The topic was about digestion but as your new i guess its ok. 😉

I found this from here: http://www.madsci.org/posts/archives/ap … .Bt.r.html

Chlorophyll gives plants their green colour. There are other pigments in the leaves too, such as xanthophylls (yellows) and carotenoids (yellows, oranges and reds). These pigments are also used in photosynthesis but occur in lesser quantities than the green chlorophyll. The combinations of the different pigments make different shades of green.

Now the reason that plants look green is that they are trying to obtain energy from the sun using a particular part of the light spectrum, mainly the red and infra red wavelengths. If you remember from your physics classes the colour you see is the colour that is reflected from the object, the other colours are absorbed. So in the case of green plants, the green wavelength is reflected and all the other colours, especially reds and blues, are absorbed to drive the energy cycle in the plants.

Chlorophyll does best in the red (around 670 nm) and blue (around 500 nm) areas of the spectrum. That’s why many plants have the additional pigments (xanthophylls and carotenoids) called accessory pigments that feed light energy to chlorophyll “a” from light. Chlorophyll is almost useless in the green part of the spectrum, and doesn’t absorb that colour. That is why most plants are green.

About the 550nm wavelength having the most energy. I think this is wrong. I knew this before but checked it here: http://www.scienceofspectroscopy.info/t … IGHT_3.HTM
The shorter the wavelength the more energy it has. So violet has the most with 380-420nm. White light is about 400-700 btw. There are simple formulas to prove all this on the website above.

because of the present of chlorophyll pigment the leaves appear green. 😀

That’s not the question, he’s asking why plants do not produce a pigment to absorb the green wavelength of light i.e. why leaves don’t appear black/red.

Well, actually, they do. When leaves turn red in the fall, it is because they lost all their green pigmented chlorophyll, but retained their red, orange, and yellow pigmented chlorophyll for a little while longer.

During the summer, leaves have all color chlorophyll except blue and violet (if I recall correctly). The reason green shows up is because it is the dominant type of chlorophyll, and green light is mostly reflected.

Blue and purple are the only colors not reflected because it is visible light that is absorbed. As it has the shortest wavelength, it has the highest energy. This is the dominant color of visible light that is used in photosynthesis.

Well, I meant red as why are they not usually red. As you said, the light wavelength with the most energy should be absorbed so blue/violet is absorbed but why isn’t green, a higher energy wavelength than red? Why did plants evolve the pigments to absorb the lower energy reds/oranges but not the greens?

the green portion of light which have the wave length of 550nm doesn’t carry the {biggest}energy content because the energy content of the wave length is inversely proportional with the wave length.
i mean if for example there is a light with 400nm ,this light will have greater energy content that that of the green light so the green light do not have the highest energy content.so when plant reflect the green light [not another light] they are already absorbing a higher energy content that that of green light.i wish i could satisfied you.

Yeah, the leaves appear green because the only wavelength of light not absorbed by the pigment produced by chlorophyll is the wavelength of light for the color green. Thus if it is not absorbed, it is seen by us in the Visible Spectrum.

Yeah, I think the leaves are green because they don’t absorb the sunlight but the sunlight is used to ‘break’ the chlorophyll and get in to the photosystem 1 and 2. (siklic and non-siklic). After that they form their chlorophyll again…

I think the responses are not quite adressing the question. The question was this: Since the spectral peak of the sun is in the yellow-green portion of the visible spectrum, why doesn’t chlorophill absorb at this wavelength? Why instead, does it reflect the most abundant wavelengths of light (not the most -energetic-).

I’m rather interested in finding out what the biological reason for this is.

Thanks,

-Josh

I had a look on google and found a couple of arguments.

The first is that chlorophyll may have been easy to evolve due to it’s similarity to cytochromes so a modification on an already existing pathway was all that was needed to capture some wavelengths of light.

Another argument is that very few plants actually have a shortage of energy input from light. It is only those that tend to grow in the shade of other plants that require further adaptations to get more light. Adaptations such as more chlorophyll and larger leaves may be easier to produce than another pigment.

The most convincing argument I found is that all plants have evolved from aquatic plants. Green light does not penetrate sea water very well so there was no advantage to being able to capture green light while plants were aquatic. Once they moved on to land the light levels were much higher than you get in water anyway so there was no need for further adaptation. There would have been no selection to develop another pigment.

I agree with that herb86, many photosynthetic plants /algae found some distance below the surface contain red pigments so that they can utilize the red wavelength, which is basically almost the only light wavelength that can reach deeper waters.

Another thing, many scientists believe that sometime in the past, chloroplasts are actually living cells that have been engulfed or had symbiotic relationship with other cells. This will explain why chloroplasts and mitochondria have their own DNA that is separate from the genomic DNA of photosynthetic cells.

So its possible that in the past, if these chloroplast ancestors were predominantly green pigmented, the leaf color that we see now are simply a carry over charateristic of those cells.

