AP BIOLOGY

Detailed explanation-1: -Osmosis and Semipermeable Membranes Semipermeable membranes, also termed selectively permeable membranes or partially permeable membranes, allow certain molecules or ions to pass through by diffusion.

Detailed explanation-2: -Cell membranes serve as barriers and gatekeepers. 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: -The plasma membrane is known as semi-permeable because it regulates the movement of substances in and out of the cell. This means that the plasma membrane allows the entry of only some substances and prevents the movement of some other materials.

Detailed explanation-4: -The correct answer is (C) A flexible lipid double layer. The cell membrane is often referred to as a “fluid mosaic, ” a flexible structure containing phospholipids as well as some proteins and other important molecules.