Small molecules, such as water and many ions, cross the membrane without assistance from the cell. This movement is called ________ and requires NO energy expenditure by the cell.
A) passive transport
B) active transport
C) facilitated diffusion
D) None of the listed responses is correct.

Question

Quizplus · Accepted Answer

Passive transport refers to the movement of molecules across a membrane without the need for the cell to expend energy. Small molecules, such as water and ions, can move across the membrane through passive transport without assistance from the cell. Facilitated diffusion, on the other hand, refers to the movement of larger molecules across the membrane with the help of membrane proteins, but it is still considered a form of passive transport as it does not require energy expenditure by the cell. Active transport, in contrast, requires the cell to expend energy to move molecules against their concentration gradient.

Small Molecules, Such as Water and Many Ions, Cross the Membrane