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Important Questions: CBSE Class 11 Biology Chapter 14 Breathing & Exchange of Gases

CBSE Class 11 Biology Chapter 14 Breathing & Exchange of Gases is a cornerstone chapter in Human Physiology, bridging anatomy with biochemical processes. Students often face challenges distinguishing between inspiration-expiration mechanics and the chemical transport of gases. This question bank provides 18 carefully curated questions mirroring the 2025 CBSE exam pattern, complete with model answers that use NCERT terminology verbatim.

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Key takeaways

✓Chapter 14 typically carries 6-8 marks in CBSE Class 11 Biology exams, appearing in both objective and descriptive formats
✓Questions on mechanism of breathing and respiratory volumes are frequently asked for 3-5 marks
✓Transport of oxygen and carbon dioxide (oxygen dissociation curve, chloride shift) are high-weightage topics
✓Diagram-based questions on human respiratory system and alveolar structure appear almost every year
✓Case-based questions on respiratory disorders (asthma, emphysema, occupational hazards) are increasingly common
✓Understanding the difference between breathing, respiration, and cellular respiration prevents conceptual errors

Chapter Overview and CBSE Exam Weightage

Chapter 14 is part of Unit VI Human Physiology, which contributes 18 marks to the CBSE Class 11 Biology theory paper (total 70 marks). Within this unit, Breathing & Exchange of Gases typically accounts for 6-8 marks distributed across different question types. The 2024 CBSE exam carried one 3-mark question on mechanism of breathing and one 5-mark question on transport of gases. The chapter covers three core NCERT topics: respiratory organs (including anatomy of lungs, trachea, bronchi, and alveoli), mechanism of breathing (inspiration, expiration, respiratory volumes, and capacities), and transport of gases (oxygen and carbon dioxide transport, oxygen dissociation curve, factors affecting it). Questions often integrate diagrams, expecting students to label structures or explain physiological processes with annotated sketches. Numerical problems on tidal volume, vital capacity, and partial pressures appear occasionally but are scoring if practised systematically.

Unit VI Human Physiology: 18 marks total; Chapter 14 contributes 6-8 marks
Common question formats: 1-mark MCQs (2-3 questions), one 3-mark descriptive, one 5-mark detailed answer
Diagram-based questions appear 70% of the time — practise labelling respiratory organs and alveolar structure
NCERT Exercise questions and exemplar MCQs are directly repeated or slightly modified in board exams

1-Mark Questions: Multiple Choice and Very Short Answer

One-mark questions test factual recall and conceptual clarity. CBSE frequently asks definition-based MCQs, identification of respiratory structures, or simple physiological facts. These questions appear in Section A of the theory paper and are crucial for scoring quickly. Students should memorise NCERT definitions verbatim, especially terms like tidal volume, vital capacity, residual volume, and partial pressure. The oxygen dissociation curve is a favourite topic for assertion-reason or diagram-based MCQs. Respiratory disorders (emphysema, asthma, occupational respiratory diseases) are also tested through one-liners. Practising NCERT Exemplar MCQs and previous years' board questions ensures familiarity with the phrasing CBSE uses. Below are six representative 1-mark questions with answers.

2-Mark Questions with Model Answers

Two-mark questions demand brief explanations or two distinct points. CBSE examiners expect students to write 30-40 words per question, using correct terminology. Common themes include differences (breathing vs respiration, inspiration vs expiration), functions of respiratory structures, and physiological concepts like the Bohr effect or Haldane effect. Students often lose marks by writing vague statements instead of specific mechanisms. For instance, when asked about the role of diaphragm, stating 'it helps in breathing' is insufficient; the answer must mention contraction increasing thoracic volume during inspiration. Below are four 2-mark questions reflecting typical CBSE phrasing.

3-Mark Questions with Detailed Answers

Three-mark questions require structured answers with 60-80 words, often involving mechanisms or multiple interrelated points. CBSE expects clear sequencing — for example, when explaining inspiration, students should describe diaphragm contraction, increase in thoracic volume, decrease in intrapulmonary pressure, and inflow of air in that order. Diagrams, when relevant, can fetch an extra mark if neatly labelled. Topics like respiratory volumes, exchange of gases across alveolar membrane, and transport mechanisms are frequently tested. Students should use NCERT terminology such as 'partial pressure gradient', 'bicarbonate formation in RBCs', and 'oxygen dissociation curve'. Below are three representative 3-mark questions with model answers.

