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Gas Exchange - Fish (Features of Gills (Gills are fragile, complex…
Gas Exchange - Fish
Features of Gills
Gills are fragile, complex structures - 4 pairs
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Along each gill filament are the gas exchange surfaces, the gill lamellae/ gill plates, which are held apart by water flowing between them (in air they collapse reducing SA and gas exchange = death)
the gill lamellae supply large surface area for gas exchange and are richly supplied with blood capillaries
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Cartilaginous fish
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blood flowing through gill capillaries in same direction as water travels across gills = parallel flow
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Counter current
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O2 diffusion gradient is maintained - blood comes into contact with water which always has a higher concentration of oxygen, maximising the rate of diffusion
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system
low oxygen blood enters the capillaries, encouraging water at the end of its travel through the gills which is also relatively low in oxygen
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Bony Fish
features
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Have the ability to create pressure by the mouth and opercular cavities opening and closing to maintain a continuous unidirectional flow so water is forced over the gill filaments without the need to keep swimming
Have blood flowing through the gill capillaries in the opposite direction as water travels across the gills = counter current flow
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Ventalation
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To maintain a continuous unidirectional flow, water is forced over the gill filaments by pressure differences
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The operculum acts as a valve to let water out and as a pump to move water across the gill fillaments
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