Talk:Water potential

Wiki Education Foundation-supported course assignment

This article is or was the subject of a Wiki Education Foundation-supported course assignment. Further details are available on the course page. Student editor(s): Rachelefriedman.

Above undated message substituted from Template:Dashboard.wikiedu.org assignment by PrimeBOT (talk) 12:43, 17 January 2022 (UTC)

Untitled

I added the critical "per unit quantity" to the definition so that the subsequent non-energy units would make sense. —Preceding unsigned comment added by 64.113.123.126 (talk) 06:51, 7 March 2010 (UTC)

Article is getting better, but it still needs some editting and references added. Will try to help more if I have time.

This is a very important topic for plant physiology and soil science, but I'm not sure how important it is for physics as a whole, so I rated it "mid".

cheers, Wcornwell 13:20, 14 April 2007 (UTC)

Hey is it really Physics??? Yep there's this "potential", but really, it contains "Osmotic"... And who would care about this other than Plant or Soil researchers? 165.132.24.81 02:27, 4 May 2007 (UTC)

I agree it's not a "basic" physic concept like gravitation, so I'll change it to "low" importance for physics and "mid" for plants. It's really hard to understand why water flows from the ground to the tops of trees without understanding water potential. Wcornwell 17:32, 4 May 2007 (UTC)

Some typical values ?

The entry should list a couple typical values —Preceding unsigned comment added by 62.202.12.176 (talk) 17:34, 13 July 2010 (UTC)

Negative and positive potential

Please be aware that it is perfectly legitimate for the water potential to be positive or negative.

While most biology books are rediculously simplistic in their coverage of water potential, if you edit this article, you should be aware of this at least.

[I'd suggest avoiding edits until you are familiar at least the ramifications of the simple relationship between water potential, pressure potential and osmotic potential.]

Complex Systems

The section on Complex Systems (those whose gravimetric and matrix effects) still really applicable to soil potential and intra-plant water potential; it should be expanded. [Even though it's more advanced than most undergrad level courses on plant biology would probably get to.]

Please don't just delete it, make it better.Dondelelcaro —Preceding signed but undated comment was added at 05:20, 24 September 2007 (UTC)

Agreed. I added a section on matrix potential, but still missing gravity and humidity...Wcornwell 00:46, 16 November 2007 (UTC)

AfD result

Hi i'm an extremely confused biology As Level student. My teacher said it was impossible for water potential to be posotive. She then said quoted the equation Ψ = Ψp + Ψs (pressure potential and solute potential). She gave an example where Ψs was posotive and Ψp was 0. She said that the overall Ψw was Zero. I asked how is that possible surely abiding by basic laws of mathematics the Ψw should be posotive. She then said she'd ask another teacher and come back to me.

HELP!

Usually Ψs is negative, and Ψp is positive. 165.132.24.81 02:24, 4 May 2007 (UTC)

Disagreement with above editor

Water potential does not "rule." It is tasteless and without merit.

I have to disagree with you here. Water does "rule" because without it you'd be dead. Think outside the box

Comment about 'free energy'

Is that real information, or is it graffiti?

Free energy is a real concept. It's basically the energy in a system that is available to do work. --Luigifan 12:49, 28 October 2007 (UTC)

Nominate for Stub status

This article is very short, and contains very little information. I believe it should be labeled a stub until it can be expanded. -- Tuvok^^{Talk|Desk|Contribs}  02:28, 13 October 2006 (UTC)

Yes, i agree, and a clean-up is needed in the explaining. Currently its extreamly hard to understand unless you have previous knowledge of the subject. Think outside the box 13:01, 13 October 2006 (UTC)

Precisely what effect does temperature have on water potential?

Okay, I get how pressure and solute concentrations affect water potential, as the article explained that quite clearly. However, I'm not sure what temperature does to the water potential. For a specific case, think of a cell with an internal concentration of 0.02 molar glucose that is placed in a test tube containing a 0.02 molar glucose solution. Assuming that no active transport of glucose occurs into or out of the cell, and there is no pressure difference, the two solutions should be isotonic to each other. However, I'm not sure if the temperature could cause the cell's internal concentration to actually be hypertonic to the solution in the test tube. Will the cell and test tube be isotonic to each other under these conditions no matter what, or could they be isotonic or hypertonic to each other based upon the temperature? I need to know this for a science assignment, so please reply quickly! --Luigifan 12:47, 28 October 2007 (UTC)

Surely there must be a "Wikipedia does not do your homework" policy statement :) Jeeb (talk) 16:59, 29 June 2008 (UTC)

Assessment comment

The comment(s) below were originally left at Talk:Water potential/Comments, and are posted here for posterity. Following several discussions in past years, these subpages are now deprecated. The comments may be irrelevant or outdated; if so, please feel free to remove this section.

* Article is getting better, but it still needs some editing and references added. This is a very important topic for plant physiology and soil science, but I'm not sure how important it is for physics as a whole, so I rated it "low". cheers, Wcornwell 13:10, 14 April 2007 (UTC) Rated as mid importance from an overall Wikipedia perspective. -- Paleorthid 16:48, 1 December 2007 (UTC)

Last edited at 16:48, 1 December 2007 (UTC). Substituted at 10:18, 30 April 2016 (UTC)

Is it just chemical potential of water?

I don't see the general thermodynamic term chemical potential mentioned at all, but that seems to be what is described here. At equilibrium, the chemical potential of water would be precisely uniform among all connected parts that allow exchange of water molecules. If it's not the same as chemical potential then I'm curious what is the distinction.

Addendum -- the answer is maybe yes? Two sources:

"For historical reasons, plant physiologists have most often used a related parameter called water potential, defined as the chemical potential of water divided by the partial molal volume of water (the volume of 1 mol of water): 18 × 10 –6 m 3 mol –1 . Water potential is a measure of the free energy of water per unit volume (J m –3 ). These units are equivalent to pressure units such as the pascal, which is the common measurement unit for water potential." --- from the Taiz & Zeiger book Plant Physiology.

Water potential is $\Psi =(\mu _{W}-{\mu _{W}}^{0})/V_{W}$ where ${\mu _{W}}^{0}$ is chemical potential at a standard reference state (and presumably at some reference grav. potential), and $V_{W}$ is the partial molal volume. http://www.appstate.edu/~neufeldhs/pltphys/waterpotential.htm

These disagree about the offset ${\mu _{W}}^{0}$, though this is a bit of a quibble since only relative potentials matter anyway. Of more technical importance I'm unclear about whether $V_{W}$ is a strict constant of 18 m³/mol, in which case water potential would just be chemical potential in different units, or $V_{W}$ is a variable, in which case it is not strictly equivalent (and so water potential would not be equal everywhere at equilibrium!). The sense I get though is that the distinction is practicalyl irrelevant since water potential is only being used to analyze the liquid state of water in plants and soil, near STP.

--Nanite (talk) 20:15, 7 October 2023 (UTC)