Plasma membrane composition The eukaryotic cell membrane is primarily composed of which class of biomolecules forming a bilayer?

Introduction / Context:
The fluid mosaic model describes biological membranes as dynamic bilayers of amphipathic lipids with embedded proteins and carbohydrates. Recognizing the major structural component of the bilayer is essential for understanding transport, signaling, membrane potential, and drug permeability in cells and organelles.

Given Data / Assumptions:

• Question asks for the primary class forming the bilayer scaffold.
• We are discussing plasma membranes of eukaryotic cells.
• Other biomolecules may be present but are not the main bilayer former.

Concept / Approach:
Phospholipids are amphipathic molecules with hydrophilic head groups and hydrophobic fatty acyl tails. In water, they self-assemble into bilayers where tails face inward and head groups face the aqueous phases. Proteins, cholesterol, and glycolipids are interspersed, but the bilayer itself is made of phospholipids (and related glycerophospholipids and sphingolipids).

Step-by-Step Solution:

Verification / Alternative check:
Biophysical measurements (X-ray scattering, cryo-EM) and biochemical fractionation show membranes enriched in phospholipids; detergents extract integral membrane proteins embedded within this lipid matrix.

Why Other Options Are Wrong:

• Lipoproteins: plasma particles for lipid transport; not membrane scaffolds.
• Cellulose: plant cell wall polysaccharide, external to the plasma membrane.
• Phosphoproteins: proteins with phosphate modifications; do not form bilayers.
• Glycogen: storage polysaccharide in cytosol, not a membrane constituent.

Common Pitfalls:
Confusing membrane proteins (abundant and critical) with the bilayer matrix. Proteins are embedded in or associated with the bilayer, but phospholipids create the sheet itself.

Final Answer:
Phospholipids