What term describes the membrane structure formed by two layers of phospholipids?

• A. Membrane protein
• B. Phospholipid bilayer
• C. Glycoprotein
• D. Cholesterol layer

Answer: (B)

The membrane is built from phospholipid molecules arranged into a phospholipid bilayer. Each phospholipid has a water-loving head and a water-fearing tail, so in water they organize with heads facing outward toward the inside and outside of the cell and tails tucked inward. This creates a flexible, semi-permeable barrier that forms the fundamental structure of all cell membranes.

Membrane proteins are proteins embedded in or attached to this bilayer, performing transport and signaling roles. Glycoproteins are specific proteins with carbohydrate chains in the membrane, not the overall membrane structure. Cholesterol is a component within the bilayer that helps modulate fluidity, not a separate layer.