Topic 3 - Gas Excahnge In Fish

Question 1

Why do fish need a specialised structure for efficient gas exchange?

Answer 1

They have a small surface area to volume ratio and their skin is impermeable so gases cannot diffuse directly through their body

Question 2

What are the structures on fish gills?

Answer 2

• Fish have four pairs of gills each supported by a bony arch
• each gill is made up of gill filaments which increase surface area for gas exchange
• lamellae are thin projections on the gill filaments further increasing the surface area

Question 3

What is the countercurrent flow?

Answer 3

Blood flows in the opposite direction to water over the Lamellae.
This maintains a steep diffusion gradient across the entire gill surface.
It insures that oxygen continuously diffuses from water into the blood maximising oxygen uptake

Question 4

How are fishes structures adapted for efficiency?

Answer 4

• Thin membranes: reduce the diffusion distance for gases
• Large surface area: provided by filaments and lamellae for maximum gas exchange
• Good blood supply: capillaries in the lamellae transport oxygenated blood efficiently

Question 5

Why are the fish gills dependent on water?

Answer 5

The projections are held apart by water flow, ensuring maximum exposure for gas exchange
In the absence of water the gill filaments stick together preventing gas exchange, this is why they cannot survive out of water.