Essential Idea:   The human body has structures and processes that resist the continuous threat of invasion by pathogens.
At SHS, Topic 6.4 is taught in the following class unit(s):​​​​​​​​
6.4.U1  Ventilation maintains concentration gradients of oxygen and carbon dioxide between air and alveolu and blood flowing in adjacent capillaries.
  • Define gas exchange and ventilation.
  • State the location of gas exchange in humans.
  • Outline the mechanism of gas exchange in humans.
  • Draw a diagram showing the structure of an alveolus and an adjacent capillary.
6.4.U2  Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange.
  • Describe how the structure of the alveoli increases surface area for gas exchange.
  • Outline the structure of type 1 pneumocytes.
6.4.U3  Type II pneumocytes secrete a solution containing surfactant that creates a moist surface inside the alveoli to prevent the sides of the alveolus adhering to each other by reducing surface tension.
  • Outline the structure and function of type II pneumocytes.
  • Describe two functions of the fluid secreted by type II pneumocytes.
6.4.U4  Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles.
  • Outline the flow of air into the lungs.
  • State the role of cartilage in the trachea and bronchi.
  • State the role of smooth muscle fibres in the bronchioles.
6.4.U5  Muscle contraction causes the pressure changes inside the thorax that force air in and out of the lungs to ventilate them.
  • State the relationship between gas pressure and volume.
  • Outline the pressure and volume changes that occur during inspiration and expiration.​
6.4.U6  Different muscles are required for inspiration and expiration because muscles only do work when they contract.
  • Explain the contraction and relaxation of muscles through the use of antagonistic muscle pairs.
6.4.A1  External and internal intercostal muscles, and diaphragm and abdominal muscles as examples of antagonistic muscle action.
  • Outline the direction of movement of the diaphragm and rib-cage during inspiration and expiration.
  • Describe the antagonistic muscle contraction and relaxation required to move the rib-cage and diaphragm during inhalation and expiration.
6.4.A2  Causes and consequences of lung cancer.
  • Outline the causes of lung cancer.
  • List symptoms of lung cancer.​
6.4.A3  Causes and consequences of emphysema.
  • Outline the causes of emphysema.
  • State the symptoms of emphysema.
  • Outline reasons why gas exchange and ventilation are less effective in people with emphysema.
  • List treatment options for people with emphysema.
6.4.S1  Monitoring of ventilation in humans at rest and after mild and vigorous exercise. (Practical 6)
  • Identify the manipulated and responding variables in a test of the effect of exercise on ventilation.
  • Outline techniques for measuring ventilation rate or lung tidal volume.
6.4.NOS  Obtain evidence for theories- epidemiological studies have contributed to our understanding of the causes of the lung cancer.
  • Define epidemiology.
  • Outline how epidemiological studies contributed to understanding the association between smoking and lung cancer
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"When we try to pick out anything by itself, we find it hitched to everything else in the Universe." 
 John Muir,   1911