What are some examples of facilitated diffusion?
Any large or polar molecule usually requires facilitated diffusion and cannot cross the lipid bilayer via simple diffusion.
Since the outer and inner parts of the lipid bilayer are non-polar, polar molecules cannot be diffused across. For example, in order for a potassium ion to enter the cell, it must pass through a specialized transmembrane protein. These ions and molecules move down the concentration gradient and therefore requires no energy. Glucose is a large molecule that relies on transport proteins and the movement of sodium ions to enter the cell, instead of ATP.
Here is a discussion of how transport proteins such as channel proteins are involved in moving materials in or out of cells by the process of facilitated diffusion.
Video from: Noel Pauller
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