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Photosynthesis

For discussing the functions of different structures of all organisms.

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Photosynthesis

Postby Atom » Wed Dec 14, 2005 2:25 pm

I have a question. Why does a plant function better in blue and violet light, than in other light? Anyone here of Engleman and his experiment?
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Postby Poison » Wed Dec 14, 2005 5:32 pm

wavelength
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Postby MrMistery » Wed Dec 14, 2005 7:59 pm

because of the affinity of chlorophil for a certain wavelength. By the way, blue light is almost useless to a plant, from the point of view of photosynthesis. Plants and green algae carry out photosynthesis best in red light.
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Postby Mjhavok » Tue Dec 20, 2005 3:21 am

I read this from Raven and Johnson Biology 7th Edition " Chlorophylls a and b absorb predominantly violet-blue and red light. Carotenoids absorb mostly blue and green light."

Caroteniods do assist in photosynthesis so saying blue light is useless isn't strictly true but red and light is more useful.
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Postby MrMistery » Tue Dec 20, 2005 7:22 pm

i said almost useless... Don't twist my words. Do you even know how chlorophil absorbs light? When a photon hits a chlorophil molecule, it increses it's energy into an instable state, called by convention excited chlorophil. This means that it's electrons are spinning faster than usual. The molecule needs to get rid of the excess energy. It does so in 3 ways: florescence, heat and by expelling an electron(if the molecule is a reaction center).

Here there are differences in light. The efficiency by which the energy is useful or not to the plant is measured by the PPFD(photosynthetic photon flax density). Now, this measures the density of photons in light and not their energy, since from every photon you get the same amount of energy. Blue light has few photons with incredible energy, so the plant can use it only in a small extent(with a low efficiency) in photosynthesis. However blue light is very important as an information source for the activity of Rubisco enzyme and the opening of stomas.

Moving on, to the role of carotenoid pigments. As we remember, the chlorophil molecule becoms excited when a photon hits it. During this state, the chlorophil molecule can pass from it's normal, singletic state into a "bad", tripletic state, by the shifting of the direction the electron moves in. If this backards moving electron jumps off the chlorophil molecule and meets with an oxygen molecule changing it from it's normal tripletic conformation to a singletic conformation that atacs double covalent bonds. Here step in carotenoids. They can take energy from the tripletic energy molecule and turn it into heat, without the danger of forming singletic oxygen. This is their vital role in photoprotection. Of course they do have a role in capturing photons, but it deffinetly comes in second.

So?
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Postby Mjhavok » Tue Dec 20, 2005 7:59 pm

I wasn't trying to twist your words perhaps I just misread what you wrote. Yes I do know how chlorophyll absorbs light.

Sorry if you where offended it wasn't my intention.
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Postby MrMistery » Tue Dec 20, 2005 8:40 pm

No prob! I just don't like when things are put into balck and white in biology since they are always shades of grey
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