I dont really understand this myself. YET 😆
This is hard to understand and explain. 😕

It has to do with the pigments absorbtion spectrum that is for that type of plant. as well as different arrangments

I expect that it has something also to do with plants becoming darker or different colored in lower light or deep shade. perhaps to do with carbon/oxygen ratio?

Most plants chlorophyll is green so obviously that is a factor 🙄 Then you have red and purple plants which reflect those colors.. 💡

I will have to do some googling i guess or text book reads. 😀

aaahhh… the ultimate question in botany. Eventually comes down to why are plants green?
Well, the answer is very complex actually. plants are green because chlorophyll reflects green light and absorbes red and blue light. But why does it work like that? The answer- evolution. During the day, in bright sunlight it doesn’t matter what the absorbtion spectrum is, because all colors are present. But in the morning and in the evening red light is present as the majority of photons making up the spectrum of the sun. And blue light? Well, since the energy of blue light is the highest, blue light is the only one that can pass through clouds. So you see, it is very important for plants to be green.

I must save this answer for my notes you explained it well 🙂

Glad to be of some help. This is the question i ask teachers when i want to humiliate them 😆

Ya I found out that there is a lot not yet understood in botany. Things my professor couldnt answer.

because god made them that way…gees

Interesting answer, but do you have more scientific background and experiments to back up your quite short explanation?

Thank you for enlightening me.

I dont think that more answers are needed since chris4 explained it very well subsequently.
But, as an addition, energy at around 380 nm is 3.1 electron volt whereas it is around 1.8 eV at above 700 nm. This proves that violet – blue range is the most energetic in visible region.
cheers

yes it is, but it does not matter. The plant can gain the same amount of energy from any photon, regardless of the actual energy it has. That is why blue light is said to be used by plants most ineficiently. Because blue light has a high energy, and the plant takes only a small part of it.

Leaves on green because the sky is blue.

Brilliant!

forgive my ignorance…

If the plant can gain any amount of energy from any photon then why do plants grow differently under different light sources? plants grown under blue are clearly different from those grown under red. Plants grown under red will stretch taller and grow larger leaves, it seems in an effort to capture more of a weaker light source. Yet if each separate coloured photon was harvestable in the same way, then the plant would have no differences in growth patterns.

I have also read that not all green light is reflected… indeed a little over 50%… is this true?

same energy per photon does not equal capture each photon equally well.

Well it seems that when it comes to either the red or the blue light source that plants can grow healthily in either or. slight differences in characteristics, but the plants grow perfectly healthily.

I have grown plants in both a blue and a red light source… i also experimented with intense UV (300w OSRAM) as a sole source of light, and aside from an initial 3 day stutter the plants grew normally (aside from a few little things) and matured quickly.

OK, I think i see the point here… although blue photons are more powerful, only a certain portion of the photon is used? How do we know this?

Some plants love light… and the more of it you give them without getting temp’s too high… the quicker, and stronger they will grow. It doesn’t make sense to me that such a rich light source would only be partly used when there is such competition with some species for light. Maybe it is the case that certain plants are incapable of absorbing a rich light source… but then there could be others that are capable.

Read up on physics and electron excitation.

Thanks 🙂

So are blue photons actually larger? or are they smaller/same size and merely more intense?

Thanks again for pointing me in the right direction. 😉

Yes, but this could differ between species of plant?

All electrons are the same size. I strongly suggest reading up the physics first. Otherwise it would be like teaching calculus without algebra.

Hello.

I was thinking about this issue today when I asked this question to Google and got there. I am a physicist and my son is a biologist. I was discussing with him exactly the issue that Hadrian addressed: if the green radiation has a great peak in solar radiation, why don´t plants use it?
Our eyes are most sensitive to green light, presumably to optimize our viewing capabilities. So, why plants have not developed a "better" strategy to absorb solar radiation?
I think it is because scattering of light could be a better strategy to share resources and propagate through the earth surface. So, the best strategy for spreading is to share, don´t you think?

Best Regards.

You are making a mistake in logics there: evolution selects for individual characterists. Generally, it is not good to share.
As for why plants do not use green, I give the same answer I gave before:
"Well, the answer is very complex actually. plants are green because chlorophyll reflects green light and absorbes red and blue light. But why does it work like that? The answer- evolution. During the day, in bright sunlight it doesn’t matter what the absorbtion spectrum is, because all colors are present. But in the morning and in the evening red light is present as the majority of photons making up the spectrum of the sun. And blue light? Well, since the energy of blue light is the highest, blue light is the only one that can pass through clouds. So you see, it is very important for plants to be green."

