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How does a tree work?

  1. Mar 4, 2016 #1
    Hello all you folks!

    This question might not be the most advanced in universe yet I wonder.

    How does a tree for instance suck up water and nutricians from the ground?

    And why does it get rid of all the leaves in the winter (if it is not a pine tree that is)?

    Does it get rid of all the leaves due to not "wanting" to loose heat, or what?

    And the sucking of water, where comes the negative pressure from?

    And if you don't mind, please explain the photo synthesis too.


    Best regards, Edison
  2. jcsd
  3. Mar 4, 2016 #2
    Dropping the leaves saves resources that would be required to protect them against low temperatures and low humidity and it reduces wind force and snow load.
  4. Mar 4, 2016 #3
    Trees don't need to suck water. The tiny capillaries increase suface tension as compared to weight of water.
  5. Mar 4, 2016 #4


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  6. Mar 4, 2016 #5


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  7. Mar 4, 2016 #6

    jim hardy

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    My junior high school science book said the same thing.

    I watched trees sway in the breeze and decided something akin to peristalsis must be going on in those capillaries too, else Royal Palms would blow apart at their base from the hydrostatic pressure.
    Decades later when Hurricane Andrew killed all the Carribean Pines around Homestead i speculated their capillaries got overstressed by the extreme compression / tension and ruptured. The trees more than a couple feet tall that didn't snap or uproot just died.

    So, i'm not alone in my speculation about peristalsis .
    Is there anyplace on earth where the wind never blows? Do trees grow there?

    old jim
  8. Mar 5, 2016 #7
    Why would that be?

    At the base of a capillary tube, in which the water level has risen higher than the free surface, the hydrostatic pressure is just pgh, where h is the depth of the base of the capillary tube from the free surface. I do not see an increase in hydrostatic pressure from the H, the height of water in the capillary tube.
  9. Mar 5, 2016 #8

    jim hardy

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    Quite so.

    How high though can capillary action raise water in a capillary ? Surely not to the top of a tall tree.

    http://web.mst.edu/~numbere/cp/chapter 3.htm#_Toc506795445]
    If σaw is 70 dynes/cm
    and cos(anything) ≤ 1
    then Pc ≤ 2 X 70 /r dynes/cm2
    if 100 microns is a typical xylem diamter
    50 microns is r and is 5X10-3 cm
    Pc is ≤ 2 X 70 / 5X10-3 = 28000 dynes/cm2

    1 dyne/cm2 = 0.0000334553 ftH2O 4°C (39.2°F)

    so Pc is 28000 X 0.0000334553 = 0.94 feet

    so capillary action seemed inadequate even for a small tree
    but this is first time i ever put a number on it.

    "Cohesion" seems counterintuitive but from what i can find is accepted.

    Cellulose and water are both remarkable substances.

    That paper continues:

    He didn't mention physical damage to the xylems from mechanical stress. So that's my personal idea and doesn't meet PF criteria, so take it as just idle chat.

    But i sure learned a good bit figuring out your post. I never thought of it quite that way, my only experience with meniscus was in manometers with comparatively large diameter.
    so thank you for challenging me. Scientific method at work. I learn by asking.
    Another introductory article here, if anybody else is curious.
    https://www.warnell.uga.edu/outreach/pubs/pdf/forestry/Water%20&%20Trees%20Manual%20pub%2012-11.pdf [Broken]

    old jim
    Last edited by a moderator: May 7, 2017
  10. Mar 5, 2016 #9
    So that is to say instead of the strong ionic forces that hold water together, it would not have been possible, for example, for another fluid like oils to rise.
  11. Mar 5, 2016 #10
    Hi old jim!

    I loved to read your posts, they were very interesting and educational. I also liked the way you verified that capillary "suction" does not work higher than roughtly a feet :) The information regarding cohesion-tension theory was also very interesting not to mention the last part of the paper regarding cavitation and embolism. Finally, I find it very nice when people like you don't just deliver links when someone is asking a question. If you know the answer why not just tell it otherwise you may as well ignore the post.

