Answers and bookmarks are saved in this browser, across visits. They do not sync to your account.
100 questions in this collection · Page 5 of 10
Question 41 of 100
📘 CLASS XI
Mineral Nutrition
During nodule development, major changes happen in the host cells. Consider the following statements:
I. Bacteria are released from the infection thread into the cells of the inner cortex. II. Inside the cells, bacteria get modified into rod-shaped bacteroids. III. The bacteroids stimulate inner cortical and pericycle cells to divide. IV. The initial division of cells to form a nodule is restricted exclusively to the outer epidermal cells.
Explanation: Statements I, II, and III are correct. Bacteria are released from the infection thread into inner cortical cells, where they differentiate into rod-shaped bacteroids and stimulate the division of inner cortical and pericycle cells. Statement IV is incorrect because nodule formation involves the inner cortex and pericycle, not the outer epidermis.
Question 42 of 100
📘 CLASS XI
Mineral Nutrition
Regarding the structural integration of a mature nodule, analyze these statements:
I. Division and growth of cortical and pericycle cells lead directly to nodule formation. II. A mature nodule establishes a direct vascular connection with the host plant for nutrient exchange. III. The vascular tissues of the nodule are continuous with those of the host root. IV. The nodule's vascular connection is strictly one-way, permitting water entry but preventing nitrogen export.
Explanation: Statements I, II, and III are correct. Mature nodules develop from cortical and pericycle cell divisions and establish vascular continuity with the host root for two-way exchange of nutrients. Statement IV is incorrect because the vascular connection allows export of fixed nitrogen as well as import of water and nutrients.
Question 43 of 100
📘 CLASS XI
Mineral Nutrition
Consider the biochemical makeup of the nitrogenase enzyme complex:
I. It is present exclusively in eukaryotic plant host cells. II. It is a Mo-Fe (Molybdenum-Iron) protein. III. It catalyzes the conversion of atmospheric nitrogen to ammonia, which is the first stable product of nitrogen fixation. IV. It is capable of converting nitrate (NO3-) into nitrite (NO2-).
Explanation: Statements II and III are correct. Nitrogenase is a molybdenum-iron protein that reduces atmospheric nitrogen to ammonia, the first stable product of biological nitrogen fixation. Statement I is incorrect because nitrogenase occurs only in prokaryotes. Statement IV is incorrect because nitrate reduction is catalyzed by nitrate reductase, not nitrogenase.
Question 44 of 100
📘 CLASS XI
Mineral Nutrition
Analyze the reaction stoichiometry and energetics of biological nitrogen fixation:
N2 + 8e- + 8H+ + 16ATP → 2NH3 + H2 + 16ADP + 16Pi
I. The reduction of one molecule of nitrogen yields two molecules of ammonia and one molecule of hydrogen gas. II. The synthesis of two molecules of ammonia requires an input of 16 ATP. III. For each molecule of ammonia produced, 8 ATP are required. IV. The high ATP requirement for nitrogen fixation is supplied by respiration of the host plant cells.
Explanation: All four statements are correct. Biological nitrogen fixation requires 16 ATP to reduce one molecule of N2 into two molecules of NH3, with one molecule of H2 also produced. This corresponds to 8 ATP per NH3, and the ATP is supplied through respiration of the host plant cells.
Question 45 of 100
📘 CLASS XI
Mineral Nutrition
Symbiotic microbes undergo physiological changes to protect the oxygen-sensitive nitrogenase. Consider these statements:
I. Nitrogenase is highly sensitive to molecular oxygen and requires anaerobic conditions. II. The symbiotic nitrogen-fixing microbes live as aerobes under free-living conditions. III. Under free-living conditions, the nitrogenase enzyme is highly active and fixes nitrogen at a rapid rate. IV. During nitrogen-fixing events, the microbes become anaerobic to protect the nitrogenase enzyme.
