What are the special structures in the cell membrane that allow water and sugar pass through it made of?

These special structures are called protein gates or protein channels. Water is able to diffuse through the cell membrane since it is a small molecule. However, there are channels called aquaporins that allow water to enter the cell. A glucose molecule cannot just diffuse into a cell. There are glucose channels on the surface of the cell membrane that bind glucose molecules and allow them to enter the cell.