B Sun's peak wavelengths and chlorophyll's green colour

[DaveC426913]

TL;DR Summary

Is there a correlation?

There is some chatter in my layperson's science circles that chlorophyll's green colour is somehow correlated with the fact that the sun's output peaks in the green wavelengths.

It seems counterintuitive, even on the face of it, since chlorophyll is green because green is the one colour it does not absorb. So why would a process "pick" the most abundant wavelengths to reject?


There is even the fanciful suggestion that hypothetical plants on planets around other stars would mimic the peak wavelengths of the star - i.e. a plants under a red star would have red leaves. (How this might be possible can only be attributed to a form of magical thinking. Chlorophyll doesn't get to pick and choose its colours.)

All that faff aside, the core question is: is there any reason to suppose that the chemical reaction our Earthly plants evolved would inversely correlate with the primary wavelength output or our star?

 

[Drakkith]

All that faff aside, the core question is: is there any reason to suppose that the chemical reaction our Earthly plants evolved would inversely correlate with the primary wavelength output or our star?

None that I know of, but my knowledge of this area is admittedly limited.

 

[Al_]

When chlorophyll first evolved the atmosphere was methane, CO2 etc. Did green light get through?

 

[DaveC426913]

When chlorophyll first evolved the atmosphere was methane, CO2 etc. Did green light get through?

Methane appears blue-green in Neptune and Uranus because red and IR wavelengths are preferentially absorbed. That would seem to suggest that green light would get through unmolested.

 

[256bits]

Methane appears blue-green in Neptune and Uranus because red and IR wavelengths are preferentially absorbed. That would seem to suggest that green light would get through unmolested.

In which case, the first organisms billions of years ago perhaps utilized the green. Other organisms with chlorophyl were thus edged out to use the red and blue. Once the chlorophyl organisms became predominant, we have our green planet, as evolution had locked in their green reflecting molecules.

 

[sophiecentaur]

TL;DR Summary: Is there a correlation?

the fact that the sun's output peaks in the green wavelengths.

This contrasts with our vision. The maximum sensitivity is pretty near the peak of received sunlight spectrum at ground level.

The best 'reason' for most of these evolutionary developments is that they are Energetically Favourable. Sounds learned and avoids needing to wave the arms about.

 

[Andy Resnick]

TL;DR Summary: Is there a correlation?

There is some chatter in my layperson's science circles that chlorophyll's green colour is somehow correlated with the fact that the sun's output peaks in the green wavelengths.

It doesn't- sunlight has maximum illuminance at 555nm (yellow).

 

[Drakkith]

It doesn't- sunlight has maximum illuminance at 555nm (yellow).

Got a source handy for that? A quick google search doesn't give me good source.

 

[OmCheeto]

Got a source handy for that? A quick google search doesn't give me good source.

Ha! First hit on my google search: https://www.agcled.com/blog/basic-information-of-the-visible-light.html

Although the chart lists 7 colors correctly, the text below it lists only 6 colors, with yellow, green, and orange transcribed incorrectly.

Just a guess.

 

[sophiecentaur]

The CIE chart could be a good source of the names of colours that we 'experience'. 555nm would appear (not very helpfully) to be seen as Yellowish Green.

so Everyone's right??? It's the green of fresh leaf growth.

 

[Andy Resnick]

This is still a nonsense thread. Chlorophyll absorption peaks in both the blue and far red:

https://www.ch.ic.ac.uk/local/projects/steer/chloro.htm

Also, there are many, many, many plants whose (pre-fall) leaves are not green, but red, or purple, or... for example:
red-leafed barberry
red-leafed japanese maple
Coleus
etc...

Finally, turning towards the evolutionary tree, the first photosynthetic organisms were cyanobacteria, and those light-absorbing compounds (especially phycocyanin) are much more matched to the solar spectrum:

https://ecampusontario.pressbooks.pub/microbio/chapter/photosynthesis/

 

[Andy Resnick]

Got a source handy for that? A quick google search doesn't give me good source.

https://www.sciencedirect.com/topics/physics-and-astronomy/solar-spectra

 

[DaveC426913]

Got a source handy for that? A quick google search doesn't give me good source.

Yeah. Lots of ways to interpret it.

 

[sophiecentaur]

This is still a nonsense thread. Chlorophyll absorption peaks in both the blue and far red:

https://www.ch.ic.ac.uk/local/projects/steer/chloro.htm

Also, there are many, many, many plants whose (pre-fall) leaves are not green, but red, or purple, or... for example:
red-leafed barberry
red-leafed japanese maple
Coleus
etc...

