Gas Exchange - Fish

Question 1

Why do fish need an adapted exchange system?

Answer 1

• fish are waterproof and have a small SA:Vol
• there’s a lower conc of oxygen in the water than air so they have special adaptation to maintain the conc gradient

Question 2

What is the structure of the gills?

Answer 2

• each gill is made up of gill filaments
• gill filaments are covered in tiny structures called lamellae positioned right angles to filaments
• lamellae have lots of blood capillaries

Question 3

How are the gills adapted for gas exchange?

Answer 3

• many gill filaments covered in many gill lamellae → large SA:Vol
• capillary network in every lamellae and very thin lamellae → short diffusion pathway (thin surface layer of cells so gases dont have far to diffuse) + good blood supply
• countercurrent flow mechanism → maintaining conc gradient - keeping it high

Question 4

What is the countercurrent system?

Answer 4

• blood flows through lamlleae in one direction and water in the opposite
• conc of oxygen in water is always higher than oxygen conc in the blood across the whole length gill filament
• water with high conc of oxygen is always flowing next to blood with low conc

Question 5

Why is a countercurrent system efficient?

Answer 5

• equilibrium is not reached so diffusion can happen continuously
• if it were concurrent (flowing in same direction) eventually the conc would equalise and diffusion would slow or stop → oxygen wouldn’t diffuse out of water into blood as water passes along gill filament