Notes # ______
Date _________
How Molecules Naturally Move
1. Molecules are constantly in Motion – Kinetic energy.
Molecules in solids - vibrate in place.
Molecules in liquids and gases - move freely.
2. Molecules move randomly colliding as they move.
3. Molecules move from areas of high concentration to where they are less concentrated
along their concentration gradient.
Concentration Gradient –the difference in the concentration of a substance from one
location to another.
Concentration Gradient of Color
Concentration – the number of molecules of a substance in a given volume.
The amount of solute / amount of solvent.
Random movements of molecules along their concentration gradient eventually cause them
to spread out evenly. This is called dynamic equilibrium which means that the
concentration is the same throughout(equilibrium) but that the molecules continue to move
(it’s dynamic!). What example did we see? ___________________________________
Wait! If the molecules of perfume continued to spread out evenly, why can’t they smell
the perfume downstairs??? ______________________________________________
Two variables that affect the rate of molecular movement are:
1. ________________________
2.________________________
Notes # ______
Date _________
METHODS OF TRANSPORT: HOW MATERIALS CROSS THE CELL MEMBRANE
CELL
Section 3.4 Passive Transport: Diffusion, Facilitated Diffusion and Osmosis
Key Concept: Some molecules move on their own into or out of cells because of
concentration differences on opposite sides of the membrane without the cell
using energy. This is called Passive Transport.
Methods of Passive Transport - Do Not Require Cell to Use Energy
1. Diffusion – Net (overall) movement of molecules from area of higher
concentration to an area of lower concentration
2. Facilitated “Helper” Diffusion – Movement of material through the cell
membrane by a “helper” transport protein (channel or carrier) that binds
specifically to the molecule
3. Osmosis – Diffusion of water molecules through a membrane from an area of
higher water concentration to one of lower water concentration.
Super Important Factoid:
Higher water concentration in solution means lower solute concentration
Lower water concentration in solution means higher solute concentration
Comparing Solutions:
Isotonic – solutions have the same solute and water concentrations
Hypertonic – Solution has a Higher solute concentration (less water concentration)
Hypotonic – Solution has a Lower solute concentration (more water concentration)
Notes # ______
Date _________
Section 3.5: Active Transport, Endocytosis, and Exocytosis
Key Concept: Cells use energy to transport materials across the cell membrane
Methods of Active Transport - Require Cell Energy:
1. Transport Protein / Membrane pumps
*Moves molecules across membrane from low to high concentration areas
*Involves a transport molecule that spans the cell membrane
*Transport molecule binds to 1 or 2 specific target molecules
*Binding causes the transport molecule to change shape and move the molecules
*The ATP (adenosine triphosphate) molecule transfers E to the transport
protein molecule giving it the E it needs to do to move molecules through the
cell membrane.
2. Endocytosis - Taking in of materials by engulfing them in a vesicle

Phagocytosis – Cell membrane engulfs large particles or whole organisms
ex. White blood cell engulf a bacteria, Amoeba engulfs paramecium

Pinocytosis – Cell membrane engulfs liquid droplets
3. Exocytosis – Release of substances from by fusing vesicle with membrane
ex. Secretory vesicles. Unicellular organism excreting waste.