Gas exchange in insects

• Insects can be very active organisms with a high oxygen demand- for example flying.
• How is an insects gas exchange system adapted?

  It supplies oxygen directly to cells.
• Exoskeleton

  • Insects are covered in a exoskeleton made of chitin
  • This causes gases to be unable to diffuse across insects body
• Spiracles

  • Spiracles are small holes found on the surface of the exoskeleton
  • They allow diffusion of gases into an insects body
• Tracheae

  • network of tubes which attach to tracheoles
  • 1mm in diameter
  • walls are reinforced with chitin to prevent collapsing when thorax or abdomen are contracting
• Tracheoles

  • hollow tubes that are one micrometre in diameter
  • provide a large surface area and short diffusion distance- allowing oxygen to rapidly diffuse into cells
• Tracheal fluid

  • located at the ends of tracheoles
  • When cells undergo anaerobic respiration water potential in cells decreases due to a release in lactic acid. This causes water from in the tracheal fluid to move into cells. This movement of water then causes air to be drawn down into tracheoles as volume of tracheal fluid is decreased.
• Problem of water loss

  • the walls of tracheoles are moist and ends contain tracheal fluid, meaning water vapour can diffuse out of spiracles.
  • to counter this spiracles are surrounded by a muscular sphincter.
• Muscular sphincter

  • located at spiracles
  • They contract and close when oxygen requirement is low, this prevents loss of water.
• Adaptations of insects

  • some insects can contract muscles in thorax and abdomen to change volume
  • causes a pressure change pushing air in and out
  • This process is called mass transport
• Air sacs

  • located in tracheae
  • changes in volumes of thorax and abdomen can squeeze air sacs causing air to move down into tracheoles
  • insects can also rely on air in sacs when spiracles are shut to prevent water loss.