Question

During biological nitrogen fixation, inactivation of nitrogenase of oxygen poisoning is prevented by
A. Cytochrome
B. Leghaemoglobin
C. Xanthophyll
D. Carotene

Answer 1

Some bacteria are harmful to us causing various diseases, even in the plants also. Some bacteria live in a close relationship with plants to provide the benefit and in return may take some flavor. It is more of a kind of mutualism.

Complete answer: The Rhizobium is the bacteria that are present in the root nodule of leguminous plants. They will fix atmospheric nitrogen by nitrogenase – oxygen labile enzyme. These roots nodules have a pigment called leghaemoglobin. This will prevent the exposure of nitrogenase to oxygen thus doing the nitrogen fixation.
Option A: Cytochrome: Electron transport chain does the redox reactions to transfer electrons from donors to acceptors. The electrons are passed from the membrane. There are 4 complexes called cytochromes used in the chain- NADH-Q, succinate Q- reductase, Complex 3, and Complex 4( cytochrome c oxidase).
Option B: Leghaemoglobin: The Rhizobium is the bacteria that are present in the root nodule of leguminous plants. They will fix atmospheric nitrogen by nitrogenase. These roots nodules have a pigment called leghaemoglobin.
Option C: Xanthophyll: They are the yellow pigments that occur in nature and is a form of carotenoid. They are found in young leaves and etiolated leaves. They form the accessory pigments of the leaf which absorb the wavelength that chlorophyll cannot. They play an important role in the protection of the excess of sunlight.
Option D: Carotene: These are the pigments responsible for the colour of many fruits. They are found in the chloroplasts found in the plastids. Plastids synthesize them and store carotenoids. They give yellow, orange, red colours.
So the answer is option B: Leghaemoglobin

Note: Rhizobium is the soil organism. They fix nitrogen to provide nitrogen to the host plant. They infect the legumes mostly. It falls under the Kingdom Bacteria. They are the prokaryotes. They are not harmful to human life as they just form a relationship with the roots of legumes.