Final answer:
The net flux of a solute crossing a membrane via a membrane protein can be described as facilitated diffusion, which is the spontaneous movement of molecules or ions across a membrane through specific transport proteins.
Step-by-step explanation:
The net flux of a solute crossing a membrane via a membrane protein can be described as facilitated diffusion. Facilitated diffusion is the spontaneous movement of molecules or ions across a membrane through specific transmembrane proteins, down a concentration gradient. Unlike passive diffusion, facilitated diffusion requires the assistance of transport proteins, which act as channels or carriers to help the solute move across the membrane.