AP BIOLOGY

Detailed explanation-1: -Many heterotrophic bacteria live in the soil and fix significant levels of nitrogen without the direct interaction with other organisms. Examples of this type of nitrogen-fixing bacteria include species of Azotobacter, Bacillus, Clostridium, and Klebsiella.

Detailed explanation-2: -Nitrogen fixation is carried out naturally in soil by microorganisms termed diazotrophs that include bacteria, such as Azotobacter, and archaea. Some nitrogen-fixing bacteria have symbiotic relationships with plant groups, especially legumes.

Detailed explanation-3: -Natural nitrogen fixation is performed by a number of microorganisms, called diazothrops. Well-known examples of diazothrops are the Rhizobium bacteria, which can be found in the root nodules of higher plants (especially leguminous plants).

Detailed explanation-4: -Efficient biological nitrogen fixation requires close interactions between bacteria and the plant host. Plant growth promotion is the result of interactions between soil type, microbiota, and the host plant.