NEET BIOLOGY

Detailed explanation-1: -Plasma membranes must allow certain substances to enter and leave a cell, while preventing harmful material from entering and essential material from leaving. In other words, plasma membranes are selectively permeable-they allow some substances through but not others.

Detailed explanation-2: -They are semi-permeable, which means that some molecules can diffuse across the lipid bilayer but others cannot. Small hydrophobic molecules and gases like oxygen and carbon dioxide cross membranes rapidly.

Detailed explanation-3: -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-4: -A membrane which allows certain substances to pass through it, but not others is called a selectively permeable membrane.

Detailed explanation-5: -The answer is proteins. Proteins dot the surface of the bilayer, floating like rafts. Some of these proteins have channels, or doors between the cell and the environment. The channels let larger things that are hydrophilic and normally couldn’t pass through the membrane into the cell.