exchange in fish

• Why can't fish simply diffuse oxygen across their surface?

  They have a small surface area to volume ratio
• What is the gas exchange surface in fish?

  The gills
• How much less oxygen does water contain compared to air?


  30 times less oxygen
• What are the three key features of every gas exchange surface?

  Large surface area, short diffusion distance, concentration gradient
• What adaptations do fish gills have for gas exchange?

  • Large surface area from gill filaments and lamellae
  • Short diffusion distance due to thin lamellae
  • Counter current flow to maintain concentration gradient
• How is the rate of diffusion calculated in gas exchange?

  Using Fick's law
• What does Fick's law state about diffusion?

  Diffusion is proportional to surface area and concentration difference
• How many layers of gills do fish have on each side of their head?

  Four layers
• What are the long parts sticking out of the gills called?

  Gill filaments
• How are gill lamellae positioned in relation to gill filaments?

  At right angles to the gill filaments
• Where does gas exchange occur in fish gills?

  On the gill lamellae
• What provides a short diffusion distance in gill lamellae?

  The thin structure of the lamellae
• What is found inside every gill lamellae that aids gas exchange?

  A capillary network
• What is the purpose of counter current flow in fish gills?

  To maintain a concentration gradient
• How does counter current flow differ from concurrent flow?

  Water flows opposite to blood flow
• What happens to oxygen concentration in blood during counter current flow?

  It never reaches 100% saturation
• Why is it advantageous that equilibrium is not reached in counter current flow?

  It allows diffusion across the entire lamellae
• What is the key reason for the advantage of counter current flow?

  It maintains a diffusion gradient
• What are the three features of gas exchange in fish gills?

  • Large surface area from stacked gill filaments and lamellae
  • Short diffusion distance due to thin lamellae
  • Counter current flow to maintain concentration gradient
• What is the main function of gills in fish?

  Gas exchange
• What happens to the oxygen concentration in water as it flows over the gills?

  It decreases from 100% to near 0%
• What is the significance of the term "entire" in relation to diffusion across the lamellae?

  It indicates diffusion occurs along the whole length