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

An element playing important role in nitrogen fixation is

1. molybdenum

2. copper

3. manganese

4. zinc

Which one of the following is not a micronutrient?

1. Molybdenum

2. Magnesium

3. Zinc

4. Boron

The free-living, anaerobic nitrogen-fixer is

1. Beijerinckia

2. Rhodospirillum

3. Rhizobium

4. Azotobacter

The common nitrogen-fixer in paddy fields is

1. Rhizobium

2. Azospirillum

3. Oscillatoria

4. Frankia

Which of the following is a symbiotic nitrogen fixer?

1. Glomus

2. Azotobacter

3. Frankia

4. Azolla

About 98 percent of the mass of every living organism is composed of just six elements

including carbon, hydrogen, nitrogen, oxygen and:

1. phosphorus and sulphur

2. sulphur and magnesium

3. magnesium and sodium

4. calcium and phosphorus