Why are plants green?

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

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  1. esbo Registered Senior Member

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    Black would be better.

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  3. S.A.M. uniquely dreadful Valued Senior Member

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  5. esbo Registered Senior Member

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    interesting, however that is an exception to 99.9% of plants.

    Also it has no leaves so basically it is a stalk.


    So not really answered my question.
     
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  7. esbo Registered Senior Member

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    Also it seems to have green leaves:-

    ht tp:/ /ww w.hegartywebberpartnership.com/wp-content/uploads/2011/04/black_bamboo.jpg


    remove 3 spaces from above url
     
  8. cosmictraveler Be kind to yourself always. Valued Senior Member

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    If we shine white light on chlorophyll, its molecules will absorb certain colors of light. The light that isn’t absorbed is reflected, which is what our eyes see
     
  9. scheherazade Northern Horse Whisperer Valued Senior Member

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    The plants respond to the color of light emitted by the sun. When growing plants indoors, one can buy light bulbs of differing light color/temperature for plants. Shade plants have differing light requirements than those that require full sun. Have you ever looked at how many different shades of green that plants come in? It's pretty exotic.

    I thought you might enjoy the following article.

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    The flora may be black on distant planets orbiting dimmer stars

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    http://www.bbc.co.uk/news/science-environment-13130740

    Plants on distant hospitable planets could have developed black foliage and flowers to survive, according to a new study.

    Flora that would appear black or grey to human eyes could have evolved on planets orbiting dim "red dwarf" stars, according to unpublished research that is being presented at the National Astronomy Meeting in Llandudno, Wales.

    This would enable plants to absorb more light to photosynthesise, using their star's light to convert carbon dioxide into organic compounds.

    Jack O'Malley-James, a PhD student and astrobiologist at St Andrews University, focused on multiple star systems thought to be common throughout the universe.

    He used models for star systems with two or three stars with various combinations of Sun-like and red dwarf stars. He then added planets to these models, orbiting around one or more of the stars.
    Exotic plantlife

    The research presumes first that plant life similar to that on Earth could evolve on an exoplanet in the "habitable zone" around its star - which is not a given, but the odds of which are difficult to estimate.

    The idea then is that photosynthesis there would resemble that seen on our own planet, whereby plants use energy from the Sun to convert carbon dioxide and water into oxygen and organic compounds, such as sugars.

    Flora on those planets would have to adapt to very different light conditions in order to photosynthesise.

    "If a planet were found in a system with two or more stars, there would potentially be multiple sources of energy available to drive photosynthesis," said O'Malley-James.

    "The temperature of a star determines its colour and, hence, the colour of light used for photosynthesis. Depending on the colours of their starlight, plants would evolve very differently."
    An impression of the Gliese 667 solar system Gliese 667 is a triple-star system with planets thought to be close in mass to our Earth

    If a planet's light source comes primarily from a red dwarf, then O'Malley-James believes any possible plant life could be black or grey - but there are other outcomes which are more exotic still.

    One possible scenario is a hospitable planet that receives light from both a red dwarf and a more distant Sun-like star.

    This could lead to two tiers of plantlife populating the same planet - plants using light from the Sun-like star which may be brighter in colour, and a second, darker array of plants using light from the red dwarf.

    "Plants with dim red dwarf suns, for example, may appear black to our eyes, absorbing across the entire visible wavelength range in order to use as much of the available light as possible," said Mr O'Malley-James.

    "They may also be able to use infrared or ultraviolet radiation to drive photosynthesis. For planets orbiting two stars like our own, harmful radiation from intense stellar flares could lead to plants that develop their own UV-blocking sun-screens," he said.

    Mr O'Malley-James's work is being supervised by Dr Jane Greaves of St Andrews, Professor John Raven of the University of Dundee and by Professor Charles Cockell of the Open University.
     
  10. esbo Registered Senior Member

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    You need to explain why plants use chlorophyll as opposed to any other number of chemicals to absorb light energy before your answer carries any weight.
     
  11. cosmictraveler Be kind to yourself always. Valued Senior Member

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    I'm only trying to be making my answer as simple as I can. If you are really interested in what I've stated then it is up to YOU to do more research into the meanings more than I.
     
  12. esbo Registered Senior Member

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    Obviously that goes without saying.

    But why does it contain chemicals which reflect green only?
     
  13. Trippy ALEA IACTA EST Staff Member

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    But they don't - although they start out green, the pigment that gives bannannas their yellow colour is always there, it's just it has more of the green pigment in it, as is the pigment resulting in the yellow colours of some leaves during the winter.

    But most importantly, we have:

    Poinsettia:

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    Shaina Upright Japanese Maple:

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    Not to mention a large variety of plants with variegated leaves, that contain red and green, or green and yellow (it strikes me that I can't recall having seen red and yellow variegation) eg:

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  14. spidergoat Valued Senior Member

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    Interesting question. This is the answer that makes most sense to me, but I'm not a scientist:

    Chlorophyll, (photosystem II and photosystem I), are based on the element Magnesium, and the structure is analogous to hemoglobin in animals which is based on iron. Iron compounds don't absorb red light, so you see red. Magnesium based compounds don't absorb the middle spectrum of visible light, so you see green. reds which are longer wavelength and blues which are shorter wavelength are absorbed in plants for energy to drive metabolic processes, and that energy turns water and carbon dioxide into carbohydrates. So plants physically have no choice but to be green, it was not a selection of evolution.
     
  15. Trippy ALEA IACTA EST Staff Member

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    Further to this:
    It's also not true that Chlorophyll reflects green only. This is the absorption spectrum of Chlorophyll:

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    It shows how much light chlorophyll absorbs at various wavelengths (or colours).

    Chlorophyll appears green to us because our eyes work by summing up the colour of the light accross the entire spectrum, and Chlorophyll absorbs the yellow-red end of the spectrum, and so appears green to us.
     
  16. origin Trump is the best argument against a democracy. Valued Senior Member

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    It is rather odd that green light is reflected and not used by plants since the green wavelenght dominates the solar spectrum. It may just be the limitations of chemistry to most efficiently use light for the manufacture of sugars requires red and blue wavelengths.

    Here is an article that discusses a possible reason. I'm skepticl (as usual) but it is an intersting hypothesis.
     
  17. Trippy ALEA IACTA EST Staff Member

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    Both of the Hypotheses presented in that article kind of make sense - avoiding too much energy and the purple earth.
     
  18. esbo Registered Senior Member

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    I understand your answer perfectly, however you answer is not an answer to my question, it is a relatively trivial fact which shows you do not understand the depth of the question.
     
  19. esbo Registered Senior Member

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    They are not true leaves and even if they were they fail to answer for the vast majority of plants, which is the question.
     
  20. esbo Registered Senior Member

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    It is not an answer as it fail to explain why chlorophyll is used to extract energy as opposed to any number of chemicals.​
     
  21. esbo Registered Senior Member

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    It is true to all extents and purposes you are just being excessively picky in the required wording of the question.

    The chlorophyll bit also is an invalid answer as I have explained.
     
  22. Trippy ALEA IACTA EST Staff Member

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    No it isn't, because Chlorophyll also reflects in the blue part of the spectrum, so the statement that it only reflects green is false.
     
  23. esbo Registered Senior Member

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    Well interesting or whatever but it not really an answer as you have to replain why retinal was purple for a start.
    It is just shifting the goal posts.

    I don't think the chemistry argument is very strong.
     
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