Which statement correctly identifies primary active transport?

Which statement correctly identifies primary active transport?

• A. Facilitated diffusion moves substrates down their gradient without energy.
• B. Secondary active transport uses ATP directly to pump against gradient.
• C. Primary active transport uses ATP directly to pump substrates against gradient.
• D. Passive diffusion always requires ATP.

Answer: (C)

Primary active transport is the process where energy from ATP hydrolysis is used directly to move substances against their electrochemical gradient. This direct use of ATP to power a pump is the defining feature, with the Na+/K+-ATPase being a classic example that maintains essential ion gradients for nerve signaling and fluid balance. This differs from other transport types. Facilitated diffusion moves substances down their gradient through a transporter without energy input, so it isn’t primary active transport. Passive diffusion also requires no energy, simply moving down a concentration gradient. Secondary active transport does use energy to move substrates against a gradient, but the energy comes from an existing ion gradient created by a primary active transporter, not from ATP directly.

Primary active transport is the process where energy from ATP hydrolysis is used directly to move substances against their electrochemical gradient. This direct use of ATP to power a pump is the defining feature, with the Na+/K+-ATPase being a classic example that maintains essential ion gradients for nerve signaling and fluid balance.

This differs from other transport types. Facilitated diffusion moves substances down their gradient through a transporter without energy input, so it isn’t primary active transport. Passive diffusion also requires no energy, simply moving down a concentration gradient. Secondary active transport does use energy to move substrates against a gradient, but the energy comes from an existing ion gradient created by a primary active transporter, not from ATP directly.