Ncert Exercises & Solutions

Reactions carried out by N₂ fixing microbes include

(i) $2 {NH}_{3}$ $2 {NH}_{3}$ $+$ $+$ $3 O_{2}$ $3 O_{2}$ $\to$ $\to$ $2 {NO}_{2}^{-}$ $2 {NO}_{2}^{-}$ $+$ $+$ $2 H^{+}$ $2 H^{+}$ $+$ $+$ $2 H_{2} O$ $2 H_{2} O$

(ii) $2 {NO}_{2}$ $2 {NO}_{2}$ $+$ $+$ $O_{2}$ $O_{2}$ $\to$ $\to$ $2 {NO}_{3}$ $2 {NO}_{3}$

Which of the following statements about these equations is not true?

1.	Step (i) is carried out by Nitrosomonas or Nitrococcus
2.	Step (ii) is carried out by Nitrobacter
3.	Both steps (i) and (ii) can be called nitrification
4.	Bacteria carrying out these steps are usually photoautotrophs

(d) Option (d) is not true because the bacteria involved in the process are not photoautotrophs but are chemoautotrophs. These bacteria oxidise inorganic substances like NH₃ and NO₂ and use the released energy hence are called chemoautotrophs.

Simultaneously, they help in the conversion of ammonia (NH₃) to absorbable form (NO₂^-and NO₃^- ) of nitrogen.

Page 201, XI NCERT

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