Which lipid class is a major component of cell membranes?

• A. Triglycerides
• B. Phospholipids
• C. Carotenoids
• D. Steroids

Answer: (B)

Membranes are built from phospholipid bilayers because phospholipids have a hydrophilic head and hydrophobic tails that drive them to arrange into a bilayer in water. This amphipathic arrangement creates a stable hydrophobic interior and a hydrophilic surface, forming a flexible barrier and a scaffold for membrane proteins. Triglycerides store energy and don’t form membranes; carotenoids are pigments/antioxidants not the main structural component; steroids like cholesterol reside in the membrane and modulate fluidity, but they do not make up the majority of the lipid content. So, phospholipids are the major lipid class in cell membranes due to their bilayer-forming, amphipathic nature.