The picture shows a piece of pork. The white layer that is on top of red muscle is fat, triglycerides, or triacylglycerol. Fat is used by animals to as a lipid for energy storage. For plants, oil is used. Some people like to fry the piece of pork with the fat facing the pan so when spices are sprinkled, it will go through the meat to the fat since fat has the power to attract the specific material toward it. Fat is composed of two materials: glycerol (an alcohol with three carbons) and fatty acids. The fatty acids are usually 16-18 carbon atoms long. The glycerol is connected to the fatty acid by an ester linkage. Saturated fats are usually solid at room temperature and have unbent fatty acid molecules while unsaturated fats are liquid at room temperature and have bent hydrophobic tails. The major difference between saturated and unsaturated fat is saturated fat is saturated with hydrogen. Fats are mainly for energy storage. In fact, one gram of fat stores twice as much energy as one gram of a polysaccharide, such as starch.