Assume that the import of a particular amino acid across the plasma membrane is observed to occur only down its concentration gradient and to slow when a different but similar amino acid is added to the extracellular fluid. The movement of the amino acid through the membrane is most likely by:

facilitated diffusion

Explanation:

The facilitated diffusion is a process through which the passive transport of ions and molecules takes place across the biological membrane through specific transmembrane integral proteins.

This process allows the diffusion of the charged molecules like aminoacids, ions and nucleosides to cross the plasma membrane.

On the basis of the above description, facilitated diffusion is the process by which the amino acids will move along across the concentration gradient.

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