5-Mark Questions and Case-Based Problems

Five-mark questions are the highest-weightage items in CBSE Class 11 Biology exams, demanding comprehensive explanations, integration of multiple concepts, and often a labelled diagram. These questions assess depth of understanding — simply reproducing NCERT text is insufficient; students must organise information logically and connect physiology with chemistry. Topics such as the complete mechanism of breathing (inspiration and expiration), transport of carbon dioxide (chloride shift, carbaminohaemoglobin, dissolved CO₂), and the oxygen dissociation curve with factors affecting it are standard. Case-based questions, introduced in recent CBSE patterns, present a clinical or real-life scenario followed by sub-questions. For instance, a case might describe a patient with chronic obstructive pulmonary disease and ask about respiratory volumes, gas exchange impairment, and compensatory mechanisms. Below are two 5-mark questions with detailed model answers.

How CBSE Frames Questions from This Chapter

CBSE question setters follow a predictable pattern when designing questions for Chapter 14, balancing factual recall with application and analysis. One-mark MCQs often test definitions, numerical values (partial pressures, respiratory volumes), or identification of structures in diagrams. Two-mark questions probe understanding of physiological processes — examiners use verbs like 'differentiate', 'explain briefly', or 'state the role of'. Three-mark questions demand sequencing of events (e.g., steps in inspiration, formation of bicarbonate) and expect students to use NCERT terms precisely. Five-mark questions integrate multiple topics; for instance, a question on 'Discuss the transport of respiratory gases' requires covering both oxygen and carbon dioxide, their chemical forms, and regulatory factors. Diagram-based questions appear in 70% of papers — students must practise labelling the human respiratory system (nasal cavity to alveoli) and the alveolar structure (type I and II cells, capillaries, surfactant). Case-based questions, now a fixture, test application: a scenario might describe high-altitude hypoxia and ask how the body compensates (increased RBC production, shift in oxygen dissociation curve). CBSE also loves assertion-reason MCQs linking structure to function, such as 'Assertion: Cartilaginous rings are present in the trachea. Reason: They prevent collapse during breathing.' Examiners reward answers that cite NCERT figures, use standard units (mm Hg for pressure, mL for volumes), and avoid colloquial language. Practising NCERT Exemplar, previous years' board papers, and sample papers from CBSE's official website is the most reliable strategy.

Diagrams fetch 1-2 marks — ensure labels are accurate (e.g., 'bronchioles', not 'small tubes'; 'diaphragm', not 'breathing muscle')
Numerical values must be precise: alveolar pO₂ is 104 mm Hg, tissue pO₂ is 40 mm Hg, tidal volume is ~500 mL
Use NCERT terms verbatim: 'carbonic anhydrase', 'chloride shift', 'oxygen dissociation curve', 'partial pressure gradient'
Questions often combine topics: a 5-mark question might ask for mechanism of breathing AND regulation by the respiratory centre
Case-based questions (4-5 marks total, split into 3-4 sub-questions) are increasingly common since 2023

Common Mistakes Students Make and How to Avoid Them

Students frequently confuse breathing with respiration — breathing is the physical process of gas exchange in lungs, whereas respiration includes cellular oxidation of glucose. CBSE specifically tests this distinction through assertion-reason MCQs. Another common error is misunderstanding the oxygen dissociation curve: students often fail to explain why the curve is sigmoid (cooperative binding of oxygen to haemoglobin) or forget factors that shift it (pH, temperature, CO₂, 2,3-BPG). When describing the chloride shift, many write vague statements like 'chloride moves in' without explaining that it maintains electrical neutrality when bicarbonate exits RBCs. In numerical problems, unit errors are frequent — pressures should be in mm Hg, volumes in mL or litres. Students also lose marks in diagram-based questions by incorrect labelling: writing 'windpipe' instead of 'trachea' or 'air sacs' instead of 'alveoli'. For mechanism of breathing, a major pitfall is not distinguishing active (inspiration) from passive (normal expiration) processes; forced expiration is active and involves internal intercostals. When asked about regulation, students often omit the role of chemoreceptors or wrongly state that oxygen is the primary regulator (it is CO₂ and H⁺). Finally, many fail to practise NCERT exercise questions thoroughly — about 40% of board questions are direct or slightly modified versions of these. Revising NCERT diagrams, tables, and in-text examples is non-negotiable.

