Pages: [1]   Go Down
Author Topic: why do leaves reflect green light?  (Read 1366 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Edison Member
*
Karma: 29
Posts: 2362
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

I was pondering why green light? Why not absorb all wavelengths? So i asked myself the question why do healthy leaves reflect back the green wavelength...

I thought evolution may have tried to absorb the ir wavelengths and into the red wavelength... so logically expected the next color to be absorbed would be the next frequency up (since it absorbs red and blue reflecting green) i then figured the next wave length up would be blue...

But no.....



Evolution decided the green wavelength was right bang in the middle  .. curious right?
Logged

NSW Australia
Offline Offline
Faraday Member
**
Karma: 80
Posts: 3233
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

As you would expect.
Logged

Offline Offline
Edison Member
*
Karma: 29
Posts: 2362
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

As you would expect.


You miss understand..   "green is the rejected wavelength" meaning the plant does not require it, the leaf could equally be red... surely from a genetic stand point all the wavelengths should be absorbed for max effiency... but green was somehow more benificial to survive..

Logged

Anchorage, AK
Offline Offline
Edison Member
*
Karma: 42
Posts: 1176
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

From the link Paul__B posted:

Quote
Not all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory pigments present. For example, in green plants, the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with peaks for violet-blue and red light. In red algae, the action spectrum overlaps with the absorption spectrum of phycobilins for red blue-green light, which allows these algae to grow in deeper waters that filter out the longer wavelengths used by green plants. The non-absorbed part of the light spectrum is what gives photosynthetic organisms their color (e.g., green plants, red algae, purple bacteria) and is the least effective for photosynthesis in the respective organisms.
Logged

Offline Offline
Edison Member
*
Karma: 29
Posts: 2362
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

From the link Paul__B posted:

Quote
Not all wavelengths of light can support photosynthesis. The photosynthetic action spectrum depends on the type of accessory pigments present. For example, in green plants, the action spectrum resembles the absorption spectrum for chlorophylls and carotenoids with peaks for violet-blue and red light. In red algae, the action spectrum overlaps with the absorption spectrum of phycobilins for red blue-green light, which allows these algae to grow in deeper waters that filter out the longer wavelengths used by green plants. The non-absorbed part of the light spectrum is what gives photosynthetic organisms their color (e.g., green plants, red algae, purple bacteria) and is the least effective for photosynthesis in the respective organisms.

I read that.... but again, this is *now*  back before plant life made it onto earth/rock. . Back way back, plants did not require humans due to the fact co2 was pretty much everywhere, we could have seen red or blue ..

So that begs the question of all the wavelengths .. why green? (Yes yes i know WHY scientifically) but not from an evolution design point.... the green is right smack in the middle of the visible wavelengths, also our strongest visual color.




Logged

Anchorage, AK
Offline Offline
Edison Member
*
Karma: 42
Posts: 1176
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Sure, ours.  But really, so what?  What significance does that have?  There's an entire spectrum we can't see.  Is it meaningful that those wavelengths aren't used for photosynthesis either?
Logged

Offline Offline
Edison Member
*
Karma: 29
Posts: 2362
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The rest of the spectrum means little in this example... i'm concerned with visible wavelengths...  or rather what they do absorb vs what they do not....

Logged

Anchorage, AK
Offline Offline
Edison Member
*
Karma: 42
Posts: 1176
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You want to know why the molecules evolved such that they can or can not absorb any given portion of the spectrum?

Well, I don't know.  Maybe I'm just not high enough to have this conversation.
Logged

Offline Offline
God Member
*****
Karma: 7
Posts: 647
"In this house, we obey the Laws of Thermodynamics" Homer J. Simpson
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
So that begs the question of all the wavelengths .. why green? (Yes yes i know WHY scientifically) but not from an evolution design point.... the green is right smack in the middle of the visible wavelengths, also our strongest visual color.

There are probably two answers to this;
  • Evolution does not have an objective, random chance just resulted in green not being used
  • It could be that the chemical/physical tricks and tools to use green don't exist or, if they do, have negative consequences. For example if you need a chemical that does not exist in soil or is damaging to the plant or whose reactions require too much energy then evolution cannot use it

Read somewhere that photosynthesis may be making use of quantum mechanical processes to allow reactions to take place. This is attracting the attention of the quantum computing people and of course could be important if you can get some reactions to take place at lower energies than classical chemistry suggests.
Logged

NSW Australia
Offline Offline
Faraday Member
**
Karma: 80
Posts: 3233
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

So that begs the question of all the wavelengths .. why green? (Yes yes i know WHY scientifically) but not from an evolution design point.... the green is right smack in the middle of the visible wavelengths, also our strongest visual color.

If you know "why" scientifically, then you do know why.

The fact is that the plants - which evolved first, before animals - use the wavelengths on either side of the green.  They presumably do so for different processes, requiring different energy levels which just happen to correspond to those frequency bands, and there is no important photosynthetic process which corresponds to the energy level of green (E=hν).

The photoreceptors in the human (or ape) eye developed later (much later,) and in all probability share the behaviour of the photosynthetic pigments.  As we know, reactions corresponding to ultraviolet wavelengths although some are useful (synthesis of Vitamin D) are more likely to be damaging to tissue, whereas infra-red wavelengths generally carry too little energy to be useful at all, so defining a "window" of important frequencies.

A particularly interesting fact is that many animals - and some humans - are red-green colour blind and lack that green sensitive pigment, so it is actually an evolutionary novelty - and presumably strong advantage - that we do respond, and do so well, to green, due to a "gifted" mutation in the red receptor gene.
Logged

SF Bay Area (USA)
Offline Offline
Tesla Member
***
Karma: 124
Posts: 6652
Strongly opinionated, but not official!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Note that green plants are also highly reflective in the near IR frequencies.
Logged

NSW Australia
Offline Offline
Faraday Member
**
Karma: 80
Posts: 3233
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Note that green plants are also highly reflective in the near IR frequencies.

Because those frequencies are not usable for photosynthesis - and they do not want to cook.
Logged

Offline Offline
God Member
*****
Karma: 7
Posts: 647
"In this house, we obey the Laws of Thermodynamics" Homer J. Simpson
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Of course being geeks and not in touch with the soil we are overlooking the fact that some plant have leaves that are red/purple and other colors.

Perhaps those plants have adapted to living in the shade of their green cousins and make do with less preferable wavelengths?
Logged

Global Moderator
Netherlands
Offline Offline
Shannon Member
*****
Karma: 212
Posts: 13531
In theory there is no difference between theory and practice, however in practice there are many...
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

If all wavelengths would be absorbed all plants/leaves would be black. would be booooooriiiiiing...

different molecules absorb different wavelengths, plants created those molecules that could be made energy efficient from the stuff available in their food smiley  You know "you are what you eat" is also true for plants;

check - http://www.wisegeek.com/how-can-i-change-the-color-of-hydrangeas.htm -

Logged

Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

Pages: [1]   Go Up
Jump to: