Insects

• Explain how the body surface of a single-celled organisms is adapted for gas exchange

  • Thin/flat shape and large SA:Vol ratio
  • Short diffusion pathway to all parts of cell - rapid diffusion e.g. of CO2 and O2
• Describe the tracheal system of an insect

  1. Spiracles = Pores on surface that can open/close to allow for diffusion
  2. Trachea = Large tubes full of air that allow diffusion
  3. Tracheoles =Smaller branches from trachea, permeable to allow for gas exchange with cells
• Insect's tracheal system

  • Tracheoles have thin walls
  • High number of highly branched tracheoles
  • Trachea provide tubes full of air
  • Contraction of abdominal muscles (abdominal pumping) changes pressure in body, causing air to move in and out
  • Fluid in end of tracheoles drawn into tissue by osmosis during exercise (Lactate produced in anaerobic respiration lowers water potential)
• How an insect's tracheal system is adapted for gas exchange

  1. Tracheoles have thin walls - So short diffusion pathway to cells

  2. High number of highly branched tracheoles - So short diffusion pathway to cells - So large surface area

  3. Trachea provide tubes full of air - So fast diffusion

  4. Contraction of abdominal muscles (abdominal pumping) changes pressure in body, causing air to move in and out - Maintains concentration gradient for diffusion

  5. Fluid in end of tracheoles drawn into tissue by osmosis during exercise (Lactate produced in anaerobic respiration lowers water potential) - Diffusion is faster through air (rather than in fluid) to gas exchange surface
• Explain structural and functional compromises in terrestrial insects that allow efficient gas exchange while limiting water loss

  • Thick waxy cuticle/exoskeleton - increases diffusion pathway so less water loss
  • Spiracles can open to allow for gas exchange and close to reduce water loss
  • Hairs around spiracles - traps moist air, reducing water potential gradient so less water loss