Class 11 Biology - Chapter 17 : Breathing and Exchange of Gases | NCERT Complete short Notes | NEET 2027

   

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As a NEET Dropper, I'm sharing my complete notes of Chapter 17: Breathing and Exchange of Gases with you all.

Nose se leke Alveoli tak - Full NCERT + PYQ + Google se Hatke Tricks! 

3-4 Questions fix aate hain NEET me is chapter se 🔥

Jo coaching me bhi nahi milta wo yaha hai =

All Respiratory Volumes + Gas Transport + Bohr & Haldane Effect + Disorders

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### *1. RESPIRATION = BREATHING + GASEOUS EXCHANGE + CELLULAR RESPIRATION*

Respiration = Catabolic process = Glucose + O2 → CO2 + H2O + ATP

Types:

A. External Respiration = Breathing = Exchange in lungs

B. Internal Respiration = Tissue level = Exchange in cells

C. Cellular Respiration = ATP formation in mitochondria

Respiratory Organs in Animals:

Porifera = Diffusion, Earthworm = Skin, 

Insects = Trachea, Fish = Gills, 

Amphibians = Skin + Lungs, 

Birds + Mammals = Lungs = Most efficient

### *2. HUMAN RESPIRATORY SYSTEM*

Figure: Nasal passage → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli

A. External Nose → Nasal Chamber

   Hair + Mucus = Filter dust, Conchae = Warm + Humidify air

   Olfactory receptors = Smell

B. Pharynx = Common passage for air + food = Nasopharynx + Oropharynx + Laryngopharynx

C. Larynx = Voice box = 9 cartilages = Thyroid = Adam's Apple

   Glottis = Opening = Epiglottis = Prevents food entry

D. Trachea = Windpipe = 10-12cm = C-shaped cartilaginous rings = Prevent collapse

   Bifurcates into 2 Bronchi at T5 vertebra

E. Bronchi → Primary → Secondary → Tertiary → Bronchioles → Terminal bronchioles

   Bronchi have cartilage, Bronchioles no cartilage

   

F. Alveoli = 300 million = Functional unit = 80 m² surface area

   Types of Cells:

   1. Type I Pneumocytes = Squamous = 95% = Gas exchange

   2. Type II Pneumocytes = Cuboidal = Secrete Surfactant = Reduce surface tension

   3. Alveolar Macrophages = Dust cells = Phagocytosis

   

   Blood Air Barrier = 3 layers = 0.5μm thin

   Alveolar membrane + Basement membrane + Capillary endothelium

G. Lungs = 2 = Left = 2 lobes, Right = 3 lobes

   Pleura = Double membrane = Pleural fluid = Reduces friction

### *3. MECHANISM OF BREATHING* `Inspiration + Expiration`

Inspiration = Active = Diaphragm contracts + External intercostal contracts

Result: Thoracic volume ↑, Pressure ↓ = Air rushes in

Expiration = Passive at rest = Diaphragm relaxes + External intercostal relaxes  

Result: Thoracic volume ↓, Pressure ↑ = Air goes out

Forceful expiration = Internal intercostal + Abdominal muscles

Respiratory Volumes & Capacities = Spirometer se measure

| **Term** | **Value** | **Meaning** |

| --- | --- | --- |

| **Tidal Volume TV** | 500 mL | Air inspired/expired in normal breathing |

| **Inspiratory Reserve IRV** | 2500-3000 mL | Extra air can inhale forcefully |

| **Expiratory Reserve ERV** | 1000-1100 mL | Extra air can exhale forcefully |

| **Residual Volume RV** | 1100-1200 mL | Air left after max exhalation |

| **Inspiratory Capacity IC** | TV + IRV = 3500 mL | Max air can inhale |

| **Expiratory Capacity EC** | TV + ERV = 1600 mL | Max air can exhale |

| **Functional Residual FRC** | ERV + RV = 2200 mL | Air left after normal exhalation |

| **Vital Capacity VC** | IRV + TV + ERV = 4600 mL | Max air can exhale after max inhale |

| **Total Lung Capacity TLC** | VC + RV = 5800 mL | Total air lungs can hold |

Trick: **V**ery **I**ntelligent **T**eacher **R**eads **E**very **V**olume

### *4. EXCHANGE OF GASES* `Alveoli ↔ Blood ↔ Tissues`

Partial Pressure in mm Hg:

| **Gas** | **Alveoli** | **Deoxygenated Blood** | **Oxygenated Blood** | **Tissues** |

| --- | --- | --- | --- | --- |

| **O2** | 104 | 40 | 95 | 40 |

| **CO2** | 40 | 45 | 40 | 45 |

Direction: High → Low pressure

O2: Alveoli 104 → Blood 40 → Tissues 40

CO2: Tissues 45 → Blood 45 → Alveoli 40

Diffusion = Simple, Passive, Based on solubility + thickness

O2 is 20x more soluble than CO2 but CO2 diffuses 20x faster due to high gradient

### *5. TRANSPORT OF GASES*

*A. O2 Transport = 97% as Oxyhemoglobin + 3% dissolved*

Hb + 4O2 ↔ Hb(O2)4 = Oxyhemoglobin

Oxygen Dissociation Curve = Sigmoid

Factors shifting right = ↓Hb-O2 affinity = O2 release:

