AHL Content Statements

• B3.1.11

  Adaptations of foetal and adult haemoglobin for the transport of oxygen
  

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  Include cooperative binding of oxygen to haem groups and allosteric binding of carbon dioxide.
  

• B3.1.12

  Bohr shift
  

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  Students should understand how an increase in carbon dioxide causes increased dissociation of oxygen and the benefits of this for actively respiring tissues.
  

• B3.1.13

  Oxygen dissociation curves as a means of representing the affinity of haemoglobin for oxygen at different oxygen concentrations

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  Explain the S-shaped form of the curve in terms of cooperative binding.

• B2.3.8

  Adaptations of type I and type II pneumocytes in alveoli
  

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  Limit to extreme thinness to reduce distances for diffusion in type I pneumocytes and the presence of many secretory vesicles (lamellar bodies) in the cytoplasm that discharge surfactant to the alveolar lumen in type II pneumocytes. Alveolar epithelium is an example of a tissue where more than one cell type is present, because different adaptations are required for the overall function of the tissue.