In insects

• Features insects have for gas exchange

  Spiracles, tracheole, air sacs, exoskeleton
• What are spiracles?

  Pores on the surface of the insect that open and close
• Features - thin walls

  Short diffusion distance
• Features - branches tracheoles

  Increases SA

  Thinner diffusion distance as covers whole body
• Features- tracheoles full of air

  Quicker diffusion rate
• Features - fluid at end of tracheoles

  Slows diffusion rate at rest so no CO2 wasted
• What does abdominal pumping do?

  Ventilates the system and maintains the pressure gradient
• Process of abdominal pumping

  Muscles contract and squeeze the trachae

  Creates a pressure gradient as pressure increases and is high where the muscle contracts

  Means faster rate of diffusion and there is a gradient
• Common features in xerophytes

  Less stomata means less water loss

  Opening and closing stomata

  Rolled up leaves means moist air trapped and less steep WP gradient

  Stomata on underside means lower temp and less KE for less water movement

  Thick cuticle prevents water loss

  Stomata in pit means air trapped and less steep WP gradient for less water movement