Assume that the transport of a particular amino acid across the plasmalemma is observed (1)to occur only down its concentration gradient and (2)to slow when a similar amino acid is added to the extracellular fluid.The movement of the amino acid through the membrane is most likely by
A)osmosis.
B)diffusion.
C)facilitated diffusion.
D)active transport.
E)pinocytosis.

Question

Quizplus · Accepted Answer

The fact that the movement only occurs down its concentration gradient suggests that it is a form of passive transport. Additionally, the slowdown when a similar amino acid is added suggests that the transport is specific and likely involves the use of a carrier protein, which is characteristic of facilitated diffusion. Osmosis (A) is the movement of water molecules, not amino acids. Diffusion (B) is a form of passive transport, but it does not involve the use of a carrier protein. Active transport (D) would require the use of ATP, which is not suggested in the question. Pinocytosis (E) is a form of endocytosis and would not be involved in the transport of a single amino acid molecule.

Assume That the Transport of a Particular Amino Acid Across