Osmosis is the spontaneous movement of water molecules through a semi-permeable membrane from a region of lower solute concentration to higher solute concentration in order to equalize the concentrations. It provides the means for water transport into and out of cells. The direction of osmosis depends on the solute concentrations on both sides of the membrane - if one side has a higher concentration than the other, water will diffuse into the lower concentration side. This movement of water allows cells to remain turgid and control their volume under different osmotic conditions by taking in or releasing water through osmosis.

1. BIPIN.S
NATURAL SCIENCE
REG No.13971012

2. Difference in concentration between solutions on
either side of semi permeable membrane called
Osmotic gradient
Osmosis is the spontaneous net movement
of solvent molecules through a partially
permeable membrane into a region of higher solute
concentration, in the direction that tends to equalize
the solute concentrations on the two sides.
Osmosis provides the primary means by
which water is transported into and out of cells

3. Concentration
gradient
Concentration Gradient - change in the concentration of a substance
from one area to another.
Osmosis
Osmosis is the movement of WATER across a semi-permeable
membrane
At first the concentration of solute is very high on the left.
But over time, the water moves across the semi-permeable
membrane and dilutes the particles.

5. Osmosis – A Special kind of Diffusion
Diffusion of water across a selectively permeable membrane (a barrier
that allows some substances to pass but not others). The cell
membrane is such a barrier.
Small molecules pass through – ex: water
Large molecules can’t pass through – ex: proteins and complex
carbohydrates

6. Hypotonic – The solution on one side of a membrane where the solute
concentration is less than on the other side. Hypotonic Solutions contain a
low concentration of solute relative to another solution.

7. Over time molecules will move across the membrane until the
concentration of solutes is equal on both sides. This type of solution
is called ISOTONIC.

8. • Cytoplasm is a solution of water and solids
(solutes dissolved in the water).
• Water moves into and out of cells because of the different
concentrations of the solutes.
• Different kinds of cells react differently depending on the solution they
are in.
• Below are examples of red blood cells in different types of solutions and
shows what happened to the red blood cells.

10. There is a greater
concentration of free water
molecules outside the cell
than inside
so water diffuses into the
cell
by osmosis
and the cell swells up
11

11. cell wall
cytoplasm
and
cell
membrane
vacuole
The cell absorbs water
by osmosis .... ....but the cell wall stops the
cell expanding any more
18

12. For osmosis we talk about the
potential water molecules have to
move – the OSMOTIC POTENTIAL.
Distilled water has the highest
potential (zero).
When water has another substance
dissolved in it, the water molecules have
less potential to move.The osmotic
potential is NEGATIVE.

13. The osmotic potential of a cell
is known as its WATER
POTENTIAL. For animal cells,
the water potential is the
osmotic potential of the
cytoplasm.

14. An animal cell with water
potential –50 is
placed in a solution…

15. If the osmotic
potential of the
solution is less
negative than the
water potential of the
cytoplasm(the
solution is
hypotonic), net
endosmosis will
occur, i.e. water will
move into the cell
from the solution.
The result will be
haemolysis (the cell
will burst)
Water potential of cytoplasm = -
50
Osmotic potential of solution= -
20

16. If the osmotic potential
of the solution is more
negative than the water
potential of the
cytoplasm (the solution
is hypertonic), net
exosmosis will occur.
The result will be
crenation (the cell will
shrivel up)
Water potential of cytoplasm= -
50
Osmotic potential of solution = -
80

17. If the
osmotic
potential of
the solution
is the same
as the water
potential of
the
cytoplasm
(the solution
is isotonic),
there will be
no net
osmosis.
Water potential of cytoplasm= -50
Osmotic potential of solution= -50

18. In animal cells, the water potential is
equal to the osmotic potential of the
cytoplasm, but this is different in plant
cells…
Plant cells have a cell wall, which
exerts an inward pressure when the
cell is turgid.This is known as the
pressure potential.
The water potential of an animal cell is
equal to the osmotic potential of the
cytoplasm plus the cell wall pressure:
W.P.= O.P. + P.P.

19. A plant cell with water
potential –50 is placed in
a solution…

20. If the solution is
hypotonic, net
endosmosis
occurs and the
cell becomes
fully turgid.
Water potential of cytoplasm = -50
Osmotic potential of solution = -20

21. If the solution is
hypertonic, net
exosmosis
occurs and
causes
plasmolysis
(the cell
membrane pulls
away from the
cell wall.The cell
wall stays intact).
Water potential of cytoplasm =
-50
Osmotic potential of solution =
-80

22. If the solution is
isotonic, no
net osmosis
occurs.The cell
is not
plasmolysed, but
it is not fully
turgid either.
Water potential of cytoplasm = -50
Osmotic potential of solution = -50

23. Conclusion:
Osmosis is a vital process in biological systems,
as biological membranes are semi permeable.
Osmosis is responsible for the ability of plant roots to
draw water from the soil.
Osmosis is a vital process in both plants and animals
to maintain their own life process.

24. Reference:
Borg, Frank (2003). "What is osmosis? Explanation and
understanding of a physical phenomenon“ Wiley international
publications.
Kramer, Eric; David Myers. "Osmosis is not driven by water
dilution". Trends in Plant Science 18 (4): 195–197.
Kosinski, R. J. "Challenging misconceptions about
osmosis.". Association for Biology Laboratory Education 30: 63–
87.