6.3: Gas exchange in fish

Question 1

Structure of the gills

Answer 1

Made up of gill filaments which are stacked up like the pages in a book. At right angles to the filaments are gill lamellae, which increase the surface area of the gills.

Water and blood flow over the gill lamellae in opposite directions - countercurrent flow

Question 2

The countercurrent exchange principle

Answer 2

Blood that is well loaded with oxygen meets oxygen which has its maximum concentration of oxygen. Therefore diffusion of oxygen from water to the blood takes places

Blood with little oxygen meets water with slighter more oxygen, diffusion of oxygen from the water to the blood takes place.

Question 3

Efficiency of the countercurrent exchange principle

Answer 3

A diffusion gradient across the entire width of the gill lamellae is formed. Therefore more oxygen diffuses from the water into the blood

80% of the oxygen available in the water is absorbed into the blood of the fish. If it was parallel, then only 50% would be.

Question 4

Importance of water flow being one way

Answer 4

Water is dense so less energy is used, whereas if it was two-way more energy would be used for the reverse.

Question 5

Question about different fish in different positions

Answer 5

Refer to the number of gill lamellae, larger surface area