SL Content Statements

• B3.1.1

  Gas exchange as a vital function in all organisms
  

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  Students should appreciate that the challenges become greater as organisms increase in size because surface area-to-volume ratio decreases with increasing size, and the distance from the centre of an organism to its exterior increases.

• B3.1.2

  Properties of gas-exchange surfaces

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  Include permeability, thin tissue layer, moisture and large surface area.

• B3.1.3

  Maintenance of concentration gradients at exchange surfaces in animals
  

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  Include dense networks of blood vessels, continuous blood flow, and ventilation with air for lungs and with water for gills.
  

• B3.1.4

  Adaptations of mammalian lungs for gas exchange
  

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  Limit to the alveolar lungs of a mammal. Adaptations should include the presence of surfactant, a branched network of bronchioles, extensive capillary beds and a high surface area.
  

• B3.1.5

  Ventilation of the lungs

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  Students should understand the role of the diaphragm, intercostal muscles, abdominal muscles and ribs.

• B3.1.6

  Measurement of lung volumes

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  AOS: Students should make measurements to determine tidal volume, vital capacity, and inspiratory and expiratory reserves.