red chlorophyll

SCHMID SCHMID at Butler.EDU
Tue Dec 17 04:31:59 EST 1996


>Help??!  My biology class has a question; why does a lot of
>chlorophyll in a container look red?  The chlorophyll should
>look green, but our teacher put a lot of chlorophyll into a
>container and asked, why is it red?  

If the chlorophyll is placed under a strong light, especially one
with a lot of ultraviolet, it can look red due to a process called
"fluorescence,"  which is the release of absorbed energy in the
form of light.  Chlorophyll fluoresces red light.

Why red?  You may have learned that different colors of light
have different energies.  For example, in a rainbow, red light has
the least energy, and violet has the most energy.  Chlorophyll is
able to absorb different colors of light, especially red and blue
light.  The relatively weak red light causes chlorophyll's electron
to jump one "energy level."  Since blue light has more energy, it
excites the chlorophyll's electrons even more:  They jump  two
levels.  (Ultraviolet has even more energy.)  However, it's very
difficult for the electron to stay at such high energy in a
chlorophyll molecule, so the electron falls very quickly from the
blue energy level to the red energy level.  (The extra energy is
lost as heat.)

OK:  now all of the energy associated with the chlorophyll is
"red" energy.  When the chlorophyll is properly arranged in the
chloroplast, that red energy is used to do the work of
photosynthesis.  However, if you take the chlorophyll out of the
chloroplasts, there's no place for the energy to go, except heat or
light!  Much of the  energy is released in the form of red
fluorescence, so the chlorophyll looks red.

Kathy Schmid
schmid at butler.edu




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