Suppose you are studying the transport of a certain polar molecule across the plasma membrane of cells in culture. Over a period of time, you measure the concentration of a polar molecule inside and outside of the cells. You find that the concentration of the molecule is lower in the cell but is gradually increasing. You also measure the ATP concentration inside the cell and find that it is not changing. Which of the following is probably responsible for the transport of this polar substance into the cell?
A)facilitated diffusion
B)secondary active transport
C)endocytosis
D)active transport
E)simple diffusion

Question

Quizplus · Accepted Answer

Since the concentration of the polar molecule is gradually increasing, it is likely that it is moving from an area of higher concentration (outside the cell) to an area of lower concentration (inside the cell) through a process that doesn't require energy. This suggests that the molecule is moving via facilitated diffusion, which uses carrier proteins to move polar or charged molecules across the membrane down their concentration gradient. The fact that ATP concentration inside the cell is not changing suggests that the process is not using energy.

Suppose You Are Studying the Transport of a Certain Polar