Cell ProcessesCellular Transport
Osmosis and
Diffusion
Types of Cellular Transport
 Passive Transport
cell doesn’t use energy
1. Diffusion
2. Facilitated Diffusion
3. Osmosis
Weeee!!
!
high
low
 Active Transport
cell does use energy
1. Protein Pumps
2. Endocytosis
3. Exocytosis
This is
gonna
be hard
work!!
high
low
Active Transport
Transport of large
particles- (whole cells or
solids)
a.Endocytosis– cell membrane folds in
and forms a small pouch
– The pouch then pinches
off from the cell
membrane to become a
vesicle
b.Exocytosis-
– Vesicle moves to the cell
membrane-fuses with it
and then releases its
contents to the outside
of the cell
Amoeba Feeding
Passive Transport- Diffusion
Diffusion is the movement of molecules from an
area of high concentration to an area of low
concentration, until evenly spread out.
Why is Diffusion Important?
All living cells rely on diffusion to live.
Cells use it for:
 Getting raw materials for respiration (dissolved
substances and gases)
 Removing waste products (eg. from respiration)
 Photosynthesis in plants (raw materials in, waste products out)
Examples…
Respiration- Gas Exchange
In breathing you exchange carbon dioxide (CO2) and oxygen (O2) between
alveoli in the lungs and the blood.
This is an example of diffusion.
Cellular Respiration- In Cells
food + oxygen  carbon dioxide + water + energy
Cellular Respiration and Diffusion
Photosynthesis
and Diffusion
carbon dioxide + water  oxygen + glucose
 Carbon dioxide
diffuses in through
the stomata

Oxygen and water
diffuse out of the stomata
Osmosis
• Osmosis is a special
case of diffusion.
• It is the movement of
WATER across a
selectively permeable
membrane from a high
concentration to a low
concentration.
Selectively Permeable?
• The cell membrane has
very small holes in it.
• Small molecules like
water can pass through
it easily.
• Larger molecules like
sugar, salt and starch
can not fit through
easily.
Model of a
Selectively Permeable Membrane
Water
Starch
Small molecules, such
as water can pass
through it.
Large molecules like starch
can not pass through the
membrane
Diagram shows the net flow of water
Osmosis What is Happening?
Water
Starch
The water molecules pass
both ways through the
membrane
The overall flow of water
molecules is from a region
with lots of water molecules
to region of less water
molecules.
Lots of water
molecules
Few water molecules
Water is described as
moving down a
concentration gradient –
from a high concentration to
a low concentration
Osmosis what is happening?
Water
Lots of water
molecules
Starch
Few water molecules
Water molecules move from
the high water concentration
to the low water
concentration. Until both
sides have an evenly
balanced water
concentration.
Water is described as
moving down a
concentration gradient –
from a high concentration to
a low concentration
Osmosis in Action
Have a look at this video
and answer the questions
on the next slide:
http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__
how_osmosis_works.html
1 Osmosis is best defined as the
movement of
A) molecules from an area of high
concentration to an area of lower
concentration.
B) molecules from an area of low
concentration to an area of higher
concentration.
C) water molecules across a membrane
from an area of low water to an area
of higher concentration.
D) water molecules across a membrane
from an area of high water
concentration to an area of lower
concentration.
E) water molecules inside a container.
2Which of the following will pass through
a cell membrane most easily?
A) small polar molecules
B) small nonpolar molecules
C) large polar molecules
D) large nonpolar molecules
E) large neutral molecules
3 A red blood cell placed in a
hypertonic medium will
A) expand.
B) burst.
C) shrink.
D) have no change in shape.
E) become a white blood cell.
4 A 5% urea solution is
hypotonic to a 10% urea
solution.
A) True B) False
5 If a cell is placed in an
isotonic medium, there will
be no net movement of
water.
A) True B) False
Plant Cell in Different Solutions
Plant cell placed in
pure water
Water moves
Into the cell
In pure water – water will
move in swelling the
vacuole which pushes out
against the cell wall.
The plant cell is described
as TURGID.
The cell does not burst
because of the cell wall.
Plant Cell in Strong Sugar Solution
Strong Sugar/Salt
Solution
In a strong salt or sugar
solution – water will move
out of the vacuole causing it
to shrink.
The cytoplasm can also
shrink away from the cell wall.
The plant cell is described as
Plasmolysed or Flaccid.
Animal Cells in Different Solutions
• A red blood cell in pure water, water will
move into the cell and the cell will BURST
(there is no cell wall to prevent this
happening)
• In a strong salt/sugar solution water will
move out and the cell will SHRINK (the cell
in described as CRENATED)
Some terms when comparing two
solutions
• Hypotonic – one that has a high water
concentration compared to surrounding
solution
• Hypertonic – one that has a low water
concentration compared to surrounding
solution
• Isotonic – one that has a water
concentration equal to the surrounding
solution
What Type of Solution are These Cells In?
A
Hypertonic
B
Isotonic
C
Hypotonic
Act it out!
1.
Nominate some sugar molecules
2.
Everyone else is a water molecule
3.
Draw a dashed line down the middle of the parking lot with chalk
(your selectively permeable membrane!)
4.
Arrange your water molecules either side of the membrane
5.
Add your sugar molecules to one side and see if equilibrium can
be restored by water moving in the right direction!
6.
What happens if you remove some of the water molecules?