Why are plants green?

Discussion in 'Earth Science' started by esbo, Jul 20, 2011.

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  1. Me-Ki-Gal Banned Banned

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    I'm the real Woo Woo around heeea! Substitutions are unacceptable.
    Yeah I benefited from Trippy too ! Great posts . Very comprehensive I might add
     
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  3. billvon Valued Senior Member

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    If you think that that graph means "leaves aren't green" you may not understand the graph.
     
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  5. Trippy ALEA IACTA EST Staff Member

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    Only because of your preconceived notions.

    Eyes see in three bands (or in some cases 4 - mostly in women, hence the stereotype regarding males) of colour.
    These bands have some overlap, which is greatest in the green-yellow part of the spectrum, hence that's where our eyes are the most sensitive.

    Likewise, Chlorophyll absorbs across the entire visible spectrum, it absorbs everything betwen 350nm and 700nm, however, some wavelengths are absorbed more efficiently than others, hence appearing green.

    Plants don't use just chlorophyll to absorb light for photosynthesis. The use auxillary, or antenna pigments to absorb light more efficiently at wavelengths where chlorophyll is less efficient.

    But then, why am I unsurprised that all you've done is sit their and say "Your argument is weak" without actually providing a useful critique of the argument, or providing an actual counter argument.

    Perhaps we should apply the same reasoning to your posts?
     
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  7. esbo Registered Senior Member

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    But they still appear green the fact they may absorb some green light is irrelevant.
     
  8. MacGyver1968 Fixin' Shit that Ain't Broke Valued Senior Member

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    That is irrelevant.

    Please Register or Log in to view the hidden image!

     
  9. Trippy ALEA IACTA EST Staff Member

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    This:
    So perfectly illustrates the source of the problem in this thread, because this:
    Is what he's responding to.

    Here:
    is the relevant portion.

    In other words, I'm stating (or strongly implying) that because I'm at work, and because I don't have the remember me button checked (a consequence of being at work), my posts occasionally get eaten.
     
  10. billvon Valued Senior Member

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    No, it's not, because the amount of various frequencies they absorb (and reflect) determines their color. To put it another way, the amount of green (and red and yellow and blue) light they absorb is quite relevant to their color.
     
  11. Trippy ALEA IACTA EST Staff Member

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    No, the fact that they are green is irrelevant to whether or not they utilize that portion of the spectrum for photosynthesis.

    The simple fact is that being green does not preclude plants from using the green portion of the spectrum for photosynthesis.

    Once again we come back to this point - based on the action spectrum of chlorphyll, and based on the spectrum of light at ground level, chlorophyll appears to be the best pigment, that is useable for photosynthesis, that has the widest band of useable frequencies.

    This fact alone may be sufficient to explain its dominance.

    It (for example) outperforms Retinal based systems because it is capable of absorbing a wider range of frequencies of light.
     
  12. Me-Ki-Gal Banned Banned

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    o.k. sounding like a broken record now . I will leave you to the argument with the closet creationist . Off to band . Play guitar because we like to
     
  13. Trippy ALEA IACTA EST Staff Member

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    Here's a simple experiment that anyone can do at home, to illustrate my point.

    It's a little rough and ready, however...

    Crack open some image editing software, for example, paint.net - anything with an actual colour wheel controled by sliders will do.

    Set Blue to zero and red to about 85 (roughly representative).

    Now, slide the green slider around and notice something - because of how our eyes work, the colour remains green until the slider gets below about 90.

    Why is this relevant? Because it shows what I (and others) have been saying.

    plants are only green because they absorb more of the red and blue ends of the spectrum than they do of the green.

    Because of the amount of Red light, and the amount of blue light chlorophyll absorbs, it would have to absorb a lot of green light for it to appear as anything other than green.
     
  14. MacGyver1968 Fixin' Shit that Ain't Broke Valued Senior Member

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    Rock on dude.
     
  15. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    What kind of idiot would say something as stupid as that?

