CP Biology
Name
______
____________
UNIT 3B: Cell Membrane & Transport
The Keys to Moving Materials Into and
Out of Cells
Introduction to Cell Transport
Transport is the name of the life process in which
materials are exchanged between and organism and its
environment.
Transport can be as simple as moving materials between a
one celled organism and its environment or as complex as
the transport systems in higher organisms such as humans.
Whether it is simple or complex, the final point of transfer
is at the cell membrane.
What types of materials need to be transported into or
out of living cells?
IN: oxygen, water,
glucose, amino acids,
other building blocks
and good things
OUT: carbon dioxide,
wastes, hormones
(packaged products),
water, salts, other bad
things
Example of transport in unicellular and multicellular
organisms:
CO2
unicellular
wastes
Blood Vessel O2
All cells live at least partly in touch with water-based
("aqueous") solutions. In order for substances to move into
or out of a cell, they must cross the cell membrane between
the water-based solution on the outside of the cell (its
ions
wastes
O2
CO2
"environment") and the water-based solution on the inside
Multicellular
(w/ organ systems)
of the cell (="cytosol" or "cell solution").
Notes, summary, questions:
What is a solution? A solute dissolved in a solvent.
In Biology, the universal solvent is water!! Many things dissolve in water.
1
CELLULAR BOUNDARIES
The Properties of Lipids
(Textbook 7.2 pg. 204)
Phosphorus group
All cells contain some type of boundary that separates the
inside of the cell from the outside environment.
What does
hydrophilic mean?
_water “loving”__
Cell Wall
Some cells have rigid supportive structure called a cell wall
surrounding the outside of the cell.
Recall: what polysaccharide makes up cell walls?
___cellulose_____________________________
Cell walls are porous and DO NOT regulate what goes in
and out of a cell.
Cell Membrane
Fatty acids
What does
hydrophobic mean?
_water “fearing”__
Phospholipids have two main portions:
1) a hydrophilic head
Contains a polar (charged)
phosphate group
2) Two hydrophobic
fatty acid tails
Non-polar (not charged)
oily regions of the
molecule
ALL cells have a cell membrane.
 Made of a double layered sheet called a phospholipid
bilayer
Use the words attracted or not attracted to fill in the
 It is a flexible structure and forms a boundary
blanks below.
between the cell and its environment.
 The cell membrane regulates what enters and leaves The hydrophilic heads are _attracted_______ to water.
the cell and also protects and supports the cell
The hydrophobic tails are __not attracted to water.
Cell membranes have this typical layered structure because
of the chemical properties of the lipids that make up the
membrane.
When these lipids are mixed with water, their hydrophobic
fatty acid "tails" cluster together while their hydrophilic
"heads" are attracted to water.
A phospholipid bilayer is the result. (see picture on next
page)
Notes, summary, questions:
2
1
The Fluid Mosaic Model
Protein (and carbs & other lipids) molecules are
embedded in the phospholipid bilayer of most cell
membranes.
Dynamic!
Because the protein molecules can move around and
"float" among the lipids (fluid), and because so many
different kinds of molecules make up the cell membrane
(mosaic), scientists describe the membrane as a “Fluid
Mosaic”, i.e.
What are all these different molecules doing?
Proteins
The Phospholipid Bilayer
a) Some proteins form channels and pumps to help
Which component of the phospholipids are hydrophobic?
move materials across the cell.
____fatty acid (lipid) tails__________________
b) Some proteins
How are they oriented (positioned) in the bilayer?
1) act as enzymes
(Which way are they facing?)
2) can attach to the cell’s cytoskeleton
________face in (or toward each other)__
(internal support structure of the cell)
helping cells to respond to the
Which component of the phospholipids are hydrophilic?
environment in order to move or change
____phosphorus head_____________________
shape.
Carbohydrates act like chemical identification signs
(markers, allowing individual cells to recognize
themselves (also to recognize itself from invaders).
How are they oriented (positioned) in the bilayer?
_____face outwards (away from the tails)
Circle a membrane protein in the diagram above.
Put a box around a carbohydrate attached to the bilayer in the
diagram above.
Notes, summary, questions:
3
1
Selective Permeability
Some materials are allowed to enter and leave a cell,
and some are not.
Since a cell needs to constantly exchange materials with its
environment, many substances can cross biological
membranes.
However, some substances are
 too large or
 too strong of a charge
to pass across the phospholipid bilayer of the cell
membrane.
