please answer this facilitated diffusion question.

[radoxme]

My teacher of uk A level biology is not sure on this.

During facilitated diffusion are the proteins that allow passage through the membrane selective in the direction of travel the substrates move in? So if outside a cell is higher concentration than inside net movement would be into the cell. But if like normal diffusion some movement would occur from low concentration to high by random kinetic theory. Do the proteins prevent this altogether in f. d.?

If so is this the case only with some proteins and with others two way random movement is allowed albeit with net movement into the cell in this case?

I felt that selective one way movement proteins would have to use some energy. I understand confirmation is passive, but I felt to be passive movement the mechanism must be symetrical.

Very many thanks. I am sure it is beneath your talents.

[Biologymad]

They can only go one way, when transported using f.d. This is because some types of molecules only enter the cell when need help getting in, yet needed for jobs within the cell such as glucose for glycolysis.