Dear Mr. Mistery,

This vision of evolution seems to be very restrictive. Plants don´t leave alone in the environment. Evolution is not only driven by individual characteristics: if a group manages to survive, the characterisitics of its individuals may propagate and, for them, it is surely good to share.
About scattering: both at dawn and at sunset, the bluish part of the spectrum is scattered more than the red-yellowish part (the distance light has to travel through atmosphere is greater). Blue light is not scattered by clouds more than red one: the propagation in the clouds is made through liquid, not through gas molecules and scattering is much more intense, for all wavelength of the spectrum (http://en.wikipedia.org/wiki/Diffuse_sky_radiation). So, blue light is present everywhere all day long, while the red-yellow component comes mainly from direct rays.
But you are sure: I´ll have to think a lot more about this subject.

Best regards.

In regards to Mistery’s view on evolution, I think you have a mistake in logic.

Yes, natural selection states "survival of the fittest" essentially. But there is a mechanism that contributes to it and what I like to say "survival of the cooperative."

If you look at some of the most successful species (i.e. Humans), we are a very social species that are altruistic and are willing to share our resources as well look out for the well being of other fellow species. This is what I guess you can say a "mutual agreement" -a strategy that actually increases our survival. It is essentially "you scratch my back I will scratch yours" strategy. It is also probability, the more individuals that stick together have an increase in chance of survival, so individuals that show this behaviour will be favoured. Think of how zebras and gazels stick together in large groups to increase their chances of survival from lions.

Look at other species, why do you think ants are social? If this sharing and social behaviour wasn’t favourable then why do you think it still persists?

This sharing behaviour is even present in fruit bats. Studies have shown that these bats are known to share food with other NON-KIN bats that have previously shared with them before. This sharing strategy increases survival of the species. So yes, evolution favours individuals who conduct social and altruistic behaviours like these.

note: the reason why I branched off and talked about social species is because it ties with organisms sharing.

I said generally guys…
Yes there are two basic cases when "sharing" (what is actually called altruism) is good:
Kin altruism – when the two organisms share part of their alleles the reproduction of one will actually increase the fitness of the other, because it passes down genes they both have. From this you can derive the "two brothers or eight cousin case" postulated by G.B.S. Haldane, in that the minimum people you should be altruistic is is either two brothers or 8 cousins, as that is equivalent with 100% of your genes.
Reciprocal altruism – what you described with the bats. I think my old textbook had the same example, though it’s been a few years. From what I remember, some of the bats stick around the cave because they need to take care of the young. The adult bats take turns in gathering food, and also feed the "baby-sitters" when they return.
About humans, it is a bit complicated: if a man is risking his life to save a complete stranger, then he is apparently risking his life to save completely different genes for no good reason. Generally in the human population this kind of altruism is never reciprocated, so i find it hard to examine how human altruism can be evolutionary good, at least in some cases. Nor do I care really.
About plants: I do not believe reciprocal altruism to be the case here, with the advent of green-reflecting pigments. It is still possible, but I honestly doubt it. In most ecosystems photosynthetic organisms are in terrible competition with each other for light, and I see no reason why this was not true when photosynthesis was just emerging.
I have to say I am not a physicist. The explanation I gave I learned from a botany book. If you think that does not agree with physics, I would be more than happy to listen to your opinions as to why not.
BTW, here is a person who apparently did some research on the topic: http://theforcethat.blogspot.com/2007/0 … green.html

I learned from a photovoltaic (PV) manufacturer that PV has over-heating problems. Commonsense tells me that to increase the energy output of PV, you can just increase the amount of light. I did this using a mirror. Doubling the amount of light increased the electrical output of PV but also it made the PV panels very hot. Hot PV fails for its wiring and other electrical systems.

A tree’s interest is to gain most amount of energy from the sunlight. It does not want to get fried in the process. Although black may be the logical color, the cooling system does not keep the leaves cool enough. Leaves have limited amount of air and water cooling mechanism. The nature’s solution is to collect some energy at the first layer of leaves, let the rest of the energy go through and catch them at the second layer of the leaves and so on. This does not overheat the leaves.
But why green?

I saw an experiment at a students’ science fair that compared the energy going through various colored glass. It was a simple experiment of placing a PV at the bottom with a light bulb at top, placing different colored glass plates in between. Green allowed the least amount of energy to go though next to black. In another word, green is the best color to collect energy but not overheating the leaves. By having the secondary layers of leaves, trees achieve their goal of the most effective energy collection.

The leaves contain chlorophyll which is green in colour.
Mostly leaves make up of MOST chlorophyll out of all other pigment make the leave green,
and they reflect the green light (thus they appears green) and abosorb other lights.

This chlorophyll carries out photosynthesis: food making process; take in carbon dioxide and give out oxygen. Changes light energy to food. Only carries out when there is light, water and carbon dioxide.

The higher rate of photosynthesis and absorbance by green leaves are
in the red (chlorophyll a: 650 nm) and violet light (chlorophyll b : 400 nm) range.
While the lowest is green which is reflected and minimal green light is also absorbed.
[ more information check out Action & Absorption Spectra]

My opinion is :
"It not only about the ‘quality’ of light ; how much energy it gives"
"it is also about the quantity that is absorbed and make use of."

