Diffusion occurs passively- no ATP is required to move substances across the cell membrane because they move down a concentration graident.
Osmossis is a form of difusion. Osmossis is the movement of water molecules from a region of high concentration to a region of low concentration.
Water potential is the tendency for water to move from one place to another.
Facilitated diffusion:
Channel Proteins are transmembrane proteins that form tunnels through the bilayer for water soluble molecules. Some channels are open all the time other open when triggered by a signalling molecule
Carrier proteins change shape to help move molecules into and out of the cell (use energy from the cell in active transport)
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