Cellular Transport
Notes
About Cell Membranes
1.All cells have a cell
membrane
2.Functions:
a.Controls what enters
and exits the cell to
maintain an internal
balance called
homeostasis
b.Provides protection and
support for the cell
TEM picture of a
real cell membrane.
About Cell Membranes (continued)
3.Structure of cell membrane
Lipid Bilayer -2 layers of
phospholipids
a.Phosphate head is polar
(hydrophilic or water
loving)
b.Fatty acid tails non-polar
(hydrophobic or water
fearing)
c.Proteins embedded in
membrane
Phospholipid
Lipid Bilayer
Polar heads Fluid Mosaic
love water
Model of the
& dissolve. cell membrane
Non-polar
tails hide
from water.
Carbohydrate cell
markers
Proteins
Membrane move
About Cell Membranes (continued)
• 4. Cell membranes have pores (holes) in it
a.Selectively permeable: Allows some
molecules in and keeps other molecules out
b.The structure helps it be selective!
Pores
About Cell Membranes (continued)
• 5. Size (macro or micro), charge (+ or -) and
solubility (lipid-soluble or not) affect a
molecule’s ability to cross the cell membrane.
 In general, small noncharged, lipid-soluble
molecules easily cross the cell membranes
Pores
Structure of the Cell Membrane
Outside of cell
Proteins
Lipid
Bilayer
Transport
Protein
Animations
of membrane
Go to structure
Section:
Carbohydrate
chains
Phospholipids
Inside of cell
(cytoplasm)
Types of Cellular Transport
•Animations of Active
Transport & Passive
Transport
•
Weeee!!
!
Passive Transport
cell doesn’t use energy
1. Diffusion
2. Facilitated Diffusion
3. Osmosis
high
low
Tonicity
Water Potential
•
Active Transport
cell does use energy
This is
gonna
be hard
work!!
high
low
Types of Cellular Transport
•
Bulk Transport
1. Endocytosis
Phagocystosis
Pinocytosis
Receptor-mediated
2. Exocytosis
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. Facilitative Diffusion – diffusion with
the help of transport proteins ,
3. Osmosis – diffusion of water
Passive Transport:
1. Diffusion
Simple Diffusion A
1. Diffusion: random movement
of particles from an area of
high concentration to an
area of low concentration.
(High to Low)
•
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
Passive Transport:
1. Diffusion
• Occurs in liquid or gas medium
Diffusion of a solute within a solvent is
affected by several factors:
 Temperature
 Pressure
 Density of the solvent
 Concentration Gradient
 Solubility of the solute
http://bio.winona.edu/berg/Free.htm
Passive Transport:
2. Facilitated Diffusion
2. Facilitated diffusion: diffusion of specific particles
through membrane transport proteins to help them move
through the cell membrane
a. Transport Proteins are specific – they “select” only
certain molecules to cross the membrane
b. Transports larger or charged molecules
c. Concentration gradient required – can’t transport from
low to high concentration
d. Energy not needed
e. Rate of transport reaches a maximum when all
membrane transport proteins are used up (saturated)
f. Membrane transport proteins are sensitive to inhibitors
that can cause them not to function
Passive Transport:
2. Facilitated Diffusion
There are 2 types of
membrane transport
proteins involved:
Channel proteins – contain
tunnels/openings that serve
as passageways of
molecules
Carrier proteins – undergo
temporary binding to the
molecule it carries resulting
in conformational change
that moves the molecule
through the membrane
A
B
Facilitated
diffusion
(Channel
Protein)
Diffusion
(Lipid
Bilayer)
Carrier Protein
Passive Transport: 2. Facilitated Diffusion
Glucose
molecules
Cellular Transport From aHigh Concentration
High
• Channel Proteins
animations
Cell Membrane
Low Concentration
Through a 
Go to
Section:
Transport
Protein
Protein
channel
Low
Passive Transport:
3. Osmosis
Osmosis
animation
• 3.Osmosis: diffusion of
water through a
selectively permeable
membrane
•Water moves freely
through pores.
•Solute (green) to large
to move across.
The water molecules will continue to cross the semi-permeable
membrane until an equilibrium is reached, where the two solutions
are of equal concentration.
Passive Transport:
3. Osmosis
Water is found inside and outside of the cell,
separated by a semi-permeable membrane
The presence of different solutes in the water
solutions in and out of the cell means concentration
of water on both sides is different.
