In a hypothetical study, cells are placed in a solution of glucose in which the concentration of glucose is gradually increased. At first, the rate at which glucose enters the cells is found to increase as the concentration of the glucose solution is increased. But when the glucose concentration of the solution is increased above 10 M, the rate no longer increases. Which of the following is the likely mechanism for glucose transport into these cells?
A) Facilitated diffusion via a carrier protein
B) Facilitated diffusion via a channel protein
C) Pinocytosis
D) Secondary active transport
E) A symporter

Question

Quizplus · Accepted Answer

Facilitated diffusion via a carrier protein is a type of passive transport that allows molecules to cross the plasma membrane with the help of a specific carrier protein. The rate of transport increases with an increase in the concentration of the transported molecule, but only up to a certain point (when all the carrier proteins are occupied), after which the rate of transport becomes constant. This is consistent with the observations in the hypothetical study. The other transport mechanisms listed (facilitated diffusion via a channel protein, pinocytosis, secondary active transport, and a symporter) do not show this pattern of transport saturation with increasing substrate concentrations.

In a Hypothetical Study, Cells Are Placed in a Solution