Fish

• How is large surface area created in the gills of a fish?

  There are millions of gill filaments stacked and held by the bony arch, and millions of gill lamellae at right angles to the filaments.
• How is a short diffusion pathway created in the gills of a fish?

  The gill lamellae are very thin.
• How is a good blood supply created in the gills of a fish?

  There are many blood vessels in and around the gill filaments and gill lamellae.
• Describe counter-current flow:


  The water over the gills and the flow of blood travel in opposite directions.
• What does counter-current flow enable?

  • The water always has more oxygen than the blood of the fish.
  • A diffusion gradient therefore exists across the entire width of the gill lamellae
  • Faster rate of diffusion -> faster metabolism -> swim faster
• Describe parallel flow:


  The water over the gills and the flow of blood travel in the same direction.
• What does parallel flow create and cause?

  • Diffusion gradient exists over only part of the width of the gill lamellae.
  • Slower rate of diffusion -> slower metabolism -> swim slower
• The volume of water passing over the gills increases if the temperature of the water increases. Explain why.

  Warmer water increases the rate of enzyme activity so the rate of respiration increases. This allows the fish to swim faster and therefore more water passes over the gills.
• Explain how the gills of a fish are adapted for efficient gas exchange (6)

  • Large surface area of gill filaments and lamellae so faster diffusion.
  • Gill lamellae are very thin so short diffusion pathway means faster diffusion.
  • Water and blood travel in opposite directions, maintaining a diffusion gradient across the entire length of the gill so faster diffusion.
  • Circulation of blood replaces blood that is saturated with oxygen, so maintains concentration gradient so faster diffusion.
  • Ventilation replaces water as oxygen is removed from it so maintains concentration gradient so faster diffusion.