Which process describes movement of molecules from higher concentration to lower concentration?

• A. Diffusion
• B. Active Transport
• C. Osmosis
• D. Facilitated diffusion

Answer: (A)

Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration because of random motion of the molecules. It’s a passive process, meaning no energy input is required, so substances naturally spread out until the concentrations even out. This makes it the best description for the scenario, since it captures the idea of spreading down the concentration gradient without needing any helpers. Other terms describe related ways molecules move but with important differences: osmosis is diffusion of water specifically across a semi-permeable membrane; facilitated diffusion still moves substances down their gradient but requires a membrane protein to help pass through; active transport moves substances against the gradient and requires energy.