3: EXCHANGE SYSTEMS AND MASS TRANSPORT - GAS EXCHANGE IN FISH

Question 1

Describe the structure of the gills

Answer 1

• each gill is made up of several thin plates called gill filaments
• each gill filament is covered in tiny structures called lamellae
• lamellae have lots of blood capillaries and a thin layer of surface cells

Question 2

How are the gills adapted for efficient gas exchange?

Answer 2

• increased SA due to gill filaments and lamellae
• short diffusion pathway as lamellae have a thin layer of surface cells
• good blood supply as lamellae have lots of capillaries

Question 3

Describe the counter-current system

Answer 3

in the gills, blood flows through lamellae in 1 direction and water flows over them in the other direction

Question 4

What is the benefit of the counter-current system?

Answer 4

• steep conc. gradient is maintained between the water and the blood over the whole length of the gill
• this is because water with a relatively high O2 conc. always flows next to blood with a lower O2 conc.