Have often wondered how plants with dark foliage, like the dark red canna, handle chlorophyll.
Wikipedia has a long article; this is the first graph:
Chlorophyll (also chlorophyl) is a green pigment found in cyanobacteria and the chloroplasts of algae and plants.[1] Its name is derived from the Gree k words ??????, chloros ("green") and ? ?????, phyllon ("leaf").[2] Chlorophyll is an extr emely important biomolecule, critical in photosynthesis, which allows plant s to absorb energy from light. Chlorophyll absorbs light most strongly in t he blue portion of the electromagnetic spectrum, followed by the red portio n. However, it is a poor absorber of green and near-green portions of the s pectrum, hence the green color of chlorophyll-containing tissues.[3] Chloro phyll was first isolated by Joseph Bienaimé Caventou and Pierre Joseph Pelletier in 1817.[4]
Read the whole thing if interested, and make any comments...appreciated.
The third section on why chlorophyll is green not black is quite interesting to me. The explanation given, which I think is widely accepted in the botanical community, is that some (apparently superior) structures and functions of living organisms have not been reached by evolution because there was no evolutionary pathway from where they came from to get there. This accounts for the less than optimal structure of many aspects of life, eg the human eye and the giraffe's neck. In fact it is characteristic of a process that proceeds by many small connected steps to have such inferior outcomes. A process of design (such as human engineering) can abandon a bad design and take a completely different approach. Evolution cannot do that. Evolution is undirected and has no 'final' target nor does it look to the future as an engineer does, it can only work incrementally on choosing which variation of structure or function is better suited to the environment the organism is in at that time.
In case anybody thinks that evolution is too academic or even off topic, I think it is fair to say that having an understanding of evolution of plants and organisms that relate to plants (eg predators and symbiots) will make you a better gardener.
In the August 2013 issue of Scientific American, the article "The Surprising Origins of Life's Complexity" suggests that evolution strongly depends, not so much on mutations that are advantageous, but more on mutations that are neutral. As such mutations accumulate in the gene pool, their combination eventually leads to changes in an organism. See .
The prospect of finding extraterrestrial life is no Ionger the domain of science fiction or UFO hunters. Rather than waiting for aliens to come to us, we are looking for them. We may not find technologically advanced civilizations, but we can look for the physical and chemical signs of fundamental life processes: ?bio-signatures.? Beyond the solar system, astronomers have discovered more than 200 worlds orbiting other stars, so-called extrasolar planets. Although we have not been able to tell whether these planets harbor life, it is only a matter of time now. Last July astronomers confirmed the presence of water vapor on an extrasolar planet by observing the passage of starlight through the planet?s atmosphere. The world?s space agencies are now developing telescopes that will search for signs of life on Earth-size planets by observing the planets? light spectra.
Photosynthesis, in particular, could produce very conspicuous biosignatures. How plausible is it for photosynthesis to arise on another planet? Very. On Earth, the process is so successful that it is the foundation for nearly all life. Although some organisms live off the heat and methane of oceanic hydrothermal vents, the rich ecosystems on the planet?s surface all depend on sunlight.
Photosynthetic biosignatures could be of two kinds: biologically generated atmospheric gases such as oxygen and its product, ozone; and surface colors that indicate the presence of specialized pigments such as green chlorophyll. The idea of looking for such pigments has a long history. A century ago astronomers sought to attribute the seasonal darkening of Mars to the growth of vegetation. They studied the spectrum of light reflected off the surface for signs of green plants. One difficulty with this strategy was evident to writer H. G. Wells, who imagined a different scenario in The War of the Worlds: ?The vegetable kingdom in Mars, instead of having green for a dominant colour, is of a vivid blood-red tint.? Although we now know that Mars has no surface vegetation (the darkening is caused by dust storms), Wells was prescient in speculating that photosynthetic organisms on another planet might not be green.
Even Earth has a diversity of photosynthetic organisms besides green plants. Some land plants have red leaves, and underwater algae and photosynthetic bacteria come in a rainbow of colors. Purple bacteria soak up solar infrared radiation as well as visible light. So what will dominate on another planet? And how will we know when we see it? The answers depend on the details of how alien photosynthesis adapts to light from a parent of different type than our sun, filtered through an atmosphere that may not have the same composition as Earth?s.
