Insects and surface area Watch

ps1265A
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#1
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I just want to clarify some stuff:
organisms with large surface are to volume ratios (which are small) do not need specialised exchange surfaces as diffusion of substances can occur passively through the body surface.
however, organisms with small surface area to volume ratios (like elephants and us) need specialised exchange surfaces such as the lungs etc. as we cannot passively diffuse substances in and out of our body surfaces

so my question is, are fishes classed as organisms with small surface area to volume ratios because they have gills? They seem pretty small to me. Or is "small" classed as something microscopic like bacteria and other single celled organisms? Also my book states that insects have a "small surface area to volume ratio to prevent water loss", and they also have specialised exchange surfaces such as spiracles. But aren't they relatively small organisms which means they should have a large Sa:v ?

Can someone just clarify this stuff, thanks!
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Tillybop
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(Original post by ps1265A)
I just want to clarify some stuff:
organisms with large surface are to volume ratios (which are small) do not need specialised exchange surfaces as diffusion of substances can occur passively through the body surface.
however, organisms with small surface area to volume ratios (like elephants and us) need specialised exchange surfaces such as the lungs etc. as we cannot passively diffuse substances in and out of our body surfaces

so my question is, are fishes classed as organisms with small surface area to volume ratios because they have gills? They seem pretty small to me. Or is "small" classed as something microscopic like bacteria and other single celled organisms? Also my book states that insects have a "small surface area to volume ratio to prevent water loss", and they also have specialised exchange surfaces such as spiracles. But aren't they relatively small organisms which means they should have a large Sa:v ?

Can someone just clarify this stuff, thanks!
Fish are classed as larger animals - which have a small surface area to volume ratio. Small organisms are usually single celled or just a few cells in size.

Fish need to provide many millions of cells with oxygen, and this means that they need a specialised system, because otherwise diffusion would take forever, and the fish wouldn't be able to survive.
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Dynamo123
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(Original post by ps1265A)
I just want to clarify some stuff:
organisms with large surface are to volume ratios (which are small) do not need specialised exchange surfaces as diffusion of substances can occur passively through the body surface.
however, organisms with small surface area to volume ratios (like elephants and us) need specialised exchange surfaces such as the lungs etc. as we cannot passively diffuse substances in and out of our body surfaces

so my question is, are fishes classed as organisms with small surface area to volume ratios because they have gills? They seem pretty small to me. Or is "small" classed as something microscopic like bacteria and other single celled organisms? Also my book states that insects have a "small surface area to volume ratio to prevent water loss", and they also have specialised exchange surfaces such as spiracles. But aren't they relatively small organisms which means they should have a large Sa:v ?

Can someone just clarify this stuff, thanks!
Small is something quite variable. In your own case, you state that insects have a small surface area to volume ration, plus specialized surfaces (which we'll ignore for now). Technically, small is a relative term; a fish is smaller compared to a human, but compared to an insect it is quite large (again, not counting the various kind of fish that are actually tiny). In your case, it is best to decide on the basis of your criteria: surface area to volume ratio. A bsic principle we can just derive from physics is:
as the size of an organism increases, the surface area to volume ratio decreases.

On the basis of that criteria, you can decide for yourself. Bacteria, microbes, small members of kingdom animalia like earthworms (which are technically not insects) etc., have a large surface area to volume ratio. Insects, a bit larger, have smaller SA/V. And fishes, even larger, have even smaller SA/V. So as we progress upwards in size, diffusion alone can't help, we need a special system for gaseous exchange.
I hope that helps
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