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Summary OCR A/AS-Level Biology 3.1.5 Gas Exchange in Other Organisms
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Revision Summary of key knowledge from OCR A/AS-Level Biology 3.1.5 Gas Exchange in Other Organisms.
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Gas Exchange in Bony FishCounter-current Flow
Blood flow in the gill lamellae is in the opposite direction to the water flow – maintains
diffusion gradient between blood and water
As blood flows through capillaries and the oxygen saturation increases, it meets water
of increasing oxygen saturation – concentration of oxygen is always higher in water than
in blood
Maximises gas exchange compared to a parallel-current system since it maintains the
concentration gradient along the whole length of the gill lamellae
up to 80% oxygen extraction rate compared to a parallel-current flow with 50%
Ventilation in Gills
Inspiration
o Opens mouth by lowering the floor of the buccal cavity
o Volume of buccal cavity increases
o Pressure inside buccal cavity decreases, drawing water into it
o Operculum is shut
Expiration
o Closes mouth by raising the floor of the buccal cavity
o Volume of the buccal cavity decreases
o Pressure inside the buccal cavity increases, forcing water out
o Water is forced across the gill filaments
o Water forces operculum open and flows out
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