If it has two higher reading for violet and red wavelenght (which they absorbed and make use of)
red is kinda the longest, lowest energy wavelengths and
violet is kinda the shortest and highest energy wavelengths.

and green (510 nm) is in between of them.
so what do you think now ?

so why is it better to be in the middle?

leaves are green for the present of chlorophyll pigment and i hope everyone knows it well. I understood that english is not you 1st language and also mine as well.

This would seem to make sense since many plant leaves with red pigments are found as understory plants, however it’s not always the case as many are found growing in full sun.

it also depends on what "red pigments" you are considering.
The red pigment mkwaje was referring to is phycoerythrin, which indeed has the role to allow the organism to use light that would otherwise be useless. However, most land plants that we see colored in red owe their color to anthocyan pigments. these pigments are stored in the central vacuole of a cell (and thus have absolutely nothing to do with photosynthesis) and serve the role of attracting insect and bird pollinators.

I would advise caution when using the word "pigment". While many classical biologists (especially botanists) still classify substances by their color, and refer to anything colored as "pigments", most of these pigments are very different chemically and some have entirely different roles. A chemical/biochemical classification would be much better in my opinion.

well I just read the original post again and realized you said that green light has the most energy.
But really it’s the blue and violet light that has the most at 400 nm wavelenght, followed by green which I think is 500. Also I think, if I remember right, that some pigments do utilize the green wavelength.

The sun is considered a "yellow star" because most of its radiation is in the yellow-green portion of the visible spectrum. The Solar Irradiance – that portion of solar radiation that reaches the surface of the Earth, is also predominantly in the yellow/green wavelengths. The other spectra of light, both lower energies toward and including red, and higher energies toward and including blue, are also present, but in lower quantities. Other writers have indicated that plants most desire light in the reddish and blueish wavelengths. In order to avoid overloading the plant system with too much energy, plants evolved the ability to shield themselves from the excessive quantities of yellow-green wavelengths by reflecting green light away. They may use some of the green, but not all of it. This is my theory – please tell me where I’m wrong. (I really want to know why plants are green!)

IMHO plants are more often suffering from insufficient irradiation, than from excessive. And even if so, they have some mechanisms, how to stay fine.

All,
I am a physicist working in the solar industry. I have always wondered why leaves of different plants have their particular color, and why by far the most plant species have green leaves. I have thought about possible explanations and have read your comments.
If I can summarize, the main postulation raised in this forum is that the color is a left-over remnant from evolution, and was originally due to plants living under water, which does not easily transmit green light. Therefore, it was never necessary for plants to develop the mechanisms to absorb green light.

The concern I have with this statement arises when I look a little deeper into evolution of plants itself. It is not exactly known, but postulated that the earliest organism utilizing photosynthesis arose around 3 Billion years ago, and the first ‘land plants’ appeared around 500 Million years ago. If we believe in evolution, to me it seems unlikely that plants would carry over such a simple characteristic that is left unchanged for 500 Million years. In light of evolution, it is not logical to state that there was no need to absorb green light, especially considering the fact once plants went ‘on land’ that wavelength was available in abundance. Furthermore, as I will show below, I have confirmed that leaves absorb, with very high efficiency, photons of wavelength that are both shorter and longer than green light, thus showing that all photons in the visible range can be used for photosynthesis, including green light.

Therefore, we need to consider the possibility that it is unlikely the evolutionary mechanisms of photosynthesis is the true explanation as to why leaves reflect green light. I want to show you some measurements I have performed on leaves. My original question was this: If I can make a solar cell BLACK because I want to use all photons available to me from sunlight, why then are leaves GREEN, since when I am looking at a leaf, I am literally looking at BILLIONS of years of evolution – and therefore (if I believe in evolution) I must be looking at the ULTIMATE OPTIMIZED form of absorbing the ‘fuel’ of sunlight to generate energy (even though the output ‘energy’ is in a different form between a solar cell and a plant – the incoming ‘fuel’ is the same: sunlight).

In that regard, I have performed transmission and reflectance measurements on leaves, as a function of wavelength. I have discovered several interesting findings, which I will show below. Before I go on though, I must mention that there is an important point to consider: we must distinguish between the front side and the back side of a leaf, which can be thought of as a bifacial solar cell. If you look closely you will see that the two sides look quite different. However, in reality there is a substantial amount of light that can be reflected from the surface underneath the leaf, and back on to the leaf from the bottom, and we need to take that into account.

