Chapter 17: Breathing and Exchange of Gases – Very Short Answer Type Questions
CBSE Class 11 Biology Very Short Answer 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: Very Short Answer Questions (VSA)
- Answer Length: 20–30 words
- Exam Utility: CBSE Class 11 Annual Examination, Unit Tests, School Assessments
Section A: Respiratory Organs (Q1–Q17)
Q1. What is respiration?
Answer:
Respiration is a biochemical process in which oxygen is used to oxidize food substances in cells, releasing energy required for growth, repair, and metabolic activities.
Q2. Name the main respiratory organ in humans.
Answer:
The lungs are the primary respiratory organs in humans, responsible for gaseous exchange between atmospheric air and blood through numerous alveoli.
Q3. State the function of nasal hairs.
Answer:
Nasal hairs trap dust particles and microbes from inhaled air, preventing them from entering the respiratory tract and protecting delicate lung tissues.
Q4. Why is the nasal cavity richly supplied with blood vessels?
Answer:
The nasal cavity contains numerous blood vessels to warm inhaled air and maintain optimal temperature before it reaches the lungs.
Q5. What is the role of the pharynx in respiration?
Answer:
The pharynx serves as a common passage for both air and food, directing inhaled air from nasal cavity towards the larynx.
Q6. Why is the larynx called the voice box?
Answer:
The larynx contains vocal cords that vibrate during airflow, producing sound, hence it is commonly called the voice box.
Q7. What is the function of epiglottis?
Answer:
The epiglottis prevents food particles from entering the trachea during swallowing by closing the glottis temporarily.
Q8. Why does the trachea not collapse?
Answer:
The trachea remains open due to the presence of C-shaped cartilaginous rings that provide rigidity and prevent airway collapse.
Q9. Differentiate bronchi and bronchioles.
Answer:
Bronchi are larger air passages with cartilage, while bronchioles are smaller, non-cartilaginous branches within lungs leading to alveoli.
Q10. What are alveoli?
Answer:
Alveoli are thin-walled, balloon-like air sacs in lungs that provide a large surface area for efficient gaseous exchange.
Q11. Why are alveolar walls very thin?
Answer:
Alveolar walls are extremely thin to facilitate rapid diffusion of oxygen and carbon dioxide between blood and alveolar air.
Q12. Name the membrane covering the lungs.
Answer:
The lungs are covered by a double-layered pleural membrane which reduces friction and allows smooth expansion during breathing.
Q13. Why is the left lung smaller than the right lung?
Answer:
The left lung is smaller because it accommodates the heart, creating space known as the cardiac notch.
Q14. How many lobes are present in the right lung?
Answer:
The right lung has three lobes, providing greater respiratory surface area compared to the left lung.
Q15. What is the function of pleural fluid?
Answer:
Pleural fluid reduces friction between lung surfaces and chest wall during breathing movements, ensuring smooth lung expansion.
Q16. What is vital capacity?
Answer:
Vital capacity is the maximum volume of air a person can breathe out after a forceful inspiration, indicating lung efficiency.
Q17. Define tidal volume.
Answer:
Tidal volume is the volume of air inhaled or exhaled during normal, quiet breathing, usually about 500 mL in adults.
Section B: Mechanism of Breathing (Q18–Q34)
Q18. What is breathing?
Answer:
Breathing is the physical process involving inhalation of oxygen-rich air and exhalation of carbon dioxide-rich air.
Q19. Name the two phases of breathing.
Answer:
The two phases of breathing are inspiration, which involves air intake, and expiration, which involves air expulsion.
Q20. Is inspiration an active or passive process? Why?
Answer:
Inspiration is an active process because it involves contraction of diaphragm and intercostal muscles, requiring energy.
Q21. What happens to diaphragm during inspiration?
Answer:
During inspiration, the diaphragm contracts, flattens, and moves downward, increasing thoracic cavity volume.
Q22. How do ribs move during inspiration?
Answer:
During inspiration, ribs move upward and outward due to contraction of external intercostal muscles.
Q23. What causes air to enter lungs during inspiration?
Answer:
Air enters lungs due to decrease in intrapulmonary pressure below atmospheric pressure caused by increased thoracic volume.
Q24. Why is expiration normally passive?
Answer:
Expiration is passive because relaxation of respiratory muscles and elastic recoil of lungs expel air without energy expenditure.
Q25. What happens to diaphragm during expiration?
