Question

Study the given biogeochemical cycle and identify the steps (i) and (ii)

A) (i) Ammonification (ii) Denitrification
B) (i) Denitrification (ii) Ammonification
C) (i) Nitrification (ii) Ammonification
D) (i) Ammonification (ii) Nitrification

Answer 1

Hint: Biogeochemical cycle – Movement of nutrients and other elements between biotic and abiotic factors is called biogeochemical cycle.
Biogeochemical cycles are of two types –
1. Geneous cycles – carbon, oxygen, nitrogen and water cycles.
2. Sedimentary cycles – sulphur, phosphorus, rock cycles etc.

Complete Answer:
Nitrogen cycle has following steps –
(i) Nitrogen fixation
(ii) Nitrification
(iii) Assimilation
(iv) Ammonification
(v) Denitrification
(i) Nitrogen fixation – Atmospheric ${N_2}$ is available in inert form, is converted into the usable form – ammonia $(N{H_3})$.
(ii) Nitrification – Ammonia is converted into nitrites and nitrates as ammonia is toxic for plants so it has to be converted to nitrite by bacteria Nitrosomonas /Nitrococcus.
$2N{H_3} + 3{O_2}\; \to \;2NO_2^ - + 2{H^ + } + 2{H_2}O$.
- The nitrite is further oxidised to nitrate by nitrobacter bacteria.
$2NO_2^ - + {O_2}\; \to \;2NO_3^ - $.
- These steps are called nitrification
(iii) Assimilation – Plants take nitrogen compounds in the form of nitrite and nitrates are used by plants in protein formation. This is called assimilation.
(iv) Ammonification – Decomposition of organic nitrogen of dead plants and animals into ammonia is called ammonification.
(v) Denitrification – Nitrogenous compound i.e. nitrates are converted back to Nitrogen $({N_2})$. Pseudomonas and Thiobacillus.

The correct option is A.

Note: $({N_2})$ cycle helps in synthesis of chlorophyll, Nitrogen is an important cell component and helps in the formation of other important compounds.