Here are the findings, all values are approximate and to simplify the discussion, for a single green leaf of a single species of plant:
(1) The front of the leaf absorbs with ~95% efficiency all photons in the 300nm – 500nm range (energy 2.5eV and above)
(2) The absorbance decreases to ~75% at ~540nm (2.3eV), and climbs back up to above 90% at 670nm.
(3) This ‘dip’ in absorbance is not symmetric in wavelength, that is there is a sharp dip from 95% at 500nm, to 75% at 540nm, followed by a gradual climb from 75% at 540nm to 95% at 670nm. I think this is very important. Looking at the data even closer, it is apparent that there are three distinct wavelengths where absorbance is reduced: at 540nm by 20%, at 590nm by 10% and at 620nm by 8%.
(4) The absorbance drops very sharply (exactly like an optical filter) from 95% at 670nm to 10% at 750nm, and stays at 10% from 750nm to 1100nm, except for a slight trough to 15% around 960nm. This is also very important, showing that the leaf is optimized not to absorb light at wavelength >~700nm (i.e. the near infra red – HEAT). The leaf does not want the heat. This makes sense because absorbing light at those wavelengths would heat up the plant and cause it to dry. It is immediately obvious that the leaf’s interaction with light has been optimized to the mechanics of photosynthesis from this standpoint.

Here is the raw data of the measurements on the front side of the leaf, in comma separated format:
wavelength (nm),ENERGY (eV),Transmission (front),Reflectance (front),Absorption (front)
300,4.132805722,-0.1083,5.162,94.9463
310,3.999489409,0.06034,5.221,94.71866
320,3.874505365,0.06543,5.184,94.75057
330,3.757096111,0.02548,5.239,94.73552
340,3.646593284,0.01933,5.131,94.84967
350,3.542404905,-0.01474,5.179,94.83574
360,3.444004769,0.01071,5.167,94.82229
370,3.350923559,-0.1436,4.984,95.1596
380,3.26274136,0.04095,5.245,94.71405
390,3.179081325,0.1646,5.558,94.2774
400,3.099604292,0.1678,6.05,93.7822
410,3.024004187,0.2932,6.422,93.2848
420,2.952004087,0.3153,6.636,93.0487
430,2.883352829,0.3518,6.696,92.9522
440,2.817822083,0.3335,6.724,92.9425
450,2.755203815,0.4274,6.759,92.8136
460,2.69530808,0.5088,6.816,92.6752
470,2.637961099,0.5315,6.863,92.6055
480,2.583003576,0.584,6.846,92.57
490,2.530289218,0.6306,6.874,92.4954
500,2.479683433,0.9116,7.192,91.8964
510,2.43106219,1.8,8.484,89.716
520,2.384310994,3.889,11.63,84.481
530,2.339323994,6.232,15.47,78.298
540,2.296003179,7.436,17.39,75.174
550,2.254257667,7.924,18.08,73.996
560,2.214003066,7.681,17.47,74.849
570,2.175160906,6.491,15.24,78.269
580,2.137658132,5.302,13.08,81.618
590,2.101426638,4.626,11.93,83.444
600,2.066402861,4.377,11.48,84.143
610,2.032527404,3.802,10.53,85.668
620,1.999744704,3.19,9.58,87.23
630,1.968002725,3.034,9.312,87.654
640,1.937252682,2.686,8.883,88.431
650,1.907448795,1.939,8.003,90.058
660,1.878548056,1.427,7.386,91.187
670,1.850510025,0.9225,6.794,92.2835
680,1.823296642,0.8207,6.713,92.4663
690,1.796872053,2.264,8.139,89.597
700,1.771202452,8.318,16.87,74.812
710,1.746255939,15.2,29.38,55.42
720,1.722002384,21.07,41.14,37.79
730,1.698413311,25.64,50.49,23.87
740,1.675461779,28.27,55.35,16.38
750,1.653122289,29.54,57.73,12.73
760,1.63137068,30.06,58.79,11.15
770,1.610184048,30.38,58.99,10.63
780,1.589540662,30.52,59.17,10.31
790,1.569419895,30.6,59.02,10.38
800,1.549802146,30.73,59.13,10.14
810,1.530668786,30.86,59.28,9.86
820,1.512002094,30.82,59.2,9.98
830,1.493785201,31.03,59.21,9.76
840,1.476002044,31.02,59.06,9.92
850,1.458637314,31.01,58.87,10.12
860,1.441676415,31.06,59.08,9.86
870,1.425105421,31.12,58.81,10.07
880,1.408911042,31.03,58.97,10
890,1.393080581,31.26,58.85,9.89
900,1.377601907,31.26,58.53,10.21
910,1.362463425,31.23,58.47,10.3
920,1.34765404,31.33,58.54,10.13
930,1.333163136,31.12,58.28,10.6
940,1.31898055,31.06,58.02,10.92
950,1.305096544,30.74,57.5,11.76
960,1.291501788,30.42,56.83,12.75
970,1.278187337,30.19,56.43,13.38
980,1.265144609,30.19,56.58,13.23
990,1.25236537,30.27,56.46,13.27
1000,1.239841717,30.49,56.65,12.86
1010,1.227566056,30.67,56.98,12.35
1020,1.215531095,31.03,57.15,11.82
1030,1.203729822,31.18,57.46,11.36
1040,1.192155497,31.44,57.78,10.78
1050,1.180801635,31.65,57.94,10.41
1060,1.169661997,31.89,57.98,10.13
1070,1.158730576,32.13,58.15,9.72
1080,1.14800159,32.24,58.17,9.59
1090,1.137469465,32.31,58.09,9.6
1100,1.127128833,32.4,58.01,9.59

