Which statement about active transport is true?

Which statement about active transport is true?

• A. Requires energy
• B. Always moves against the gradient
• C. Does not require a carrier
• D. Is the same as facilitated diffusion

Answer: (C)

Active transport moves substances uphill, against their concentration or electrochemical gradient, and it requires both energy and a carrier protein (a pump or transporter) to do this work. The energy can come directly from ATP hydrolysis (primary active transport) or indirectly from the flow of another ion down its gradient (secondary active transport). Because a carrier protein is essential to move the solute against the gradient, the statement that active transport does not require a carrier is not correct. This process is distinct from facilitated diffusion, which also uses carrier proteins but does not consume energy and moves substances down their gradient. So the defining feature of active transport is the energy requirement coupled with carrier-mediated movement against the gradient.

Active transport moves substances uphill, against their concentration or electrochemical gradient, and it requires both energy and a carrier protein (a pump or transporter) to do this work. The energy can come directly from ATP hydrolysis (primary active transport) or indirectly from the flow of another ion down its gradient (secondary active transport). Because a carrier protein is essential to move the solute against the gradient, the statement that active transport does not require a carrier is not correct. This process is distinct from facilitated diffusion, which also uses carrier proteins but does not consume energy and moves substances down their gradient. So the defining feature of active transport is the energy requirement coupled with carrier-mediated movement against the gradient.