Question

diffusion diffusion active transport passive transport facilitated diffusion

Explanation:

Diffusion is a type of passive transport. Passive transport does not require energy input as substances move down their concentration gradient (from an area of higher concentration to an area of lower concentration). In the case of simple diffusion (as depicted in the image where a substance spreads out in a liquid), there is no energy expenditure. Active transport, on the other hand, requires energy (usually in the form of ATP) to move substances against their concentration gradient. Facilitated diffusion is a form of passive transport that requires transport proteins (channels or carriers) but still does not use energy as it follows the concentration gradient. Since the question is about the general category of diffusion (without any indication of protein - mediated which would be facilitated diffusion), and diffusion is a passive process.

Answer:

Passive Transport