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Photosynthesis occurs in all plant life and makes plant green

  1. Dec 24, 2006 #1
    Photosynthesis occurs in all plant life and is responsible for making them green.

    Why are not all plant life green. I.e. flowers can be yellow, red and some leaves too like the leaves of Poinsettia. Is the reason because no photosynthesis goes on in them? Or is something else more dominant which gives them their distinct colours. If so what usually is that something?

    Does the red or yellow autum leaves suggest their photosynthetic abilities have died? So does that colour suggest death soon for these leaves (i.e. sign of old age)?
     
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  3. Dec 25, 2006 #2

    Gokul43201

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    You've got this backwards. It is the green pigment (chlorophyll a) which primarily enables photosynthesis, and not the other way round.
     
  4. Dec 25, 2006 #3
    Thats interesting. I read in a (physics) book that the fact that plants are green suggest photosynthesis recquires all colours except green. From what you suggest, this seems wrong?
     
  5. Dec 25, 2006 #4

    Gokul43201

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    There may be some truth to this, though I'm fairly certain that there are some other pigments which also enable photosynthesis, and are not green (I think chlorophyll b is one). These, I think, are a minority.

    In any case, I misinterpreted the statement in the OP, thinking you were suggesting that photosynthesis is directly responsible for the formation of the green pigments.
     
  6. Dec 25, 2006 #5

    jim mcnamara

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    Not all plants have chlorophyll a - Cuscuta spp (dodder, a parasitic plant) are an example.

    FWIW.
     
  7. Dec 25, 2006 #6
    So they wouldn't look green.
     
  8. Dec 26, 2006 #7

    jim mcnamara

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    In fact they are pale yellow.
     
  9. Dec 26, 2006 #8

    marcusl

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    I remember reading that plants reflect light at the colors (yellow-green) where the sun's intensity is greatest. Furthermore, chlorophyll is related to the light-sensitive compounds used in rods and cones. The conclusion is that appropriately useful light-sensitive compounds are rare and nature used the one it found even though its efficiency is sub-optimal.

    Edit: am not a biologist, would appreciate knowledgeable comments!
     
  10. Dec 26, 2006 #9

    jim mcnamara

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    Chlorophyll a has an absoprtion spectrum with maximum at about 430nm with a secondary max at 662nm. Chlorophyll b: 453 & 642.

    That means if they appear green, green is the color they reflect the most.
    Chl a is light green, Chl b is kinda turquoise.

    Ancillary pigments reflect different colors - xanthins, flavonoids, anthocyanins, etc. Those show up in the Fall when leaves turn colors.

    I don't think the absorption spectrum works out the way you think. Plants want to maximize the light energy they absorb - short wavelengths have more energy. Violet has the most energy in the visible spectrum. Chl a absorbs violet/indigo pretty well.
     
  11. Dec 26, 2006 #10

    iansmith

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    Not all photosynthetic will produce a green pigment. Bacteria have a few different otosynthetic pigment that will produce a different colour. These pigment also absorb at a different wavelength

    Wikipedia has a list but i don`t know how extensive it is.
    http://en.wikipedia.org/wiki/Bacteriochlorophyll
     
  12. Dec 26, 2006 #11
    What about this question in the OP

    "Does the red or yellow autum leaves suggest their photosynthetic abilities have died? So does that colour suggest death soon for these leaves (i.e. sign of old age)?"
     
  13. Dec 27, 2006 #12

    jim mcnamara

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    It means the abscission layer has formed - ie., the main plant has cut off the leaf from the vascular system of the tree/shrub/bush. Your answer is yes, the leaf is dying.
     
  14. Dec 27, 2006 #13
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