How Can Trees Be Taller Than 10m?
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11 жыл бұрынAnswer video: • How Trees Bend the Law...
The longest vertical straw you can use is 10.3 m • World's Longest Straw
This is because the weight of water in the straw must be supported by the pressure difference at its two ends. At the bottom, the pressure is atmospheric, and at the top, the lowest pressure you can create is a perfect vacuum (pressure = 0). Atmospheric pressure can support a water column about 10m high - BUT with 0 pressure at the top, the water would start boiling. This is called cavitation and it obviously can't be happening in trees.
After I posted the straw video, I received a lot of questions about how trees could be taler than 10m. I assumed there was a simple answer because there are plenty of trees taller than that. But as I asked around and read articles about it, I couldn't really find an explanation I was happy with.
Maybe there is not a continuous water column inside the tree, so each section only lifts water a little ways? This could be but it seems to require a series of pump mechanisms, and how would you join this pump sections together? Perhaps capillary action is holding the water up? But the xylem tubes in a tree seem too wide (~50 um) for this effect to be significant. Maybe osmotic pressure could push the water from below rather than sucking it up from above? But some trees live in mangroves, where there is much higher solute concentration in the sea water than in their roots, so osmosis would work the other way.
Eventually I spoke to a plant biologist and sorted this all out, but I wanted to give you a little back to school challenge. How do you think this could work?
@French20cent 8 жыл бұрын
You see that hair, you know you're in good hands
@afrocalibergaming4942 8 жыл бұрын
1:21 This guy looks like science
@daskanguru140 7 жыл бұрын
Afrocaliber Gaming This guy is science
@martandrmc 7 жыл бұрын
Afrocaliber Gaming He's from Periodic Videos
@vijeykrishnaa2230 6 жыл бұрын
Afrocaliber Gaming Deserved top comment!
@bebo91body32 5 жыл бұрын
i can smell his science from here
@Orbis92 5 жыл бұрын
It's Professor Sir Martyn Poliakoff, he has a channel, too: kzfaq.info :)
@veritasium 11 жыл бұрын
I don't think so - osmotic pressure specifically refers to pressure generated across a membrane with different concentrations of solute on either side.
@veritasium 11 жыл бұрын
The pressure at ground level is not 10atm. It's about 1atm. The xylem tubes are not that thin - they can be as wide as 0.2mm so it is certainly not a chain of single water molecules. Although water is evaporating from the stomata, it is the evaporation from nanoscale cell wall pores behind the stomata that allow huge negative pressures to be created. I read a lot of answers online and I didn't feel any explained it adequately, and given your explanation I think my assessment was justified.
@veritasium 11 жыл бұрын
ok so transpiration reduces the pressure at the top, but atmospheric pressure can only push water up 10m, so for a 100m tree, where are the other 9 atm of pressure coming from?
@veritasium 11 жыл бұрын
So would you say there is or is not a ~10atm pressure difference between the top and bottom of a tall tree?
@veritasium 11 жыл бұрын
Hey! I want to pass along a personal apology - things have been incredibly hectic and I haven't prioritised the follow-up video. I really want it to be awesome so I'm not going to rush the answer. Hope you can hang in there, I guarantee it will be worth it!
@ahmedalnajar1155 10 ай бұрын
Where is the follow up video?
@crunchyblade6829 9 ай бұрын
@@ahmedalnajar1155bro.. its been 10 years.
@josephjohnson8835 7 жыл бұрын
is it the cohesive tention theory, because the xylems in a tree do in fact make up a continuous waters coloumb , as water is evapotranspiration from the leaves due to the heating effect of the sun, water is drawn up the tube in a continuous column, due to the cohesive propities of water( due to the hydrogen bonds between water molecules). Thier is a number of pieces of evidence for this; as the water is being drawn up the tree, the water is under negative pressure, this leads to the trunk of the tree being lower in diameter during the day when evapotranspiration is greatest, and becoming thicker at night.
@Anonyoussisbeke 6 жыл бұрын
Joseph Johnson i think that the credit for veritasiums new vedio about the trees absorbing water goes to u but why is there a nagative pressure created ,why does the water not just evaporates derrek said that its because there is no dissolved air in the water in the xylem vessel and so there is negative pressure ,but why??
