3.2.11 A-A* Gas exchange

Question 1

Describe the countercurrent system

Answer 1

The countercurrent system is set up in the
gills by pumping blood through the lamellae in the opposite direction to the flow of water. The movement of water through the gills is created by the movement of the fish. This is why fish must always keep moving otherwise they cannot take up oxygen from the water.

Question 2

Describe how the countercurrent system works?

Answer 2

If blood and water flowing in the same direction through the gills, the deoxygenated blood would take up oxygen from the oxygenated water and soon the blood and the water would have an equal concentration of oxygen - there would be no concentration gradient for diffusion. This would mean that only half of the oxygen would be transferred from water to blood.

Question 3

What are lamellae?

Answer 3

At right angles to the gill filaments, give an increased SA. Blood and water flow across them in opposite directions (countercurrent exchange system).