Question

The given figure shows the nitrogen cycle. Match the following table according to the given figure and select the correct option.

	Bacteria		Letters
(a)	Able to form nodules with plants	(i)	R
(b)	Able to denitrify	(ii)	Q
(c)	Able to nitrify	(iii)	S
(d)	Able to use ammonium as energy source	(iv)	T
(e)	Able to fix nitrogen from air	(v)	P

• A. (a)- (iv), b- (v), (c)- (i)/(ii), (d)- (i), (e)- (ii)/(v)
• B. (a)- (v) ,(b)- (iv), (c)- (iii), (d)- (iv), (e)- (v)
• C. (a)- (v), (b)- (iii), (c)- (i), (d)- (iv), (e)- (ii)
• D. (a)- (v), (b)- (iv), (c)- (i)/(iii), (d)- (i), (e)- (ii)/(v)

Answer 1

Answer: (D)

• Rhizobia (P) are soil bacteria that fix nitrogen (diazotrophs) after becoming established inside the root nodules of legumes (Fabaceae).
• A group of bacteria that reduces nitrates or nitrites to nitrogen-containing gases are called denitrifying bacteria (T).
• They are heterotrophic facultative anaerobic bacteria. Examples include - Thiobacillus denitrificans, Micrococcus denitrificans, Paracoccus denitrificans and Pseudomonas.

Nitrifying bacteria (S) are chemoautotrophic or chemolithotrophs which oxidizes nitrite to nitrate. Examples include - Nitrosomonas, Nitrosococcus, Nitrobacter, Nitrococcus.

Anaerobic ammonia-oxidizing (anammox) bacteria (R) are able to oxidize ammonia and reduce nitrite to produce N2 gas. Rhizobia (P) or Clostridium or Azotobacterare (Q) soil bacteria can fix nitrogen from air.