No, nothing like what you said. Osmosis is not a big part of how plants get water to their leaves. It is a totally insignificant part.
Utter nonsense as usual Dr. Deth. Plants are perfectly capable of operating in soils with osmotic potentials well below that of their cells. Osmosis exists therefore plants use it to save some energy, but even if osmosis didn’t exist plants woud absorb exactly as much water.
Your claim that if there were no osmosis there would be no water is total rubbish. As usual you have half understood the science, extrapolated wildy and posted ignorant rubbish as a result.
Just for once it would be nice if you just conceded the point and walked away. The constant moving of the goalposts that you engage in in these circumstances is tiresome and hardly in the spirit of fighting ignorance.
So just for the record:
Osmosis plays essentially no role in lifting water in plants. If osmosis didn’t exist at all plants would stil be able to lift just as much water just as high.
Dr. Deth’s assertion that osmosis plays a large role is utter nonsense. His assertion that if there was no osmosis there would be no water uptake is even worse nonsense.
Osmosis is essential as far as we know in priming newly created vessel elements but it plays no significnat role in actualy moving water through them.
And http://www.amjbot.org/cgi/content/abstract/85/7/897
"Some predictions of the recently proposed theory of long-distance water transport in plants (the Compensating Pressure Theory) have been verified experimentally in sunflower leaves. The xylem sap cavitates early in the day under quite small water stress, and the compensating pressure P (applied as the tissue pressure of turgid cells) pushes water into embolized vessels, refilling them during active transpiration. The water potential, as measured by the pressure chamber or psychrometer, is not a measure of the pressure in the xylem, but (as predicted by the theory) a measure of the compensating pressure P. As transpiration increases, P is increased to provide more rapid embolism repair. In many leaf petioles this increase in P is achieved by the hydrolysis of starch in the starch sheath to soluble sugars. At night P falls as starch is reformed. A hypothesis is proposed to explain these observations by pressure-driven reverse osmosis of water from the ground parenchyma of the petiole. Similar processes occur in roots and are manifested as root pressure. The theory requires a pump to transfer water from the soil into the root xylem. A mechanism is proposed by which this pump may function, in which the endodermis acts as a one-way valve and a pressure-confining barrier. Rays and xylem parenchyma of wood act like the xylem parenchyma of petioles and roots to repair embolisms in trees. The postulated root pump permits a re-appraisal of the work done by evaporation during transpiration, leading to the proposal that in tall trees there is no hydrostatic gradient to be overcome in lifting water. Some published observations are re-interpreted in terms of the theory: doubt is cast on the validity of measurements of hydraulic conductance of wood; vulnerability curves are found not to measure the cavitation threshold of water in the xylem, but the osmotic pressure of the xylem parenchyma; if measures of xylem pressure and of hydraulic conductance are both suspect, the accepted view of the hydraulic architecture of trees needs drastic revision; observations that xylem feeding insects feed faster as the water potential becomes more negative are in accord with the theory; tyloses, which have been shown to form in vessels especially vulnerable to cavitation, are seen as necessary for the maintenance of P, and to conserve the supplementary refilling water. Far from being a metastable system on the edge of disaster, the water transport system of the xylem is ultrastable: robust and self-sustaining in response to many kinds of stress. "
and:
"Sap Ascent in Vascular Plants: Challengers to the Cohesion Theory Ignore the Significance of Immature Xylem and the Recycling of Münch Water
JOHN A. MILBURN
Department of Botany, University of New England, Armidale, N.S.W. 2351, Australia
January 31, 1996 ; May 16, 1996