Answer:
During expiration, the diaphragm relaxes and returns to dome-shaped position, decreasing thoracic cavity volume.
Q26. Define intrapulmonary pressure.
Answer:
Intrapulmonary pressure is the pressure inside the lung alveoli that changes during breathing to facilitate airflow.
Q27. What is residual volume?
Answer:
Residual volume is the volume of air remaining in lungs after maximum forced expiration, preventing lung collapse.
Q28. Name the respiratory rhythm center.
Answer:
The respiratory rhythm center is located in the medulla oblongata and regulates the basic rhythm of breathing.
Q29. How does CO₂ regulate breathing?
Answer:
Increase in carbon dioxide concentration stimulates chemoreceptors, increasing breathing rate to expel excess CO₂.
Q30. What is inspiratory reserve volume?
Answer:
Inspiratory reserve volume is the additional air that can be forcibly inhaled after a normal inspiration.
Q31. Define total lung capacity.
Answer:
Total lung capacity is the maximum amount of air the lungs can hold after forceful inspiration.
Q32. What is pneumotaxic center?
Answer:
The pneumotaxic center in pons regulates breathing pattern by controlling duration and rate of inspiration.
Q33. What is functional residual capacity?
Answer:
Functional residual capacity is the volume of air remaining in lungs after normal expiration.
Q34. Why is breathing rhythm continuous?
Answer:
Breathing rhythm is continuous to ensure uninterrupted oxygen supply and efficient removal of carbon dioxide.
Section C: Transport of Gases (Q35–Q50)
Q35. What is partial pressure?
Answer:
Partial pressure is the pressure exerted by an individual gas in a mixture of gases, determining diffusion direction.
Q36. How does oxygen diffuse in alveoli?
Answer:
Oxygen diffuses from alveolar air into blood due to higher partial pressure in alveoli than in deoxygenated blood.
Q37. Name the respiratory pigment in humans.
Answer:
Haemoglobin is the respiratory pigment in humans that binds oxygen reversibly and transports it to tissues.
Q38. In what form is oxygen mainly transported?
Answer:
About 97 percent of oxygen is transported bound to haemoglobin as oxyhaemoglobin.
Q39. What is oxyhaemoglobin?
Answer:
Oxyhaemoglobin is a reversible compound formed when oxygen binds with haemoglobin in red blood cells.
Q40. What is oxygen dissociation curve?
Answer:
Oxygen dissociation curve shows the relationship between partial pressure of oxygen and haemoglobin saturation.
Q41. State Bohr effect.
Answer:
Bohr effect states that increased carbon dioxide concentration and decreased pH reduce haemoglobin’s affinity for oxygen.
Q42. How is carbon dioxide mainly transported?
Answer:
Most carbon dioxide is transported as bicarbonate ions formed in red blood cells and carried through plasma.
Q43. Name the enzyme involved in CO₂ transport.
Answer:
Carbonic anhydrase catalyzes conversion of carbon dioxide into carbonic acid inside red blood cells.
Q44. What is chloride shift?
Answer:
Chloride shift is the exchange of bicarbonate and chloride ions between plasma and red blood cells to maintain ionic balance.
Q45. What is carbaminohaemoglobin?
Answer:
Carbaminohaemoglobin is formed when carbon dioxide binds with amino groups of haemoglobin.
Q46. Where does internal respiration occur?
Answer:
Internal respiration occurs in tissues where oxygen diffuses from blood to cells and carbon dioxide diffuses into blood.
Q47. Why is CO₂ more soluble than O₂?
Answer:
Carbon dioxide is more soluble in blood plasma than oxygen due to its higher chemical solubility.
Q48. Name the gas exchange mechanism.
Answer:
Gaseous exchange occurs by simple diffusion across alveolar and tissue membranes following partial pressure gradients.
Q49. What happens to oxygen at tissues?
Answer:
Oxygen dissociates from haemoglobin at tissues due to lower partial pressure and is utilized in cellular respiration.
Q50. Why is haemoglobin essential for respiration?
Answer:
Haemoglobin increases oxygen-carrying capacity of blood, ensuring efficient oxygen transport from lungs to tissues.
NCERT & CBSE Compliance Note
✔ Strictly based on NCERT Class 11 Biology
✔ Answer length maintained at 20–30 words
✔ Board-exam oriented language and terminology
✔ Fully aligned with prescribed framework coverage