INSECTS

• what are spiracles


  tiny pores on an insects surface
• how are spiracles opened/closed

  vavle
• what is the trachea


  an internal network of tubes which are supported by internal rings to prevent them from collapsing
• what do tracheoles extend throughout


  body tissues/muscle fibre
• how do tracheoles provide a short diffusion pathway


  atmospheric air (containing oxygen) is brought directly to respiring tissues
• what are three ways carbon dioxide and oxygen are moved in and out of the tracheal system

  1. along a diffusion gradient
  2. mass transport
  3. ends of tracheoles are filled with water
• along a diffusion gradient

  1. respiring cells use oxygen causing oxygen concentration in trachoeles to drop
  2. oxygen concentration in insect is lower than atmosphere creating a diffusion gradient
  3. carbon dioxide is produced in respiration causing an increase in tracheoles
  4. this creates a diffusion gradient as the atmosphere has a lower carbon dioxide concentration than insect
• mass transport


  contraction of muscles squeezes trachea enabling mass movement of air in/out
• end of tracheoles filled with water

  1. muscle cells respire anaerobically in periods of major activity creating lactate
  2. this is soluble and lowers water potential of the muscle cells
  3. water potential in tracheoles is higher so water moves into muscle cells via osmosis
  4. this decreases tracheole volume, increasing pressure forcing oxygen in
• two limitations of insect gas exchange

  1. relies mostly on diffusion to exchange gases between atmosphere and insect
  2. short diffusion pathway limits size of organism