What molecule is primarily used for energy storage in living organisms?

Lipids are primarily used for energy storage in living organisms due to their high energy density and structural properties. They are composed of long chains of carbon and hydrogen atoms, which can store a significant amount of energy in their chemical bonds. When the body requires energy, lipids such as triglycerides can be broken down through metabolic processes to release energy more efficiently than carbohydrates and proteins can.

In addition to energy storage, lipids play crucial roles in forming cell membranes and serving as signaling molecules, which underscores their importance in biological systems. While carbohydrates can also serve as an energy source, they are typically used for short-term energy storage and are more readily metabolized than lipids. Proteins, although they can be used for energy, primarily serve structural and functional roles in the body. Nucleic acids are involved in storing and transmitting genetic information, but they do not function in energy storage. Thus, lipids are the most efficient molecules for energy storage in living organisms.