Chapter 17: Breathing and Exchange of Gases – Short Answer Type Questions
CBSE Class 11 Biology 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: Short Answer Questions (SAQs)
- Answer Length: 60–80 words
- Exam Relevance: CBSE Class 11 Annual Exam, Unit Tests, School Assessments
Section A: Respiratory Organs (Q1–Q15)
Q1. Describe the human respiratory system.
Answer:
The human respiratory system consists of nostrils, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and lungs. These organs work together to facilitate intake of oxygen and removal of carbon dioxide. The lungs contain millions of alveoli that provide a large surface area for efficient gaseous exchange between air and blood.
Q2. Explain the role of nasal cavity in respiration.
Answer:
The nasal cavity conditions incoming air before it reaches the lungs. It filters dust and microbes using nasal hairs and mucus, warms air through a rich blood supply, and moistens it. These functions protect delicate lung tissues and ensure efficient gaseous exchange by maintaining optimal temperature and humidity of inhaled air.
Q3. What is the significance of cartilaginous rings in trachea?
Answer:
The trachea contains C-shaped cartilaginous rings that prevent its collapse during breathing. These rings maintain airway patency while allowing flexibility. The open side of the rings faces the esophagus, permitting expansion during swallowing without obstructing the air passage, ensuring uninterrupted airflow to lungs.
Q4. Describe the structure and function of alveoli.
Answer:
Alveoli are tiny, balloon-like air sacs present at the ends of bronchioles. They have thin, moist walls and are surrounded by capillary networks. This structure provides a large surface area and minimal diffusion distance, enabling rapid exchange of oxygen and carbon dioxide between alveolar air and blood.
Q5. Why are lungs spongy in nature?
Answer:
Lungs are spongy due to the presence of millions of alveoli filled with air. This spongy texture allows lungs to expand and recoil efficiently during breathing. The elasticity also helps maintain air pressure differences necessary for inhalation and exhalation.
Q6. Explain the role of pleural membranes.
Answer:
Pleural membranes surround the lungs and secrete pleural fluid. This fluid reduces friction between lungs and chest wall during breathing movements. It also creates a pressure gradient that keeps lungs expanded, facilitating smooth and efficient respiration.
Q7. Why is the left lung smaller than the right lung?
Answer:
The left lung is smaller because it shares space with the heart, which occupies the left side of the thoracic cavity. This indentation, called the cardiac notch, reduces the size of the left lung, making it two-lobed instead of three-lobed like the right lung.
Q8. Differentiate between bronchi and bronchioles.
Answer:
Bronchi are larger airways branching from the trachea and supported by cartilaginous rings. Bronchioles are smaller branches within the lungs that lack cartilage. Bronchioles regulate airflow and terminate into alveolar ducts and alveoli for gas exchange.
Q9. State the importance of moist respiratory surfaces.
Answer:
Moist respiratory surfaces dissolve gases, facilitating their diffusion across membranes. Oxygen and carbon dioxide must be in dissolved form to diffuse efficiently. Moisture also prevents drying of tissues and maintains elasticity of alveolar walls, essential for proper lung function.
Q10. What is vital capacity and why is it important?
Answer:
Vital capacity is the maximum volume of air expelled after a forceful inspiration. It indicates lung efficiency and respiratory health. Higher vital capacity suggests better oxygen supply to tissues, while reduced vital capacity may indicate respiratory disorders.
Q11. Explain the term tidal volume.
Answer:
Tidal volume refers to the amount of air inhaled or exhaled during normal breathing. In an average adult, it is about 500 mL. It represents the basic unit of ventilation and ensures continuous gas exchange during resting conditions.
Q12. Describe the function of epiglottis.
Answer:
The epiglottis is a flap-like structure that closes the glottis during swallowing. It prevents food and liquids from entering the trachea, directing them into the esophagus. This protective mechanism prevents choking and aspiration into the lungs.
Q13. Why are alveoli richly supplied with blood capillaries?
Answer:
Alveoli are surrounded by dense capillary networks to facilitate efficient gaseous exchange. The close association allows rapid diffusion of oxygen into blood and carbon dioxide out of blood, driven by partial pressure gradients.
Q14. How does pleural fluid aid breathing?
