Insects

• Define The Tracheal system:

  A system of air-filled tubes responsible for gaseous exchange in insects
• Why do insects not transport oxygen in blood?

  Insects have an open circulatory system so cannot easily direct the flow of blood to the tissues that need it most
• Name the three main features of an insect's tracheal system:

  • Spiracles
  • Tracheoles
  • Tracheae
• Define Tracheae in insects:

  Large tubes with rings of chitin that run from the spiracles and throughout an insect’s body, then divides further into smaller tracheoles.
• Define Spiracles:

  Pores along the thorax and abdomen of insects
• Define Spiracle sphincters:

  Small muscles that opens and closes the spiracles to control water loss and gas exchange in insects
• Define Tracheoles:

  Small branches of the tracheae that run throughout the tissues of an insect, forming a complex network, containing tracheal fluid at the ends
• Insects have slow circulation and it can be affected by movement.
• Define Tracheal fluid:

  The fluid found at the ends of the tracheoles
• The amount of tracheal fluid affects the surface area available for gaseous exchange and water loss.

  
  

  Role:

  allows gasses to dissolve and then diffuse into the cells
• In insects, oxygen is transported directly to tissues undergoing respiration
• Insects have an open circulatory system, in which their body fluid acts as blood and tissue fluid
• In insects, gaseous exchange occur between...

  • air in the tracheoles
  • tracheal fluid
• Explain what happens in insects when they are active:

  • their tissues are active/ respire more
  • the tracheal fluid can be withdrawn into the body fluid to increase the surface area of the tracheoles walls which is exposed to air
  • allows more oxygen to diffuse into the tissues
• Outline three ways insects can ventilate:

  through...

  • the expansion of walls
  • movement of wings
  • specialised breathing movements
• Explain how insects can ventilate through the movement of wings:

  • alters the volume of the thorax
  • when decreased, air in the tracheal system is put under pressure and is pushed out of the tracheal system
  • when increased, the pressure drops and air from outside is pushed into the tracheal system
• Explain how insects can ventilate through specialised breathing movements:

  • alters the volume of the abdomen
  • when increased, spiracles at the front end of the body opens and air enters the tracheal system
  • when decreased, spiracles at the rear end of the body opens and air leaves the tracheal system
• Explain how insects can ventilate through the expansion of walls:

  • the tracheal fluid can be withdrawn into the body fluid to increase the surface area of the tracheoles walls which is exposed to air
  • allows more oxygen to diffuse into the tissues
  • sections of the tracheal system have flexible walls
  • they act as air sacs which can repetitively contract and expand
• Outline and describe gaseous exchange in insects:

  • spiracle sphincters relax so the spiracles can open to allow air inside
  • the air travels through the tracheae and into the tracheoles
  • the air dissolves into the tracheal fluid
  • a diffusion gradient allows oxygen to diffuse into the body tissues and carbon dioxide to diffuse out
  • some exchange can also occur across thin walls of the tracheoles
• Outline how are tracheoles adapted for gas exchange?

  • There are many highly branching tracheoles - large surface area
  • Thin walls - short diffusion distance
• In insects, blood fluid (haemolymph) circulates through the body cavity (haemocoel)