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100 questions in this collection · Page 3 of 10
Question 21 of 100
📘 CLASS XI
Mineral Nutrition
Consider the following statements regarding the process of denitrification:
I. It is the process of reducing nitrate present in the soil to gaseous nitrogen (N2). II. Denitrification is carried out by bacteria such as Nitrobacter and Nitrococcus. III.Pseudomonas and Thiobacillus are the primary bacteria responsible for denitrification.
Which of the statements given above is/are correct?
Statements I and III are correct. Denitrification converts nitrate into gaseous nitrogen and is carried out mainly by Pseudomonas and Thiobacillus. Statement II is incorrect because Nitrobacter and Nitrococcus are nitrifying bacteria.
Question 22 of 100
📘 CLASS XI
Mineral Nutrition
Identify the correct statements regarding various nitrogen-fixing microbes:
I.Azotobacter and Beijerinckia are free-living, aerobic nitrogen-fixing microbes. II.Rhodospirillum is an anaerobic, free-living nitrogen-fixing bacterium. III.Frankia is a symbiotic microbe that produces nitrogen-fixing nodules on the roots of leguminous plants like Alnus. IV. Both Rhizobium and Frankia are free-living in soil but can fix atmospheric nitrogen only as symbionts.
Select the correct options.
Statements I, II, and IV are correct. Azotobacter and Beijerinckia are free-living aerobic nitrogen fixers, Rhodospirillum is a free-living anaerobic nitrogen fixer, and both Rhizobium and Frankia fix nitrogen effectively only in symbiosis. Statement III is incorrect because Alnus is a non-leguminous plant.
Question 23 of 100
📘 CLASS XI
Mineral Nutrition
Consider the following statements regarding nodule formation in leguminous plants:
I. Rhizobia attach to epidermal cells, causing the root hair to curl and allowing the bacteria to invade. II. The infection thread carries the bacteria into the cortex, where they get modified into spherical bacteroids and cause outer epidermal division. III. A mature nodule establishes a direct vascular connection with the host for nutrient exchange. IV. The central portion of the nodule is pink or red due to the presence of leg-haemoglobin.
Which of the statements given above are correct?
Statements I, III, and IV are correct. Rhizobia invade through curled root hairs, mature nodules develop vascular connections with the host, and leg-haemoglobin imparts a pink colour. Statement II is incorrect because bacteria differentiate into rod-shaped bacteroids and stimulate division of the inner cortex and pericycle, not the outer epidermis.
Question 24 of 100
📘 CLASS XI
Mineral Nutrition
With respect to the nitrogenase enzyme and the energetics of nitrogen fixation, analyze the statements:
I. Nitrogenase is a Mo-Fe protein that catalyses the conversion of atmospheric nitrogen to ammonia. II. It is highly sensitive to molecular oxygen, requiring strictly anaerobic conditions. III. The biological synthesis of two molecules of ammonia (NH3) requires a total input of 8 ATP. IV. Symbiotic microbes live as aerobes under free-living conditions but become anaerobic during nitrogen-fixing events.
Which of the statements given above are correct?
Statements I, II, and IV are correct. Nitrogenase is a molybdenum-iron protein and is extremely oxygen-sensitive. Symbiotic nitrogen-fixing microbes function under anaerobic conditions during nitrogen fixation. Statement III is incorrect because reduction of one N2 molecule to two NH3 molecules requires 16 ATP, not 8 ATP.
Question 25 of 100
📘 CLASS XI
Mineral Nutrition
Consider the following statements regarding the fate of ammonia in plants:
I. At physiological pH, ammonia is protonated to form NH4+ ions, which are toxic and cannot accumulate in plants. II. Reductive amination involves the reaction of ammonia with α-ketoglutaric acid to form glutamic acid in the presence of glutamate dehydrogenase. III. Transamination involves the transfer of an amino group from glutamic acid to the keto group of a keto acid, catalyzed by transaminase. IV. Amides like asparagine and glutamine contain less nitrogen than amino acids and are transported exclusively via phloem.
Which of the statements given above are correct?
Statements I, II, and III are correct. Ammonia is rapidly converted to NH4+ and assimilated through reductive amination and transamination. Statement IV is incorrect because amides contain more nitrogen than amino acids and are transported mainly through the xylem.
