Which statement best differentiates passive transport from active transport across a cell membrane?

• A. Passive transport moves substances down their electrochemical gradient without an energy input, whereas active transport moves substances against their electrochemical gradient using energy (e.g., ATP hydrolysis or coupling to another gradient).
• B. Passive transport can move solutes against their electrochemical gradient, whereas active transport can move solutes only down their electrochemical gradient.
• C. Passive transport requires ATP-driven pumps, whereas active transport occurs only through open ion channels.
• D. Passive transport occurs only via carrier-mediated symporters, whereas active transport occurs only by simple diffusion through the lipid bilayer.

Answer: (A)

Verified step by step guidance

1. Step 1: Understand the concept of passive transport. Passive transport is the movement of substances across a cell membrane without the input of cellular energy, typically moving substances down their electrochemical gradient (from high to low concentration or electrical potential).
2. Step 2: Understand the concept of active transport. Active transport requires energy, often from ATP hydrolysis or coupling to another gradient, to move substances against their electrochemical gradient (from low to high concentration or electrical potential).
3. Step 3: Compare the direction of movement relative to the electrochemical gradient. Passive transport moves substances down the gradient, while active transport moves substances against the gradient.
4. Step 4: Recognize the energy requirement difference. Passive transport does not require energy input, whereas active transport requires energy to function.
5. Step 5: Evaluate the given statements based on these principles to identify the correct differentiation between passive and active transport.