StringJunky Posted September 16, 2011 Posted September 16, 2011 Your absorption graph is a bit misleading here is a clearer one. You are ducking the question when you just say it's the best compromise, you have to explain why. Clearly plants are green, we can see that with our own eyes. Thus the only thing which remains to be explained is why they are green and not red or blue or purple or orange. Why is it misleading? The absorption data for the whole leaf is the one that really matters...that's what plants use . It's the best compromise because if it was black it obviously can't maintain Homeostasis, given the intensity and output spectrum of our star as filtered by the prevailing atmospheric conditions here on Earth, otherwise they would have evolved that way. Plants may look completely green but in fact contain different pigments...the proportion of which will vary between species. I think this basically distills what you've already been informed of.
esbo Posted September 17, 2011 Author Posted September 17, 2011 Why is it misleading? The absorption data for the whole leaf is the one that really matters...that's what plants use . It's the best compromise because if it was black it obviously can't maintain Homeostasis, given the intensity and output spectrum of our star as filtered by the prevailing atmospheric conditions here on Earth, otherwise they would have evolved that way. Plants may look completely green but in fact contain different pigments...the proportion of which will vary between species. I think this basically distills what you've already been informed of. You have not provide an answer you have basically said plants are green because that is how they evolved, unfortunately I was looking for a little more that stating the blindly obvious. Surely you can do better?
Ringer Posted September 17, 2011 Posted September 17, 2011 When animals evolve they don't do what's best, they do what works. To ask why something evolved the way it did is useless. The only reason you can give is that something evolved the ability to absorb light at certain frequencies and that is all they needed to win the genetic lottery. Then other species happened to absorb that other species and they evolved together like mitochondria before them. It works, whether or not there is an alternative didn't matter.
esbo Posted September 17, 2011 Author Posted September 17, 2011 When animals evolve they don't do what's best, they do what works. To ask why something evolved the way it did is useless. The only reason you can give is that something evolved the ability to absorb light at certain frequencies and that is all they needed to win the genetic lottery. Then other species happened to absorb that other species and they evolved together like mitochondria before them. It works, whether or not there is an alternative didn't matter. The big flaw with our answer is that I know why plants are green. Maybe you would like to try again? I mean you know why polar bears are white don't you?? -1
Ringer Posted September 17, 2011 Posted September 17, 2011 Because they aren't white. Their fur is fairly translucent and thus gives a slight reflection of their surroundings. Would you like to try again? My answer doesn't have a flaw. You knowing an answer doesn't cause another answer to have a flaw. Especially since you are apparently trying annoy people by telling them their answers have non-existent flaws by moving goal posts. You're OP asked, "wouldn't black be better?" It may be that black would be better, but that doesn't matter in the context of evolution. You moving the goal posts doesn't make me wrong.
Greg Boyles Posted September 17, 2011 Posted September 17, 2011 (edited) The big flaw with our answer is that I know why plants are green. Maybe you would like to try again? I mean you know why polar bears are white don't you?? Here is a more detail possible explanation for you esbo, from another forum.... This is a good question for the chemists. Chlorophyll is a complex biomolecule containing magnesium. The molecule contains special ring shaped structures that capture preferred wavelengths of light. Green is not "captured" so it is reflected back to our eye. I do know that plants may contain modified chlorophyll and other pigments to take advantage of the type of light available to them. One example are sea plants where only certain wavelengths of light may reach specific depths and the plants have evolved to capture this light for energy. Michael B Lomonaco. We can also look at this from another angle. Why does chlorophyll reflect ("throw away") green light, which is the most abundant color in sunlight, and utilize instead the weaker reds and blue? Scientists theorize that it may have been because competing organisms were absorbing much of the green wavelengths billions of years ago, so algae (the earliest plants) reflected the green away and instead absorbed the red and blue hues that remained. Early in Earth's history, the oceans were dominated by archaea, bacteria-like organisms that are often purple in color, due to a pigment used to create energy from the sun in a process analogous to photosynthesis (but completely differently at the chemical level). As algae came along, they would have found a beneficial niche by utilizing the unused red and blue wavelengths (and reflecting the green). If you compare the absorption spectra of chlorophyll (plants) and retinal (the pigment in archaea), they are mirrors of each other, which supports this theory. Why archaea never evolved into complex organisms like algae did into plants and trees is not known (to me, at least), but another roll of the evolutionary dice might have led to large, purple archaea-trees that could outcompete plants (since plants use only the weaker red/blue wavelengths). Today, archaea ancestors remain as microorganisms that tend to inhabit extreme environments (geysers, salt ponds, etc.) where their purple (and red) colors can still be seen. For more info, see: "Extreme Microbes", S. DasSarma, www.americanscientist.org/issues/feature/2007/3/extreme-microbes "Early Earth was Purple, Study Suggests", Ker Than, www.livescience.com/environment/070410_purple_earth.html Paul Bridges And another explanation from Wikipedia..... Why green and not black Black plants can absorb more radiation, and yet most plants are greenIt is as of yet unclear exactly why plants have mostly evolved to be green. Green plants reflect mostly green and near-green light to viewers rather than absorbing it. Other parts of the system of photosynthesis still allow green plants to use the green light spectrum (e.g. through a light-trapping leaf structure, carotenoids, etc.). Green plants do not use a large part of the visible spectrum as efficiently as possible. A black plant can absorb more radiation, and this could be very useful, notwitstandanding the problems of disposing of this extra heat (e.g. some plants must close their openings, called stoma, on hot days to avoid losing too much water). More precisely, the question becomes why the only light absorbing molecule used for power in plants is green and not simply black. The biologist John Berman has offered the opinion that evolution is not an engineering process, and so it is often subject