Mechanisms of Transport: Passive Transport

Passive Diffusion

the movement of molecules across a membrane from an area of high concentration to an area of low concentration, driven by the concentration gradient and requiring no added cellular energy.

• two main types

Simple Diffusion

the passive movement of small, uncharged molecules straight across the membrane, from an area where they are more concentrated to an area where they are less concentrated, without any help from proteins or cell energy.

• small, nonpolar molecules like O2 and CO2

Facilitated Diffusion

a type of passive transport where substances move across a cell membrane down their concentration gradient with the help of transport proteins, such as channels or carriers, without requiring direct energy

• polar, charged, and small molecules

Osmosis

The movement of water from an area of high concentration to low concentration through both facilitated diffusion (aquaporins) and simple diffusion (straight through the bilayer)

• dependant on solute concentration; will move to the area with less solutes