Please plot it yourself and take a look – it is quite interesting. At this stage I will not put forth any suggestions as to what may be the true explanation why the leaf has reduced absorbance at certain wavelengths (although I do have some ideas). I will stop here and wait for responses and further discussion, before I flood you with more data and findings.
Thanks.

1) just because plants absorb light doesn’t mean they use it for photosynthesis. We absorb some light too yet we’re not photosynthesizing 😉

2) if is something beneficial, you do not need to change it even after long time. Look into histones, they are pretty much conserved, much more then proteins of chlorophyll biosynthesis. Additionally, the proteins are evolving, but to create whole new pathway you need a little bit more 😉 More additionally, if you even created new pathway for biosynthesis of new pigment, you would need new pathway for electron transfer.

Great to see this question is still being debated after 5 years on here. I particularly liked Physicist0017’s work on the subject and look forward to reading more.

As I understand it from reading the points here and some other work elsewhere the following is true:

1) We percieve plants as green because they reflect light that has mostly the green wavelength.

2) Green is the most effective colour for plants, if not they would have evolved a different colour by now.

3) Due to the properties of other wavelengths the question "why are plants green" is synonymous with "why are plants not black".

It’s been suggested that absorbing all colours, and therefore becoming black, would cause plants to suffer heat issues whereas being green allows them to capture a steady stream of light from sunrise to sunset.

2) no, they do NOT use green light! So it can NOT be the most effective colour for plants.

3) plants are sometimes experiencing overheating even when absorbing blue and red (FR is the "heat light" anyway) and yet they can handle it, so absorbing the whole spectra would not cause much more troubles. But they had to have pigments for all these wavelengths.

Please note I said most effective, I didn’t say that it absorbs most light. You seem to equate the most effective colour being that which absorbs most light, which of course would lead to the logical conclusion that black plants are most effective. So my question to you is, if black was a more effective colour than green then why are plants not black?

The way I see it, if plants are experiencing overheating then by definition they "can’t handle it". If they can then surely they aren’t overheating. For example put me in a sauna and at a certain temperature and for a certain length of time then there’s a range of temperatures and time periods I can handle. I will sweat, maybe feel uncomfortable, but the moment I collapse and need to be dragged out, that for me is when I am overheating and I can’t handle it.

My personal gut feeling is that being black would cost the plant more in trying to cope with heat than it would gain from the extra energy. I also think data like that provided by Physicist0017 will show that plants still absorb a lot of the energy.

2) OK, now I understood you mean the color of plants, not the absorbed color.

3) for you, overheating means being dead, for me, overheating and oversunning means not ideal conditions, which do not have to lead to death if handled properly.

Actually my original statement which was "would cause plants to suffer heat issues" is probably more similar to your understanding of overheating than the one you incorrectly painted me as having. For me suffering heat issues means the plant has to make sacrifices that it wouldn’t ordinarily need to do, either that or face an inability to procreate (apologies if "procreate" is the wrong term for plants). Either way it’s ability to procreate successfully is harmed in some way, if not entirely negated. Having suffered "heat issues" the plant would lose out to more efficient designs which did not have to make such sacrifices. Ultimately I believe green is the most effective colour for plants because it’s the colour that is most dominant.

I’m hoping that if I’m wrong someone could explain to me why so I can understand plant biology better. I dont think that it’s enough to say "there’s enough light in the blue and red spectrum to suffice". I’d love to be proved wrong though.

Also if green is the most effective colour but for some other reason than heat than I’d love to know the reason.

Personally I have a son who is very inquisitive and I hate giving him half answers.

A chlorophyll strongly absorbs radiation in the red and blue wavelengths but reflect green wavelength. The internal structure of healthy leaves act as diffuse reflector of near-infrared wavelengths. Measuring and monitoring the infrared reflectance is one way that scientists determine how healthy particular vegetation may be.
Leaves appear greenest to us in summer and become red or yellow with decrease in chlorophyll content in autumn.

Majority of the radiation incident upon water is not reflected but either is absorbed or transmitted. Longer visible wavelengths and near-infrared radiations are absorbed more by water than the visible wavelengths. Thus water looks blue or blue-green due to stronger reflectance at these shorter wavelengths and darker if viewed at red or near-infrared wavelengths. The factors that affect the variability in reflectance of a water body are depth of water, materials within water and surface roughness of water.

