Within a cell membrane, which component attaches directly to the lipid bilayer?

• A. Phospholipids
• B. Carbohydrates
• C. Proteins
• D. Nucleic acids

Answer: (A)

The key idea is that the membrane’s structure is built by phospholipid molecules forming the lipid bilayer. Phospholipids have a hydrophobic tail region and a hydrophilic head, so they arrange themselves with tails inward and heads outward, creating the continuous bilayer that directly makes up the membrane. Carbohydrates are typically attached to membrane proteins or lipids on the surface as glycoproteins or glycolipids and extend outward from the bilayer, but they don’t form the bilayer itself. Nucleic acids aren’t membrane components. While proteins can associate with or span the membrane, the direct component that attaches to and constitutes the lipid bilayer is the phospholipid.