Finally, turning towards the evolutionary tree, the first photosynthetic organisms were cyanobacteria, and those light-absorbing compounds (especially phycocyanin) are much more matched to the solar spectrum:
https://ecampusontario.pressbooks.pub/microbio/chapter/photosynthesis/

Evolution is always a lot more complicated and there are never any straightforward answers to the 'why's. The population of plants today depends on many factors, of course. Evolutionary changes require energy to achieve and only take place when needed. Re-organising the chemistry of photosynthesis would involve many Fails before a better system came along. The present system is a least worst - as with all life.

Bacteria can evolve pretty quickly, though so there may be some better reason than an historical one for the continuing choice of such an old system. There are bacteria which have adapted to all sorts of hostile environments with odd energy sources and light wavelengths. This link tells you all you'd need to know about what they've been doing over billions of years and I guess their evolution allows for a bigger range of systems.

 

[hutchphd]

TL;DR Summary: Is there a correlation?

It seems counterintuitive, even on the face of it, since chlorophyll is green because green is the one colour it does not absorb. So why would a process "pick" the most abundant wavelengths to reject?

The explanation I like best (warning it may be my own synthesis) follows from the fact a mixture of red algae and green algae in a bucket looks uniformly gray (I.e. black):
I think the green algae likely developed in the slightly lower waters beneath the surface red algae and by necessity used whatever light was left over at depth. Being lower in the water it was predominantly these green algae that attached to the bottom thereby making the transition to dwelling on land easier when it became necessary. That's my understanding and I'm sticking to it.

 

[256bits]

@hutchphd
@Andy Resnick
That what is proposed in post #5
and there is a theory about.
https://en.wikipedia.org/wiki/Purple_Earth_hypothesis

The Purple Earth Hypothesis (PEH) is an astrobiological hypothesis, first proposed by molecular biologist Shiladitya DasSarma in 2007, that the earliest photosynthetic life forms of Early Earth were based on the simpler molecule retinal rather than the more complex porphyrin-based chlorophyll, making the surface biosphere appear purplish rather than its current greenish color. It is estimated to have occurred between 3.5 and 2.4 billion years ago during the Archean eon, prior to the Great Oxygenation Event and Huronian glaciation.

 

[sophiecentaur]

there are many, many, many plants whose (pre-fall) leaves are not green

There reason for those colours (in many cases) is that the tree gets rid of toxins etc. by moving them into the leaves and dumping them. There are no other mechanisms in plants for excretion to get the ooh nasty a decent way from the plant.

Many decorative pants are cultivars of common wild plants and they are bred to encourage colours and shapes; evolution gets overtaken by Adam the Gardener. (Anyone remember him?)

 

[DaveC426913]

This is still a nonsense thread.

How is it a "nonsense thread"? I'm asking questions, that I do not know the answers to, of people who know more than I do.

Chlorophyll absorption peaks in both the blue and far red:

Right. The question asks the corollary: i.e. that it does not absorb green.

https://www.ch.ic.ac.uk/local/projects/steer/chloro.htm

Also, there are many, many, many plants whose (pre-fall) leaves are not green, but red, or purple, or... for example:
red-leafed barberry
red-leafed japanese maple
Coleus
etc...

Relevance?

I'm asking about chlorophyll - the molecule that's sustained life on Earth for ~3.8 billion years.

Barberry and Japanese maple use chlorophyll like any other plant.

Finally, turning towards the evolutionary tree, the first photosynthetic organisms were cyanobacteria, and those light-absorbing compounds (especially phycocyanin) are much more matched to the solar spectrum:

https://ecampusontario.pressbooks.pub/microbio/chapter/photosynthesis/

OK. And?

 

[hutchphd]

How is it a "nonsense thread"? I'm asking questions, that I do not know the answers to, of people who know more than I do.

The last biology course I took was in high school......I remember being confused by this very question but I figured it was such an obvious question that it would either be answered in due course or I was not a very good biology student and the answer was somehow trivial. It turns out that neither was true! (and the answer is interesting indeed) The biology course was otherwise excellent ....the then brand-new BSCS blue curriculum (with thaanks to Mr Carl Braun).

 

[DaveC426913]

and the answer is interesting indeed

Care to share?

 

[Drakkith]

Yeah. Lots of ways to interpret it.

Indeed. Each spectrum diagram I look up appears to be slightly different.

 

[Andy Resnick]

How is it a "nonsense thread"? I'm asking questions, that I do not know the answers to, of people who know more than I do.

But nobody seems to be receptive to answers- there is still arguing over (essentially) what color the sun is

Right. The question asks the corollary: i.e. that it does not absorb green.

