1. Diluted sugar Concentrated
solution sugar solution

2. Hypotonic solution Hypertonic solution

3. A B
 Balance the concentration on
both sides
If solute is of large molecules
 Only water molecules can
diffuse through
 In order to balance, we need
to add water on the more
concentrated side (B)
 So, water molecules from A
(more dilute) will diffuse to B
(more concentrated)
Before After
A B A B
Water 10 5 5 10
Solute 5 10 5 10

4. A B
If solute is of small molecules
 Both water and solute
molecules can diffuse through
the semi-permeable membrane
 Diffusion of both molecules
occur until A and B are isotonic
Before After
A B A B
Water 11 5 8 8
Solute 5 11 8 8

5. By now, you should know that:
 Movement of substances across plasma membrane
depends on the concentration of the solutions.
 Water diffuse from more dilute solution (hypotonic) to
more concentrated solution (hypertonic).

6. Terms to take note and remember!!
 Hypertonic – solution with higher concentration of
solutes than cell
 Hypotonic – solution with lower concentration of
solutes than cell
 Isotonic – solution of equal solute concentration with
cell
Which one has high solute concentration and low water
concentration? Hypertonic
The process where water diffuses across plasma
membrane from hypotonic soln. to hypertonic soln. is ...?
Osmosis

7. Effects of hypertonic, hypotonic & isotonic solutions on
plant cells
Hypertonic solution  H2O diffuses out from cell by osmosis
 H2O lost from vacuole & cytoplasm
 Vacuole shrinks
 Cytoplasm & plasma membrane shrinks and is
pulled away from the cell wall
 Cell becomes flaccid. Plant wilts.
 Process : Plasmolysis
 If immersed in a hypotonic solution, H2O
diffuse into the cell, making it turgid.
 Process : Deplasmolysis

8. Effects of hypertonic, hypotonic & isotonic solutions on
plant cells
Hypotonic solution
 H2O diffuses into the cell by osmosis
 Vacuole gains water, expands and exert
pressure outwards on the cell wall
 This pressure (tugor pressure) causes the
cell to be turgid (firm)
 Turgidity gives plant mechanical support
Isotonic solution  No net movement of water across plasma
membrane
 Water diffuses across the plasma membrane
at the same rate in both directions
 Cell’s volume and shape maintains

9. Effects of hypertonic, hypotonic & isotonic solutions on
animal cells
Hypertonic solution
 H2O diffuses out of cell by osmosis
 H2O is rapidly lost
 Red blood cells shrivel and probably die
 Process : Crenation
Hypotonic solution  H2O diffuses into the cell by osmosis
 Red blood cells gain water and swell and
finally burst (because have no cell wall)
 Process : Haemolysis
 For other animal cells, the process is known as
lysis

10. Effects of hypertonic, hypotonic & isotonic solutions on
animal cells
Isotonic solution
 No net movement of water across plasma
membrane
 Water diffuses at the same rate in both
directions
 Red blood cells maintain their shape

11. Hypertonic Isotonic Hypotonic
Flaccid No change Turgid

12. Osmosis in everyday life
1. Wilting plants
 Excess use of chemical fertilisers which dissolve in
soil
 Soil becomes hypertonic to the root cells
 Water diffuses out from root cells into soil
 Root cells becomes flaccid and undergo plasmolysis
 Wilt and may eventually dies
2. Preservation of food
 Salted fish
 Preserved fruits