Most biological membranes are selectively permeable,
which means some substances can pass across the
membrane, while others cannot pass through
What does it mean if we say that a membrane is
impermeable to a substance?
The membrane
does not allow that substance to pass through.
Which of the following materials would move easily
through the cell membrane?

water __yes – because it is small (even though it is
slightly charged, polar, – we’ll talk about aquaporins
later).
 small molecules like O2 and CO2 __YES – small
and nonpolar (not charged!).____
 charged particles
NO – hydrophobic lipid tails
of the membrane are nonpolar and do not like charged
substances.
any other particles that the cell must have to
survive __DEPENDS! – may or may not, depends on
their size and charge (the cell will find a way if it is
important to survival).
Selectively permeable membranes can also be referred to as
semipermeable membranes.
selectively
permeable
Not the same as selectively permeable!
Notes, summary, questions: The cell wall is an example of a semi-permeable membrane.
4
1
I.
PASSIVE TRANSPORT
Solute: a substance that is dissolved in a solution
Solvent: the dissolving substance in a solution
One of the most important functions of the cell membrane
is to keep the cell's internal conditions relatively stable.
Two examples of solutions (solutes in a solvent):
In order to maintain this condition of homeostasis, the
1) particles in air (faster)
cell membrane must control the transport of materials
into or out of the cell (in other words, from one side of
Examples: _food cooking, __
the membrane to the other).
_smoke, perfume, body odor,
Passive Transport: the movement of materials across a
cell membrane without using cellular energy(No added
ATP!!!).
Passive transport includes:
1) Diffusion
2) Facilitated Diffusion
3) Osmosis
_etc.______________________
2) particles in liquid (slower)
Examples: _apple juice, iced tea, Kool-Aid, lemonade,
____coffee, swimming pool, salt water___
All matter contains a certain amount of heat. This heat
causes molecules to tend to spread out into the available
space. In any solution, particles are moving constantly
because of the kinetic energy of the particles.
Every living cell exists in a liquid environment; therefore
we can look at the movement of molecules between the
solution inside the cell and the solution outside the cell.
How does heating a liquid affect the movement of solutes and
solvents? It speeds up the movement of the particles,
because you are increasing the kinetic energy.
Notes, summary, questions:
5
1
Diffusion
As a result of molecules moving constantly, colliding with
one another and spreading out randomly the particles tend
to move from an area where they are more concentrated to
an area where they are less concentrated. (High  Low)
Concentration: the amount of particles in a given area
(solution) in relation to other particles (often expressed as
a percent). Usually the amount of solute per unit of
solvent.
Diffusion: the process by which particles move from an
area of high concentration to an area low lower
concentration.
The process of diffusion drives the movement of many
molecules which move across cell membranes.
Suppose a substance is present in unequal amounts on
either side of a cell membrane. If the substance can cross
the membrane, the particles will tend to move toward the
area where it is less concentrated until it is evenly
distributed.
Diffusion of dye (solute) in water (solvent):
Medicine dropper
High conc.
gradient
Lower conc.
gradient
No (zero)
conc.
gradient
In your own words summarize what occurred when the dye
was placed in the water.
_______________________________________________
_______________________________________________
_______________________________________________
Concentration Gradient: conditions in which the
concentration of particles in two different areas are
different.*NOTE each molecule has its own concentration
gradient in any given solution.
Notes, summary, questions:
6
1
When a solute is first added to a solvent, the concentration What will happen to the concentration gradient over time
gradient is high. After the solute spreads out, the
as diffusion continues?_____________________________
concentration gradient is low (or non-existent). In
__high gradient  low gradient  no (zero) gradient
diffusion, molecules move "down" or "with" the
concentration gradient, from higher concentration to lower
concentration.
Once the concentration of the substance on both sides of
the cell membrane is the same, equilibrium is reached.
Particles of the solution will continue to move across the
membrane in almost equal numbers, so there is no further
net change to the concentration of the solutions inside or
outside the cell.
Dynamic Equilibrium: condition in which the
concentration of solute particles in a given area is equal
throughout the entire area.
NO CONCENTRATION GRADIENT REMAINS.
There is no “net” movement!
When dynamic equilibrium is reached, diffusion is equal in
all directions. Do the molecules in the solution stop
moving? ________________________________________
________________________________________________
________________________________________________
Notes, summary, questions:
7
1
Facilitated Diffusion
Molecules which pass most easily through the cell
Carrier,
Transport
Protein
membrane tend to be small and not charged allowing them
to dissolve easily in the membrane's lipid environment.
