Why do you need proteins to allow ions to cross the cell membrane and enter the muscle cell? Solution The transfer of ions are required for the conductance of muscle impulse. The proteins are attached to, or associated with the membrane of a cell or an organelle. Facilitated diffusion is the spontaneous passage of molecules or ions across a biological membrane passing through specific transmembrane integral proteins. The use of proteins along with different proteins used in the transport of ions are listed below:.