In recent years the cohesion theory has been attacked on the grounds that direct measurements made with the pressure probe indicate that sap tensions are much less (maximum tension approx. 0.7 MPa) than indicated by parallel measurements made with the more conventional methods: osmotic methods, pressure bomb, or psychrometer. It has also been claimed that other direct methods do not support the cohesion theory. Thus a re-examination using the Renner technique indicated sap tensions of approx. 2.5 MPa. Also an independent method based on mercury penetrometry provides evidence that sap tensions of at least 2.0 MPa can be demonstrated directly implying, that serious limitations arise from the pressure probe method itself. Without tensions exceeding 2.0 MPa mangroves would be unable to extract fresh water for transpiration from seawater. It is suggested that the pressure probe is susceptible to bias because it investigates the least mature xylem conduits while they are still under varying degrees of turgor pressure and only partially interconnected with the main xylem system. This supposition is supported by claims that the xylem sap sampled by the probe contains significant concentrations of solutes.** Additionally water, supplied by reverse osmosis from the sieve tubes** (‘Münch water’), is continually being liberated in the vicinity of the outermost xylem vessels hydrating them to an atypical degree which can explain several of the discrepancies claimed. These results, which are supported by the work of others, demonstrate that the challenges to the cohesion theory for the ascent of sap are ill-founded. The release of water from the phloem can explain not only some discrepancies claimed by the cohesion challengers, but also explain the refilling of cavitated xylem conduits: a hitherto unsuspected role for the phloem transport system."
A classic example of what I was talking about and what Dr. Deth is so famous for. As usual he has half understood the science, extrapolated wildy and posted ignorant rubbish as a result.
One of those articles are talking about the role of osmosis in moving solute through protplasm. Apparently Dr. Death doesn’t understand that the conducting elements that take water to the leaves don’t even contain protoplasm, they are hollow pipes. What Dr. Deth has done is exactly the same as saying that since solutes move through human protoplasm via osmosis therefore blood pressure is the result of osmosis. Seriously folks , it is excatly the same.
And FFS two of the articles are referring to reverse osmosis from the vessels, ie the forcing of water out of the vessel against the osmotic gradient. That’s why it’s called reverse osmosis Dr. Deth. How could anyone possibly think this is referring to pressure being generated in the vessel as a result of an osmotic gradient?
Quite clearly Dr. Deth has done nothing more than put “osmosis” into Google scholar and pasted the results here. Had he actually understood or read the artciles he would have realised that reverse osmosis requires pressure to operate, it doesn’t generate pressure.
But keep going buddy. If you haven’t totally destroyed your credibility in GQ this thread should certainly do it. Anyone can put term sinto google scholar and find refernces where they are used in the same article. The trick is knowing tha just because they appear in the same article doesn’t mean they actually support your position.
Anyway I will cease this hijack here. The truth has been stated. Osmosis is insignificant in moving water up trees. Anyone who wants to believe a man who thinks that osmosis and reverse osmosis are the same thing is free to do so.
Vacuums don’t suck. All they do contribute is an absence of shove. You can create a vacuum in the laboratory that is harder than a space vacuum and it still won’t raise water more than about 30’ up a pipe, because what’s providing the shove is atmospheric pressure. It doesn’t matter whether you’ve got a few hundred million miles of vacuum between Earth and Jupiter or not - the water won’t get past the first 30’. If you want to raise water higher, you can’t suck it, you have to push it - that is, give it more of a shove than the 14.5 PSI it gets from the atmosphere.
OK so I set up the pipeleine, prime it, and then let it siphon. After all the Jupiter end will more “downhill” than the edge of the Earth’s gravity well, which is the furthest “uphill” point. A little energy needed to pump a gajillion gallons of water umpteen billion miles to prime the line, but after that it’s problem solved.
I know, I know, the water column would break with the pressure needed to lift it out of Earth’s gravity well and the vacuum would be lost. Bloody laws of physics.
All you need to do is set up a wormhole that leads from about 10’ above Earth sea level to somewhere in Jupiter’s atmosphere and the problem’s solved for you. You may introduce one or two attendant problems in doing this, but hey, the devil’s always in the details.
