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Do plants need direct sunlight?

  1. Oct 13, 2015 #1
    We all know the famous theory that an asteroid hits the earth and kill the dinosaurs by starting a chain reaction where the dust is all over the atmosphere preventing sunlight to reach plants causing them eventually to die thus causing herbivorous to die thus causing carnivorous to die.
    But when that happens did a complete darkness fell to the earth or a twilight ? I mean do plants need direct sunlight to make photosynthesis or can they do ok with dim lights too?? isn't visible lights' photons is enough for photosynthesis even scattered from clouds like in an overcast day? do they really "see" the sun directly? does that also mean they need UV too?
  2. jcsd
  3. Oct 13, 2015 #2
    I believe some plants need sunshine and others which are fond of living in the shades cannot stand direct sunshine; so just culture them based on different characteristics.
  4. Oct 14, 2015 #3

    jim mcnamara

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    Staff: Mentor

    It just is not that simple.

    Many plants survive for years as a propagule - a spore, as seed. Example: bean seeds found in Anasazi ruins in the Southwest US were dated to about 1250CE, 700+ years ago. One researcher planted a few of them for fun, and some germinated. This is the source of Anasazi beans - those blantantly spotty brown and white beans. See the picture in the middle of the page:

    Plants can go dormant for long periods of time. Arctic willows can go dormant for years until a "warm enough" summer happens.

    Note: the arctic willows and Anasazi bean plants are full-sun species, meaning they need direct sun or at least no shade for most of the day.

    Also, the mass extinction at the end of the Cretaceous, took out 50% of species. See:
    The other 50% had to have been some plants and algae (for food) or none of the mammal species would have survived. Algae and plants have to exist in a terrestrial ecosystem. They are the source of energy for everything else. Also, species that existed well before the extinction are still with us. Tuatara (lizard that neeeds warmth), palm species, and tulip poplar trees, for example.

    So you may want to rethink your assumptions about the Creataceous mass extinction event. It is not a black-and-white turning off the sun kind of thing which unfortunately, some people mention.
    Last edited: Oct 14, 2015
  5. Oct 14, 2015 #4
    Not all of the photosynthesising plants died out, if they did there would be none left in existence today.
    There would still have been some parts of the Earth able to maintain an ecosystem at a reduced level, while in other parts it collapsed due to food shortages.
    What photosynthesis does is capture light and converts the energy into chemical forms that the plant needs for growth and reproduction, it's really quite a complex cycle of biochemistry with several stages involved.
    These chemical forms, sugars etc, are also food as far as herbivores are concerned.
    Most plants use visible light particularly in the blue and red parts of the spectrum
    UV doesn't seem to be important and in excess can be damaging to plants.
    Some plant species require a lot of light and grow rapidly, others get by with much less light but grow slowly.
    Last edited: Oct 14, 2015
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