Q.91 Botany ⭐ 360° Option Elimination Active
NEET 2025 Botany Question 91 Solution
Topic: Respiration in Plants · Official NTA Booklet Code 45
Question
The complex II of mitochondrial electron transport chain is also known as
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Verified Against NTA Final Answer Key
Option (2) : Succinate dehydrogenase
📚 Respiration in Plants Easy
📋 Given Parameters & Problem Setup
Target Complex Complex II of the mitochondrial Electron Transport Chain (ETC)
Organelle Location Inner mitochondrial membrane
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⏱️ Save ~25 seconds The 30-Second Exam Hall Shortcut: ⚡ ETS Enzyme Complex Fingerprint
Complex I = NADH dehydrogenase, Complex II = Succinate dehydrogenase, Complex III = Cytochrome bc₁, Complex IV = Cytochrome c oxidase, Complex V = ATP synthase! Complex II is Succinate dehydrogenase!
1 Recall the 5 multi-protein complexes of the inner mitochondrial membrane:
2 - Complex I: NADH dehydrogenase (transfers electrons from NADH to ubiquinone).
3 - Complex II: Succinate dehydrogenase (oxidizes succinate to fumarate in Krebs cycle and transfers electrons to ubiquinone via FADH₂).
4 - Complex III: Cytochrome bc₁ complex.
5 - Complex IV: Cytochrome c oxidase (contains cytochromes a and a₃ and two Cu centres).
6 - Complex V: ATP synthase (coupling factor F₀-F₁).
7 Complex II is uniquely Succinate dehydrogenase!
8 Select Option (2) in under 5 seconds!
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Why You Can 100% Trust This Shortcut: NCERT Biology · Respiration in Plants (Mitochondrial ETS: Complex II is succinate dehydrogenase).
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Step-by-Step Rigorous Workflow & Mathematical Proof
Step 1
Organization of the Mitochondrial Electron Transport System (ETS)
Metabolic oxidation of NADH + H⁺ and FADH₂ generated during glycolysis and the TCA cycle transfers electrons through a series of enzyme complexes embedded in the inner mitochondrial membrane:
- • Complex I transfers electrons from NADH to ubiquinone (coenzyme Q) with concomitant proton pumping.
Step 2
Identification and Dual Role of Complex II
Complex II functions simultaneously as an enzyme of the Krebs cycle and a component of the electron transport chain:
- • Electrons from FADH₂ are transferred to ubiquinone to generate ubiquinol (QH₂).
- • Unlike Complexes I, III, and IV, Complex II does not pump protons across the inner mitochondrial membrane.
Step 3
Review Complexes III, IV, and V
Contrast Complex II with the other options:
- • Thus Complex II is specifically Succinate dehydrogenase, matching Option (2).
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4-Option Deep Scan
360° Option Elimination Engine Key Feature
Diagnose every choice: Know exactly why the right option works and why distractors fail.
1 A
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Cytochrome bc₁ is Complex III.
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Student Fallacy (Why candidates pick this trap): Confusing Complex II with Complex III.
2 B
✓ 100% Correct Verdict & Scientific Reason:
100% correct. Complex II is canonically Succinate dehydrogenase.
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Why this is airtight: None; verbatim NCERT recall.
3 C
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Cytochrome c oxidase is Complex IV.
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Student Fallacy (Why candidates pick this trap): Confusing terminal complex with Complex II.
4 D
✗ Incorrect Verdict & Scientific Reason:
Incorrect. NADH dehydrogenase is Complex I.
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Student Fallacy (Why candidates pick this trap): Confusing Complex I with Complex II.
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NTA Trap Alert: Scrambling Numbers of ETS Complexes
Candidates often mix up Complex I (NADH dehydrogenase) and Complex II (Succinate dehydrogenase). Remember that NADH enters first at Complex I, while FADH₂ enters at Complex II!
🛡️ How to avoid the -1 mark: Order of electron entry: NADH at Complex I; Succinate/FADH₂ at Complex II!
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Core NEET Syllabus Standard
NEET Biology Core Syllabus · Respiration in Plants Standard Benchmark
Core Scientific Principle Tested:
"Complex II of mitochondrial ETS is succinate dehydrogenase."
Syllabus Focus: Electron Transport System (ETS) and Oxidative Phosphorylation
✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗
1 = NADH, 2 = Succinate, 3 = bc₁, 4 = Cytochrome c Oxidase ⟹ Complex II = Succinate (Option 2)!
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