A semipermeable membrane is a porous barrier that:

A semipermeable membrane is a porous barrier that:

• A. Allows for only certain sized particles to cross
• B. Allows all particles to cross
• C. Blocks all particles
• D. Only water crosses

Answer: (A)

A semipermeable membrane is designed with pores that allow passage based on particle size. This selectivity means smaller particles can cross while larger ones are blocked, so the membrane effectively lets only certain sized particles through. In hemodialysis, this lets small waste molecules move from blood into the dialysate while keeping larger proteins and cells in the blood. The other statements don’t fit because not all particles cross, not everything is blocked, and saying only water crosses is too narrow a description for a semipermeable membrane.

A semipermeable membrane is designed with pores that allow passage based on particle size. This selectivity means smaller particles can cross while larger ones are blocked, so the membrane effectively lets only certain sized particles through. In hemodialysis, this lets small waste molecules move from blood into the dialysate while keeping larger proteins and cells in the blood. The other statements don’t fit because not all particles cross, not everything is blocked, and saying only water crosses is too narrow a description for a semipermeable membrane.