1. The document discusses various types of molecular movement including diffusion, osmosis, and active transport. 2. Diffusion is the movement of molecules from an area of high concentration to low concentration down a concentration gradient. Osmosis is the movement of water molecules through a partially permeable membrane from high to low water potential. 3. Active transport moves molecules against their concentration gradient from low to high concentration areas and requires energy in the form of ATP.

1. MOVEMENT OF MOLECULES
Do they ever stop moving?!!

2. DIFFUSION
 All molecules move about. In gaseous state, they
are widespread and with weak bonds holding them
together. In liquid state, they are closer with
stronger bonds holding them together. In solids they
are very close and could only vibrate in their place.

3. NOW PUT UP YOUR HAND AS SOON AS YOU
CAN DETECT THE SMELL OF THE AIR
FRESHENER.

4. WHAT DO YOU NOTICE?
 Who were the first to detect the smell?
 Who were last to detect the smell?
 Why isn’t there anyone who did not detect the
smell?
 Explain how you could smell the scent although you
are far away from the air freshener.
 What if we opened the door or window? Would
others outside be able to smell the scent?

5. DIFFUSION
Is the movement of molecules from a
high concentration area to a low
concentration area, down a
concentration gradient.

6. WHAT WOULD HAPPEN TO A LUMP OF SUGAR
PLACED IN A CUP OF WATER?

7. WHAT WOULD MAKE MOLECULES
MOVE/SPREAD OUT FASTER OR SLOWER?
 Temperature
 Stirring/ air currents
 Number of molecules
 Surface area
 Distance/ thickness of membrane
 Difference between molecule concentration in both
areas

8. OSMOSIS
 A special type of diffusion involving the movement
of water molecules only, through a partially
permeable membrane.
 Partially permeable membrane is a membrane
with small holes that can allow only small molecules
to pass through.

10. NOW I NEED FOUR VOLUNTEERS!

11. OSMOSIS
Is the movement of water molecules
from a dilute solution (high water
potential) to a concentrated solution
(low water potential) through a partially
permeable membrane.
 A cell membrane is a partially permeable
membrane.

12. WHAT HAPPENS TO ANIMAL CELLS IF THEY WERE
PLACED IN A SOLUTION OF A DIFFERENT
CONCENTRATION THAN OF THEIR CYTOPLASM?

13. WHAT ABOUT PLANT CELLS?

14. OSMOSIS IN PLANT CELLS.
 Water enters a plant
cell, the water
molecules put pressure
on the walls. The rigid
cell wall will prevent the
cell from bursting. This
plant cell is said to be
turgid.
 This keeps the plant
firm.

15. OSMOSIS IN PLANT CELLS
 When water leaves the
plant cell the elastic
cell membrane shrinks,
while the rigid cell wall
keeps the shape of the
cell fixed. This plant
cell is said to be
plasmolysed.

17. CAN YOU DRAW AND LABEL WHAT YOU SEE?

19.  ACTIVE TRANSPORT
 In some situations, there is a need to move
molecules from a region of low concentration to a
region of high concentration.
 A root hair cell needs to take in minerals from the
soil, even if the concentration in the soil is lower
than that in the cells.
 Active transport is the movement of molecules from
an area of low concentration to an area of high
concentration against the concentration gradient,
this requires energy and the presence of a
membrane carrier.

20. ACTIVE TRANSPORT, PROTEIN CARRIER
ATP

21. TABLE 4: DIFFUSION, OSMOSIS & ACTIVE TRANSPORT
Diffusion Osmosis Active
transport
Type of
molecules
Movement of
molecules
Energy & Carrier
required
Movement of
molecules down
or against
concentration
gradient
Examples
All molecules Only water Molecules that
have membrane
carriers
From high
concentration
to low
concentration
From high water
potential to low
water potential
From low
concentration
to high
concentration
No No Yes
Down Down Against
Ink drop spreading
in water
Water entering
root hair cells
Glucose
absorbed in
small intestine

22. USEFUL VIDEOS
 Plasmolysis in red onion cells:
https://www.youtube.com/watch?v=mXKqYrlmeMs

23. CH3 CHECKLIST
 Define diffusion as the net movement of particles from a region of
their higher concentration to
a region of their lower concentration down
a concentration gradient, as a result of their random movement
 Describe the importance of diffusion of gases and solutes
 State that substances move into and out of cells by diffusion
through the cell membrane
 State that water diffuses through partially permeable membranes
by osmosis
 State that water moves in and out of cells by osmosis through the
cell membrane
 Investigate and describe the effects on plant tissues of immersing
them in solutions of different concentrations
 State that plants are supported by the pressure of water inside the
cells pressing outwards on the cell wall
 Define active transport as the movement of particles through a
cell membrane from a region of lower concentration to a region of
higher concentration using energy from respiration