to various limitations that an engineer or other designer is not. Even if black leaves were better, evolution's limitations can prevent species from climbing to the absolute highest peak on the fitness landscape. Berman wrote that achieving pigments that work better than chlorophyll could be very difficult. In fact, all higher plants (embryophytes) are believed to have evolved from a common ancestor that is a sort of green algae - with the idea being that chlorophyll has evolved only once. [7] Shil DasSarma, a microbial geneticist at the University of Maryland, has pointed out that species of archae do use another light-absorbing molecule, retinal, to extract power from the green spectrum. He described the view of some scientists that such green-light-absorbing archae once dominated the earth environment. This could have left open a "niche" for green organisms which would absorb the other wavelengths of sunlight. This is just a possibility, and Berman wrote that scientists are still not convinced of any one explanation. And let's not forget red marine algae Limitations on evolution Limitations on evolution Although this is not intended to be an exhaustive list of the various factors that limit how evolution works, we have highlighted two broad categories that commonly affect how a population can evolve. Constraints All of the forces of evolution work within constraints. We do not intend to list all these possible constraints in detail here but, rather, point to some of the major constraints that any student of evolution should keep in mind as they interpret evolutionary information. The inherent genetic variation of the parental generation constrains the possible allelic combinations that can be observed in the offspring (plus additional variation from mutation). Hence, genetic variability is a large constraint on how evolution proceeds. No matter how strong a selection pressure there may be you will not be able to select for horses to grow wings, as modern horses simply lack the genetic variance for wing growth. Evolutionary biologists also often refer to phylogenetic constraints—the evolutionary history of common ancestors, reflected in the DNA, limit the ways in which the genome can change in the future. Another common constraint is the general pattern of developmental processes and stages that individuals have to go through. For example, frogs are constrained to go through a tadpole stage and cannot skip ahead. Only a change to developmental regulator genes could alter such a developmental sequence. Time is also a considerable constraint on how evolution progresses. As evolution is defined as heritable allelic changes over time, if sufficient time does not pass, evolution may not happen. Evolutionary time is often measured in terms of generations, so “time” in bacterial evolution will pass at a much faster rate than “time” in terms of elephant evolution. Physical properties also constrain evolution. For example, the much feared giant insects of B movie classics cannot evolve because of the ways in which insects respire and the physical relations between surface area:body size ratios. Insects get oxygen for the bodies through small holes in the surface of their cuticles--these holes are called spiracles. The size of spiracles increases with the surface area of the insect and, hence, increases as a two-dimensional plane of length and breadth. However, insect body size increases in three-dimensions (length, breadth, and height); hence, body size increases more quickly than spiracle area as insects get larger and larger. In other words, larger insects have a smaller surface area relative to their body size than smaller insects. The physical properties of how insects respire mean that insects have an upper limit as to how large they can get, as if they get too large they suffocate as they cannot get enough oxygen through their spiracles to supply their increasing body mass. In the natural world, physical constraints commonly limit how evolution can proceed. Non-independence of traits Genes, and their allelic varieties, are commonly not independent of each other. For example, genes physically located next to each other on a chromosome are physically linked and will often be inherited together from parent to offspring. If one of these genes if highly beneficial whereas the other is mildly deleterious (harmful), the deleterious gene can "hitchhike" with its buddy and increase in frequency even though it will lead to the increase in frequency of a maladaptive trait. A similar phenomenon can occur at the phenotypic level through a genetic property known as pleiotropy. Pleiotropy is when a single gene (or gene complex) influences the expression of multiple phenotypic traits. Pleiotropy is fairly common and results in phenotypic traits being correlated with each other through common genetic mechanisms. Hence, if one traits is highly adaptive but another pleiotopically linked trait is mildly deleterious, the deleterious trait can be selected for because of its pleiotropic association with the more advantageous trait. Again, maladaptive states can evolve because of this form of correlation among traits. Traits can also be linked to each other through trade-offs in allocation of energy and resources. For example, a growing organism has a set energy budget based on what it eats, and that energy can be allocated to various traits and behaviors, which will trade-off against each other because of limited resources. An organism could invest more in reproductive activities, or more in growth, but cannot maximize both. Hence, the evolution of life history traits (which are often closely associated with fitness) is limited because of trade-offs. So from the limitations on evolution...... It may indeed be theoretically possible to come up with a biological pigment that absorbs all or most wavelengths of light and that can be coupled to the cellular energy producing machinery. But there may simply not be the genetic capacity with the current stock of green plants to synthesize such a pigment or the means to synthesize any intermediary molecules that couple that pigment to the cellular machinery. Perhaps, if any such primitive plants with other than chlorophyll did exist, they lost the evolutionary race hundreds of millions of year ago and the genes required for it lost forever. Or until they arise again through random mutation. As I have poreviously said, there have been billions of evolutionary steps between the first autotrophs and modern plants. To try and figure out why chlorophyll containing macroscopic autotrophs are now dominant on Earth is akin to trying to figure out why a particular rain drop came to fall on your nose. The pathway that led to current reality is just to long and complex to compute. Edited September 17, 2011 by Greg Boyles 1
jeskill Posted September 17, 2011 Posted September 17, 2011 The big flaw with our answer is that I know why plants are green. Maybe you would like to try again? I mean you know why polar bears are white don't you?? So if you know why plants are green, then why did you ask the question? And how come you haven't yet described your theory of why plants are green? I can't speak for others, but I would love to hear your reasoning.
