Which of the following descriptions of movement of molecules across the plasma membrane is correct?
A)If two similar molecules can both combine with the same carrier, the presence of one of these molecules increases the rate of entry of the other.
B)In simple diffusion, the rate of transport of a molecule is inversely proportional to the molecule's extracellular concentration.
C) When a carrier becomes saturated, the maximum rate of transport is reached.
D) Large molecules can cross the plasma membrane through nonselective, receptor-mediated endocytosis.

Question

Quizplus · Accepted Answer

When a carrier becomes saturated, it means all the available carrier proteins are in use, and no more molecules can be transported. This is the maximum rate of transport for that molecule. Option A is incorrect because the presence of one molecule does not affect the transport of another unless they are transported by the same carrier. Option B is incorrect because the rate of transport is directly proportional to the extracellular concentration of the molecule. Option D is incorrect because nonselective, receptor-mediated endocytosis involves the uptake of large extracellular substances by engulfing them into a vesicle, rather than crossing the plasma membrane.

Which of the Following Descriptions of Movement of Molecules Across