NEET Biology Biological Classification Based Practice Questions & Answers with Viewers Discussion and Detailed Explanation

Answer: (b)

A few free living bacteria are able to pick up dinitrogen from the soil atmosphere and convert it into organic nitrogenous materials like amino acids, e.g., Azotobacter. Symbiotic nitrogen fixing bacteria of the genus Rhizobium occur in the root nodules of a number of legumes. Root nodules containing symbiotic nitrogen bacteria also occur in Casuarina and Alnus. Leaf nodules containing such bacteria are found in Ardisia. Many cyanobacteria (blue-green algae) fix atmospheric nitrogen due to presence of heterocysts.