Blake. While we appreciate your scientific input, you really need to learn to do it without the tone of personal attack and derision. This is not a formal warning, just a suggestion.
Can I hijack a little and take it into silly land? What happens if we manage to build a tower 75 miles high, and we pass the tube up through the tower, heating, cooling and supporting it as necessary and then we develop a super pump (or series of pumps) to actually shove the water up the tube all the way into space? And let’s say we’ve got the technology to really geyser it up there (because eliminating a liter per second will get us nowhere). Let’s say we’re pushing water up the tube into space at, I dunno, for the sake of argument, 1000 liters per second. So what happens to the water? If I understand correctly, water has to exist as a gas or a solid in space – it can’t be a liquid. So it’s vapor or ice once it leaves the end of the tube. I assume the temperature plunges just outside our tube, so does the water freeze immediately? Does it vaporize? Does it drift away fairly quickly as ice crystals or vapor, or does a big ice ball start to develop just a little past the end of the tube, where it receives more and more water and gets bigger and bigger? What is the effect of the vacuum? Does it help pull the developing ice ball tighter into itself until it forms a dense object? With our fancy-pants tube, do we quickly create a massive ten-mile wide chunk of ice that eventually gets drawn back into the atmosphere until it plunges toward earth, this time without Bruce Willis and a bunch of yahoos to save the day?
Or, since there’s a vacuum and, I think, very little friction, does the water shoot out of the tube, changing immediately to vapor, crystals or a solid column of ice, and just keep going and going, given that we’re ejecting it with some force and there’s nothing to slow its momentum? If we pumped 1000 liters per second for 12 hours, would we send a thick, ridiculously long column of ice rocketing out into the universe, like a giant Mr. Freezie shot out of its plastic wrap by a snotty little kid?
Anyway, please don’t heap abuse on me; I was just curious what would happen to the water if we ever managed to get it out of our atmosphere through a tube in a serious quantity.
“Temperature” isn’t really a meaningful concept in a vacuum - the water isn’t coming into contact with cryogenically cold space, because it isn’t coming into contact with anything. I’m guessing it will boil away as vapour and will gradually lose heat by radiation into space, tho’ I’m not sure if it will pick up solar heat faster than it can radiate away. It might re-accrete as snow, I guess.
Wherever you’ve built the Space Fountain, its top end isn’t moving much over 1000mph, so the stuff being pumped out is well below low-orbit velocity. It’ll form a short-lived vapour/ice crystal trail behind the Fountain and drop back into the upper atmosphere. I’m not sure how long it’ll take to come down then, or if there’ll be a lot more nacreous and noctilucent cloud for a while, but I imagine there’d be a visible plume trailing the Fountain after a while.
You could pump the stuff up with Cavorite, of course, as long as the Fountain itself was firmly fixed. Indeed, the Cavorite would make the whole thing easier to managed as the Fountain wouldn’t need to support its own weight.
I’d guess a similar thing would happen as what happened when the Apollo craft vented waste water/urine. You end up with a cloud of tiny ice particles. I’m not too sure of the detailed physics of it - WAG, the water evaporates almost instantly due to the very low ambient pressure (75 miles up is not a true vacuum but not far off), and as it expands and cools it accretes into “diamond dust”. The warmth of the sun would make those tiny ice particles gradually sublimate into vapour over time in the vacuum of space, I imagine.
A blob of water in vacuum would start evaporating immediately, but the water vapor carries away heat. So the blob will get colder. Depending on the size of the blob and initial temperature, it may all evaporate, or it may become a chunk of ice.
But at 75 miles there’s still strong gravity. It’s a tower, so it’s fixed to the ground, not moving at anywhere close to orbital speed. So unless the nozzle can shoot water at several thousand mph, all you have is chunks of water falling down towards the ground. Plus an expanding/falling cloud of water vapor.
