Answer:
To serve as a channel for the transport of molecules between extracellular and intracellular fluid.
Explanation:
The composition of cell membrane shows that the cell membrane is composed of the lipids, cholesterol and the proteins in the cell membrane.
These proteins could be embedded in the cell membrane layer called "integral membrane" or "membrane proteins" and attached to either the inner or outer layer of the cell membrane called "peripheral proteins".
The membrane proteins which are embedded in the membrane form channel proteins which allow the selective transport of the molecules, ions and other substances into and out of the cell.
Thus, the selected option is the correct answer.