Transpiration - please help!

[thewax]

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"???????????????????

[mith]

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.

[thewax]

Thanks for the response!
Can anyone else (answer all my questions)??????????

[lehaiyen]

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.

[thewax]

THANKS EVERYONE!!!!!!