Transport is a very important action for living beings. So today
we’ll study about Transportation..
• Water and minerals move upward
through the xylem
• Dissolved sugars and hormones
are transported in the phloem
• Methods of water and solute movement
• Basic principles underlying movement of
water across membranes, phenomena of diffusion,
imbibition, osmosis, mass flow and concept of water potential.
• Diffusion ; evaporation as an example
• Osmosis as a special kind of diffusion taking place when two solution of different concentrations are separated by a selectively permeable membrane which allows passage of water molecules but not of solute molecules.
• Imbibition as adsorption of water molecules
to hydrophilic substances such as proteins, agar etc,
• Mass flow as a method of movement of water
and dissolved solutes in bulk (not in the form of
molecules) due to pressure gradient or gravity .
Concept of water potential:
• Any system containing water
has a water potential. Water potential is related to kinetic energy of
water molecules, affected by factors like pressure, dissolved
substances, hydrophilic substances,
etc.
• Water potential is denoted
by Ψ and is measured by the units of pressure (atm,
Pa, M Pa).
• Pure water at atmospheric
pressure has the highest water potential.
• Arbitrarily, the water
potential of pure water at atmospheric pressure is considered as zero.
• When solutes dissolve in
water, the water potential is decreased and it becomes negative.
• Therefore, the water
potential of most naturally occurring aqueous systems is negative.
• As the solute concentration
increases, the water potential decreases.
• Therefore, the water
potential is inversely proportional to solute concentration of the system.
• The component of water
potential decreased due to the solute concentration is called solute
potential and is denoted by Ψ s.
