Hemoglobin isn't actually blue; it appears bright red when oxygenated. The statement in the provided reference regarding hemoglobin absorbing mostly blue light explains why it appears red, not blue.
The Color of Hemoglobin: A Deeper Look
The color of hemoglobin, the protein responsible for carrying oxygen in our blood, is directly related to its interaction with oxygen and the way it absorbs and reflects light.
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Oxygenated Hemoglobin (Oxyhemoglobin): When hemoglobin binds to oxygen, the iron atom within its structure changes its electronic configuration. This change affects how the molecule interacts with light. Oxygenated hemoglobin absorbs mostly blue light, reflecting red light more strongly, resulting in its characteristic bright red color. This is why arterial blood, rich in oxygen, appears bright red.
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Deoxygenated Hemoglobin (Deoxyhemoglobin): In contrast, deoxygenated hemoglobin has a different electronic configuration around the iron atom. This altered configuration affects light absorption differently, causing it to appear a darker, purplish-red color. This is the color observed in venous blood, which has lower oxygen content.
The reference states that "when iron binds to oxygen, it absorbs mostly blue light, so it appears bright red". This highlights that the color we perceive is a consequence of the wavelengths of light that are not absorbed, but rather reflected back to our eyes. The absorption of blue light leads to the perception of red.
Therefore, hemoglobin is not blue; its color depends on its oxygenation state and its corresponding light absorption properties.
