Rocket Through the 2025 BONENT STAR Practice Exam – Shine as a Dialysis Dynamo!

A semipermeable membrane is characterized by having pores that allow certain substances to pass through while restricting others, typically based on size. This selective permeability is crucial in biological systems where the transport of specific ions and molecules is needed while preventing the passage of larger or unwanted entities.

For instance, in a cellular context, a semipermeable membrane enables the cell to maintain homeostasis by regulating the movement of water, ions, and nutrients in and out of the cell. This characteristic is fundamental to processes such as osmosis and diffusion, which rely on the membrane's selective nature to facilitate the proper balance of substances.

The other options do not accurately describe a semipermeable membrane: allowing all substances to pass describes a freely permeable membrane, impermeability to all compounds suggests a membrane that does not permit any substances to cross, and selectively absorbing only nutrients implies a process different from mere selective permeability. Thus, the statement regarding pores that restrict passage based on size correctly identifies the essential features of a semipermeable membrane.