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Biology: Simple Transpiration

  1. May 19, 2007 #1
    Explain this:
    This is what may book says:
    I say if the humidity increases, atmospheric pressure will decrease. Transpiration rate should be more.
    again in my book:
    Isnt this point gets biased with the first one.

    Please explain these.
  2. jcsd
  3. May 19, 2007 #2
    So no one (like me) knows about transpiration it seems.....
  4. May 21, 2007 #3

    jim mcnamara

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    Staff: Mentor

    Air pressure is the pressure from ALL of the molecules, including water vapor.

    So, if humidity goes up transpiration rate goes down. This is why plants in arid environment often have small leaves or no leaves at all - like cactus. The humidity is so low that transpiration has to be restricted or the plant will wilt.
    Plants also have other mechanisms to control opening and closing stomata to control trspirational water loss.
  5. May 23, 2007 #4


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    Staff Emeritus
    Science Advisor
    Gold Member

    This statement is the incorrect assumption that is leading to the confusion.

    Also, as Jim alluded to, if you have lower air pressure, water more easily vaporizes from liquid to gas. Have you taken any chemistry classes yet? This is easiest to understand if you have had a chemistry class and recall those diagrams of how temperature and pressure affect the phase transitions from solid to liquid to gas of molecules.
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