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Author Topic: How do Trees Really lift Water to their Leaves?  (Read 179341 times)

Andrew K Fletcher

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How do Trees Really lift Water to their Leaves?
« on: 23/04/2005 11:07:06 »
Osmosis Capillary action and root pressure are accepted as the driving force for lifting water to the canopy of a giant Californian Redwood, towering a hundred metres and more? And these forces are producing flow rates up to and in excess of a 1000 litres a day in a single tree?

Another theory is that the leaves, which are porous, can somehow suck water from the soil and evaporate it through the pores of the leaves? Ever tried sucking on a straw with a hole in it?


Maybe there is another explanation:

Herald Express, July 6, 1995, page 19.   (local paper in Torbay, Devon)

Eureka!

Cliff experiment pulls plug on 300 year old law of physics

A Revolutionary breakthrough claimed by a Paignton man is to be investigated by top scientists.
Ideas man Andrew K Fletcher claims he has disproved a fundamental law of physics dating back to the 17th century.
And impressed by the historic experiment at Overgang cliff, Brixham, to raise water 78 feet without the support of any artificial aids,
John Hunt, Senior forestry Officer for Devon and Somerset who witnessed the experiment's success last Friday said: 'It was quite impressive.

The rule that water will only rise 32 feet under atmospheric pressure when in a column was effectively disproved."

But Mr Hunt explained that he is a professional forester not a scientist and a report on the experiment would be sent to the Forestry commission 's Alice
Holt Research Station, near Farnham in Surrey, for further investigation.
Mr Fletcher's experiment involves a long water filled plastic tube, strung up the cliffside with both open ends placed in two filled demijohns.
A small amount of a salt solution is added at the top of the tube before it is completely filled with water, this acts as a liquid pulley says
Mr Fletcher, lifting water from one demijohn to the other, thereby disproving Torriceli's 17th century law.
This explains how trees can raise water to their tops beyond the 32 feet limit."
said an ecstatic Mr Fletcher. He believes that the discovery also suggests a mechanism by which all life on earth has evolved from the ground.

The Experiment at Brixham Overgang Cliffs where water flowed vertical up a single 6 mm bore tubing using 10 mils of salt solution, demonstrating that a tiny amount of denser solution can lift effortlessly many thousands of times it’s own volume in water without any artificial aids, demonstrating clearly a non living physical cause of bulk flow in plants trees, animals and humans. The 10 metre limit for lifting water clearly needs some serious revision. View The Historic Event on Youtube as it unfolded all those years ago and ask why has this important discovery been ignored for so long.

Radio Interview with Patrick Timpone on One Radio Network
https://www.youtube.com/watch?v=x68PLE8MXJE
20 years ago Andrew made a phenomenal discovery in circulation and how gravity acts upon fluid density changes that take place in all fluids where water is evaporated. In trees (Where this theory began) evaporation from the leaves alters the density of sap. In the body, the warm lungs and airways provide the same density changes in the blood and other fluids. It was not long before it became obvious that posture was incredibly more important than anyone could imagine. To make use of these density changes and allow them to assist the circulation all we needed to do was to manage our posture.
This was a Eureka moment of such magnitude it went off the scale for Andrew and instantly gave birth to Inclined Bed Therapy.
Show Highlights:
-Andrew explains how learning about how trees uptake water led him to understand the benefits of inclined bed therapy

Video of the Brixham Experiment on Youtube: http://www.youtube.com/watch?v=sz9eddGw8vg

Video introduction to density flow on Youtube: http://www.youtube.com/watch?v=PVwSIeWMSkc

Video of a scaled down version of the Brixham Experiment on youtube: http://www.youtube.com/watch?v=FjWe6kLHcLU

Video of a simple experiment to show density flow in boiling sugar syrup. http://www.youtube.com/watch?v=187awfsgHoY


http://andrewkennethfletcher.blogspot.com/


Andrew K Fletcher


Medical Physics Newsletter publications:

http://groups.iop.org/ME/archive_newsletter2002010.htm

http://www.iop.org/activity/groups/subject/med/Newsletter/2003_Archive/page_8262.html

 
Let's start with Osmosis
The work Of Professor H.T.Hammel:
EVERYTHING YOU WERE TAUGHT ABOUT OSMOSIS IS WRONG.


