Which process moves water and solutes across a membrane due to pressure differences?

• A. Filtration
• B. Diffusion
• C. Osmosis
• D. Active Transport

Answer: (A)

Filtration is the movement of water and small solutes across a membrane driven by a pressure difference, typically hydrostatic pressure. The pressure pushes fluid through pores in the membrane, so water and dissolved particles pass through while larger molecules are retained. This is why you see it described in places like capillary exchange and the kidney’s filtration process.

Diffusion moves substances from an area of higher concentration to one of lower concentration, not because of pressure differences. Osmosis specifically describes water moving across a semipermeable membrane to balance solute concentrations. Active transport, on the other hand, uses cellular energy to move substances against their concentration or electrochemical gradient.