Why are plants green?

[gold333]

I don't buy the "plants are green because they evolved in an era where certain spectral absorption ranges were used by a competing organism".

 

Sunlight isn't air or food. It's an unlimited source. Reflection or refraction of a reduced range of light (after absorption of a certain range) would play a minimal role compared to the abundance of light from above.

 

If it was a perfect system plants would be black with a level of transparency that decreases with foliage height (of the same genus).

 

 

And who is to say evolution has ended and what plants will look like in another 2 billion years.

Edited November 17, 2011 by gold333

[esbo]

Esbo, do you know what chlorophyll do? Do you know how much energy is needed for the chlorophyll to manipulate ADP into ATP, and are you certain that the addition of wavelengths being absorbed could cause this reaction to be processed more efficiently? If so would you show us how it would do so?

 

Well I believe chlorophyll extracts energy from the sun and uses it to help it absorb co2 which helps it grow in some way.

I don't know what ADP or ATP are, they appear to be a meaning less sequence of letters, if you know what they are perhaps

you could let me in on the secret.

Could you explain to me why I need to know what ADP And ATP are?

And why do I need to know all this other stuff you are on about, you seem to be basing your post

on some massive assumption which is irrelevant.

 

I mean I think you need to explain why I need to know all this stuff before requiring me to solve problems

in all this stuff you are on about, problems which may be irrelevent to any answer I have.

[granpa]

what pigments do green plants use to protect themselves from ultraviolet light?

[questionposter]

Sorry but your reply was just waffle and nonsense, the is no explanation as to why plants are green as opposed to any other colour

in your reply. All your reply contains are a few big words to make you appear clever but as far as an explanation goes you post is null and

void. Are you aware of that? DO you actually believe your reply is a credible answer?????

 

Plants are green because of evolution, because that is the most efficient wavelength for them to reflect. The actual reasoning for it appearing green to us is again because of the light's wavelength. White light will hit a plant, and only green will be reflected, and that green then hits the retinas of our eyes. When light hits our retinas, a particular wavelength will only excite the receptors in our retinas a certain way, so every visible wavelength is perceived as a color that corresponds to how it excites the receptors. Most wavelengths however do not excite our receptors enough or excite them too much, either not sending a powerful enough signal to our brain or just destroying and ionizing a receptor. And some wavelengths can't excite every receptor and only excite certain ones, like red blue and green. As I understand it, red pigments don't absorb blue light because the wavelength is too high, and this has to do with the structure of the molecules of the retina. Maybe red does absorb blue I can't remember exactly how it works, but the reason for any particular eye pigment only picking up specific frequencies of light is the same.

Black isn't efficient because that absorbs too much light and would over-heat the plant too fast.

In the jungles in along the equator, there are in fact darker colored plants that contain purple or nearly black pigmentation, and that's because those plants don't receive as much light due to the canopy.

Edited February 8, 2012 by questionposter

[Ringer]

Well I believe chlorophyll extracts energy from the sun and uses it to help it absorb co2 which helps it grow in some way.

I don't know what ADP or ATP are, they appear to be a meaning less sequence of letters, if you know what they are perhaps

you could let me in on the secret.

Could you explain to me why I need to know what ADP And ATP are?

And why do I need to know all this other stuff you are on about, you seem to be basing your post

on some massive assumption which is irrelevant.

 

I mean I think you need to explain why I need to know all this stuff before requiring me to solve problems

in all this stuff you are on about, problems which may be irrelevent to any answer I have.

 

The CO2 doesn't come into play until the Calvin Cycle of photosynthesis, which isn't important to this discussion because it's not light dependent. A simplified explanation is that chlorophyll uses the energy from light to make electrons higher in energy. These high energy electrons are used to push hydrogen ions across a electrochemical gradient so ATP can be made. ATP, adenosine triphosphate, is an extremely important molecule that is used in most chemical reactions that occur in organisms, including how plants make sugars. Why you would need to know this is because this is why plants are green, because those certain wavelengths seem to impart the amount of energy necessary for the plant to be autotrophic. Unless you can show that different wavelengths would be better suited to creating these molecules you cannot say the plant would be better if it absorbed those wavelengths.

