How do Trees Really lift Water to their Leaves?

Dave:
I don't see how the two quotes you have made strengthen your case, the first one just says that cohesion theory means that the experiment that you have carried out is possible, the second one is an extract from this thread:
E.L. Hemetis brings up most of the same criticisms as I have.

quote:I have never seen a bowl of water at the top of any tree other than those left by the owners of apple trees to prevent scrumpers.


Of course there isn't!!! This is because the whole process is driven by evaporation concentrating salts and sugars in tthe leaf, which causes osmosis to suck water out of the top of the xylem, and then the cohesion of water means that the whole column is pulled up, so it sucks more water in at the bottom.
So the water leaving the top is as a gas, so it won't fill up a bowl.

Just to make it clear, it is not water cohesion that is doing the pulling, but osmosis, cohesion just means that the water behaves like a wire, so if you pull the top water gets sucked in at the bottom.

quote:In the case of a tree, we could place a plastic bag over a branch and collect and extract the condensed water in its canopy.


Exactly, because evaporation is providing the energy to lift water against gravity, so the water coming out of the tree is a vapour.

quote:It is possible to design a model that can lift sea water, extract pure water and return the denser ballast to the sea through a tube in order to provide the pumping for the desalination. But I have long since given up jumping though loops to amuse people.


It isn't to amuse people, it is to address what is the fundamental challenge to your hypothesis. The experiment in Brixham didn't lift more water than it dropped down. A tree lifts 50 times more water up the xylem than comes down the phloem.

It takes one joule of energy to lift 1 a kg of 1 metre. A litre of water weighs 1kg a litre of sap may weigh 1.5kg (a generous estimate). The litre of sap falling 10m will release 15J of energy, this is enough to lift 1.5l of water back up the 10m. However a tree lifts 50l of water etc. up a tree this means that you need to get 48.5J of energy from somewhere. In the conventional model this energy comes in the form of heat evaporating water at the top of the tree. Where is it coming from in your model.

If your model can do this with no other energy inputs there would be a lot more interest in it than just from plant biologists as you would have built a perpetual motion machine.

One only needs to show the method of circulation. Evaporation is an inevitable consequence of water flowing through the massive surface area of a tree.

Evaporation with a plastic bag over a branch? maybe water oozing from the leaves is a more likely explanation. Evaporation requires a dry air, suns energy and wind. High humidity shuts down transpiration (common knowledge) The environment inside the plastic bag would be near 100% humidity. So where does your accepted without question theory address this Mine fits with it like a glove.

Maybe you would like to explain how evaporation from the trees leaves can alter the concentration of solutes at an elevated point, and gravity does not affect the flow of these concentrated solutes. I wait with bated breath

Dave:
quote:One only needs to show the method of circulation. Evaporation is an inevitable consequence of water flowing through the massive surface area of a tree.

If evaporation is driving the process, you do not need a downward tube to lift water up the tree! If evaporation is not putting in the energy you need to get energy from somewhere for your hypothesis to work.

There are phloem in a tree, but they are not needed in order to lift water up.

quote:Evaporation with a plastic bag over a branch? maybe water oozing from the leaves is a more likely explanation. Evaporation requires a dry air, suns energy and wind. High humidity shuts down transpiration (common knowledge) The environment inside the plastic bag would be near 100% humidity. So where does your accepted without question theory address this Mine fits with it like a glove.

The definition of 100% humidity is that water will condense at the same rate as it is evaporating. So for some evaporation you either need a humidity of less than 100% or the leaf to be at a higher temperature than the air (if you boil a pan of water it will still evaporate, even if you are in a room at 100% humidity), which it will be on a sunny day. So what is happening in your bag is the water is evaporating from the leaves which are hot as they are a dark colour and condensing on the plastic bag which is cooled by the external air.

