Edexcel iGCSE Biology-2.40 B diffusion in gas exchange- Study Notes- New Syllabus

Role of Diffusion in Gas Exchange

📝 Introduction

Gas exchange = process by which oxygen enters the body and carbon dioxide is removed.
This happens by diffusion – movement of particles from high concentration → low concentration.

🔑 How Diffusion Works in Gas Exchange

• Oxygen (O₂):
  • Higher conc. in air (alveoli or leaf air spaces)
  • Lower conc. in blood (capillaries) or cells
  • Diffuses into blood/cells
• Carbon dioxide (CO₂):
  • Higher conc. in blood/cells (waste product of respiration)
  • Lower conc. in alveoli/leaf air spaces
  • Diffuses out into lungs/atmosphere

🌟 Adaptations for Efficient Diffusion

In Humans (Lungs – Alveoli):

• Large surface area (millions of alveoli)
• Thin walls (one cell thick → short diffusion distance)
• Moist lining (gases dissolve → easier diffusion)
• Good blood supply (maintains steep conc. gradient)
• Constant ventilation (fresh O₂ in, CO₂ out)

In Plants (Leaves):

• Broad surface area → more diffusion
• Thin structure → short diffusion distance
• Air spaces inside leaf → faster movement of gases
• Stomata (pores) open/close to regulate gas exchange

⚡ Why Diffusion is Important

• Supplies oxygen for respiration
• Removes carbon dioxide (toxic if builds up)
• Maintains efficient energy release (ATP) in cells
• In plants → balance between photosynthesis & respiration

📌 Quick Recap 
Gas exchange = by diffusion (high → low conc.)
O₂ in, CO₂ out
Humans: alveoli adaptations (large SA, thin walls, moist, blood supply, ventilation)
Plants: stomata + air spaces + thin leaves
Essential for respiration and energy supply