How do passive diffusion, facilitated diffusion, and active transport differ in energy use and protein involvement?

How do passive diffusion, facilitated diffusion, and active transport differ in energy use and protein involvement?

• A. Passive diffusion uses energy and does not require transport proteins.
• B. Facilitated diffusion moves substances down their gradient using transport proteins; no energy required.
• C. Active transport uses energy to move substances against their gradient via pumps or co-transporters.
• D. Osmosis is the only form of passive diffusion and uses no energy.

Answer: (C)

Moving substances across membranes hinges on energy use and whether transport proteins are involved. Passive diffusion relies on random molecular motion to move down a concentration gradient and requires no cellular energy or transport proteins. Facilitated diffusion also moves down the gradient and uses membrane proteins—channels or carriers—but still does not require energy input. Active transport stands out because it uses energy to push substances against their gradient, with membrane pumps or co-transporters driving the uphill movement. Osmosis, diffusion of water, is a form of passive transport, not the only kind, since other solutes can diffuse passively as well. Therefore, the statement that active transport uses energy to move substances against their gradient via pumps or co-transporters best captures the difference.

Moving substances across membranes hinges on energy use and whether transport proteins are involved. Passive diffusion relies on random molecular motion to move down a concentration gradient and requires no cellular energy or transport proteins. Facilitated diffusion also moves down the gradient and uses membrane proteins—channels or carriers—but still does not require energy input. Active transport stands out because it uses energy to push substances against their gradient, with membrane pumps or co-transporters driving the uphill movement. Osmosis, diffusion of water, is a form of passive transport, not the only kind, since other solutes can diffuse passively as well. Therefore, the statement that active transport uses energy to move substances against their gradient via pumps or co-transporters best captures the difference.