Chapter 17: Breathing and Exchange of Gases – Long Answer Type Questions
CBSE Class 11 Biology Long 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: Long Answer Questions (LAQs)
- Answer Length: 120–150 words
- Exam Relevance: CBSE Class 11 Annual Examination
Section A: Respiratory Organs (Q1–Q8)
Q1. Describe the human respiratory system and its components.
Answer:
The human respiratory system consists of nostrils, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles, and lungs. Air enters through nostrils and is filtered, warmed, and moistened in the nasal cavity. The pharynx acts as a common passage for air, while the larynx maintains an open airway and produces sound. The trachea, supported by cartilaginous rings, conducts air to the bronchi, which further divide into bronchioles within the lungs. Bronchioles terminate into alveoli, which are thin-walled, highly vascular air sacs. Alveoli provide a large surface area for gaseous exchange. The lungs are covered by pleural membranes containing pleural fluid that reduces friction during breathing movements. Together, these structures ensure efficient respiration.
Q2. Explain the structure and significance of alveoli.
Answer:
Alveoli are microscopic, balloon-like air sacs present at the terminal ends of bronchioles in the lungs. Each alveolus has extremely thin walls composed of squamous epithelium and is surrounded by a dense network of blood capillaries. This close association between alveolar air and blood minimizes diffusion distance, facilitating rapid gaseous exchange. Alveoli are moist, allowing oxygen and carbon dioxide to dissolve before diffusion. Their large number, approximately 300 million, provides an enormous surface area essential for efficient respiration. The elastic nature of alveoli helps in expansion and recoil during breathing. Thus, alveoli play a critical role as the primary site of exchange of oxygen and carbon dioxide between the lungs and blood.
Q3. Describe the role of nasal cavity in respiration.
Answer:
The nasal cavity plays an important preparatory role in respiration. As air enters through the nostrils, it passes into the nasal cavity where it is filtered, warmed, and moistened. Nasal hairs and mucus trap dust particles, microbes, and other foreign substances, preventing them from entering the lower respiratory tract. The rich blood supply in the nasal cavity warms the inhaled air to body temperature, protecting sensitive lung tissues. Moistening of air prevents drying of alveolar membranes, ensuring efficient diffusion of gases. By conditioning the air, the nasal cavity enhances respiratory efficiency and protects the lungs from potential damage.
Q4. Explain the importance of pleural membranes and pleural fluid.
Answer:
Pleural membranes are double-layered membranes that surround each lung. The outer layer, parietal pleura, lines the thoracic cavity, while the inner layer, visceral pleura, covers the lung surface. The space between these layers contains pleural fluid. This fluid reduces friction between lungs and chest wall during breathing movements, allowing smooth expansion and contraction. Additionally, pleural fluid maintains negative pressure in the pleural cavity, which keeps the lungs inflated and prevents their collapse. Thus, pleural membranes and pleural fluid are essential for efficient breathing mechanics and lung stability.
Q5. Why are cartilaginous rings present in the trachea?
Answer:
The trachea is supported by C-shaped cartilaginous rings that prevent its collapse during breathing. These rings maintain the airway open even when pressure changes occur during inspiration and expiration. The incomplete nature of the rings allows flexibility and permits expansion of the esophagus during swallowing. Without these cartilaginous supports, the trachea could collapse, obstructing airflow to the lungs. Hence, the cartilaginous rings ensure uninterrupted air passage and efficient conduction of air to the bronchi.
Q6. Differentiate between bronchi and bronchioles.
Answer:
Bronchi are large air passages that arise from the trachea and enter the lungs. They possess cartilaginous rings and smooth muscles, which help maintain their structure. Bronchi divide repeatedly to form smaller air passages called bronchioles. Bronchioles lack cartilage and are mainly composed of smooth muscle. They regulate airflow within the lungs and terminate into alveolar ducts and alveoli. While bronchi primarily conduct air, bronchioles play a role in regulating air distribution and facilitating gaseous exchange indirectly.
Q7. Explain lung volumes and vital capacity.
Answer:
Lung volumes refer to different measurable quantities of air associated with breathing. Tidal volume is the air inhaled or exhaled during normal breathing. Inspiratory reserve volume and expiratory reserve volume represent additional air inhaled or exhaled forcefully. Residual volume is the air remaining after maximum expiration. Vital capacity is the maximum volume of air expelled after a forceful inspiration and includes tidal volume, inspiratory reserve volume, and expiratory reserve volume. Vital capacity reflects lung efficiency and respiratory health, making it clinically significant.
Q8. Why is the left lung smaller than the right lung?
Answer:
The left lung is smaller than the right lung to accommodate the heart, which is located slightly towards the left side of the thoracic cavity. This space is known as the cardiac notch. As a result, the left lung has only two lobes, whereas the right lung has three lobes. This anatomical arrangement ensures proper placement of vital organs within the thoracic cavity without compromising respiratory function.
Section B: Mechanism of Breathing (Q9–Q16)
Q9. Describe the mechanism of inspiration in humans.
Answer:
Inspiration is an active process involving muscular contraction. During inspiration, the diaphragm contracts and flattens, while external intercostal muscles contract, causing the ribs to move upward and outward. These movements increase the volume of the thoracic cavity. As thoracic volume increases, intrapulmonary pressure falls below atmospheric pressure. Due to this pressure gradient, air flows from the atmosphere into the lungs. The expansion of lungs allows alveoli to fill with air, enabling oxygen to reach the alveolar surfaces for gaseous exchange.
