Which process is classified as an example of passive transport?

• A. Active transport
• B. Facilitated diffusion
• C. Endocytosis
• D. Exocytosis

Answer: (B)

Passive transport is a process by which substances move across cell membranes without the need for energy input. This movement occurs along the concentration gradient, meaning molecules move from an area of higher concentration to an area of lower concentration.

Facilitated diffusion is a specific type of passive transport that involves the movement of molecules through a membrane via protein channels or carriers, which help polar or large molecules that cannot easily pass through the lipid bilayer. This process does not require energy because it is driven by the concentration gradient.

In contrast, active transport requires energy input, usually in the form of ATP, to move substances against their concentration gradient. Endocytosis and exocytosis are forms of bulk transport that also require energy, as they involve the engulfing of substances into the cell or the expulsion of materials from the cell, respectively.

Thus, facilitated diffusion is correctly classified as passive transport because it occurs spontaneously and does not require energy expenditure, leveraging the natural tendency of molecules to move toward equilibrium.