1. (Biochemistry) the sum total of the chemical processes that occur in living organisms, resulting in growth, production of energy, elimination of waste material, etc. 2. (Biochemistry) the sum total of the chemical processes affecting a particular substance in the body: carbohydrate metabolism; iodine metabolism.
It is found only in cultivation, where it is the most commonly grown of all plants in the Nicotiana genus, and its leaves are commercially grown in many countries to be processed into tobacco.It grows to heights between 1 to 2 metres.he concentration of nicotine increases with the age of the plant. Tobacco leaves contain 2 to 8% nicotine combined as malate or citrate. The distribution of the nicotine in the mature plant is widely variable: 64% of the total nicotine exists in the leaves, 18% in the stem, 13% in the root, and 5% in the flowers.
History of Tobacco. Tobacco has a long history in the Americas. The Mayan Indians of Mexico carved drawings in stone showing tobacco use. These drawings date back to somewhere between 600 to 900 A.D. Tobacco was grown by American Indians before the Europeans came from England, Spain, France, and Italy to North America. Native Americans smoked tobacco through a pipe for special religious and medical purposes. They did not smoke every day. Tobacco was the first crop grown for money in North America. In 1612 the settlers of the first American colony in Jamestown, Virginia grew tobacco as a cash crop.