Which statement about facilitated diffusion is true?

Which statement about facilitated diffusion is true?

• A. Requires energy input
• B. Is saturable and uses transporter
• C. Occurs without carrier proteins
• D. Is not subject to competition

Answer: (B)

Facilitated diffusion is a carrier- or channel-mediated form of passive transport that moves substances down their concentration gradient without direct energy input. The defining feature is its saturability: there are a finite number of transporters in the membrane, so once all are occupied, increasing the solute concentration cannot accelerate transport. Because the process depends on specific transporter proteins, substances that use the same transporter will compete for binding and passage, affecting the rate. This is why the statement describing facilitated diffusion as saturable and using a transporter is true. The other options are inconsistent because facilitated diffusion does not require energy, it does involve carrier proteins, and it can be affected by competition among substrates.

Facilitated diffusion is a carrier- or channel-mediated form of passive transport that moves substances down their concentration gradient without direct energy input. The defining feature is its saturability: there are a finite number of transporters in the membrane, so once all are occupied, increasing the solute concentration cannot accelerate transport. Because the process depends on specific transporter proteins, substances that use the same transporter will compete for binding and passage, affecting the rate. This is why the statement describing facilitated diffusion as saturable and using a transporter is true. The other options are inconsistent because facilitated diffusion does not require energy, it does involve carrier proteins, and it can be affected by competition among substrates.