Question

Passive transport of molecules across the cell membrane is by

• A. diffusion only
• B. osmosis only
• C. both diffusion and osmosis
• D. neither diffusion nor osmosis

Answer 1

The correct option is C both diffusion and osmosis

When molecules are transported along the concentration gradient (from higher to lower concentration), there is no utilization of energy. This is called passive transport.

Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration until a level of equilibrium is reached.

Osmosis is the movement of solvent molecules across a selectively permeable membrane from a region of its higher concentration to a region of its lower concentration till a level of equilibrium is reached.
Both of these processes do not require energy and are examples of passive transport. So, passive transport of molecules across the cell membrane is carried out by both diffusion and osmosis.