Mineral Nutrition MCQs for NEET – Page 4

Question 31 of 100

📘 CLASS XI

Mineral Nutrition

In nature, atmospheric nitrogen oxides (NO, NO₂, N₂O) are generated by various energy inputs and activities. Identify the correct sources from the statements below:

I. Lightning and ultraviolet radiation provide the energy in nature to convert nitrogen to nitrogen oxides.
II. Industrial combustions and forest fires act as sources of atmospheric nitrogen oxides.
III. Automobile exhausts and power-generating stations contribute to atmospheric nitrogen oxides.
IV. Symbiotic nitrogen-fixing bacteria actively release nitrogen oxides as products of nitrogenase activity.

Select the correct combination.

Statements I, II, and III are correct. Lightning, UV radiation, industrial combustion, forest fires, vehicle exhausts, and power plants generate atmospheric nitrogen oxides. Statement IV is incorrect because nitrogenase produces ammonia, not nitrogen oxides.

Question 32 of 100

📘 CLASS XI

Mineral Nutrition

Analyze the following definitions of processes in the nitrogen cycle:

I. Decomposition of organic nitrogen of dead plants and animals into ammonia is called ammonification.
II. Conversion of ammonia into nitrate by soil bacteria is called nitrification.
III. Reduction of nitrate present in the soil to gaseous dinitrogen (N₂) is called denitrification.
IV. Conversion of nitrate to ammonia directly in soil by anaerobic fungi is called ammonification.

Which of the statements given above are correct?

Statements I, II, and III are correct. Ammonification converts organic nitrogen into ammonia, nitrification converts ammonia into nitrate through bacterial oxidation, and denitrification converts nitrate back into gaseous nitrogen. Statement IV is incorrect because it does not describe ammonification.

Question 33 of 100

📘 CLASS XI

Mineral Nutrition

Which of the following statements regarding the steps and microbes involved in nitrification are correct?

I. Ammonia is first oxidized to nitrite by the bacteria Nitrosomonas and/or Nitrococcus.
II. Nitrite is further oxidized to nitrate with the help of the bacterium Nitrobacter.
III. These nitrifying bacteria are chemoautotrophs.
IV. These nitrifying bacteria are photoautotrophs that utilize sunlight to oxidize nitrogen compounds.

Explanation: Statements I, II, and III are correct. Ammonia is oxidized to nitrite by Nitrosomonas/Nitrococcus, followed by oxidation of nitrite to nitrate by Nitrobacter. These nitrifying bacteria are chemoautotrophs that derive energy from oxidation of inorganic nitrogen compounds. Statement IV is incorrect because they are not photoautotrophs.

Question 34 of 100

📘 CLASS XI

Mineral Nutrition

Consider the following statements regarding the fate of nitrate absorbed by plants and denitrification:

I. Nitrate absorbed from the soil is transported to the leaves where it is reduced to form ammonia.
II. The ammonia formed in leaves finally forms the amine group of amino acids.
III. Nitrate present in the soil can be reduced to gaseous nitrogen by the process of denitrification.
IV. Denitrification is carried out exclusively by the chemoautotrophic bacteria Nitrosomonas and Nitrobacter.

Explanation: Statements I, II, and III are correct. Nitrate absorbed by plants is reduced to ammonia and incorporated into amino acids. Denitrification converts nitrate into gaseous nitrogen. Statement IV is incorrect because denitrification is carried out mainly by Pseudomonas and Thiobacillus, not by Nitrosomonas or Nitrobacter.

Question 35 of 100

📘 CLASS XI

Mineral Nutrition

Read the statements about biological nitrogen fixation:

I. Very few living organisms can utilize nitrogen in the form of atmospheric N₂.
II. Only certain prokaryotic species are capable of fixing nitrogen.
III. The enzyme nitrogenase, which is capable of nitrogen reduction, is present exclusively in eukaryotes.
IV. Nitrogen-fixing microbes are called N₂-fixers.

Explanation: Statements I, II, and IV are correct. Only certain prokaryotes possess nitrogenase and are capable of fixing atmospheric nitrogen. These organisms are called N₂-fixers. Statement III is incorrect because nitrogenase is found only in prokaryotes, not eukaryotes.

Question 36 of 100

📘 CLASS XI

Mineral Nutrition

Consider the following statements regarding free-living 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. Cyanobacteria like Anabaena and Nostoc are exclusively symbiotic and cannot fix nitrogen under free-living conditions.

Explanation: Statements I and II are correct. Azotobacter and Beijerinckia are free-living aerobic nitrogen fixers, whereas Rhodospirillum is a free-living anaerobic nitrogen fixer. Statement III is incorrect because Anabaena and Nostoc can also fix nitrogen under free-living conditions.

Question 37 of 100

📘 CLASS XI

Mineral Nutrition

Regarding the symbiotic relationship of Rhizobium in plants:

I. Rhizobium is a rod-shaped bacterium.
II. It has a symbiotic relationship with the roots of several legumes such as alfalfa, sweet clover, sweet pea, lentils, garden pea, broad bean, and clover beans.
III. Rhizobium forms near-spherical outgrowths on leaves called nodules.
IV. Nodules are small outgrowths commonly found on the roots of legume plants.

Explanation: Statements I, II, and IV are correct. Rhizobium is a rod-shaped bacterium that forms root nodules on legumes. Statement III is incorrect because nodules develop on roots, not on leaves.

Question 38 of 100

📘 CLASS XI

Mineral Nutrition

Analyze the following statements regarding the microbe Frankia:

I. Frankia produces nitrogen-fixing nodules on the roots of non-leguminous plants.
II. A classic example of a non-leguminous plant that associates with Frankia is Alnus.
III. Frankia is obligately symbiotic and cannot live as a free-living organism in the soil.
IV. Both Rhizobium and Frankia are free-living in soil, but as symbionts, can fix atmospheric nitrogen.

Explanation: Statements I, II, and IV are correct. Frankia forms nitrogen-fixing nodules on non-leguminous plants such as Alnus. Both Frankia and Rhizobium occur free-living in soil but fix nitrogen effectively only in symbiosis. Statement III is incorrect because Frankia is not obligately symbiotic.

Question 39 of 100

📘 CLASS XI

Mineral Nutrition

Identify the correct statements about the color and biochemical adaptation of nodules:

I. If you cut through a legume root nodule, the central portion is red or pink.
II. The red/pink color of the nodule is due to the presence of leg-haemoglobin.
III. Leg-haemoglobin acts as an oxygen scavenger to protect the oxygen-sensitive nitrogenase enzyme.
IV. Leg-haemoglobin is present in high concentrations in free-living aerobic soil bacteria before they infect roots.

Explanation: Statements I, II, and III are correct. Leg-haemoglobin gives root nodules their characteristic pink color and binds oxygen to protect the oxygen-sensitive nitrogenase enzyme. Statement IV is incorrect because leg-haemoglobin is produced only in functional root nodules during symbiosis.

Question 40 of 100

📘 CLASS XI

Mineral Nutrition

The initial stages of nodule formation involve sequential interactions. Analyze these statements:

I. Rhizobia multiply, colonize the root surroundings, and attach to epidermal and root hair cells.
II. Successful infection of the root hair causes it to curl.
III. An infection thread is produced, which carries the bacteria into the cortex of the root.
IV. The infection thread directly deposits bacteria into the xylem vessels, bypassing the cortical cells.

Explanation: Statements I, II, and III are correct. Rhizobia attach to root hairs, induce curling, and enter the cortex through infection threads. Statement IV is incorrect because infection threads do not enter xylem directly; bacteria first reach cortical cells where nodules develop.