All other life on earth depends on these. These are called procaryotes and achieve this chemical change by the use of an enzyme called nitrogenase. An enzyme is a protein produced in a cell and aids a specific chemical reaction to take place. Blue-green algae also require cobalt as a micronutrient, i.e. a trace element. Plants may contain nitrifying bacteria in their tissues from which they get usable nitrogenous chemicals or absorb the chemicals discharged into the soil from other decomposing dead plants.
Acacias usually obtain usable nitrogen in both ways.
Root nodules, an anatomical modification of the plant root, caused by these specific bacteria, are the result of a symbiotic association between the plant and bacteria. The bacteria take in atmospheric nitrogen and by use of an enzyme make it available to the host plant. The host makes sugars available to the bacteria in return. Sugars are high energy carbon compounds used in cell growth and function. The bacteria attach to the hair on the concave side.