Which function pertains to a lipid molecule?

A lipid molecule primarily is used as a storage mechanism for the cell as ATP doesn't last very long before degenerating.

The lipid molecules like the sterols, glycerides, and phospholipids play a vital role in the various cellular processes. Some their roles are:

Energy storage and energy provision. The triacylglycerols are the primary energy storage molecules that are used to power the cells during fasting.Chemical messengers.Maintenance of temperature. The layers of fat under the skin help in providing insulation from cold outside.Formation of lipid layer and vesicles. The membranes of the cells are made up of lipid molecules. They protect the cells and separate the cellular environment from the external changing environment.Formation of cholesterol. Cholesterol help in maintaining the fluidity of the membranes.Role in inflammation