Which process refers to the movement of substances across a cell membrane without using energy by the cell?

Which process refers to the movement of substances across a cell membrane without using energy by the cell?

• A. Active Transport
• B. Diffusion
• C. Passive Transport
• D. Facilitated diffusion

Answer: (C)

Movement across a cell membrane without using the cell’s energy is passive transport. In passive transport, substances move down their concentration gradient because molecules are in constant random motion, so no cellular energy is required. This broad category includes diffusion, where small or nonpolar molecules pass directly through the lipid bilayer, and facilitated diffusion, where transport proteins help certain molecules cross the membrane. The defining feature is that no ATP or other energy input is needed, unlike active transport, which requires energy to move substances against their gradient. So the process described fits passive transport, the general term for non-energy-requiring movement across the membrane (diffusion is a specific form within it).

Movement across a cell membrane without using the cell’s energy is passive transport. In passive transport, substances move down their concentration gradient because molecules are in constant random motion, so no cellular energy is required. This broad category includes diffusion, where small or nonpolar molecules pass directly through the lipid bilayer, and facilitated diffusion, where transport proteins help certain molecules cross the membrane. The defining feature is that no ATP or other energy input is needed, unlike active transport, which requires energy to move substances against their gradient. So the process described fits passive transport, the general term for non-energy-requiring movement across the membrane (diffusion is a specific form within it).