Blood red in oxygen
Why does blood turn red when it is exposed to oxygen?
Oxygen in the blood of vertebrates is carried by a special protein called
hemoglobin. This allows the blood to carry about 50 times more oxygen than if the
oxygen were simply dissolved in the fluid of the blood. When hemoglobin binds to
oxygen (each hemoglobin molecule binds four oxygen molecules), it changes shape.
In its new shape, it absorbs light differently, and for this reason appears red.
Click here to return to the Biology Archives
Update: June 2012