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PLANTS and LIGHT

  1. Jan 12, 2004 #1
    i have avery simple question that has been bothering me since my childhood. why are plants green? an object is green because it absorbs all colors except green or combinations of colors forming green... what is in the green color that plants do not absorb? why are plants not black so that it can absorb all colors eventually getting more energy from the sun?.... hehe... it may be nonsense but i really need to know.
     
  2. jcsd
  3. Jan 13, 2004 #2
    It's all about Chlorophyll
     
  4. Jan 13, 2004 #3
    It's as Moni says.
    I did a Google search on chlorophyll and found an article of possible interest to you: http://scifun.chem.wisc.edu/chemweek/CHLRPHYL/Chlrphyl.html

    I am sure there are other similar articles that may give you more info, but I found this one to be helpful.
     
  5. Jan 13, 2004 #4
    Yeah i get it, chlorophyll is green, and physics has nothing to do with that...
    if a plant then is exposed to a green light it will not undergo photosynthesis because is reflects green color and eventually not absorbing any energy. is this true?
     
  6. Jan 13, 2004 #5
    In a sense you have this correct, and certainly on the right track. As noted in the article, chlorophyll is sensitive to the actions of specific light wavelenghts more so than other particular wavelenghts. The key is "more so than others"
    That is, chlorophyll photosynthesis can indeed occur with green light only, but, very poorly.
    I suppose the crux of your question is not the mechanisms involved, but rather why. Why is "green" the predominate color in plant nature?
    Luther, the answer is in evolution. That is, yes, we as humans could devise a method that plants could more efficiently utilize the sunlight, but natural evolution really doesn't care what we think. It will progress, very slowly, on it's own terms, regardless of what we think.
    As well, the current situation in plants tends to avoid over-heating from, say, a black pigment.
    Could it be optimized? Of course! But nature works slowly.
     
  7. Jan 14, 2004 #6
    THANKS
    If that be the case humans can alter the composition of the chloropyll to improve its efficiency.

    i cannot really understand ur point...
     
  8. Jan 14, 2004 #7
    The various pigments in plants absorb plenty of sunlight. I do not see how altering the composition of chlorophyll will improve the plant's efficiency. Chlorophyll is not the only pigment in a plant and not even the only of it's kind (there are alpha and beta forms of Chlorophyll that absorb different wavelengths)! Don't take this as being harsh ;)

    As the other guy said, evolution has/is taken/taking care of it ;)
     
  9. Jan 14, 2004 #8
    in physics sense, something is green because it absorbs any collor except green, when something is black, it absorbs all colors.. eventually totally using up energy given by the sun.

    i know not all plants are green, but majority are green... say, a plant is red, it absorbs all colors but red..

    if a plant's chlorophyll is black it can absorb all colors then getting more energy...

    PEACE!
     
  10. Jan 14, 2004 #9
    I think you're missing the point. There is no need for chlorophyll to be black to absorb all colors. The pigments present already absorb a wide range of colors. You would have to change everything the photosystems within the process of photosynthesis also. I'm sure the idea would not pan out.
     
    Last edited: Jan 14, 2004
  11. Jan 14, 2004 #10

    selfAdjoint

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    Photosynthesis uses a particular molecule that employs photons in the deep red portion of the spectrum. This is far from the most efficient use of solar energy, but it's what the plants evolved with and they're stuck with it. Since light falling on the plants has to have this red extracted from it, what is reflected is when lumped together green.
     
  12. Jan 14, 2004 #11
  13. Jan 15, 2004 #12
  14. Jan 15, 2004 #13
    Topically, the answer is because the plants are green, duh :smile: but seriously,

    When you talk about the inefficiency of photosynthesis, does the losing of electrons constitue wastefulness and ineffcieicy? If so, the energy the e- give is used to unite stray ADP+P into ATP. Just a thought, dunno about it's validity.

    I know your ultimate goal is to figure out a way to alter the composition of chlorophyll to make it more efficient. Do you know how this can possibly effect the environment? I don't think making chlorophyll black will solve anything.

    When palladin mentioned overheating I believe he was right. If a plant were to work so hard an absorb all possible energy, it would die. It would transpirate at a much higher rate due to a high internal temperature. I am also not sure if the supply of H2O would hold up.

    Also, you got your answer to the green light question. The plant is still able to go through photosynthesis , but at a poor rate. When would plants be exposed to only green light in nature? Never.

    Now, if your goal is to understand photosynthesis to create more efficient solar panels, that's a different story. I also believe that kind of stuff is already being done.

    Do you understand photosynthesis and it's mechanisms? If not, you should do that before trying to assume you can simply alter the composition of chlorophyll to make it and the plant more "efficient".
     
  15. Jan 15, 2004 #14
    what can be the reasons why the plant has the lowest rare of absorption in a green spectrum? white light compose all colors and one of them is green...

    organisms find their way to survive...

    there is nothing to lose if we try!!!
     
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