|MadSci Network: Biochemistry|
Insects do indeed have a different oxygen "carrier;" it's anatomical rather than biochemical, though! Insects have an extensive tracheal system, a network of chitinous tubes that branch off of larger tubes which ultimately coalesce to openings on the external body wall of insects called spiracles. Air moves into the spiracles, through the tracheal system, and delivers oxygen directly to the tissues. This system is remarkably effcient - no insect cell is very far away from a branch tip of the tracheal system. Insects DO have a circulating fluid in their body cavitieis - and recall that insects have an OPEN CIRCULATORY system (no enclosed vessels like the circulatory system found in humans), which is called haemolymph. The haemolymph contains proteins and carbohydrates, ions, lipids, and dissolved gases, much the same as one would expect in any blood-like tissue. But since they have their tracheal system, a respiratory pigment (such as haemoglobin) is not as necessary. Other arthropods (like crustaceans, for example) DO have respiratoy pigments; in fact, the respiratory pigment of crustaceans is hemocyanin - perhaps that may serve as a little evolutionary hint. Why CO and not HCN is toxic I'm not sure - but I am answering this as an invertebrate zoologist, not as a biochemist! The reason CO is so deadly in humans is that it binds more readily to haemoglobin than oxygen, but I don't think the parallel can be drawn to insects.
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