@RyanMellor1993 11 жыл бұрын
I vaguely remember leaning about this in biology and if I remember correctly it's a combination of several processes. The pressure from the roots and capillary action play a small role but it is mainly down to transpiration (water evaporating from the leaves). This creates a potential difference at the top of the plant and water moves up the xylem (tubes) by osmosis.
@Pegar 11 жыл бұрын
Really love how you've started working with the other science channels. Good work and keep it up!
@shashwat4920 2 жыл бұрын
I liked your comment after 8 years.
@veritasium 11 жыл бұрын
yes comments on that video got me to do this. I thought the answer would be simple but it's more complicated than I imagined.
@veritasium 11 жыл бұрын
but how do you get the big pressure difference? Or does a big pressure difference not exist? If we're talking 100m that's got to be at least 10 atmospheres...
@Toastwig 11 жыл бұрын
I love the professor's tie :D
@the0123x 11 жыл бұрын
I'M SEEING ALL MY FAVORITE SCIENCE SHOWS IN ONE VIDEO
@veritasium 11 жыл бұрын
I posted the answer last week - did you not see it?
@papagummybear 11 жыл бұрын
I love these collaborations that all you youtubers are doing!
@skwisgaarskwigelf331 8 жыл бұрын
I ams tallers than a trees.
@PaulTheSkeptic 5 жыл бұрын
Yez, you ams. And Toki Wartooth ams not a bumblebee. William Murderface Murderface Murderface, Pickles the Drummer doodily doo ding dong doodily doodily doo, Nathan Explosion.
@shashwat4920 2 жыл бұрын
@@PaulTheSkeptic lol
@ur1234562001 9 жыл бұрын
Trees suck!!! :) :)
@veritasium 11 жыл бұрын
less viscous, maybe, but less heavy? That pressure difference is required to support the weight of the water column - there would have to be at least 10atm difference in pressure between the top and the bottom of a 100m tree
@sshko101 11 жыл бұрын
You are really great man Derek, you made me google that. It took about 30min to read and understand how does xylem, phloem and other tree's tissues works. The greatest thing is that thousands of people around the world made exactly the same thing. Thanks!
@mowu8459 7 жыл бұрын
imma say inertia
@simassvabas4129 7 жыл бұрын
what does this have to do with inertia
@mowu8459 7 жыл бұрын
nothing, it's a joke
@JJ-ru6ls 6 жыл бұрын
Idk why but this comment made me laugh
@buttonasas 5 жыл бұрын
Why do venomous reptiles live in hot areas? Probably because of inertia...
@veritasium 11 жыл бұрын
It can be - so what are the factors?
@veritasium 11 жыл бұрын
It's called "trees are freaking awesome" because I thought that would be better than "how trees transport water"
@veritasium 11 жыл бұрын
why is everyone looking at this vid now? I got the impression no one was terribly interested in the answer which is one of the reasons I've put it off.
@veritasium 11 жыл бұрын
I don't have the Hero3 yet - but when I get it, you'll see it in the vids. This is still the 2.
@ereklo 11 жыл бұрын
I love that all the best science youtube channels have started to cooperate :)
@veritasium 11 жыл бұрын
I annotated to the answer video at the end and in the description.
@veritasium 11 жыл бұрын
interesting ideas but you should check out the answer video - no valves are involved.
@scottseptember1992 11 жыл бұрын
**The xylem diameter must be very thin for any capillary action to occur. I think this prevents the water from vaporizing at room temperature when atmospheric pressure above it decreases (boiling of water will occur when atmospheric pressure = vapor pressure by, in this case, H2O) and meets the vapor pressure of water, thus preventing "cavitation".
@nickwoo2 11 жыл бұрын
I think it is a combination of capillary action in the lower parts of the tree, pressure through different section up the tree, and siphoning from sugars coming down the tree from the leaves.
@Jaybiiird 4 жыл бұрын
Lol your old videos were so great, so short and concise
@yellowjellotime 11 жыл бұрын
I was thinking this exactly. And even if the pressure is proportional to the tube area, the water will still be raised higher because there is more surface area and therefore more cohesion drawing the water up.
@robsim37 11 жыл бұрын
I love how everyone on youTube seems to know each other. That's awesome! I can't wait to see Veritasium on Geek & Sundry's Table Top, lol.
