<P> Organic compounds may be classified in a variety of ways . One major distinction is between natural and synthetic compounds . Organic compounds can also be classified or subdivided by the presence of heteroatoms, e.g., organometallic compounds, which feature bonds between carbon and a metal, and organophosphorus compounds, which feature bonds between carbon and a phosphorus . </P> <P> Another distinction, based on the size of organic compounds, distinguishes between small molecules and polymers . </P> <P> Natural compounds refer to those that are produced by plants or animals . Many of these are still extracted from natural sources because they would be more expensive to produce artificially . Examples include most sugars, some alkaloids and terpenoids, certain nutrients such as vitamin B, and, in general, those natural products with large or stereoisometrically complicated molecules present in reasonable concentrations in living organisms . </P> <P> Further compounds of prime importance in biochemistry are antigens, carbohydrates, enzymes, hormones, lipids and fatty acids, neurotransmitters, nucleic acids, proteins, peptides and amino acids, lectins, vitamins, and fats and oils . </P>

Which one of the following is not a difference between organic and inorganic compounds