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Topic 2- Gas Exchange
`Surface Area: Volume' Ratio
The rate of exchange of substances depends of the organism's surface area.
The ability of an organism to meet it requirements depends on the surface area: volume ratio.
As organisms get bigger their surface area: volume ratio decreases.
This makes it more…

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Short diffusion pathway because the blood flowing though the lamellae is only separated from water by a thin layer of
cells.
Fish don't have tidal flow because they don't have the
problem of water loss. Instead the water flows one way
though their mouth and out the opercula valve.
Fish…

Page 3

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To prevent water loss plants close their stomata by using guard cells. They can't keep them shut because they need to
keep taking in oxygen and carbon dioxide for gas exchange.
By just shutting some stomata they can maintain a balance between gas exchange and water loss.
Plants in drier…

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