Osmosis is the reason that a fresh water fish placed in the ocean desiccates and dies. Osmosis is the reason that blisters form on fiberglass boat hulls. Osmosis is how waste products of metabolism enter and leave the blood stream. Osmosis determines how you, me and every living thing lives and dies. One would think that a civilization that spends billions of dollars every year on medical research would understand something as basic as osmosis. Wrong, wrong, wrong.
Source: http://www.yarbroughlaw.com/Osmosis.htm
 
Or what about Root Pressure?

Roots can squeeze water to the tops of trees? You what?. ROFLMAO. Sorry but every time I read about root pressure it makes me cringe.

Or maybe capillary action? In other words, a tree is a giant sponge capable of blotting water from below ground level to heights in excess of a hundred metres at flow rates that can exceed a thousand litres of water a day in a single tree.

Does the cohesion tension theory suck? How can leaves create suction when there are pores in them open to the air? Is it not like trying to suck water through a straw with holes in it? And what about when the leaves have fallen in Autumn, where is this magical cohesion generated when there are no leaves?

And then there is the problem with Strasburger's experiments, where he killed all of the living cells in a tree suspended vertically in a bath of picric acid with the roots removed and observed the continued evaporation of the poison several weeks after the death of the tree.


Andrew
« Last Edit: 17/07/2014 07:47:35 by Andrew K Fletcher »

daveshorts

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Re: How do Trees Really lift Water to their Leaves?
« Reply #1 on: 23/04/2005 11:51:55 »
There is a copy of this in the science trivia section, it might make sense to post comments there, as otherwise the discussion will get fragmented.

Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #2 on: 23/04/2005 16:47:04 »

l_kryptonite
 
[Another theory is that the leaves, which are porous, can somehow suck water from the soil and evaporate it through the pores of the leaves? Ever tried sucking on a straw with a hole in it?]

I don't get it
Is there a typo here or am I terminally thick?
 
 
Andrew K Fletcher
 
I don't get it either!

 
Andrew K Fletcher

Strange, I thought everyone would be rushing in to defend these pathetic substitutes for common sense
 
l_kryptonite

 Posted - 17 Apr 2005 :  10:16:38    
 
I think you'll find that is supposed to read, "...leaves, which are porous, can somehow suck water from the air and evaporate it..."

This is true. Plants absorb nutrients from a liquid foliar feed faster than from the root system. it is even possilbe to force feed too much by this method.
Imagine, if you will, the effect and absorption rate of a drug which is spread over the entire surface of one's skin, compared to that ingested. the differences would be radical.
 
 
Andrew K Fletcher

 Posted - 17 Apr 2005 :  15:38:34          
 
Nope, the cohesion theory states the long thin threads of water are drawn up to replace the evaporated water,

But there is definately a mechanism for trees to draw water from the atmosphere. I removed a budlia. The trunk had virtually rotted in half and the small shrub like tree fell with very little effort. It remained on my drive throughout the end of last summer and appeared to be dead. The drive is concrete btw. I removed it a few weeks ago to the tip and was amazed to find that it had began growing vertically, despite having no root system and had been thoroughly dehydrated during the summer. I was also amazed at a new species of magnolia, which came from a seed found in a grain storage container, found buried in one of the Egyptian Pyramids.

The bit about absorption though the skin is something I am familiar with and have used to good effect a freshly squeezed lemon, rubbed over my body when I feel a cold coming on, it either vanishes or does not infect me, even though the people around me have it :)

Still does nothing for the conventional theories.

Good point though

 
Andrew K Fletcher

 Posted - 23 Apr 2005 :  11:48:42          
--------------------------------------------------------------------------------
« Last Edit: 16/05/2005 20:58:54 by Andrew K Fletcher »

Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #3 on: 24/04/2005 14:20:35 »
What is the purpose of the massive loss of water in the transpiration process? 98% all water drawn through the roots is evaporated through the leaves and trunk. So what is the purpose of this? And what about the massive loss of moisture from the respiratory system, eyes and the skin, Anyone shed some light on its function?

Death is natures way of telling us to slow down.

daveshorts

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Re: How do Trees Really lift Water to their Leaves?
« Reply #4 on: 24/04/2005 19:42:52 »
There is a really good link that explains a lot about water transpot in plants here:
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/X/Xylem.html

Plants do appear to waste a whole lot of water, I guess that is because they have to move a certain amount of minerals up the tree each day.