[esbo]

Really!

 

Black surfaces with the sole purpose of absorbing solar energy as opposed to providing camoflage!

 

Then name them Esbo!

 

Blackbirds.

 

The CO2 doesn't come into play until the Calvin Cycle of photosynthesis, which isn't important to this discussion because it's not light dependent. A simplified explanation is that chlorophyll uses the energy from light to make electrons higher in energy. These high energy electrons are used to push hydrogen ions across a electrochemical gradient so ATP can be made. ATP, adenosine triphosphate, is an extremely important molecule that is used in most chemical reactions that occur in organisms, including how plants make sugars. Why you would need to know this is because this is why plants are green, because those certain wavelengths seem to impart the amount of energy necessary for the plant to be autotrophic. Unless you can show that different wavelengths would be better suited to creating these molecules you cannot say the plant would be better if it absorbed those wavelengths.

 

I think we can say that there are a range of wavelengths which can be used to extract energy. There are many ways to cook and egg.

I don't think the mechanism is too important just that there is spare energy there which could be used.

All the energy comes from the sun in a plant (and fertiliser) there are many chemical reactions in a plant,

I can't believe that they are all based on a narrow band of wavelengths?

 

Plants are green because of evolution, because that is the most efficient wavelength for them to reflect. The actual reasoning for it appearing green to us is again because of the light's wavelength. White light will hit a plant, and only green will be reflected, and that green then hits the retinas of our eyes. When light hits our retinas, a particular wavelength will only excite the receptors in our retinas a certain way, so every visible wavelength is perceived as a color that corresponds to how it excites the receptors. Most wavelengths however do not excite our receptors enough or excite them too much, either not sending a powerful enough signal to our brain or just destroying and ionizing a receptor. And some wavelengths can't excite every receptor and only excite certain ones, like red blue and green. As I understand it, red pigments don't absorb blue light because the wavelength is too high, and this has to do with the structure of the molecules of the retina. Maybe red does absorb blue I can't remember exactly how it works, but the reason for any particular eye pigment only picking up specific frequencies of light is the same.

Black isn't efficient because that absorbs too much light and would over-heat the plant too fast.

In the jungles in along the equator, there are in fact darker colored plants that contain purple or nearly black pigmentation, and that's because those plants don't receive as much light due to the canopy.

 

OK so not black but why reflect just green, why not reflect red or blue?

That is the question.

 

 

 

 

Thanks to all for the recent replies by the way!!!

 

(forgot to say earlier!!)

[Ringer]

Blackbirds.

 

Blackbirds aren't black for the purpose of absorbing energy, he's really asking a question that can't be answered because there aren't any known surfaces that do this.

 

 

I think we can say that there are a range of wavelengths which can be used to extract energy. There are many ways to cook and egg.

I don't think the mechanism is too important just that there is spare energy there which could be used.

 

I don't mean this in any way disrespectfully, but I think that is part of the problem. You think too much without understanding what you are thinking about. I cannot stress enough how important mechanisms are in understanding why and how plants are how they are. Look at different photosynthetic pathways, without understanding how the mechanisms work for, say, a CAM plant, you could ask why it doesn't allow carbon fixation at all times instead of just at night. That's a process the plant needs to survive so why would a plant only want to do something like that, which also need energy from sunlight to proceed, at a time when it would be less useful? Well it's an adaptation to arid environments, so if plants kept their stomata, pores, open all the time for that process they would lose all their water.

 

Short version: You can't make assumptions about a process you don't understand then start assuming something else would work better.

 

All the energy comes from the sun in a plant (and fertiliser) there are many chemical reactions in a plant,

I can't believe that they are all based on a narrow band of wavelengths?

 

Believe what you want, nature doesn't need you to accept what it does to be true. When you look at the visible light spectrum, it's just an extremely small portion of the entire electromagnetic that happens to react with molecules in our eye.

 

 

OK so not black but why reflect just green, why not reflect red or blue?

That is the question.

 

This is a pointless question until you prove that those would work better.

