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Photosynthesis May Rely On Quantum Effect
forgethistory sends us to PhysOrg for a summary of new research suggesting that the near instantaneous energy transfer achieved by photosynthesis may rely on quantum effects. From the article: "Through photosynthesis, green plants and cyanobacteria are able to transfer sunlight energy to molecular reaction centers for conversion into chemical energy with nearly 100-percent efficiency. Speed is the key — the transfer of the solar energy takes place almost instantaneously so little energy is wasted as heat. How photosynthesis achieves this near instantaneous energy transfer is a long-standing mystery that may have finally been solved."
I wonder if ferns ever look at us and laugh saying that non-quantum-sourced energy is so 3 billion years ago.
I'm sorry, please clarify: did you actually say anthing in that post?
... it's also been discovered that *all* physical phenomena may also rely on Quantum Effect.
I don't know about consciousness, but in his novel Blue Mars (last book of the Mars trilogy), published a decade ago already, Kim Stanley Robinson made use of research that suggests that memory relies on a quantum effect.
Was there any specific quantum effect you had in mind or did your spell checker mysteriously substitute the phrase "quantum effects" for the word magic ?
All interactions at the atomic level are quantum effects. A photon can only interact through quantum effects. The statement in the article is totally meaningless.
We have known that photosynthesis is a quantum effect since Einstein's paper on black body radiation.
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I can't seem to find the link (Google is not friendly today), but does this perhaps justify the researcher who postulated that the sense of smell comes from something akin to detecting nuclear resonance, not a simple chemical interaction? I recall that one detractor said that his theory was as outlandish as saying that food was digested in the stomach via tiny nuclear reactors. But it explained many things that didn't make sense otherwise -- like why cyanide smells like almonds.
He's apparently gone on to success in the perfume industry.
Someone find the link... this is driving me nuts.
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Would that mean that attempts to upload human minds to computers would fall foul of the no-cloning theorem? Such constraints on the duplication of quantum information would have interesting effects on philosophical problems of identity.
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None that weren't already stated in numerous terms thousands of years ago in virtually every culture.
When a photon strikes a chlorophyll, it adds its energy to an electron, allowing the electron to escape from its atom (previously known quantum mechanics). It was previously thought that the electron would then go bouncing around between chlorophyll molecules until it found a pheophytin molecule (slightly different chlorophyll). Once it hits that molecule, it activates an electron-transport chain (a similar process happens when burning glucose in a mitochondrion).
TFA suggests that the hopping uses quantum superposition to traverse the chlorophyll molecules more quickly. When the traversal reaches the pheophytin, the superposition collapses into that single state which found the pheophytin.
(IANAL)
This explains why the hedge in my yard wasn't doing so well until it was temporarily taken over by the spirit of a wise and charming fern from the future, which corected everything that was wrong in the hedge's life before moving on to my neighbor's lawn ten years ago.
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The summary is slightly misleading, but this disconnect has big implications for the reader's understanding (imho)...
j ablonski.gif Unfortunately, this scheme doesn't show photofragmentation or energy transfer to another molecule, but I'm in a rush so it'll do.
I can name plenty of chemical reactions that are complete on the femtosecond scale, and while speed helps, that's certainly not the whole picture. What matters is how mismatched the energy levels between the reactant and the product are. When transitioning between energy levels, either energy is transferred out of the system by nonradiative release (heat), luminescence, photofragmentation, or transfer to a chemical partner - this last case is what the article is referring to. Getting to an energy level which can react is going to result in a heat deposition for at least some photons because any photon of a higher energy than the reacting state must deposit some of that energy just to be able to react at all.
http://www.monos.leidenuniv.nl/smo/basics/images/
The squiggly lines show possible heat depositions - the molecule starts in the ground state, absorbs a photon (the yellow up arrow), then relaxes to the excited state. This excited state then does whatever it's going to do. If 100% of the time under a set of conditions (i.e. a quantum yield of 1.00), the excited molecule follows a particular pathway we call that perfectly efficient. In the specific example of photosynthesis, this means that all of the absorbing chlorophylls transfer the energy along the photosynthetic pathway (I'm lumping all the subsequent processes together here). It does not mean that 100% of the energy got transferred along the way - there will always be some photon that deposits more energy than the reacting state has, meaning some energy will be converted to heat.
In short form (if you didn't feel like reading all this): efficiency in this case refers primarily to how often the molecule dumps its energy into photosynthesis instead of all to heat, luminescence, etc. It's not referring to the energy throughput, as some photons will always be an imperfect energy match, and the extra energy will end up as heat.
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Why do you need to invoke one mystery to "explain" another? I can't see why consciousness "may not be so easily explained without taking into account quantum effects". What particular things about consciousness seem to indicate quantum effects to you?
Other people have proposed this before, but present a theory of why quantum effects may be necessary. Roger Penrose makes the argument that we can compute things that a Turing-style computer could not compute, so something else must be going on. His proof that some things we do cannot be done by a Turing style computer isn't exactly accepted though, and no-one seriously believes that the brain works in this way in any case.
Also, consciousness is not the same thing as "self-awareness". Is a dog conscious? Is it self-aware? What about a rabbit? When I dream, I'm not usually self-aware, but there's some sort of consciousness there. What about phenomena like blind-sight, where a person is self-aware, but unconscious of visual information, even though they can access that information by guessing remarkably accurately, just without any direct consciousness of it. Does this mean that these supposed quantum-consciousness effects have broken down only for information originating in visual centers, but keeps working on all other information?
Of course, coming from quantum theory, there is the Copenhagen Interpretation which places a special status on the 'observer' - but no-one has managed to define what an observer is, or whether they must be conscious or not.
Yeah, sure the energy transfer efficiency is 100% for every photon that participates in the reaction. But of all the photons falling on the leaf, hardly 2% of them participate in reactions. Some gets reflected, some gets absorbed without any reaction. Even solar cells have better energy conversion efficiency than plants. Really. As for quantum effects, almost all the photo reactions are quantum mechanics. They have to be. The film camera emulsion has greater percentage of photons participating in reaction than chlorophyll.
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Yes, but while knowing the mechanism netted someone their PhD (or some PhD their tenure,) a workable implementation will net some company billions of dollars. Nearly 100% efficient solar cells? Yes, please. Pass the chlorophyll over here.
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Well, that's only part of the story. The original capture loses very little energy...
1) If and only if the photon is of the proper energy. In general, during solar energy conversion of all kinds, you require a certain amount of energy to kick an electron out of the pigment. Less than that energy, and nothing happens. More than that energy, and the excess is wasted.
2) This only applies to the original photon capture. The total process of turning solar energy to sugars in plants is about 35%. Due to losses for biochemistry, the overall system is very inefficient -- usually just 1-2% in most crop plants, and a fraction of a percent in non-crop plants. Sugarcane is exceptionally high at 8%, still well below most silicon cells.
Now, dye-based cells *are* in development. The key for them is not that they're very efficient (they tend to be very inefficient), but that they should be very cheap to produce (no silicon refining needed). Of course, a few companies (such as Nanosolar) are working on commercializing high-efficiency dye-based cells. I read nanosolar's main patent at one point; basically, the efficiency problem with most organic solar cells is an uneven distribution of electron donors and receivers that leads to most of the electrons being wasted. In Nanosolar's case, they build a crystalline scaffolding that the dye gets embedded into at regular intervals, then dissolve the scaffolding.
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