Cell Transportation
How things get in and out of Cells
Transportation is defined as… the
movement of materials in or out of a
cell…… or the movement of materials
throughout an organism…. example:
transportation could be the movement of
oxygen into a cell and the movement of
carbon dioxide out of a cell…..
What is Brownian Movement?
• Albert Einstein observed the movement of
small particles in water. He realized that the
particles moved because they were being
bombarded by moving water molecules. He
later, in one of his first scientific papers,
postulated that every particle in a fluid is in
constant motion. This constant movement, first
observed by Robert Brown, is called
Brownian Movement.
How Temperature affects the motion
of molecules
Temperature is defined as the average transitional velocity (speed) of the
molecules in a system.
An increase in temperature is actually an increase in the speed of the
molecules…. @ 70 degrees Fahrenheit air molecules are traveling at
1,500 mph
All molecules exhibit some kind of motion. Therefore, all molecules have
temperature.
Absolute Zero – temperature at which all motion stops…absolute zero is
-459 Fahrenheit…. Welcome to
Bruno’s world!!
Semi- Permeability
• The Plasma Membrane is semi-permeable
( also referred as “selectively permeable” ).
• A selectively permeable membrane allows the
passage of some materials in or out of a cell,
and restricts the passage of some materials in
or out of the cell.
Solutions
• Cells are filled and surrounded by many
solutions. Solutions are composed of
solutes and a solvent.
• Solute + Solvent
Substance to be
dissolved
Salt
Solution
The Dissolver
+
Water
Saltwater
Bulk Flow
• The movement of some materials is
referred to as “Bulk Flow”. Bulk flow is the
collective movement of substances in the
same direction in response to a force or
pressure.
• Blood moving through a blood vessel is
“bulk flow”.
2 Types of Cell Transportation
Passive Transport
* Materials flow
down the
concentration
gradient.
* The cell does not
use any energy.
Active Transport
* Movement of
solutes against a
concentration
gradient.
* Requires that the
cell use energy.
Passive Transport
Solutes flow down the concentration gradient.
* The cell does not use any energy.
The 3 most common types of Passive Transport are:
1. Diffusion
2. Osmosis
3. Facilitated Diffusion
Simple Diffusion
Diffusion is the flow of substances from an area,
or region, of greater molecular concentration to
an area, or region, of lesser molecular
concentration. The overall direction of the
movement is referred to as the Gradient.
Molecules usually move “down the concentration
gradient”..... flow from high concentration to low
concentration. Eventually a state of “equilibrium”
is reached where molecules are uniformly
distributed but continue to move randomly.
Simple Diffusion
Direction of Diffusion
Down the Concentration
Gradient
High Concentration of solutes
Low Concentration of solutes
Osmosis
The Diffusion of water across a membrane
• All living cells must be surrounded by Water.
• These water environments are classified as by
the concentration of solutes in the solution.
The environments are classified as:
1. Isotonic
2. Hypertonic
3. Or, Hypotonic
Isotonic Environment
** In an Isotonic solution, the
concentration of solutes outside and inside
the cell are equal.
** Under these conditions, water diffuses
into and out of the cell at equal rates, so
there is NO Net Movement of Water.
Hypertonic Environment
• Concentration of solutes is greater outside
the cell than inside the cell.
97% Water
3% solute
95% Water
5% solute
• Water will move outside the cell… the cell
will shrink and die.
Hypotonic Environment
• Concentration of solutes is greater inside
the cell than outside the cell.
95% Water
5% solute
97% Water
3% solute
• Water will move inside the cell… the cell
will swell, or burst, and die.
Facilitated Diffusion
• The diffusion of solutes through channel proteins
in the plasma membrane. Glucose moves in and
out of cells through facilitated diffusion.
Pressure
• Force (push) exerted on a surface as it is
bombarded by moving particles.
• The amount of pressure can be
determined using the following formula:
Pressure =
Force
Area
Osmotic Pressure
If there are solute molecules only in one side of the system, then the
pressure that stops the flow of the solutes is called the
osmotic pressure.
