Substance whose molecules contain one or more (often many more) carbon atoms (excluding carbonates, cyanides, carbides, and a few others; see inorganic compound). Until 1828 (see urea), scientists believed that organic compounds could be formed only by life processes (hence the name). Since carbon has a far greater tendency to form molecular chains and rings than do other elements, its compounds are vastly more numerous (many millions have been described) than all others known. Living organisms consist mostly of water and organic compounds: proteins, carbohydrates, fats, nucleic acids, hormones, vitamins, and a host of others. Natural and synthetic fibres and most fuels, drugs, and plastics are organic. Hydrocarbons contain only carbon and hydrogen; organic compounds with other functional groups include carboxylic acids, alcohols, aldehydes, ketones, phenols, ethers, esters, and other, more complex, molecules, including heterocyclic compounds, isoprenoids, and amino acids.