Which of the following is true about diffusion in cells?

Diffusion is a fundamental process that describes the movement of molecules from an area of higher concentration to an area of lower concentration until equilibrium is reached. One of the key characteristics of diffusion is that it operates effectively over short distances. In cellular contexts, this means that small molecules can quickly exchange between the inside and outside of a cell when the distances involved are minimal. This efficiency deteriorates as the distance increases, making diffusion less effective in larger cells or over longer distances.

The other options are inaccurate reflections of how diffusion operates. For instance, diffusion is not restricted to solid materials; it can occur in liquids and gases as well. Additionally, diffusion is a passive transport mechanism that does not require energy input from the cell, which distinguishes it from active transport processes that do require energy to move substances against their concentration gradients. Finally, diffusion generally occurs more slowly than active transport, particularly over longer distances or for larger molecules, but this consideration does not detract from the fact that diffusion is efficient over short distances where it is predominantly utilized in cellular functions.