Chapter 20, Problem 1ACQ

Figure 20.12 Which of the following statements about the nitrogen cycle is false?

a. Ammonification converts organic nitrogenous matter from living organisms into ammonium $\left({\text{NH}}_{\text{4}}{}^{+}\right)$ .

b. Denitrification by bacteria converts nitrates $\left({\text{NO}}_{\text{3}}{}^{-}\right)$ to nitrogen gas $\left({\text{N}}_{\text{2}}\right)$ .

c. Nitrification by bacteria converts nitrates $\left({\text{NO}}_{\text{3}}{}^{-}\right)$ to nitrites $\left({\text{NO}}_{\text{2}}{}^{-}\right)$ .

d. Nitrogen fixing bacteria convert nitrogen gas $\left({\text{N}}_{\text{2}}\right)$ into organic compounds.

Summary Introduction

Introduction:

Nitrogen cycle is a biogeochemical cycle that involves the movement of nitrogen between environment and living organisms. The nitrogen in atmosphere is converted to usable form by bacteria and this process is known as nitrogen fixation.

Correct answer:

The correct answer is option (c).

Explanation of Solution

Explanation for the correct answer:

Option (c) is given as nitrification by bacteria converts nitrates (NO₃^-) to nitrates (NO₂^-), which is incorrect because nitrification is the process of conversion of ammonia intro nitrites and then to nitrates by bacteria. Hence, option (c) is the answer

Explanation for the incorrect options:

Option (a) is given as ammonification converts organic nitrogenous matter from living organisms into ammonia. The statement is correct because ammonia is made either from the excreta of the living organisms or the decomposition of dead plants and animals. Hence, option (a) is incorrect.

Option (b) is given as denitrification by bacteria converts nitrates to nitrogen gas. The statement is correct because certain bacteria such as Thiobacillusdenitrificans can convert nitrates to free nitrogen. Hence, option (b) is incorrect.

Option (d) is given as nitrogen fixing bacteria converts nitrogen gas into organic compounds. The statement is true because nitrogen fixation is the process by which atmospheric nitrogen is converted into nitrates, nitrites or ammonia that can easily be assimilated by plants. Hence, option (d) is incorrect.

Conclusion

Nitrogen fixation is the process by which atmospheric nitrogen is converted into organic compounds that can be used by plants. Nitrification is the process of conversion of ammonia into nitrates through nitrites.