Answer:
Pleural fluid reduces friction between lungs and chest wall during respiratory movements. It also maintains negative pressure in the pleural cavity, keeping lungs inflated and enabling smooth expansion and contraction during breathing.
Q15. Name and explain any two lung capacities.
Answer:
Inspiratory capacity is the maximum air inhaled after normal expiration, while total lung capacity is the total volume of air lungs can hold after maximum inspiration. Both indicate lung health and respiratory efficiency.
Section B: Mechanism of Breathing (Q16–Q30)
Q16. Explain the process of inspiration.
Answer:
Inspiration is an active process involving contraction of diaphragm and external intercostal muscles. The diaphragm flattens and ribs move upward and outward, increasing thoracic volume. This decreases intrapulmonary pressure below atmospheric pressure, allowing air to enter lungs.
Q17. Describe expiration in humans.
Answer:
Expiration is usually a passive process. During expiration, respiratory muscles relax, the diaphragm becomes dome-shaped, and ribs move downward and inward. Thoracic volume decreases, increasing intrapulmonary pressure and forcing air out of lungs.
Q18. Differentiate between inspiration and expiration.
Answer:
Inspiration is an active process involving muscle contraction and increased thoracic volume, while expiration is generally passive involving muscle relaxation. Inspiration decreases intrapulmonary pressure, whereas expiration increases it, causing air movement in opposite directions.
Q19. Explain the role of diaphragm in breathing.
Answer:
The diaphragm is the primary muscle of respiration. Its contraction flattens it, increasing thoracic volume during inspiration. Relaxation restores its dome shape during expiration, decreasing thoracic volume and aiding air expulsion.
Q20. What is intrapulmonary pressure?
Answer:
Intrapulmonary pressure is the pressure within alveoli of lungs. Changes in this pressure relative to atmospheric pressure cause air to move into or out of lungs during breathing cycles.
Q21. What is residual volume and its significance?
Answer:
Residual volume is the air remaining in lungs after maximum expiration. It prevents lung collapse, ensures continuous gas exchange between breaths, and maintains alveolar inflation.
Q22. Explain regulation of breathing by medulla oblongata.
Answer:
The medullary respiratory center controls basic breathing rhythm. It responds to changes in carbon dioxide and hydrogen ion concentrations, adjusting breathing rate to maintain normal blood gas levels.
Q23. Describe the role of pneumotaxic center.
Answer:
The pneumotaxic center in pons regulates breathing pattern by controlling duration of inspiration. It fine-tunes breathing rate, preventing over-inflation of lungs and ensuring rhythmic respiration.
Q24. How do chemoreceptors regulate respiration?
Answer:
Chemoreceptors detect changes in carbon dioxide, oxygen, and hydrogen ion concentrations in blood. Increased CO₂ stimulates respiratory centers to increase breathing rate, maintaining acid-base balance.
Q25. Explain functional residual capacity.
Answer:
Functional residual capacity is the volume of air remaining in lungs after normal expiration. It acts as a buffer, ensuring continuous gas exchange and stabilizing oxygen and carbon dioxide levels.
Q26. What is total lung capacity?
Answer:
Total lung capacity is the maximum volume of air lungs can hold after forceful inspiration. It includes all lung volumes and reflects overall lung size and function.
Q27. Why is breathing rhythmic?
Answer:
Breathing is rhythmic to maintain continuous oxygen supply and carbon dioxide removal. Respiratory centers generate regular impulses that ensure uninterrupted respiration throughout life.
Q28. Explain inspiratory reserve volume.
Answer:
Inspiratory reserve volume is the additional air inhaled forcibly after normal inspiration. It increases oxygen intake during exercise or stress, enhancing respiratory efficiency.
Q29. Why does intrapleural pressure remain negative?
Answer:
Intrapleural pressure remains negative due to opposing elastic recoils of lungs and chest wall. This negative pressure keeps lungs expanded and prevents their collapse.
Q30. How does elastic recoil aid expiration?
Answer:
Elastic recoil of lungs results from stretched alveolar walls during inspiration. When muscles relax, this recoil reduces lung volume, increasing pressure and aiding air expulsion.
Section C: Transport of Gases (Q31–Q50)
Q31. Explain gaseous exchange at alveoli.