@naronaroyan323 11 жыл бұрын
I think its a little of all of the options happening all at the same time helping the water go up, and another thing that would be nice to try is to make the drinking straw into a spiral so it spirals up instead of going straight up there for causing less pressure going down from less steepness .
@proudargie 11 жыл бұрын
Three different forces: the 2 you've mentioned (osmotic pressure 1. in the roots and 2. through up the tree), plus capillarity, plus the vaccum caused by the evaporation of water on the surface of the leaves.
@MrMartinBigger 11 жыл бұрын
the water is much different in a tree then in a tube. when the water is high up in the tree it cannot drop freely since it is absorbed by the solid parts in the tree. (much like a spunge) causing alot of resistance. That resistance coupled with capillary action allows it to overcome the gravitational force onto the water.
@loqiloqi 11 жыл бұрын
0:38 - You can exceed 1030 cm drinking straw by narrowing the straw. If your straw is skinnier than a raindrop, water cohesion becomes important. The skinnier it is, the more atmospheres it can overcome. 0:50 - Actually, cavitation does happen in trees, but in the xylem, not the leaves. You can actually hear it in some trees. Henry is closest. Sunlight drives the pump by evaporation, which sucks a straw a few microns wide. A column of water that skinny has an amazingly high tensile strength.
@BiophysicalChemist 11 жыл бұрын
The key is that when "sucking" water up with a straw, you are actually relying on the atmospheric pressure to PUSH the water up the straw when you supply the vacuum at the top end. Starting with a straw that is already full, sucking water up would result in the hydrogen bonds (which are much stronger of course than the atmospheric pressure and can support a whole column of water) pulling each water molecule below it up. This is why trees tend to use a fraction the amount of water they suck up.
@ytroadfox 11 жыл бұрын
Yes, I also think this is the "bulk" of the forces that transport water up. But does it work even when the water is not pure (sap)? I´m looking forward to the answer video. Veritasium is claims it is going to be great.
@Slayer-Knight 7 жыл бұрын
In case anybody reads this, I have two questions: If cavitation happens, and bubbles or voids are created within the liquid, are the implosions of those voids the same as describing them as water "boiling"? I don't understand precisely why Veritasium says cavitation would occur if we managed to create a perfect vacuum on the top end of the straw. Is it correct to say that it is due to the changes in pressure within the straw?
@grieske 11 жыл бұрын
The water in the roots is at a pressure near ambient pressure. The pressure gradient that is necessary to overcome gravity and viscous friction is really there. Therefore, the pressure at the top is negative, which is below vapor pressure (wikipedia: Superheating). Xylem vessels are short. Trees can contain cavitation within a single xylem vessel. The vessels are connected by membranes whose pores are so small that the Laplace pressure is sufficient.
@Joru666 11 жыл бұрын
Taking a formula for capilary radius for certain height and fluid which is: r = 2T/(qgh) where T is surface tension and q - water density, it turns out that for a 100m capilary to fill it would need to be roughly 150 nm radius -> 300 nm in diameter. Another source states that capilaries in trees are roughly the diameter of 10 nm, so I suppose the capilary action is enough for trees to work.
@ThatBritBloke 11 жыл бұрын
It is a combination of 3 factors - Adhesion between the water and the xylem's (tube's) wall (Capillary action),Cohesion between water molecules and transpiration.Water molecules form a single long chain all the way down the xylem, adhesion helps to prevent the water molecules falling down, as a water molecule is lost the the surrounding environment from the top of the xylem it then pulls the next molecule in the chain up by cohesion, this molecule then leaves and pulls the next one up and so on
@Heeby-Jeebies 11 жыл бұрын
If i remember right, moisture flows via xylum (flowing upward delivering water and ground nutrients) and phloem (flowing down delivering nutrients created from photosynthesis). My guess is that the flow of xylum is held in place by capillary action, but is otherwise "sucked" up by the plant when moisture is evaporated out of the plants leaves. I'd further guess that this action is aided by the downward flow of phloem, so it's more of an exchange than a "push" or "suck".
@NickCybert 11 жыл бұрын
Straight from my AP bio texbook (well paraphrased): First root pressure (called osmotic pressure in the vid I think?) occurs from roots taking water up from the ground and pushing up our theoretical water column. Early in the morning you can see this pushing effect for yourself in small plants as water droplets will literally be pushed out of leaves although be carful not to be confused by dew from the atmosphere.
