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.
  

• B3.1.7

  Adaptations for gas exchange in leaves

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  Leaf structure adaptations should include the waxy cuticle, epidermis, air spaces, spongy mesophyll, stomatal guard cells and veins.
  

• B3.1.8

  Distribution of tissues in a leaf

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  Students should be able to draw and label a plan diagram to show the distribution of tissues in a transverse section of a dicotyledonous leaf.
  

• B3.1.9

  Transpiration as a consequence of gas exchange in a leaf

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  Students should be aware of the factors affecting the rate of transpiration.
  

• B3.1.10

  Stomatal density

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  AOS: Students should use micrographs or perform leaf casts to determine stomatal density.
  NOS: Reliability of quantitative data is increased by repeating measurements. In this case, repeated counts of the number of stomata visible in the field of view at high power illustrate the variability of biological material and the need for replicate trials.
  

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.