The xylae must be at a considerable negative pressure, so to move water etc from them into the leaves there must be much more salts and sugars in the leaves to draw the water by osmosis out of a xylem. this means that to get a decent difference you must need a very dilute solution in the xylem. So to move a given amount of nutrients up the tree you need to use lots of water.

I expect there are much more efficient ways of moving nutrients but they would involve changing an awful lot of evolution. Also if water is cheap but energy is expensive, why waste sugar moving the nutrients when you can do it with water and a bit of heat...

Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #5 on: 25/04/2005 08:29:36 »
Hi David

I agree that there may be a density change at the leaf, due to the very high evaporation rates from the sap, which contains sugars produced by the leaves and minerals drawn up in dilute form from the soils? In fact, it would be impossible for this massive loss of moisture to not alter the density of the sap at the leaf, would you agree with this statement?

Andrew

Leaves do after all look more like washing hung out to dry than effective solar panels.



Death is natures way of telling us to slow down.

Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #6 on: 25/04/2005 08:45:24 »
GCSE Basic Physiology and water transport.

OSMOSIS ?

"I have chosen to relate to the following text book because it is written by a person who like myself is not entirely satisfied by the explanations put forward in the relevant subjects".

 
Figure C’s results raise the questions; What is osmosis and how are its qualities explained in the text books.

For the currently accepted view of osmosis and all other views on water transport I will refer to one of the standard GCSE text books entitled GCSE BIOLOGY, D.G. Mackean. ISBN 0-7195-4281-2 first published in 1986.

Page 34 fig 3 Diffusion gradient

Page 36 OSMOSIS

Osmosis is the special name used to describe the diffusion of water across a membrane, from a dilute solution to a more concentrated solution. In biology this usually means the diffusion of water into or out of cells Osmosis is just one special kind of because it is only water molecules and their movement we are considering. Figure 3 showed that molecules will diffuse from a region where there are a lot of them to a region where they are fewer in number; that is from a region of highly concentrated molecules to a region of lower concentration. Pure water has the highest possible concentration of water molecules; it is 100% water molecules, all of them free to move.

Figure 9 shows a concentrated sugar solution, separated from a dilute solution by a membrane, which allows water molecules to pass through. The dilute solution, in effect contains more water molecules than the concentrated solution. As a result of this difference in concentration, water molecules will diffuse from the dilute to the concentrated solution. The level of the concentrated solution will rise or, if it is confined to an enclosed space, its pressure will increase. The membrane separating the two solutions is often called selectively permeable or semi-permeable because it appears as if water molecules can pass through it more easily than sugar molecules can.

Osmosis then is the passage of water across a selectively permeable membrane from a dilute solution to a concentrated solution.

This is all you need to know in order to understand the effects of osmosis in living organisms, But a more complete explanation is given below.

ALTERNATIVE EXPLANATION FOR OSMOSIS

The current text book explanation for osmosis appears to have ignored the effects of gravity on liquids. The constant pull of gravity acts differently on concentrated solutions than dilute solutions i.e. The concentrated solution is heavier than the dilute solution and will always settle at the bottom of a reservoir or in this case a vessel.

 
To see this clearly, picture Fig 9 without the membrane; the result would be that the concentrated solution would sink and the dilute solution would rise. This effect will not stop because of the membrane. The concentrated solution will still cause the dilute solution to rise as we have seen earlier; and as the concentrated solution moves into the opposite side containing the dilute solution, the dilute solution is dragged through the membrane in a circular motion. For every action there must be a reaction. In order to prove this point add a little dye to the sugar solution and watch the exchange between the liquids.

"When the effect that gravity exerts on concentrated solutions is added to the equation of water transport and osmosis, it gives us a very clear understanding of the driving mechanisms involved".

Chapter 7 Transport in plants

page 71

The main force which draws water from the soil and through the plant is caused by a process called transpiration. Water evaporates from the leaves and causes a kind of ‘suction ‘ which pulls water up the stem. The water travels up the vessels in the vascular bundles and this flow of water is called the transpiration stream. The water vapour passes by diffusion through the air spaces in the mesophyll and out of the stomata. It is this loss of water vapour from the leaves which is called transpiration. The cell walls which are losing water in this way replace it by drawing water from the nearest vein. Most of this water travels along the cell walls without actually going inside the cells. Thousands of leaf cells are evaporating water like this and drawing water to replace it from the xylem vessels in the veins. As a result , water is pulled through the xylem vessels and up the stem from the roots. This transpiration pull is strong enough to draw up water 50 metres or more in trees.