    Best regards, Edison
    I also love your signature :)
  12. Mar 5, 2016 #11

    jim hardy

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    I think that might be so.
    The Missouri University page i linked is really speaking to extracting oil out of sand, and the graphs (if i understand them) show more height from capillary action with lesser concentrations of water.
  13. Mar 5, 2016 #12

    jim hardy

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    Why, Thanks Edison for your kind words. Helps an old guy feel less useless.

    As you can tell that's something i've wondered about for years.
    It always feels good when a previously dark corner of my abysmal ignorance gets partly illuminated.

    Serendipitously, that school in Missouri is my old Alma Mater(bsee 1969) so it was nostalgic to see that old paper with its cgs units. Fresman year I took drafting in the creaky old mining building with its "quaint" 1920's drafting tables and stools.
    Looking to understand Mr 256Bits' inquiry, stumbling across that link took me right back to 1964..

    Thanks to all .

    .....I still wonder why all the Caribbean Pines died.....

    old jim
  14. Mar 6, 2016 #13
    Let's make room for ingnorant me. After rereading the above papers so thankfully supplied by jim hardy a third time, I have come to a tiny understanding of it all when it comes to the sucking part. Water can evaporate (from the leaves?) faster than it can be taken up (by the xylem=cells?) so this creates a tension (suction in my ignorant book). This tension pulls water from the soil up the roots, the stem and to the leaves where it evaporates (again).

    How close to the truth am I?

    Best regards, Edison
  15. Mar 6, 2016 #14
    Hi DrStupid!

    Would you mind explaining exactly all you say here because it does not make any sense at all to ignorant me?

    To make it easy for you:

    1) Saves resources-in what way?
    2) Protection against low temperatures-why and how?
    3) Low humidity-why is that a problem (water and nutricians comes from the ground)?
    4) Wind force and snow load-how can that at all be a problem (and if so, how can the tree know that)?

    Best regards, Edison
  16. Mar 6, 2016 #15
    All processes in living cells need resources and even more resources under stress. These cost for keeping the leaves alive needs to be out- or even overbalanced by a corresponding benefit. It seems this is not the case for broad-leafed trees in winter.

    Living cells must not freeze. That can be prevented by antifreezing compounds.

    In most cases ground water is recharged by precipitation. In winter the average precipitation is significant lower compared to other seasons. That means there is less water available but transpiration is increased due to low humidity of the air.

    The risk to brake off by spring or autumn storms is increased for trees with leaves compared to similar trees without leaves. That's an advantage in evolution.
  17. Mar 6, 2016 #16

    jim hardy

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    I think you're pretty close to the generally accepted 'cohesion' hypothesis ,
    which is what my junior high school science book offered ca 1959 .

    Sounds counterintuitive, doesn't it? Well, it does to anybody who's siphoned gas .

    That's why i latched onto a "pumping action" from the tree's swaying in the breeze which places its opposing sides alternately in tension and compression. Not unlike human veins, where the check valves let our leg muscles aid in pumping blood back toward our heart.

    But there's only scant mention of "check valves" in tree articles.

    I did some searching, check valve xylem
    found a plumbing supply company named Xylem that makes check valves

    and this article which says botanists are developing new techniques to study wood cells

    and this spinoff from it

    Some mechanical pumping aid would sure be easier for me to accept.

    So many interesting questions, so little time..

    old jim
  18. Mar 6, 2016 #17
    I agree with you, check valves in trees just sounds stupid :D

    Best regards, Edison
  19. Mar 6, 2016 #18

    jim hardy

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  20. Mar 6, 2016 #19
    I like this reply. You can almost relate to it by being a human being. The last sentence is however not understood but interesting.
    Understood but in what way does a tree with or without its leaves not freeze? I don't understand the difference if it's not the fact that the actual area of leaves makes heat escape (transpire?) the tree if it would keep them in winter.
    So if there is a low amount of water vapor in the air (low humidity) vapor exchange (transpiration) with the air is higher? How can that be? How can a low humidity give rise to higher tranpiration? Would I sweat more if the air was dry? I would almost believe the contrary!
    Please don't just referre to evolution like that, I would almost call that ignorant.

    Finally, thank you for all the detailed answers, I am much obliged!

    Best regards, Edison
  21. Mar 6, 2016 #20
    I think I like you idea better :)

    Best regards, Edison
    But of course these check valves are nice companions to any animal's life.
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