A Level Biology Practice Exam

What component do phospholipids contain that differentiates them from triglycerides?

1. A second fatty acid

2. A phosphate group

3. A glycerol backbone

4. A nucleic base

The correct answer is: A phosphate group

Phospholipids contain a phosphate group, which is the key component that differentiates them from triglycerides. In phospholipids, this phosphate group is attached to one of the fatty acid chains, and it contributes to the molecule's amphipathic nature—having both hydrophilic (water-attracting) and hydrophobic (water-repelling) properties. This unique structure allows phospholipids to form bilayers, which are essential for the formation of cell membranes, creating a barrier that separates the internal environment of the cell from the external surroundings. In contrast, triglycerides are composed of a glycerol backbone and three fatty acid chains but do not contain a phosphate group. Therefore, the presence of the phosphate group in phospholipids is what sets them apart structurally and functionally from triglycerides. This distinction is vital for understanding cellular structures and functions in biology.