3.2.2 gas exchange (fish)

Why do fish require a gas exchange surface

They are waterproof and have a small SA:V

Why is water harder for gas exchange

Water has 30x less oxygen than air, so fish must have a special adaptation to maintain the concentration gradient

Explain the anatomy of fish gills

• 4 layers of gills on both sides

• Made up of stacks of gill filaments

• Each filament is covered in lamellae (at a right angle to the filaments)

• Creating a large SA

Adaptations for efficient gas exchange- large SA:V

Created by many gill filaments and many gill lamellae

Adaptations for efficient gas exchange- short diffusion distance

Due to the capillary network and very thin gill lamellae

Adaptations for efficient gas exchange- maintaining a concentration gradient

Countercurrent flow mechanism

Explain the countercurrent flow mechanism

• water flows over the gills in the opposite direction to the flow of blood in the capillaries

• Ensures equilibrium is not reached Also

• Also ensures that a diffusion gradient is maintained across the entire length of the gill lamellae

Calculation for diffusion