Edexcel iGCSE Biology-2.48 Alveoli: Adaptations for Gas Exchange- Study Notes- New Syllabus

Alveoli – Adaptations for Gas Exchange

📝 Introduction

Gas exchange happens in the alveoli, tiny air sacs in the lungs.
Oxygen (O₂) diffuses from alveoli → blood.
Carbon dioxide (CO₂) diffuses from blood → alveoli.
Exchange occurs by diffusion (movement from high to low concentration).

🌟 Key Adaptations of Alveoli

• Large Surface Area
  Millions of alveoli in lungs (like bunches of grapes).
  Huge surface area for maximum diffusion of gases.
• Thin Walls
  Alveolar walls are 1 cell thick.
  Short diffusion distance → gases move quickly.
• Rich Blood Supply
  Surrounded by a dense network of capillaries.
  Maintains steep concentration gradient for O₂ and CO₂.
• Moist Lining 
  Dissolves gases (O₂ and CO₂) → makes diffusion easier.
• Elastic Walls
  Stretch and recoil during breathing.
  Helps push air out and draw air in efficiently.
• Good Ventilation
  Constant airflow in alveoli → keeps O₂ levels high and CO₂ levels low.
  Maintains strong diffusion gradient.

🔄 Diffusion Process

• Oxygen (O₂):
  High concentration in alveoli → diffuses into low concentration blood (in capillaries).
• Carbon Dioxide (CO₂):
  High concentration in blood → diffuses into alveoli → exhaled.

📊 Summary Table

⚡ Quick Recap
Alveoli = tiny air sacs for O₂ in, CO₂ out.
SA ↑ + thin walls + capillaries + moist lining + ventilation = perfect for diffusion.
Diffusion always goes high → low concentration.