Facilitated diffusion needs the help of what to move large/charged molecules?

Facilitated diffusion is a process that allows substances, particularly large or charged molecules, to cross cell membranes without the expenditure of energy. The correct answer, which specifies the use of a carrier protein, highlights the role these proteins play in assisting this transport mechanism.

Carrier proteins are specific proteins embedded in the cell membrane that bind to the molecules needing transport. Once a molecule binds to the carrier protein, it undergoes a conformational change, allowing the molecule to move across the membrane and release it on the other side. This process is selective and ensures that only certain substances can pass through, maintaining the cell's internal environment.

Other components mentioned, such as cholesterol and phospholipids, serve structural roles in the cell membrane but do not directly facilitate the movement of large or charged molecules. Ionic channels, while they do help in transporting ions, are specific types of proteins that open or close to allow selective passage of ions, rather than transporting larger molecules like carrier proteins do. Thus, the function of carrier proteins is critical for enabling facilitated diffusion of larger, charged molecules across the cell membrane efficiently.