Last Updated: April 2026
The Human Respiratory System is a consistently tested chapter in NEET Biology, contributing 3–5 questions per paper. In NEET 2025, all 4 respiratory system questions were directly from NCERT Class 11 Chapter 17. This guide provides chapter notes, MCQ patterns and 10 practice questions with explanations.
Respiratory System — NEET Weightage Analysis
| Chapter | Class | Avg NEET Questions | Difficulty |
|---|---|---|---|
| Breathing and Exchange of Gases (Ch 17) | Class 11 | 3–5 | Medium |
| Body Fluids and Circulation (Ch 18) | Class 11 | 3–4 | Medium |
| Excretory Products and Elimination (Ch 19) | Class 11 | 3–4 | Medium-High |
Key Concepts — Breathing and Exchange of Gases
- Respiratory organs: Nostrils → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli
- Alveoli: ~300 million in human lungs; total surface area ~80 sq.m
- Tidal Volume (TV): 500 mL — air inspired/expired in normal breathing
- Inspiratory Reserve Volume (IRV): ~2500–3000 mL
- Expiratory Reserve Volume (ERV): ~1000–1100 mL
- Residual Volume (RV): ~1100–1200 mL — air left after forceful expiration
- Vital Capacity (VC): TV + IRV + ERV = ~3500–4500 mL
- Total Lung Capacity (TLC): VC + RV = ~6000 mL
Lung Volumes and Capacities — Key Table
| Volume/Capacity | Value | Components |
|---|---|---|
| Tidal Volume (TV) | 500 mL | Normal breathing |
| IRV | 2500–3000 mL | Extra inhale after normal |
| ERV | 1000–1100 mL | Extra exhale after normal |
| Residual Volume (RV) | 1100–1200 mL | Cannot be exhaled |
| Inspiratory Capacity (IC) | 3500 mL | TV + IRV |
| Functional Residual Capacity (FRC) | 2200 mL | ERV + RV |
| Vital Capacity (VC) | 4500 mL | TV + IRV + ERV |
| Total Lung Capacity (TLC) | 6000 mL | VC + RV |
Gas Exchange — Key Facts
- Partial pressure of O2 in alveoli: 104 mmHg; in deoxygenated blood: 40 mmHg → O2 diffuses into blood
- Partial pressure of CO2 in deoxygenated blood: 45 mmHg; in alveoli: 40 mmHg → CO2 diffuses out
- Haemoglobin carries O2 as oxyhaemoglobin (97%) and CO2 as carbaminohaemoglobin (20–25%)
- CO2 primarily transported as bicarbonate ions (HCO3⁻) in plasma (~70%)
- Bohr Effect: Increased CO2 / decreased pH reduces O2 affinity of Hb → more O2 released to tissues
10 Practice MCQs — Respiratory System NEET Level
- Which of the following cannot be exhaled even after maximum expiration?
A) Tidal Volume B) ERV C) Residual Volume D) IRV
Answer: C — Residual Volume (1100–1200 mL) always remains in lungs - The partial pressure of O2 in alveolar air is approximately:
A) 40 mmHg B) 104 mmHg C) 159 mmHg D) 45 mmHg
Answer: B — 104 mmHg in alveoli; 159 mmHg in atmospheric air - Carbaminohaemoglobin refers to:
A) O2 bound to Hb B) CO2 bound to Hb C) CO bound to Hb D) N2 bound to Hb
Answer: B — CO2 binds to haemoglobin forming carbaminohaemoglobin - Vital Capacity equals:
A) TV + IRV B) TV + ERV C) TV + IRV + ERV D) TV + IRV + ERV + RV
Answer: C - The Bohr Effect refers to:
A) Increased O2 binding at high CO2 B) Decreased O2 affinity of Hb at low pH C) Increased Hb synthesis D) CO2 transport as bicarbonate
Answer: B
Frequently Asked Questions — NEET Respiratory System
How many questions come from Breathing and Exchange of Gases in NEET?
NEET typically has 3–5 questions from Chapter 17 (Breathing and Exchange of Gases) from Class 11 NCERT Biology. This chapter covers respiratory organs, lung volumes, gas exchange mechanics, and transport of gases — all directly testable from NCERT text and diagrams.
What is the difference between Vital Capacity and Total Lung Capacity?
Vital Capacity (VC) = TV + IRV + ERV (~4500 mL) — the maximum air you can breathe out after maximum inhalation. Total Lung Capacity (TLC) = VC + RV (~6000 mL) — includes the Residual Volume that cannot be expelled even by forceful expiration.
How is CO2 primarily transported in blood?
CO2 is primarily transported as bicarbonate ions (HCO3⁻) dissolved in plasma — approximately 70% of total CO2. About 20–25% is carried as carbaminohaemoglobin (bound to Hb), and ~7% is dissolved directly in plasma.
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