esbo Posted September 18, 2011 Author Posted September 18, 2011 So if you know why plants are green, then why did you ask the question? And how come you haven't yet described your theory of why plants are green? I can't speak for others, but I would love to hear your reasoning. I am sure you would, however I am reluctant to give it for a number of reason, one of which is it is not 100% 'cast iron', there may be a few problems at the fringes shall we say. I would say it is better than the explanations listed above thought, which I could easily pick holes in. I asked because I wanted to know if other people had the same theory as me which they don't seem to however I did see one which seemed to have part of my solution. But as I said there are one or two issues I would like to iron out with my theory before posting.
Ringer Posted September 18, 2011 Posted September 18, 2011 I am sure you would, however I am reluctant to give it for a number of reason, one of which is it is not 100% 'cast iron', there may be a few problems at the fringes shall we say. I would say it is better than the explanations listed above thought, which I could easily pick holes in. I asked because I wanted to know if other people had the same theory as me which they don't seem to however I did see one which seemed to have part of my solution. But as I said there are one or two issues I would like to iron out with my theory before posting. Even if you can poke holes in someone's explanation it doesn't mean you're right. Pretty much everyone here has given you an answer that is more or less true regardless of it you don't like it. Your 'picking apart' of my argument consisted of, "no, you're wrong because I'm right." That has pretty much been all your posts have been. If we wanted to be mean the first response would have been not all plants are green. The color green is not necessary for photosynthesis, it's just what most plants use. Your OP is based on a false pretense. Then we could go on to say that it doesn't matter what our eyes see, the plants don't care. Most of us have given you simplified explanations because none of us know how educated you are so we start of easy. None of us know how detailed you can, or want, to get into something. Do you want the molecular mechanisms involved in photosynthesis and information on why it uses certain wavelengths of light? Do you want to talk about the electron excitation of the molecules in the photosynthesizing molecules that give off certain wavelengths? Do you want to know how chlorophyll and cyanobacteria could evolve? If you want detailed explanations actually show us that you are educated in this area. It is none of our jobs to listen to you try to be condescending, we are here to try to help. 4
Essay Posted September 18, 2011 Posted September 18, 2011 Your absorption graph is a bit misleading here is a clearer one. You are ducking the question when you just say it's the best compromise, you have to explain why. Clearly plants are green, we can see that with our own eyes. Thus the only thing which remains to be explained is why they are green and not red or blue or purple or orange. Well from the graph above you can clearly see why plants are green, but I assume you're asking why chlorophyll absorbs as it does and not in some other way. It's an interesting question about why chlorophyll "has a hole" (green) in its absorption spectrum. I'm speculating, but I notice.... The more primitave pigments seem to absorb a narrow band of color or frequency, but chlorophyll seems to have two "narrow bands" (blue & red) where it absorbs light. I think chlorophyll is a tetramer of smaller units, which originally were probably "more primitave pigments" absorbing in the low-energy end of the spectrum. But as a tetramer, perhaps a resonance or harmonic of the lower-energy absorbance structure permitted the additional (new) absorption of higher energy (blue) light. The "b-chlorophyll" seems to have mutated enough to favor absorbing the blue somewhat more over the red. The many interesting points in previous posts [which all seem valid] about more ancient life forms and their pigments certainly suggest that environmental light conditions may have driven much of the evolution in pigment utilization, which were originally important in establishing protection from UV and other high energy light. Competition for light is not one of the most obvious environmental problems, but it seems at times it must be very significant. === But it seems obvious that the very complex pigment, chlorophyll--as a tetramer and as a molecule that functions only with the coordinated absorption of two photons, iirc--must have evolved fairly late in the sequence of early "basic physiological" biochemistry. I don't know if the absorbed photons need to be of the same color or not; but if not, that would be a vote in favor of a strong evolutionary advantage for the tetramer's capability. === The point here is that it is unusual enough when any molecule can absorb light energy and reliably convert it into chemical or redox potential; but when it does happen, it will most likely be "tuned" for a single frequency (or color range). It would be difficult to get a single molecule to absorb equally efficiently over a broad range of frequencies [due to the physics of conjugated double bonds in chromophores]. So getting a single molecule (or dimer or tetramer) to absorb two different ranges of light equally well is quite an evolutionary feat, imho. I can now see why it was rewarded with such dominance. === Or maybe I'm speculating way too much with confused or outdated information, eh? But... esbo, does your idea about plant color have to do with the physics of the biochemistry involved, or is it based on some ideas related to crystal vibrations or some god's (or microbe's) favorite color perhaps? Give us a clue.... ~ 2
John Cuthber Posted September 18, 2011 Posted September 18, 2011 Most plants that we see are green because the red algae got there first. With them absorbing the green light there was only one way to compete- use a different colour of light. What's truly astounding is that it took 31 posting of bickering and insults before someone cited another site which actually answered the question.
