Lipids are essential biological molecules that perform multiple functions in living organisms. They are the primary components of cell membranes, forming the phospholipid bilayer that controls the movement of substances in and out of the cell. Lipids also serve as an efficient energy storage system, providing more than twice the energy per gram compared to carbohydrates and proteins. Additionally, they act as insulators, helping organisms maintain body temperature. Lipids are also precursors of hormones such as steroids (e.g., estrogen, testosterone) and fat-soluble vitamins like A, D, E, and K, which are vital for various metabolic and physiological processes.