Do not write 'respiration' when the question asks about 'breathing' — they are distinct processes
Always specify which respiratory volume cannot be measured by spirometry (residual volume) — common 1-mark question
In oxygen dissociation curve questions, mention 'sigmoid shape due to cooperative binding' and at least two factors affecting it
Use correct chemical notation: HbO₂ (oxyhaemoglobin), HCO₃⁻ (bicarbonate), CO₂, O₂
Practise writing the carbonic anhydrase reaction equation — it appears frequently in 2-3 mark questions
Avoid colloquial terms: 'breathing muscles' should be 'diaphragm and intercostal muscles'; 'voice box' should be 'larynx'

Leveraging CBSETUTOR.ai for Mastery of Chapter 14

Many CBSE Class 11 students struggle with the physiological mechanisms and numerical aspects of Breathing & Exchange of Gases, especially when coaching support is limited or inconsistent. CBSETUTOR.ai offers a 24×7 AI tutor designed specifically for Indian CBSE students across classes 6-12. Students can photograph any question from NCERT, exemplar, or previous years' papers, and receive step-by-step solutions using NCERT terminology. For Chapter 14, the platform explains complex concepts like the oxygen dissociation curve, chloride shift, and regulation of breathing through interactive prompts and annotated diagrams. Unlike generic tutoring apps, CBSETUTOR.ai is grounded in the CBSE syllabus and marking scheme, ensuring answers match board exam expectations. The platform costs a flat ₹999 per month for unlimited access across all subjects — one price regardless of class. Parents in metros juggling work and commute, and students in Tier-2/3 cities without access to quality coaching, find this round-the-clock support invaluable. A 3-day free trial allows students to test the platform risk-free, uploading practice questions and comparing AI-generated answers with their own to identify gaps. For Chapter 14, practising all NCERT exercise questions, exemplar MCQs, and sample paper questions on CBSETUTOR.ai builds both conceptual clarity and exam confidence.

Upload photos of diagrams (respiratory system, alveolar structure) and get labelled, exam-ready versions instantly
Ask conceptual doubts like 'Why is the oxygen dissociation curve sigmoid?' and receive NCERT-aligned explanations
Practise 5-mark questions and compare your answers with model solutions, learning how to structure long-form responses
Access topic-wise question banks and previous years' board questions filtered for Chapter 14
Available 24×7 — ideal for late-night revision or last-minute doubt clearing before exams
₹999/month flat fee for classes 6-12, all subjects; 3-day free trial with no credit card required

Revision Strategy for Chapter 14

With 6-8 marks at stake, Chapter 14 demands focused, strategic revision. Start by creating a topic checklist: respiratory organs and their functions, mechanism of breathing (inspiration and expiration), respiratory volumes and capacities, exchange of gases (partial pressure gradients), transport of oxygen (haemoglobin binding, oxygen dissociation curve, factors affecting it), transport of carbon dioxide (dissolved, carbaminohaemoglobin, bicarbonate formation, chloride shift), and regulation of respiration (medulla, chemoreceptors). Devote separate sessions to each, ensuring you can explain mechanisms step-by-step without referring to notes. NCERT diagrams are critical — redraw the human respiratory system, alveolar structure, and oxygen dissociation curve multiple times until you can label them blindfolded. Practise at least 10 previous years' board questions and 5 case-based scenarios to familiarise yourself with CBSE phrasing. Make flashcards for numerical values (partial pressures, respiratory volumes) and revise them daily. For 5-mark questions, time yourself — aim to write a complete answer in 8-10 minutes, including a diagram if required. Group study can help: quiz each other on 1-mark MCQs and peer-review 3-mark answers for completeness and terminology. In the final week, focus on NCERT exemplar MCQs and assertion-reason questions, as these are often repeated. Finally, avoid last-minute cramming of new material; instead, consolidate what you have practised. Confidence in this chapter boosts overall performance in Unit VI Human Physiology.

