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Transpiration - please help!

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Transpiration - please help!

Postby thewax » Sun Mar 08, 2009 1:15 am

Note: This is not a homework question. I poured many hours into investigating this problem (including researching into websites and textbooks) and I still can't figure it out! Please help!

Question: My textbook uses a lot of complicated terms (and complicated descriptions) to describe transpiration. It emphasizes the importance of (lowering) water potential and my first question is: what role does water potential (and please describe water potential too) play in transpiration???????? I did a bit of research and from research I gathered that, relevant to this question, water potential was mainly due to osmosis. However, reading on a little more in my book, it emphasized how osmosis/diffusion was NOT the main force for transpirational pull. It talked about negative pressure (tension). My second question is: what role does negative pressure (tension) play in transpirational pull?????????????? My book talked about bulk flow, mainly pressure, was the main force for transpirational pull (not diffusion). It talked about how how transpiration reduced the pressure in the xylem. Could someone explain to me how the reduction of pressure would help with the transpirational pull??????????? Here's what I think - (and could anyone tell me if my idea is right?) - it is based on the principle that "a fluid tends to flow from an area of high pressure to an area of low pressure"???????????????????
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Postby mith » Sun Mar 08, 2009 8:32 pm

You should know what water potential and diffusion means, both terms are used in the accepted model to describe water evaporating from leaves. Note how it affects "pressure" and you're almost there.
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Postby thewax » Sun Mar 08, 2009 8:50 pm

Thanks for the response! :)
Can anyone else (answer all my questions)??????????
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Re: Transpiration - please help!

Postby lehaiyen » Mon Apr 20, 2009 5:24 am

Hi, this is the answer of 1st question:

Water make the guard cells to be full, the slot between 2 cells open widely.So, the traspiration takes play strongly.

There are some association between the water molecules together as well as the water molecules and the pipe's wall, so the transpiration takes place constantly.
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Postby thewax » Sun Apr 26, 2009 5:41 am

THANKS EVERYONE!!!!!! :)
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Postby Pokie » Tue Aug 02, 2011 7:47 am

Hydrogen Bonding is extremely important in the process of Transpiration as it is what hold the water molecules together and push it up the xylem.

During Transpiration, water on the cell walls of the spongy mesophyll cells evaporate, leaving a thin layer of water due to the presence of hydrophilic cell wall of the plants which holds onto the water. Due to the difference in water potential between the inter-cellular air spaces and the water on the mesophyll cells, the film is pulled towards the spaces of the cells, to evaporate, thus with hydrogen bonds between each molecule (as water is polar molecule, there are weak hydrogen bonds between each and every molecule) water is pulled upwards due to the tension at the film of water on the mesophyll cells. Furthermore due to the hydrophilic walls of the xylem (as it is made up of hydrophilic cell walls), passing water molecules can create hydrogen bonds with it, which is then destroyed as the water moves upwards, and created again with a different section of the wall. By doing so, water counter the pull of gravity and move upwards to the leaf for transpiration without the water breaking off into sections.
Source(s):
My Biology Textbook :)
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