utv
Badges: 14
Rep:
?
#1
Report Thread starter 2 years ago
#1
water potential is the ability of water molecules to move.

my question is why is measured in Pascal's and how can you have a negative pressure ?
1
reply
macpatgh-Sheldon
Badges: 20
Rep:
?
#2
Report 2 years ago
#2
Water potential is a relatively recent piece of terminology - the term traditionally used was osmotic pressure; interestingly, a low osmotic pressure is equivalent to a high water potential because water potential describes the force with which water can move across a semi-permeable membrane (NOT just movement of water as you say) FROM an area of HIGH WATER POTENTIAL to an area OF LOW WATER POTENTIAL; whereas, with osmotic pressure, water moves from an area of low osmotic pressure to an area of high osmotic pressure.

The osmotic pressure is related to the number of particles of solute dissoved in the water (really now solution).

To understand the current usage of "water potential", try to think of it almost as if it was diffusion of water - because if there is less solute dissolved in it [low osmotic pressure], in a way the "concentration of water" is higher, so it "diffuses" (sort of) to an area with more solute [high osmotic pressure] i.e. "lower conc-n of water".

It is measured in Pascals because of the historic term "osmotic pressure".

Hope this helps!

M (specialist biology tutor)
2
reply
utv
Badges: 14
Rep:
?
#3
Report Thread starter 2 years ago
#3
thanks for your help and detailed explanation. I've tried to search up the term osmotic pressure but I am unsure . what is it in simple terms and how does it relate to osmosis. sorry for the constant questions but great response
0
reply
macpatgh-Sheldon
Badges: 20
Rep:
?
#4
Report 2 years ago
#4
Hi, Firstly, thanks so much for the rep - it makes it worthwhile to spend time to help out when students show their appreciation!

It might be easier to understand osmotic pressure if we take an example:-

In the human body, maintenance of the correct osmotic pressure of the blood is crucial to survival. The main solutes that confer osmotic pressure to the blood are the plasma proteins, particularly albumin. The osmotic pressure, as explained in the previous post, tends to pull water towards the "compartment" with high osmotic pressure. So, to keep blood within blood vessels as much as necessary, the blood osmotic pressure must not be too low.

In liver failure, the blood albumin level becomes too low (because the liver synthesizes most protein the body), so the osmotic pressure of the blood drops, AND FLUID LEAKS OUT OF BLOOD VESSELS giving a swollen tummy (called oedema).

The same happens if the amount of protein in the diet is reduced drastically as in extreme starvation causing a disease called kwashiorkor (the word [in West Africa] literally means "the disease the first child gets when the 2nd child is born"). [you might remember seeing babies with bulging tummies in ads asking for charity money for children].

I hope this helps further.
0
reply
utv
Badges: 14
Rep:
?
#5
Report Thread starter 2 years ago
#5
great explanation thanks again sir.
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Feeling behind at school/college? What is the best thing your teachers could to help you catch up?

Extra compulsory independent learning activities (eg, homework tasks) (0)
0%
Run extra compulsory lessons or workshops (3)
18.75%
Focus on making the normal lesson time with them as high quality as possible (2)
12.5%
Focus on making the normal learning resources as high quality/accessible as possible (2)
12.5%
Provide extra optional activities, lessons and/or workshops (7)
43.75%
Assess students, decide who needs extra support and focus on these students (2)
12.5%

Watched Threads

View All
Latest
My Feed