Page 72

Most of this water evaporates from the leaves; only a tiny fraction is retained for photosynthesis and to maintain the turgor of the cells. The advantage to the plant of this excessive evaporation is not clear.

A rapid water flow may be needed to obtain sufficient mineral salts, which are in very dilute solution in the soil. Evaporation may also help to cool the leaf when exposed to intense sunlight.

Against the first possibility it has to be pointed out that, in some cases, an increased transpiration rate does not increase the uptake of minerals.

Many biologists regard transpiration as an inevitable consequence of photosynthesis, in order to photosynthesise, a leaf has to take in carbon dioxide from the air. The pathway that lets carbon dioxide in will also let water vapour out whether the plant needs to lose water or not. In all probability, plants have to maintain a careful balance between the optimum intake of carbon dioxide and a damaging loss of water.

Page 73

Humidity if the air is very humid, i.e. contains a great deal of water vapour, it can accept very little more from the plants and so transpiration slows down. In dry air, the diffusion of water vapour from the leaf to the atmosphere will be rapid. ( " I will deal with this point later on because it is very important and has implications for human health ") Air Movements: In still air, the region round a transpiring leaf will become saturated with water vapour so that no more can escape from the leaf. In these conditions, transpiration slows down. In moving air the water vapour will be swept away from the leaf as fast as it diffuses out. This will Speed up the transpiration. Furthermore, when the sun shines on the leaves, they will absorb heat as well as light. This warms them up and increases the rate of evaporation.

Page 73 continued Water movement in the xylem

You may have learned in physics that you cannot draw water up by suction to a height of more than about ten metres. Many trees are taller than this yet they can draw up water effectively. The explanation offered is that, in long vertical columns of water in very thin tubes, the attractive forces between the water molecules are greater than the forces trying to separate them. So in effect the transpiration stream is pulling up thin threads of water which resist the tendency to break.

There are still problems however, it is likely that the water columns in some of the vessels do have air breaks in them and yet the total water flow is not affected. The evidence all points to the non-living xylem vessels as the main route by which water passes from the soil to the leaves.

"This statement suggests that the long thin tubes of the tree ,are used for water transport, which are none-living , therefore must represent the tubes used in my experiments at Brixham."

Page 74

Root Pressure

In Experiment 8 on page 79 it is demonstrated that liquid may be forced up a stem by root pressure from the root system. The usual explanation for this is that the cell sap in the root hairs is more concentrated than the

soil water and so water enters by osmosis (see page 36). The water passes from cell to cell by osmosis and is finally forced into the xylem vessels in the centre of the root and up the stem.

This is rather an elaborate model from very little evidence. For example, a gradient of falling osmotic potentials from the outside to the inside of a root has not been demonstrated. However, there is some supporting evidence for the movement of water as a result of root pressure.

root pressures of 1-2 atmospheres have been recorded, and these would support columns of water 10 or 20 metres high. Some workers claim pressures of up to eight atmospheres (i.e. 80 metres of water)

" A column of water 80 metres high would undoubtedly cause water pressures of eight atmospheres at the roots. However It is very difficult to see how a root could generate 8 atmospheres of pressure."

However, root pressure seems to occur mainly in the young herbaceous (i.e. non-woody) plants or in woody plants early in the growing season and though in many species it must contribute to water movements in the stem. The observed rates of flow are too fast to be explained by root pressure alone.

Transport of salts

The liquid which travels in the xylem is not, in fact pure water. It is a very dilute solution, containing from 0.1to1.0% dissolved solids, mostly amino acids, other organic acids and mineral salts. The organic acids are made in the roots; the mineral salts come from the soil. The faster the flow in the transpiration stream, the more dilute is the xylem sap. Experimental evidence suggests that salts are carried from the soil to the leaves mainly in the xylem vessels.

Transport of food


The xylem sap is always a very dilute solution, but the Phloem sap may contain up to 25 per cent of dissolved solids, The bulk of which consists of sucrose and amino acids.