    Leaves are green because chlorophyll doesn't use the blue green yellow part of the spectrum to make sugars.
    Not efficiently anyway.
    Those colours are reflected back from the plant.
    I'm not going to go back and read all the posts, but how in God's name has this thread gone on so long?

    Also, by design or chance, or something we know nothing about, nature contrives to be beautiful.
    Imagine if grass was red for example. Awful.
     
    Last edited: Jul 22, 2011
  16. Enmos Staff Member

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    The whole thread is irrelevant. Green Plants have been doing extremely well for at least two billion years.
    They have problems? Hmm..
     
  17. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    That's partially true. But our eyes don't need to capture and transport masses of energy.
    A single photon will excite a photoreceptor.

    Nature has efficiently used a very similar molecule for the carrying of oxygen in the blood and the capturing of energy in plants.

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    Neat trick, don't you think?

    When you said there was no engineering problem in plants using the whole spectrum you were probably wrong.
    You need to go a bit more into detail if you want to support that argument.

    Green plants actually use two energy gathering molecules, Chlorophyll and erm, another one.
    Each takes energy from only a small part of the spectrum.
    Chlorophyll is the main one, and the other one augments it.

    There must be a problem with using more chemicals to capture the missing frequencies, otherwise nature would have done it.
    It is likely that it would make the system less efficient.

    By the way. If you are disagreeing with Trippy on matters concerning Chemistry, it is far more likely that you have misunderstood him, than that he has made a mistake. Have some humility, and go back over his answers.
     
    Last edited: Jul 22, 2011
  18. MacGyver1968 Fixin' Shit that Ain't Broke Valued Senior Member

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    Read the first sentence of your post for the the answer.
     
  19. esbo Registered Senior Member

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    I got high grades in Chemistry at school, I was the best in my class.
    There is no problem with chemicals capturing other frequencies, if Tricky is good at chemistry he should know that. I am not saying he has made a mistake just barking up the wrong tree.
     
  20. Me-Ki-Gal Banned Banned

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    How much longer before you give us your Hypothesis then ? Patiently waiting for your world to change
     
  21. billvon Valued Senior Member

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    I don't think that's true. Photosynthesis is remarkably inefficient; even a perfectly set up experiment produces only 11% conversion efficiency, with most plants clocking in at 3 to 6%. Commercial solar PV panels can hit 16%, and we've made cells that hit 42%.

    The important part is that photosynthesis in plants is efficient _enough._ Most plants are more raw material limited (water, nutrients) than sunlight limited.
     
  22. adoucette Caca Occurs Valued Senior Member

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    Energy varies by the frequency of the photons and "Blue" photons have much more energy (thus plants prefer them over green and there are many more "Red" photons then "green" photons, even though they have less individual energy)

    As Trippy's graphs show, plants do absorb and utilize a considerable fraction of green photons, and photosynthetically active radiation for plants is the entire visible range (400-700 nm). Plants also have accessory light harvesting pigments such as chlorophyll b and carotenoids that have absorbance in the green range, such that for the whole leaf a good fraction of green photons are absorbed, but still there is a slightly greater reflectance of green light compared to blue or red which is what makes plants look green to us, partly because our eyes are more sensitive to green. If our eyes were sensitive to Infrared we would not think of leaves as green at all.

    http://www.giss.nasa.gov/research/briefs/kiang_01/
     
  23. Trippy ALEA IACTA EST Staff Member

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    Plants use Chlorophyll a& Chlorophyll b. The difference in structure between them is in one of the groups attached to the ring. Chlorophyll a has a methyl group where Chlorophyl b has a formyl group. The formyl group extends the conjugation in the ring system, and has the net effect of compressing the peaks - the high energy peak is shifted to a lower wavelength, and the lower energy peaks are shifted to higher energy peaks, which improves the frequency coverage.

    Additionally, plants use a variety of antenna pigments that improve coverage in the green part of the spectrum, absorbing sunlight and passing the energy to Chlorophyll a (chlorophyll b is also classed as an antenna pigment) which then uses that energy to extract an electron from water, which is passed along to the electron transfer chain.
     
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