Question Bank — Breathing and Exchange of Gases

NCERT Class 11 Biology · Chapter 14 · CBSE Board Pattern

Class 11 Biology Chapter 14 Question Bank CBSE Board Pattern

Section A — MCQs (10 questions, 1 mark each)

1. Which of the following is the primary site of exchange of gases in the human respiratory system?
(a) Bronchioles (b) Alveoli (c) Trachea (d) Nasal chamber

2. The volume of air that remains in the lungs even after a forcible expiration is called:
(a) Tidal volume (b) Expiratory reserve volume (c) Residual volume (d) Inspiratory reserve volume

3. Assertion (A): The diffusion membrane of alveoli is extremely thin (much less than a millimetre).
Reason (R): A thin diffusion membrane facilitates rapid diffusion of O₂ from alveoli to blood and CO₂ from blood to alveoli.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

4. In the alveoli, the conditions favouring formation of oxyhaemoglobin are:
(a) High pO₂, low pCO₂, low H⁺ concentration (b) Low pO₂, high pCO₂, high H⁺ concentration
(c) High pO₂, high pCO₂, high temperature (d) Low pO₂, low pCO₂, low temperature

5. Assertion (A): About 70% of CO₂ is transported as bicarbonate ions in blood.
Reason (R): RBCs contain a high concentration of carbonic anhydrase which catalyses the formation of H₂CO₃ from CO₂ and H₂O.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.

6. The respiratory rhythm centre is located in:
(a) Pons (b) Medulla oblongata (c) Cerebrum (d) Cerebellum

7. Which of the following statements is correct regarding the conducting part of the respiratory system?
(a) It is the site of actual gas exchange (b) It humidifies and warms the air
(c) It consists only of alveoli (d) It has no cartilage

8. A healthy human breathes approximately how many times per minute under normal conditions?
(a) 8–10 (b) 12–16 (c) 20–24 (d) 30–35

9. The enzyme carbonic anhydrase is mainly present in:
(a) Plasma only (b) RBCs (c) Alveolar epithelium (d) Diaphragm

10. Emphysema is caused due to:
(a) Inflammation of bronchi (b) Damage to alveolar walls leading to reduced respiratory surface
(c) Accumulation of fluid in lungs (d) Infection by bacteria

Section B — Very Short Answer (6 questions, 2 marks each)

11. Differentiate between the conducting part and the respiratory part of the human respiratory system.
12. What is the role of the epiglottis during swallowing?
13. Define tidal volume and state its approximate value in a healthy adult.
14. Why is the solubility of CO₂ higher than that of O₂ important for gas exchange?
15. Name the two neural centres involved in the regulation of respiration and state their locations.
16. What is the oxygen dissociation curve? Why is it sigmoid-shaped?

Section C — Short Answer (5 questions, 3 marks each)

17. Describe the role of the diaphragm and intercostal muscles in inspiration.
18. Explain the transport of carbon dioxide in blood with the help of the reactions involved.
19. Distinguish between IRV and ERV. How do these volumes contribute to vital capacity?
20. What factors affect the binding of oxygen with haemoglobin? How do these factors differ in alveoli versus tissues?
21. Write a short note on asthma and emphysema as disorders of the respiratory system.

Section D — Long Answer (3 questions, 5 marks each)

22. Describe the human respiratory system with the help of a labelled diagram. Mark and label the following parts: external nostrils, larynx, trachea, primary bronchi, bronchioles and alveoli. Explain the function of the conducting and respiratory parts.
23. Explain the mechanism of breathing in humans. Describe how pressure gradients are created during inspiration and expiration. Add a note on the role of additional abdominal muscles.
24. Describe the transport of oxygen and carbon dioxide in blood. Explain the oxygen dissociation curve and the factors that favour dissociation of oxygen at the tissues.

