NCERT Solutions for Class 11 Biology Chapter 14 Breathing and Exchange of Gases
NCERT Solutions for Class 11 Biology Chapter 14 Breathing and Exchange of Gases provides concise revision notes and detailed textbook solutions covering respiratory organs, human respiratory system, mechanism of breathing, respiratory volumes and capacities, exchange and transport of gases, regulation of respiration, and respiratory disorders.
Overview of Topics & Subtopics (Click to Jump)
1. Respiratory Organs & Human Respiratory System
Short Note:
• Respiratory Organs across Animals: Lower invertebrates (sponges, coelenterates) use general body surface; earthworms use moist cuticle; insects use tracheal tubes; aquatic arthropods and molluscs use gills; reptiles, birds, and mammals use lungs.
• Human Respiratory Tract: External nostrils → Nasal chamber → Pharynx → Larynx (sound box) → Trachea → Primary/Secondary/Tertiary Bronchi → Bronchioles → Alveoli.
• Lungs & Pleura: Paired lungs enclosed in a double-layered pleural membrane with pleural fluid that reduces friction on the lung surface.
• Conducting vs. Respiratory Part: Conducting part (nostrils to terminal bronchioles) clears, humidifies, and warms incoming air; Respiratory part (alveoli and their ducts) is the actual site of gas diffusion.
2. Mechanism of Breathing & Respiratory Volumes
Short Note:
• Inspiration: Active process initiated by contraction of the diaphragm and external intercostal muscles, increasing thoracic volume and lowering intra-pulmonary pressure below atmospheric pressure.
• Expiration: Passive process caused by relaxation of the diaphragm and external intercostal muscles, reducing thoracic volume and increasing intra-pulmonary pressure above atmospheric pressure.
• Respiratory Volumes & Capacities:
- Tidal Volume (TV): Volume inspired or expired during normal respiration (~500 mL).
- Inspiratory Reserve Volume (IRV): Additional volume inspired forcibly (~2500–3000 mL).
- Expiratory Reserve Volume (ERV): Additional volume expired forcibly (~1000–1100 mL).
- Residual Volume (RV): Air remaining in lungs after forcible expiration (~1100–1200 mL).
- Vital Capacity (VC): Maximum air inspired after forced expiration (VC = ERV + TV + IRV ~4000–4600 mL).
- Total Lung Capacity (TLC): Total air volume held in lungs after forced inspiration (TLC = VC + RV).
3. Exchange & Transport of Gases (O₂ & CO₂)
Short Note:
• Gas Exchange at Alveoli: Diffusion driven by partial pressure gradients (pO2 in alveoli = 104 mmHg vs. 40 mmHg in deoxygenated blood; pCO2 in alveoli = 40 mmHg vs. 45 mmHg in deoxygenated blood).
• Diffusion Membrane: Composed of alveolar squamous epithelium, capillary endothelium, and intervening basement membrane.
• Transport of Oxygen: ~97% carried as Oxyhemoglobin in RBCs; ~3% dissolved in plasma. Each hemoglobin molecule binds up to 4 O2 molecules.
- Oxygen-Hemoglobin Dissociation Curve: Sigmoid curve. High pO2, low pCO2, low H+ concentration, and low temperature in alveoli favor oxyhemoglobin formation. High pCO2, high H+, and high temperature in tissues favor dissociation (Bohr Effect).
• Transport of Carbon Dioxide: ~70% as Bicarbonate ions (HCO3-) aided by Carbonic Anhydrase enzyme; ~23% as carbamino-hemoglobin; ~7% dissolved in plasma.
4. Regulation of Respiration & Respiratory Disorders
Short Note:
• Neural Regulation:
- Respiratory Rhythm Centre: Located in medulla oblongata, primarily regulates respiratory rhythm.
- Pneumotaxic Centre: Located in pons region, can moderate the functions of the rhythm center and reduce inspiration duration.
- Chemosensitive Area: Adjacent to rhythm center, highly sensitive to CO2 and hydrogen ions (H+).
• Respiratory Disorders:
- Asthma: Difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles.
- Emphysema: Chronic disorder where alveolar walls are damaged, decreasing respiratory surface area (major cause: cigarette smoking).
- Occupational Respiratory Disorders: Caused by long exposure to dust in grinding/stone-breaking industries (e.g., Silicosis, Asbestosis), leading to lung fibrosis.
Intext & Conceptual Questions
• Definition: The Oxygen Dissociation Curve is a sigmoid graph obtained when percentage saturation of hemoglobin with oxygen is plotted against partial pressure of oxygen (pO2).
• Factors Shifting the Curve to the Right (Decreased Affinity / Increased O₂ Release in Tissues):
1. High partial pressure of carbon dioxide (high pCO2).
2. Increased H+ ion concentration (lower pH / acidic medium).
3. Higher body temperature.
4. Lower partial pressure of oxygen (low pO2).
About 70% of CO2 produced by tissues diffuses into RBCs where it reacts with water to form carbonic acid (H2CO3), catalyzed by the enzyme Carbonic Anhydrase:
CO2 + H2O ⇔ H2CO3 ⇔ HCO3- + H+In tissue capillaries where pCO2 is high, HCO3- ions are formed and diffuse into plasma. At the alveolar site where pCO2 is low, the reaction reverses to release free CO2 gas, which is then exhaled.
Textbook Chapter End Exercise Questions
| Feature | Inspiratory Capacity (IC) | Expiratory Capacity (EC) |
|---|---|---|
| Definition | Total volume of air a person can inspire after a normal expiration. | Total volume of air a person can expire after a normal inspiration. |
| Components Formula | IC = TV + IRV | EC = TV + ERV |
| Approximate Value | ~3000 mL to 3500 mL | ~1500 mL to 1600 mL |
| Feature | Vital Capacity (VC) | Total Lung Capacity (TLC) |
|---|---|---|
| Definition | Maximum volume of air a person can breathe in after a forced expiration. | Total volume of air accommodated in the lungs at the end of a forced inspiration. |
| Inclusion of Residual Volume | Excludes Residual Volume (RV). | Includes Residual Volume (RV). |
| Components Formula | VC = ERV + TV + IRV | TLC = VC + RV |
| Approximate Value | ~4000 mL to 4600 mL | ~5200 mL to 5800 mL |
Read More & Chapter Resources
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