1. The nonsymbiotic bacteria which fix nitrogen live in the soil independently are

A. Azotobacter
B. Clostridium
C. considerably less important in comparison to the symbiotic bacteria
D. all of the above

2.  Nitrogen fixation by the microorganisms can be detected by adopting the approach of

A. demonstrating growth in a nitrogen free medium
B. cultivating the microorganisms in the presence of nitrogen labeled with isotropic nitrogen
C. measuring¹⁵N₂ by mass spectrometer
D. all of the above

3. Which of the following is not the biofertilizer producing bacteria?

A. Nostoc
B. Anabaena
C. Both (a) and (b)
D. Clostridium

4. Which of the following is capable of oxidizing sulfur to sulfates?

A. Thiobacillus thiooxidans
B. Desulfotomaculum
C. Rhodospirillum
D. Rhodomicrobium

5. Most soil protozoa are flagellates or amoebas, having their dominant mode of nitrogen as

A. ingestion of bacteria
B. ingestion of mold
C. ingestion of fungi
D. all of these