Which of the following processes involves the movement of molecules through a membrane with the assistance of a protein?

Facilitated diffusion is the correct choice as it specifically refers to the process where molecules move across a membrane with the assistance of proteins, known as transport proteins. These proteins help in the transport of substances that cannot freely cross the lipid bilayer due to their size, charge, or polarity. This process occurs along the concentration gradient, meaning that molecules move from an area of higher concentration to an area of lower concentration without the expenditure of energy.

In contrast, simple diffusion involves the direct movement of small or nonpolar molecules through the lipid bilayer without the need for protein assistance. Active transport, on the other hand, requires energy to move molecules against their concentration gradient, and thus is not reliant solely on protein channels for movement. Osmosis specifically refers to the movement of water molecules through a selectively permeable membrane, primarily via special channels called aquaporins, and does not apply to other types of solute molecules.