Which statement correctly distinguishes passive transport from active transport?

Which statement correctly distinguishes passive transport from active transport?

• A. Passive transport requires energy to move substances against gradients.
• B. Active transport moves substances down their concentration gradient without energy.
• C. Both forms of transport are driven by energy in all cases.
• D. Passive transport requires no energy and includes diffusion, osmosis, and facilitated diffusion; active transport uses energy to move substances against gradients.

Answer: (D)

This question tests how energy use and movement direction distinguish passive from active transport. In passive transport, substances move with their concentration gradient and no cellular energy is required. Diffusion is the random spread from high to low concentration, osmosis is the movement of water across a membrane, and facilitated diffusion uses a membrane protein to help diffusion without using energy. In active transport, substances are moved against their gradient, from low to high concentration, and this process requires energy input—often from ATP—through pumps or other energy-dependent mechanisms. The statement that best captures these ideas is that passive transport requires no energy and includes diffusion, osmosis, and facilitated diffusion; active transport uses energy to move substances against gradients. The other options mix up energy use and gradient direction, which is why they’re not correct. For example, passive transport does not require energy and does not move against the gradient, while active transport does require energy and moves against it.

This question tests how energy use and movement direction distinguish passive from active transport. In passive transport, substances move with their concentration gradient and no cellular energy is required. Diffusion is the random spread from high to low concentration, osmosis is the movement of water across a membrane, and facilitated diffusion uses a membrane protein to help diffusion without using energy. In active transport, substances are moved against their gradient, from low to high concentration, and this process requires energy input—often from ATP—through pumps or other energy-dependent mechanisms. The statement that best captures these ideas is that passive transport requires no energy and includes diffusion, osmosis, and facilitated diffusion; active transport uses energy to move substances against gradients. The other options mix up energy use and gradient direction, which is why they’re not correct. For example, passive transport does not require energy and does not move against the gradient, while active transport does require energy and moves against it.