What is the major role of lipids in biological systems?

Lipids serve several crucial functions in biological systems, and one of their major roles is as a source of stored energy. They are particularly efficient because they contain long hydrocarbon chains, which, when metabolized, provide more energy per gram than carbohydrates or proteins. This high energy density makes lipids an ideal form of energy storage.

In addition to energy storage, lipids also contribute to the structure of cell membranes, acting as a barrier that regulates the movement of substances in and out of cells. While they are indeed involved in transporting molecules across membranes and can play a role in signaling and cellular communication, these are more auxiliary functions compared to their primary role in energy storage.

Overall, lipids are vital for energy reserves within an organism, particularly in terms of providing a long-lasting source of fuel compared to other macromolecules.