Harvesting Light
In trying to figure out how photosynthesis might operate other planets, the first step is to explain it on Earth. The energy spectrum of sunlight at Earth?s surface peaks in the blue-green, so scientists have long scratched their heads about why plants reflect green, thereby wasting what appears to be the best available light .The answer is that photosynthesis doesn?t depend on the total amount of light energy but on the energy per photon and the number of photons that make up the light. Whereas blue photons carry more energv than red ones, the sun emits more of the red kind. Plants use blue photons for their quality and red photons for their quantity. Tin green photons that lie in between have neither the energy nor the numbers, so plants have adapted to absorb fewer of them.
The basic photosynthetic process, which fixes one carbon atom (obtained from carbon dioxide, CO2) into a simple sugar molecule, requires a minimum of eight photons. It takes one photon to split an oxygen-hydrogen bond in water H2O and thereby to obtain an electron for bio-chemical reactions. A total of four such bonds must be broken to create an oxygen molecule (O2). Each of those photons is matched by at least one additional photon for a second type of reaction to form the sugar. Each photon must have a minimum amount of energy to drive the reactions.
The way plants harvest sunlight is a marvel of nature. Photosynthetic pigments such as chlorophyll are not isolated molecules. They operate in a network like an array of antennas, each tuned to pick out photons of particular wavelengths. Chlorophyll preferentially absorbs red and blue light, and carotenoid pigments (which produce the vibrant reds and yellows of fall foliage) pick up a slightly different shade of blue. All this energy gets funneled to a special chlorophyll molecule at a chemical reaction center, which splits water and releases oxygen. The tunneling process is the key to which colors the pigments select. The complex of molecules at the reaction center can perform chemical reactions only if it receives a red photon or the equivalent amount of energy in some other form. To take advantage of blue photons, the antenna pigments work in concert to convert the high energy (from blue photons) to a lower energy (redder), like a series of step-down transformers that reduces the 100,000 volts of electric power lines to the 120 or 240 volts of a wall outlet. The process begins when a blue photon hits a blue-absorbing pigment and energizes one of the electrons in the molecule. When that electron drops back down to its original state, it releases this energy?but because of energy losses to heat and vibrations, it releases less energy than it absorbed.
The pigment molecule releases its energy not in the form of another photon but in the form of an electrical interaction with another pigment molecule that is able to absorb energy at that lower level. This pigment, in turn, releases an even lower amount of energy, and so the process continues until the original blue photon energy has been downgraded to red. The array of pigments can also convert cyan, green or yellow to red. The reaction center, as the receiving end of the cascade, adapts to absorb the lowest-energy available photons. On our planet?s surface, red photons are both the most abundant and the lowest energy within the visible spectrum.
For underwater photosynthesizers, red photons are not necessarily the most abundant. Light niches change with depth because of filtering of light by water, by dissolved substances and by overlying organisms themselves. The result is a clear stratification of life-forms according to their mix of pigments. Organisms in lower water layers have pigments adapted to absorb the light colors left over by the layers above. For instance, algae and cyanobacteria have pigments known as phycobilins that harvest green and yellow photons. Nonoxygen-producing (anoxygenic) bacteria have bacteriochlorophylls that absorb far-red and near-infrared light, which is all that penetrates to the murky depths.
Organisms adapted to low-light conditions tend to be slower-growing, because they have to put more effort into harvesting whatever light is available to them. At the planet?s surface, where light is abundant, it would be disadvantageous for plants to manufacture extra pigments, so they are selective in their use of color. The same evolutionary principles would operate on other worlds.
Just as aquatic creatures have adapted to light filtered by water, land dwellers have adapted to light filtered by atmospheric gases. At the top of Earth?s atmosphere, yellow photons (at wavelengths of 560 to 590 nanometers) are the most abundant kind. The number of photons drops off gradually with longer wavelength and steeply with shorter wavelength. As sunlight passes through the upper atmosphere, water vapor absorbs the infrared light in several wavelength ands beyond 700 nm. Oxygen produces absorption lines?narrow ranges of wavelengths that the gas blocks?at 687 and 761 nm. We all know that ozone (O3) in the stratosphere strongly absorbs the ultraviolet (UV). Less well known is that it also absorbs weakly across the visible range.
Putting it all together, our atmosphere demarcates windows through which radiation can make it to the planet?s surface. The visible radiation window is defined at its blue edge by the drop-off in the intensity of short-wavelength photons emitted by the sun and by ozone absorption of UV. The red edge is defined by oxygen absorption lines. The peak in photon abundance is shifted from yellow to red (about 685 nm) by ozone?s broad absorbance across the visible.
