Exchange surfaces in fish and insects

• how are gases transported in an insect?

  • don’t transport oxygen in their haemolymph
  • gases need to be transported directly to the respiring tissue, insects do this using their tracheal system
• how is an unidirectional flow of water is maintained over the gills of a fish?

  • mouths opens (operculum closed)
  • buccal cavity floor is lowered
  • increases volume and decreases pressure of buccal cavity compared to outside
  • water rushes into mouth down pressure gradient
  • opercular cavity expands
  • buccal cavity floor raised
  • pressure inside buccal cavity is higher than opercular cavity
  • water moves from buccal cavity over gills into opercular cavity
  • mouth is closed and operculum opens
  • sides of opercular moves inwards, increasing pressure
  • water rushes out of fish through operculum
• what is the difference between concurrent and counter current?

  concurrent is flowing in the same direction whereas counter current is flowing in opposite directions
• what do gills have to increase surface area?

  lamella (folds)
• how can gas exchange occur much quicker in fish?

  water is flowing past in opposite direction to blood flow -maintaining high concentration gradient across entire length of gill lamella
• what does the high concentration gradient across the gill lamella cause?

  oxygen to diffuse down the oxygen concentration gradient from the water to the blood
• how does the concentration gradient cause the movement of oxygen?

  • even when the concentration gradient of oxygen in the water is low at the opercular cavity end of the lamella, blood has just entered the gill lamella - therefore, is even lower in oxygen concentration
  • this means there is still a diffusion gradient allowing the diffusion of oxygen from water into the blood
  • with parallel/concurrent flow, the concentration of oxygen in the water and in the blood in the gills will equalise, no more oxygen exchange would take place
• what is the difference between active tissue and resting tissue of insects?

  In active:

  • gas/water interface moves closer to muscle
  • when oxygen demands build up, a lactic acid build up in tissue results in water moving out of tracheoles
  • this exposes more surface area for gas exchange and means that exchange of gases occurs nearer the cell In Resting:
  • gas/water interface is further apart at rest (lower demand)
  • ends of tracheoles contain fluid which limits the penetration of air for diffusion
• how is ventilation achieved in larger insects?

  • mechanical ventilation of trachea system by using a pumping movement of thorax and/or abdomen, this changes in pressure within the body allowing air to be drawn in and out of trachea
  • collapsible enlarged trachea or air sacs act as air reservoirs, they are used to increase the movement of air through the system and are inflated and deflated by movements of the thorax and abdomen
• label the diagram

  A) direction of water flow

  B) operculum (gill cover)

  C) gill arch

  D) gill arch

  E) blood vessels

  F) gill filaments

  G) net diffusion of oxygen from water to blood

  H) countercurrent exchange

  I) blood flow through capillaries in lamella

  J) water flow between lamellae

  K) lamella

  L) oxygen-rich blood

  M) oxygen-poor blood

  
• label the diagram

  A) spiracle

  B) trachea

  C) tracheoles

  D) chitin

  E) collapsing