If you pull up a soybean or bean plant and shake off the dirt, you might see odd swellings or bumps, like rheumatic finger joints, on its roots. Inside the cool, soil-covered bumps are bacteria that are making nitrogen with the help of an enzyme, something chemical factories can do only with the help of a catalyst and at high temperature and pressure. The bacteria, typically members of the genus Rhizobia, break the strong triple bond between the nitrogen molecules in the air and repackage the nitrogen atoms in chemical compounds the plant can use. In return, the plant supplies the bacteria with the energy needed to split the nitrogen molecules in the form of sugar.
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