@TiberiusWallace 11 жыл бұрын
My answer is Capilary action, made possible by the fact the xylem vessels are very narrow and form a network and not a single line from foot to tree top. Similar to shaving cuts (if you still remember them ;) ) not exploding out with the same force as arterial bleeding.
@tanqs789 11 жыл бұрын
It is a combination of root pressure(living cells around the xylem in the root use active transport to pump ions into vessels, lowering water potential and water enter xylem and flow upwards through osmosis), capillary action(interaction between water molecules and surface of xylem)and transpiration pull(the main suction force produced by transpiration). It is mainly transpiration pull doing the job in tree that are taller than 10m.
@DaKineDel 11 жыл бұрын
It is being pulled up but not due to a vacuum but primarily due to capillary action even though capillary action is not the only process in operation. The cohesion of water molecules holds column of water together. Some trees have a positive root pressure but that pressure caused by osmosis is not strong enough to get the water that high. As you have pointed out a vacuum at the top is insuffient to raise it very high.
@AlecTBM 11 жыл бұрын
Cavitation is about liquids forming bubbels under sudden pressure changes. I think outgassing is the reason that the water starts to boil. Try to fill a jam jar halfway with water and make a small hole in the top, put your vacuum cleaner at the top at max and voila, "boiling" water at room temperature. My knowlegde is from serviceing high-vacuum chambers for the last 2 years.
@MrOdomonkey 11 жыл бұрын
I was taught (way back in highschool so it's that level of understanding) to remember CAT- Cohesion, Adhesion and Transpiration. Transpiration draws drop after drop out through the stomata, each drop drawn out draws up the next drop in line because water droplets are cohesive (sticks to each other), and the drops are also adhesive because they stick to the walls of the xylem.
@SeanF7326 11 жыл бұрын
It's a combination of capillary action (the phloem really are that small), cohesive forces, adhesive forces, and transpiration. None of them do a majority of the work, but they're all key components. The cohesive forces basically use the polarity of water to make it into a "chain" that holds itself together, transpiration pulls up on that chain as the top parts of the chain evaporate away, and capillary action and adhesive forces keep the chain from falling down.
@katzunjammer 4 жыл бұрын
do the tubes in a tree branch off ?..you were using a single pipe, but if you had a branched pipe with one pipe at the bottom and many at the top with different people sucking up, could you draw water up higher than 10 meters? but i thin the other factors are also invoved
@TiberiusWallace 11 жыл бұрын
I did a little bit of botany at uni but I could be way out here. Thing to remember is that Xylem vessels are dead material and not living tissue and are formed when new phloem vessels are made on the outside for movement downwards of sugars from photosynthesis. I think the fundamental misconceptions here are; a) it's not actually pure water we're talking about here but fluids made by the tree. b) xylem vessels don't make a continuous line between the roots and the tree tops.
@veritasium 11 жыл бұрын
it does and more - did you see the answer video?
@KyleCorbeau 11 жыл бұрын
A combination between 1 and 3. Where the tree curves and bends much like veins and create cavities that fill with water, essentially creating a new base line to go from, and the being pressed upwards from a ion/chemical imbalance all the way up the tree. Think of it kind of like shoots and ladders. There's no continuous ladder to get to the end, but sometimes the fastest way there is to make a detour sideways or even down. I would also assume capillary action is for localized areas may also help
@eduradbah 11 жыл бұрын
It is important to consider that the tallest trees are located in coastal regions with cold oceans. The low temperature and high humidity allows water to condensate right above the surface of the sea in the form of clouds/fog that moves towards the coast. Tall cone shaped trees (conifers) can capture this water from the air. In general, trees use capillary action of the phloem (cellulose cell walls plays an important role) and osmotic pressure to pump water and nutrients from the soil.
@theresaflanders1395 11 жыл бұрын
I think it is a synergistic effect of all these properties working together along with transpiration at the ends of branches where leaves are guttating.
@handsomesterling43 11 жыл бұрын
Leaves and bark can absorb water from the rain, and environment, so it doesn't need to push it all the way up. Also, guessing that heat from sunlight, would cause existing water in the sap to expand, which would help to circulate it throughout... Just a thought...
@jeremyhanson 11 жыл бұрын
Have you tried drawing or pushing water up a coiled straw? Maybe these trees have developed a way to pull in water not only through the roots, but also through the bark. If so, then these trees could rely also on fog to get water.
