AP BIOLOGY

Detailed explanation-1: -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-2: -It is true that a membrane which allows only certain substances to pass through, but does not allow others to pass through it is called a selectively permeable membrane. For example, the plasma membrane of eukaryotic cells.

Detailed explanation-3: -Small uncharged molecules can diffuse freely through a phospholipid bilayer. However, the bilayer is impermeable to larger polar molecules (such as glucose and amino acids) and to ions.

Detailed explanation-4: -The cell membrane is semipermeable (or selectively permeable). It is made of a phospholipid bilayer, along with other various lipids, proteins, and carbohydrates.

Detailed explanation-5: -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).