A scientist is investigating transport across cell membranes. She is interested in a type of transport that does not use metabolic energy and does not depend on a sodium gradient, but is carrier-mediated. Which type of transport is she likely studying?
Cotransport
Countertransport
Facilitated diffusion
Primary active transport
Simple diffusion
Correct answer
Facilitated diffusion
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correct answer: C
Facilitated diffusion (Choice C) is a passive process that does not use metabolic energy and does not depend on a sodium gradient. It is, however, carrier mediated.
Cotransport (Choice A) is a secondary active process that uses metabolic energy and depends on a Na gradient (solutes move in same direction as the sodium across the cell membrane). Countertransport (choice B) is similar except that solutes and sodium move in the opposite direction.
Primary active transport (Choice D) is not dependent on a sodium gradient but uses metabolic energy.
Simple diffusion (Choice E) does not depend on a sodium gradient or use metabolic energy but is not carrier-mediated.