**Question:** At low concentrations, phospholipids form:-

A. Micelles
B. Liposomes
C. Bilayers
D. Bacterial cell wall

**Core Concept:** Phospholipids are amphipathic molecules found in cell membranes and play a crucial role in maintaining membrane integrity and function. They consist of a hydrophilic head group and two hydrophobic tails.

**Why the Correct Answer is Right:** When phospholipids are present at low concentrations, they spontaneously arrange themselves into a structure that minimizes the contact between the hydrophobic tails and the surrounding aqueous environment. In this case, phospholipids form bilayers.

**Why Each Wrong Option is Incorrect:**

A. Micelles are formed when lipophilic substances, such as fats and oils, aggregate in the presence of an excess of water, not phospholipids.
B. Liposomes are vesicles formed by the self-assembly of phospholipids, not at low concentrations.
D. Bacterial cell walls are composed of peptidoglycan, not phospholipids.

**Clinical Pearl / High-Yield Fact:** Bilayers are essential components of biological membranes, representing the foundation for various membrane functions, including selective permeability, signal transduction, and protein interactions.

**Correct Answer:** C. Bilayers