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Breathing and Exchange of Gases – Detailed NCERT Class 11 Biology Chapter Explanation for NEET, CBSE, and State Board Students

 Here's a detailed NCERT-based explanation for the chapter "Breathing and Exchange of Gases" from Class 11 Biology, written in a blog-style format, ideal for publishing on Blogspot. You can customize or expand it further based on your audience.



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Breathing and Exchange of Gases – Class 11 Biology NCERT Explanation


🔬 Introduction


Breathing is the physical process of inhaling oxygen and exhaling carbon dioxide, whereas respiration is a biochemical process that uses oxygen to produce energy. In this chapter, we focus on how our body takes in oxygen, transports it, and removes carbon dioxide—a process critical for life.



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🌬️ 1. Respiratory Organs in Humans and Animals


Different organisms have evolved various respiratory structures:


Skin – Earthworm (cutaneous respiration)


Gills – Fishes (aquatic respiration)


Tracheal System – Insects


Lungs – Reptiles, Birds, Mammals, including Humans




In humans, lungs are the primary respiratory organs located in the thoracic cavity.



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🫁 2. Human Respiratory System


Major parts:


Nostrils & Nasal cavity – Filters, warms, and moistens air


Pharynx – Common passage for food and air


Larynx (Voice Box) – Produces sound


Trachea (Windpipe) – Supported by cartilaginous rings


Bronchi – Two branches of trachea entering lungs


Bronchioles – Finer branches inside lungs


Alveoli – Balloon-like structures; site of gas exchange



👉 Note: The alveoli are surrounded by blood capillaries. This is where oxygen diffuses into the blood and CO₂ diffuses out.



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⚙️ 3. Mechanism of Breathing


Breathing involves two main steps:


Inspiration (Inhalation):


Diaphragm contracts and flattens


External intercostal muscles contract


Thoracic cavity expands, pressure decreases


Air enters the lungs



Expiration (Exhalation):


Diaphragm relaxes and curves up


Internal intercostal muscles contract


Thoracic cavity volume decreases


Pressure increases, air is pushed out




🧠 This is an involuntary process controlled by the medulla oblongata.



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📊 4. Respiratory Volumes and Capacities


Term Description Normal Value


Tidal Volume (TV) Air inhaled/exhaled in normal breath ~500 mL

Inspiratory Reserve Volume (IRV) Extra air that can be inhaled ~2500-3000 mL

Expiratory Reserve Volume (ERV) Extra air that can be exhaled ~1000-1100 mL

Residual Volume (RV) Air left after forceful exhalation ~1100-1200 mL



🔁 Vital Capacity (VC) = TV + IRV + ERV



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🔄 5. Exchange of Gases


Occurs by simple diffusion based on pressure gradients:


In alveoli, oxygen partial pressure is high, so it diffuses into blood.


In tissues, CO₂ partial pressure is high, so it diffuses into blood and carried to lungs.




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🩸 6. Transport of Gases





🔹 Oxygen Transport:


98.5% carried by hemoglobin (as oxyhemoglobin)


1.5% dissolved in plasma



🔹 Carbon Dioxide Transport:


70% as bicarbonate ions


20-25% as carbaminohemoglobin


5-7% dissolved in plasma



Chloride Shift (Hamburger Phenomenon): Exchange of Cl⁻ and HCO₃⁻ in RBCs to maintain ionic balance.



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📉 7. Regulation of Respiration


Controlled by:


Respiratory rhythm center (medulla oblongata)


Pneumotaxic center (pons)


Chemosensitive area – Sensitive to CO₂ and H⁺ in blood



⏱️ High CO₂ levels stimulate breathing rate more than low O₂.



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💉 8. Disorders of Respiratory System


Asthma – Allergic inflammation of bronchi


Emphysema – Damage to alveoli, usually from smoking


Occupational Diseases – Due to exposure to pollutants (e.g., silicosis, asbestosis)




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📚 Conclusion


Understanding breathing and gas exchange helps appreciate how delicate yet efficient our respiratory system is. From a yawn to a sprint, every breath is part of a finely tuned process that keeps us alive.



📝 Tags


#Class11Biology #BreathingAndExchangeOfGases #NCERTBiolog

y #HumanRespiratorySystem #Alveoli #BlogspotBiology #NEETBiology



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