Exchange in single-called organisms and insects

• In single-felled organisms:

  • they have a large surface area to volume ratio
  • oxygen is absorbed by diffusion across their body surface
  • carbon dioxide diffuses out across their body surface
• Gas exchange in insects:

  • insects have an internal network called trachae
  • these divide into tracheoles
  • these extend throughout the body of the insect so air can be brought directly into respiring tissues
  • gases enter through tiny pores called spiracles, which can be opened and closed
• How gases move in and out of the tracheal system:

  • along a diffusion gradient
  • mass transport
  • ends of tracheoles are filled with water