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Important questions on Biogeochemical Cycles

Which one helps in absorption of phosphorus from soil by plants?

A

Frankia

B

Anabaena

C

Glomus

D

Rhizobium

View Answer

Frankia, Anabaena and Rhizobium are nitrogen-fixing bacteria that absorbs nitrogen from the soil. Glomus is a myccorhizal fungi. The fungal symbiont in these associations absorbs phosphorus from soil and passes it to the plant.
Thus, the correct answer is option (C). 

Consider the following prokaryotes:
Nitrobacter, E.coil, Lactobacillus, Frankia,Azospirillum,Streptomyces,Beijerinckia,Rhodopseudomonas,Rhizobium
How many of the above can fix atmospheric nitrogen?

A

Four

B

Six

C

Five

D

Seven

View Answer

How many organisms In the list given below are fixer autotrophs?
Azotobacter, Chromobum, Azospirillum, Rhodospirillum, Rhizobium, Nitrobacter, Aulosira, Nostoc, Osallatona

A

Three

B

Four

C

Five 

D

Six

View Answer

Nitrogen-fixing bacteria are capable of fixing atmospheric nitrogen to inorganic substances usable by plants. Example from the given list are Azetobactor, Azospirillum, Rhizobium, Nitrobactor and Nostoc.
So the correct answer is 'five'.

Nitrogen fixation is inhibited by oxygen. However, in aerobic nitrogen-fixing bacteria, nitrogen is fixed in the presence of oxygen. Nitrogenase in such organisms is protected by which one of the following mechanisms.

A

Channelizing oxygen to form ozone.

B

Removal of oxygen by metabolic activity.

C

Utilizing oxygen for membrane remodeling.

D

Utilizing oxygen for synthesis of pentapeptide chain in peptidoglycan.

View Answer

Nitrogen fixation is a process by which nitrogen () is converted into ammonia (). Nitrogen fixation is carried out naturally in the soil by nitrogen-fixing bacteria such as Azotobacter. Some nitrogen-fixing bacteria have symbiotic relationships with some plant groups, especially legumes. Nitrogen fixation is carried out by the enzyme nitrogenase, which is found in microbes.
Conversion of  to ammonia () by bacteria is energetically expensive and extremely sensitive to . Both proteins that makeup nitrogenase are irreversibly denatured by the presence of . All systems that support nitrogenase have evolved mechanisms of creating a low  environment at the site of  fixation. The  is removed by the organism through various metabolic pathways.
So, the answer is B.

Which of the following is the function of nitrifying bacteria?

A

Oxidise to

B

Oxidise to

C

Convert to

D

Convert to

View Answer

Nitrifying bacteria is an aerobic bacteria that use inorganic chemicals as an energy source. They are important in the nitrogen cycle as converters of soil ammonia to nitrates by the process of oxidation.
So the correct answer is 'oxidise NH to NO-'.

Bacteria involved in two-step conversion ammonia into nitrate are

A

Azotobacter and Nitrosomonas

B

Pseudomonas and Nitrobacter

C

Azotobacter and Achromobacter

D

Nitrosomonas and Nitrobacter

View Answer

Nitrification is a process of conversion of ammonium ions to nitrites and nitrites to nitrates. It is a two-step process. The bacteria that carry out this process are called as nitrifying bacteria. Nitrosomonas, Nitrosospira, Nitrosococcus convert ammonia into nitrites. Nitrobacter, Nitrospina, Nitrococcus convert nitrites into nitrates.
Thus, the correct answer is 'Nitrosomonas and Nitrobacter.' 

Which of the following is a free living aerobic non - photosynthetic nitrogen-fixer ?

A

B

C

D

View Answer

Azotobacter is a free-living nitrogen-fixing bacterium, which is used as a biofertilizer in the cultivation of most crops. Azotobacter respires aerobically, receiving energy from redox reactions, using organic compounds as electron donors. Azotobacter can use a variety of carbohydrates, alcohols, and salts of organic acids as sources of carbon. 
Rhizobium fixes nitrogen by symbiotic association. Nostoc is photosynthetic. Azospirillum is anaerobic. 
So, the correct option is 'Azotobacter'.

Which gene cluster is responsible for nitrogen fixation in bacteria?

A

Nod, Nif, Nfx

B

Nod, Nif, Fix

C

Nod, Ndf, Nfx

D

Ndx, Nif, Fix

E

Ndx, Nif, nix

View Answer

Nitrogen fixation is a process by which nitrogen present in the atmosphere is converted into ammonia. It is essential to life because fixed inorganic nitrogen compounds are required for the biosynthesis of all nitrogen-containing compounds. This process is done with the help of nitrogen-fixing bacteria that have Nod, Nif and Fix gene clusters responsible for nitrogen fixation.
So the correct answer is 'Nod, Nif, Fix'.

Enzyme nitrogenase will be absent in 

A

Frankia

B

Azotobacter

C

Anabaena

D

Nitrococcus

View Answer

Match the columns and choose the correct option.
III
(a)Free-living aerobic nitrogen fixers1.Anabaena and Nostoc
(b)Anaerobic nitrogen fixers2.Pseudomonas and Thiobacillus
(c)Nitrogen-fixing cyanobacteria3.Nitrosomonas and Nitrosococcus
(d)Denitrifying bacteria4.Azotobacter and Beijerinckia
(e)Nitrifying bacteria5.Rhodospirillum

A

a - 4, b - 5, c - 1, d - 2, e - 3 

B

a - 5, b - 4, c - 1, d - 3, e - 2

C

a - 4, b - 5, c - 2, d - 3, e - 1

D

a - 4, b - 3, c - 1, d - 2, e - 5

E

a - 4, b - 5, c - 3, d - 2, e - 1

View Answer

a) Free-living aerobic nitrogen fixers - Azotobacter and Beijernikia
b) Anaerobic nitrogen fixers - Rhodospirillum
c) Nitrogen-fixing cyanobacteria - Anabaena and Nostoc
d) Denitrifying bacteria - Pseudomonas and Thiobacillus
e) Nitrifying bacteria - Nitrosomonas and Nitosococcus
So the correct answer is 'a-4, b-5, c-1, d-2, e-3'

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