Answer:
Gaseous exchange at alveoli occurs by diffusion. Oxygen diffuses from alveolar air into blood due to higher partial pressure, while carbon dioxide diffuses from blood into alveoli along its gradient.
Q32. What is partial pressure and its significance?
Answer:
Partial pressure is the pressure exerted by an individual gas in a mixture. Differences in partial pressures drive diffusion of oxygen and carbon dioxide during gas exchange.
Q33. Describe oxygen transport in blood.
Answer:
Oxygen is mainly transported bound to haemoglobin as oxyhaemoglobin. A small fraction is dissolved in plasma. This binding increases oxygen-carrying capacity of blood.
Q34. Explain oxygen dissociation curve.
Answer:
The oxygen dissociation curve shows relationship between partial pressure of oxygen and haemoglobin saturation. Its sigmoid shape ensures efficient oxygen loading in lungs and unloading in tissues.
Q35. What is Bohr effect?
Answer:
Bohr effect states that increased carbon dioxide concentration and decreased pH reduce haemoglobin’s affinity for oxygen, promoting oxygen release at tissues.
Q36. Describe carbon dioxide transport in blood.
Answer:
Carbon dioxide is transported mainly as bicarbonate ions, partly as carbaminohaemoglobin, and a small amount dissolved in plasma. This ensures efficient CO₂ removal.
Q37. Role of carbonic anhydrase in respiration.
Answer:
Carbonic anhydrase catalyzes conversion of carbon dioxide and water into carbonic acid in red blood cells, facilitating bicarbonate formation for CO₂ transport.
Q38. Explain chloride shift.
Answer:
Chloride shift involves exchange of bicarbonate and chloride ions between plasma and red blood cells to maintain electrical neutrality during CO₂ transport.
Q39. What is carbaminohaemoglobin?
Answer:
Carbaminohaemoglobin is formed when carbon dioxide binds to amino groups of haemoglobin. It accounts for a significant portion of CO₂ transport.
Q40. Why is CO₂ more soluble than O₂?
Answer:
Carbon dioxide has higher solubility in plasma due to its chemical properties, allowing efficient transport compared to oxygen.
Q41. Explain exchange of gases at tissues.
Answer:
At tissues, oxygen diffuses from blood into cells due to lower partial pressure, while carbon dioxide diffuses from tissues into blood.
Q42. Why does haemoglobin release oxygen at tissues?
Answer:
Lower oxygen partial pressure, higher carbon dioxide, increased temperature, and acidic pH reduce haemoglobin affinity, causing oxygen release.
Q43. State the importance of haemoglobin.
Answer:
Haemoglobin enhances oxygen transport efficiency by binding oxygen reversibly, ensuring adequate oxygen supply to all tissues.
Q44. How does temperature affect oxygen binding?
Answer:
Increased temperature reduces haemoglobin affinity for oxygen, promoting oxygen release in metabolically active tissues.
Q45. Explain respiratory quotient briefly.
Answer:
Respiratory quotient is the ratio of carbon dioxide produced to oxygen consumed during respiration, indicating type of substrate oxidized.
Q46. What is internal respiration?
Answer:
Internal respiration refers to exchange of gases between blood and tissues, enabling oxygen utilization and carbon dioxide removal.
Q47. Why is diffusion suitable for gas exchange?
Answer:
Diffusion is effective due to thin respiratory membranes, large surface area, and steep partial pressure gradients.
Q48. Explain role of plasma in gas transport.
Answer:
Plasma transports dissolved oxygen and carbon dioxide and carries bicarbonate ions formed during CO₂ transport.
Q49. How does exercise affect breathing and gas transport?
Answer:
Exercise increases breathing rate and cardiac output, enhancing oxygen delivery and carbon dioxide removal to meet metabolic demands.
Q50. Why is efficient gas transport essential?
Answer:
Efficient gas transport ensures adequate oxygen supply for cellular respiration and removal of carbon dioxide, maintaining energy production and homeostasis.
NCERT & CBSE Compliance Note
✔ Strictly as per NCERT Class 11 Biology
✔ Answer length maintained (60–80 words)
✔ Framework-aligned and board-exam focused
✔ Suitable for CBSE school and annual examinations