Final answer:
The net distance a molecule travels through the cytosol via diffusion is relatively short, because movement governed by diffusion alone is a random process most effective over short distances.
Step-by-step explanation:
The movement governed by diffusion alone is a random process that is most effective for the dispersion of small molecules over short distances. Diffusion relies on the passive movement of molecules from regions of higher concentration to regions of lower concentration.
This process is driven by the inherent kinetic energy of the molecules and does not require additional energy. As molecules spread out, or diffuse, they move in a random and unpredictable manner, which becomes less efficient over long distances.
For example, when a drop of food coloring is placed in still water, it diffuses throughout the water until the concentration is equal everywhere. This free diffusion demonstrates how molecules move in a random direction, which is efficient for short-range dispersion but not for longer distances where precise targeting or speed is required. In contrast, polar substances and larger molecules often require facilitated transport to cross cell membranes due to their hydrophilic nature or size.