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Asked by to Anna, Chris, Jane, Iain, Nick on 18 Mar 2014. This question was also asked by .
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Iain Moal answered on 18 Mar 2014:
Our blood is read because blood cells contain a protein molecule called haemoglobin, which is used to carry oxygen around our bodies. This molecule has a part called a porphyrin. Chemically, porphyrins have lots of double bonds next to one another, and molecules like this can absorb visible light and therefore appear coloured. In the case of haemoglobin, this colour is red.
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Anna Middleton answered on 18 Mar 2014:
Hi Olly2lol
Haemoglobin is red because it contains iron and when this reacts with oxygen the red colour is created. -
Chris Cole answered on 18 Mar 2014:
The red colour comes from red blood cells which are full of a protein called haemoglobin – so full, in fact, that there’s no room for a nucleus!
Haemoglobin is the molecule which binds oxygen and carries it from your lungs to the rest of your body, and because of the iron containing porphyrin it is red in colour. The colour is bluer with decreasing amounts of oxygen, hence why your veins (which carry blood with low oxygen) look blue.
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Jane Charlesworth answered on 18 Mar 2014:
Red blood cells are specialised cells that carry oxygen around the body. We breathe in oxygen through our lungs and it is picked up by red blood cells, which contain a molecule called hameoglobin that binds oxygen (“haemo” means blood, “globin” refers to the shape of the protein). In the lungs, the blood vessels are very fine, so much so that oxygen can pass through them from the lungs to the blood. The red blood cells look red because the haemoglobin molecules reflect red light. You may have noticed that the blood in your veins looks much bluer–this is because the haemoglobin molecule changes its shape depending on whether or not it is carrying oxygen, and the spectrum of light that it reflects changes.
Not all animals have red blood–insects are much smaller and their blood circulates much more quickly, so they don’t need a special molecule to carry oxygen around their bodies. This limits how big insects can get, however (although in the past, when there was a lot more oxygen in the air, there were giant insects).
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