A carbohydrate is a type of organic compound that is primarily composed of carbon, hydrogen, and oxygen. Carbohydrates are an essential structural component of living cells and are an important source of energy for both animals and humans. They include simple sugars, which consist of just one or two sugar molecules, as well as more complex carbohydrates, which can contain hundreds of sugar molecules. Carbohydrates are classified based on the number of sugar molecules they contain (monosaccharides, disaccharides, oligosaccharides, and polysaccharides).