Scientist studying an image of nodules containing bacteria on the roots of a leguminous plant (family Fabaceae). The plant and the bacteria have a symbiotic relationship. The bacteria convert (fix) atmospheric nitrogen in the soil to ammonia. The plant cannot carry out this process itself, but it is vital for the production of amino acids, the building blocks of proteins. In return the plant passes carbohydrates produced during photosynthesis to the bacteria for use as an energy source.