The process by which bacteria convert nitrogen in the atmosphere into a usable form for plants is called nitrogen fixation. This process primarily occurs in the root nodules of certain plants, like legumes, where bacteria like Rhizobium convert atmospheric nitrogen (N₂) into ammonia (NH₃). This ammonia can then be utilized by plants to synthesize essential amino acids and other organic compounds, thereby contributing to the nitrogen cycle. Without nitrogen fixation, plants would struggle to obtain this vital nutrient, significantly impacting ecosystems and food webs.