The diagram shows a trout swimming in a fast-flowing stream. Water enters its mouth, passes over the gill filaments and leaves beneath the gill cover. The f...
Question 1 Report
The diagram shows a trout swimming in a fast-flowing stream. Water enters its mouth, passes over the gill filaments and leaves beneath the gill cover. The fish needs oxygen for respiration in its cells.
(a) Name the structures on gill filaments where most gas exchange occurs. [1]
(b) Describe the route taken by water from the mouth to the outside of the fish. [2]
(c) Explain how a rapid water flow over the gills helps the trout take in oxygen. [2]
(d) Suggest two reasons why trout may struggle to survive in warm, still water. [2]
Answer Details
(a) Most gas exchange occurs at the gill lamellae. [1]
(b) Water enters through the mouth [1], passes over the gill filaments, and leaves beneath the gill cover, through the operculum. [1]
(c) Rapid flow continually brings fresh water with more dissolved oxygen to the gills. [1] This maintains a steep concentration gradient, so oxygen diffuses quickly into the blood. [1]
(d) Warm water holds less dissolved oxygen. [1] Also, in still water, oxygenated water is not replaced rapidly at the gills. [1] Consequently oxygen uptake can fall and aerobic respiration may be limited.
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