Why… is blood red?
Objects appear red because they reflect red light and absorb other colours. Blood’s colour comes from the red blood cells it carries. These cells pick up oxygen from our lungs and carry it to where it is needed in the body. But why are they red in the first place?
Well, it’s all about our bodies’ chemistry. Red blood cells have a protein in them called haemoglobin that contains iron. When oxygen is bound to the iron, the haemoglobin reflects red light, so the blood appears bright red in colour. However, when oxygen is released, haemoglobin interacts with light slightly differently, making the blood now appear a much darker, maroon colour.
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