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Why are leaves green?

Plants!

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Re:

Postby skunk » Fri Oct 03, 2008 1:10 pm

MrMistery wrote: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.


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?
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Postby mith » Fri Oct 03, 2008 2:05 pm

same energy per photon does not equal capture each photon equally well.
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Re: Why are leaves green?

Postby skunk » Fri Oct 03, 2008 9:37 pm

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.
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Postby mith » Fri Oct 03, 2008 10:23 pm

Read up on physics and electron excitation.
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Re: Why are leaves green?

Postby skunk » Sat Oct 04, 2008 9:25 am

Thanks :)
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Postby skunk » Sat Oct 04, 2008 9:51 am

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. ;)
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Re:

Postby skunk » Sat Oct 04, 2008 9:52 am

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


Yes, but this could differ between species of plant?
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Postby mith » Sat Oct 04, 2008 2:35 pm

All electrons are the same size. I strongly suggest reading up the physics first. Otherwise it would be like teaching calculus without algebra.
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Re: Why are leaves green?

Postby CaduSaMotta » Fri Nov 28, 2008 11:57 am

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.
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Postby MrMistery » Fri Nov 28, 2008 4:20 pm

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."
"As a biologist, I firmly believe that when you're dead, you're dead. Except for what you live behind in history. That's the only afterlife" - J. Craig Venter
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Re: Why are leaves green?

Postby CaduSaMotta » Fri Nov 28, 2008 5:27 pm

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.
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Re: Why are leaves green?

Postby Darwin420 » Fri Nov 28, 2008 10:05 pm

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.
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