Question

What is the correct order of nitrogen assimilation?

• A. $N _{2} \rightarrow NO _{2} \rightarrow NO _{3} \rightarrow NH _{2} OH \rightarrow NH _{3}$
• B. $N _{2} \rightarrow NO _{3} \rightarrow NO _{2} \rightarrow NH _{2} OH \rightarrow NH _{3}$
• C. $N _{2} \rightarrow NO _{2} \rightarrow NO _{3} \rightarrow NH _{3} \rightarrow NH _{2}OH$
• D. $N _{2} \rightarrow NO _{3} \rightarrow NO _{2} \rightarrow NH _{3} \rightarrow NH _{2} OH$

Answer 1

Answer: (D)

Nitrogen is the fourth most abundant element of living system. Its deficiency results in stunted growth and chlorosis in plants. Its regular supply is maintained through nitrogen cycle.
The process of nitrate reduction to ammonia is completed in two steps.
(i) First, the nitrate is reduced to nitrite by an enzyme called nitrate reductase.
$NO _{3}^{-}+ NADPH + H ^{+} \xrightarrow[FMN/FAD]{{\text { Nitrate reductase }}} NO^-_{2} + H_2O +NAD(P)^{+}$
(b) Nitrite ions are then reduced to ammonia by an enzyme called nitrite reductase.
$2NO _{2}^{-}+ 7NAD(P)H + 7H ^{+} \xrightarrow[\text{Ferredoxin}]{{\text { Nitrate reductase }}} 2NH_{3} + 4H_2O +7NAD(P)^{+}$
Thus, overall reaction is
$N _{2} \rightarrow NO _{3} \rightarrow NO _{2} \rightarrow NH _{3} \rightarrow NH _{2} OH$