse across the membrane
- many channels can be opened or closed
Carrier proteins
- flip around so that only one side of membrane is open
- high concentration: substance binds
- low concentration: substance is released
