What defines a phospholipid?

A phospholipid is defined by its structure, which consists of a hydrophilic (water-attracting) head and two hydrophobic (water-repelling) tails. This unique composition is crucial for its role in biological membranes, such as the cell membrane. The hydrophilic head is typically composed of a phosphate group that interacts well with water, while the hydrophobic tails are made of fatty acid chains that do not interact favorably with water. This amphipathic nature allows phospholipids to form bilayers, creating a barrier that protects the interior of cells while regulating the movement of substances in and out of the cell. The structural properties of phospholipids enable cell membranes to maintain their integrity and function effectively in various environments.