@gibcote 11 жыл бұрын
Is the suction pressure developed in the leaf exactly comparable to the one generated by the mouth? Because when we suck the air in, we are reducing the air pressure. But in plants, since they're a closed system, the air pressure has no influence on the upwardly moving water column? Isn't it so? Please throw more light on this and correct me if I'm wrong. Thanks a ton.
@Liiiiightbody 11 жыл бұрын
cohesion tension theory. water molecules are slightly positive at one end and slightly negative at the other end, this causes them to "stick"together. As water evaporates from the leaves at the top of the tree, the long line of connected water molecules stretching from the tip of the leaves down the xylem to the roots is pulled upwards. its the transpiration pull which forces the water upwards vast distances
@evilyig 11 жыл бұрын
I imagine the water moves up and pools in segments where it's then pulled up and pooled again. Or I imagine the straw like tubes are in segments which can form barriers between segments in some way, pinching the water up each segment over time. Wild guesses.
@DustinRodriguez1_0 8 жыл бұрын
Do they take water up from the roots? They don't absorb water through their leaves? What about the water being captured in the cells when they are 'new' and then being 'lifted' by mechanical force from below upwards?
@ParakramPratapSingh 11 жыл бұрын
"Active transport" is the movement of a substance across a cell membrane against its concentration gradient (from low to high concentration). In all cells, this is usually concerned with accumulating high concentrations of molecules that the cell needs, such as ions, glucose and amino acids. If the process uses chemical energy, such as from adenosine triphosphate (ATP), it is termed primary active transport. Secondary active transport involves the use of an electrochemical gradient.
@TheAdamant94 11 жыл бұрын
My understanding is that the cohesive properties of water allow water to be pulled up the tree as water molecules in the leaves evaporate; as the molecules are ripped away from the tree they produce enough pull on the adjacent molecules to be replaced by them. A continuous chain of water molecules pulling more water molecules, with the energy for it supplied by thermal and kinetic energy of the air surrounding the leaf.
@BenMFowler 11 жыл бұрын
What you need to remember is that its not a solid column of water, its microscopic amounts of water being absorbed and being transferred. As you've said most of the mass of the tree is from co2, its not like a hollow straw. I think the difference in pressure, generated by the trees own perspiration is different enough to pull up the water it needs.
@testp5 11 жыл бұрын
Evaporation at leaves helps suck water up = negative hydrostatic pressure distal to the positive hydrostatic pressure at roots. Net effect helps push and pull water up the tree. (Only considering pressure and not counter current flow with glucose)
@jackyliang42 11 жыл бұрын
positive osmotic pressure at the roots are too weak to push the water up, but the negative pressure created by plants' transpiration on leaves are strong enough to pull water up through xylem. the water loss creates a pressure on leaves' surfaces with a lower water potential than the roots'. the surrounding water immediately replace the lost water, initiating a long process to pull the water chain up the tree with water connecting to each other w/ cohesion and to xylem cell walls w/ adhesion.
@NickCybert 11 жыл бұрын
allowing the water in effect climb up the xylem (adhesion also helps here). There are no valves in the xylem and since the cells are dead the valves would function anyways. water moving cell to cell like a bucket chain works but not fast enough for a tree's needs. If it helps think of it as water moving from high concentrations at the base of the tree to low concentrations in the air. Also i misspoke earlier i dont think there's any evaporation in transpiration. sorry for all the spelling errors
@DunkRyan 11 жыл бұрын
I can think of two conceptual problems that might make a difference. First, the xylem is always filled with water, so it only has to suck a little bit each time. Second, the water the roots are taking in is underground, not an open pool, so I think there would be a greater pressure than just atmospheric pressure balancing it.
@lewiseverett 11 жыл бұрын
It happens through a process called transpiration - the transport of water up and plant and then out through holes in the leaves called stomata. Water is absorbed by the roots through osmosis. When the water is inside, it climbs tubes in the tree called xylem vessels. The climbing is achieved partly by capillary action but past a certain height, only changes in pressure can pull the water up further. As more water leaves through the leaves, pressure at the top decreases pulling the water up.