There is a good deal of evidence to support the view that sucrose amino acids and may other substances are transported in the phloem. The movement of water and salts in the xylem is always upwards, from the soil to the leaf. But in the phloem the sap may be travelling up or down the stem. The carbohydrates made in the leaf during photosynthesis are converted to sucrose and carried out of the leaf to the stem. From here the sucrose may pass upwards to growing buds and fruits or downwards to the roots and storage organs. All parts of a plant which cannot photosynthesise will need a supply of nutrients bought by the phloem. It is possible for substances to be travelling upwards and downwards at the same time in the phloem.

"note the dual flow has been observed in experiments with concentrated solution and water filled tubes."

 
 

Page 74 continued

There is no doubt that substances travel in the sieve tubes of the phloem But the mechanism by which they are moved is not fully understood.

There are several theories, which attempt to explain how sucrose and other solutes are transported in the phloem but none of them is entirely satisfactory.

Page 75

Uptake of water and salts

The water tension developed in the vessels by a rapidly transpiring plant is thought to be sufficient to draw water through the root from the soil. The precise pathway taken by the water is the subject of some debate, but the path of least resistance seems to be in or between the cell walls rather than through the cells.

When transpiration is slow, e.g. at night time or just before bud burst in a deciduous tree, then osmosis may play a more important part in the uptake of water.

One problem for this explanation is that it has not been possible to demonstrate that there is an osmotic gradient across the root cortex which could produce this flow of water from cell to cell. Nevertheless, root pressure developed probably by osmosis can be shown to force water up the root system and into the stem

page 76

The methods by which roots take up salts from the soil are not fully understood. Some salts may be carried in with the water drawn up by transpiration and pass mainly along the cell walls in the root cortex and into the xylem.

It may be that diffusion from a relatively high concentration in the soil to a lower concentration in the root cells accounts for uptake of some individual salts. But it has been shown (a) that salts can be taken from the soil even when their concentration is below that in the roots and (b) that anything which interferes with respiration impairs the uptake of salts. This suggests that active transport (p.35) plays an important part in the uptake of salts.

The thing that becomes clear from reading the established explanations for water transport is that if it were a bucket, very little water would be transported due to the large number of holes in it !



Death is natures way of telling us to slow down.
« Last Edit: 25/10/2008 08:55:11 by Andrew K Fletcher »

l_kryptonite

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Re: How do Trees Really lift Water to their Leaves?
« Reply #7 on: 25/04/2005 10:08:04 »
Okay, now that I've found the other thread...

I was not disputing the cohesion theory; rather trying to make sense of the sentence in question.
 [the leaves, which are porous, can somehow suck water from the soil]
A leaf cannot possibly suck water from the soil because it is not in contact with the soil.  I assumed incorrectly that you were talking about osmosis.  Although not the main method of fluid movement, it is still an important factor in a plant's survival.


{the leaves, which are porous, can somehow suck water from the soil}
Not all leaves look like this; it is dependant on how much sunlight is needed, and how much danger there is of being scorched.
Plants in areas with competition for light will usually have leaves which lie outstretched and will follow the sun's path to some extent.  An easy example is the rubber plant, a jungle dweller which adapts itself singularly well to stuffy, ill-lit dens all over Scotland.
Take a eucalypt in Africa, however, and notice the immediate difference. Long narrow leaves which seemingly hang limp from the branches actually turn during the course of the day to piont the blade like edge toward the sun in an attempt to restrict water loss and scorching.

It seems that you fellows have given me quite a bit of reading to do.

Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #8 on: 25/04/2005 11:28:02 »
With regards to the direction that leaves face due to direction of sunlight or energy, could it be that the internal tension on sap is altered or imbalanced due to more tension on one side of a stem than the less exposed side, causing the stem to contort towards the direction of the energy? I.E. Shrinkage on one side of the relatively new stems in new growth supporting leaves.

Andrew

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daveshorts

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Re: How do Trees Really lift Water to their Leaves?
« Reply #9 on: 25/04/2005 11:54:32 »
What exactly does figure 9 show?

I am not really convinced that gravity can have much affect on osmosis as osmosis will move water from an area of low salt (or other things which won't go through the membrane) concentration to one of high salt concentration whether it be up down or sideways.

