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MCQ on Plant physiology - Biological Nitrogen Fixation



1. The conversion of nitrogen to ammonia or nitrogenous compounds is called as
a) Nitrogen assimilation
b) Nitrogen fixation
c) Denitrification
d) Nitrification

2. Plants absorbs N2 in the form of 
a) nitrites (NO2-)
b) nitrates (NO3-)
c) ammonium (NH4+)
d) all of the above

Biological Nitrogen Fixation
Biological Nitrogen Fixation
3. Plants cannot absorb molecular N2 in the atmosphere because
a) N2 has double bonds making it highly stable
b) Abundance in the atmosphere inhibits absorption
c) N2 has triple bonds making it highly stable
d) None of these

4. Symbiotic N2 fixing cyanobacteria are present in all except
a) Anthoceros
b) Azolla
c) Cycas
d) Gnetum

5. All the following are free living N2 fixers except
a) Rhizobium
b) Azotobacter
c) Rhodospirillum
d) Clostridium

6. Which of the following N2 fixer is involved in symbiotic association with legumes forming root nodules?
Root Nodules
Root Nodules
a) Rhizobium
b) Azotobacter
c) Rhodospirillum
d) Clostridium

7. Anabaena, a  N2 fixer is present in the root pockets of
a) Marselia
b) Salvinia
c) Pistia
d) Azolla

8. Splitting of dinitrogen molecule into free nitrogen atom in biological N2 fixation is carried out by
a) hydrogenase
b) nitrogenase
c) dinitrogenase
d) nitrate reductase

9. The conversion of amino acids to ammonium by soil decomposers is called
a) ammonification
b) mineralization
c) deamination
d) Both a and b

10. Industrial fixation is accomplished by
a) Helmonts process
b) Haber process
c) Friedel- Crafts reaction
d)Reimer Tiemann Reaction

11. To fix one molecule of nitrogen
a) 6 ATP molecules are required
b) 12 ATP molecules are required
c) 16ATP molecules are required
d) 20 ATP molecules are required

12. The root nodules of legumes contain a pink pigment which has high affinity for oxygen is
a) nod haemoglobin
b) leghaemoglobin
c) haemoglobin
d) bacterial haemoglobin

13. Conversion of NO2- to NO3- is carried out by
a) Nitrosomonas
b) Nitrososcoccus
c) Nitrobacter
d) Clostridium

14The process of conversion of soil NO3- to N2 is called
a) nitrification
b) denitrification
c) ammonification
d) nitrogen fixation

15. Leghaemoglobin creates
a) Anaerobic condition for optimum activity of nitrogenase
b) Aerobic condition for optimum activity of nitrogenase
c) Required oxygen concentration for optimum activity of nitrogenase
d) Suitable environment for nodule formation

Answers:

1-b
2-d
3-c
4-d
5-a
6-a
7-d
8-b
9-d
10-b
11-c
12-b
13-c
14-b
15-a