**Core Concept**
Phospholipids are a class of lipids that are crucial components of cell membranes, serving as the primary structural and functional units. They are composed of a glycerol backbone, two fatty acid chains, and a phosphate group linked to a polar head group. This unique composition enables phospholipids to form lipid bilayers, which are essential for maintaining cellular integrity and facilitating cell signaling.

**Why the Correct Answer is Right**
The correct answer will reflect the standard composition of a phospholipid molecule. Phospholipids consist of a glycerol backbone, two fatty acid chains (also known as acyl chains), and a phosphate group linked to a polar head group, typically choline, ethanolamine, or serine. This unique molecular structure allows phospholipids to interact with water and other polar molecules, while also forming non-polar tails that interact with each other, thereby creating a lipid bilayer.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately reflect the composition of a phospholipid. Phospholipids do not contain glycerol as a separate entity but rather as a backbone.
**Option B:** This option is incorrect because it is incomplete. Phospholipids consist of more than just a phosphate group and a glycerol backbone.
**Option C:** This option is incorrect because it is overly simplistic. Phospholipids are more complex molecules than just a fatty acid and a phosphate group.

**Clinical Pearl / High-Yield Fact**
Phospholipids play a crucial role in maintaining cellular integrity and facilitating cell signaling. They are also important components of lung surfactant, which reduces surface tension in the lungs and facilitates breathing.

**Correct Answer: D. Glycerol backbone, two fatty acid chains, and a phosphate group linked to a polar head group.**