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a SUPER DUPER DIFFICULT QUESTION!!!! PLEASE HELP!!!!!!

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a SUPER DUPER DIFFICULT QUESTION!!!! PLEASE HELP!!!!!!

Postby thewax » Sun Apr 05, 2009 11:43 pm

I'm not sure where this question should go, as there is some chemistry involved. But I saw this concept in my biology book, so I placed my super hard question here. Any help is greatly appreciated.

NOTE: This is NOT a homework question. This is just a question I stumbled upon as I was trying to understand the text.

We know that gas flows from a region of higher pressure to a region of lower pressure (a very important concept in the mammarian breathing mechanism). WHY does this happen???????

I guess my confusion stems from the fact that (according to my book) the property above and diffusion are totally different things, as evident in transpiration. Diffusion would take forever, but thanks to transpirational pull ( which utilizes the property above), transpiration does not a decade to bring a water molecule up the stem. But I can't think of anything else either than diffusion's mechanism that would explain how the property that gas flows from a region of higher pressure to a region of lower pressure works. Please help!!!!

I thank you in advance.
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Postby plasmodesmata11 » Sun Apr 05, 2009 11:58 pm

According to wiki...
Mass flow is caused by the decrease in hydrostatic (water) pressure in the upper parts of the plants due to the diffusion of water out of stomata into the atmosphere. Water is absorbed at the roots by osmosis, and any dissolved mineral nutrients travel with it through the xylem.
could there be any other actions at work, like the capillary effect? I don't know much about transpiration, though...
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Postby thewax » Mon Apr 06, 2009 12:01 am

ummm... that's not my question
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Postby plasmodesmata11 » Mon Apr 06, 2009 1:47 am

is the question the differentiation between transpirational pull and diffusion? i don't understand
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Postby thewax » Mon Apr 06, 2009 3:06 am

sorry. you were right. I will now try to make it a little more clear. There is a main question (bold) and then a side question (italized).

I'm not sure where this question should go, as there is some chemistry involved. But I saw this concept in my biology book, so I placed my super hard question here. Any help is greatly appreciated.

NOTE: This is NOT a homework question. This is just a question I stumbled upon as I was trying to understand the text.

We know that gas flows from a region of higher pressure to a region of lower pressure (a very important concept in the mammarian breathing mechanism). WHY does this happen???????

I guess my confusion stems from the fact that (according to my book) the property above and diffusion are totally different things, as evident in transpiration. Diffusion would take forever, but thanks to transpirational pull ( which utilizes the property above), transpiration does not a decade to bring a water molecule up the stem. But I can't think of anything else either than diffusion's mechanism that would explain how the property that gas flows from a region of higher pressure to a region of lower pressure works. Please help!!!!

I thank you in advance.
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Postby mith » Mon Apr 06, 2009 4:13 am

It is diffusion, note that the gas has a much higher velocity than water molecules.
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Postby thewax » Mon Apr 06, 2009 6:06 am

uh... what question are you answering?
In the future, please post the question you are answering and then answering.
Thanks for answering, though. :)
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Postby thewax » Mon Apr 06, 2009 7:07 am

how about this: why does gas flow from a region of hihger pressure to a region of lower pressure????
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Postby mith » Mon Apr 06, 2009 3:29 pm

It answers both.
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Postby thewax » Mon Apr 06, 2009 4:50 pm

THANKS! :)

So let me clarify:
Question: why does gas flow from a region of higher pressure to a region of lower pressure - WHAT IS ITS MECHANISM??????
Answer: This is the same mechanism as diffusion (as gas molecules move much faster than water molecules).

Question: My book says that a FLUID (MEANING EITHER LIQUID OR GAS) flows from a region of higher pressure to a region of lower pressure - WHAT IS ITS MECHANISM?????? In terms of water ( in transpiration), diffusion WILL NOT diffuse fast enough up the stem.

Question: Explain the MECHANISM of negative pressure.

Please answer the last two questions and see if the answer to the first question was correct. I appreciate any help and insight made into this difficult question.
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Postby Darby » Mon Apr 06, 2009 7:10 pm

There is one additional component - space.

Lower-pressure gas is fewer molecules in space - closer to a vacuum. What's happening is essentially diffusion, but the particles move faster because there's almost nothing in their way. In liquid, there are more collisions and redirections of the particles as they diffuse.
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Postby thewax » Thu Apr 09, 2009 5:58 am

Thanks very much! :)

ARE YOU SAYING THAT NEGATIVE PRESSURE IS DIFFUSION??????????????
Can someone verify this?
Wiki doesn't seem to have this... :(

Excerpted from Campbell, Reece biology: "Diffusion in a solution is fairly efficient for transport over distances of cellular dimensions (less than 100 umeters), but it is much too slow to function in long-distance transport within a plant. For example, diffusion from one end of a cell to the other takes seconds, but diffusion from the roots to the top of a giant redwood would take decades or more... In xylem, it is actually tension (negative pressure) that drives long-distance transport... In contrast, bulk flow depends only on pressure..."

PLEASE EXPLAIN!!!

The stuff from my last post are pasted here as the questions weren't really answered.

Question: why does gas flow from a region of higher pressure to a region of lower pressure - WHAT IS ITS MECHANISM??????
Answer: This is the same mechanism as diffusion (as gas molecules move much faster than water molecules).

Question: My book says that a FLUID (MEANING EITHER LIQUID OR GAS) flows from a region of higher pressure to a region of lower pressure - WHAT IS ITS MECHANISM?????? In terms of water ( in transpiration), diffusion WILL NOT diffuse fast enough up the stem.

Question: Explain the MECHANISM of negative pressure.

Please answer the last two questions and see if the answer to the first question was correct. I appreciate any help and insight made into this difficult question.
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