Plants are adapted to this spectrum, which is determined largely by oxygen?yet plants are what put the oxygen into the atmosphere to begin with. When early photosynthetic organisms first appeared on Earth, the atmosphere lacked oxygen, so they must have used different pigments from chlorophyll. Only over time as photosynthesis altered the atmospheric composition, did chlorophyll emerge as optimal.
The firm fossil evidence for photosynthesis dates to about 3.4 billion years ago (Ga), but earlier fossils exhibit signs of what could have been photosynthesis. Early photosynthesizers had to start out underwater, in part because water is a good solvent for biochemical reactions and in part because it provides protection against solar UV radiation?shielding that was essential in the absence of an atmospheric ozone layer. These earliest photosynthesizers were underwater bacteria that absorbed infrared photons. Their chemical reactions involved hydrogen, hydrogen sulfide or iron rather than water, so they did not produce oxygen gas. Oxygen-generating (oxygenic) photosynthesis by cyanobacteria in the oceans started 2.7 Ga. Oxygen levels and the ozone layer slowly built up, allowing red and brown algae to emerge. As shallower water became safe from UV, green algae evolved. They lacked phycobilins and were better adapted to the bright light in surface waters. Finally, plants descended from green algae emerged onto land? two billion years after oxygen had begun accumulating in the atmosphere.
And then the complexity of plant life exploded, from mosses and liverworts on the ground to vascular plants with tall canopies that capture more light and have special adaptations to particular climates. Conifer trees have conical crowns that capture light efficiently at high latitudes with low sun angles; shade-adapted plants have anthocyanin as a sunscreen against too much light. Green chlorophyll not only is well suited to the present composition of the atmosphere but also helps to sustain that composition?a virtuous cycle that keeps our planet green. It may be that another step of evolution will favor an organism that takes advantage of the shade underneath tree canopies, using the phycobilins that absorb green and yellow light. But the organisms on top are still likely to stay green.
This application of complexity theory is not universally accepted. No matter the point that I was trying to make, that the outcomes of evolution are limited by the availablity of pathways from the previous situation to a new one remains. Whether this postulated mechanism opens up more pathways that permit greater leaps from one state to another remains to be seen, as does how often it might occur.
It's interesting that nature didn't come up with the wheel, one of the most energy-efficient ways of moving around (or did I read a few years ago that there was some strange organism which could move like a wheel? I believe that there are some desert spiders which can escape predators by pulling themselves into a ball shape and rolling down sand dunes, but that not really the same thing as a wheel). It's probably because the moving parts of a wheel are completely separate from each other, and it would not be possible to repair the revolving part of the wheel if it was damaged, as it would have no blood supply.
That's not quite true. If it is assumed that life started in the sea, it should have stayed in that environment, but it didn't. Some animals changed (evolved?) to make use of land. Even more oddly, some changed back (eg seals) to make lesser or greater use of their "old" environment, whilst others, such as dolphins evolved (or should that be regressed?!) to become totally dependent on their old marine environment.
Yes, that's true. There are quite a few examples of parallel evolution (cacti and other succulents; alpines - particularly the giant lobelias and puyas) to support that. If you know how to grow cacti - which are really all New World plants - you will have little trouble if you decide to grow lithops from South Africa.
And if you find it impossible to grow giant lobelias, you will find it just as impossible to grow puyas! :-)
The wheel is the most natural phenomina in nature. The wheel has existed since the creation of the universe... nothing is more natural than the "orbit" (straight lines don't exist in this universe). The wheel has always existed, man has only relatively recently
*discovered* the wheel. Anyone who thinks man invented the wheel is the same kind of pinhead who thinks man invented fire.
I haven't seen this article, I will have a look time permitting. One reason a wheel is not much use for transport biologically is that they require roads to be efficient. Legs are much better on broken ground and can be adapted to climbing, become wings, flippers etc.
