Selectively Permeable Membrane


A selectively permeable membrane, also known as a semipermeable membrane, refers to a type of biological or synthetic barrier that allows the selective passage or transport of certain molecules or ions while restricting the movement of others. This unique characteristic is crucial for maintaining homeostasis and regulating the internal environment of cells and organisms.

Properties and Function:

1. Selective Transport: A selectively permeable membrane possesses the ability to discriminate between different types of molecules or ions, permitting only specific substances to pass through. This selectivity is determined by several factors, including size, charge, solubility, and concentration gradient.

2. Diffusion and Osmosis: One of the key processes enabled by a selectively permeable membrane is diffusion, which involves the spontaneous movement of molecules from an area of higher concentration to an area of lower concentration. Osmosis, on the other hand, refers specifically to the diffusion of water molecules across a selectively permeable membrane.

3. Transport Proteins: Selectively permeable membranes often contain highly specialized proteins, such as channel proteins and carrier proteins, that aid in the facilitated transport of specific molecules or ions across the membrane. These proteins possess specific binding sites and undergo conformational changes to facilitate molecule transport.

4. Regulation and Homeostasis: By regulating the movement of substances into and out of cells or organelles, selectively permeable membranes play a crucial role in maintaining internal balance or homeostasis. They allow cells to control their internal environment by selectively importing essential substances and exporting waste products or toxic substances.

5. Cellular Communication: Selectively permeable membranes are essential for cellular communication, as they enable the passage of signaling molecules, such as hormones, neurotransmitters, and growth factors, across the membrane. This facilitates intercellular communication and coordination of cellular activities.


– Cell Membrane: The plasma membrane that encloses cells is a prime example of a selectively permeable membrane. It permits the passage of small non-polar molecules (e.g., oxygen and carbon dioxide) via simple diffusion, while relying on transport proteins for the selective transport of larger molecules and ions.

– Blood Capillaries: The walls of blood capillaries are also selectively permeable, allowing essential molecules like oxygen and nutrients to enter tissues while restricting the passage of proteins and larger particles.

– Dialysis Tubing: In laboratory settings, dialysis tubing is commonly used as a semipermeable membrane to separate small molecular solutes from larger ones based on their ability to diffuse across the membrane.