Hal. Posted September 18, 2011 Posted September 18, 2011 You can't ask a plant like you can ask a human , is your tea too hot ? Abstraction breeds abstraction .
StringJunky Posted September 18, 2011 Posted September 18, 2011 (edited) Most plants that we see are green because the red algae got there first. With them absorbing the green light there was only one way to compete- use a different colour of light. What's truly astounding is that it took 31 posting of bickering and insults before someone cited another site which actually answered the question. So that's the definitive answer as assessed by you? Your confidence is inspiring. There are possible paths but no definite answers. For starters, cyanobacteria are blue/green which are thought to be the precursors to algae and plants, so, the evolutionary shift to a dominant green was made earlier than algae might you not think? I alternatively suggest that the green algae dominated and the red algae evolved to utilise the spectrum space that was left. I've not noticed anyone being bad-tempered...earnest maybe. Regardless, I've learnt a few things from this thread which is why I read these boards. Edited September 18, 2011 by StringJunky
John Cuthber Posted September 18, 2011 Posted September 18, 2011 It rather depends on the (admittedly loose) definition of plants. The cyanobacteria were, for starters, starters. They were among the earliest organisms and predate the algae and the plants. However what I actually said was that by the time plants (specifically the ones we see like grass and trees and such) evolved, there were already a lot of algae. There could have been herds of unicorns before them, but it doesn't detract from what I said. from wiki "Probably an algal scum formed on land 1,200 million years ago. In the Ordovician period, around 450 million years ago, the first land plants appeared.[1] " There were, according to the fossil record, red algae 1200 million years ago. The green plants are about half as old. in any event, it's a better answer than "they are green because they absorb red light".
Greg Boyles Posted September 18, 2011 Posted September 18, 2011 (edited) Also from wikipedia..... Phycobilins (from Greek: φύκος (phykos) meaning "alga", and from Latin: bilis meaning "bile") are chromophores (light-capturing molecules) found in cyanobacteria and in the chloroplasts of red algae, glaucophytes and some cryptomonads (though not in green algae and higher plants). They are unique among the photosynthetic pigments in that they are bonded to certain water-soluble proteins, known as phycobiliproteins. Phycobiliproteins then pass the light energy to chlorophylls for photosynthesis. The phycobilins are especially efficient at absorbing red, orange, yellow, and green light, wavelengths that are not well absorbed by chlorophyll a. Organisms growing in shallow waters tend to contain phycobilins that can capture yellow/red light, while those at greater depth often contain more of the phycobilins that can capture green light, which is relatively more abundant there. The phycobilins fluoresce at a particular wavelength, and are, therefore, often used in research as chemical tags, e.g., by binding phycobiliproteins to antibodies in a technique known as immunofluorescence. Phycobilins, the red pigment in red algae, are not independant of chlorophyll. So chlorophyll came still first and phycobilin is an add-on. So where does that leave us? Autotrophs are fundamentally green? It is biochemically possible for phycobilins, or other light absorbing biomolecules, to be directly copuled to the photosynthetic machinery without any requirement for chorophyll? Or is it the case that the genes/proteins that could make this possible simply never evolved? http://www.livescien...y-suggests.html Possible answer DasSarma thinks it is because chlorophyll appeared after another light-sensitive molecule called retinal was already present on early Earth. Retinal, today found in the plum-colored membrane of a photosynthetic microbe called halobacteria, absorbs green light and reflects back red and violet light, the combination of which appears purple. Primitive microbes that used retinal to harness the sun's energy might have dominated early Earth, DasSarma said, thus tinting some of the first biological hotspots on the planet a distinctive purple color. Being latecomers, microbes that used chlorophyll could not compete directly with those utilizing retinal, but they survived by evolving the ability to absorb the very wavelengths retinal did not use, DasSarma said. "Chlorophyll was forced to make use of the blue and red light, since all the green light was absorbed by the purple membrane-containing organisms," said William Sparks, an astronomer at the Space Telescope Science Institute (STScI) in Maryland, who helped DasSarma develop his idea. Chlorophyll more efficient The researchers speculate that chlorophyll- and retinal-based organisms coexisted for a time. "You can imagine a situation where photosynthesis is going on just beneath a layer of purple membrane-containing organisms," DasSarma told LiveScience. But after a while, the researchers say, the balance tipped in favor of chlorophyll because it is more efficient than retinal. "Chlorophyll may not sample the peak of the solar spectrum, but it makes better use of the light that it does absorb," Sparks explained. DasSarma admits his ideas are currently little more than speculation, but says they fit with other things scientists know about retinal and early Earth. For example, retinal has a simpler structure than chlorophyll, and would have been easier to produce in the low-oxygen environment of early Earth, DasSarma said. Also, the process for making retinal is very similar to that of a fatty acid, which many scientists think was one of the key-ingredients for the development of cells. "Fatty acids were likely needed to form the membranes in the earliest cells," DasSarma said. Lastly, halobacteria, a microbe alive today that uses retinal, is not a bacterium at all. It belongs to a group of organisms called archaea, whose lineage stretches back to a time before Earth had an oxygen atmosphere. Taken together, these different lines of evidence suggest retinal formed earlier than chlorophyll, DasSarma said. The team presented its so-called "purple Earth" hypothesis earlier this year at the annual meeting of the American Astronomical Society (AAS), and it is also detailed in the latest issue of the magazine American Scientist. The team also plans to submit the work to a peer-reviewed science journal later this year. So it is a false assumption from the start that a hole in the absorption spectrum of chlorophyll represents an inefficient sunlight harvesting mechanism. Edited September 18, 2011 by Greg Boyles 2