The majority of radiation on a surface is either reflected or absorbed and little is transmitted. The characteristics of soil that determine its reflectance properties are its moisture content, texture, structure iron-oxide content. The soil curve shows less peak and valley variations. The presence of moisture in soil decreases its reflectance.
When chlorophyll is abundant in the leaf, it dominates both reflection (in the green) and absorption (in blue and red). This accounts for the two absorption bands on either side of the green reflectance band and explains why a leaf appears green.

Some blue leaves would be nice!

I think it’s pretty clear why plants appear green, the question that still seems unanswered is why plants evolved to be green and not (for example) black?

Oh well sorry to do this but it’s a five year old thread and there hasn’t been anything added for five months so…

*bump*

You never know

Plants might have evolved to be green because during evolution there was another species that absorbed all the green light, which in the spectrum of sunlight contains most energy and is therefor technically most efficient for photosynthesis in our solar system.

A likely canditate is the Halobacterium which shows up as purple because it absorbs most of the green light. what remains is red and blue (mixed into purple).

Andrew Goldsworthy has proposed this theory and thinks that Halobacterium floated on top of the water during the evolution of plants, and algea evolved under water. Because the Halobacterium would have absorbed all the green light, the only light remaining is blue and red. Algea have evolved to absorb this remaining light, red and blue very efficiencly using chlorophyll. Because red and blue are absorbed and green is not absorbed but reflected or passes through, the leaves show up to be green.

Why not black?
You will notice that leaves at the bottom of the tree are darker than leaves at the top, this is because at the bottom there is less risk of overheating because there is more shade. Therefore there is a benefit to reflect some light (remain lighter) because it prevents overheating of the leaves (and death of the plant).

Quinten – Thank you for rejuvenating the discussion.

I think I agree more on the physics reason that the biggest energy containment is not in the green spectra, because there is a relation between wavelength and energy content. Theres a formula for it. I kinda forget.

Therefore, I think it is naturally for plant not to absorbed the not-so-big energy, and when they reflect it, they appear green.

Regards,

Quinten. Thanks for that. I remember reading Goldsmiths theory back in the late 80’s/early 90’s (showing my age now 😳 ) and for me it conjured images of life trying to overcome the problem of light only being on a certain point of earth for limited hours of the day. I was of the opinion that the need to overcome this limitation was the driver for life developing motor functions.

I have to say I was less struck by his assertion of the halobacterium causing algae to be green, because algae would not have had heat issues, just light issues, and there would surely always be some opportunity to absorb blue and red light so they would have favoured black.

Also halobacterium would have more reason to be black, it couldn’t store energy so would need to make use of all available energy and again, I don’t see them having heat issues.

Why would they absorb blue AND red then?

because it has bigger energy than the GREEN?

BOTH blue and red?

in desending wavelength absorbtion, Carotenoids, Chlorophyll b and Chlorophyll a are the major light aborbing pigments in the plant and form part of the light absorbing complex.

In this complex energy is absorbed by all pigments, but not all pigments have the capasity for photosynthesis. This meens that lots of non-photosynthesizing pigments surround a active photo-center.

Energy is caried over from one pigment to another by inductive resonance till it reaches the photo-center. For this to happen there needs to be a decline in energy levels from example Carotenoids to Chlorophyll b and Chlorophyll a. This funnels the energy to the reaction center where it drives photosynthesis.

If there was a pigment that absorbed green light the gradient of energy between pigments would by less and energy could travel back to Carotenoids or travel lateraly away from the reacion center.

More than this the plants ability to adjust to high light intensities by synthesis of antosianin would be destroyed. As antosianin absorbs green light reducing green light scattering.

As a side note, shade plants do absorb green light by use of their long intercelluler spaces deflecting green light till some of the enery is lost and it can be absorbed.

If we forget about photosythesis for the moment we can look at light senceing molecules such as Phototropin (Blue light), Chryptochrome (Blue and UV-A) and Fitochrome (Red and far Red). Resposible for Phototropism, photomorfogenesis, circadian rhythm, sensitivity to IAA and stomata opening/closeing.

The functioning of these molecules depend on the large gap between red and blue light, if green light was absorbed it would influance the activities of these molecules and plant responses.

Don’t forget that any wavelength above 680nm can not be used to drive photosinthesis, as the photosistems work at 680nm or 700nm.

Blue, yellow and green light reduces their energy levels in the plant by floresence and chemical heat dissipation to be able to drive photosynthesis. If to much energy must be dissipated reactive oxigen radicals can form which damages DNA and RNA as well as lots of other prosseses in the plant.

It is logical then that plants do not wish for green light to be absorbed

Six pages of discussion and I didn’t spot one alternative solution: the light of our sun has not always conformed to its current radiation spectrum.

If our skies were purple, ie high red/ blue (+ UV) then not only did plants benefit.

