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 to meet gas exchange criteria?

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

  Using Fick's law
• How many layers of gills do fish have on each side of their head?

  Four layers
• What are the structures called that stick out from the gills?

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

  At right angles to the gill filaments
• What is the purpose of the capillary network in gill lamellae?

  To provide a short diffusion distance
• How does water flow through the fish's gills?

  It rushes in through the mouth
• What is the counter current flow in fish gills?

  Water flows opposite to blood in capillaries
• Why is counter current flow advantageous for fish?

  It prevents equilibrium, maintaining diffusion
• What happens in concurrent flow compared to counter current flow?

  Equilibrium is reached in concurrent flow
• What is the significance of maintaining a diffusion gradient in fish gills?

  It allows continuous oxygen diffusion
• What are the three features of gas exchange in fish gills?

  1. Large surface area from stacked gill filaments
  2. Short diffusion distance due to thin lamellae
  3. Counter current flow to maintain concentration gradient
• What is the role of gill lamellae in fish?

  Site of gas exchange
• How does the concentration of oxygen change as water flows over the gills?

  It decreases from 100% to near zero
• What is the importance of the entire length of the lamellae in gas exchange?

  It allows diffusion across the entire surface
• What should be noted about the term "counter current" in gas exchange?

  It means opposite flow of water and blood
• What happens if equilibrium is reached in gas exchange?

  Diffusion stops across the gill lamellae
• How does the structure of gills contribute to their function?

  Stacks of filaments increase surface area
• What is the role of the mouth in fish gas exchange?

  It allows water to enter for oxygen extraction
• What is the primary function of gills in fish?

  To facilitate gas exchange
• Why is it important for fish to have adaptations for gas exchange?

  To efficiently extract oxygen from water