biology form 4 chap3 part2

1. CHAPTER 3 :
MOVEMENT OF SUBSTANCES ACROSS
THE PLASMA MEMBRANE

2. LEARNING OUTCOMES
• Explain what hypotonic, hypertonic &
isotonic solutions are;
• Explain the effects of hypotonic,
hypertonic & isotonic solutions on plant
cell & animal cell;
• Explain plasmolysis, deplasmolysis,
haemolysis & crenation.
• Relate the movement of substances across
the plasma membrane with concentration
gradient.
• Explain the phenomenon of wilting in
plants using examples.
• Explain the preservation of food using
examples.

3. HYPOTONIC, HYPERTONIC
& ISOTONIC SOLUTION
• The direction of movement of
substances across the plasma
membrane in the cell depends on the
concentration of the solution around
it.
• There are 3 types of solution;
hypotonic, hypertonic & isotonic
solution.

4. HYPOTONIC, HYPERTONIC
& ISOTONIC SOLUTION
• HYPOTONIC SOLUTION : a solution
that contains a LOWER concentration of
solute molecules (HIGHER concentration of
water molecules) than the other solution
(cell).
• HYPERTONIC SOLUTION : a solution
that contains a HIGHER concentration of
solute molecules (LOWER concentration of
water molecules) than the other solution
(cell).

5. HYPOTONIC, HYPERTONIC
& ISOTONIC SOLUTION
• ISOTONIC SOLUTION : a solution has the
SAME solute concentration (EQUAL water
concentration) than the other solution (cell).
• Water diffuses across the plasma membrane
from the HYPOTONIC solution to the
HYPERTONIC solution. (osmosis)
• The concentration of the solution around the
cell has different effects on plant cells &
animal cells.

6. EFFECTS OF HYPOTONIC, HYPERTONIC &
ISOTONIC SOLUTIONS ON PLANT CELLS
• HYPOTONIC SOLUTION (distilled water)
:
– The plant will become turgid (very
firm). Water tends to enter the cells
into the vacuole & causes its size to
increase, pushing the cytoplasm towards
the cell wall, (not burst due to the
presence of cell wall).
• HYPERTONIC SOLUTION (30% sucrose) :
– would shrink & become flaccid because
it is losing water to the outside of
the cell. This process is called
plasmolysis.

8. PLASMOLYSIS

9. EFFECTS OF HYPOTONIC, HYPERTONIC &
ISOTONIC SOLUTIONS ON PLANT CELLS
– Deplasmolysis : plant cell are
replaced back into hypotonic
solution after undergone
plasmolysis in a hypertonic
medium.
• ISOTONIC SOLUTION (5% sucrose) :
– No changes. Water molecules move
into & out at the same rate. No
net movement of water molecules.

11. EFFECTS OF HYPOTONIC, HYPERTONIC &
ISOTONIC SOLUTIONS ON ANIMAL CELLS
• HYPOTONIC SOLUTION (Distilled
water) :
– Increase in size (swell) & may
finally burst because water enters
the cells via osmosis to try to
balance the total concentration of
solutes between the inside & the
outside of the cell.
• Red blood cell = haemolysis

13. EFFECTS OF HYPOTONIC, HYPERTONIC &
ISOTONIC SOLUTIONS ON ANIMAL CELLS
• HYPERTONIC SOLUTION (4% NaCl) :
– the cells would shrink because water
leaves the cell via osmosis in an
attempt to balance the total
concentration of solutes between the
inside & the outside of the cell.
– Water is rapidly lost
• Red blood cell = crenation  will
shrivel & probably die.

15. EFFECTS OF HYPOTONIC, HYPERTONIC &
ISOTONIC SOLUTIONS ON ANIMAL CELLS
• ISOTONIC SOLUTION (0.85% NaCl) :
– no changes.
– Water molecules flow across the
plasma membrane at the same rate.
– No net movement.
– Red blood cells maintain their
shape.

16. THE EFFECTS & APPLICATION OF
OSMOSIS IN EVERYDAY LIFE
• Haemolysis & crenation very seldom
occur in human being / animal
because homeostasis always ensures
that the extracellular fluid is
isotonic to the intracellular fluid.
• When there is a disturbance in
homeostatic balance, there is always
a compensatory mechanism.

17. THE EFFECTS & APPLICATION
OF OSMOSIS IN EVERYDAY LIFE
• The glucose level in the
extracellular fluid of a diabetic
patient is high  drinks  water
bring down the extracellular solute
concentration  isotonic to
intracellular fluid.
• Urine more concentrated to help
bring down the extra cellular solute
concentration.

18. THE EFFECTS & APPLICATION
OF OSMOSIS IN EVERYDAY LIFE
• Normal person  drinks a lot
of water  not experience
severe hypotonic condition 
kidney excrete the excess
water.
• Our cells are protected from
haemolysis or crenation 
osmoregulation.

19. THE EFFECTS & APPLICATION
OF OSMOSIS IN EVERYDAY LIFE
• Application :
– Osmoregulation in Amoeba &
Paramecium
– Plant wilting (excess fertilizer)
– Food preservation (salt &
minerals)

20. PHENOMENON OF WILTING IN PLANTS
• Excessive use of chemical fertilisers will
cause plants to wilt.
• Fertilisers will dissolve in the soil &
cause the soil water to be hypertonic to
the root cells of the plant.
• Water diffuses out of the root cells 
cells lose water to their surrounding &
shrinks  plasmolysis occurs  flaccid
 plant wilt.
• No water is given  continue wilt &
die.

21. PRESERVATION OF
FOOD
• Based on the concept of osmosis
& plasmolysis.
• Method of preservation : drying,
pickling, smoking, salting &
sugar-curing.
• Mostly using salt & sugar.

22. PRESERVATION OF
FOOD
• Fish – covered with salt  the
moisture around the fish to be
hypertonic  water diffuse out of
the cells by osmosis  plasmolysis.
• Lack of water prevents the growth of
microorganisms  salted fish can
last longer.
• Fruit pickles  use sugar solution,
vinegar @ salt.