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Facilitated Diffusion
• Substances, that are too
large or have too strong of
a charge can still get across
the cell membrane• How? Proteins act as
tunnels or channels
• This is still diffusion
though, and does not
require the cell’s energy-
Example
• Red blood cells: have a protein
channel for glucose.
• Only glucose can pass through this
channel, and it can move through in
either direction.
• 100’s of different protein channels
have been found that allow particular
substances to cross different
membranes.