During nitrogen fixation, nitrite is oxidized to nitrate with the help of the bacterium:

1. Nitrosomanas
2. Pseudomonas
3. Nitrobacter
4. Thiobacillus

Nitrogen-fixing nodules on the roots of non-leguminous plants like Alnus are produced by
1. Rhizobium
2. Beijernickia
3. Azotobacter
4. Frankia

For each molecule of ammonia produced by nitrogenase, the number of ATP molecules required are:
1. 4
2. 8
3. 12
4. 16

Which one of the following is not a nitrogen-fixing organism?

1. Anabaena

2. Nostoc

3. Azotobacter

4. Pseudomonas

Select the mismatch.

1. Frankia                      Alnus

2. Rhodospirillium            Mycorrhiza

3. Anabaena                   Nitrogen fixer

4. Rhizobium                 Alfa-fa

Which one of the following is the wrong statement?

1. Anabaena and Nostoc are capable of fixing nitrogen in a free-living state also

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

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

4. Nitrosomonas and Nitrobacter are chemoautotrophs

A nitrogen fixing microbe associated with Azolla in rice fields is

1. Spirulina

2. Anabaena

3. Frankia

4. Tolypothrix

The function of leghaemoglobin in the root nodules of legumes is 

1. oxygen removal

2. nodule differentiation

3. expression of nif gene

4. inhibition of nitrogenase activity

Nitrifying bacteria

1. convert free nitrogen to nitrogen compounds

2. convert proteins into ammonia

3. reduce nitrates to free nitrogen

4. oxidize ammonia to nitrates

An organism used as a biofertilizer for raising soyabean crop is

1. Azospirillum

2. Rhizobium

3. Nostoc

4. Azotobacter