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Biology AS CIE

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  1. 1-cell-structure
    10 主题
  2. 2-biological-molecules
    19 主题
  3. 3-enzymes
    13 主题
  4. 4-cell-membranes-and-transport
    16 主题
  5. 5-the-mitotic-cell-cycle
    8 主题
  6. 6-nucleic-acids-and-protein-synthesis
    9 主题
  7. 7-transport-in-plants
    11 主题
  8. 8-transport-in-mammals
    16 主题
  9. 9-gas-exchange
    6 主题
  10. 10-infectious-diseases
    6 主题
  11. 11-immunity
    10 主题
课 8, 主题 9
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8-2-transport-of-oxygen-and-carbon-dioxide AS red-blood-cells-haemoglobin-and-oxygen

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Exam code:9700

Red blood cells, haemoglobin & oxygen

  • The majority of oxygen transported around the body is bound to the protein haemoglobin in red blood cells

  • Each molecule of haemoglobin contains four haem groups, each able to bond with one molecule of oxygen

    • This means that each molecule of haemoglobin can carry four oxygen molecules, or eight oxygen atoms in total

Diagram of a red blood cell with haemoglobin, highlighting 280 million molecules. Shows haem prosthetic group, alpha and beta-globin subunits.
Haemoglobin proteins are made up of four subunits, each of which contains a region called a haem group to which oxygen can bind
  • When oxygen binds to haemoglobin, oxyhaemoglobin is formed

Transport of carbon dioxide

  • Carbon dioxide produced in respiration is transported in the blood in three main ways:

    • A small proportion is dissolved directly in the plasma

    • Some binds to haemoglobin, forming carbaminohaemoglobin

    • The majority is carried as hydrogencarbonate ions in the plasma

The role of carbonic anhydrase

  • Inside red blood cells, carbon dioxide combines with water to form carbonic acid

    • This reaction is catalysed by the enzyme carbonic anhydrase

  • The carbonic acid then dissociates into hydrogencarbonate ions (HCO₃⁻) and hydrogen ions (H⁺)

  • The hydrogencarbonate ions move out of the red blood cells into the plasma, where they are carried in solution

Haemoglobinic acid

  • The hydrogen ions released in the dissociation of carbonic acid could lower blood pH

  • To prevent this, haemoglobin acts as a buffer:

    • Haemoglobin binds with hydrogen ions to form haemoglobinic acid (HHb)

    • This maintains the blood at a stable pH while still allowing haemoglobin to transport oxygen

Carbaminohaemoglobin

  • Some carbon dioxide binds directly to the amino groups of haemoglobin, forming carbaminohaemoglobin (HbCO₂)

    • This binding occurs more readily when haemoglobin has released oxygen in the respiring tissues

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