water potential solute potential and pressure potential

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Aslam o alikum
I am Hassam ur Rahman and I am teaching Fsc biology since 2014 .I am always trying to improve myself and provide best lecture to students.i am taking content for the lecture from authentic and relevant sources but human errors are possible . you are requested to please highlight the mistakes.My lectures are equally reliable for Fsc and mdcat students
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This lecture is about
Water Potential (Symbolized By Greek Letter Psi = yw )
Water molecules possess kinetic energy which means that in liquid or gaseous form, they move
about rapidly and randomly from one place to another. So, greater the concentration of the water
molecules in a system the greater is the total kinetic energy of water molecules. This is called water
potential (yw).
In plant cells two factors determine water potential.
i) Solute concentration (Osmotic or solute potential = ys)
ii) Pressure generated when water enters and inlates plant cells (Pressure potential = yp).
Pure water has maximum water potential which by deinition is zero.
Water moves from a region of higher yw to lower yw .
All solutions have lower yw than pure water and so have negative value of yw (at atmospheric
pressure and at a deined temperature). So osmosis can be deined as:
“The movement of water molecules from a region of higher water potential to a region of lower
water potential through a partially permeable membrane”.
Osmotic (Solute) Potential = ys
The osmotic (solute) potential ys is a measure of the change in water potential(ys) of a system
due to the presence of solute molecules. ys is always negative. More solute molecules present,
lower (more negative) is the ys.
Pressure Potential (yp)
If pressure greater than atmospheric pressure is applied to pure water or a solution, its water
potential increases. It is equivalent to pumping water from one place to another. Such a situation
may arise in living systems.
When water enters plant cells by osmosis pressure may be built up inside the cell making the cell
turgid and increasing the pressure potential. Thus the total water potential is sum of ys and yp.
yw = ys + yp
water potential solute potential pressure potential
If we use the term water potential, the tendency for water to move between any two systems can
be measured; not just from cell to cell in a plant but also from soil to root from leaf to air or from
soil to air. The steeper the potential gradient the faster is the low of water along it.
The following example would help understand the concept of water potential. Two adjacent
vacuolated cells are shown with yw, yp and ys.
Fig. 14.3 Two adjacent vacuolated cells.
Q. a) Which cell has the higher water potential?
b) In which direction will water move by osmosis?
c) What will be the water potential of the cells at equilibrium?
d) What will be the solute potential and pressure potential of the cells at
equilibrium?