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Edexcel A Level (IAL) Biology -1.9 The Role of Haemoglobin - Study Notes- New Syllabus

Edexcel A Level (IAL) Biology -1.9 The Role of Haemoglobin- Study Notes- New syllabus

Edexcel A Level (IAL) Biology -1.9 The Role of Haemoglobin- Study Notes -Edexcel A level Biology – per latest Syllabus.

Key Concepts:

  • (i) understand the role of haemoglobin in the transport of oxygen and carbon dioxide 
  • (ii) understand the oxygen dissociation curve of haemoglobin, the Bohr effect and the significance of the oxygen affinity of fetal haemoglobin compared with adult haemoglobin

Edexcel A level Biology-Study Notes- All Topics

Haemoglobin & Gas Transport

🌱 Introduction

Haemoglobin is a protein in red blood cells responsible for transporting oxygen (Oâ‚‚) from lungs to tissues and helping carry carbon dioxide (COâ‚‚) from tissues back to lungs.

🧩 Role of Haemoglobin

  • Oxygen Transport
    Each haemoglobin molecule can bind up to 4 oxygen molecules.
    Forms oxyhaemoglobin in high Oâ‚‚ environments (lungs).
    Releases Oâ‚‚ in low Oâ‚‚ environments (tissues).
  • Carbon Dioxide Transport
    COâ‚‚ binds to haemoglobin forming carbaminohaemoglobin.
    Helps carry COâ‚‚ from tissues to lungs for exhalation.

📈 Oxygen Dissociation Curve

  • Graph shows percentage saturation of haemoglobin with oxygen vs partial pressure of Oâ‚‚ (pOâ‚‚).
  • Sigmoid (S-shaped) curve:
    – At high pOâ‚‚ → haemoglobin binds Oâ‚‚ readily (lungs)
    – At lower pOâ‚‚ → haemoglobin releases Oâ‚‚ easily (tissues)
  • Bohr Effect
    Increased CO₂ or lower pH → haemoglobin releases more O₂.
    Significance: tissues with high respiration (more COâ‚‚) get more oxygen.

👶 Fetal vs Adult Haemoglobin

FeatureAdult HaemoglobinFetal HaemoglobinSignificance
Oxygen affinityLowerHigherFetus can absorb O₂ from mother’s blood efficiently
Dissociation curveRight-shiftedLeft-shiftedLeft shift → higher O₂ binding at lower pO₂

âš¡ Key Points

  • Haemoglobin = main Oâ‚‚ & COâ‚‚ transporter
  • Oxygen dissociation curve shows how Oâ‚‚ loading/unloading changes with pOâ‚‚
  • Bohr effect helps active tissues get more Oâ‚‚
  • Fetal haemoglobin has higher Oâ‚‚ affinity → ensures effective Oâ‚‚ transfer from mother

💡 Quick Recap 
Haemoglobin: binds Oâ‚‚ in lungs, releases in tissues
COâ‚‚ transport: forms carbaminohaemoglobin
Bohr effect: ↑ CO₂ → more O₂ released
Fetal Hb: binds O₂ better than adult → fetal survival

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