Explanation: Statements I, II, and IV are correct. Nitrogenase is oxygen-sensitive. Nitrogen-fixing microbes are aerobic under free-living conditions but maintain anaerobic conditions during nitrogen fixation to protect nitrogenase. Statement III is incorrect because nitrogenase is not actively fixing nitrogen under normal free-living aerobic conditions.
Question 46 of 100
📘 CLASS XI
Mineral Nutrition
Consider the fate of ammonia in plant tissues and its toxicity:
I. At physiological pH, ammonia is protonated to form NH4+ (ammonium) ions. II. Most plants can assimilate nitrate as well as ammonium (NH4+) ions. III. Ammonium (NH4+) ions are quite toxic to plants and cannot accumulate in them. IV. To avoid toxicity, plants store free, unmetabolized ammonium ions in the central vacuoles of root epidermal cells.
Explanation: Statements I, II, and III are correct. At physiological pH ammonia exists mainly as NH4+. Plants can utilize both nitrate and ammonium, but ammonium is toxic and must be rapidly assimilated into amino acids. Statement IV is incorrect because plants do not store free ammonium ions.
Question 47 of 100
📘 CLASS XI
Mineral Nutrition
Regarding the process of reductive amination in plants, consider the statements below:
I. Ammonia reacts with α-ketoglutaric acid to form glutamic acid. II. The reaction is catalyzed by the enzyme glutamate dehydrogenase. III. The reaction is represented by: α-ketoglutaric acid + NH4+ + NADPH → glutamate + H2O + NADP+ (Glutamate Dehydrogenase). IV. Reductive amination requires FADH2 as a reducing power instead of NADPH.
Explanation: Statements I, II, and III are correct. Reductive amination converts α-ketoglutaric acid into glutamate using NH4+, NADPH and the enzyme glutamate dehydrogenase. Statement IV is incorrect because the reducing power is supplied by NADPH, not FADH2.
Question 48 of 100
📘 CLASS XI
Mineral Nutrition
Analyze the following statements regarding transamination:
I. It involves the transfer of an amino group from one amino acid to the keto group of a keto acid. II. Glutamic acid is the main amino acid from which the transfer of NH2 takes place. III. Other amino acids are formed through transamination catalyzed by the enzyme transaminase. IV. Transamination is a spontaneous, non-enzymatic reaction that does not require any cellular catalysts.
Explanation: Statements I, II, and III are correct. Transamination transfers the amino group from glutamate to other keto acids to synthesize different amino acids. The reaction is catalyzed by transaminase enzymes. Statement IV is incorrect because transamination is an enzyme-mediated process.
Question 49 of 100
📘 CLASS XI
Mineral Nutrition
Consider the following statements regarding amides in plants:
I. Asparagine and glutamine are two important amides found in plants and are structural parts of proteins. II. They are formed from the amino acids aspartic acid and glutamic acid by adding another amino group. III. In amides, the hydroxyl part of the amino acid is replaced by another NH2 radical. IV. Since amides contain less nitrogen than amino acids, they are transported exclusively via phloem.
Explanation: Statements I, II, and III are correct. Amides such as asparagine and glutamine are formed by replacing the hydroxyl group of aspartic acid and glutamic acid with an amino group. Statement IV is incorrect because amides contain more nitrogen than amino acids and are transported through xylem vessels.
Question 50 of 100
📘 CLASS XI
Mineral Nutrition
Analyze the following statements about ureides and nitrogen transport in some plants:
I. Along with the transpiration stream, the nodules of some plants (e.g., soybean) export fixed nitrogen as ureides. II. Ureides are characterized by a particularly low nitrogen-to-carbon ratio. III. These compounds are transported to other parts of the plant via xylem vessels. IV. Soybean plants exclusively export nitrogen as free ammonium ions rather than ureides.
Explanation: Statements I and III are correct. Soybean and some other legumes export fixed nitrogen as ureides through xylem vessels. Statement II is incorrect because ureides possess a high nitrogen-to-carbon ratio. Statement IV is incorrect because soybean exports ureides rather than free ammonium ions.