fish

• problems fish have with gas exchange

  -water has a lower concentration of oxygen

  -water is more dense than air

  -active- swim at 50mph

  -gases can't diffuse into their skin
• fish are cold blooded- lower respiration rate- less energy required to heat the body
• adaptations of gills


  -large surface area- allow for more diffusion

  -permeable membranes- allows gases to diffuse

  -thin (flattened cells)- shorter diffusion distance

  -good blood supply- maintains steep concentration gradient for diffusion
• gill structure


  -most teleosts (bony fish) have 5 gills on either side

  -covered by a bony plate called operculum

  -operculum protects gills and ensures water flows in the right direction

  -each gill is supported by a gill arch- contains blood vessels supplying blood to gill plates

  -each gill is formed of 2 rows of many gill filaments- increases surface area

  -each gill filament is covered in tiny gill plates which increase the surface area further
• ram ventilation


  -used by fish species including sharks and rays.

  -mouth opened during swimming so water is forced through the mouth across the gills and into the gill slits
• buccal pumping


  -movements of operculum are coordinated by the movement of the buccal cavity (space inside the mouth)

  -this is to change the volume and therefore pressure inside the fish

  -water flows down the pressure gradient
• buccal pumping stages


  -fish open their mouths and lower the floor of the buccal cavity

  -this causes the volume to increase and the pressure to decrease

  -pressure is higher outside the fish so water flows into the buccal cavity

  -the fish moves the buccal cavity to close its mouth, increasing pressure inside the fish

  -water flows form buccal cavity (high pressure) into the gill cavity (low pressure)

  -pressure increases in the gill cavity so the operculum opens, allowing water to exit the gills

  -operculum is pulled shut when the buccal cavity lowers at the start of the next cycle
• gill rakers


  -food filtered out of the water by the gill rakers

  -they point forward and inward from gill arches and aren't involved in gas exchange

  -fish don't take in separate mouthfuls for gas exchange and feeding- the processes happen simultaneously
• counter- current systems fish gills

  -2 substances flow in opposite directions

  -exchange happens between them

  -blood flows opposite to water

  -oxygen concentration gradient across entire lamella

  -continued diffusion

  -if there is concurrent (same way) an equilibrium is reached so no diffusion occurs
• fish- gills

  -filaments of thin tissue that are highly branched and folded

  -creates a large surface area

  -gill filaments are highly folded areas called lamellae- responsible for the high surface area

  -gills are covered by an operculum (gill cover)
• diffusion of oxygen- fish

  -mouth opens and water enters into the buccal cavity as its increased in volume

  -opercula remains closed

  -mouth closes- internal volume decreases, forcing water across the gills

  -when water flows through the gills, oxygen from water diffuses into the bloodstream

  -oxygen can diffuse into blood because of the counter current system
• counter current system

  -blood flows through lamellae in the opposite direction to water in the gills

  -ensures there is always a steep concentration gradient between the water and the blood