Question

Leguminous plants are able to fix atmospheric nitrogen through the process of symbiotic nitrogen fixation. Which one of the following statements is not correct during this process of nitrogen fixation?
A. Nitrogenase is insensitive to oxygen.
B. Leghemoglobin scavenges oxygen and is pinkish in color.
C. Nodules act as sites for nitrogen fixation.
D. The enzyme nitrogenase catalyzes the conversion of atmospheric \[{N_2}\] to \[N{H_3}\].

Answer 1

Hint: Nitrogen fixation is a process in which the diatomic nitrogen found in the atmosphere is converted to ammonia which can be metabolized by the plants. The nitrogen found in the atmosphere is nonreactive by nature, therefore, it is needed to be converted to ammonia before it can be used up by the organisms.

Complete answer: The first statement states that the Nitrogenase is insensitive to oxygen. This statement is incorrect. This is because the nitrogenase enzyme is extremely sensitive to molecular oxygen. The Nitrogenase enzyme requires an anaerobic environment for the process of nitrogen fixation. However, it survives as an aerobic enzyme under free-living conditions. Therefore, this statement is not correct.
-The second statement given to us is that the Leghemoglobin scavenges oxygen and is pinkish in color. This statement is correct. This is because the Leg-hemoglobin provides an anaerobic environment or anaerobic conditions for the nitrogenase enzyme. Moreover, Leg-hemoglobin protects the nitrogenase enzyme from oxygen by scavenging oxygen. Leg-hemoglobin is pinkish in color. Therefore, this statement is correct.
-The third statement given to us is that the nodules act as sites for nitrogen fixation. This statement is correct. This is because the root nodules of the leguminous plants contain necessary biochemical components. These components help in fixing atmospheric nitrogen to inorganic ammonia. Hence, the root nodules act like sites of nitrogen fixation. Therefore, this statement is correct.
-The fourth statement given to us is that the enzyme nitrogenase catalyzes the conversion of atmospheric \({N_2}\) to \(N{H_3}\). This statement is correct. This is because the nitrogenase catalyzes the conversion of atmospheric nitrogen to inorganic ammonia. Therefore, this statement is correct.
Thus, from the above information, we can conclude that Nitrogenase is insensitive to oxygen is not the correct statement for the process of nitrogen fixation.
Hence, the correct answer is option (A).

Note: The process of nitrogen fixation is important for organisms as nitrogen compounds like ammonia are needed for the biosynthesis of organic compounds containing nitrogen. Symbiotic nitrogen fixation takes place in plants that have these bacteria capable of nitrogen fixation like legumes. Both these organisms have the ability to survive independently but together they can accomplish nitrogen fixation.