A membrane that allows certain molecules or ions to pass through it by diffusion while blocking others.
Here's why this definition is best:
* It emphasizes selectivity: Semipermeable membranes are not simply porous barriers. They actively choose which substances can pass through based on factors like size, charge, and chemical properties.
* It highlights diffusion: The movement of substances across a semipermeable membrane is primarily driven by diffusion, the natural tendency of molecules to move from an area of high concentration to an area of low concentration.
* It's concise and clear: The definition is straightforward and easily understood, avoiding unnecessary technical jargon.
Other definitions may include:
* A membrane that allows the passage of some molecules but not others.
* A membrane that selectively filters molecules based on size, charge, or other properties.
All of these definitions are essentially correct, but the first one is the most comprehensive and accurate.