Biology - Chapter 14: Breathing and Exchange of Gases

Respiratory Organs, Mechanism of Breathing, and Gas Transport

1. Human Respiratory System

The human respiratory system includes organs from nasal passage to alveoli in lungs, where gas exchange occurs.

Term	Description	Average Value
Tidal Volume (TV)	Air inhaled or exhaled during normal breathing	500 mL
Inspiratory Reserve Volume (IRV)	Additional air that can be inhaled forcefully	2500 – 3000 mL
Residual Volume (RV)	Air remaining in lungs after forced exhalation	1100 – 1200 mL
Vital Capacity (VC)	Maximum air that can be exhaled after deep inhalation	4000 – 4600 mL

💡 Quick Concept: TV = Normal breathing IRV = Extra inhale RV = Air always remains VC = Maximum breathing capacity

Q1. Why are alveoli suitable for gas exchange?

Answer: • Very thin walls
• Large surface area
• Rich capillary network → Enables rapid diffusion of gases

Structure of Alveoli

Q2. How is oxygen transported in blood?

Answer: About 97% oxygen is transported by haemoglobin forming oxyhaemoglobin. One haemoglobin molecule can carry up to four oxygen molecules.

Q3. How is CO₂ transported in blood?

Answer:
• 70% as bicarbonate ions
• 20–25% as carbaminohaemoglobin
• 7% dissolved in plasma

Q4. Explain mechanism of breathing.

Answer:
• Inspiration: Diaphragm contracts → chest expands → air enters
• Expiration: Diaphragm relaxes → chest contracts → air leaves

Q5. What factors affect oxygen dissociation curve?

Answer: High CO₂, high temperature, and low pH shift the curve to the right, promoting oxygen release to tissues.

Q6. Name two respiratory disorders.

Answer:
• Asthma: Difficulty in breathing due to inflammation
• Emphysema: Damage to alveoli (common in smokers)

🔥 Exam Booster: Alveoli = Gas exchange Hb = Oxygen transport CO₂ = Mostly bicarbonate