What does it mean for a membrane to be selectively permeable

Selective permeability of membranes means the cell membrane allows certain substances through while others cannot.  

Cell membrane allows selective movement of materials in and out of the cell.

Further Explanation A cell membrane is an organelle whose role is to protect the cell from the outer environment. The membrane contains phospholipid bi-layer and proteins that are embedded in the bi-layer. Cell membranes contain receptors and channels that only allow specific molecules to pass through the cell membrane.  Selective permeability  Selective permeability is one of the properties of cell membranes, such that the cell membrane only allow certain materials to pass through while others cannot. Movement of substances across the cell membrane may either be passive or active. Passive transport of molecules across cell membranes occurs without energy input while active transport of substances occurs with energy input in the form of ATP.

Examples of materials than can diffuse freely through the cell membrane

Small uncharged molecules  Small non polar molecules such as CO2 and O2  Small uncharged polar molecules such as H2O

Examples of materials that cannot diffuse freely through the membrane

Larger uncharged polar molecules such as glucose Small and larger charged molecules such as ions cannot diffuse freely through the membrane. However, ions and most polar molecules such as glucose that cannot diffuse through the cell membrane freely, can pass across the membrane through transporters such as trans-membrane proteins.  

Keywords: Selective permeability, transport, cell membrane

Learn more about: Selective permeability: Active and passive transport: Cellular transport:

Level: High school  

Subject: Biology  

Topic: Cellular transport and physiological processes

Sub-topic: Role of cell membrane in transport