The eyes of humans, animals and birds are mainly peak sensitive in the 550nm range (green light). So eyes are naturally adapted to give a more equal energy spread, taking advantage of what was (is) most plentiful.

you are a little contradictory, aren’t you? Or what are you saying?

I think Nature appears contradictory, actually!
1) Why be inefficient and provide our eyes with too much sensitivity in the Green zone?
2) Why do plant leaves reflect the highest energy part of the current sun’s spectrum?
3) UV is not particularly abundant, and yet birds, reptiles and insects are fitted with UV sensors?
4) Plants make big use of UV to attract insects, why not use a higher energy colour?

Marinz says

Thanks for supporting my theory – obviously Nature took advantage of the time when Blue and Red were the most abundant wavelengths in the sky. And it still works, even in our yellow sun era.

so leaves are really "clear"? please email me at [e-mail address] im very interested thanx 😀

how did you come to that it should be clear?

I think I have read/seen a very interesting answer to this.

Firstly, we have to understand endosymbiotoc theory: the organelles responsible for photosynthesis of plants, chloroplasts are captured cyanobacteria: cyanobacteria/chloroplasts are green.

Cyanobateria evolved a long time ago, but they were not the first photosynthetic organisms.

Purple bacteria existed already, they absorb green light and reflect blue and red(that’s why they are purple). They don’t use H2O to create O2, they use different elements, most commonly H2S to create S. They do not like oxygen and die is exposed to too much of it.
The early earth had an atmosphere without oxygen: purple bacteria were free to roam whereever they wanted (now they are kindof rare) and dominated the seas.

Purple bacteria evolved to use the most abundant photons (yellow-green), they had(have) the solution that was optimal… cyanobacteria evolved later, in a world dominated by purple bacteria… the cyanobacteria had to live from the light ‘left over’: the blue and green. This was optimal for them because the green light was not available (purple bacteria used it all). And that’s why they developed pigments that absorb blue and red light. After cyanobacteria appeared, their color was fixed in evolution, in the same way as other solutions that made sense once but no longer do are fixed (air and food in same opening is a bad solution, but lungfishes evolved lungs by ‘swallowing’ air…today it works, so no change): today green leaves get the job done, so why change it (even if it could be better). After cyanobacteria changed the atmosphere (without them (in ocean and in plants) there would be no oxygen in the air) purple bacteria lost their dominating status…

Purple bacteria are older than cyanobacteria according to molecular geneticist, and there are papers that claim the chemical markers of purple bacteria are widespread in ancient sediments. This is not generally accepted (yet), though.

The problem with this argument is that today, the position is reversed: purple (sulphur) bacteria live in deeper, oxygenstarved water, where they live from the light that is not absorbed by the green organisms higher in the watercolumn.

So all in all I am not sure that this is true, reading more about it as we speak, but it sounds rather convincing to me.

The heat argument doesnt make sense to me: why are pinetrees in siberia not black? We don’t see color differences in plants between hot and cool places. If heat was so important, tropical plants should have different colors than arctic plants.

The argument that there’s more than enough light so it is not limiting makes no sense either: plants have lots of tricks to grow tall and block the light of competitors, and many seedlings in the forest don’t make it for lack of light. Every photon is precious in the struggle for life.

The scattering/sharing argument is just not the way biology works. Evolution creates very selfish beings. I don’t think ants or humans are an exception, actually… communism failed to work for the reasons of selfish evolutionary biology (but that’s another discussion).

The argument of other-spectrum sun is interesting, but at first makes no sense either: if the sun used to be bluer, why do plants also use red light… if the sun used to be redder, why do they use blue?
BUT if the yellow-green light was filtered away by gasses in atmosphere… that’s close to the purple bacteria argument… the atmosphere used to be different as well, perhaps back then yellow-green light was absorbed by atmosphere before it reached the ground (purple skies). hmmm, should read on what was composition of atmosphere…

After all, it might also be chemical restrictions:
the water-oxygen reaction is taken for a reason: oxygen is a far better electron receptor than atoms used by alternative photosynthetic organisms: more energy is released using oxygen than when using sulphur or any other possibility. Perhaps there simply is no pigment possible that uses oxygen and green light. This is not very satisfing and convincing to me, though.

So after all, I think the case for purple bacteria world domination is pretty good.

This is were i read it: http://theforcethat.blogspot.com/2007/0 … green.html

http://www.livescience.com/1398-early-e … gests.html

AH! now i know where i saw it… BBC… how to grow a planet:
http://www.youtube.com/watch?v=1VNt0mwStZI

watch from 12-14 minutes

Hello, leaves are green because of a compound called chlorophyll. The purpose of cholorphyll is to help plants in photo synthesis which the way plants make food.

according to everyday science mcqs Plants and leaves seem green because a “unique pair” of chlorophylls utilizes the red end of the visible light range to power processes in each cell. We notice the leftover green light that is mirrored off the leaf.