What is the key difference between a triglyceride and a phospholipid?

The key difference between a triglyceride and a phospholipid lies in their structure and function. Triglycerides consist of a glycerol molecule bonded to three fatty acids, serving primarily as a form of energy storage in the body. They are hydrophobic (water-repelling) and are stored in adipose tissue, providing a concentrated energy source.

In contrast, phospholipids are composed of a glycerol backbone, two fatty acid tails, and a phosphate group, which is often linked to other polar molecules. This unique structure makes phospholipids amphipathic; they contain both hydrophobic and hydrophilic regions. This characteristic is crucial because phospholipids form the fundamental building blocks of cell membranes, creating a bilayer that separates the interior of the cell from the external environment. This bilayer structure is essential for maintaining cellular integrity and facilitating cellular communication and transport.

Understanding these roles helps clarify why the correct answer emphasizes the distinct functions of triglycerides and phospholipids in biological systems.