Mineral Nutrition — NEET UG practice

Recall micronutrient functions - Each micronutrient in plants performs a specific biochemical role.

Match Iron - Iron is essential for chlorophyll synthesis and also acts as an activator of the enzyme catalase. So, (A) Iron matches (III) Activator of catalase.

Match Zinc - Zinc is required for the synthesis of the plant growth hormone auxin (IAA). So, (B) Zinc matches (I) Synthesis of auxin.

Match Boron - Boron is essential for cell elongation, differentiation, and pollen germination. So, (C) Boron matches (IV) Cell elongation and differentiation.

Match Molybdenum - Molybdenum is a component of the enzyme nitrate reductase, which reduces nitrate to nitrite. So, (D) Molybdenum matches (II) Component of nitrate reductase.

Conclusion - Putting it together: A-III, B-I, C-IV, D-II. Hence, the answer is Option B.

Understand remobilization - In plants, remobilization means nutrients move from older, mature tissues (like older leaves) to younger, actively growing tissues (like new leaves or developing seeds/fruits) when the plant needs them.

Ions that are remobilized - Elements such as potassium, nitrogen, and phosphorus are highly mobile inside the plant body. They can be withdrawn from senescing (aging) tissues and sent to growing regions.

Why calcium behaves differently - Calcium gets deposited as part of the cell wall (as calcium pectate) and other structural components once absorbed. Because it becomes structurally bound, it cannot be pulled back out and moved to new tissues.

Eliminating other options - Since potassium (A), nitrogen (C), and phosphorus (D) are all known to be remobilized, they cannot be the correct answer.

Conclusion - Hence, the mineral ion that is not remobilized in plants is Calcium, so the answer is Option B.

Recall the nitrogen cycle - Nitrogen fixation converts atmospheric $N_2$ into ammonia ($NH_3$); nitrification converts ammonia to nitrite and then nitrite to nitrate; denitrification converts nitrate/nitrite back into atmospheric nitrogen.

Match Nitrococcus - Nitrococcus is a nitrifying bacterium that carries out the first step of nitrification. So, (A) Nitrococcus matches (II) Conversion of ammonia to nitrite.

Match Rhizobium - Rhizobium lives in root nodules of legumes and performs biological nitrogen fixation. So, (B) Rhizobium matches (IV) Conversion of atmospheric nitrogen to ammonia.

Match Thiobacillus - Thiobacillus is a denitrifying bacterium that converts nitrate/nitrite back to nitrogen gas. So, (C) Thiobacillus matches (I) Denitrification.

Match Nitrobacter - Nitrobacter carries out the second step of nitrification, converting nitrite to nitrate. So, (D) Nitrobacter matches (III) Conversion of nitrite to nitrate.

Conclusion - Putting it together: (A)-(II), (B)-(IV), (C)-(I), (D)-(III). Hence, the answer is Option C.