3.1.I SA:Vol Ratio and Gas Exchange Insects

• What structures do insects possess thatassist in limiting water loss?

  Insects have a waterproof coating over their body surfaces, this is usually a rigid exo-skeleton which is covered in a waterproof cuticle.

  They also have a small surface area to volume ratio to minimise the area of which water is lost.
• Describe the movement of oxygen through an insect.

  Oxygen enters the insect through the spiracles and them moves into the trachea, the spiracles then close. Oxygen then moves through the trachea into the tracheoles, where it is delivered straight to respiring tissues. The carbon dioxide produced in respiration moves in the opposite direction and leaves via the spiracles when they're open.
• Describe the role of spiracles in insects.

  Gas enters and leaves the insect through these tiny pores. They are opened and closed to control water loss by evaporation.
• Describe the tracheoles in insects.

  They are small tubes which extend throughout the body's tissues.
• Describe the trachea in insects.

  A network of tubes supported by strengthened rings.
• Why does diffusion occur in the gas exchange of insect? Describe the process for oxygen.

  Tissues respire using oxygen. This reduces the concentration of oxygen at the tissue. Oxygen moves from a high to a low concentration, so moves from the trachea to the tissue. This lowers the oxygen concentration in the trachea. So oxygen moves into the trachea from outside the insect via the spiracles. The opposite applies for the movement of carbon dioxide.
• How does the movement of an insect also speed up gaseous exchange?

  The movement of the insects muscles creates a mass movement of air in and out of the trachea. This speeds up gaseous exchange.
• The ends of an insects tracheoles are moist - the fluid moves into the cells during exercise so the tracheole only contains air.
• Even without circulation, a diffusion gradient is maintained via respiration, using oxygen. Ventilation can pump the body to move air around the trachea system.
• How is water loss reduced in insects?

  Spiracles can close.

  They have hairs around spiracles to trap water.

  Their body has a small surface area to volume ratio.

  They have waterproof coverings over their body surfaces - waterproof cuticle over exoskeleton and trachea.