Question

How many of the following are the symbiotic nitrogen fixing micro-organisms?
Rhizobium, Anabaena, Frankia, Azotobacter, Nostoc, Clostridium, Beijerinckia, Klebsiella

• A. 2
• B. 3
• C. 4
• D. 5

Hint:

Easy grouping: Symbiotic = Rhizobium, Frankia, Anabaena, Nostoc
Free-living = Azotobacter, Clostridium, Beijerinckia, Klebsiella

Answer 1

The Correct Option is C

Concept: Nitrogen-fixing microorganisms can be classified into symbiotic and free-living types.
• Symbiotic nitrogen fixers: Live in association with plants
• Free-living nitrogen fixers: Exist independently in soil or water

Step 1: Identify symbiotic organisms.
• Rhizobium: Symbiotic (root nodules of legumes)
• Anabaena: Symbiotic (with Azolla)
• Frankia: Symbiotic (with non-leguminous plants)
• Nostoc: Symbiotic (with some plants like Cycas)

Step 2: Identify free-living organisms.
• Azotobacter: Free-living
• Clostridium: Free-living
• Beijerinckia: Free-living
• Klebsiella: Free-living

Step 3: Count symbiotic organisms.
Total symbiotic = 4

Step 4: Conclusion.
Thus, four organisms in the list are symbiotic nitrogen fixers. Final Answer: Option (C)