Outside
of cell
However, some substances seem to pass more quickly
through the membrane than they should - as though they
have a shortcut through the membrane.
Ex: water aquaporins, ions like Cl- and sugars like glucose
Inside of
cell
Solute
How does this happen? Proteins in the cell membrane act
as carriers or channels making it easy for certain molecules There are hundreds of examples of these special proteins
which are very specific (like enzymes) and change shape in
to cross.
order to allow the passage of certain substances into or out
of the cell. Although facilitated diffusion is fast and
specific, it is still diffusion so it does NOT require any
Facilitated Diffusion: process in which molecules that
energy from the cell. Also the net movement will still tend
cannot directly diffuse across the cell membrane pass
to be with or along the concentration gradient (high-->
through special protein channels.
low). ATP is not needed and it will continue until
equilibrium is reached.
Ex: RBC's have special protein carriers that allow glucose
to pass in/out of the cell
Notes, summary, questions:
8
1
OSMOSIS - an example of facilitated diffusion.
Water has been added to the list of molecules that enter
cells by facilitated diffusion, thanks to surprising new
research.
Why would water molecules normally have a hard time
getting across the cell membrane?
_Water is a polar molecule (slightly charged), the fatty
acid tails of the lipid bilayer are hydrophobic (water
fearing) and will not allow water to pass through.____
Many cells have special water channel proteins called
aquaporins which allow water to pass right through them
by facilitated diffusion. This extremely important
biological process is given a special name: osmosis.
Osmosis: the diffusion of water across a selectively
permeable membrane.
Osmosis deals ONLY with the diffusion of WATER.
Osmosis is similar to other types of diffusion but in the case
of osmosis the water (solvent) will move and not the solute
particles.
The water molecules will tend to move from an area of high
concentration to an area of low concentration until
equilibrium is reached.
Notes, summary, questions:
9
1
PREDICTING THE DIRECTION OF OSMOSIS IN
CELLS
Types of Solutions Outside the Cell that Affect the
Direction of Water Movement
The direction of water movement into or out of a cell can
have dire consequences on the survival of a cell. By
knowing the concentrations of solute and solvent on the
inside and outside of a cell, we can predict the direction of
osmosis and the result on the cell.
Solutions on the outside of a cell (in its environment, in
other words) can be described based on how they affect
the cell:
Where is the concentration of
water the highest?
_inside the cell_______
HYPERTONIC = "ABOVE strength"
Cell Shrinks-the solution outside the cell has a higher
concentration of solutes compared to the solution inside the
Which direction does the
water move?
___out of the cell____
cell. Water moves outside of the cell and the cell shrinks.
This type of environment is called a Hypertonic Solution.
HYPOTONIC = "BELOW strength"
Cell Swells-the solution outside the cell has a lower
concentration of solutes compared to the solution inside the
cell. Water moves into the cell and the cell swells. This
type of environment is called a Hypotonic Solution.
Where is the concentration of
water the highest?
___outside the cell_____
Which direction does the
water move?
___into the cell________
Notes, summary, questions:
10
1
ISOTONIC = "SAME strength"
Cell Stays the Same-the solution outside the cell has the
same concentration of solutes compared to the solution
inside the cell. Water moves equally in and out of the cell
and the cell remains the same size. This type of
environment is called an Isotonic Solution.
What is the solvent concentration of a solution with a 3%
Solute and solvent concentrations can be expressed as
concentration of solute? ___97% (solvent)
percentages of the entire solution.
When added together, the solute and solvent concentrations
must equal 100%. A solution with a 10 % solute
concentration has a 90% solvent concentration.
