• Experiment showing osmosis
• What is osmosis?
• What is water potential?
• Water potential of sucrose solution
• Water movement across a differentially permeable membrane
• Osmosis and plant cells
• Osmosis and red blood cells
initial mark
initial mark
final mark
Experiment showing osmosis
30 minutes later
What is osmosis?• The net movement of water molecules
across a differentially permeable membrane from a less concentrated solution to a more concentrated solution
• The net movement of water molecules across a differentially permeable membrane from a region of higher water potential to a region of lower water potential
What is water potential?• The probability of water molecules moving through a membrane from each side of the differentially permeable membrane
• Value as the concentration of solutes (i.e. as the concentration of water molecules )
• Distilled water: water potential = 0greatest water potential
• Solutions: water potential < 0 (-ve value)
0
Water potential of sucrose solution
0
+
-
Water potential (arbitrary unit)
Concentration of sucrose solution (M)
net movement of water moleculeswater molecule sucrose moleculelow water potential high water potential
Water movement across a differentially permeable membrane
Osmosis and plant cells
• distilled water
in distilled water for 30 minutes
When young plant cells are immersed in
they become turgid, bigger and heavier
in concentrated sucrose solution for 30 m inutes
water out
water out
water out
Osmosis and plant cells
• concentrated sucrose solutionWhen young plant cells are immersed in
they become soft, smaller and lighter
in distilled water for 30 m inutes
cell bursts, cell content is released
Osmosis and red blood cells
• distilled water
When red blood cells are immersed in
they burst and release red pigments
Osmosis and red blood cellsWhen red blood cells are immersed in
in concentrated sucrose solution for 30 minutes
water out
water out
water out
• concentrated sucrose solutionthey shrink
Summary• Osmosis: the net movement of water
molecules across a differentially permeable membrane down a water potential gradient
• Effect of osmosisWhen put in a solution with water potential
> cell = cell < cell
Plant cells turgid no change flaccid
Animal cells swell,may burst
no change shrink