Which process does not require energy for molecular movement?

The process that does not require energy for molecular movement is diffusion. Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, driven by the concentration gradient. This means that molecules naturally spread out in a solution or across membranes without the need for any external energy source.

Diffusion occurs spontaneously as molecules are in constant motion, and this process continues until equilibrium is reached, where the concentration of molecules is the same throughout the space. It's a fundamental concept in biology, as it helps facilitate the transport of gases and small solutes in and out of cells, contributing to cellular processes without consuming ATP or other forms of energy.

In contrast, osmosis specifically refers to the diffusion of water across a selectively permeable membrane, while active transport utilizes energy to move substances against their concentration gradient. Facilitated diffusion also involves the movement of molecules down their gradient but relies on specific transport proteins, without requiring energy. Thus, diffusion stands out as a purely passive process, making it a key mechanism of molecular movement in biological systems.