A lab technician is given three test tubes: one contains pure oil mixed with water, one contains a solution of phospholipids and water, and one contains pure cholesterol crystals in water. After centrifugation, which patterns of separation or assembly will you expect and why?

• A. Oil + water will form two distinct immiscible layers with oil floating; phospholipids in water will self-assemble into micelles or bilayers depending on concentration (forming dispersed particles rather than a separate bulk layer); cholesterol crystals will largely remain insoluble and may form sediment or small aggregates due to its largely hydrophobic nature with minimal polar headgroups.
• B. Oil will form micelles identical to phospholipids at any concentration; the cholesterol will act as a surfactant and prevent any phase separation in all tubes, producing a single phase.
• C. Oil will immediately polymerize into a gel that binds water molecules; phospholipids will form crystalline salts with water at room temperature; cholesterol will segregate into the air phase above the solution due to its low density.
• D. Oil will dissolve uniformly because stirring negates hydrophobic effects; phospholipids will form a single homogeneous solution identical to water; cholesterol will chemically react with water to form soluble ions and disappear after centrifugation.

Answer: (A)