1. High pCO2 = Bohr Effect

2. High H+ = Low pH

3. High Temp = 37°C → 40°C during exercise

4. High 2,3-BPG in RBC

Factors shifting left = ↑Hb-O2 affinity = O2 binding:

Low pCO2, High pH, Low Temp, Low 2,3-BPG

At Alveoli: pO2 high, pCO2 low, pH high → O2 binds

At Tissues: pO2 low, pCO2 high, pH low → O2 releases = Bohr Effect

CO Poisoning = CO binds Hb 200x stronger than O2 = Death

*B. CO2 Transport = 70% as Bicarbonate + 20% as Carbamino-Hb + 7% dissolved*

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3- = Carbonic anhydrase in RBC

HCO3- goes to plasma = Chloride shift = Cl- enters RBC

At Tissues: CO2 high → HCO3- formed

At Alveoli: HCO3- + H+ → H2CO3 → CO2 + H2O → Exhaled

Carbamino-Hb = CO2 binds directly to Hb at NH2 group = 20-25%

CO2 is 20-25x more soluble than O2

### *6. REGULATION OF RESPIRATION*

A. Neural Control = Medulla + Pons

1. Respiratory Rhythm Centre = Medulla = Auto-excitable = Primary centre

2. Pneumotaxic Centre = Pons = "Switch off" inspiration = Limits IRV

3. Chemo-sensitive Area = Medulla = Sensitive to pCO2 + H+

B. Chemical Control = Chemoreceptors

1. Central = Medulla = Respond to H+ in CSF = pCO2 main stimulus

2. Peripheral = Aortic body + Carotid body = Respond to ↓pO2, ↑pCO2, ↓pH

During exercise: ↑CO2 + ↓O2 + ↓pH → Rate increases

Haldane Effect: Oxyhemoglobin has less affinity for CO2

### *7. DISORDERS OF RESPIRATORY SYSTEM* `NEET 1Q Pakka`

1. Asthma = Bronchioles spasm = Wheezing = Allergy = Bronchodilators

2. Bronchitis = Bronchi inflammation = Smoking = Cough + Mucus

3. Emphysema = Alveolar wall damage = ↓Surface area = Smoking = Breathlessness

4. Occupational Respiratory Disease = Silicosis, Asbestosis = Fibrosis

5. Pneumonia = Alveoli filled with fluid = Bacterial = Strep pneumoniae

6. Tuberculosis = TB bacteria = Chest pain + Cough + Hemoptysis

### *8. PYQ HOTSPOTS 2017-2024* 🔥

1. *Vital Capacity* = IRV + TV + ERV = NEET 2024

2. *Bohr Effect* = High CO2 → O2 release = NEET 2024

3. *Surfactant* = Type II pneumocytes = NEET 2023

4. *Carbonic anhydrase* = In RBC = NEET 2023

5. *Haldane Effect* = OxyHb releases CO2 easily = NEET 2022

6. *Tidal Volume* = 500mL = NEET 2022

7. *Pneumotaxic centre* = Pons = Switch off inspiration = NEET 2021

8. *Chloride shift* = HCO3- exchange with Cl- = NEET 2021

9. *Emphysema* = Smoking = Alveoli damage = NEET 2020

10. *Residual Volume* = 1100-1200mL = NEET 2020

11. *Partial pressure O2 in alveoli* = 104 mmHg = NEET 2019

12. *CO poisoning* = 200x affinity for Hb = NEET 2019

13. *Bronchioles* = No cartilage = NEET 2018

14. *Total lung capacity* = 5800mL = NEET 2018

15. *Diffusion membrane thickness* = 0.5μm = NEET 2017

### *9. GOOGLE SE HATKE TRICKS* 🧠

*A. Volumes Yaad Karne Ka*

**T**idal = **T**ypical = 500mL

**R**esidual = **R**emain = 1200mL

**V**ital = **V**ery **I**mportant **T**otal = IRV+TV+ERV

Trick: **T**o **R**ead **V**olumes = **T**V **R**V **V**C

*B. Gas Transport*

O2 = **H**b = **O**xy**H**b = 97%

CO2 = **B**icarbonate = **B**iggest = 70%

Trick: **O**ne **B**oy = **O**2 **B**y Hb, **C**O2 **B**y Bicarbonate

*C. Bohr vs Haldane Effect*

**Bohr** = **B**lood **O**2 **R**elease due to **CO2**

**Haldane** = **H**b **O**xy form **R**eleases **CO2** easily

*D. Respiratory Centres*

**M**edulla = **M**ain rhythm

**P**ons = **P**ause inspiration = Pneumotaxic

Trick: **M**ummy **P**uts **B**aby to sleep = Medulla Pons Brain

*Diagrams*: Human Respiratory System, Oxygen Dissociation Curve, Mechanism of Breathing  

*Board Practical*: Spirometer reading, Test for CO2, Rate of respiration  

*NEET Weightage*: 2Q Gas transport + 1Q Volumes + 1Q Regulation = 12+ Marks Pakka