Understand the process of osmosis.
Know the effects of osmosis on plant and
animal cells.
Osmosis
Diffusion
Particles move randomly
Particles move randomly
Water moves down a
concentration gradient
Substances move from an area
of high concentration to low
concentration
Doesn’t require a membrane
Involves a partially permeable
membrane
Needs water for movement
Does not require cell energy for
movement
Doesn’t need water for
movement
Does not require cell energy for
movement

It is the net movement of water across a partially
permeable membrane from an area of high water
concentration to an area of low water concentration.
Partially permeable membrane
 The cell membrane has very small holes in it. Small
molecules can pass through, but larger ones cant.

The cell membrane separates the contents of
the cell from the outside

It has tiny holes in it

This allows small molecules to
pass through it but not large
molecules

It is PARTIALLY PERMEABLE
Low water concentration
Equal water
outside the cell
concentrations inside &
out
(i.e. concentrated
solution outside)
(i.e.equal solute
concentrations inside
& out)
High water
concentration
outside the cell
(ie pure water or
dilute solution
outside)

Flaccid (plasmolysed)
Wilting plant
Turgid
upright plant

Animal cells do
not have a cell
wall.

This means they
either swell and
burst OR shrink
if too much
water leaves
Lysis
Crenated- Can no longer
carry blood around body
If an animal cells are put in pure water they take in
water by osmosis until they burst.
haemolysed
normal
turgid then burst
If an animal cells are put in a concentrated solution (LWC)
they lose water by osmosis until they become shrunken or
haemolysed.
normal
haemolysed
http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/Osmosis_Anima
tion.htm
Important things to remember (and
almost always got wrong by students)
When there is a high concentration of a solute e.g.
salt, there is a low concentration of water
When there is a low concentration of the solute, there
is a high concentration of water.
1. What is a partially permeable membrane?
A membrane that only lets small molecules through it
2. Which substance moves by osmosis? Water, H2O
3. What happens to plant cells that take up water by osmosis, and
what do you call the cell?
The cells become ‘full’ of water and are called turgid
4. What happens to plant cells that lose water by osmosis, and
what do you call the cell?
The cytoplasm comes away from the cell wall and the cells are
called plasmolysed.
5. What does ‘haemolysed’ mean? How does it happen?
Animals cells which have lost water become shrunken and are called
haemolysed.
Turgid
Osmosis
Partially
Turgid
permeable
Diffusion
Plasmolysed
Partially
Osmosis
permeable
Plasmolysed
Diffusion
When water enters a plant cell and pushes on the
cell wall causing the cell to swell
A membrane that allows some substances to
pass through and others cannot.
The movement of particles from an area of high
concentration to an area of low concentration
The movement of water molecules from an area
of their high concentration to an area of their
low concentration
When water leaves a plant cell, the cell contents
shrink and the cell membrane pulls away from
the cell wall