Water Potential – term for movement of water
molecules as it undergoes osmosis
- The measure of the difference between the “force”
that pushes water molecules and the “force” exerted
by the membrane
Passive Transport:
3. Osmosis
Water solution with less solute (more diluted solution because of more water) =
higher water potential
Water solution with more solute (more concentrated solution) = lower water
potential
Water Potential Gradient - when 2 solutions of different water potentials are
separated by a semipermeable membrane, thus allowing osmosis to occur
Osmotic Pressure – “force” that moves water molecules through a semipermeable membrane
Passive Transport:
3. Osmosis
Tonicity – strength
of a solution in
relation to osmosis
3 Types:
Isotonic
Hypotonic
Hypertonic
Remember: Salt is a solute, when it is concentrated inside or outside
the cell, it will draw the water in its direction. This is also why you
get thirsty after eating something salty.
If the concentration of solute (salt) is equal on both sides, the water will
move back in forth but it won't have any result on the overall amount of
water on either side.
"ISO" means the same
"HYPO" means less
In this case there are less solute
(salt) molecules outside the cell,
since salt sucks, water will move
into the cell, causing it to swell.
The cell will gain water and grow
larger. As osmosis continues,
osmotic pressure builds up inside
the cell causing cell lysis.
In plant cells, the vacuoles will fill and the plant becomes stiff and rigid.
The pressure exerted by the water molecule is called TURGOR
PRESSURE, and the phenomenon TURGIDITY. The turgor pressure in
plants will not result in cell lysis as the cell wall keeps the plant from
bursting.
TURGIDITY is important in maintaining the firm and erect position of a
plant.
"HYPER" means more
In this case there are more solute (salt) molecules outside the cell, which
causes the water to be sucked in that direction.
Causes cells to shrink and lose shape because of water loss.
In plant cells, the central vacuole loses water and the cells shrink, causing
wilting (plasmolysis). In animal cells, the cells also shrink.
In both cases, the cell may die.
Active Transport
•cell uses energy (ATP or Adenosine Triphosphate)
•actively moves molecules to where they are needed
•Movement of molecules against concentration gradient
(concentration gradient not required)
•Movement from an area of low concentration to an
area of high concentration (Low  High)
•Transport proteins are highly specific
•Involves carrier proteins (like facilitated diffusion) often
called pumps because they use energy to move
molecules against a concentration gradient
Example: Sodium
-Potassium Pumps
are important in nerve
responses. They
transfer Na and K
ions in and out of the
nerve and muscle
cells.
Sodium
Potassium Pumps
(Active Transport
using proteins)
Protein changes
shape to move
molecules: this
requires energy!
Types of Bulk Transport
1. Endocytosis:
taking bulky
material that can’t use transport
proteins (like macromolecules)
into a cell
• Uses energy
• Cell membrane in-folds
around the macromolecule to
be transported
• 3 Types:
 Phagocytosis
 Pinocytosis
 Receptor-mediated
Endocytosis
Types of Bulk Transport
Phagocytosis – “cell eating”
-
Process by which cells take in large particles by
infolding the cell membrane to form endocytotic
vesicles
Ex. WBC capture and kill invading bacteria
Types of Bulk Transport
Pinocytosis – “cell drinking”
-
Process of taking in fluids into the cell by invagination
of the cell membrane. Any solute or small particles
in the fluid will be moved into the cell.
Types of Bulk Transport
Receptor-mediated Endocytosis – “cell drinking”
-
Compared to pinocytosis, is very specific. The plasma membrane
becomes indented and forms a pit. The pit lined with receptor proteins
picks specific molecules from its surroundings. The pit will close and pinch
off to form a vesicle which will carry the molecules inside the cytoplasm.
Types of Active Transport
2. Exocytosis: 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
Effects of Osmosis on Life
• Osmosis- diffusion of water through a
selectively permeable membrane
• Water is so small and there is so much
of it the cell can’t control it’s movement
through the cell membrane.
Hypotonic Solution
•
Osmosis
Animations for
isotonic, hypertonic,
and hypotonic
solutions
Hypotonic: The solution has a lower concentration of
solutes and a higher concentration of water than
inside the cell. (Low solute; High water)
Result: Water moves from the solution to inside the
cell): Cell Swells and bursts open (cytolysis)!
Hypertonic Solution
•
Osmosis
Animations for
isotonic, hypertonic,
and hypotonic
solutions
Hypertonic: The solution has a higher concentration
of solutes and a lower concentration of water than
inside the cell. (High solute; Low water)
shrinks
Result: Water moves from inside the cell into the
solution: Cell shrinks (Plasmolysis)!
•
Isotonic Solution
Osmosis
Animations for
isotonic, hypertonic,
and hypotonic
solutions
Isotonic: The concentration of solutes in the solution
is equal to the concentration of solutes inside the cell.
Result: Water moves equally in both directions and
the cell remains same size! (Dynamic Equilibrium)
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. In plants the pressure exerted on
the cell wall is called tugor pressure.
•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.
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