[Santalum]

The CO2 doesn't come into play until the Calvin Cycle of photosynthesis, which isn't important to this discussion because it's not light dependent. A simplified explanation is that chlorophyll uses the energy from light to make electrons higher in energy. These high energy electrons are used to push hydrogen ions across a electrochemical gradient so ATP can be made. ATP, adenosine triphosphate, is an extremely important molecule that is used in most chemical reactions that occur in organisms, including how plants make sugars. Why you would need to know this is because this is why plants are green, because those certain wavelengths seem to impart the amount of energy necessary for the plant to be autotrophic. Unless you can show that different wavelengths would be better suited to creating these molecules you cannot say the plant would be better if it absorbed those wavelengths.

 

Purple bacteria use green and yellow wavelengths and reflect the blue and red wavelengths.

 

It is undoubtedly a case of there being a very limited number of suitable light absorbing molecular arrangements that are also suitable for photosynthesis in biological systems.

 

So if you like light absorbing molecules suitable for photosynthesis are quantised due to the biochemical restraints of biological systems.

 

Evolution has come up with a red and blue absorbing/green reflecting one, a green and yellow absorbing/ red and blue reflecting one and a few others used by other type of autotrophic organisms.

 

Presumeably it is far more difficult for evolution to succesfully couple the myriad of other light absorbing molecules in nature to the ATP generation machinery within cells.

[Ringer]

Purple bacteria use green and yellow wavelengths and reflect the blue and red wavelengths.

 

It is undoubtedly a case of there being a very limited number of suitable light absorbing molecular arrangements that are also suitable for photosynthesis in biological systems.

 

So if you like light absorbing molecules suitable for photosynthesis are quantised due to the biochemical restraints of biological systems.

 

Evolution has come up with a red and blue absorbing/green reflecting one, a green and yellow absorbing/ red and blue reflecting one and a few others used by other type of autotrophic organisms.

 

Presumeably it is far more difficult for evolution to succesfully couple the myriad of other light absorbing molecules in nature to the ATP generation machinery within cells.

 

IIRC other pigments are for very specific conditions, such as underwater where longer wavelengths are more likely to pass through, and are an exception to the rule. Since esbo is asking very general terms I didn't see a point going into even more technicalities, and I'm not very familiar with the different mechanisms that other pigments use other than some of their names.

[questionposter]

OK so not black but why reflect just green, why not reflect red or blue?

That is the question.

 

Plants don't reflect blue because they absorb it, but they reflect green so we see it. Plants don't have a choice, it's randomly in there genes how their chlorophyll works, and those genes that happened to code for absorbing all colors but green happened to be able to work so well they got passed down. Perhaps plants could have absorbed green light and reflected red or blue, but most don't because they didn't evolve that way, it's just not efficient enough to work without reflecting green.

Edited February 9, 2012 by questionposter

[Essay]

I can't believe that they are all based on a narrow band of wavelengths?

 

But it is based on a narrow range. Any higher and the molecules are broken apart, and lower energy isn't strong enough to kick the electrons around as needed. Then within that narrow range (colors), as Ringer points out, there are only certain molecules that are easy to make, stable, and that work. Evolution worked out using these chromophoric molecules first as protection, then to channel energy, and then modified those to make the tetrameric chlorophyl, which is much more efficient than single pigments. Scientific American (Jan. 2012) had an article, entitled "Tweaking Photosynthesis," which talked about genetically modifying plants to absorb more energy, and suggested maybe black plants would result; but i'd think it'd absorb too much heat (so they'd have to change many enzymes too, istm). Rather than trying to transcend nature, we should aspire to be as good as nature and use the natural systems already in place, imho.

 

~

[questionposter]

It is a pretty narrow range, but it's also an efficient range, it's one of the most efficient and abundant ranges of on Earth. And the only reason bugs see ultraviolet during the early stages of the evolution of life, ultra-violate rays were more prevalent and when the first land animals came on land the Earth's ozone was only 15% of what it was now so any animals would have had to have bodies more suitable for living in higher UV land.

Infra-red is even more prevalent than visible frequencies, and I think some bugs and some reptiles see in those ranges as well, though I don't know why not more.

Edited February 9, 2012 by questionposter

[Essay]

Earth's ozone was only 15% of what it was now so any animals would have had to have bodies more suitable for living in higher UV land.

