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Thread: Photosynthesis: exact point in time of its initiation?

  1. #1 Photosynthesis: exact point in time of its initiation? 
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    I want to know the exact point in time of initiation of photosynthesis process in majority of green plants, as a general rule. What is the time at dawn or location of sun below horizon when this process begins. Thanks in advance.


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    This should be in biology.

    I think plants photosynthesize at least to some minute extent 24/7, due to the unnoticeable amount of light that is emitted even in a pitch black room. Though, I'm not sure how much of the spectrum most plants chlorophyll can absorb (most of this light is infrared).


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    Universal Mind John Galt's Avatar
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    This will depend externally upon light intensity and internally upon precise photosynthetic 'arrangement'. Light intensity will depend upon latitude, season, cloud cover, humidity, aerosol content, slope position, adjacent structures and plants, etc.

    In short, a general answer is going to be really hard to come by and an exact point will likely be impossible. (Although you could be precise about the light intensity required for individual speies/genera/families.)
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    Forum Cosmic Wizard paralith's Avatar
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    http://www.marietta.edu/~spilatrs/bi.../photosyn.html

    You can skip the first section about O2 evolution curves, and go right for the photosynthesis response curves. Basically, whenever light energy at any level is available, photosynthesis occurs to some degree - though it may not be detectable by measuring O2 output because some processes within the plant do in fact use up oxygen, and at very low irradiation levels any oxygen that is synthesized is immediately used up. However, different plants have different responses to changing levels in light, depending on the conditions they are adapted to, and these variations can be determined by making photosynthesis response curves.
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    Quote Originally Posted by paralith
    http://www.marietta.edu/~spilatrs/biol103/photolab/photosyn.html

    You can skip the first section about O2 evolution curves, and go right for the photosynthesis response curves. Basically, whenever light energy at any level is available, photosynthesis occurs to some degree - though it may not be detectable by measuring O2 output because some processes within the plant do in fact use up oxygen, and at very low irradiation levels any oxygen that is synthesized is immediately used up. However, different plants have different responses to changing levels in light, depending on the conditions they are adapted to, and these variations can be determined by making photosynthesis response curves.
    I am grateful. I had already gone through the above site. My question is simple and elementary rather. My requirement is to know the point in time at dawn before sunrise when the process is first trigered, as a simple rule; or in other words when before sunrise, when sun is below horizon, the "visible light" becomes available necessary for photosynthesis.
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    Forum Cosmic Wizard spuriousmonkey's Avatar
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    if you had tried to follow the argument constructed in Kalster's post and his source, you would have derived the conclusion that any light of the right quality that hits the plant at the right spot triggers photosynthesis.

    That would mean that there is basically always photosynthesis, unless it is really pitchblack.
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    That would mean that there is basically always photosynthesis, unless it is really pitchblack
    .

    I don't think there is anything of the sort "pitchblack" in the atmosphere, and also it is hard to believe that there is basically always photosythesis. Plants take a "sleep/rest" perhaps like us.

    Search of Britannica has helped somewhat.
    The colour of dawn are never as intense as the colours of sunset except in the range of yellow's and oranges that are in and around the sun and hence reflected on the borders of clouds.

    At dawn because of the long passage the dominant blue wavelengths of light are scattered and blocked, leaving the longer, unobstructed red wavelengths to reach the Earth. Chlorophylls absorb these wavelenghts much more strongly.
    Thanks for the help.
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    Quote Originally Posted by spuriousmonkey
    if you had tried to follow the argument constructed in Kalster's post and his source, you would have derived the conclusion that any light of the right quality that hits the plant at the right spot triggers photosynthesis.

    That would mean that there is basically always photosynthesis, unless it is really pitchblack.
    Thanks, but you mixed me up with Paralith.
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    Forum Cosmic Wizard i_feel_tiredsleepy's Avatar
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    Photosynthesis occurs at all times, I suspect your question is about the light dependent reactions of photosynthesis, and all they require to be triggered is the presence of photons at a wavelength of around 500-800 for plants. Technically all that is required for photosynthesis to happen is two photons to hit a chlorophyll molecule, although no noticeable amounts of light-dependent photosynthesis will happen until daytime.
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