What is diffusion?

• A. Movement of particles from high concentration to low concentration due to random motion
• B. Active transport using cellular energy
• C. Movement of electrons in an electrical field
• D. Osmosis

Answer: (A)

Diffusion is the random spreading of particles from areas of higher concentration to areas of lower concentration. Because molecules are constantly moving and colliding, they tend to spread out over time, creating a net movement down the concentration gradient until balance is reached. This process is passive, meaning it does not require energy from the cell.

If we contrast with other ideas, diffusion itself doesn’t require cellular energy, whereas moving substances using cellular energy is active transport. Moving electrons in an electrical field is driven by the electric force and is not the same as diffusion, which arises from random motion. Osmosis is a specific type of diffusion focused on the movement of water across a semipermeable membrane, not the diffusion of all substances in general.