Section E — Case/Source-Based (2 questions, 4 marks each)

25. Case: A 45-year-old man who has been smoking heavily for 20 years complains of breathlessness. His doctor suspects emphysema.
(a) What is emphysema? (1 mark)
(b) How does cigarette smoking lead to emphysema? (1 mark)
(c) Why does the patient experience breathlessness? (1 mark)
(d) Name one other major disorder caused by inflammation of bronchi and bronchioles. (1 mark)

26. Case: A person climbs to a high altitude where atmospheric pO₂ is lower than at sea level. He experiences increased breathing rate initially.
(a) Which centre in the brain detects changes in pCO₂ and H⁺ concentration? (1 mark)
(b) How does low atmospheric pO₂ affect the formation of oxyhaemoglobin? (1 mark)
(c) Name the receptors that can sense changes in blood CO₂ levels and send signals to the respiratory centre. (1 mark)
(d) Why is the role of oxygen insignificant in regulating respiratory rhythm? (1 mark)

▶ Answer Key Attempt all questions first,
then tap to reveal

Section A

  1. (b) Alveoli
  2. (c) Residual volume
  3. (a) Both true and R explains A
  4. (a) High pO₂, low pCO₂, low H⁺
  5. (a) Both true and R explains A
  6. (b) Medulla oblongata
  7. (b) It humidifies and warms the air
  8. (b) 12–16
  9. (b) RBCs
  10. (b) Damage to alveolar walls

Section B

  1. Conducting part (nostrils to terminal bronchioles) transports, cleans, humidifies and warms air (1 mark); respiratory part (alveoli) is site of actual gas exchange (1 mark).
  2. Prevents entry of food into larynx (2 marks).
  3. Volume of air inspired/expired during normal respiration ≈ 500 mL (2 marks).
  4. CO₂ diffuses 20–25 times faster than O₂ across the membrane for the same partial pressure difference (2 marks).
  5. Respiratory rhythm centre – medulla (1 mark); pneumotaxic centre – pons (1 mark).
  6. Plot of % saturation of Hb with O₂ vs pO₂ (1 mark); sigmoid shape due to cooperative binding of four O₂ molecules (1 mark).

Section C

  1. Contraction of diaphragm increases thoracic volume antero-posteriorly (1 mark); external intercostals lift ribs and sternum increasing dorso-ventral volume (1 mark); overall increase lowers intra-pulmonary pressure causing inspiration (1 mark).
  2. 20–25% as carbamino-haemoglobin (1 mark); 70% as HCO₃⁻ via carbonic anhydrase reaction (1 mark); 7% dissolved in plasma (1 mark).
  3. IRV = 2500–3000 mL (1 mark); ERV = 1000–1100 mL (1 mark); VC = ERV + TV + IRV (1 mark).
  4. pO₂, pCO₂, H⁺ concentration, temperature (1 mark); alveoli favour binding, tissues favour dissociation (2 marks).
  5. Asthma – inflammation of bronchi/bronchioles causing wheezing (1½ marks); emphysema – damaged alveolar walls reducing surface area, mainly due to smoking (1½ marks).

Section D

  1. Diagram with all labelled parts (3 marks); conducting part transports, cleans, humidifies air (1 mark); respiratory part is site of diffusion (1 mark).
  2. Inspiration: diaphragm contracts, external intercostals contract, thoracic volume ↑, intra-pulmonary pressure ↓ (2 marks); expiration: relaxation reverses the process (2 marks); abdominal muscles increase force (1 mark).
  3. O₂ transport: 97% oxyhaemoglobin, 3% dissolved (1 mark); CO₂ transport: 20–25% carbamino, 70% HCO₃⁻, 7% dissolved (1 mark); oxygen dissociation curve explanation with favourable conditions in alveoli vs tissues (3 marks).

Section E

  1. (a) Chronic disorder with damaged alveolar walls (1 mark)
    (b) Smoking damages alveolar walls (1 mark)
    (c) Reduced respiratory surface decreases gas exchange (1 mark)
    (d) Asthma (1 mark)
  2. (a) Chemosensitive area in medulla (1 mark)
    (b) Lower pO₂ reduces oxyhaemoglobin formation (1 mark)
    (c) Receptors in aortic arch and carotid artery (1 mark)
    (d) Regulation is mainly by pCO₂ and H⁺ (1 mark)
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All questions are answerable from the NCERT chapter text. Reviewed by GFIS faculty.