Osmosis is the spontaneous movement of water molecules through a semi-permeable membrane from an area of higher water concentration to lower water concentration in order to equalize the concentration of water molecules on both sides of the membrane. The movement occurs due to differences in solute concentration between solutions separated by the semi-permeable membrane. Osmosis plays a key role in transporting water into and out of cells and the response of cells to their external environment depends on whether the outside solution is hypo-tonic, iso-tonic, or hyper-tonic compared to the cell cytoplasm.

1. BIPIN.S
NATURAL SCIENCE
REG No.13971012

2. 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
Difference in concentration between solutions on
either side of semi permeable membrane called
Osmotic gradient

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
11
so water diffuses into the
cell
by osmosis
and the cell swells up

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.