They have a small surface area to volume ratio because they are relatively large organisms
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What is their specialised gas exchange system?
The gills
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Where are the gills located?
Within the body of the fish, behind the head
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What are the gills made up of?
Gill filaments
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What are located at right angles to the gill filaments?
Gill lamellae
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What feature does gill lamellae provide?
Increased surface area
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How does water move through the fish?
Water enters the mouth, is forced over the gills and out through an opening on each side of the body
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How does water pass through the gills?
It flows between the gill lamellae where gas exchange occurs
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How does blood flow through lamellae?
Flows through the gill lamellae in the opposite direction to that in which water flows over them
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What is this process called?
Counter-current flow
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Explain one thing that this arrangement means
Blood that is already well loaded with oxygen meets water, which has its maximum concentration of oxygen. Therefore diffusion of oxygen from the water to the blood takes place.
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Explain another thing that this arrangement means
Blood with little or no oxygen in it meets water which has had most, but not all, of its oxygen removed. Diffusion of oxygen from the water to the blood takes place.
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What percentage of oxygen available in the water is absorbed into the blood of the fish?
80%
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What does counter-current flow allow?
Constant rate of diffusion across the entire length of the gill
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What would happen if the flow of water and blood had been in the same direction?
The diffusion gradient would only be maintained across part of the length of the gill lamellae and only 50% of the available oxygen would be absorbed by the blood
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Explain the diffusion of oxygen using the counter-current flow
There is a diffusion gradient favouring the diffusion of oxygen from water into the blood all the way across the gill lamellae
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Explain the diffusion of oxygen using the parallel flow
There is a diffusion gradient favouring the diffusion of oxygen from water to blood for only part of the way across the gill lamellae. Only 50% of the oxygen from the water diffuses into the blood
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Other cards in this set
Card 2
Front
What is the surface area: volume ratio like?
Back
They have a small surface area to volume ratio because they are relatively large organisms
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