The diagram shows part of a salmon gill filament with many thin lamellae. Water flows over the outside of each lamella while blood flows through capillaries...
Question 1 Report
The diagram shows part of a salmon gill filament with many thin lamellae. Water flows over the outside of each lamella while blood flows through capillaries inside it. Table 1 gives the percentage oxygen concentration at positions along one lamella.
| Position along lamella | Oxygen in water / % | Oxygen in blood / % |
|---|---|---|
| Near water entry | 10 | 7 |
| Middle | 7 | 4 |
| Near water exit | 4 | 1 |
(a) Name the process by which oxygen enters the blood. [1]
(b) Use Table 1 to state the oxygen concentration difference near the water entry. [1]
(c) Explain why oxygen can diffuse into the blood at every position shown. [3]
(d) Describe two features of gill lamellae that increase the rate of diffusion. [2]
(e) Explain how the opposite directions of water and blood flow help maintain oxygen uptake. [3]
(f) State one substance that diffuses from the blood into the water at the gills. [1]
(g) Suggest why a fish may ventilate its gills faster in warm water. [1]
Answer Details
(a) Oxygen enters the blood by diffusion. [1]
(b) Near water entry, the difference is \(10\% - 7\% = 3\%\). [1]
(c) At every position shown, oxygen concentration is higher in the water than in the blood: \(10\%>7\%\), \(7\%>4\%\), and \(4\%>1\%\). Oxygen therefore diffuses down a concentration gradient across the thin lamella and capillary walls into the blood. [3]
(d) Gill lamellae have a large surface area and very thin walls, giving a short diffusion distance. A good blood supply is another acceptable feature because it maintains the gradient. [2]
(e) Water and blood flow in opposite directions, so blood meets water with a higher oxygen concentration all along the lamella. This maintains a concentration gradient and allows oxygen to continue diffusing into the blood. [3]
(f) Carbon dioxide diffuses from the blood into the water. [1]
(g) Warm water contains less dissolved oxygen, so the fish ventilates its gills faster to move more water over them. [1]
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