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NEET 2020 Zoology Question 75 Solution

Topic: Body Fluids and Circulation · Official NTA Booklet Code E1
NEET 2020 Zoology Question 75: Standard Electrocardiogram (ECG) Waves: QRS Complex Represents Ventricular Depolarisation

Question

The QRS complex in a standard ECG represents:

  1. (1)Repolarisation of auricles
  2. (2)Depolarisation of auricles
  3. (3)Depolarisation of ventricles
  4. (4)Repolarisation of ventricles
✓
Verified Against NTA Final Answer Key
Option (3) : Depolarisation of ventricles
📚 Body Fluids and Circulation Easy
📋 Given Parameters & Problem Setup
Diagnostic Waveform QRS complex in a standard ECG
Question Objective Identify which cardiac electrophysiological event is represented
⚡

The 30-Second Exam Hall Shortcut: ⚡ "P = Atrial Depol; QRS = Ventricular Depol; T = Ventricular Repol!"

⏱️ 20 seconds

P wave represents depolarisation of atria. QRS complex represents DEPOLARISATION OF VENTRICLES (triggering ventricular contraction/systole). T wave represents repolarisation of ventricles. Mark Depolarisation of ventricles (Option 3) in 5 seconds!

1 P-wave = Depolarisation of the atria.
2 QRS complex = Depolarisation of the ventricles.
3 T-wave = Repolarisation of the ventricles.
4 Select Option (3) Depolarisation of ventricles.
🛡️
Why You Can 100% Trust This Shortcut: NCERT Biology · Human Physiology: Body Fluids and Circulation (Electrocardiograph: ECG)
📐

Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Review the Components of a Standard ECG

A standard ECG tracing records the electrical changes propagating through the myocardium during a cardiac cycle, consisting of a P wave, a QRS complex, and a T wave.

Step 2

Analyze the QRS Complex

The QRS complex represents the electrical depolarisation of the ventricles, which initiates the ventricular contraction (ventricular systole shortly after Q).

Step 3

Analyze Other Waveforms

The P-wave represents the electrical excitation (or depolarisation) of the atria, which leads to atrial contraction. The T-wave represents the return of the ventricles from excited to normal state (repolarisation of ventricles).

Step 4

Clinical Application

By counting the number of QRS complexes that occur in a given time period, one can determine the heart beat rate of an individual.

⭐

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 A
✗ Incorrect
Verdict & Scientific Reason:

Incorrect; atrial repolarisation occurs during ventricular depolarisation and is obscured/masked by the large QRS complex; it is not represented by QRS.

⚠️
Student Fallacy (Why candidates pick this trap): Assuming every chamber repolarisation has an isolated named wave.
2 B
✗ Incorrect
Verdict & Scientific Reason:

Incorrect; depolarisation of auricles (atria) is represented by the P-wave, not QRS.

⚠️
Student Fallacy (Why candidates pick this trap): Confusing P-wave with QRS complex.
3 C
✓ 100% Correct
Verdict & Scientific Reason:

Factually exact; the QRS complex marks electrical depolarization spreading rapidly through the ventricular myocardium.

💡
Why this is airtight: None; fundamental ECG interpretation.
4 D
✗ Incorrect
Verdict & Scientific Reason:

Incorrect; ventricular repolarisation is represented by the T-wave.

⚠️
Student Fallacy (Why candidates pick this trap): Confusing depolarisation with repolarisation of the ventricles.
⚠️

NTA Trap Alert: Depolarisation vs Repolarisation in ECG

P = Atrial Depol. QRS = Ventricular Depol. T = Ventricular Repol. (Auricular repolarization is hidden inside QRS).

🛡️ How to avoid the -1 mark: Quick summary: P -> Atria Depol; QRS -> Ventricle Depol; T -> Ventricle Repol!
📖

Core NEET Syllabus Standard

Zoology · Body Fluids and Circulation Standard Benchmark
Core Scientific Principle Tested:

""

Syllabus Focus: Standard Electrocardiogram (ECG) Waves: QRS Complex Represents Ventricular Depolarisation
✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

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