During biological nitrogen fixation, inactivation of nitrogenase by oxygen poisoning is prevented by
1. leghaemoglobin
2. xanthophyll
3. carotene
4. cytochrome

Deficiency symptoms of nitrogen and potassium are visible first in

The first stable product of fixation of atmospheric nitrogen in leguminous plants is
1. ${\mathrm{NO}}_2^{-}$
2. ammonia
3. ${\mathrm{NO}}_3^{-}$
4. glutamate

A nitrogen fixing microbe associated with Azolla in rice fields is
1. Spirulina
2. Anabaena
3. Frankia
4. Tolypothrix

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

A plant requires magnesium for