 

Infra-red is even more prevalent than visible frequencies, and I think some bugs and some reptiles see in those ranges as well, though I don't know why not more.

...that (IR vision) might have only developed once endothermy evolved to become common.

 

But....

That point about exoskeletons and UV abundance is very insightful; do you know of any citation for that, it seems so obvious now that you mention it.

 

The point about visible light hinges upon the fact that it is not energetic enough to destroy too many biological molecules--as does UV. Visible light causes a lot of nuanced excitation of biological molecules (but not enough to break or destroy them) and so a lot of information about the environment can be perceived if you tune into that range. IR causes less nuanced excitation of biological molecules, so less information can be sensed. I think those various ways that molecules respond to light determines how they get used in particular biological systems, and why certain frequency ranges are favored for perception. And it is a fairly narrow range (the visible) where they respond usefully.

Edited February 9, 2012 by Essay

[esbo]

Really!

 

Black surfaces with the sole purpose of absorbing solar energy as opposed to providing camoflage!

 

Then name them Esbo!

 

 

Pilea repens

Black-Leaf Panamiga

 

 

 

Otherwise know as the plant which broke evolution!!!

 

Edited February 9, 2012 by esbo

[questionposter]

...that (IR vision) might have only developed once endothermy evolved to become common.

 

But....

That point about exoskeletons and UV abundance is very insightful; do you know of any citation for that, it seems so obvious now that you mention it.

 

The point about visible light hinges upon the fact that it is not energetic enough to destroy too many biological molecules--as does UV. Visible light causes a lot of nuanced excitation of biological molecules (but not enough to break or destroy them) and so a lot of information about the environment can be perceived if you tune into that range. IR causes less nuanced excitation of biological molecules, so less information can be sensed. I think those various ways that molecules respond to light determines how they get used in particular biological systems, and why certain frequency ranges are favored for perception. And it is a fairly narrow range (the visible) where they respond usefully.

 

Well infra-red doesn't have "less" information, it merely takes more energy for information to be taken from it since infra-red has less energy, which is probably why fewer animals have it since it requires a more energy to operate eyes that can see it. Animals such as reptiles are cold-blooded and don't heat their body up using their metabolism, so they can direct more energy to other processes such as infra-red vision. I only know about the insect evolution thing from a book, but I'll look for a link later.

 

Pilea repens

Black-Leaf Panamiga

 

 

 

Otherwise know as the plant which broke evolution!!!

 

 

That's not really black, this is closer

And those plants with darker leaves are almost always in the jungle, where there is often little sunlight reaching the ground.

Edited February 9, 2012 by questionposter

[Moontanman]

Animals such as reptiles are cold-blooded and don't heat their body up using their metabolism, so they can direct more energy to other processes such as infra-red vision.

 

 

No reptiles can have heat vision because their own bodies are cooler than their surroundings and that allows them to use heat as vision better. Their own body heat doesn't interfere with their heat vision. A mammal with heat vision would get lots of interference from their own body heat, it's why really sensitive infrared telescopes use liquid helium to cool their detectors.

[derrick.s]

Slightly off-topic: All this talk about "us being sensitive to light which we interpret as green" is making me wonder... If there are extra-terrestrial beings out there, I wonder if what we interpret as green is also green to them (if that makes sense)? In other words, I wonder if what we see as green looks magenta to them, etc.?

[JohnStu]

The question is invalid, a lot of plants aren't green at all.

 

 

[questionposter]

OK so not black but why reflect just green, why not reflect red or blue?

That is the question.

 

 

They don't reflect blue or red because they absorb red and blue, and you can't absorbs and reflect the same light at the same time. Why they absorb those colors is because those colors are most efficient to absorb for most plants rather than all the colors driven by random chance in genetic mutation. Some plants do reflect blue or red in some parts because they don't absorb red but instead absorb green, probably because of random genetic mutations that have survived.

Edited March 4, 2012 by questionposter

[zapatos]

 

Slightly off-topic: All this talk about "us being sensitive to light which we interpret as green" is making me wonder... If there are extra-terrestrial beings out there, I wonder if what we interpret as green is also green to them (if that makes sense)? In other words, I wonder if what we see as green looks magenta to them, etc.?

