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 Solution Substance to be

dissolvedThe Dissolver

Salt + 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 TransportSolutes 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

High Concentration of solutes Low Concentration of solutes

Direction of Diffusion

Down the Concentration Gradient

OsmosisThe 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.

• Water will move outside the cell… the cell will shrink and die.

95% Water

5% solute

97% Water

3% solute

Hypotonic Environment

• Concentration of solutes is greater inside the cell than outside the cell.

• Water will move inside the cell… the cell will swell, or burst, and die.

97% Water

3% solute

95% Water

5% solute

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 PressureIf 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.

PlasmolysisPlasmolysis 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 ofPassive 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 TransportSpecial 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 endocytosis1. phagocytosis2. 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

• 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 ProteinMolecule being ingested

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

H2O Osmosis

Glucose (C6H12O2) Facilitated Diffusion

Ions Special Transport

Large Solids (starch, etc) Phagocytosis

Large Liquids (oils) Pinocytosis

Hormones Receptor-Mediated