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

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

Which one of the following elements is not an essential micronutrient for plant growth?

1. Mn

2. Zn

3. Cu

4. Ca

Which one of the following is not a micronutrient?

1. Molybdenum

2. Magnesium

3. Zinc

4. Boron

An organism used as a biofertilizer for raising soyabean crop is

1. Azospirillum

2. Rhizobium

3. Nostoc

4. Azotobacter

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

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

A nitrogen fixing microbe associated with Azolla in rice fields is

1. Spirulina

2. Anabaena

3. Frankia

4. Tolypothrix

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