Question

multiple choice question
in active transport, the \active\ refers to ______.

○ the active movement of molecules across a membrane
○ the rate at which molecules move across a membrane
○ the use of energy by the cell to power the movement of molecules across a membrane
○ the presence of proteins that move molecules across a membrane

Explanation:

Active transport in biology is defined by the cell using energy (like ATP) to move molecules across a membrane, usually against their concentration gradient. The first option is incorrect as "active movement" is not the key; passive transport also moves molecules. The second option is about rate, not the "active" aspect. The fourth option refers to transport proteins (which can be used in both active and passive, like facilitated diffusion), so it's not specific to active transport. The third option correctly identifies that "active" in active transport relates to energy use by the cell for molecule movement.

Answer:

C. the use of energy by the cell to power the movement of molecules across a membrane