試題詳解

20. In some cells, there are many ion electrochemical gradients across the plasma membrane even though there are usually only one or two proton pumps present in the membrane. The gradients of the other ions are most likely accounted for by ________.
(A) osmosis
(B)ion channels
(C) pores in the plasma membrane
(D) passive diffusion across the plasma membrane
(E) cotransport proteins