In living organisms, lipids play the important roles of storing energy and ensuring proper cell membrane development. Lipids come in several different varieties, and exist in all locations throughout the bodies of humans and animals. They retain crucial supplies of fat and nutrients, which allows people and animals to survive for several days without eating food, if necessary.
In addition to humans and other animals, lipids exist in plants and microorganisms. They pack large amounts of energy, storing up to twice the amount of fat per gram as 1 gram of carbohydrate. Lipids come in several shapes and varieties, which in turn indicates their specific function. Triglycerides are among the most common lipids. These lipids from a combination of four molecules: three fatty molecules and one molecule of glycerol. These lipids exist in the cytoplasm of living organisms. They float freely, moving around as objects insoluble in water. Triglycerides exist in two primary forms, which are saturated and unsaturated. Steroids, which consist of four rings of molecules, exist as natural lipids too. They come in several common forms including cholesterol, vitamin D2, testosterone and estrogen. Glycolipids, or sugar chains, exist throughout human and animal bodies. They protect against disease and illness by boosting immune systems, while waxes, such as found in human ears and on bird wings, offers insulation and protection.