Which transport mechanism uses membrane protein channels to move substances across the membrane, with some channels being specific?

• A. Facilitated Diffusion
• B. Active Transport
• C. Endocytosis
• D. Osmosis

Answer: (A)

Facilitated diffusion uses membrane protein channels to move substances across the membrane. These channels provide a passage for specific ions or molecules, and their selectivity means only certain substances can pass through each channel. It’s a passive process, so no energy is required and movement occurs down the concentration gradient. This matches the description best. Active transport, by contrast, uses energy to move substances against their gradient; endocytosis involves wrapping material in a vesicle rather than passing through a channel; osmosis is the diffusion of water (often through aquaporins) rather than general solute transport through channels.