esbo Posted September 19, 2011 Author Posted September 19, 2011 Even if you can poke holes in someone's explanation it doesn't mean you're right. Pretty much everyone here has given you an answer that is more or less true regardless of it you don't like it. Your 'picking apart' of my argument consisted of, "no, you're wrong because I'm right." That has pretty much been all your posts have been. If we wanted to be mean the first response would have been not all plants are green. The color green is not necessary for photosynthesis, it's just what most plants use. Your OP is based on a false pretense. Then we could go on to say that it doesn't matter what our eyes see, the plants don't care. Most of us have given you simplified explanations because none of us know how educated you are so we start of easy. None of us know how detailed you can, or want, to get into something. Do you want the molecular mechanisms involved in photosynthesis and information on why it uses certain wavelengths of light? Do you want to talk about the electron excitation of the molecules in the photosynthesizing molecules that give off certain wavelengths? Do you want to know how chlorophyll and cyanobacteria could evolve? If you want detailed explanations actually show us that you are educated in this area. It is none of our jobs to listen to you try to be condescending, we are here to try to help. I am not actually a biologist, I dropped the subject at school I went on to do maths physics and chemistry at A level and the a degree in electronics at uni (didn't get very good grade in that, but hen I didn't put any effort in). I don't need to know too much about biology because in the end it all boils down to chemistry. As for the picking holes bit, one of the arguments seems to be that plants didn't use green because something else was using it. That is a pretty poor argument even if you know no science, because you would have to explain clearly why something else was using green. So that argument is basically just kicking the can (problem) further down the road. To give a proper answer you have to get rid of the can. You see your type of answer seems to involve delving into the detail and explaining some fairly complicated point in that detail, however the thing you explain does not seem to be an answer. What I want to know is why plants don't use green to the same extent as they use wavelengths either side of it. It would be like living in a world where we have big things and small things but nothing in between, ie animals, fish, people. We do not tend to see that in nature. Well from the graph above you can clearly see why plants are green, but I assume you're asking why chlorophyll absorbs as it does and not in some other way. It's an interesting question about why chlorophyll "has a hole" (green) in its absorption spectrum. I'm speculating, but I notice.... The more primitave pigments seem to absorb a narrow band of color or frequency, but chlorophyll seems to have two "narrow bands" (blue & red) where it absorbs light. I think chlorophyll is a tetramer of smaller units, which originally were probably "more primitave pigments" absorbing in the low-energy end of the spectrum. But as a tetramer, perhaps a resonance or harmonic of the lower-energy absorbance structure permitted the additional (new) absorption of higher energy (blue) light. The "b-chlorophyll" seems to have mutated enough to favor absorbing the blue somewhat more over the red. The many interesting points in previous posts [which all seem valid] about more ancient life forms and their pigments certainly suggest that environmental light conditions may have driven much of the evolution in pigment utilization, which were originally important in establishing protection from UV and other high energy light. Competition for light is not one of the most obvious environmental problems, but it seems at times it must be very significant. === But it seems obvious that the very complex pigment, chlorophyll--as a tetramer and as a molecule that functions only with the coordinated absorption of two photons, iirc--must have evolved fairly late in the sequence of early "basic physiological" biochemistry. I don't know if the absorbed photons need to be of the same color or not; but if not, that would be a vote in favor of a strong evolutionary advantage for the tetramer's capability. === The point here is that it is unusual enough when any molecule can absorb light energy and reliably convert it into chemical or redox potential; but when it does happen, it will most likely be "tuned" for a single frequency (or color range). It would be difficult to get a single molecule to absorb equally efficiently over a broad range of frequencies [due to the physics of conjugated double bonds in chromophores]. So getting a single molecule (or dimer or tetramer) to absorb two different ranges of light equally well is quite an evolutionary feat, imho. I can now see why it was rewarded with such dominance. === Or maybe I'm speculating way too much with confused or outdated information, eh? But... esbo, does your idea about plant color have to do with the physics of the biochemistry involved, or is it based on some ideas related to crystal vibrations or some