Also have a look at the bacterial flaggelum, it isn't a wheel that supports weight for transport but it does rotate and it is powered by biochemistry.
well now that there is an active designer in the house the game will significantly change... already it has begun and we're only in the few slivers of time in terms of the past and how long things have gone before.
i would love to be able to sleep for five hundred or a thousand years and be able to come back and see what has happened.
it is not an assumption, it is based upon the fossil record found to date with the oldest specimens showing that life did start in the seas.
the exact process and steps are not known completely yet, but as time goes on we are getting more answers and finer details of how it could be possible.
the only thing required for any change in an organism to continue is that organism procreates. the causes/effects of selection, environment, mutations, etc. may be completely orthogonal to the simple fact of procreation.
how niches in the environment become occupied is also orthogonal. the sea to land migration of both plants and animals is pretty well understood now. i don't think they are missing any significant steps in those two processes.
i agree about understanding how life came about and learning what you can about life is valuable to a gardener. it's also just amazingly interesting. :)
for one thing the possibilities are there that life moved back and forth from the sea to land from land to the sea several times as different disasters happened. not every- thing previously is wiped out, so different creation phases coexist (and still do).
but in the past few hundred years life has woken up and been able to start taking a direct look at itself and the processes invovled... all i can say now is watch out it's gonna get very interesting.
but some would say hydrothermal vents and crusts of certain compounds may also be likely candidates.
i'm more in favor of foam/bubbles/oils/clays/muds. i've seen them in action (building what used to be called a skimmer in reef aquarium keeping as a means to get organic materials out of the water, pump a lot of bubbles through a column of water and what comes to the top is gunk like the foam that collects on beaches).
I wasn't clear. The two statements I see no evidence for are:
1) "that's not quite true"
2) "it should have stayed in that environment"
I see no relation between your reply and what I said. I said evolution is undirected. Saying dolphins "regressed" suggests that when they (their ancestors really) were land animals they were 'higher' than as aquatic. The same goes for tapeworms that had ancestors that had not lost so many functions (that the tapeworm no longer needs). Fitness depends entirely on environment and only has meaning in the context of an environment so one organism is not more evolved in absolute terms but better or less fit for a specified environment.
True but I don't see the relevance to this matter of regression.
saying that evolution is undirected is false. it is directed (sometimes in ways that are contradictory (one day it is cold, the next day it is hot), sometimes orthogonal to the variation (the change favors big feet with webs between the toes but the species lives on rocks not in or near water) but now there is a new more potent form of direction, an actual designer who can get around poor starting designs by coming up with something completely different.
i for one would like a newly redesigned spine that isn't succeptible to disk bulges which pinch nerves. it is likely that within a few hundred to a thousand years we may actually get a differently designed spinal column (or leave biological forms behind in various ways).
Just to make sure we are not misunderstanding each other, what I mean is there are no targets or goals in structure or function the process aims for. That is there is no specific direction set from the outset, no planning. That doesn't mean that there is no change for the better (better only in the sense of more adapted to the current environment) but that such changes are reached by a combination of natural mechanisms that could well reach some other position. Evolution may or may not result in the reproductive success of the organism, if it does the organism is sufficiently suited to the environment if not it dies out. This is a critical point, there may be many possible adaptations, or combinations of them, that bring about a similar result but they are not known in advance.
If you accept that then we agree. If not why do you say that?
OK, who or what is this designer and how does she/it do this designing? What evidence do you have that such exists and please give an example of it doing its thing.
How will that happen? How do you know it will happen?
(or leave biological forms behind in
Are you talking about entering The Matrix or what?
If you are tending towards religion or mysticism then you are outside the scope of science and there is no point in us going any further with this.
i've written similarly in this thread, so can't disagree in that it is how evolution used to happen and will likely happen somewhat like that into the future. the difference is now that humans are adjusting and removing different species at a rate much faster than blind evolution will ever accomplish. i.e. the process will become more efficient and more directed. we'll continue to select species we like and moderate or alter those we don't like (or get rid of them completely if we can -- i.e. polio, smallpox, t.b., saber toothed tigers) on the hit list at present i'm sure rats and mosquitoes are up there in the sights of some. weeds, certainly some species of those would be a target for elimination if various corporations and scientists could come up with a means.
humans, some scientists, some not, each acts as a selective agent that previously did not exist.
science keeps advancing or working on the big problems. damaged and painful spinal problems are a huge health care need at present. some can be remedied with the right approaches, but others require a more radical intervention like surgery (with all the risks associated with that it is something many people would like to avoid if the option existed).
so i know that science continues to work on the problem. that it might come up with a differently designed spine, be able to encode it in genes so that it is expressed as humans develop, and then have the right outcome is many years in the future. perhaps it won't be needed. i can't really predict the future, but i do know it is currently a huge problem.
