Cell Transport

Passive Transport

• Passive transport- the movement of materials

across the cell membrane without using energy

Passive Transport

• Diffusion: the process by which solute particles move from an area of high concentration to an area of lower concentration.

• Solution Solute + solvent

• Concentration

amount of substance in a given volume

• Cytoplasm: A solution of many different substances (solutes) dissolve in water.

Concentration Gradient

Concentration Gradient: change in concentration

Concentration: the amount of substance in a specific area

HighConcentration

Low

Concentration

Which side is high

concentration? Which side is

low concentration?

HIGH LOW

Passive Transport

• Diffusion• Down concentration gradient

• From higher concentration to lower concentration

• Affected by size (more you have, the longer it takes)

• TYPES of diffusion:

•Simple diffusion•Diffusion through the lipid bilayer

(small molecules like O2, CO2)

•Facilitated diffusion•Diffusion through a channel protein

(small molecules)

•EXAMPLE : Osmosis •water molecules through aquaporins

Demo 1: Dye in Water

Observe what happens when

drops of dye are put in water

How is it different in hot water?

Why?

What direction are the dye molecules moving in terms of concentration gradient???

HIGH Low Until it reaches equilibrium

Demo 2: Fragrance in Air

Raise your hand when you smell the lotion?

With a Partner

Where was the concentration the

highest?

What slowly happened?

Please describe the two demos in terms of

concentration gradient.The ___________ moved from a _________

concentration to a __________

concentration.

High Concentration

Low

Concentration

DIFFUSION:

Definition: The movement of any substance from a

HIGH concentrationto a LOW

concentration

Remember: NO ENERGY is required!

Simple Diffusion

• Suppose a substance is present in unequal

concentrations on either side of a cell membrane.

Simple Diffusion

• If the substance can cross the cell membrane, its particles

will tend to move toward the area where it is less

concentrated until it is evenly distributed.

Simple Diffusion

• At that point, the concentration of the substance on both

sides of the cell membrane is the same, and equilibrium

is reached.

Simple Diffusion

• Even when equilibrium is reached, particles of a solution

will continue to move across the membrane in both

directions.

• Because almost equal numbers of particles move in each

direction, there is no net change in the concentration on

either side.

Factors that Affect

Rate of Diffusion

Facilitated Diffusion

• Cell membranes have

proteins that act as

channels!

• Facilitated diffusion:

Molecules that cannot

directly move across the

membrane pass through

special protein channels.

Osmosis: An Example of Facilitated Diffusion

• OSMOSIS: the movement of water through cell membranesextremely important processmovement of water molecules

from an area of higherconcentration to an area of lowerconcentration

The inside of a cell’s lipid bilayer is hydrophobic—or “water-hating.”(Water molecules struggle to get through!)

Aquaporins - water channel proteins

How Osmosis Works

• Isotonic: the concentrations of solutes is the same inside and outside the cell

• Hypotonic: the solution has a lower solute concentration than the cell

• Hypertonic: the solution has as higher solute concentration than the cell

Osmosis Practice

Below are animal cells placed in beakers of various

concentrations. Draw an error to

show which the water would move by osmosis.

Identify the type of solutions (isotonic, hypertonic, and hypotonic).

Passive Transport

1) Movement of particles with NO ENERGY required.

2) Both osmosis and diffusion are types of PASSIVE TRANSPORT

Moving DOWN a concentration gradient.

Active Transport

REQUIRES ENERGY!

Definition: Movement from a low concentration to a high concentration using a protein channel

HIGH

LOW

Active Transport = NEED ENERGY

• Active transport- the movement of

materials against a concentration

difference• low concentration to high

concentration

• Requires energy (ATP)

• Carried out by transport proteins, or

protein “pumps”• Examples: endocytosis and exocytosis

Which direction are the

molecules moving in active

transport?

The ___________ are moving from a _________ concentration to a __________ concentration. They are moving ____________________________

Active Transport

Endocytosis vs. Exocytosis

• Endocytosis: Taking

material into cell by means of

pockets through cell

membrane

• Exocytosis: Many cells also

release large amounts of

material from the cell

• membrane of the vacuole

surrounding the material

fuses with the cell

membrane, forcing the

contents out of the cell.

Endocytosis

Exocytosis