During biological nitrogen fixation, inactivation of nitrogenase by oxygen poisoning is prevented by

(1) leghaemoglobin

(2) xanthophyll

(3) carotene

(4) cytochrome

Auxin can be bioassayed by

1. Avena coleoptile curvature

2. hydroponics

3. potometer

4. lettuce hypocotyl elongation

Minerals known to be required in large amounts for plant growth include

1. Phosphorus, potassium, sulphur, calcium

2. calcium, magnesium, manganese, copper

3. potassium, phosphorus, selenium, boron

4. magnesium, sulphur, iron, zinc

Deficiency symptoms of nitrogen and potassium are visible first in

1. senescent leaves

2. young leaves

3. roots

4. buds

The most abundant intracellular cation is

1. Na⁺

2. Ca²⁺

3. H⁺

4. K⁺

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

Best defined function of manganese in green plants is

1. photolysis of water

2. Calvin cycle

3. nitrogen fixation

4. water absorption

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