Question

In the higher plants, nitrate ions absorbed from the soil are converted to ammonia in two steps. In the second step, the electrons required for the reduction of nitrate ions are donated by
A. Cytochrome P450​
B. Nitrate reductase
C. Ferredoxin
D. Nitrite reductase

Answer 1

Hint: Plants can absorb both nitrate and ammonium ions (some prefer one to the other). These ions provide nitrogen to the plant, allowing it to produce its amino acids for protein synthesis. Even in very high nitrogen soils, adding extra nitrate stimulates plant growth.

Complete answer:
- Cytochromes P450 (CYPs) are a superfamily of enzymes that function as monooxygenases and contain heme as a cofactor. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics and are essential for compound clearance as well as hormone synthesis and breakdown. As a result, option A is false.
- Nitrate assimilation begins with the uptake of nitrate from the root system and is first reduced to nitrite by nitrate reductase and then reduced to ammonia by nitrite reductase. Ammonia is then inserted into amino acids through the GS-GOGAT pathway. As a result, Option B is also incorrect.
- Nitrate assimilation is the mechanism by which consumed nitrate is converted into nitrite by an inducible enzyme called nitrate reductase with the aid of reduced coenzymes. Nitrite is further reduced into ammonia by the enzyme nitrite reductase, which uses reduced coenzymes and ferredoxin. Ferredoxin provides electrons one at a time for this elimination. As a result, the right answer is 'Ferredoxin.'
- Nitrite reductase (NiR) is a stromal enzyme that catalyzes a six-electron step nitrite-to-ammonium reduction using reduced Fd as an electron donor. A single gene clustered with other nitrate assimilation genes encodes the holoenzyme. As a result, alternative D is also incorrect.

Hence the correct answer is 'Ferredoxin.'(C).

Note: Nitrate absorption is an energy-demanding mechanism that is induced by nitrogen deficiency and suppressed by ammonium or nitrite. Nitrate enters the cell through complex transport systems and is converted to nitrite in the cytosol by nitrate reductase. Nitrogen fixation is the mechanism of converting nitrogen gas to nitrates. Nitrogen-fixing bacteria carry it out. Bacteria can be found in soil and the roots of legumes such as peas.