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100 questions in this collection · Page 8 of 10
Question 71 of 100
📘 CLASS XI
Mineral Nutrition
Consider the following statements regarding the chemical properties of nitrogen:
I. Nitrogen is a dinitrogen molecule (N2) containing two nitrogen atoms joined by a very strong triple covalent bond (N ≡ N). II. Conversion of nitrogen (N2) to ammonia is termed nitrogen fixation. III. Plants do not compete with soil microbes for nitrogen because it is highly abundant in the soil.
Explanation: Statements I and II are correct. Atmospheric nitrogen exists as N2 with a strong triple bond, and its conversion into ammonia is called nitrogen fixation. Statement III is incorrect because plants compete with soil microbes for the limited available nitrogen in soil.
Question 72 of 100
📘 CLASS XI
Mineral Nutrition
Analyze the following statements regarding natural sources of nitrogen oxides (NO, NO2, N2O):
I. Lightning and ultraviolet radiation provide enough energy in nature to convert nitrogen to nitrogen oxides. II. Industrial combustion, forest fires, automobile exhausts, and power-generating stations are major sources of atmospheric nitrogen oxides. III. Ammonification is the process of converting nitrogen oxides back into gaseous dinitrogen.
Explanation: Statements I and II are correct. High-energy natural events and combustion processes generate nitrogen oxides. Statement III is incorrect because ammonification is the conversion of organic nitrogen into ammonia, not the reduction of nitrogen oxides.
Question 73 of 100
📘 CLASS XI
Mineral Nutrition
With respect to nitrification, consider the following statements:
I. Ammonia is first oxidized to nitrite by Nitrosomonas and/or Nitrococcus. II. Nitrite is further oxidized to nitrate with the help of Nitrobacter. III. The bacteria carrying out nitrification are photoautotrophs. IV. Nitrifying bacteria are chemoautotrophs.
Explanation: Statements I, II, and IV are correct. Nitrification involves oxidation of ammonia to nitrite by Nitrosomonas/Nitrococcus and nitrite to nitrate by Nitrobacter. These bacteria are chemoautotrophs, not photoautotrophs.
Question 74 of 100
📘 CLASS XI
Mineral Nutrition
Analyze the statements regarding biological nitrogen fixation:
I. Very few living organisms can utilize nitrogen in the form of N2. II. The enzyme nitrogenase, which reduces nitrogen, is present exclusively in prokaryotes. III. Microbes capable of biological nitrogen fixation are called N2-fixers. IV. Biological nitrogen fixation is commonly performed by eukaryotic crop plants without microbial help.
Explanation: Statements I, II, and III are correct. Only certain prokaryotes possess nitrogenase and can fix atmospheric nitrogen. Statement IV is incorrect because crop plants cannot fix nitrogen independently and require symbiotic or free-living prokaryotes.
Question 75 of 100
📘 CLASS XI
Mineral Nutrition
Consider the following statements regarding the free-living and symbiotic nature of nitrogen-fixing microbes:
I.Azotobacter and Beijerinckia are free-living, aerobic nitrogen-fixers. II.Rhodospirillum is a free-living, anaerobic nitrogen-fixing bacterium. III. Cyanobacteria like Anabaena and Nostoc can function as free-living nitrogen-fixers. IV.Rhizobium can fix atmospheric nitrogen actively under free-living, aerobic conditions in the soil.
Explanation: Statements I, II, and III are correct. Azotobacter and Beijerinckia are free-living aerobes, Rhodospirillum is a free-living anaerobe, and Anabaena and Nostoc can fix nitrogen under free-living conditions. Statement IV is incorrect because Rhizobium fixes nitrogen only in symbiotic association with host plants.
Question 76 of 100
📘 CLASS XI
Mineral Nutrition
Consider the following statements regarding symbiotic nitrogen-fixing microbes:
I. Both Frankia and Rhizobium are free-living in soil but can fix nitrogen only as symbionts. II.Frankia produces nitrogen-fixing nodules on the roots of leguminous plants like Alnus. III.Rhizobium forms symbiotic relationships with plants like alfalfa, sweet clover, and sweet pea. IV. The enzyme nitrogenase is active in free-living Rhizobium under highly aerobic conditions.
Explanation: Statements I and III are correct. Both Frankia and Rhizobium are free-living in soil but fix nitrogen only in symbiotic association. Rhizobium associates with legumes such as alfalfa, sweet clover, and sweet pea. Statement II is incorrect because Alnus is a non-leguminous plant. Statement IV is incorrect because nitrogenase functions only under anaerobic conditions and is not active in free-living aerobic Rhizobium.
Question 77 of 100
📘 CLASS XI
Mineral Nutrition
Analyze the following statements about hydroponic plant production:
I. In 1860, Julius von Sachs demonstrated for the first time that plants can be grown to maturity in a defined nutrient solution in the complete absence of soil. II. Hydroponics allows for the identification of essential elements and their deficiency symptoms. III. It is essential to use tap water containing natural trace minerals to run successful hydroponic trials. IV. Hydroponic techniques require that the nutrient solution be adequately aerated to obtain optimum root growth.
Explanation: Statements I, II, and IV are correct. Julius von Sachs pioneered hydroponics, the technique is useful for identifying essential elements and deficiency symptoms, and nutrient solutions must be adequately aerated. Statement III is incorrect because purified water with defined mineral nutrients is required rather than tap water.
Question 78 of 100
📘 CLASS XI
Mineral Nutrition
Regarding the natural sources of atmospheric nitrogen oxides, consider the following statements:
I. Lightning and ultraviolet radiation provide enough energy in nature to convert nitrogen to nitrogen oxides (NO, NO2, N2O). II. Industrial combustions, forest fires, automobile exhausts, and power-generating stations are major sources of atmospheric nitrogen oxides. III. Plants absorb nitrogen oxides directly through their stomata to satisfy their entire nitrogen requirement.
Explanation: Statements I and II are correct. Natural high-energy events and combustion processes generate atmospheric nitrogen oxides. Statement III is incorrect because plants obtain nitrogen mainly by absorbing nitrate and ammonium ions from the soil, not atmospheric nitrogen oxides.
Question 79 of 100
📘 CLASS XI
Mineral Nutrition
Which of the following statements strictly define the criteria for the essentiality of an element in plants?
I. The element must be absolutely necessary for supporting normal growth and reproduction. II. The requirement of the element must be specific and replaceable by another similar element. III. In the absence of the element, the plants do not complete their life cycle or set seeds. IV. The element must be directly involved in the metabolism of the plant.
Explanation: Statements I, III, and IV are the accepted criteria for essentiality. Statement II is incorrect because an essential element cannot be replaced by another element.
Question 80 of 100
📘 CLASS XI
Mineral Nutrition
Analyze the following statements regarding the categorization of essential mineral nutrients:
I. Micronutrients are needed in very small amounts, less than 10 mmole Kg-1 of dry matter. II. Iron, manganese, copper, molybdenum, zinc, boron, chlorine, and nickel are micronutrients. III. Carbon, hydrogen, oxygen, nitrogen, phosphorus, sulphur, potassium, calcium, and magnesium are macronutrients. IV. Sodium, silicon, cobalt, and selenium are macronutrients required by all plants.
Explanation: Statements I, II, and III are correct. Micronutrients are required in trace amounts, whereas C, H, O, N, P, S, K, Ca, and Mg are macronutrients. Statement IV is incorrect because sodium, silicon, cobalt, and selenium are beneficial elements rather than essential macronutrients.