Q.137 Botany ⭐ 360° Option Elimination Active

NEET 2021 Botany Question 137 Solution

Topic: Mineral Nutrition · Official NTA Booklet Code M1

Question

Match Column - I with Column - II. (a) Nitrococcus (i) Denitrification (b) Rhizobium (ii) Conversion of ammonia to nitrite (c) Thiobacillus (iii) Conversion of nitrite to nitrate (d) Nitrobacter (iv) Conversion of atmospheric nitrogen to ammonia Column - I Column - II Choose the correct answer from options given below. (a) (b) (c) (d)

(1)(ii) (iv) (i) (iii)
(2)(i) (ii) (iii) (iv)
(3)(iii) (i) (iv) (ii)
(4)(iv) (iii) (ii) (i)

✓

Verified Against NTA Final Answer Key

Option (1) : (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)

📚 Mineral Nutrition Easy

📋 Given Parameters & Problem Setup

Column I (Microbes) (a) Nitrococcus, (b) Rhizobium, (c) Thiobacillus, (d) Nitrobacter

Column II (Processes) (i) Denitrification, (ii) Ammonia to nitrite, (iii) Nitrite to nitrate, (iv) Atmospheric nitrogen to ammonia

⚡

The 30-Second Exam Hall Shortcut: ⚡ Fast Nitrogen Pairing: Rhizobium Fixes N2 (b-iv) & Thiobacillus Denitrifies (c-i)

⏱️ Save ~20 seconds

Nitrococcus converts Ammonia $\to$ Nitrite (a-ii); Rhizobium fixes N2 $\to$ NH3 (b-iv); Thiobacillus/Pseudomonas carry out Denitrification (c-i); Nitrobacter converts Nitrite $\to$ Nitrate (d-iii). Gives (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii) $\implies$ Option (1)!

1 (a) Nitrococcus (and Nitrosomonas):

2\text{NH}_3 + 3\text{O}_2 \to 2\text{NO}_2^- + 2\text{H}^+ + 2\text{H}_2\text{O} \implies

(ii).

2 (b) Rhizobium: Symbiotic biological nitrogen fixation (

N_2 \to NH_3

)

\implies

(iv).

3 (c) Thiobacillus (and Pseudomonas): Denitrification (

NO_3^- \to N_2

)

\implies

(i).

4 (d) Nitrobacter:

2\text{NO}_2^- + \text{O}_2 \to 2\text{NO}_3^- \implies

(iii).

5 Match Option (1).

🛡️

Why You Can 100% Trust This Shortcut: Canonical NCERT Mineral Nutrition on Nitrogen Cycle and Microorganisms.

📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Microbiological Steps of the Nitrogen Cycle

The biological transformation of nitrogen involves distinct specialized bacterial taxa:

\begin{aligned} \text{\textbf{1. Ammonia to Nitrite:}} & \quad 2\text{NH}_3 + 3\text{O}_2 \xrightarrow{\text{\textit{Nitrosomonas} / \textit{Nitrococcus}}} 2\text{NO}_2^- + 2\text{H}^+ + 2\text{H}_2\text{O} \implies \text{(a)-(ii)} \\[4pt] \text{\textbf{2. Nitrite to Nitrate:}} & \quad 2\text{NO}_2^- + \text{O}_2 \xrightarrow{\text{\textit{Nitrobacter}}} 2\text{NO}_3^- \implies \text{(d)-(iii)} \\[4pt] \text{\textbf{3. Nitrogen Fixation:}} & \quad \text{N}_2 + 8\text{e}^- + 8\text{H}^+ + 16\text{ATP} \xrightarrow{\text{\textit{Rhizobium}}} 2\text{NH}_3 + \text{H}_2 + 16\text{ADP} + 16\text{P}_i \implies \text{(b)-(iv)} \\[4pt] \text{\textbf{4. Denitrification:}} & \quad \text{NO}_3^- \xrightarrow{\text{\textit{Pseudomonas} / \textit{Thiobacillus}}} \text{N}_2 \implies \text{(c)-(i)} \end{aligned}

Step 2

Matching Assembly

The correspondence yields (a)-(ii), (b)-(iv), (c)-(i), (d)-(iii), which is uniquely found in Option (1).

⭐

360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 1

✓ 100% Correct

Verdict & Scientific Reason:

Every bacterial species is mapped precisely to its biochemical metabolic step in the nitrogen cycle.

💡

Why this is airtight: None. Textbook accurate mapping.

2 2

✗ Incorrect

Verdict & Scientific Reason:

Mismatches Nitrococcus with denitrification and Nitrobacter with nitrogen fixation.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing nitrifiers with denitrifiers.

3 3

✗ Incorrect

Verdict & Scientific Reason:

Inverts Nitrococcus with Nitrobacter and Rhizobium with denitrification.

⚠️

Student Fallacy (Why candidates pick this trap): Swapping step 1 and step 2 of nitrification.

4 4

✗ Incorrect

Verdict & Scientific Reason:

Gross misassignment across all four bacterial classes.

⚠️

Student Fallacy (Why candidates pick this trap): Random guessing.

⚠️

NTA Trap Alert: Nitrosomonas/Nitrococcus vs Nitrobacter Step Inversion

Nitrosomonas and Nitrococcus convert NH3 to NO2- (Nitrite). Nitrobacter converts NO2- to NO3- (Nitrate).

🛡️ How to avoid the -1 mark: Alphabetical memory: "Coccus comes before Bacter"

\implies

Nitrococcus first (

NH_3 \to NO_2^-

), Nitrobacter second (

NO_2^- \to NO_3^-

📖

Core NEET Syllabus Standard

NEET / NCERT Biology · Mineral Nutrition Standard Benchmark

Core Scientific Principle Tested:

"Ammonia is oxidized to nitrite by Nitrosomonas and/or Nitrococcus. Nitrite is oxidized to nitrate by Nitrobacter. Denitrification is carried out by Pseudomonas and Thiobacillus."

Syllabus Focus: Metabolism of Nitrogen: Nitrogen Cycle

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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NEET 2021 Botany Question 137 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Fast Nitrogen Pairing: Rhizobium Fixes N2 (b-iv) & Thiobacillus Denitrifies (c-i)

Step-by-Step Rigorous Workflow & Mathematical Proof

Microbiological Steps of the Nitrogen Cycle

Matching Assembly

360° Option Elimination Engine Key Feature

NTA Trap Alert: Nitrosomonas/Nitrococcus vs Nitrobacter Step Inversion

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

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