The question is invalid, a lot of plants aren't green at all

 

What does the fact that some plants are not green, have to do with whether or not aliens would interpret green the same as we would?

[Chap]

The SIMPLE reason why plants are green is that it didn't need to be any other color!

 

Evolution of an organism depends upon the selection pressures that the organism experiences. So initially the chemical chlorophyll would have evolved in plants, which doesn't absorb green light. Why didn't some chemical which absorbs all light, even green light (let's call it blacknophyll) evolve? Well, as others have pointed out, chlorophyll might have been a simpler molecule (which can absorb just the right amount of energy without breaking a apart) than "blacknophyll".

 

However, down the evolutionary line, there was very little need (selection pressure) for the plants to evolve a completely different kind of molecule, to capture light better. Any inefficiencies in leaves (with respect to capturing the light energy) of primitive plants would have been eliminated (or minimized to significant degree) by simple evolutionary traits, such as increasing surface area etc... But the process was never SO inefficient that a whole new molecule needed to be found. Instead, the selection pressures put on plant were mainly based on factors like reproduction and growth.

 

That's my thought on this. I welcome any corrections on this post; from anyone.

[esbo]

They don't reflect blue or red because they absorb red and blue, and you can't absorbs and reflect the same light at the same time. Why they absorb those colors is because those colors are most efficient to absorb for most plants rather than all the colors driven by random chance in genetic mutation. Some plants do reflect blue or red in some parts because they don't absorb red but instead absorb green, probably because of random genetic mutations that have survived.

 

How can you sweepingly say it " they absorb those colors is because those colors are most efficient to absorb for most plants" clearly that is a very weak and flawed

statement, it would be most efficient to absorb the whole of the spectrum. infact your statement is full of such vague and wooley statements.

ie "probably because of random genetic mutations that have survived.".

That is really not a good enough answer becasue you fail to explain why they survived, ie you omit to answer the question at all.

 

You might as well say 'because that how it is".

 

I am basically saying how did something evolve in such a way and you answer is "because that is how it evolved" - brilliant!!

 

The SIMPLE reason why plants are green is that it didn't need to be any other color!

 

Evolution of an organism depends upon the selection pressures that the organism experiences. So initially the chemical chlorophyll would have evolved in plants, which doesn't absorb green light. Why didn't some chemical which absorbs all light, even green light (let's call it blacknophyll) evolve? Well, as others have pointed out, chlorophyll might have been a simpler molecule (which can absorb just the right amount of energy without breaking a apart) than "blacknophyll".

 

However, down the evolutionary line, there was very little need (selection pressure) for the plants to evolve a completely different kind of molecule, to capture light better. Any inefficiencies in leaves (with respect to capturing the light energy) of primitive plants would have been eliminated (or minimized to significant degree) by simple evolutionary traits, such as increasing surface area etc... But the process was never SO inefficient that a whole new molecule needed to be found. Instead, the selection pressures put on plant were mainly based on factors like reproduction and growth.

 

That's my thought on this. I welcome any corrections on this post; from anyone.

 

"However, down the evolutionary line, there was very little need (selection pressure) for the plants to evolve a completely different kind of molecule, to capture light better." that is just a sweeping statement plucked out of nowhere.

 

That is a bit like saying there is very little need to plug holes in a petrol (gas) tank, as long as you fill it up a lot.

You answer is a round about way of saying "because that is how it evolved", any question on evolution coudl be answered in

such a manner.

[hypervalent_iodine]

How can you sweepingly say it " they absorb those colors is because those colors are most efficient to absorb for most plants" clearly that is a very weak and flawed

statement, it would be most efficient to absorb the whole of the spectrum. infact your statement is full of such vague and wooley statements.

ie "probably because of random genetic mutations that have survived.".

That is really not a good enough answer becasue you fail to explain why they survived, ie you omit to answer the question at all.

 

You might as well say 'because that how it is".

 

I am basically saying how did something evolve in such a way and you answer is "because that is how it evolved" - brilliant!!

 

 

 

"However, down the evolutionary line, there was very little need (selection pressure) for the plants to evolve a completely different kind of molecule, to capture light better." that is just a sweeping statement plucked out of nowhere.

