Carbohydrates are macromolecules composed of carbon, hydrogen and oxygen. Biologists are interested in carbohydrates because they serve as energy storage and as structural frameworks within cells. Simple carbohydrates consist of only 1 or 2 monomers, or monosaccharide's, while complex carbohydrates, or polysaccharides, are chains of monomers. Some types of carbohydrates are sugars, starches and cellulose. Plants manufacture carbohydrates through photosynthesis.