Chapter 7.3
The Cell Membrane; Active & Passive Transport
Diffusion
• Molecules tend to “spread out”
• Move from an area of high concentration to
low concentration
• Requires no energy
Diffusion
= The movement of molecules from an area
of high concentration to an area of low
concentration
Equilibrium
What’s this have to do with cells?
Think about it…cells are like a nation
• Cells need things like a nation needs things…
– Exports, imports
– Has borders
• Why may a cell need materials to leave or
enter a cell?
• How might this occur?
Cell Membrane Function:
the GATEKEEPER
1)
2)
3)
Cell Membrane Structure
Characteristics:
Cell Wall
• Found in most prokaryotes and some
eukaryotes (plants, fungi, algae)
• Main function is support
•Animations of Active
Transport & Passive
Transport
Types of Cellular Transport
•
Weeee!!
!
Passive Transport
cell doesn’t use energy
1. Diffusion
2. Facilitated Diffusion
3. Osmosis
high
low
•
Active Transport
cell does use energy
1. Protein Pumps
2. Endocytosis
3. Exocytosis
This is
gonna
be hard
work!!
high
low
Passive Transport
•
•
•
cell uses no energy
molecules move randomly
Molecules spread out from an area of high
concentration to an area of low
concentration.
• (HighLow)
•
Three types:
3 Types of Passive Transport
1. Diffusion
2. Facilitated Diffusion – diffusion with the
help of transport proteins
3. Osmosis – diffusion of water
Lesson Overview
Cell Transport
Diffusion
In a cell:
- cytoplasm a solution of many different substances dissolved
in water.
As you know:
-In any solution, solute particles tend to move from an area
where they are more concentrated to an area where they are
less concentrated.= Diffusion
Diffusion---- the driving force behind the
movement of many substances across the
cell membrane.
Passive Transport:
1. Diffusion
Simple Diffusion
Animation
1. Diffusion: random movement of
particles from an area of ______
concentration to an area of
_______ concentration.
(__________________)
•
Diffusion continues until all
molecules are evenly spaced
(equilibrium is reached)-
•
Note: molecules will still move
around but stay spread out.
http://bio.winona.edu/berg/Free.htm
7-15 diagram pg 209
• Discuss with a friend and DRAW: What would be different in
7-15 if the high concentration of solutes had been inside the
cell to start with?
Passive Transport:
2. Facilitated Diffusion A
2. Facilitated diffusion: diffusion
of specific particles through
transport proteins(protein
channels/carriers) found in
the membrane
a. Transport Proteins are
specific – they “select” only
certain molecules to cross
the membrane
b.Transports larger or
charged molecules
Facilitated
diffusion
(Channel
Protein)
Carrier Protein
B
Diffusion
(Lipid
Bilayer)
Passive Transport: 2. Facilitated Diffusion
Glucose
molecules
Cellular Transport from a
High Concentration
High
• Channel Proteins
animations
Cell Membrane
to a Low Concentration
Through a 
Go to
Section:
Transport
Protein
Protein
channel
Low
Lesson Overview
Cell Transport
Osmosis: A Type of Facilitated Diffusion
• Inside of a cell’s lipid bilayer is
hydrophobic—or “water-hating.”
• water has a hard time getting through.
• Water channel proteins, known as
______________________ allow water
to pass right through them.
This movement of water is an extremely
important biological =
Passive Transport:
3. Osmosis
Osmosis
animation
• 3.Osmosis: diffusion of
water through a
selectively permeable
membrane
• Water moves from high to
low concentrations
•Water moves freely
through pores.
•Solute (green) too
large to move across.
Rule for Osmosis:
Water will get sucked to
wherever there is a higher
concentration of salt.
Osmosis
= The diffusion of water across a selectively
permeable membrane
ONLY THE WATER is moving.
Lesson Overview
Cell Transport
How Osmosis Works
Barrier below is permeable to water but not to sugar.
-water molecules can pass through the solute, sugar, cannot.
Lesson Overview
Cell Transport
How Osmosis Works
•
•
More sugar molecules on the
The concentration of water is __________________________
where more of the solution is made of sugar.
Lesson Overview
Cell Transport
How Osmosis Works
There is a net movement of water into the compartment containing
the concentrated sugar solution.
Water will tend to move across the barrier until equilibrium is reached.
At that point, the concentrations of water and sugar will be the same
on both sides.
Lesson Overview
Cell Transport
How Osmosis Works
When the concentration is the same on both sides
of the membrane, the two solutions will be
______________ which means “same strength.”
Lesson Overview
Cell Transport
Osmotic Pressure
The net movement of water out of or into a
cell produces a force known as osmotic
pressure.
= the force created by the net movement of
water through a cell membrane.
Isotonic Solution
iso=same
Isotonic: The concentration of solutes in the solution
is __________________ concentration of solutes
inside the cell.
Result: Water moves equally in both directions and
the cell remains same size!
Isotonic
Hypotonic Solution
Hypo=less
Hypotonic: The solution has a _______ concentration
of solutes and a __________ concentration of water
than inside the cell. (_______solute; _______water)
Result: Water moves from the solution to inside the
cell: Cell Swells and bursts open
Hypotonic
Hypertonic Solution
hyper = more
Hypertonic: The solution has a ________ concentration
of solutes and a ________ concentration of water than
inside the cell. (_______ solute; ________ water)
shrinks
Result: Water moves from inside the cell into the
solution: Cell shrinks
Hypertonic
What type of solution are these cells in?
A
B
C
Hypertonic
Isotonic
Hypotonic
How Organisms Deal with
Osmotic Pressure
•
Paramecium
(protist) removing
excess water video
•Bacteria and plants have cell walls that prevent them
from over-expanding. Pressure can damage the cell wall
though.
•A protist like paramecium has contractile vacuoles that
collect water flowing in and pump it out to prevent them
from over-expanding.
•Salt water fish pump salt out of their specialized gills so
they do not dehydrate.
•Animal cells are bathed in blood. Kidneys keep the
blood isotonic by remove excess salt and water.
Passive Transport Review
• Requires no energy
• Diffusion
• Osmosis = Diffusion of water
• Facilitated Diffusion: carrier
proteins “help” molecules
across the membrane like a
tunnel
Active Transport
•cell uses energy
•actively moves molecules to where they are
needed
•Movement from an area of low concentration
to an area of high concentration
•(Low  High)
•Three Types:
Types of Active Transport
Sodium
Potassium Pumps
(Active Transport
using proteins)
1. Protein Pumps –
•Example: Sodium /
Potassium Pumps
are important in nerve
responses.
Protein changes
shape to move
molecules: this
requires energy!
Lesson Overview
Cell Transport
Active Transport
• Small molecules pumped
into or out of cell by
transport proteins on the
cell membrane.
• Transport goes against a
concentration gradient
• Requires cellular energy
(ATP)
Types of Active Transport
• 2. _________________:
taking bulky material into a
cell
• Uses energy
• Cell membrane in-folds
around food particle
• “cell eating”
• forms food vacuole &
digests food
• This is how white blood
cells eat bacteria!
Types of Active Transport
3. __________________Forces
material out of cell in bulk
• membrane surrounding the
material fuses with cell
membrane
• Cell changes shape –
requires energy
• EX: Hormones or wastes
released from cell
Endocytosis &
Exocytosis
animations
Lesson Overview
Cell Transport
Molecular Transport
A considerable portion of the energy used by cells in
their daily activities is devoted to providing the energy
to keep this form of active transport working.
The use of energy in these systems enables cells to
concentrate substances in a particular location, even
when the forces of diffusion might tend to move these
substances in the opposite direction.
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