What is a primary function of phospholipids?

Phospholipids serve a crucial role as the building blocks of cell membranes, which is their primary function. They are composed of a hydrophilic (water-attracting) phosphate head and two hydrophobic (water-repelling) fatty acid tails. This unique structure allows phospholipids to arrange themselves into a bilayer, forming the fundamental structure of the cell membrane. The bilayer creates a semi-permeable barrier that not only protects the internal environment of the cell but also regulates the passage of substances in and out of the cell. This characteristic is vital for maintaining cellular integrity and facilitating communication with the external environment.

In contrast, while triglycerides are involved in energy storage, hormonal signaling pertains to different classes of lipids, and digestive enzymes are primarily proteins. Each of these has distinct functions that do not overlap with the structural role of phospholipids in biological membranes.