god's (or microbe's) favorite color perhaps? Give us a clue.... ~ Well the way I see it is that there is this big source of energy available (the sun) and you would think plants would make best use of it. I don't need to go into biology of chlorophyll or whatever, I can just say that nature is clever enough to get energy from any wavelength (pretty much). I mean plants can produce flowers of any colour so they have no problem absorbing or reflecting any part of the spectrum. So I think there must be some reason why it leaves green out. You say absorbing two different ranges of light is quite a feat, well yes it is in a way, but then you are underestimating evolution to some extent. How do you think creating DNA compares to absorbing two bands of light? Infinitely harder I would say. So I then say that not absorbing green was done for a reason, ie plants could easily have done it, but choose not to. Furthermore evolution is not a completed process, it is an ongoing one, which is why arguments which hark back to the past seems fundamentally flawed to me. As for God's favourite colour, that's a good one!! Maybe it is God's favourite colour, however I did not come here with a theological solution, but as you mention it, in a way you could turn my answer into a God's favourite colour if you said he had a favourite colour and he designed a world in which green would be dominant. However I don't see much scripture saying God favoured green, although that doesn't mean he doesn't! Most plants that we see are green because the red algae got there first. With them absorbing the green light there was only one way to compete- use a different colour of light. What's truly astounding is that it took 31 posting of bickering and insults before someone cited another site which actually answered the question. Unfortunately that is a pretty lame answer in my opinion. It gets you nowhere because I can simply ask, why does red algae only absorb red (or rather not red). Also from wiki http://en.wikipedia.org/wiki/Plant "The earliest fossils clearly assignable to Kingdom Plantae are fossil green algae from the Cambrian." That statement seems to blow a rather large hole below the water-line in the hull of the good ship Red Algae!!! It rather depends on the (admittedly loose) definition of plants. The cyanobacteria were, for starters, starters. They were among the earliest organisms and predate the algae and the plants. However what I actually said was that by the time plants (specifically the ones we see like grass and trees and such) evolved, there were already a lot of algae. There could have been herds of unicorns before them, but it doesn't detract from what I said. from wiki "Probably an algal scum formed on land 1,200 million years ago. In the Ordovician period, around 450 million years ago, the first land plants appeared.[1] " There were, according to the fossil record, red algae 1200 million years ago. The green plants are about half as old. in any event, it's a better answer than "they are green because they absorb red light". Wiki says the earliest fossilised algae were green. Hence I don't think there is much mileage in the red algae theory. I can think of so many problem with the red algae think I don't even now where to begin, it would seem like a waste of time, a wild goose chase.
Essay Posted September 19, 2011 Posted September 19, 2011 (edited) You say absorbing two different ranges of light is quite a feat, well yes it is in a way, but then you are underestimating evolution to some extent. How do you think creating DNA compares to absorbing two bands of light? Infinitely harder I would say. So I then say that not absorbing green was done for a reason, ie plants could easily have done it, but choose not to. I'm not sure hooking a variety of molecules together can be compared to finding a unique way of converting electromagnetic energy into work via a single molecule. However.... I think you are underestimating the limits that physics imposes upon evolution. It's not about creating a pigment that absorbs all light frequencies, such as melanin; but it's about finding a pigment that will reliably generate chemical or redox potential, regardless of what it absorbs as an energy source. When you put the constraint of translating that absorption into work rather than simply heat, then you constrain the possible structures available for evolving a workable absorption system (I would say). === But still no clue as to why you think this is important? ~ p.s. All this biochemistry evolved long before land-based life evolved, by about a billion years I think. That's why the red algae point is relevant. Edited September 19, 2011 by Essay 1
Grandioz Posted September 19, 2011 Posted September 19, 2011 Plants are green because they have a substance called chlorophyll in them. Understanding why chlorophyll is green requires a little biology, chemistry and physics. If we shine white light on chlorophyll, its molecules will absorb certain colors of light. The light that isn’t absorbed is reflected, which is what our eyes see. A red apple appears red because the molecule of pigment in the apple’s skin absorbs blue light, not red. Thus, we see red. Chlorophyll molecules absorb blue light and some red light. The other colors are reflected resulting in the green color that we associate with plants. Plants get their energy to grow through a process called photosynthesis. Large numbers of chlorophyll molecules acts as the antenna that actually harvest sunlight and start to convert it in to a useful form. Here’s where the absorbent properties of the chlorophyll molecule come into play. It turns out that eons of evolutionary design have matched the absorbance of chlorophyll to the actual color of the sunlight that reaches the leaves. Sunlight consists of primarily blue and red light mixed together, which are exactly the colors that chlorophyll molecules like to absorb. Light is a form of energy, so the chlorophyll is able to harvest the sunlight with little waste.
