MadSci Network: General Biology

Re: Why does crabs have blue - greenish blood?

Date: Tue Jun 8 20:49:21 1999
Posted By: Phyllis Pugh, Post-doc/Fellow, Neurobiology, Medical College of Ohio
Area of science: General Biology
ID: 927821976.Gb

I found a major portion of this answer at http://

Blood gets its color from oxygen-carrying respiratory pigments, and there are a number of different types. The iron-containing pigments found in blood include haemoglobins (red), myoglobins (red), chlorocruorins (green) and haemerythrins (violet). Haemocyanin (blue), which is found in horseshoe crabs and other organisms, contains copper not iron.

Some haemocyanins have a higher affinity for oxygen than most haemoglobins and probably function more as an oxygen storage medium than as an oxygen transport medium.

To counteract this, organisms that live in environments in which the pH varies usually have a respiratory pigment that is less sensitive to pH change than the pigments found in animals which live in more stable environments. Thus a haemocyanin that is very sensitive to pH would be detrimental to an organism that lives in a pH-labile environment, even if in other respects it is a & quot;better" oxygen carrier. Conversely, a pH-stable haemoglobin might be a "better& quot; oxygen carrier, even though its saturation curve is less efficient than a particular haemocyanin at a certain pH.

Compiled from answers by:

PETER MORGENROTH Retired lecturer in zoology Royal Melbourne Institute of Technology
JON RICHFIELD Dennesig, South Africa

The reason for the "blue" is that that is the color of copper oxide. Chemical "colors" are the result of light absorption in the chemical bond, the transitions between energy levels that are allowed. You should be able to find out more about this in a good chemistry text. There is more information in an answer about the Borax test, here at MadSci!

You can learn more about copper at Web Elements.

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