In fish

• Advantages of living in water

  More dense -gills held open by density of water

  Organisms won’t dry out (desiccation)
• Disadvantages of living in water

  More dense - harder to move and change direction

  Less oxygen in water
• How do fish get oxygen?

  Take in water through the mouth

  Into buccal cavity

  Removes oxygen into the blood and leave co2 to go back into the water

  Force water out through slits in their face
• Water and blood move in … directions

  Opposite
• What is it called when water and blood move in opposite directions?

  counter current principle
• Counter current principle

  Diffusion gradient always maintained

  Almost all oxygen into the blood
• features - many lamellae

  Large SA
• Features - thin lamellae epithelium

  Short diffusion pathway
• Features - counter current

  Maintains concentration gradient
• Features - ventilation of gills

  Fish always breathing, constant supply of oxygen from water, maintains concentration gradient
• Features - circulation

  Blood always moving, maintains concentration gradient
• Higher number of lamellae means

  Increased SA and faster diffusion
• Thinner lamellae means

  Small diffusion distance

  Increased diffusion
• A fish moving quicker needs more or less diffusion?

  More

  More oxygen from respiration which makes ATP
• A fish that needs less diffusion and moves less has …

  Thick lamellae and small number of lamellae per mm
• A fish with a larger SA moves …

  More
• ventilation - inspiration

  mouth opens

  gill flap closes

  floor of mouth lowers

  increases the volume

  decreases the pressure

  water enters from high to low pressure
• what does the mouth do in inspiration?

  opens
• what does the gill flap do in inspiration?

  closes
• what does the floor of the mouth so in inspiration?

  lowers
• is the volume increased or decreased in inspiration?

  increased
• is the pressure increased or decreased in inspiration?

  decreased
• ventilation - expiration

  mouth closes

  gill flap opens

  raises the floor of the mouth

  volume decreases

  pressure increases

  water moves out from high to low pressure
• what does the mouth do in expiration?

  closes
• what do the gill flaps do in expiration?

  open
• what does the floor of the mouth do in expiration?

  raises up
• is the volume increased or decreased in expiration?

  decreased
• is the pressure increased or decreased in expiration?

  increased