@Websta213 11 жыл бұрын
The idea of the xylem and phloem is similar to how blood gets transported up the veins in our legs, but science has shown that when the blood gets too backed up inside the venules (micro-veins) we shake our leg to induce muscular contractions and expansions AROUND the venules, which in tandum with a damming effect, creates fluid motion opposite the pull of gravity. Therefore with logic I can hypothesis that the motion of fluid in a tree is due not only to xylems but stresses in the trunk etc.
@Cinqmil 11 жыл бұрын
I have other questions based on yours. Is the process different in smaller trees compared to larger trees? Do they use the same method? Does the method change during the life of a tree?(meaning is it the same method when the tree was smaller/younger?)
@wowsa0 11 жыл бұрын
I think the key point would be that the pressure at the base of each compartment has to be the same the whole way up the tube in order to maintain the concentration gradient between the solute which is more concentrated at the base of the compartment than the top. At the top of the tube where water hasn't reached yet there is a big pressure difference which keeps sucking the water up.
@mikesutton2765 4 жыл бұрын
Mate that was an awesome video!!!
@loqiloqi 11 жыл бұрын
It's not like a bundle of parallel drinking straws. It's an interlinked network, which roughly follow the topology of the tree with tiny root hairs, a thick trunk, and tiny twigs. It's like our own circulatory system with tiny capillaries at the extremities, but instead of being a closed circuit pumped by a heart, it's an open system pulling from the soil and evaporating to the air. Valves can do nothing to lift water. They only function with a reciprocating pump. Trees are a continuous pump.
@genDJ91 11 жыл бұрын
That's why when you cut roses you should do it with the stem under water to prevent air bubbles from blocking water uptake
@LaughterOnWater 11 жыл бұрын
Under ideal circumstances, capillary action plays a very large part. Discounting the effects of Phloem, Xylem cell walls are likely the ideal diameter for getting water up to the top leaves. However, capillary action also likely has a pressure-induced height limit. California redwoods have what amount to near ideal conditions for available water and structural integrity, and probably come close to the height limit of what is achievable strictly through capillary action.
@kurtilein3 11 жыл бұрын
true only for redwood trees i think. they use 4, capillary action, like all trees, but redwoods have roots in small soil pockets at different altitudes above the ground, so in addition they use 1, no continuous water column. Which is why they grow so damn high.
@qhack 11 жыл бұрын
I have always thought it was a combination of capilary action and the cells of the tree acting like one way valves. Albeit bi-directional as the sap in a tree can travel down back into the roots during freezing conditions.
@cgolubovic 11 жыл бұрын
The movement of water from soil to the top of the tree is called "transpiration". And for transpiration to happen trees use a lot of their own energy. There is a science method called "pipe method" of which we learned in college classes. Basically this method is used to determine how strong the bonds are between the leaves and their roots (it's assumed that every leave or needle on the tree has its own rootlet in the soil). So I'll go for capillary action.
@jayapandey2541 5 жыл бұрын
Option 1 and 4, both seem possible. So their might be a chance that it is somewhat the combo of these two that helps the water to rise.
@LaFranceBonjour 11 жыл бұрын
I heard that the giant California Redwoods can absorb the fog through their needles and dont actually need rain as the trees can get all the moisture they need from the regular fogs. That of course describes a specific and rare scenario and doesnt answer the general question for most other plant species.
@GalrieXII 11 жыл бұрын
I assume that it is due to the fact that water also falls on trees which allows a great deal of collection. If a tree gets wet, it can take that moisture (As well as moisture from the air) and use it for it's watering needs.
@thesciencelair9556 6 жыл бұрын
I think there are multiple tubes (individual cells maybe?) That make a vacuum. The water goes up one, then is transported to another, etc.
@MewCat100 11 жыл бұрын
The largest the tubes are is 800 microns, so you are off by a factor of 4. However, the tubes are not hollow like straws in all cases, but rather the ends are perforated and each of those perforations is exceedingly small. In cases where the ends are open, you won't find a diameter much greater than 30 microns. At any rate, the keys to water movement are: 1. Cohesion - Sticking to each other 2. Adhesion - Sticking to other stuff (the walls of xylem). CONT
@basJonas 11 жыл бұрын
Wouldn't you be able to raise the water column higher than 10.3 meters if the straw-diameter was smaller? Or is the argument (presumption) that the pressure, in effect, is proportional to the tube-area?