OK, but it doesn’t have to be exactly 75 miles. I picked that distance mainly because someone mentioned it earlier. Make it 200 miles, or 500, if necessary, to get it out of our atmosphere. And in my silly land, yes, we’re firing it out the end of the tube pretty quickly. Where does it go? From the responses so far, it evaporates/crystallizes/becomes tiny particles, but it’s still there. Does it roar through space for trillions of kilometres until it hits the gravitational pull of something or other? Does it disperse much? What disperses it in a vacuum? I read recently that astronomers are convinced there’s an astonishing amount of water in space, even though none of it’s in the form we typically recognize as water.
OK, Blake just to fight ignorance: Note that Blake doesn’t say what does allow Water Transport in plants. That’s because he doesn’t know - in fact no one knows. I posted those two links to show there are two competing theories for the mechanism:
**the Compensating Pressure Theory **and the Cohesion Theory.
Both are hotly arguing their side, as can be seen clearly in the links and cites I provided. Blake’s links and cites do not show otherwise. (Yes, I know he hasn’t provided any, but still… )
Osmosis (or reverse osmosis, which uses the identical mechanism) begins (and sometimes ends, but the mechanism here is mostly Transpiration) the water transport system- as again can be seen clearly in the links and cites I provided. Yes, it is NOT the major mechanism of Transport between the two. But exactly what that mechanism is hotly debated.
It is true that someone could have argued the “big” in* “Osmosis is a big part of it”.* A good rebuttal could have explained that the water transport system does *start *with Osmosis, gone on to explain the two competing theories and transpiration, and concluded that “big” was likely too strong a word. Of course, a good rebuttal would have included some interesting cites and links, too. But instead of fighting ignorance, some here would rather fight other posters through personal attacks.
Blake, you are a smart guy, but I am done with you. I debate by cites and facts, you use ad hominen and presonal attacks. I will no longer debate with you until you change your tactics.
It depends on how fast it’s moving. If the water is ejected at less than 7 km/s or so, it will simply fall back down to earth. If it’s moving faster, but below 11 km/s or so, it will go into orbit around the earth. If it’s faster than 11 km/s, it will break free of earth’s gravity, but it will still orbit the sun. I can’t remember off hand how fast it needs to be to escape the solar system entirely.
You guys are nuts. I agree that constructing a 75-mile high column and pumping seawater to the top are simple enough, but it’s purpose would be defeated so quickly, it hardly seems worth the effort. Upon exposure to space, the water would “flash” into tiny crystals, as has been witnessed on many space missions. I shall dismiss the effects of the crystals that reenter the atmosphere and vaporize.
The part that matters here, is this: much of the water will recondense at the top of the column, more at the leading edge than the trailing side; I leave it to others to calculate the exact percentages. Soon, there will be a HUGE block of ice, two blocks, in fact, one on the exterior, the other on the interior, attached to the top of the tube. They will reach a critical mass, at which point, they will begin to slide down, much like a popsicle on it’s stick on a warm day. The resulting splash will inundate all areas that got a reprieve from rising ocean levels.
Just tell me something about transpiration in trees. The loss of water at the leaves pulls up the water through the xylem, is that correct? There’s no other mechanism needed to push the water up, is that right? And this alone allows the water to go higher than 30’. Is that right, or have I misunderstood?
Is there any limit to how high water can go through transpiration?
So, on the subject of the space hose, what if you started by pumping water through the hose to start with, let it evaporate from the far end. Would that be enough to continually pull up water through the hose by transpiration?
Assume for the sake of argument that the far end is in geostationary orbit, much greater than 75 miles in the OP.
Right. The water is pulled up, not pushed up. Transpiration relies on the electrostatic attraction between the positive end of one water molecule and the negative end of another. The molecules “stick” together. The strength of this attraction determines how much total weight of water there can be below the to junctions between molecules which determines how high the tree can get. There is a limit but I don’t know what it is. It must be at least over 375’ which is the height of the tallest of the coast redwoods.
