Final answer:
Facilitated diffusion is the type of diffusion that becomes saturated if all the protein carriers are in use. It is a specific and passive process of molecule or ion transport across membranes through specific transmembrane proteins.
Step-by-step explanation:
The type of diffusion that is specific and passive, and which becomes saturated if all the protein carriers are in use is facilitated diffusion.
Facilitated diffusion is the spontaneous passage of molecules or ions across membranes through specific transmembrane proteins. The rate of solute movement in facilitated diffusion is directly proportional to the number of transport proteins in the membrane.