Final answer:
Sodium ions (Na+) cannot pass through the nonpolar lipid bilayer of the membrane, but their diffusion is facilitated by membrane proteins that form sodium channels, allowing them to move down their concentration gradient.a. The solute was too large to fit through the pores
Step-by-step explanation:
Even though sodium ions (Na+) are highly concentrated outside of cells, these electrolytes are charged and cannot pass through the nonpolar lipid bilayer of the membrane. T
heir diffusion is facilitated by membrane proteins that form sodium channels (or "pores"), so that Na+ ions can move down their concentration gradient from outside the cells to inside the cells. There are many other solutes that must undergo facilitated diffusion to move into a cell, such as amino acids, or to move out of a cell, such as wastes. Because facilitated diffusion is a passive process, it does not require energy expenditure by the cell.