What is the Difference Between Semipermeable and Selectively Permeable Membrane?

The main difference between semipermeable and selectively permeable membranes lies in the type of molecules they allow to pass through them:

• Semipermeable membranes allow the movement of solvent molecules through them but prevent the movement of solute particles. They permit the passage of only some particles, depending on their size. These membranes act as an ideal partition between two osmotically active solutions or between a solution and a solute, and they do not allow solute particles to pass through. Semipermeable membranes are generally not present in biological systems.
• Selectively permeable membranes are an extension of semipermeable membranes, allowing the passage of both solvent and selected solutes. These membranes permit the entry of both solvent and, to a selected extent, solutes. They do not allow solute particles to pass through, but they allow selected solutes to pass through to a limited extent. Selectively permeable membranes are present in biological systems and serve various functions, such as maintaining turgidity while retaining the ability to absorb solutes.

In summary, semipermeable membranes allow only solvent molecules to pass and block solute particles, while selectively permeable membranes allow both solvent and selected solute particles to pass through them.

Comparative Table: Semipermeable vs Selectively Permeable Membrane

Here is a table comparing the differences between semipermeable and selectively permeable membranes:

In summary, semipermeable membranes permit the entry of only one solvent and do not allow solutes to pass through, while selectively permeable membranes allow the entry of both solvents and selected solutes to a limited extent. Semipermeable membranes do not exist in biological systems, whereas almost all biological membranes are selectively permeable.