Fish

• What is the specialized gas exchange surface in bony fish?

  Gills
• Why do bony fish have a specialized gas exchange surface?

  They have greater oxygen needs
• What is the role of gill filaments in fish?

  They provide a large surface area
• Why must water be forced over the gill filaments?

  Water is dense with low oxygen content
• How does water flow over the gills in bony fish?

  It flows in a unidirectional manner
• What allows continuous water passage across the gills?

  Ventilation mechanism during resting
• What causes the pressure changes in the buccal and opercular cavities?

  Mouth opening and closing
• What are the three stages of the ventilation mechanism in bony fish?

  1. Mouth opens, buccal cavity lowers, water enters
  2. Mouth closes, buccal cavity contracts, water forced across gills
  3. Pressure increases, operculum opens, water exits
• What happens during Stage 1 of fish ventilation?

  Mouth opens, water is pulled in
• What occurs in Stage 2 of the ventilation process?

  Mouth closes, water is forced across gills
• What happens in Stage 3 of fish ventilation?

  Pressure forces operculum open
• Why do gills have an extensive network of capillaries?

  To allow efficient diffusion of oxygen
• What is the role of haemoglobin in fish?

  It carries oxygen throughout the fish
• How does water flow in relation to blood flow across gill plates?

  Water flows opposite to blood flow
• What is counter current flow in fish gills?

  Blood and water flow in opposite directions
• How does counter current flow affect oxygen diffusion?

  It maintains a steep concentration gradient
• What is the effect of counter current flow on oxygen saturation?

  Higher percentage oxygen saturation
• What is parallel flow in cartilaginous fish?

  Water and blood flow in the same direction
• What happens to the concentration gradient in parallel flow?

  It is not maintained, equilibrium is reached
• Compare counter current flow and parallel flow in fish gills.

  Counter Current Flow:

  • Opposite directions of water and blood
  • Maintains steep concentration gradient
  • High rate of diffusion
  • Higher oxygen absorption

  
  

  Parallel Flow:

  • Same direction of water and blood
  • Concentration gradient not maintained
  • Lower rate of diffusion
  • Lower oxygen absorption
• What is the result of equilibrium in parallel flow?

  Diffusion does not occur across entire gill plate
• What is the main disadvantage of parallel flow in fish gills?

  Lower percentage oxygen saturation