What distinguishes secondary active transport from primary active transport?

• A. Secondary active transport involves passive diffusion, while primary active transport involves active transport.
• B. Secondary active transport uses the energy from an electrochemical gradient, while primary active transport uses ATP directly.
• C. Secondary active transport moves substances in opposite directions, while primary active transport moves them in the same direction.
• D. Secondary active transport uses ATP directly, while primary active transport uses an electrochemical gradient.

Answer: (B)