If the water was oozing out of the leaves and not evaporating this would bring up the problem with energies I mentioned earlier.

quote:Maybe you would like to explain how evaporation from the trees leaves can alter the concentration of solutes at an elevated point, and gravity does not affect the flow of these concentrated solutes. I wait with bated breath

The solutes are in cells and therefore behind cell membranes which are impermiable to the solutes. As Rosy mentioned earlier a cell has to use energy to pump large molecules through a cell membrane.

Rosy:

So, guys, do we know what *does* happen when you tie a plastic bag to a tree?? I'd expect it to reach a certain humidity level (higher than atmospheric) within the bag and then even out.

You would possibly then find that the leaves started to release xylem sap, by pumping ions across the cell membrane (and energy-expensive process) and allowing water to follow them. Also via a transport protein but not (this time) one which requires energy to function (I'm a bit hazy here, and my cell biology notes are 60 miles away, but that's the gist).

From plantphys.info/Plant_Physiology/transpiralec.html

quote:
Root pressure is also sometimes visible on leaves. Under conditions of high humidity, cool temperature, and low light exposure root pressure can push xylem fluids through leaf mesophyll and out some larger pores in the leaves called hydathodes. Thus on a cool morning as you walk across the grass you notice a drop of liquid on the tip of each blade. You may have thought this was dew, but because it is on the upward pointing tip, you realize that this cannot be so. A test of solutes would demonstrate that this is xylem sap, not condensed humidity! The process by which this exudes is called guttation and it is driven by root pressure.



I don't know how much plant physiology/cell biology you've studied, so forgive me if I'm teaching my grandmother to suck eggs... Plant cell membranes are impermeable to sugars such as sucrose. Transfer of sugars from cell to cell, as in the phloem, occurs only when the cell "chooses" to expend energy on the process. Thus, except where sugars *are* being moved about by active transport, there essentially isn't a "flow of concentrated solutes" to deal with, any more than there's a "flow of cells".

@ Dave Please read
standard GCSE text books entitled GCSE BIOLOGY, D.G. Mackean. ISBN 0-7195-4281-2 first published in 1986.

Posted earlier

To state that solutes and sugars stay put and are not acted upon by gravity is absurd! How do we tap rubber, harvest amber and maple syrup?????? There is an obvious downward flow!!!! And for every action there must be a reaction !!!!!

Please repeat the simple experiments, or give me an address and i will personally come to you and set them up so that you can see what exactly we are talking about here.

Andrew

@ Rosy
Rosy, my point is that accepted explanations for bulk flow are erroneous, and do not account for this amazingly simple, yet hitherto overlooked paradigm

Rosy:
quote:
To state that solutes and sugars stay put and are not acted upon by gravity is absurd! How do we tap rubber, harvest amber and maple syrup?????? There is an obvious downward flow!!!! And for every action there must be a reaction !!!!!



Maple syrup is quoted on various websites as being an anomally in that it is harvested from the xylem and has a concentration of sugar as high as 2%. This is given as a remarkably high concentration not normally found in the xylae.
Presumably to make the syrup we're familiar with as a pancake dressing they have to boil it up a bit
We don't harvest amber, it's a fossilised form of tree resin.
Sap and rubber are secreted by trees in response to injury.
Rubber is not part of the tree's transport system at all.
From www.worldwildlife.org/bsp/bcn/learning/primer/impacts.htm

quote:
It is useful in this context to briefly examine the physiology of rubber production by Hevea trees. Rubber latex is manufactured in special cells using stored carbohydrates. In addition to rubber, the latex contains proteins, sugars, tannins, alkaloids, and mineral salts. Although the exact biological function of this rich concoction is unknown, biochemically it is very expensive for the tree to produce. The abundant production of rubber latex by Hevea trees is an abnormal response to injury--a tapped tree produces hundreds of times more latex than it would have formed had it not been tapped. The net result is that commercial tapping regimes cause the tree to divert a considerable proportion of the resources normally used for growth and reproduction to the production of rubber.



Resin (the sticky stuff that you see on the outside of, say, pine trees when they're injured) is a defence mechanism rather than something involved in bulk flow.