Greg Boyles Posted September 19, 2011 Posted September 19, 2011 Plants are green because they have a substance called chlorophyll in them. Understanding why chlorophyll is green requires a little biology, chemistry and physics. If we shine white light on chlorophyll, its molecules will absorb certain colors of light. The light that isn't absorbed is reflected, which is what our eyes see. A red apple appears red because the molecule of pigment in the apple's skin absorbs blue light, not red. Thus, we see red. Chlorophyll molecules absorb blue light and some red light. The other colors are reflected resulting in the green color that we associate with plants. Plants get their energy to grow through a process called photosynthesis. Large numbers of chlorophyll molecules acts as the antenna that actually harvest sunlight and start to convert it in to a useful form. Here's where the absorbent properties of the chlorophyll molecule come into play. It turns out that eons of evolutionary design have matched the absorbance of chlorophyll to the actual color of the sunlight that reaches the leaves. Sunlight consists of primarily blue and red light mixed together, which are exactly the colors that chlorophyll molecules like to absorb. Light is a form of energy, so the chlorophyll is able to harvest the sunlight with little waste. That is not what the original poster is asking though. The debate has been about why plants didn't evolve a form of chlorophyll, or some other pigment, that absorbs light from across the spectrum rather than just from the red and blue end of it. For reasons of efficient use of solar energy. I'm not sure hooking a variety of molecules together can be compared to finding a unique way of converting electromagnetic energy into work via a single molecule. However.... I think you are underestimating the limits that physics imposes upon evolution. It's not about creating a pigment that absorbs all light frequencies, such as melanin; but it's about finding a pigment that will reliably generate chemical or redox potential, regardless of what it absorbs as an energy source. When you put the constraint of translating that absorption into work rather than simply heat, then you constrain the possible structures available for evolving a workable absorption system (I would say). === But still no clue as to why you think this is important? ~ p.s. All this biochemistry evolved long before land-based life evolved, by about a billion years I think. That's why the red algae point is relevant. Although, as I found in Wikipedia a few posts back, red algae are using the red phycobilin as an add-on to chlorophyll so they are of limited relevance to the debate. Yes they abosrb a greater proportion of the spectrum but they never the less rely on and are evolved from chlorphyll only containing ancestors. Of more relevence is the suggestion that the early earth's oceans were dominated by autotrophic members of Archae that use the light absorbing pigment bacteriorhodopsin, related to retinol. This appears red-purple and absorbs mostly the green and yellow part of the spectrum. This left the chlorophyll containing ancestors of modern algae and plants to aborb the red and blue parts of the spectrum that the Archae did not absorb. This was at a time when there was little or no oxygen in the atmosphere. Under these conditions it has been suggested that bacteriorhodopsin was easy to synthesis but that the system was not as efficient as the chlorophyll system. So over time and as the oxygen built up in the atmosphere perhaps, the ancestors of modern algae and plants took over dominance from the autotrophic archae, which were relegated to extreme habitats - high salinity and high temperatures where bacteriorhodopsin and other unique features of archae are more stable. So, although chlorophyll absorbs only a small proportion of the visible spectrum, the energy conversion process of light to chemical energy is more efficient. So the original poster's starting assumption that chlorophyll is inefficient because it 'throws' away a large amount of energy from the visible spectrum, is flawed. 1
esbo Posted September 19, 2011 Author Posted September 19, 2011 So the original poster's starting assumption that chlorophyll is inefficient because it 'throws' away a large amount of energy from the visible spectrum, is flawed. Clearly it is flawed that is just undeniable, if it was not flawed plants would be black, not green and plants are by and large green. Or do you deny that plants are green? - lets do this a step at a time.
Essay Posted September 19, 2011 Posted September 19, 2011 (edited) Although, as I found in Wikipedia a few posts back, red algae are using the red phycobilin as an add-on to chlorophyll so they are of limited relevance to the debate. Yes they abosrb a greater proportion of the spectrum but they never the less rely on and are evolved from chlorphyll only containing ancestors. Of more relevence is the suggestion that the early earth's oceans were dominated by autotrophic members of Archae that use the light absorbing pigment bacteriorhodopsin, related to retinol. This appears red-purple and absorbs mostly the green and yellow part of the spectrum. This left the chlorophyll containing ancestors of modern algae and plants to aborb the red and blue parts of the spectrum that the Archae did not absorb. This was at a time when there was little or no oxygen in the atmosphere. Under these conditions it has been suggested that bacteriorhodopsin was easy to synthesis but that the system was not as efficient as the chlorophyll system. So over time and as the oxygen built up in the atmosphere perhaps, the ancestors of modern algae and plants took over dominance from the autotrophic archae, which were relegated to extreme habitats - high salinity and high temperatures where bacteriorhodopsin and other unique features of archae are more stable. So, although chlorophyll absorbs only a small proportion of the visible spectrum, the energy conversion process of light to chemical energy is more efficient. So the original poster's starting assumption that chlorophyll is