Use the graphs below to answer the last two questions: Graph B Graph A 100% 100%

Question

Use the graphs below to answer the last two questions: Graph B Graph A 100% 100% 5096 50% 0% 096 Distance along gills Distance along gills Graph C Graph D 100% 50% 0% 100% 50% 0% Distance along gills Distance along gills water Key to graphs: -.blood 5. (1 pt) which of the above graphs demonstrates countercurrent exchange across the surface of the gills in fish? a. Graph A b.Graph B c Graph C d. Graph D 6. (1 pt) Which of the above graphs demonstrates concurrent exchange, in which blood&water; are flowing in the same direction? a. Graph A b. Graph B c.Graph C d. Graph D

Explanation / Answer

5. A) GRAPH A

When blood flows in opposite direction to the water, it flows next to the water which has given up less of its oxygen.

This causes the blood to absorb more and more oxygen as it moves along. Even as the blood reaches the end of the lamella and is 80% or so saturated with oxygen, it flows past the water which is at the beginning of the lamella and is 90 or 100% saturated.

Hence when the blood is highly saturated, having flowed past most of the length of the lamellae, there is still a concentration gradient and it can still continue to absorb oxygen from the water.

6. GRAPH D-

When water and blood flows over and through the lamellae in the same direction.

When blood first comes in contact to water, the water is fully saturated with oxygen and the blood has very little.

Therefore there is a very large concentration gradient and oxygen diffuses out of the water and into the blood.

As you move along the lamella, the water becomes slightly less saturated and the blood slightly more but water still has more oxygen in it so it diffuses from water to blood.

This continue until the water and the blood have reached equal saturation.

After this the blood can pick up no more oxygen from the water because there is no more concentration gradient. The maximum saturation of the water is 100% so the maximum saturation of the blood is 50%.

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