A group of unsaturated hydrocarbons present in plants (see essential oil). Terpenes consist of isoprene units, CH2:C(CH3)CH:CH2. Monoterpenes have two units, C10H16, sesquiterpenes three units, C15H24, diterpenes four units, C20H32, etc. Terpenoids, which are derivatives of terpenes, include abscisic acid and gibberellin (plant growth substances) and the carotenoid and chlorophyll pigments.
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