On the other hand, there are a number of arthropods (horseshoe crabs and some spiders) that have blue blood due to the fact that their blood contains copper as the oxygen binder rather than iron. Oxidized iron is red, but oxidized copper is blue (cyan even!). So maybe Tau blood contains Hemocyanin instead of hemoglobin. Check out this interesting theory by Sephiroth as posted on the BlackLibrary.com boards:
Tau Blood - A Theory on cyan colouration of Tau Blood, a much more accurate reality than 'Red' blood.
The basics of it:
To have cyan blood, the Tau would need to have a circulatory system comprising of a plasma with free floating oxygen carrying Hemocyanin, which unlike human blood is not infused in corpuscles cells (hemocytes), due to it's size (larger) and nature (relation to oxygen and carrying it). To be as efficient as haemoglobin, most hemocyanin users have high density of blood. Which for Tau, would account for their strong grey-blue complexion. Therefore, the less oxygen a Tau has, they more grey faced they become... then white and die.
Tau, by this (I believe far better fitting) theory, have a blue blood circulatory system based on hemocyanin usage.
It affects and accounts for a notable traits in Tau:
- Grey/Blue Complexion
Like humans, we are coloured by our blood (put a torch behind your finger and turn it on), our skin pigmentation the only altering factor. Tau also exhibit this.
- General lack of strength
Smaller muscles require less oxygen, a system using hemocyanin would starve larger muscles, this physiological adaptation suits their circulatory system.
- Vision
I will confirm this, but so far, there may be a connection between poor vision and this form of oxygen carrying circulatory system.
Hemo what?
Hemocyanin is a bluish, copper-containing protein with an oxygen-carrying function similar to that of haemoglobin (at least it is blue when it is oxygenated, but colourless after the oxygen is released) which is present in the blood of certain animals such as crustaceans. Hemocyanin is much like haemoglobin except that the iron atom in the protein molecule is replaced by one of copper.
Quite a few animals have varying coloured blood (unsurprising) and some creatures simply bathe their organs in the finer-sized haemoglobin, just like a hemocyanin species. But it is a poor usage of haemoglobin. Hemocyanin is far better in this role. Still, a blue-blooded creature's system can, among other tasks, devour bacteria, foreign substances and bits of dead tissue. Just how a human blood system, with red corpuscle cells infused with haemoglobin, would perform.
Have a look!
In Depth;
Hemocyanins (also spelled haemocyanins) are respiratory proteins containing two copper atoms that reversibly bind a single oxygen molecule (O2). Oxygenation causes a colour change between the colourless Cu(I) deoxygenated form and the blue Cu(II) oxygenated form. Hemocyanins carry oxygen in the blood of most molluscs, and some arthropods such as the horseshoe crab. They are second only to haemoglobin in biological popularity of use in oxygen transport.
Although the respiratory function of hemocyanin is similar to that of haemoglobin, there are a number of differences in its molecular structure and mechanism. Whereas haemoglobin carries its iron atoms in porphyrin rings (heme groups), the copper atoms of hemocyanin are bound as prosthetic groups comprised of histidine peptides. Hemocyanin binds with oxygen non-cooperatively and is only one-fourth as efficient as haemoglobin at transporting oxygen.
Haemoglobin binds oxygen cooperatively due to steric conformational changes in the protein complex, which increases haemoglobin?s affinity for oxygen when partially oxygenated. Hemocyanin does not have an increased affinity for oxygen when only partially oxygenated.
Hemocyanin is made of individual subunit proteins, each of which contains two copper atoms and can bind one oxygen molecule (O2). Each subunit weighs about 75 kilo Daltons (kDa). Subunits are arranged in chains or bundles in weights exceeding 1500 kDa. Because of the large size of hemocyanin, it is usually found free-floating in the blood, unlike haemoglobin, which must be contained in cells because its small size would lead it to clog and damage blood filtering organs such as the kidneys. This free-floating nature allows for higher densities of hemocyanin in the blood (as compared to haemoglobin), and helps offset its low efficiency.
- Physiology and Biology labs, Sa'Cea Fio'Ar'Tol.
Naturally, when Mr Spurrier's Xenology comes out it might all be shown to be null and void... still, fun to speculate and ponder until February, huh?
