The glucose transporter used by cells to obtain glucose from the media is a protein embedded in the membrane. When researchers first started to investigate the glucose transporter's structure they had trouble because it seemed to have 2 differnet shapes! Eventually they realized that the glucose transporter changes shape as it moves glucose into the cell but does not require energy to do it's work. Which of the following is the best description for the glucose transporter?

a. It's a carrier protein doing facillitated diffusion
b. It's a carrier protein doing active transport
c. It's a protein channel doing facillitated diffusion
d. It's a protein channel doing active transport

Facilitated diffusion may be defined as the transportation of molecules from a high concentration to a low concentration that is down the concentration gradient without input of the energy. Whereas the active transport is transportation of the molecules from the low concentration to the high concentration which is against concentration gradient by the membrane protein.

The glucose transportation process requires membrane protein for the transport and does not require any energy. Therefore, it is carrier protein which is doing the facilitated diffusion.