Insects

• What is the network of vessels in an insect?

  The tracheal system.
• Describe and explain the function of spiracles:

  These are valve-like openings on the surface of an insect's body. They control gas exchange and prevent excessive water loss by staying closed most of the time.
• Describe and explain the function of the tracheae:

  They are supported by strengthened rings made of chitin to prevent them from collapsing. They transport gases from the spiracles to the tracheoles- no gas exchange occurs here.
• Describe and explain the function of the tracheoles:


  They are branched, dead end tubes which extends through all the body tissues of the insect. Their walls are very narrow. This means that oxygen is brought directly to respiring tissues, and there is a short diffusion pathway.
• What are the three ways gas exchange is enabled?

  1. Along a diffusion gradient.
  2. Mass transport.
  3. The ends of the tracheoles are filled with water.
• How is a diffusion gradient created?

  Cells in the insect are respiring, so there is a low concentration of oxygen, whereas the concentration is higher outside the insect. This causes oxygen to move down the diffusion gradient.
• Describe how abdominal pumping speeds up gas exchange:

  The contraction of muscles in an insect squeezes the trachea, enabling mass movement of air in and out more quickly. This is due to a higher pressure gradient.
• Abdominal pumping increases the efficiency of gas exchange between the tracheoles and the muscle tissue of the insect. Explain why. (2)

  Oxygen enters more quickly, so this maintains a greater concentration gradient for faster diffusion.
• How does the tracheole ends being filled with water enable gas exchange?

  During vigorous activity, the muscle cells around the tracheoles respire anaerobically.

  This produces lactate, which lowers the water potential of the muscle cells. Water then diffuses into them by osmosis.

  This means the final diffusion pathway is in a gas therefore diffusion is more rapid.
• What is the danger of the water diffusing into muscle cells during anaerobic respiration?

  It causes greater water evaporation, which is dangerous in the long-term.