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

• A. Osmosis
• B. Active transport
• C. Filtration
• D. Diffusion

Answer: (D)

Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. This happens because the molecules are constantly moving and tend to spread out over time, so they naturally spread from where there are many of them to where there are fewer. It’s a passive process, meaning the cell doesn’t need to spend energy for it to occur. An example is a scent spreading through a room, or oxygen moving from the lungs into the blood. Other terms differ: osmosis is the diffusion of water across a membrane, active transport requires energy to move substances against their concentration gradient, and filtration moves particles through a membrane mainly due to pressure rather than a concentration difference.