Which of the following describes a semipermeable membrane's function in dialysis?

A semipermeable membrane's primary function in dialysis is to selectively allow the passage of certain molecules while restricting others based on their size and other characteristics. In this context, the correct answer accurately describes how the membrane works during dialysis: it permits small molecules, such as ions, glucose, and urea, to pass through while retaining larger molecules like proteins and cells within the compartment.

This selective permeability is fundamental to the dialysis process, which aims to remove waste products from the blood while preserving essential molecules. For example, in medical dialysis treatments for patients with kidney failure, the membrane enables toxins and waste products to be cleared from the blood, while crucial components like proteins remain in the bloodstream, thus maintaining proper physiological function.

The other options do not correctly characterize the semipermeable membrane's function in this process. It is essential to understand that the process of dialysis relies on the size-selective properties of the membrane to achieve its therapeutic goals.