Identify a type of molecular movement which is highly selective and requires special membrane proteins but does not require energy.
Facilitated diffusions the molecular movement and the diffusion of the substance is highly dependent on the liquid solubility. The diffusion cannot happen if the substance has hydrophilic moiety and to facilitate it, the special membrane proteins come to the rescue. As diffusion occurs from a region of high concentration to low concentration, energy is not spent; instead, the process is natural. This process is highly selective and does not allow all substances to pass through.