Biology Problems for Medical Entrance Exams on “Mineral Nutrition – Metabolism of Nitrigen-2”.
1. N2 + A e– + A H+ + B ATP → C NH3+ H2 + D ADP + D Pi
In the equation given above, C is present in how much quantity?
a) 8
b) 16
c) 2
d) 1
Answer: c
Clarification: As per question, e– and H+ is present 8 in number per N2 molecule fixed. ATP, ADP and Pi are present in 16 times per N2 molecule fixed. NH3 is present two times per N2 molecule fixed.
2. The bacteria have to modify into rod- shaped bacterium in order to initiate division of inner cortical and pericycle cells.
a) True
b) False
Answer: a
Clarification: The bacteria enter the plant body through root hair with the help of formation of an infection thread. After entering inside the cell, the bacteria change its form to rod-shaped bacterium in order to initiate division of inner cortical and pericycle cells.
3. Statement A: Nitrogenase is a Cu-Mn protein.
Statement B: It catalyses the conversion of atmospheric nitrogen to the form absorbed directly by plants.
a) Both the statements are true
b) Both the statements are false
c) Statement A is true but Statement B is false
d) Statement B is true but Statement A is false
Answer: b
Clarification: Nitrogenase is an important enzyme for the process of nitrogen fixation. It is basically a Mo-Fe protein. It catalyses the conversion of atmospheric nitrogen into the first stable form that is ammonia.
4. Which microbe is capable of fixing nitrogen in non-leguminous plants?
a) Bacillus
b) Beijernickia
c) Anabaena
d) Frankia
Answer: d
Clarification: Frankia is a microbe that is capable of fixing nitrogen in non-leguminous plants such as Alnus. It also produces nodules in the roots of plant. It can freely live in soil but fixes nitrogen as a symbiont. Bacillus is a free living anaerobic nitrogen fixer. Beijernickia is an aerobic nitrogen fixer. Anabaena is a microbe among the cyanobacteria that is capable of nitrogen fixation.
5. Statement A: At physiological pH, NH3 is protonated to form NH4+ ion.
Statement B: The NH4+ ion is further converted to another form in order to be accumulated.
a) Both the statements are true
b) Both the statements are false
c) Statement A is true but Statement B is false
d) Statement B is true but Statement A is false
Answer: a
Clarification: At physiological pH, NH3 is protonated to form NH4+ ion. Since it is toxic for plants, it is not stored in this form and is further used in the processes of reductive amination and transamination to form amides. The amides obtained are essential parts of protein structure of plants.
6. Statement A: Nodule that arises from root hair cells contains enzyme nitrogenase.
Statement B: The nodule gets it pink color from nitrogenase.
a) Both the statements are true
b) Both the statements are false
c) Statement A is true but Statement B is false
d) Statement B is true but Statement A is false
Answer: c
Clarification: Nodules are associations between bacteria and plant roots. It arises from root hair cells and contains enzyme nitrogenase and leghaemoglobin pigment. The nodule gets its pink from leghaemoglobin.
7. Leg-haemoglobin protects nitrogenase enzyme from anaerobic conditions.
a) True
b) False
Answer: b
Clarification: Leg-haemoglobin is a pigment present in root nodules of leguminous plants. It acts as oxygen scavenger. It protects nitrogenase enzyme from aerobic conditions as it is highly sensitive to molecular oxygen.
8. Statement A: In reductive amination, NH4+ reacts with α-ketoglutaric acid to form asparagine.
Statement B: The process takes place in presence of glutamate dehydrogenase.
a) Both the statements are true
b) Both the statements are false
c) Statement A is true but Statement B is false
d) Statement B is true but Statement A is false
Answer: d
Clarification: In reductive amination, NH4+ reacts with α-ketoglutaric acid to form glutamic acid. The process takes place in presence of glutamate dehydrogenase. Glutamine contains 2 molecules of nitrogen and 5 molecules of carbon. It is a part of structural protein of the plant cell.
9. Which enzyme catalyses the process of transamination?
a) Lipase
b) Nitrogenase
c) Transaminase
d) Glutamate dehydrogenase
Answer: c
Clarification: Transaminase is the enzyme which catalyses the process of transamination. Nitrogenase is responsible for nitrogen fixation. Glutamate dehydrogenase has role in the process of reductive amination. Lipase is a linking enzyme and has no role to play in nitrogen metabolism.
10. Amides are transported to other parts of the plant through ________
a) phloem parenchyma
b) phloem companion cells
c) xylem vessels
d) phloem fibre
Answer: c
Clarification: Amides contain more nitrogen than amino acids. They are transported to other parts of the plant through xylem vessels. Phloem tissue has no function in relation to translocation of amides.
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