Question

Select the correct matches.
(a) Nitrosomonas- nitrite to nitrate
(b) Thiobacillus- denitrification
(c) Nostoc- free-living nitrogen fixer
(d) Azotobacter- anaerobic nitrogen fixer
A. a and b
B. b and c
C. a and c
D. c and d
E. b and d

Answer 1

Hint: These two bacteria are helpful in the metabolism of nitrogen. Both the microbes play the significant role in nitrogen cycle and biological nitrogen fixation respectively in the soil.

Complete Answer:
- Nitrogen is the most abundantly present element in the atmosphere that comprises about 78% of Earth's air.
- Apart from carbon,hydrogen and oxygen, nitrogen is the most prevalent element in living organisms and is a constituent of aminoacids, proteins, hormones, chlorophyll and many of the vitamins. Therefore it is necessary for converting atmospheric nitrogen into ammonia or other nitrogen containing compounds that are beneficial for the plants.
- For this various microorganisms play a significant role in the cycle.
- For example Thiobacillus and Pseudomonas are helpful in the process of denitrification. Similarly Anabaena and Nostoc free living nitrogen fixers that are responsible for nitrogen fixation.

The correct option is B i.e. b and c.

Additional information: Nitrosomonas and/or Nitrococcus is responsible for converting ammonia into the first oxidized product that is nitrite. Azotobacter and Beijernickia are the free living nitrogen-fixing aerobic microorganisms that are responsible for biological nitrogen fixation.

Note: Nitrogen is a limiting nutrient for both natural and agricultural ecosystems and is used as a fertilizer on the crop for the better yield of the crop because NPK (Nitrogen, phosphorus and potassium) are the three major element that is required by the plant but present in little amount in the soil. Some anaerobic bacteria that are responsible for nitrogen fixing are Rhodospirillum.
- Some plants have symbiotic biological nitrogen fixation association like Rhizobium, a rod shaped bacteria has symbiotic relationship with leguminous plants like sweet clover,sweet pea,lentils and garden pea etc.