Q10. Explain the process of expiration.
Answer:
Expiration is generally a passive process that occurs due to relaxation of respiratory muscles. During expiration, the diaphragm relaxes and becomes dome-shaped, while intercostal muscles also relax, causing the ribs to move downward and inward. This reduces the volume of the thoracic cavity. Consequently, intrapulmonary pressure rises above atmospheric pressure, forcing air out of the lungs. Elastic recoil of lung tissues also contributes to air expulsion. During forced expiration, additional muscles may contract to expel air more rapidly.
Q11. Differentiate between inspiration and expiration.
Answer:
Inspiration is an active process involving contraction of diaphragm and intercostal muscles, leading to increased thoracic volume and decreased intrapulmonary pressure. Expiration is usually passive and involves relaxation of these muscles, decreasing thoracic volume and increasing intrapulmonary pressure. During inspiration, air enters the lungs, while during expiration, air is expelled. Both processes are essential for maintaining continuous gaseous exchange and effective respiration.
Q12. Explain the role of diaphragm in breathing.
Answer:
The diaphragm is a dome-shaped muscular partition between thoracic and abdominal cavities and plays a central role in breathing. During inspiration, the diaphragm contracts and flattens, increasing thoracic cavity volume and allowing air to enter lungs. During expiration, it relaxes and resumes its dome shape, decreasing thoracic volume and aiding air expulsion. Its rhythmic contraction and relaxation ensure effective ventilation of lungs.
Q13. Describe regulation of breathing.
Answer:
Breathing is regulated by respiratory centers located in the medulla oblongata and pons. The medullary respiratory rhythm center generates basic breathing rhythm. Chemoreceptors sensitive to carbon dioxide, hydrogen ions, and oxygen levels regulate breathing rate. Increased carbon dioxide concentration stimulates respiratory centers, increasing breathing rate to expel excess CO₂. The pneumotaxic center in pons fine-tunes breathing pattern by controlling inspiration duration.
Q14. Explain intrapulmonary and intrapleural pressures.
Answer:
Intrapulmonary pressure refers to pressure within alveoli and changes during breathing to facilitate airflow. Intrapleural pressure exists between pleural membranes and remains negative. This negative pressure keeps lungs expanded and prevents collapse. Changes in these pressures drive the mechanics of inspiration and expiration.
Q15. What is residual volume and its significance?
Answer:
Residual volume is the volume of air remaining in lungs after maximum expiration. It prevents lung collapse, maintains alveolar inflation, and allows continuous gas exchange between breaths. Residual volume is essential for sustaining respiration even during pauses between breathing cycles.
Q16. Explain lung capacities and their importance.
Answer:
Lung capacities are combinations of lung volumes. Vital capacity, total lung capacity, inspiratory capacity, and functional residual capacity indicate lung efficiency. These capacities help assess respiratory health and diagnose lung disorders.
Section C: Transport of Gases (Q17–Q25)
Q17. Explain gaseous exchange at alveoli.
Answer:
Gaseous exchange at alveoli occurs by simple diffusion. Oxygen diffuses from alveolar air into blood due to higher partial pressure in alveoli. Carbon dioxide diffuses from blood into alveoli due to higher partial pressure in blood. Thin alveolar walls and large surface area facilitate rapid diffusion.
Q18. Describe transport of oxygen in blood.
Answer:
Oxygen is mainly transported bound to haemoglobin as oxyhaemoglobin. A small amount remains dissolved in plasma. Haemoglobin increases oxygen-carrying capacity, ensuring efficient transport from lungs to tissues.
Q19. Explain oxygen dissociation curve.
Answer:
The oxygen dissociation curve shows the relationship between oxygen partial pressure and haemoglobin saturation. Its sigmoid shape ensures efficient oxygen loading in lungs and unloading in tissues.
Q20. Explain Bohr effect.
Answer:
Bohr effect states that increased carbon dioxide concentration and decreased pH reduce haemoglobin’s affinity for oxygen. This facilitates oxygen release in metabolically active tissues.
Q21. Describe transport of carbon dioxide in blood.
Answer:
Carbon dioxide is transported mainly as bicarbonate ions, partly as carbaminohaemoglobin, and a small amount dissolved in plasma. This ensures efficient removal of CO₂ from tissues.
Q22. Role of carbonic anhydrase in respiration.
Answer:
Carbonic anhydrase catalyzes conversion of carbon dioxide into carbonic acid in red blood cells, facilitating bicarbonate formation and CO₂ transport.
Q23. Explain chloride shift.
Answer:
Chloride shift involves exchange of bicarbonate and chloride ions between plasma and red blood cells to maintain ionic balance during CO₂ transport.
Q24. Explain gaseous exchange at tissues.
Answer:
At tissues, oxygen diffuses from blood to cells due to lower oxygen partial pressure, while carbon dioxide diffuses from tissues into blood along its gradient.
Q25. Importance of efficient gas transport.
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 (120–150 words)
✔ Framework-aligned and exam-oriented
✔ Ideal for CBSE Class 11 board exams