Which statement best describes diffusion, osmosis, and active transport?

Which statement best describes diffusion, osmosis, and active transport?

• A. All three require energy to move substances.
• B. Diffusion and osmosis are passive movements down a gradient; active transport requires energy to move substances against a gradient.
• C. Diffusion requires energy; osmosis and active transport do not.
• D. Osmosis is active transport of water, while diffusion and active transport move solutes.

Answer: (B)

Understanding diffusion, osmosis, and active transport centers on energy use and gradients. Diffusion and osmosis are passive processes; substances move from higher to lower concentrations (or water moves from higher to lower water potential) without cellular energy input. Active transport, in contrast, requires energy to move substances against their gradient, typically using transport proteins powered by ATP. So the best description is that diffusion and osmosis occur passively down a gradient, while active transport uses energy to move substances against a gradient. The other statements misstate energy use or the nature of osmosis, such as claiming all three require energy or that osmosis is active transport.

Understanding diffusion, osmosis, and active transport centers on energy use and gradients. Diffusion and osmosis are passive processes; substances move from higher to lower concentrations (or water moves from higher to lower water potential) without cellular energy input. Active transport, in contrast, requires energy to move substances against their gradient, typically using transport proteins powered by ATP. So the best description is that diffusion and osmosis occur passively down a gradient, while active transport uses energy to move substances against a gradient. The other statements misstate energy use or the nature of osmosis, such as claiming all three require energy or that osmosis is active transport.