Cell
Membrane
• Also known as the
Plasma
Membrane
• Surrounds the
cell
• Semi-permeable
• Selectively
permeable –
”chooses” what
enters and leaves
• MOST OF TIME
BASED ON SIZE OF
MOLECULE
• Made of a bilayer
(2) of lipids AND
proteins
Concentration
Gradient
Difference in
concentration
between the 2
areas
Cells
1. PASSIVE
transport
TRANSPORT
materials When particles move from
an area of high
by the
concentration
to
an
area
following
of low concentration
processes
Molecules Move with
the gradient
no energy
needed
2. ACTIVE TRANSPORT
When particles move
from an area of low
concentration to an
area of high
concentration
Molecules Move
against the
gradient
energy required
HIGH
LOW
Passive
Transport
2 Types
1. Diffusion
2. Osmosis
• No energy
• High  low
Diffusion
Substances other
than water that
move from HIGH
 LOW
DIFFUSION
LOW
HIGH
Molecules
eventually
stop moving
when…..
Equilibrium is
reached
no further change in
conc. occurs & both
sides are equal
Diffusion through a membrane
Cell membrane
Inside cell
Outside cell
Diffusion through a membrane
Cell membrane
diffusion
Inside cell
Outside cell
Diffusion through a membrane
Cell membrane
Inside cell
Outside cell
EQUILIBRIUM
Do Now: Identify this process
by name and explain why you
chose that process.
Osmosis • DIFFUSION OF
WATER INTO AND
OUT OF THE CELL
• Movement of WATER from
HIGH  LOW
Concentration
• With the Conc. Gradient
• NO ENERGY
NEEDED!
Osmosis
Cell membrane
Inside cell
High conc. of water
molecules.
Outside cell
Low conc. of water
molecules.
Osmosis
Cell membrane
OSMOSIS
Inside cell
High conc. of water
molecules.
Outside cell
Low conc. of water
molecules.
Osmosis
Cell membrane
OSMOSIS
Inside cell
Outside cell
EQUILIBRIUM. Equal water
concentration on each side.
What
• 1. Salt water:
happens • CELL SHRINKS bc
when you osmosis occurs 
water
moves
out
of
cell
place a
cell in:
Red blood cells that were placed in
a salt solution
**Plant cells don’t shrink b/c of
rigid cell wall  cell membrane
pulls away from cell wall**
Onion Skin Cells
• 2. Distilled/ pure water
• Cell fills up with water bc
water moves into cell due to
osmosis
•Animal cells =
•swell & burst
• Plant cells =
• swell, but do not burst b/c
of their cell wall
Red blood cell in distilled water
about to burst
Animal Cells
Same
amount of
water inside
and outside
the cell
Distilled water
Salt solution
Plant Cells
Same amount
of water
inside and
outside the
cell
Distilled water
Salt solution
TOPIC: CELLS
AIM: HOW DOES ACTIVE TRANSPORT OCCUR?
DO NOW:
In your own
words describe
the similarities
and differences
of diffusion and
osmosis.
The similarities of
diffusion and
osmosis are
______________
_______________
The differences of
diffusion and
osmosis are ______
_______________
_______________
Active
Transport
• Movement of molecules
from an area of low
concentration to an area
of high concentration
• Against the Conc.
Gradient
• ENERGY IS NEEDED!
L
H
L
H
CELL MEMBRANE
PROTEIN
LOW
(energy)
What process is each cell carrying out?
Active
Transport
Passive
Transport
Endocytosis
Taking substances into
cell by surrounding it
with the cell
membrane
How some uni-cellular
organisms take in
food
Form of ACTIVE
TRANSPORT (energy
required)
Cell membrane folds
in causing a vesicle
to form
Exocytosis
Vesicle fuses with cell
membrane causing the
materials inside to be
released
Also a form of Active
Transport