What is facilitated diffusion?
Diffusion that is assisted by proteins in the membrane
Ions and small polar molecules are transported by channel proteins that act like pores in the membrane
Some of these can open and close; they are called gated channels
Larger polar molecules use carrier proteins
These are specific to the substance they are transporting
The substance binds to the inside of the protein, and the protein then changes shape, transferring the substance to the other side