Fish

• How does water get into a fish's gills?

  Mouth opens- large buccal cavity volume - water rushes into mouth Mouth closed- small buccal cavity volume - water rushes over gills under high pressure
• Gill adaptations- features+explanations

  Many lamellae- so large SA

  One layer of cells so short diffusion path+ many capillaries same effect

  Countercurrent mechanism- so conc gradient is maintained along the length of the gill filament/ capillary
• Counter-current mechanism

  -Water and blood flow in opposite directions along the gill filament

  Water always more oxygenated than blood so oxygen diffuses from water to blood

  Countercurrent system maintains conc gradient along the length of the gill filament/ capillary