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• What is a key feature of gas-exchange surfaces that speeds up the rate of change?

  Large surface area
• Why are gas-exchange surfaces very thin?

  To keep the diffusion pathway short
• How does the thickness of gas-exchange surfaces affect material crossing?

  It allows materials to cross rapidly
• What is another essential feature of gas-exchange surfaces?

  Efficient blood supply
• How does an efficient blood supply benefit gas-exchange surfaces?

  It enhances the transport of gases
• describe the sequence of events that leads to atmospheric oxygen entering the bloodstream. (6 marks)

  Diaphragm muscles contract so volume in lungs increases and pressure decreases

  Oxygen drawn in from the nose passes through the trachea then bronchi, bronchioles, and alveoli

  Oxygen dissolve then diffuses through the alveolus lining and the lining of the capillary
• Describe how the insect is able to obtain oxygen and limit water loss. 6 marks

  • Body covered with (waterproof) waxy layer/cuticle
  • So insects have spiracles are able to close (and open)
  • Air enters through (open) spiracles;
  • Down diffusion gradient
  • (through) in trachea
  • Tracheae closely associated with cells