NCERT Solutions for Class 11 Biology Chapter 17 – Breathing and Exchange of Gases
Students looking for comprehensive and exam-ready NCERT Solutions for Class 11 Biology Chapter 17 Breathing and Exchange of Gases will find exactly what they need at Myclass24. This chapter is a critical part of the Human Physiology unit and is extensively covered in both Class 11 board exams and the NEET entrance exam. The chapter explains the entire process of human breathing, the mechanics of respiration, the transport of respiratory gases in blood, and common respiratory disorders. Must check the CBSE resources and NCERT Solutions.
Myclass24 provides solutions that are crafted by subject experts and are aligned with the latest NCERT textbook edition. Whether you are a student from Lucknow, Pune, Ahmedabad, Jaipur, or any other city preparing for your annual exams, these solutions will give you a thorough understanding of each concept. The answers are written in a clear and straightforward manner, making complex topics like haemoglobin dissociation curves and partial pressures of gases easily understandable. Bookmark Myclass24 for all your NCERT biology solution needs and ace your exams with confidence.
NCERT Solutions for Class 11 Biology Chapter 17 PDF – Breathing and Exchange of Gases
Get the free PDF of NCERT Solutions for Class 11 Biology Chapter 17 Breathing and Exchange of Gases from Myclass24. The PDF includes all textbook question answers, diagrams of the respiratory system and the oxygen dissociation curve, and chapter-wise key points. Download it for free and study anywhere, anytime.
Breathing and Exchange of Gases – Chapter Overview, Key Facts & Concepts
Breathing, or pulmonary ventilation, is the mechanical process of moving air in and out of the lungs. This is different from respiration, which is the biochemical process of releasing energy from glucose. The human respiratory system consists of external nostrils, nasal chambers, pharynx, larynx, trachea, bronchi, bronchioles, alveoli, and the lungs. The alveoli are the primary sites of gas exchange and their thin walls (one cell thick) along with a rich blood supply make them ideal for this function. Check out NCERT Solutions for Class 11 Biology and NCERT Solutions for Class 11 for the rest of the chapters.
Breathing involves two stages: Inspiration (inhalation) and Expiration (exhalation). During inspiration, the diaphragm contracts and flattens, the external intercostal muscles contract, the thoracic volume increases, intrapulmonary pressure decreases below atmospheric pressure, and air flows in. During expiration, the reverse happens and air is pushed out. Normal breathing rate in adults is 12–16 breaths per minute.
Respiratory Volumes and Capacities
| Term | Volume (approx.) | Definition |
| Tidal Volume (TV) | 500 mL | Air breathed in/out in normal breathing |
| Inspiratory Reserve Volume (IRV) | 2500–3000 mL | Extra air inspired beyond tidal inspiration |
| Expiratory Reserve Volume (ERV) | 1000–1100 mL | Extra air expired beyond tidal expiration |
| Residual Volume (RV) | 1100–1200 mL | Air remaining after forceful expiration |
| Vital Capacity (VC) | ~4000 mL | TV + IRV + ERV |
| Total Lung Capacity (TLC) | ~6000 mL | VC + RV |
Gas exchange at the alveolar level is governed by the partial pressure differences of oxygen and carbon dioxide. Oxygen moves from the alveoli (pO2 = 104 mmHg) to the blood (pO2 = 40 mmHg), and CO2 moves from the blood (pCO2 = 45 mmHg) to the alveoli (pCO2 = 40 mmHg), both by simple diffusion.
Oxygen Transport: About 97% of oxygen is transported by haemoglobin (Hb) as oxyhaemoglobin. The remaining 3% is dissolved in plasma. Each Hb molecule can carry 4 molecules of O2. The oxygen-haemoglobin dissociation curve is sigmoid (S-shaped) and shows the cooperative binding of O2. The curve shifts to the right (Bohr effect) in conditions of increased CO2, low pH, high temperature, and high altitude, causing Hb to release more O2 to tissues.
Transport of CO2 in Blood
| Form of Transport | Percentage |
| As bicarbonate ions (HCO3-) in plasma | ~70% |
| As carbaminohaemoglobin (bound to Hb) | ~23% |
| Dissolved in plasma | ~7% |
Common Respiratory Disorders
| Disorder | Description |
| Asthma | Difficulty in breathing due to inflammation and narrowing of bronchioles |
| Emphysema | Damage to alveolar walls, reducing surface area for gas exchange |
| Bronchitis | Inflammation of the bronchi; chronic form associated with smoking |
| Pneumonia | Alveoli fill with fluid; caused by Streptococcus pneumoniae |
| Occupational Lung Disease | Silicosis and asbestosis from industrial dust inhalation |
Regulation of breathing is done by the respiratory centre in the medulla oblongata of the brain. Chemoreceptors in the medulla and aortic/carotid bodies detect changes in CO2 and H+ levels in blood and signal the respiratory centre to adjust the rate and depth of breathing. Interestingly, CO2 is a stronger stimulus for breathing than a lack of O2.
A key fact often asked in exams: the partial pressure of O2 in alveoli is 104 mmHg and in deoxygenated blood is 40 mmHg, making the difference 64 mmHg, which drives O2 diffusion. Carbonic anhydrase is the enzyme that catalyses the conversion of CO2 + H2O into carbonic acid inside RBCs, facilitating CO2 transport. This enzyme is 5000 times faster than the spontaneous reaction.