Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why don't plants absorb green light?

  1. Jul 17, 2011 #1
    Seems odd there is a big hole in the spectrum between where they absorb red and blue light?
  2. jcsd
  3. Jul 17, 2011 #2


    User Avatar

    Staff: Mentor

    Please provide a source so that everyone can be on the same page, thanks.
  4. Jul 17, 2011 #3
    Do I really need to provide a source to convince you that plants are green?

    Last edited by a moderator: Apr 18, 2017
  5. Jul 17, 2011 #4


    User Avatar

    Staff: Mentor

    It's the rule. Please provide a source that explains your OP. Not everyone that reads these threads can read your mind.

    And by posting a source for your question, you would also find an answer, which is another good reason to flesh out your question with a preliminary search.


    Last edited: Jul 17, 2011
  6. Jul 17, 2011 #5
  7. Jul 17, 2011 #6
    It is a question, are questions forbidden?

    Will this do?


    It is difficult to find peer review stuff on such an obvious fact, ie that plants absorb red and blue, but not green light.

    It is not the kind of thing which will win you the Nobel prize for biology!!!
  8. Jul 17, 2011 #7


    User Avatar

    Staff: Mentor

    For the sake of people that don't know what you are missing that prompted the question (especially when it's something taught in elementary school), you need to show a source so we can figure out where you are confused or not understanding. Anyway, I posted a very simple explanation for you above.

    In other words, it's for everyone's benefit.
  9. Jul 17, 2011 #8


    User Avatar
    Staff Emeritus
    Science Advisor

    Plants don't absorb green because the molecule they use to absorb EM radiation is chlorophyll, which is itself green. Potentially another molecule could be used but this is how life evolved and having a different pigment molecule may be hard to evolve because of the necessary huge morphological difference i.e. thermoregulation.
  10. Jul 17, 2011 #9
    Evo, I think you are being a bit hard on Joe, even if he does put his questions in a rather awkward way.

    Assuming the question translated is:

    Why do plants reflect the most abundant wavelengths (green/yellow) rather than use them for photosynthesis?

    I thought this a very good question was motivated by this question to trawl the net since I don't know the answer either.

    Firstly a search of PF itself didn't yield an answer.

    Secondly I could cetainly find plenty of people asking this question on the net, but couldn't see one satisfactory answer, although one smart alec offered to email the 'true' answer if you emailed your attempt.

    I found plenty of references to other potential chemical systems using other molecules, including one which used hydrogen sulphide not water as the mediator. This system is chemically favourable over chlorophyll/water and fors the basis of the purple planet theory.

    Fourthly, I found plenty of references to the 'purple planet theory' that early organisms used anaerobic chemistry to photosythesise.

    So I too would be pleased if some knowledgeable member would explain.
    Last edited: Jul 17, 2011
  11. Jul 17, 2011 #10


    User Avatar

    Staff: Mentor

    Firstly - it's the forum rules which Joe chooses not to follow.

    Secondly - I posted an answer. It took me .05 seconds to pull it up in a google search. There was also an answer from a scientist at argonne, but it didn't go into as much detail.


    Asking questions is fine, but an effort should be made to provide some thought or background along with it.
    Last edited: Jul 17, 2011
  12. Jul 17, 2011 #11
    With the greatest respect none of the posts here, or the links they contain, answer the question I posed.

    Joe, since you are online perhaps you would confirm whether my translation is right or correct it if not?
  13. Jul 17, 2011 #12


    User Avatar

    Staff: Mentor

    I don't think you will find any better answers than the ones Ryan and I furnished.
  14. Jul 17, 2011 #13
    No none of the post or links do answer the question.

    I am not sure what you mean by 'my translation' (are you not english speaking normally).

    No the links do not explain it, however I have a theory, but not allowed to post it (or indeed anything).
  15. Jul 17, 2011 #14

    Which is exactly what I said in my first post.

    But I do find it interesting that life may not have originally carried out photosynthesis using more efficient chemistry which utilised the green light (reflecting the red and blue) and later switched to the green coloured chlorophyll using the red and blue and reflecting the green.

    So I think it is a pretty fundamental question to ask why this was, even if we cannot at this moment provide and answer.
  16. Jul 17, 2011 #15


    User Avatar

    Staff: Mentor

    I have no problem with the question, it was how it was posted, it could have been posed much better in order to be clear to anyone that happened upon the post.
  17. Jul 17, 2011 #16
    English is very definitely my native tongue.

    As such I can tell you that your first post was not actually a question, even though it ended with a question mark.
    So Evo was right to seek clarification.
    I also think your response was an over-reaction.

    Having seen several of your other threads develop like this I tried to introduce a bit of softening to re-establish focus for the benfit of all.
  18. Jul 17, 2011 #17

    The problem is saying 'that is how life evolved' is not an answer because that does not explain how or why it evolved that way.

    Eg saying giraffes have long necks because that is how they evolved is hardly a great answer.
  19. Jul 17, 2011 #18
  20. Jul 17, 2011 #19

    My first post was:-
    The first line very definitely was a question, by anybodies definition surely?

    The second line is actually a statement, but it is a statement posed as a question.

    You still do not appear to have explained what you mean by "my translation"?

    Note the above line is not a s straight forward question either but is again posed as a question in the unlikely event you did explain it but I failed to recognise the explanation.
  21. Jul 17, 2011 #20


    User Avatar

    Staff: Mentor

    Why plants use chlorophyl is explained in my first link.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Why don't plants absorb green light?
  1. Greening Earth (Replies: 8)