Photonics of Photosynthetic Auxilliary Pigments

INTRODUCTION: What are auxilliary pigments all about in chloroplasts? Some texts say that they capture the light and direct it over to the main chloroplast excitation location where an electron is boosted up to a high orbital. WRONG! The light is not routed around - an electron is. And free electrons can only go one way - downhill a la one of the laws of thermodynamics. And what does downhill mean? Falling towards the RED, because longer wave red light has less energy in it that does blue light.

Now if a photon hits the main chlorophyll "a" or "b", that is what we want because that electron is bounced up to a highly excited orbital and when it falls back (yielding RED fluorescence IF its fall goes to waste, or otherwise it is sent into the ATP mill to make ATP. But if one of the many other bluer colors (anything shorter wavelength than red such as yellow or blue), then that is absorbed by one of the auxilliary pigments which bounces up one of its higher energy electrons. But before that electron falls back in a flash of orange, yellow or blue fluorescence, it finds itself stolen by another, "lower" pigment, and then on to yet a further "lower" pigment until it finally finds itself possessing the energy of an excited electron of chlorophyll "a" or "b". And from there is can fall through the ATP mill and onwards back down to ground state.

In a fashion, this microscopic collection of pigment molecules is for a millionth of a second something like a metal where the excited electrons don't really know where their home atom is located, and they wander about - jumping from one atom's excited orbital to that of another atom.

Ah, but you ask: "Why doesn't a chloroplast fluoresce at least a little blue or a little green or a little yellow? Why only RED? The answer is that it does fluoresce various shades of infrared. Those are the wavelengths emitted as the highly excited blue electron drops down a short step (relatively low energy) to the highly excited green quantum orbit on its inexorable swirling way to finding the low energy excited RED quantum orbit, where the ATP mill acts like a slurping, sucking drain. So indeed there are other colors fluorescing - it's just that they are in the infrared, which is also known as HEAT!

(This is a tricky question!) Discuss why there are no auxilliary pigments to absorb the truly high energy ultraviolet photons.

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