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Important questions on Biogeochemical Cycles

Nitrosomonas and Nitrobacter convert

A

Carbon dioxide to carbohydrates

B

Ammonium ion into nitrate

C

Nitrate ion into nitrogen molecule

D

Nitrogen into nitrate

View Answer

Nitrification is a process of conversion of ammonium ions to nitrites and nitrites to nitrates. 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 'Ammonium ion into nitrate.' 

In excess,

A

Accelerates growth

B

Does not influence growth

C

Inhibits growth

D

Slows down growth

View Answer

Atmospheric carbon dioxide is used by plants to produced food. Due to industrialization, large amount of carbon dioxide is released in the atmosphere. This CO provides nutrient source to certain plants. However, excess amount of CO inhibits growth in plants. It inhibits nitrate assimilation in certain plants. It basically inhibits absorption of nitrogen.
Thus, the correct answer is option C.

Nitrifying bacteria convert the

A

Nitrates into nitrites

B

Nitrites into nitrates

C

Ammonium salts into nitrates

D

Ammonium salts into amino acids

View Answer

Nitrification is a process of conversion of ammonium salts to nitrites and nitrites to nitrates. 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 'Ammonium salts into nitrates.'

Free living nitrogen fixing biofertilizer is

A

Glomus

B

Rhizobium

C

Azotobacter

D

Pseudomonas

View Answer

Azotobacter is a heterotrophic free living nitrogen fixing bacteria present in alkaline and neutral soils.

Which one of nitrogen fixing bacteria form a symbiotic association with a gymnosperm roots ?

A

Nostoc

B

Anabaena

C

Rhizobiurn

D

Aulosira

View Answer

The symbiotic association is seen between Nostoc and roots of cycad roots. Nostoc is also known as blue-green algae or cyanobacteria. It helps it by increasing the of nitrogen fixation.
Hence correct answer is option A . 

Which one of the following is a wrong statement ? 

A

Phosphorus is a constituent of cell membranes, certain nucleic acids and all proteins

B

Nitrosomonas and Nitrobacter are chemoautotrophs

C

Anabaena and Nostoc are capable of fixing nitrogen in free living state

D

Root nodule forming nitrogen fixers live as aerobes under free living conditions

View Answer

A. Phosphorus is constituent of cell membranes in the form of phospholipids and also present in nucleic acids as phosphate in the sugar-phosphate backbone.
B. Nitrosomonas and Nitrobacter are nitrifying bacteria. These bacteria derive energy by oxidizing inorganic nitrogenous compounds. Hence, they are called chemoautotrophs.
C. Anabaena and Nostoc are cyanobacteria (also known as blue-green algae). They are free-living bacteria and can fix nitrogen because they have specialized cells called heterocysts with the help of which they can fix atmospheric nitrogen.
D. Root nodule forming nitrogen-fixing microbes live freely in the soil as aerobes. They form a symbiotic association with the roots of plants when some chemicals or factors are released by the plants. For example, Rhizobium.
Hence, statement A is incorrect.
So, the correct answer is 'Phosphorus is a constituent of cell membranes, certain nucleic acids, and all proteins'.

Explain how Nitrification is different from Nitrogen fixation. Mention the role of Thiobacllus in nitrogen cycle? What do you understand by biological Nitrogen fixation?

View Answer

  • Nitrification is the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of the nitrite to nitrate. Nitrogen fixation is a process by which nitrogen in the Earth's atmosphere is converted into ammonia or related nitrogenous compounds.
  • Thiobacillus helps in the conversion of nitrates in the soil to free atmospheric nitrogen, thus depleting soil fertility and reducing agricultural productivity.
  • Biological nitrogen fixation is the process whereby atmospheric nitrogen (N=N) is reduced to ammonia in the presence of nitrogenase. Nitrogenase is a biological catalyst found naturally only in certain microorganisms such as the symbiotic Rhizobium and Frankia, or the free-living Azospirillum and Azotobacter.

Non-symbiotic nitrogen-fixation takes place by

A

Anabaena, Nostoc, Rhizobium

B

Nostoc, Azotobacter, Clostridium

C

Azotobacter, Nitrosomonas, Rhizobium

D

Anabaena, Nitrosomonas, Pseudomonas

View Answer

Nostoc is a free-living cyanobacterium. Azotobacter is obligate aerobic bacteria. Clostridium is anaerobic bacteria. All of them are free-living and fix nitrogen in the soil. They do not reside in the roots of the plant. They remain in the soil and convert the atmospheric nitrogen into the soluble form. Thus, the correct answer is option B.

Nitrite is changed to nitrate by

A

Nitrobacter

B

Nitrosomonas

C

Clostridium

D

Pseudomonas

View Answer

There are two steps in nitrification process by which ammonia is converted into nitrite and nitrite into nitrate. The bacteria that convert ammonia to nitrites include NitrosomonasNitrosospira and the bacteria that convert nitrites to nitrates include NitrobacterNitrospina
Thus, the correct answer is 'Nitrobacter.'

The common nitrogen fixer organism in paddy fields is

A

Azospirillum

B

Oscillatoria

C

Frankia

D

Rhizobium

View Answer

Atmospheric nitrogen is not available to plants. There are certain nitrogen fixing bacteria which converts atmospheric nitrogen into ammonium compounds and make it available to the plants. Examples include Azotobacter, Frankia, Rhizobium, Azospirillum. Out of these, Azospirillum is widely used as nitrogen fixer organism in paddy fields. It is used as biofertilizer in rice fields. It promotes the plant growth.
Thus, the correct answer is 'Azospirillum.'

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