Gas exchange in fish

Question 1

What is the structure of gills?

Answer 1

• gills are located in the body of fish behind the head
• they are made of gill filaments
• at right angles of the gill filaments, there are gill lamellae

Question 2

Explain the countercurrent exchange principle?

Answer 2

• the flow of blood and oxygen are in the opposite direction so that:
• Blood with a relatively high concentration of oxygen is always in contact with water at its maximum concentration of oxygen, so diffusion occurs from the water into the blood
• Blood with a low concentration of oxygen is always in contact with water with a higher concentration, so diffusion occurs

Question 3

What is therefore maintained?

Answer 3

• a constant steep gradient is maintained across the whole length of the lamellae

Question 4

How much of waters oxygen is diffused into the blood of fish in the countercurrent principle vs the parallel principle?

Answer 4

• 80% in the countercurrent
• 50% in the parallel