Which cell structure is referred to as the gatekeeper because it directs substances to move into and out of the cell? a cell wall b nucleus c vacuole d cell membrane?

Molecules like glucose and amino acids are not lipid soluble, so cannot cross the cell membrane by simple diffusion. instead, they are shuttled across by carrier proteins in the membrane from high to low concentration. does this process require energy from the cell? this is an example of what type of molecular movement?