Glucose is taken up by red blood cells by binding to a specific pocket in a membrane protein which then allows it to cross the membrane and move down its concentration gradient. What would be the best definition of this process?

The correct answer is Facilitated Diffusion.

Explanation:

Facilitated Diffusion can be defined as the mechanism by which molecules are made to translocate from a region where their concentration is high to a region where their concentration is low through an integral membrane protein that spans the plasma membrane forming a channel across the membrane connecting  the cell interior with the cell exterior.Here, as the molecules move along or down their concentration gradient so no expenditure of energy in the form of ATP or Adenosine Triphosphate occurs.Polar molecules like glucose form hydrogen bonds with water molecules. They are not allowed to diffuse directly across the lipid bilayer because the lipid bilayer is hydrophobic and avoid water molecules and also polar molecules.Hence, the glucose molecules need to get transported through protein channels that span the lipid bilayer of the plasma membrane.These proteins have amphipathic nature, that is, they are composed of both polar and non-polar amino acid residues. The non-polar residues face towards the lipid molecules in the membrane and form hydrophobic interactions with them while the polar residues face the lumen of the channel and form hydrogen bonds with the polar molecules those are translocated across the membrane.