A plant contains a great number of chemical compounds. The major compound in all plants is water. Thepercent of the plant's weight that is water varies greatly from one kind of plant to another, from less than 20% tomore than 90%. After the water isremoved, the bulk of the dry plant material consists of carbohydrate compoundscontaining the elements carbon, hydrogen, and oxygen. Using the energy of sunlight in a process calledphotosynthesis, plants make carbohydrates in their leaves. The carbon and oxygen in carbohydrates come fromcarbon dioxide, which the plant absorbs from the air, and the hydrogen comes from water absorbed both throughthe roots and through the leaves. About 90% of the weight of carbohydrates is carbon and oxygen. Therefore, aplant obtains around 90% of its dry weight from the air.
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