Which statement best describes the structure of the cell (plasma) membrane?

• A. A lipid bilayer where hydrophilic heads face inward and hydrophobic tails face the aqueous environments
• B. A fluid mosaic: a phospholipid bilayer with embedded proteins, where hydrophobic tails face inward and hydrophilic heads face outward
• C. A rigid cellulose wall that provides most of the cell’s selective permeability
• D. A single layer of phospholipids with proteins attached only on the cytosolic surface

Answer: (B)

Verified step by step guidance

1. Recall the basic structure of the cell (plasma) membrane, which is primarily composed of a phospholipid bilayer.
2. Understand that phospholipids have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
3. Recognize that in the bilayer, the hydrophilic heads face the aqueous environments both outside and inside the cell, while the hydrophobic tails face inward, away from water.
4. Know that the membrane is described as a 'fluid mosaic' because it contains various proteins embedded within or attached to the bilayer, allowing fluidity and functional diversity.
5. Eliminate incorrect options: the membrane is not a rigid cellulose wall (which is found in plant cell walls), nor is it a single phospholipid layer, and the orientation of heads and tails must be correct.