EVERYDAY SCIENCE

Detailed explanation-1: -A membrane which allows certain substances to pass through it, but not others is called a selectively permeable membrane.

Detailed explanation-2: -The membrane is selectively permeable because substances do not cross it indiscriminately. Some molecules, such as hydrocarbons and oxygen can cross the membrane. Many large molecules (such as glucose and other sugars) cannot. Water can pass through between the lipids.

Detailed explanation-3: -Selective permeability is mediated by special proteins that traverse the cellular membrane. They are involved in the movement of ions and small molecules as well as large polymers such as RNA and proteins.

Detailed explanation-4: -A membrane that has selective permeability allows only substances meeting certain criteria to pass through it unaided. In the case of the cell membrane, only relatively small, nonpolar materials can move through the lipid bilayer at biologically relevant rates (remember, the lipid tails of the membrane are nonpolar).

Detailed explanation-5: -The cell membrane is selectively permeable, meaning it only lets certain things in and out of the cell.