Question 26 of 100
📘 CLASS XI
Mineral Nutrition
Consider the following statements regarding manganese toxicity in plants:
I. The prominent symptom of manganese toxicity is the appearance of brown spots surrounded by chlorotic veins. II. Manganese competes with iron and magnesium for uptake and with magnesium for binding with enzymes. III. Manganese promotes calcium translocation to the shoot apex, causing structural rigidity. IV. Excess of manganese may, in fact, induce deficiencies of iron, magnesium, and calcium.
Which of the statements given above are correct?
Statements I, II, and IV are correct. Excess manganese competes with iron and magnesium for uptake and enzyme binding, leading to induced deficiencies of iron, magnesium, and calcium. Brown spots surrounded by chlorotic veins are characteristic symptoms. Statement III is incorrect because manganese inhibits, rather than promotes, calcium translocation to the shoot apex.
Question 27 of 100
📘 CLASS XI
Mineral Nutrition
Analyze the following statements regarding the mechanism of mineral absorption by plants:
I. In the first phase, an initial rapid uptake of ions into the apoplast is passive. II. The passive movement of ions into the apoplast usually occurs through ion channels, which are selective pore-forming transmembrane proteins. III. In the second phase, ions are taken in slowly into the symplast of the cells through active processes requiring metabolic energy. IV. The inward movement of ions into the cells is called efflux, while the outward movement is called influx.
Which of the statements given above are correct?
Statements I, II, and III are correct. Mineral absorption occurs in two phases: a rapid passive uptake into the apoplast followed by a slower active uptake into the symplast requiring metabolic energy. Statement IV is incorrect because inward movement is called influx and outward movement is called efflux.
Question 28 of 100
📘 CLASS XI
Mineral Nutrition
With respect to the translocation of solutes in plants, consider the following statements:
I. Mineral salts are translocated through xylem along with the ascending stream of water. II. The translocation is driven solely by positive root pressure with no contribution from transpirational pull. III. Analysis of xylem sap chemically proves the presence of mineral salts in it. IV. The use of radioisotopes of mineral elements substantiates the view that they are transported through xylem.
Which of the statements given above are correct?
Statements I, III, and IV are correct. Mineral salts move upward through the xylem with the transpiration stream. Chemical analysis of xylem sap and radioisotope studies confirm xylem transport of minerals. Statement II is incorrect because transpirational pull is the principal driving force, while root pressure plays only a limited role.
Question 29 of 100
📘 CLASS XI
Mineral Nutrition
Consider the following statements regarding the role of soil as a reservoir of essential elements:
I. Weathering and breakdown of rock minerals enrich the soil with dissolved ions and inorganic salts. II. Since these essential nutrients are derived from rock minerals, plant nutrition is referred to as mineral nutrition. III. Soil acts as a sterile matrix, meaning it holds water and supplies air but does not harbor any microbial life.
Which of the statements given above is/are correct?
Statements I and II are correct. Weathering of rocks supplies mineral ions to the soil, which is why plant nutrition is known as mineral nutrition. Statement III is incorrect because soil harbors numerous microorganisms, including nitrogen-fixing bacteria, in addition to supplying water and air.
Question 30 of 100
📘 CLASS XI
Mineral Nutrition
Regarding nitrogen as a plant nutrient, analyze the statements below:
I. Nitrogen is a constituent of amino acids, proteins, hormones, chlorophylls, and many vitamins. II. Plants do not compete with soil microbes for nitrogen because microbes utilize a different pool of soil nitrogen. III. Nitrogen exists in the atmosphere as two nitrogen atoms joined by a very strong triple covalent bond (N≡N). IV. The process of conversion of nitrogen (N2) to ammonia is termed nitrogen fixation.
Which of the statements given above are correct?
Statements I, III, and IV are correct. Nitrogen forms proteins, nucleic acids, chlorophyll, hormones, and vitamins. Atmospheric nitrogen possesses a strong triple bond, and its conversion into ammonia is called nitrogen fixation. Statement II is incorrect because plants and soil microbes compete for the same available nitrogen pool.