All plants require an adequate supply of inorganic nutrients, such as fixed nitrogen (usually in the form of ammonia or nitrate), for growth. A special group of flowering plants thus depends on close symbiotic relationships with nitrogen-fixing bacteria as a source of fixed nitrogen. The plant provides specialized root nodules as housing for its bacterial benefactors, which allows them to make use of energy-rich organic carbon compounds in return for the ammonia they generate from atmospheric nitrogen. Thus, both partners reap advantages from the relationship.