I don't understand the arguement above, if the salt is above the membrane, gravity can't cause it to move below the membrane as the membrane is by definition impermiable to the salt...

l_kryptonite

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Re: How do Trees Really lift Water to their Leaves?
« Reply #10 on: 25/04/2005 12:04:32 »
I'm getting way out of my depth here but I don't believe that the same change in tension would cause leaves in one plant to pull one way, and have the reverse effect on another.

Maybe if we knew what makes the leaves of a carnivorous plant move?  Not the trigger, but the motion itself.
The leaves of one mimosa will close at a single touch.  I do know that this is not heat sensitivity because I've tested it.

Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #11 on: 25/04/2005 15:08:04 »
quote:
Originally posted by daveshorts

What exactly does figure 9 show?




FIG 9 represents the standard drawing of osmosis in the GCSE Biol Book referenced above, nothing has changed.



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Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #12 on: 25/04/2005 15:15:43 »
Why not? It simpy depends where the tension is applied surely.

quote:
Originally posted by l_kryptonite

I'm getting way out of my depth here but I don't believe that the same change in tension would cause leaves in one plant to pull one way, and have the reverse effect on another.



I have also thought about the carnivorous plants, and have a venus flytrap in front of me now.

could the insects movement stimulate the release of solutes stored at the leaf to be suddenly released and begin to flow rapidly down the stem, altering the internal pressures in front of the falling solutes to become positive and behind the falling solutes to become negative inducing the leaves to be pulled down around the captured insect by said hydraulic forces?

Andrew

Death is natures way of telling us to slow down.

l_kryptonite

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Re: How do Trees Really lift Water to their Leaves?
« Reply #13 on: 26/04/2005 01:09:23 »
Hm, I believe you may be on to something there.  I'll look into it further.  Maybe interview Dierdrie when she's finished sunning herself this morning.

daveshorts

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Re: How do Trees Really lift Water to their Leaves?
« Reply #14 on: 26/04/2005 17:29:01 »
According to:
http://www.news.harvard.edu/gazette/daily/2005/01/26-flytrap.html
and in more detail
http://www.ias.ac.in/jbiosci/bobji2652.pdf

The fly trap leaf is designed so when primed it is a bit like those toy rubber hemispheres which you could turn inside out and were just about stable, but would turn back the right way round quite violently (the toys would jump in the air).

The Flytrap leaf is just about stable open but with a small change in the rigidity of certain parts of the trap near the trigger cells (possibly due to some osmosis related mechanism) it will flip into it's preferred closed configuration, trapping the poor fly.

Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #15 on: 26/04/2005 18:02:44 »
Thanks Dave, I think Harvard are stating the obvious
You have to admit, it is a bit like saying, when we release the string on a bow, the arrow flies through the air, without adding that we place tension manually on the bow with the addition of a string, then even more tension is added, until the bow string is manually released.

I think what we are trying to establish is how the plant places the charge in its leaves, and the mechanism that causes the leaves to close, which I believe to be a simple hydraulic process, that is easy to demonstrate using very basic and inexpensive lab equipment.

I was hoping that many of the scientists here would rush to defend all the old accepted explanations for fluid transport.



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Re: How do Trees Really lift Water to their Leaves?
« Reply #16 on: 26/04/2005 18:51:17 »
The opening of the trap is less interesting as it happens much more slowly, I would have thought it happened by cells changing shape by gaining or loosing water (possibly by pumping ions in and out of the cells and water following them by osmosis) or by the cells actually growing. I believe it is quite an expensive process energetically for the plant as you can kill it by triggereing it too many times without feeding it.

What do you mean by "all the old accepted explanations for fluid transport." the stuff in the like I posted earlier seemed to be pretty consistent, what is the exact problem?

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Re: How do Trees Really lift Water to their Leaves?
« Reply #17 on: 26/04/2005 20:04:20 »
David

There is no paradigm in the accepted literature that comes remotely close to addressing the bulk flow rates observed in plants and trees.
The new Cohesion theory requires non-cavitation to even begin,let alone addressing the fact that it is impossible for leaves to generate the suction required to pull water from the ground and out through thoe pores, and therefore is a non-starter. Osmosis is utter nonsense when placed against the flow rates, capillary action is laughable and root presure, well, let's not go there :)

quote:
Originally posted by daveshorts



What do you mean by "all the old accepted explanations for fluid transport." the stuff in the like I posted earlier seemed to be pretty consistent, what is the exact problem?



