h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Apropos of a question elsewhere to do with evolutionary advantages and stuff, this question occurred to me:

My blood is red. It is this colour (as I understand it) because the chemistry of blood is based on the oxidation of iron.

ALL blood I am aware of in the natural world is red. Is blood chemistry based on iron a universal feature of life on earth? (Life with a cardio-pulmonary system, that is?). Or are there any organisms with a blood chemistry based on, say, copper? (And can we get the references to Mr. Spock out of the way as quickly as possible, this is a serious question...)

SoRB

Horseshoe crabs have copper-based blood.

They seem to come from a pretty ancient lineage. (I know we *all* do, but you know what I mean).

PS
Horseshoe crab blood is blue.

It's also has various medical uses - good for us, but not unfortunate for them.

It's one of those nights.

'It's also has' -> 'It also has'

'not unfortunate' -> 'not necessarily fortunate'

If seems they are distantly related to spiders, scorpions, etc.

http://www.enviroliteracy.org/article.php/1029.html

This says that 'copper is part of the blue blood in snails and lobsters.'

Which is supported by...
http://www.weichtiere.at/Mollusks/Schnecken/morphologie/atmung.html

I guess the "point" of blood is to get oxygen molecules into the body. I think from a chemistry perspective there are lot of metal ion complexes that could be good at this. I don't know why iron crops up the most often for the job. But I'll ask someone who might.

I'd hazzard a guess its something to do with the binding potential or some such thing of the iron in HB with oxygen being suitable so it can bind it, but not so strong it won't rlease it again in the tissues mind, I know a few people with 'clear' blood, in such cases alcohol is used for transporting anything that might be required

"I guess the "point" of blood is to get oxygen molecules into the body."

From a Biology perspective, there's not many words in that sentence I approve of. But your essential point remains sound

B

And from a Chemistry perspective, I'm thinking iron is so common for the job because:

a) It's abundant, therefore has a high probability of incorporating itself somehow into organic life.
b) It has a variety of oxidation states, which make it particularly flexible in terms of complex formation.

B

This was an interesting one .

All molluscs have blue blood. Their branch of the family split from ours so long ago that we hadn't even evolved blood at the time. So we and the molluscs developed it independently and differently.

We have red blood based on iron (haemoglobin). They have blue blood based on copper (cyanoglobin). Iron is more efficient, but try telling them that! As far as I know the cyano in the name is nothing to do with cyanide, it is purely based on the colour.

Molluscs include squids and octopuses (cephalopods); snail, slugs and limpets (gastropods); and cockles, mussels, oysters and clams (bivalves).

I believe that arthropods don't use blood to bring oxygen around their bodies. They use it for transporting digested nutrients. So their blood could be any colour. For oxygen, they rely on a network of air tubes, which I can't remember the name of.

wikipedia thinks "cyanide" also gets it's name from the colour blue in Greek.

Zube

I think the air tubes are called 'invaginations'.

Ah, one I do know... arthropods breathe through spiracles.

SoRB

Spiracles? Aren't they a type of gemstone found in the Ramtops?

That's the only place I've heard the word before.

TRiG.

Traveller in Time some things cleared
"Well that explains the green 'blood' of caterpillars and locusts.

I thought their resperatory system was called tracheae, but it appears to be only the opening. "

Not all arthpropods use air tubes, just insects. The tubes are called tracheae, while the holes are known as spiracles. They suck air through these, and the oxygen diffuses into a mixture of blood and lymph called haemolymph.

Arachnids, on the other hand, have an apparatus called 'book lungs,' which consist of a series of tissue flabs with blood vessels close to the surface. Air diffuses across the membrane and into the blood; the mechanism here is not unlike that of gills.

Crustaceans have gills. These work basically the same as book lungs, except in water.

All arthropods use copper to transport oxygen, though there is some variety to their blood colour. Lobsters, for example, famously have blue blood, but some spiders have green. I've seen flies with what appeared to be yellow blood, though that may have been mixed with whatever else was in their bodies.

Ah, so arthropods still use blood to transport oxygen, it is just the method of getting the oxygen into the blood that is different from us?

What is the biological definition of blood? It might be that the without the ability to transport oxygen then it is no longer blood....

*goes off to find out*