Question

Nitrogen gas returns to the atmosphere by the action of __________
A. Nitrogen fixing
B. Denitrifying bacteria
C. Nitrifying bacteria
D Nitrate fertilizers

Answer 1

Hint: The process of denitrification occurs as a part of the nitrogen cycle. The action of denitrifying bacteria results in the formation of atmospheric nitrogen.

Complete answer:
A diverse bacterial group encompassing different types of phyla causes denitrification. This group of bacteria is known as Denitrifying bacteria. Denitrifying bacteria take part in the nitrogen cycle as one of the nitrifying agents along with the denitrifying archaebacteria and denitrifying fungi.

All these denitrifying agents perform the process known as Denitrification in which they cause the reduction of nitrates into free nitrogen. This free nitrogen returns to the environment as atmospheric nitrogen. The process of denitrification is very important in nitrogen recycling for factors like health of soil, growth of plants and microbes, and also health of animals.
The action of denitrifying bacteria can also have adverse effects on the environment such as global warming. Denitrifying bacteria results in removal of nitrate which decreases fertility of soil thus, reducing the agricultural yield and productivity.
Some of the examples of denitrifying bacteria are thiobacillus species ,pseudomonas, etc. All these denitrifying bacteria are anaerobic and they are found in the areas where accumulation of water occurs such as in swampy soil. Denitrifying bacteria constitute about 10-15%of the total bacterial population present in water and soil.

So, the correct answer is B.

Note: Denitrification can also occur in the presence of oxygen where nitrate gets converted into gaseous nitrogen. This process of formation of gaseous nitrogen is called aerobic denitrification.