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daveshorts

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Re: How do Trees Really lift Water to their Leaves?
« Reply #18 on: 26/04/2005 20:45:50 »
Why is it impossible for leaves to produce the suction required? If you work out the osmotic pressure produced by just the sugar in orange juice (as an example plant fluid it is easy to get figures for) it comes out at about 9.8 atmospheres, enough to suck water up about 100m (about 300 feet), so as long as the water in the xylem doesn't cavitate it should work fine!

A large tree has tens, or hundreds, of thousands of leaves. So each leaf would only have to suck, by osmosis,   a few militres a day to make up the  1000 litres a day you quoted earlier. Surely this is a perfectly reasonable rate?

I don't think the cavitation problem is as bad as it sounds - for a start we can observe that there are xylem in a tree that are 100m long and they don't cavitate, and in the link I posted earlier it says that branches have been spun in centrifuges so they are experiencing negative pressures equivalent to 92metres of water. So the question isn't "is it reasonable for a xylem not to cavitate?" but why isn't the xylem cavitating?

I would guess the answer to this is related to nucleation. It is possible to heat water above it's boiling point, without it boiling, if you do so in a very clean container. This is because although it is (free) energetically favourable for all the water to boil, to do so it would have to form a bubble. Creating a bubble is difficult because you have to fight against suface tension, and it turns out that to be stable the bubble has to be more than a critical size. Now if the xylem is smaller than this critical size it would be impossible for a bubble to form until the tension is so large that the critical size of the bubble is smaller than the diameter of the xylem.

 I will do some calculations at some point but I guess this will be at considerable negative pressures.

chris

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Re: How do Trees Really lift Water to their Leaves?
« Reply #19 on: 26/04/2005 20:49:05 »
Sorry to elbow in on the discussion. Dave got there with the answer to the flytrap question first (I'm away on holiday this week !), but just so as you know, we did discuss this issue on the radio show in February :

How a flytrap snaps shut

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Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #20 on: 27/04/2005 11:41:00 »
Tubular Water
One way to envision water pulled into and up a capillary tube is to use a suspension bridge model. The column of water is suspended against gravity by its adherence to the walls of the tube. Cohesive force keep all the water molecules together. Capillary movement is greater as tube diameter decreases. Extremely small diameter tubes, pores, or spaces can attract water and move it a relatively long way.
Capillary movement is responsible for within- and between-cell water movement in trees, and small pore space movements in soils. Cell wall spaces are extremely small (interfibral) and can slowly wick-up water. The water conducting tissues of trees (xylem), does not utilize capillary movement for water transport. If xylem were open at its top, a maximum capillary rise of 2-3 feet could be obtained. Xylem transport is by mass movement of water not capillary action.
Capillary movement is a matter of inches, not dragging water to the top of a 300 feet tall tree. Capillary movement components can be seen where liquid water touches the side of a glass. The water does not abruptly stop at the glass interface, but is drawn slightly up the sides of the glass. This raised rim is called a "meniscus." The meniscus is the visible sign of adhesive forces between the glass and water pulled up the side of the glass. The smaller the diameter of the glass, the greater the adhesive forces pulling-up on the water column and the less mass suspended behind.
Tiny Bubbles
Gas bubble formation in water columns is called cavitation. As temperatures rise and tension in the water column increases, more gases will fall out of solution and form small bubbles. These tiny bubbles may gather and coalesce, "snapping" the water column. As temperatures decrease, water can hold more dissolved gasses until it freezes. Freezing allows gases to escape and potentially cavitates water conducting tissue when thawed. Trees do have some limited means to reduce these cavitation faults.
On The Move
Water movement and transportation of materials is essential to tree life. The three major forms of transport are driven by diffusion, mass flow, and osmosis forces.
Diffusion – Diffusion operates over cell distances. Diffusion is the movement of dissolved materials from high concentrations areas to low concentration areas. Diffusion can move a dissolved molecule in water across a cell in a few seconds. Diffusion does not operate biologically over larger distances. It would take decades to diffuse a molecule across a distance of one yard / one meter.
Mass Flow – Most movements we visualize are due to the mass flow of materials caused by pressure differences. Wind, gravity, and transpiration forces initiate and sustain small differences in pressure. These small differences drive water and its dissolved load of materials in many different directions. Because pressure is the driving force in mass flow, (not concentration differences as in diffusion), the size of the conduit is critical to flow rates. If the radius of the conduit is doubled, volume flow increases to the fourth power of the size increase (double conduit radius and flow rate increases by 16 times — 24).
Osmosis – Osmosis is the movement of water across a membrane. Membranes in living tree cells separate and protect different processes and cellular parts. Membranes act as selective filters, preventing materials with large hydration spheres or layers from passing through. Small, uncharged materials may pass freely. The driving force to move materials in osmosis is a combination of pressure and concentration forces called a "water potential gradient."