Again- not receptive to answers- there are photosynthetic molecules that do absorb green. Chlorophyll is just one photosynthetic molecule (and interestingly, when you replace the Magnesium atom with Iron, has the exact same structure as hemoglobin). Multiple, independent, solutions to a single problem are common in biology- different photosynthetic compounds, different structures of eyes (compound vs. refractive), different oxygen-carrying molecules in blood:

https://www.vox.com/xpress/2014/10/31/7133779/blood-blue-green-purple

I'm asking about chlorophyll - the molecule that's sustained life on Earth for ~3.8 billion years.

Again- not receptive to answers. There is not a single photosynthetic molecule, and different forms appeared at different points in time:

https://genomebiology.biomedcentral.com/articles/10.1186/gb-2006-7-12-245

 

[DaveC426913]

Topical discussion in black. Meta discussion low-lit in grey.

But nobody seems to be receptive to answers- there is still arguing over (essentially) what color the sun is

OK. We call that a discussion. It's a nuanced issue, with no definitive answer.
It's different from
1. Question.
2. Definitive answer.
3. Lock thread.

Again- not receptive to answers- there are photosynthetic molecules that do absorb green. Chlorophyll is just one photosynthetic molecule

OK, good to know. That's a valid point. I'm not sure it invalidates the premise in the title.

I'm not sure where "not receptive to answers" comes from, since, AFAIK it wasn't proffered until just now.

Again- not receptive to answers. There is not a single photosynthetic molecule, and different forms appeared at different points in time:

Again, good point.

An argument can be made based on the fact that green chlorophyll is, by far, the most successful. That strengthens the premise in the topic title, since the implication is that "nature" has tried several sun absorbing molecules and the green-rejecting one worked way better.


Again though: where was that previously answered, such that participators have been "not receptive" to it?

Is there any way we can remove the frustration and argumentative components to make way for actual discussion about the topic? Maybe we don't need the meta-discussion about how you feel the discussion is going? It's distracting.

If you feel it's a nonsense topic, the best thing to do is to report it for lockage.

 

[Pphantom]

The reasoning above has one significant flaw. The point is that the Sun's spectrum peaks in the yellow-green part of the optical range only if intensity is defined per unit wavelength interval.

However, if intensity is defined per unit frequency interval (or per unit photon energy interval – it doesn't matter, as they are linearly related), then it turns out that the peak in the spectrum falls within the near-infrared range (corresponding to wavelengths of 900-1000 nm). These are distribution functions dependent on different variables, so this result is quite normal, although it may seem counterintuitive.

Since photosynthesis reactions ultimately involve individual photons, it's crucial that photons (with suitable energy) are more abundant, and this is achieved near the "frequency-based" intensity maximum. Therefore, leaves need to absorb primarily the near-infrared range, while their specific color in the optical range is more of a secondary consequence of their structure.

 

[hutchphd]

The reasoning above has one significant flaw. The point is that the Sun's spectrum peaks in the yellow-green part of the optical range only if intensity is defined per unit wavelength interval.

What is "the reasoning above"?? I do not know what you are trying to say.
However one parameterizes the solar intensity,the figure of merit is not the "peak" value of the intensity but the appropriate convolution of that intensity with the peaked absorption curve of the pigment under consideration. This result does not depend upon the details of wavelength vs wavenumber althugh one must in fact do the calculation (and instrument calibration) correctly.
Incidenally I thought my previous answer(s?) to be exactly on point. Please disabuse me of this notion.

 

[Pphantom]

What is "the reasoning above"?? I do not know what you are trying to say.
However one parameterizes the solar intensity,the figure of merit is not the "peak" value of the intensity but the appropriate convolution of that intensity with the peaked absorption curve of the pigment under consideration. This result does not depend upon the details of wavelength vs wavenumber althugh one must in fact do the calculation (and instrument calibration) correctly.
Incidenally I thought my previous answer(s?) to be exactly on point. Please disabuse me of this notion.

This is an inherently quantum process, so energy considerations alone are insufficient: what matters is not only the total energy flux density, but also how many individual photons provide it.

 

[hutchphd]

What is "this"????". Yes the world lives by Quantum Rules so that all processes are inherently quantum proocesses. So far you have said true and yet largely irrelevant things. What are you trying to say that is salient? I think one needn't use the term "photon" to answer the original question and therefore why complicate.?

 

[Ken Fabian]

I suspect there are limited ways that biochemistry can utilise the energy from photons effectively. Could be less about where in the spectrum most of the photons are than what biochemistry can do with them.