Dialysis
• The diffusion of
solutes across a
selectively
permeable
membrane. The
term dialysis is
usually used when
different solutes
are separated by a
selectively
permeable
membrane.
Plasmolysis
• Movement of water out of a cell that results in the
collapse of the cell, especially in plant cells with
central water vacuoles.
Normal cells
Plasmolyzed Cells
Turgor Pressure
Internal pressure applied
to a cell wall when
water moves by
osmosis out of the
cell. The pressure
pushes the plasma
membrane against the
cell wall.
Plasmolysis is the loss
of Turgor Pressure…
therefore the cell
collapses.
Countercurrent Exchange
• Diffusion of
substances
between two
regions in
which
substances are
moving by bulk
flow in
opposite
directions.
Oxygen Flow
Factors which affect the rate of
Passive Transport
• Temperature – the faster the molecules
move, the faster they diffuse… the slower the
molecules move, the slower they diffuse.
• Pressure – as you increase, or decrease
pressure…. You can affect the rate and
direction of flow.
• Concentration – the larger the population of
solutes, the greater the chance of random
access through a membrane.
Active Transport
*Solutes flow against the concentration gradient.
* The cell uses energy….ATP.
*Requires Transport Proteins
Types of Active Transport are:
1. Exocytosis
2. Endocytosis
a.) Special Transport
b.) Phagocytosis
c.) Pinocytosis
d.) Receptor-mediated
Special Transport
• Ions are atoms with either a positive or negative
electrical charge…. their electron number is not equal to
their proton number.
• Some, not all, ions need to be transported by
Special Transport.
Simply put….during Special Transport, ions are captured
by surface proteins and pushed’ or pulled, into the cell….
Because they are forced, the ions can flow, if necessary,
against the concentration gradient.... The ions can even
flow through like electrical charges on the plasma
membrane.
Exocytosis
(exo = outside, Cyto = cell)
moving substances outside the cell
• Process of vesicles fusing with the plasma
membrane and releasing their content to the
outside of the cell.
Endocytosis
(endo = inside, cyto = cell)
Capture of substances outside the cell when the
plasma membrane merges to engulf it.
***There are three types of endocytosis
1. phagocytosis
2. pinocytosis
3. receptor-mediated
Phagocytosis
(phago = to eat, cyto = cell)
Phagocytosis occurs
when undissolved solids
enter a cell. The plasma
membrane wraps
around the solid
material and engulfs it,
forming a vesicle.
Phagocytic cells, such
as white blood cells,
attack and engulf
bacteria in the manner.
Pinocytosis
(pino = to drink, cyto = cell)
Pinocytosis occurs
when dissolved
materials enter a cell.
The plasma membrane
folds inward to form a
channel allowing the
liquid to enter. The
plasma membrane
closes off the channel,
encircling the liquid
inside a vesicle. Oils
enter cells through
pinocytosis
Receptor-Mediated Endocytosis
Molecule being ingested
• Occurs when specific
molecules bind to specialized
“receptors” (proteins) in the
plasma membrane. The
membrane, the receptors, and
the specific molecules, called
ligands, fold inward forming
vesicles. Hormones target
special “target cells” by
receptor-mediated
endocytosis.
Ligand
Receptor Protein
Vesicular Transport
• Vesicles are small membrane-bound
macromolecules of the cell and carry
materials between organelles in the cell.
• Cells can use vesicles to transport large
particles across the plasma membrane.
• Both exocytosis and endocytosis are types
of vesicular transport.
Summary
Molecule
Mode of Transportation
O2
Diffusion
CO2
Diffusion
H 2O
Osmosis
Glucose (C6H12O2)
Facilitated Diffusion
Ions
Special Transport
Large Solids (starch, etc) Phagocytosis
Large Liquids (oils)
Pinocytosis
Hormones
Receptor-Mediated