Week 1: Cover respiratory organs and mechanism of breathing; practise 1-mark and 2-mark questions
Week 2: Master transport of gases (both O₂ and CO₂); solve 3-mark and 5-mark questions
Week 3: Revise respiratory volumes, regulation, and disorders; attempt case-based questions
Week 4: Full-chapter mock test (8-10 questions, 30 minutes); identify weak areas and revise targeted topics
Daily: Memorise one numerical value or definition; redraw one NCERT diagram
Use CBSETUTOR.ai for instant doubt resolution and model answer comparison

Frequently asked questions

How many marks does Chapter 14 Breathing & Exchange of Gases carry in CBSE Class 11 Biology?+

Chapter 14 typically contributes 6-8 marks to the CBSE Class 11 Biology theory paper (70 marks total). Questions appear as 1-mark MCQs, 2-3 mark short answers, and one 5-mark long answer, often integrated with a diagram or case-based scenario.

Which topics in Chapter 14 are most frequently asked in CBSE board exams?+

Mechanism of breathing (inspiration and expiration), transport of carbon dioxide (bicarbonate formation and chloride shift), oxygen dissociation curve and factors affecting it, and respiratory volumes are the most frequently tested topics. Diagram-based questions on the human respiratory system and alveolar structure also appear almost every year.

What is the oxygen dissociation curve, and why is it important for exams?+

The oxygen dissociation curve is a sigmoid graph showing the relationship between partial pressure of oxygen and percentage saturation of haemoglobin. It is important because CBSE often asks 3-5 mark questions on factors shifting the curve (pH, temperature, CO₂, 2,3-BPG) and their physiological significance in oxygen delivery to tissues.

How should I prepare diagram-based questions for Chapter 14?+

Practise redrawing NCERT diagrams (human respiratory system from nasal cavity to alveoli, alveolar structure with type I and II cells, oxygen dissociation curve) at least 5-7 times. Label each part using NCERT terminology. In exams, draw neatly, use a pencil for diagrams, label with arrow lines, and write labels horizontally for clarity. Diagrams can fetch 1-2 marks.

What is the chloride shift, and how do I explain it in exams?+

The chloride shift (Hamburger phenomenon) is the movement of chloride ions into red blood cells from plasma to maintain electrical neutrality when bicarbonate ions diffuse out. In a 2-3 mark answer, describe CO₂ entering RBCs, carbonic anhydrase catalysing formation of bicarbonate and H⁺, bicarbonate exiting, and chloride entering. Use the equation: CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃⁻.

What are the common mistakes to avoid in questions on mechanism of breathing?+

Common mistakes include not distinguishing that inspiration is active (diaphragm and external intercostals contract) while normal expiration is passive (muscles relax). Also, students often confuse intrapulmonary pressure changes — pressure decreases during inspiration (air flows in) and increases during expiration (air flows out). Use NCERT terminology precisely.

How is carbon dioxide mainly transported in blood, and what percentage?+

About 70% of carbon dioxide is transported as bicarbonate ions (HCO₃⁻) in plasma, formed inside RBCs by the enzyme carbonic anhydrase. Approximately 20-23% is carried as carbaminohaemoglobin (bound to globin), and about 7% is dissolved in plasma. CBSE often asks for these percentages in 2-mark questions.

What respiratory volumes cannot be measured by spirometry?+

Residual volume (RV) — the volume of air remaining in lungs after maximum expiration — cannot be measured by spirometry. This is a favourite 1-mark MCQ in CBSE exams. Total lung capacity, which includes residual volume, also cannot be directly measured by spirometry alone.

How does CBSE test the regulation of respiration in exams?+

CBSE typically asks 3-5 mark questions on how the respiratory rhythm centre in the medulla oblongata and pons regulates breathing rate and depth. You must mention chemosensitive areas responding to CO₂ and H⁺ levels, peripheral chemoreceptors (carotid and aortic bodies) detecting low oxygen, and the pneumotaxic centre preventing over-inflation.

Can CBSETUTOR.ai help me practise Chapter 14 questions with instant feedback?+

Yes, CBSETUTOR.ai allows you to upload photos of any question from Chapter 14 — NCERT exercises, exemplar MCQs, or previous years' papers — and receive step-by-step solutions using NCERT terminology. The AI tutor explains mechanisms, provides labelled diagrams, and helps structure 5-mark answers. It is available 24×7 at ₹999/month (one price for all classes 6-12) with a 3-day free trial.

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