Question

Which of the following criteria does not pertain to facilitated transport?

• A. Requirement of special membrane proteins
• B. High selectivity
• C. Transport saturation
• D. Uphill transport

Answer 1

The correct option is D Uphill transport

Facilitated transport or facilitated diffusion is the spontaneous passage of molecules or ions across a biological membrane passing through specific transmembrane integral proteins. Facilitated diffusion is mediated by protein channels or carrier proteins. Most transport proteins that mediate facilitated diffusion are very selective and only transport certain molecules. Neither channels nor carrier proteins require energy to facilitate the transport of substances; they enable the substances to move down their concentration gradients (downhill transport). There is only a certain number of molecules of these carriers or channels in a membrane. If the concentration of the substance being transported is so high that all the channel or carrier molecules are occupied, then the transport is said to undergo saturation, i.e. a further increase in the concentration gradient will not speed up the transport process.