Biology CLEP Prep Practice Exam

The movement of molecules across a cell membrane is termed:

1. Osmosis

2. Active transport

3. Diffusion

4. Endocytosis

The correct answer is: Active transport

Active transport involves the movement of molecules or ions against the concentration gradient, requiring the use of energy. This process is important for maintaining an optimal concentration of materials within the cell. Osmosis, on the other hand, refers specifically to the diffusion of water molecules across a semipermeable membrane. Diffusion, like osmosis, does not require energy and occurs when molecules move from an area of high concentration to low concentration. Endocytosis involves the engulfing of particles or molecules by the cell, which requires energy and is used for the uptake of larger materials into the cell. Therefore, while all of these processes involve the movement of molecules across a cell membrane, active transport specifically refers to the movement against the concentration gradient, making it the correct answer.