The common nitrogen-fixer in paddy fields is

(1) Frankia

(2) Rhizobium

(3) Azospirillum

(4) Oscillatoria

Which of the following bacteria reduce nitrate in soil into nitrogen?

1. Nitrobacter

2. Thiobacillus

3. Nitrococcus

4. Nitrosomonas

A free living aerobic soil bacterium capable of
fixing nitrogen is
1. Azotobacter

2. Clostridium

3. Rhizobium

4. Streptococcus

Thiobacillus is a group of bacteria helpful in carrying out:

1. Denitrification

2. Nitrogen fixation

3. Chemoautotrophic fixation

4. Nitrification

Which of the following is a flowering plant with nodules containing filamentous nitrogen-fixing microorganism?

1. Casuarina equisetifolia

2. Crotolaria juncea

3. Cycas revoluta

4. Cicer arietinum

Manganese is required in:
1. nucleic acid synthesis
2. plant cell wall formation
3. photolysis of water during photosynthesis
4. chlorophyll synthesis

The oxygen evolved during photosynthesis comes from water molecules. Which one of the following pairs of elements are involved in this reaction?

1. Manganese and chlorine

2. Manganese and potassium

3. Magnesium and molybdenum

4. Magnesium and chlorine

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

1. Leghaemoglobin

2. Xanthophylls

3. Carotene

4. Cytochrome