Small, charged molecules such as ions can cross the cell membrane through:

S mall charged molecules such as ions can pass through cell membranes by facilitated diffusion using specific transmembrane protein channels, which act as transporters that are implanted into the plasma membrane. Such transport proteins regulate the selective permeability of cell membranes and play a critical function in cell membrane.

Moreover, this specific transmembrane protein have multiple membrane-spanning regions that create a passage through the phospholipid bilayer, allowing charged molecules to pass the membrane through a protein pore without interacting with the fatty acid chains of the membrane.