no, it may have been science fiction in the past to talk about interfacing humans to computers directly and many other techniques of biological processes getting taken over by biological chips or many other technologies only now coming along. still many years to go there too.
but tell me this, if people are so willing to wear devices like hearing aids, have cochlear implants, have retinal implants to restore vision, develop kidneys and bladders from layers of cells, have heart pumps, drug pumps, etc. all implanted if needed. well tattoos alone tell you that many people don't care exactly what happens to their body as long as enough others will go along. in the case of a redesigned spine i'm pretty sure many people would gladly sign up for it as soon as it became generally available. would you deny your children a better spine that could resist injury or heal itself back to original form if it were damaged? would you not accept a better kidney if yours were already failing and it could be accomplished easily enough for a fairly modest use of resources? how about an extra heart or more memory for the brain? extra capacity for food storage or liquid storage? none of these things are that far-fetched.
i really don't see any end to body modifications once that gets going and they are already going. thicker skin that can resist cold or heat but still have all the sensitivity of the original? who'd care about mosquitoes and bugs if they couldn't get through the skin or we didn't even have blood any longer? would we be able to design a skin that could resist the cold and vaccuum of space? perhaps somewhat. there is a ton of science still to be done. we're really just at the leading edge of this and once it does get going we will likely have a huge explosion in different forms of human. to exploit the new niches that become available once we get out of the gravity well of planets.
anyways, no, i am not mystical in the sense that i would consider it impossible to leave biological processes behind. i don't think the mind exists apart from biology/matter/energy/physics and i'm fairly sure that the form may be able to change once we understand the basic arrangements and requirements.
i do know that if we can ship minds to far away places along with whatever they need to create a manufacturing ability at the other end using local materials then we no longer have to solve the huge problem of shipping habitat and all the supporting life forms. instead we ship information and storage for information and basic manufacturing to ramp up at the other end. all of which can be sent at much higher accelerations and at less risk of failure (many copies of the same thing could be sent knowing most of them might not make it, but it only takes a few to get a new colony going). so we take a trick from the biological processes we have learned about here, but we kick it up a notch and go with a designed goal to reach other planets or star systems.
as far as mysticism would go i would say that it is for the purpose of space travel that humans have been created (general problem solvers with minds flexible enough to solve the problem of reconfiguring their own existence so they can get out of the static trap they are in and move on to more adaptable forms).
not that i'm biased against the biological world. i just see the danger of being a life-form, aware as we are, and being in only one location and subject to catastrophe so i want backup plans up and running ASAP.
I was referring to the earliest stages of evolution when structures that we now call organelles were "free swimming", and not protected by membranes. My point was that one can't go back, without going forward first. I don't mean forward to perfection. I mean forward to adaptation. If a mutation by radiation works, it works by improving an organisms ability to survive, buy then you have short term, and long term.
A number of engineering problems exist in the human body, e.g. BONES THAT LOSE MINERALS AFTER AGE 30, FALLIBLE SPINAL DISKS, MUSCLES THAT LOSE MASS AND TONE, LEG VEINS PRONE TO VARICOSITY, RELATIVELY SHORT RIB CAGE, JOINTS THAT WEAR, WEAK LINK BETWEEN RETINA AND THE BACK OF EYE. These problems may be addressed some day, but how will that effect the memory of survival that is/was stored in our genes?
We have existed as a Family (Hominidae) for 20 million years, and as a species for 200,000 years. We have gone through a lot of evolutionary change to get to where we are. That evolutionary trip is thought to reside in what we call our junk DNA. We prize biodiversity in plants, and animals. We need to prize it in ourselves as well. If we adapt to a time, as we have noted in some of our food cultivars, can we change again when the time changes?
Changing to the time is why we continuously need to make room for new generations to try their hand at adapting, and for that we need all our biodiversity tricks.
That was wrong. Mutations only help, if they help get you selected.
Sorry, time seems to only go forward (physicists may disagree). Conceptual thinking may not be as good as red claws, and teeth in the long run for survival, but as climax forests show us, there does come a time when a given approach to life maxes out, and a new direction needs to be taken.
But the water is still the medium that allows for reactants to move together, and assume the proper position for interaction, like an oxygen atom dropping a proton [H3O+] as it rotates in to get a p-orbital look at a Carbon nucleus as in a carboxylate ester.
Foam/bubbles/oils/clays/muds are just the results of having an aqueous environment. Chunks don't really count, it's the ions and molecules with charge separation that are important (in an aqueous solution).
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