Everything acted on by gravity must by definition go downwards?
Really? Even if it's on top of something else? I don't usually find myself going through the floor into the basement. The sugars are on top of an (impermeable, to them) cell membrane, so there's no reason why they shouldn't stay put.

@ Rosy
Rosy
instruct1.cit.cornell.edu/courses/biog10...5/cuttreephotos.html
Your statement about maple syrup merely serves to highlight that the flow and pathway of sugars can be reverted under certain environmental conditions, namely late winter, in which it is currently thought that the cold nights cause co2 gas bubbles to form due to the hydrolysis of starch, which expands during the warmer daytime altering the pressure in the xylem from negative to positive.
This is precisely why sugars and minerals are found to be more abundant in the roots of deciduous trees during the fall.
I have also mentioned this in my paper, as pressure changes are observed in the xylem when cavitation occurs, or when the leaves cease to function of fall in autumn. Fits perfectly with the new paradigm.
Amber by the way is Harvested in Poland and the Ukraine to make ornaments and jewellery, it is also heated up to form shapes in moulds, while retaining the trapped insects, although this often fragments the insects, whereas naturally formed amber maintains the insects perfectly.
Under normal transpiring conditions, the sugar pathway and flow is in the phloem. But as you state, it is harvested when the water transport is suppressed by winter.

Rosy:
My apologies, the structure of this post may be a little confused as I had to go to a class part way through writing it and haven't time to start from scratch and make it into comprehensible prose(!!)
I think I've made all the points I intended to, however!


If the primary system for moving water up trees is this convection type system you're proposing, how do the sugars get *up* the trees to the ends of the branches for leaf formation in the spring? According to your model, if there aren't any leaves yet how does the flow get started and worse how does it draw more sugars (and amino acids and whatever else it needs) up than it drops down (which it must in order to construct new leaves)? It's got to use active transport in the phloem.

OK, my understanding of the current model (and I'm in no sense a plant scientist).
In the leaf cells, sugar is produced and water is lost by evaporation from the leaves.
Sugars are transferred by (mainly passive) transport (depending on the concentrations) into the phloem. Given the sugars are already (since they're made in the leaves and moved to other parts of the plant) moving down a concentration gradient, there is no reason for more water to follow them across the cell.
Loss of water from the leaves results in water being drawn up from the roots via the xylae(osmosis).
The sugars want to move to a position of lower energy/higher entropy (and so to places where there is less sugar already). There *is* an energy gain in going downwards, yes, but as Dave points out it isn't actually very big if you're losing a whole load of water at the top. Your Brixham experiment depends on using the weight of the water coming over the top of the loop to draw the water below it up. In order to produce any energy at all the salt/sugar solution has actually to move downwards, which in your model it can't do unless the water which it pulls up follows it straight back down the opposite tube. Indeed, as was pointed out by EL Hemetis, there is before us the evidence of plants quite happily growing with their leaves below their roots. I'm far more convinced by the idea that that concentration effects dominate.

Where is the need for a "simpler" explanation? The current model doesn't strike me as any more complicated than yours (and you have yourself shown that provided there's a sufficient upwards "pull" water can sustain the "tension" required), given that the mechanisms I've outlines are undoubtedly present in generalised cells and therefore presumably in trees.

Amber really is just the fossilized stuff. The "amber" people harvest is probably copal, which I *think* is a form of resin.
www.emporia.edu/earthsci/amber/copal.htm

Also, the falling through the floor thing... if I eat too many doughnuts I may fall through the floor. But only by breaking the floor. The only way of applying the same argument to sugar solution is to say that the sieve plates between phloem cells rupture. Which is OK unless the tree's ever going to want to move nutrient solutions "uphill", which is going to require (energy expensive) active transport because as you so rightly say, all other things being equal heavy solutions (and indeed rocks) want to move downwards with gravity *if the thing they're resting on can move out of the way to allow this*.