|Why is blood red?
|Question Date: 2010-10-20
Blood is red because it is made up of cells
that are red, which are called red blood cells.
But, to understand why these cells are red you
have to study them on a molecular level. Within
the red blood cells there is a protein called
hemoglobin. Each hemoglobin protein is made up
subunits called hemes, which are what give
blood its red color. More specifically, the hemes
can bind iron molecules, and these iron molecules
bind oxygen. The blood cells are red because of
the interaction between iron and oxygen. (Even
more specifically, it looks red because of how the
chemical bonds between the iron and the oxygen
reflect light.) And it's very important for blood
to be able to carry oxygen because when blood
flows through the lungs, the blood picks up
oxygen, and the blood carries this oxygen to the
rest of the body until the oxygen is all used up
-- the blood then returns to the lungs to get more
Here's more information on
Blood is red from the protein, hemoglobin.
Hemoglobin has a molecule called a "heme" which
has the metal iron in it. When the iron is
oxygenated, it becomes red. When the iron is
deoxygenated, it becomes darker red.
Blood is red because of the hemoglobin inside
our red blood cells. Hemoglobin is a protein that
forms a complex with iron molecules and together
they transport oxygen molecules throughout the
body. Iron has the property of reflecting red
light and because there is so much iron in our
blood, blood looks red. When hemoglobin is
carrying a lot of oxygen (like when just leaving
the lungs), blood is bright red. When most of the
oxygen has been released to the body, blood is
dark red. Therefore, contrary to popular belief,
blood is never blue. Veins under light colored
skin only look blue because the skin changes the
optical properties of the light that passes
through the skin. In other words, skin changes the
way light is reflected from the blood and we
perceive that as being a different color.
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