What is the solvent concentration of a solution with a 15%
concentration of glucose? ___85% (solvent)
What is the solute concentration of a solution with 98%
solvent? __2% (solute)___________
What is the solute concentration of a solution with 75%
water? ____25% (solute)_________
Given what you have
learned about the
movement of water ,
complete the
following table:
Conditions
Water will…
Environment is…
Solute concentration in
the environment is
equal to that in the cell
Solute concentration in
the environment is
greater than the cell
Solute concentration in
the environment is less
than the cell
Move equally in and out of the
cell
(no net movement)
Net movement of water OUT of
the cell
Isotonic solution
(cell will stay the same)
Net movement of water INTO the
cell
Hypotonic
(cell swells)
Hypertonic solution
(cell shrinks)
Ex: cell with 3% solute, 97% solvent
Beaker (environment) with 3% solute, 97% solvent
a) _Water moves equally in and out (no net movement)
b) __Cell stays the same size_________
c) __Isotonic solution__________
Environment
3% solute
97% water
Cell
3% solute
97% water
Ex: cell with 3% solute, 97% solvent
Beaker (environment) with 10% solute, 90% solvent
Environment
10% solute
90% water
a) __Net movement of water OUT of the cell
b) __Cell shrinks____________________
c) __Hypertonic solution____________
Cell
3% solute
97% water
Ex: cell with 3% solute, 97% solvent
Beaker (environment) with 1% solute, 99% solvent
Environment
1% solute
99% water
a) __Net movement of water INTO the cell
b) __Cell swells______________________
c) ___Hypotonic solution___________
-
Cell
3% solute
97% water
Notes, summary, questions:
11
1
Osmotic Pressure
Driven by differences in solute concentration, the net movement of water into or out of a cell produces a force known as
osmotic pressure.
Because cells contain a variety of solutes (sugars, proteins, salts, etc.), they are almost always hypertonic fresh water; as a
result, a typical cell exposed to fresh water will tend to swell up quickly from the entering water. This may in fact cause
an animal cell to swell like an overinflated balloon.
Plant cells contain a central vacuole which stores excess water - shrinking and swelling as water enters or exits the cell.
Plant cells wouldn't generally burst thanks to their protective cell walls. In fact, most cells in large organisms are not in
contact with fresh water on a regular basis - rather, they tend to be bathed in blood or other isotonic fluids which have
solute concentrations approximately equal to themselves.
Cells which are plump and rigid in hypotonic environments are called turgid; when a cell shrinks in a hypertonic
environment this is called plasmolysis.
.
Given what you have learned about the movement of water, complete the following table:
3%
5%
97%
95%
Out of the cell
Shrink
Hypertonic
20%
20%
80%
80%
Equally in and out/no net mvt
Stay the same
Isotonic
Notes, summary, questions:
12
1
Conditions
Environment
Plant Cell (leaf cell)
Before
After
Animal cell (blood cell)
Before
After
Solute concentration in
the environment is equal
to that in the cell:
Isotonic solution
Solute concentration in
the environment is
greater than the cell:
Hypertonic
Solution
Solute concentration in
the environment is less
than the cell:
Hypotonic Solution
13
1
II.
ACTIVE TRANSPORT
Active transport is any type of transport into or out of a
cell that requires energy (ATP).
solute
Active transport may involve the movement of molecules
against a concentration (gradient)difference, OR it may
involve the movement of large materials or clumps of
materials into or out of a cell (requiring changes to the
shape of the cell membrane).
A) Molecular Transport - smaller
Outside of cell
Low Solute
concentration
Inside of cell
High Solute
concentration
solute
In active transport, small molecules and ions are carried
across the cell membrane by special proteins in the
membrane that act like pumps and change their shape to
move molecules into or out of the cell against the
Example: ___Na+, K+, wastes, etc.____________
concentration gradient.
The advantage of this type of transport (which requires a lot
of a cell's daily energy!) is that it enables cells to
concentrate substances in a particular location, even when
diffusion might normally move the molecules in a different
direction.
Notes, summary, questions:
14
1
B) Bulk Transport
Endocytosis
The exact way in which large molecules or even clumps
of material move across the cell membrane depends on the
size and shape of the material being moved into or out of
the cell. Due to the large changes made to the cell
membrane, this is also a form of active transport and ATP
is required.
Endocytosis: process of taking material into the cell by
means of infoldings or pockets of cell membrane.
The "pocket" that is formed will break loose from the cell
membrane and form a vesicle or vacuole within the
cytoplasm. Some cells use this method to engulf large
molecules, food, or other cells. Two types include:
Ex: amoeba feeding
Ex: WBC engulfing RBC
Exocytosis
 Phagocytosis: type of endocytosis where solid (bulk)
materials like foods are transported into a cell.
Ex: Amoeba engulfing food
 Pinocytosis: type of endocytosis where liquids (like
solutions) are transported into a cell.
Ex: cell in
the
pancreas
exporting
insulin
Exocytosis: the membrane of the vacuole surrounding the
material fuses with the cell membrane, forcing the contents
out of the cell.
Example: Contractile vacuole in paramecium
Notes, summary, questions:
15