IT’S A
GREEN WORLD
WATER, WATER
EVERYWHERE
Starter
Raise your hand when you can smell the
perfume…………………
Why is perfume put on
the warm places of
the body such as the
neck and wrists?
Water, water everywhere
Learning objectives
 Describe osmosis
 Describe the effects of
the uptake and loss of
water on plant and
animal cells.
 Explain the key terms:
flaccid, plasmolysed,
turgid, crenation and
lysis
Success criteria
 Know the definition of
osmosis
 Be able to understand
and describe the
effects of different
concentrations of sugar
solutions on plant cells
 Be able to understand
and therefore use the
key terms correctly
Recap of diffusion
Diffusion and concentration
Why can the student smell the sock from a distance?
The sock can be smelt because sweat and other
molecules are moving away from it and spreading out in
the air. This is called diffusion.
Where is the smell strongest?
The smell is strongest at the sock. The smell becomes
weaker further away from the sock.
Changing concentrations
During diffusion molecules move from an area of high
concentration to an area of low concentration. They are
said to move down a concentration gradient.
Diffusion is a passive
process which means that
no energy is needed.
high
concentration
low
concentration
Molecules diffuse until they
are evenly spaced apart
and equilibrium is reached.
The rate of diffusion depends on several factors, such as
the distance the particles have to travel and the
difference in concentration.
What is osmosis?
Osmosis is the diffusion of water molecules from a low
concentration solution to high concentration solution,
across a partially-permeable membrane.
A partially-permeable membrane has holes in it that permit
water molecules through but are too small to allow larger
molecules through. Osmosis can be demonstrated using
visking tubing filled with a solution and placed in a beaker
of pure water.
partiallypermeable
membrane
(visking tubing)
water
glucose
Osmosis demo
Before
After
Dilute vs. concentrated
During osmosis, water molecules diffuse from pure water or
dilute solution to more concentrated solutions.
 Dilute solutions have a high concentration of
water molecules.
 Concentrated solutions have a low concentration
of water molecules.
pure water
dilute solution
concentrated
solution
Support in plant cells
Water can move in and out of a plant cell
through its
 Cell wall - permeable
 Cell membrane – partially permeable
The presence of water in a plant cell gives it
 Shape
 Support
The cell wall also provides support
Support in plant cells
What happens when water uptake and
water loss are not balanced a plant?
The plant will wilt.
Osmosis and cells
Plant and animal cells are surrounded by a partiallypermeable plasma membrane. This allows water and other
small molecules to diffuse across.
Plant cells additionally have a strong cell wall surrounding
the membrane which offers support and protection.
plasma
membrane
cell wall
plant cell
red blood cell
HD only
- More on osmosis
When a potato chip is in salt water the chips
become flaccid (soft and floppy).
WHY?
There is a higher concentration of water
molecules inside the potato cells than
outside. Water leaves the cells by osmosis
and the cells become plasmolysed.
Osmosis and plant cells
Osmosis and animal cells
Animal cells do not have a cell wall. This means they
respond differently to plant cells to the gain and loss of
water.
In dilute solutions, osmosis can
cause animals cells, such as red
blood cells, to swell up and burst.
This is called lysis.
In concentrated solutions, water
loss causes the cells to shrink.
When this happens to red blood
cells, it is called crenation.
Osmosis and animal cells
Osmosis in onion cells
 Follow instructions on w/s B4b5 –
osmosis in onion cells
Osmosis
Weak solution
Concentrated solution
Lysed
Normal
Turgid
Normal
crenated
Plasmolysed
Plenary - Predicting osmosis
Water, water everywhere
Learning objectives
 Describe osmosis
 Describe the effects of
the uptake and loss of
water on plant and
animal cells.
 Explain the key terms:
flaccid, plasmolysed,
turgid, crenation and
lysis
Success criteria
 Know the definition of
osmosis
 Be able to understand
and describe the
effects of different
concentrations of sugar
solutions on plant cells
 Be able to understand
and therefore use the
key terms correctly