Facilitated diffusion involves what mechanism?

Facilitated diffusion involves what mechanism?

• A. Active transport requiring ATP
• B. Endocytosis of particles
• C. Movement of specific molecules across membranes through protein channels
• D. Simple diffusion across lipid bilayer

Answer: (C)

Facilitated diffusion moves specific molecules across membranes with the help of membrane proteins, and it does so down the concentration gradient without using cellular energy. The key idea is that certain substances, especially polar or charged ones, cannot pass through the lipid bilayer easily on their own. Channel proteins form pores that let ions or water pass through, providing a selective route, while carrier proteins bind the molecule and change shape to shuttle it across. This process is limited by the number of transport proteins available and can become saturated, since each protein can transport only a finite amount at a time. It’s not active transport, which requires energy (ATP) to move substances against their gradient. It’s not endocytosis, which involves vesicles pulling material into the cell. And it’s not simple diffusion through the lipid bilayer, which would occur without proteins and mainly applies to small nonpolar molecules. The defining mechanism of facilitated diffusion is movement through membrane protein channels or carriers.

Facilitated diffusion moves specific molecules across membranes with the help of membrane proteins, and it does so down the concentration gradient without using cellular energy. The key idea is that certain substances, especially polar or charged ones, cannot pass through the lipid bilayer easily on their own. Channel proteins form pores that let ions or water pass through, providing a selective route, while carrier proteins bind the molecule and change shape to shuttle it across. This process is limited by the number of transport proteins available and can become saturated, since each protein can transport only a finite amount at a time.

It’s not active transport, which requires energy (ATP) to move substances against their gradient. It’s not endocytosis, which involves vesicles pulling material into the cell. And it’s not simple diffusion through the lipid bilayer, which would occur without proteins and mainly applies to small nonpolar molecules. The defining mechanism of facilitated diffusion is movement through membrane protein channels or carriers.