Molecules moving from an area of low concentration to an area of high concentration is called what?

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

Answer: (A)

Moving molecules from a low concentration to a high concentration is active transport. This is the process cells use when they need to move substances uphill, against their natural diffusion direction, and it requires energy—usually from ATP. Transport proteins act like pumps to push specific ions or molecules across the membrane, keeping concentrations in a cell or region at the desired level, even when diffusion would oppose that.

In contrast, diffusion lets particles spread out from areas of high concentration to low concentration without using energy. Osmosis is a special case of diffusion for water across a membrane. Facilitated diffusion also moves substances down their concentration gradient but uses protein helpers and still doesn’t require energy.