72. What is the difference between active transport and passive diffusion?
Active transport involves movement of materials against a concentration gradient or moving large molecules through the membrane that would be incapable of passing through due to their large size. Active transport involves the expenditure of energy, namely using up a molecule of ATP.
Passive diffusion moves only with a concentration gradient (high to low) and only small molecules (not water) are involved. No energy is used this this process. They may pass through the membrane or through the transport proteins.
Facilitative transport (osmosis) involves only water molecules move through the transport proteins without the expenditure of energy.