inefficient because it 'throws' away a large amount of energy from the visible spectrum, is flawed. Thank you, thank you, thank you! Yes, I was completely confusing those two (red algae vs. purple non-sulfur bacteria) ...or whatever the autotrophs were, which used the rhodopsin. I should review phylogeny; plus it's changed since the 70's when I studied.... I should also review when the chloroplasts were adopted as endosymbiotes... (or whatever it is called when an independant organism adopts a host and becomes dependant and incorporated by the host as a fundamental organelle). ...and the whole prokaryote/eukaryote revolution. Where does chlorophyll fit in to that timeline? === http://mbe.oxfordjou...nt/22/1/21.full All three prochlorophyte genera have been shown to have light-harvesting Chl a/b–binding (Pcb [prochlorophyte chlorophyll–binding]) proteins that are homologous to the iron stress-induced proteins (IsiA) of cyanobacteria, rather than to the light-harvesting Chl a/b–binding (Lhc) proteins of plants (La Roche et al. 1996). ...demonstrate a single origin of pcb genes for Chl b–containing and Chl d–containing organisms, together with an ancient duplication of the genes. Given the positions of these organisms in 16S rRNA trees, this strongly suggests a widespread lateral transfer of the genes for these light-harvesting systems. http://faculty.clint...es/prokaryo.htm Photosynthetic ProkaryotesThe first photosynthetic prokaryotes to evolve did not produce oxygen. Cyanobacteria evolved later with the same kinds of chlorophyll found in plants. The green sulfur bacteria and purple sulfur bacteria do not split water during photosynthesis. Instead, they split H2S; oxygen is therefore not released. Photosynthetic prokaryotes have extensions of the plasma membrane called thylakoids. Many of the molecules needed in the reactions of photosynthesis are found within the thylakoid membrane. ...hmmmm. Thylakoids are a normal part of chloroplasts, aren't they? http://www.enotes.co.../photosynthesis Like higher plants, they all have chlorophyll-a as a photosynthetic pigment, two photosystems (PS-I and PS-II), and the same overall chemical reactions for photosynthesis. Algae differ from higher plants in having different complements of additional chlorophylls. Cyanobacteria. These bacteria were formerly called the blue-green algae and were once considered members of the plant kingdom. However, unlike the true algae, cyanobacteria are prokaryotes, in that their DNA is not sequestered within a nucleus. Like higher plants, they have chlorophyll-a as a photosynthetic pigment, two photosystems (PS-I and PS-II), and the same overall equation for photosynthesis (equation 1). Cyanobacteria differ from higher plants in that they have additional photosynthetic pigments, referred to as phycobilins. Phycobilins absorb different wavelengths of light than chlorophyll and thus increase the wavelength range, which can drive photosynthesis. Anaerobic photosynthetic bacteria is a group of bacteria that do not produce oxygen during photosynthesis and only photosynthesize in environments that are devoid of oxygen. These bacteria use carbon dioxide and a substrate such as hydrogen sulfide to make carbohydrates. They have bacteriochlorophylls and other photosynthetic pigments that are similar to the chlorophylls used by higher plants. But, in contrast to higher plants, algae and cyanobacteria, the anaerobic photosynthetic bacteria have just one photosystem that is similar to PS-I. These bacteria likely represent a very ancient photosynthetic microbe. {emphasis added} Wow! But to the point/OP: This (adding additional pigments) is how evolution handles the need to absorb additional wavelengths, it seems. The physics of molecules with conjugated, double-bonded regions/structures, just doesn't favor developing a single way (molecule) for absorbing adjacent frequencies over a wide range of colors, I'm betting. I still think getting two useable absorption peaks from one molecule is rare, and an evolutionary coup. ....Such a long amazing journey! ...and thanks again! ~ Edited September 19, 2011 by Essay
Hal. Posted September 19, 2011 Posted September 19, 2011 (edited) Thoughts upon the colour of plants . NASA In the near infrared maybe they look like a hazy shade of the 1970's . Edited September 19, 2011 by Hal. 1
esbo Posted September 19, 2011 Author Posted September 19, 2011 But to the point/OP: This (adding additional pigments) is how evolution handles the need to absorb additional wavelengths, it seems. The physics of molecules with conjugated, double-bonded regions/structures, just doesn't favor developing a single way (molecule) for absorbing adjacent frequencies over a wide range of colors, I'm betting. I still think getting two useable absorption peaks from one molecule is rare, and an evolutionary coup. ....Such a long amazing journey! ...and thanks again! ~ I don't think I ever said "The physics of molecules with conjugated, double-bonded regions/structures, just doest favor developing a single way (molecule) for absorbing adjacent frequencies over a wide range of colors" Whether that is true or not is irrevelant. Secondly even if it were relevant you would have to show how it relates to my original post (you haven't). So a fair bit of work needed there. Furthermore it is not remarkable to get two absorption peaks. THe level of difficulty between adding 1+1+1 to get 3 is not signification greater than adding 1+1 to get 2.
Greg Boyles Posted September 19, 2011 Posted September 19, 2011 (edited) Clearly it is flawed that is just undeniable, if it was not flawed plants would be black, not green and plants are by and large green. Or do you deny that plants are green? - lets do this a step at a time. I question your assumption that the fact that plants do not absorb the green and yellow proportion of the visible spectrum means that photosynthesis is inefficient. Clearly it is more efficient than the retinol system despite the fact that the cholorophyll system absorbs less of the visible spectrum than the retinol system. Edited September 19, 2011 by Greg Boyles
Recommended Posts