@robertej09 11 жыл бұрын
The thickness, or radius, of the straw is not taken into account. This is because of the definition of Pressure: Pressure=Force/Area. The Force exerted by the water is equal to the mass of water multiplied by the acceleration due to gravity. F=mg So P=mg/A m can be written in terms of density and volume because D=m/V so m=DV P=D*V*g/A V=2*pi*r*h and A=2*pi*r P=D*2*pi*r*h*g/(2*pi*r) The 2*pi*r cancels out and we get P=Dgh So Pressure only depends on the height of the water column :)
@idiota115 11 жыл бұрын
(i didn't read the comments) i think this is my answer: It's a combination of all those factors. It's like a push and pull configuration. What is pushing? The osmotic pressure in the roots pushes the water up while capillary action holds onto xylem (i think) walls. What is pulling? water molecules are evaporated from the bottom of the leaves, thus creating a "vaccum" and drawing the water upwards. The water column is continuous at all times.
@D1Trini4u 11 жыл бұрын
I know - very silly premise, but do leaves aide in water retention? Perhaps leaves assist in the process, and/or act as a storage mechanism for some water. Though highly likely, if I am wrong, can you touch on the topic?
@mcvoid1 11 жыл бұрын
1) the 10.3 meter figure assumes a straw radius that's much larger than the vessels carrying the water in a tree. Smaller radius = longer length. 2) Evaporation in the leaves causes a negative pressure, so you don't solve for zero, you solve for some negative number depending on the amount of direct sunlight, the temperature, and the dew point. The more the sun evaporates water, the stronger the suck. When the temperature drops, the suck decreases until you hit the dew point.
@2570hp 11 жыл бұрын
Water can go up the tree the same way blood goes up your veins in your legs. Blood piles up until until it reaches a certain height. There is a one way valve at that height so that blood cannot go back down. If you were to keep piling blood past this height and go past subsequent one way valves, the blood would return to your heart. The same way, water reaches the top of the tree and gets to the leaves.
@DunkRyan 11 жыл бұрын
I taught an intro plant biology lab for two years and the explanation we gave of how xylem vessels work is that water enters a plant's roots due to osmotic pressure, but it is the negative pressure caused by transpiration from a leaf's stomata that helps draw water up through the xylem, aided of course by capillary action and the cohesion of water. I think xylem vessels are small enough in diameter to accomplish this task. (to be continued)
@bearistotle2820 7 жыл бұрын
If there was a positive pressure within a tree from the roots, wouldn't cutting a tree in half cause water to start billowing up through the xylem?
@goaliedude32 11 жыл бұрын
Something about the surface tension of water and the hydrogen bonds, along with the other forces in you commented on? I'm thinking along the lines of how soap reduces the surface tension of water. I'm guessing the hydrogen bonds in the water are weakened by minerals/chemicals in the tree/ground, allowing the tree to more easily pull the water apart via capillary action. I do not see any reason for there to be a continuous water column. I don't know anything about osmotic pressure, but sure
@DoctaBeetz 11 жыл бұрын
Love your guest stars.
@51westgateclose 11 жыл бұрын
Have you considered the Cohesion-tension theory? Water is a polar molecule, the watermolecules form a hydrogen-bond (neagtive oxygen forms bond with positive hydrogen). Plants lose water through transpiration. When water molecules are lost others are pulled upwards/along through cohesion and adhesion. Further more transpiration creates a differential pressure thus, the water is simply sucked in one direction (upwards).
@Aklys 11 жыл бұрын
Isn't it a mix of evapotranspiration from the leaves helping to pull the water up with the capillary action and osmotic pressure of the way the roots absorb the water?
@yellowjellotime 11 жыл бұрын
Has anyone thought about the with of the tube that the water is flowing up? Xylem is composed of tubes that are much thinner than the straw used in the longest straw video. If gravity is what is stopping the water from going farther up the tube, then if tube 1 had half the diameter of tube 2, wouldn't the water go 4 times as high? Because it's still the same volume of water, just stretched out more.
@amandarandom89 11 жыл бұрын
Water is very cohesive (at least, at small scales). trees contain very thing tubes of dead cells going from the roots to the leaves. When one molecule of water evaporates, it creates a tiny bit of suction, which pulls in another molecule. Because of the cohesion of water, this molecule is "Stuck" to the next, and that to the next, and so on. Basically, by pulling on the top molecule, you can drag a whole "chain" of molecules up.