To answer your question at a fundamental
level, it is because Chlorophyll A and
Chlorophyll B are different proteins. Every
protein is made up of small building blocks called
amino acids. There are only 20 amino acids that
make up every protein in our world! All the
variety we see in the world is due to the
different types and number of amino acids in each
protein. Therefore, Chlorophyll A and
Chlorophyll B absorb different light wavelengths
better because each type of chlorophyll protein is
made up of a different combination of amino
acids, which react differently to light.
On a more general level, though, why would a
plant need to have two different types of
chlorophyll to absorb different wavelengths of
light? By having different types of chlorophyll
that absorb light at different wavelengths, plants
can use more of the light produced by the sun. If
a plant can only absorb light at one wavelength,
it can only use that one type of light to make
energy. Imagine if people were only able to use
carbohydrates, like bread and rice, for energy. We
would be in big trouble if we couldn’t find this
sort of food to eat. Having different types of
chlorophyll that absorbs different wavelengths of
light is similar to our ability to use
carbohydrates, fats, and proteins for energy.
Hope that helped!
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