by Dr. Kim D. Coder
Daniel B. Warnell School of Forest Resources
University of Georgia
6/99


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daveshorts

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Re: How do Trees Really lift Water to their Leaves?
« Reply #21 on: 27/04/2005 13:30:59 »
Yep that all sounds about right.

As far as I can work out the presently accepted way water gets up a tree is:

The xylem are full of water from the beginning, as each year they grow up from the roots and are full of water from the start.
 This column of water is essentially hanging from the top of the column, and is stable (despite being under considerable negative pressure) because the xylem is so small and covered with hydrophillic substances so cavitation is difficult as I described above (this is known as the cohesiveness of water).

  Now the tissue around the xylem have more sugar and other salts dissolved in them than are in contents of the xylem so they suck water across the cell membranes surrounding the xylem by osmosis. You are right to point out that osmosis is a slow process, but this is happening over the whole area of the tree so it adds up.

Because the water is cohesive if you pull on the top the whole column moves up like a piece of string so it sucks water in at the bottom.

The water in the cells evaporates concentrating the salts and sugars in them, and allowing them to draw more water in by osmosis. So the energy to power the whole process comes from the sun evaporating water in the leaves.

Where is the problem with this picture?

Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #22 on: 27/04/2005 13:36:18 »
Dave, lets not forget the limit which suction can work under normal atmospheric pressure in physics. I.E. a pump/suction placed above a water source has a ceiling. Above 10 metres, the pump fails to work, and the water level remains at 10 metres, and the space above the 10 metres is vacuum, the limit was discovered by Galileo, while asked to work out why water at 40 feet below the surface could not be drawn up by a pump. Cavitations do occur and can be heard as cracking noises in a tree using a stethoscope.

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daveshorts

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Re: How do Trees Really lift Water to their Leaves?
« Reply #23 on: 27/04/2005 14:17:04 »
As I mentioned earlier it is possible to get water below ther pressure  it should cavitate and therefore be able to suck it up more than 10metres, (in the same way as you can super heat water) especially if you are in a very thin tube covered in hydrophillic substances (or a xylem as it is otherwise known). In fact looking at the web (and from a conversation we had in Brixham once) you have syphoned water 24m vertically using quite a large tube, so it must be possible to do better with this using a smaller tube.

Yes cavitation does happen, especially in drought conditions, but surely that shows that the water in the xylae is under tension and therefore unstable, so is evidence for the standard theory. There are a lot of xylae in a tree and it will be ok as long as the tree is growing the xylae faster than they are breaking due to cavitation.

Andrew K Fletcher

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Re: How do Trees Really lift Water to their Leaves?
« Reply #24 on: 27/04/2005 15:29:38 »
Dave, the water at Brixham was not siphoned, as you well know a siphon will not work at those heights. In fact, to prove it was not a siphon that was taking place, I lowered one of the bottles in my experiment to see if siphon would occur, and because there was no saline solution at the centre of the loop of tubing no circulation took place, therefore disproving that we were looking at a siphon.

We can agree now on the fact that cavitations are known to occur. I believe that when a cavity occurs, the pressure changes reverse to a positive downward force, which has a direct influence on fluids in the rest of the tree, forcing the fluids in nearby tubes to rise higher and repair the cavitations, therefore enabling the bulk flow to continue.

Having said that, I am intrigued as to where and when we met, did you attend the demonstration in 1994?

Andrew


Death is natures way of telling us to slow down.
« Last Edit: 27/04/2005 15:49:40 by Andrew K Fletcher »

 

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