Chapter 17: Breathing and Exchange of Gases – Case-Based / Source-Based Questions with Answers
CBSE Class 11 Biology Case-Based Questions – Breathing and Exchange of Gases (NCERT)
Course & Examination Details
- Course: CBSE Class 11 Biology
- Prescribed By: Central Board of Secondary Education
- Based On: NCERT
- Unit: Unit V – Human Physiology
- Chapter: Chapter 17 – Breathing and Exchange of Gases
- Question Type: Case-Based / Source-Based Questions
- Exam Relevance: CBSE Class 11 Annual Examination, Unit Tests, Competency-Based Assessments
Section A: Respiratory Organs (Case 1–9)
Case 1
A student observes that inhaled air becomes warm and moist before reaching the lungs.
Q1. Which part of the respiratory system is responsible for this change?
Answer:
The nasal cavity is responsible for warming and moistening inhaled air.
Q2. State one advantage of this modification.
Answer:
It protects delicate alveolar surfaces and ensures efficient gaseous exchange.
Case 2
A patient with damaged alveoli shows reduced oxygen uptake.
Q3. Why does alveolar damage reduce oxygen absorption?
Answer:
Alveolar damage reduces surface area and increases diffusion distance, lowering oxygen diffusion into blood.
Case 3
During a dissection, the trachea is found to have C-shaped rings.
Q4. What is the function of these rings?
Answer:
They prevent collapse of the trachea and maintain an open air passage.
Case 4
Food accidentally enters the windpipe during swallowing.
Q5. Which structure normally prevents this?
Answer:
The epiglottis prevents food from entering the trachea.
Case 5
A smoker shows loss of lung elasticity.
Q6. Which respiratory structure is mainly affected?
Answer:
Alveoli are affected due to destruction of elastic walls.
Case 6
Pleural fluid volume is reduced in a patient.
Q7. How will this affect breathing?
Answer:
Breathing becomes painful due to increased friction during lung movements.
Case 7
A radiograph shows the left lung smaller than the right.
Q8. Give the reason.
Answer:
The left lung is smaller to accommodate the heart.
Case 8
Dust particles are trapped before reaching lungs.
Q9. Name the structure responsible.
Answer:
Nasal hairs and mucus trap dust particles.
Section B: Mechanism of Breathing (Case 10–17)
Case 9
During exercise, breathing rate increases significantly.
Q10. Which gas concentration mainly stimulates faster breathing?
Answer:
Increased carbon dioxide concentration stimulates faster breathing.
Case 10
A student records rib movements during breathing.
Q11. How do ribs move during inspiration?
Answer:
Ribs move upward and outward during inspiration.
Case 11
A person holds breath for a long time.
Q12. Why does breathing restart automatically?
Answer:
Accumulation of carbon dioxide stimulates respiratory centers to resume breathing.
Case 12
The diaphragm is surgically damaged.
Q13. How will this affect breathing?
Answer:
Breathing becomes difficult as thoracic volume changes are impaired.
Case 13
Pressure inside lungs falls below atmospheric pressure.
Q14. Which phase of breathing is occurring?
Answer:
Inspiration is occurring.
Case 14
A spirometer shows air remaining after forced expiration.
Q15. Name this volume.
Answer:
Residual volume.
Case 15
Breathing continues even during sleep.
Q16. Which brain part controls this rhythm?
Answer:
The medulla oblongata controls breathing rhythm.
Case 16
A patient has collapsed lungs due to loss of pleural pressure.
Q17. Why is intrapleural pressure important?
Answer:
It keeps lungs inflated and prevents collapse.
Section C: Transport of Gases (Case 18–25)
Case 17
Oxygen diffuses from alveoli into blood.
Q18. What drives this diffusion?
Answer:
Difference in partial pressure of oxygen drives diffusion.
Case 18
Blood reaching tissues releases oxygen easily.
Q19. Which factor reduces haemoglobin affinity for oxygen?
Answer:
High carbon dioxide concentration and low pH reduce affinity.
Case 19
Most carbon dioxide is carried in blood in one form.
Q20. Name this form.
Answer:
Bicarbonate ions.
Case 20
An enzyme in RBCs speeds up CO₂ transport.
Q21. Name the enzyme.
Answer:
Carbonic anhydrase.
Case 21
A shift of ions occurs during CO₂ transport.
Q22. Name this phenomenon.
Answer:
Chloride shift.
Case 22
Haemoglobin binds oxygen reversibly.
Q23. Name the compound formed.
Answer:
Oxyhaemoglobin.
Case 23
Oxygen is released in metabolically active tissues.
Q24. Name the effect responsible.
Answer:
Bohr effect.
Case 24
CO₂ binds directly with haemoglobin.
Q25. Name the compound formed.
Answer:
Carbaminohaemoglobin.
NCERT & CBSE Compliance Note
✔ Strictly based on NCERT Class 11 Biology
✔ Competency-based, source-linked questions
✔ Fully aligned with CBSE assessment pattern
✔ Ideal for school exams and internal assessments