gas exchange in single celled organisms

• Spiracle - tiny pores that allow gases to enter and leave the tracheae, opened and closed by a valve
• tracheae - a large internal network of tubes in insects with supported rings to prevent them from collapsing
• the tracheoles penetrate the individual body cells so that gases are directly exchanged between cells and the atmosphere
• For an insect air enters the trachea through the spiracles, gases will diffuse in and out of the spiracles down their concentration gradient
• tracheoles have thin walls to shorten the distance of diffusion
• tracheoles are highly branched to increase surface area for gas exchange
• there's fluid in the ends of trachea where it joins the tissue to allow:

  • gas exchange from air to liquid occurs in the tracheole which allows gases to diffuse to tissues faster
  • tracheal fluid can be withdrawn into the body fluid to increase the surface area of the tracheole exposed to air
• muscles pump body and force are in/out to maintain the concentration gradient
• spiracles can be closed to prevent water loss
• insects contract their muscles to pump gases in and out of their body as a from of ventilation
• single celled organisms have a large surface area to volume ratio, so gases can be exchanged directly from the atmosphere
• layers of chitin form a waterproof, barrier on the surface of an insect