 

That is a bit like saying there is very little need to plug holes in a petrol (gas) tank, as long as you fill it up a lot.

You answer is a round about way of saying "because that is how it evolved", any question on evolution coudl be answered in

such a manner.

 

You can't refute everything told to you by saying that you simply don't like the arguments presented. That's disingenuous. Try arguing with science instead of 'I don't like it'.

 

Have a read of this paper: http://onlinelibrary...0563.x/abstract

 

An important part I would like to draw your attention to is found in the abstract, which states that chlorophyll pigments act to maximise energy harvesting during low light (undersaturation) conditions as well serving a protective function in over-saturation conditions. That last part is key within the context of this thread. Too much light is not a good thing and is in fact harmful to a plant, as they would have to dissipate a lot more excess energy as heat. From that argument alone you should be able to see why using pigments that absorb all the entire spectrum is not a good thing. As such, higher order plants have developed pigments that are adapted to highly variable light conditions. So yes, 'evolution', happens to be a shortened but no less correct version of the answer.

 

As an aside, evolution of pigments is actually a pretty interesting thing and can tell you a lot about the development of the Earth's atmosphere. If you're really that interested in it, you should read that paper and do a search on it in Google.

[esbo]

You can't refute everything told to you by saying that you simply don't like the arguments presented. That's disingenuous. Try arguing with science instead of 'I don't like it'.

 

Have a read of this paper: http://onlinelibrary...0563.x/abstract

 

An important part I would like to draw your attention to is found in the abstract, which states that chlorophyll pigments act to maximise energy harvesting during low light (undersaturation) conditions as well serving a protective function in over-saturation conditions. That last part is key within the context of this thread. Too much light is not a good thing and is in fact harmful to a plant, as they would have to dissipate a lot more excess energy as heat. From that argument alone you should be able to see why using pigments that absorb all the entire spectrum is not a good thing. As such, higher order plants have developed pigments that are adapted to highly variable light conditions. So yes, 'evolution', happens to be a shortened but no less correct version of the answer.

 

As an aside, evolution of pigments is actually a pretty interesting thing and can tell you a lot about the development of the Earth's atmosphere. If you're really that interested in it, you should read that paper and do a search on it in Google.

 

 

Well I think when I ask a question as to how something evolved and the answer is "because that is how it evolved" or a rather round about way of

saying it "because that is the most efficient" (even though it isn't!!) that I can refute such answers. You say try arguing with the science however as there is no science present to argue against that is rather difficult?!!

The paper linked too goes into a lot of depth but still fails to explain why plants are green. It seems to contain a lot of unnecessary science.

I do not think today pigments would tell you much about the development of the atmosphere no more than than we could explain dinosaurs from modern mammals.

It's an interesting paper none the less but goes into a lot of detail about stuff which may be unimportant.

Edited March 12, 2012 by esbo

[hypervalent_iodine]

Well I think when I ask a question as to how something evolved and the answer is "because that is how it evolved" or a rather round about way of

saying it "because that is the most efficient" (even though it isn't!!) that I can refute such answers. You say try arguing with the science however as there is no science present to argue against that is rather difficult?!!

The paper linked too goes into a lot of depth but still fails to explain why plants are green. It seems to contain a lot of unnecessary science.

 

You're starting to sound very much like a troll.

 

The question you asked was 'why are plants green?' followed by, 'surely black would be better?'. The answer is, because they evolved that way. Because most plants live in habitats that have variable light conditions and as such they need to have a pigment that optimises energy harvesting when there is not much light, but protects the plant when there is too much. Under the highly variable light conditions I mentioned before, green-reflecting pigments are well suited to both of these functions, where as a pigment that absorbs the full visible spectrum would result in a dead plant.

 

I do not think today pigments would tell you much about the development of the atmosphere no more than than we could explain dinosaurs from modern mammals.

It's an interesting paper none the less but goes into a lot of detail about stuff which may be unimportant.

 

You are misrepresenting what I said entirely. My quote was this:

 

 

As an aside, evolution of pigments is actually a pretty interesting thing and can tell you a lot about the development of the Earth's atmosphere. If you're really that interested in it, you should read that paper and do a search on it in Google.