Proteins are large molecules. They enter a cell through

A. passive transport.

B. active transport.

C. diffusion.

D. osmosis.

The answer is; active transport

This means that energy is expended in the process. Because large protein cannot be transported through protein channels in the plasma membrane for being too big, they are transported through endocytosis. This means a vesicle merges with the plasma membrane and forms an invagination that engulfs the protein. The vesicle then encloses with the protein inside and moves into the cell.