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METHODS OF TRANSPORT: HOW MATERIALS CROSS THE CELL MEMBRANE
How Molecules Naturally Move
1. Molecules are constantly in Motion – Kinetic energy.
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 – Diffenrence in concentration
of a substance across space.
Section 3.4 Diffusion and Osmosis
Key Concept: Some materials can move in and out of cells through their
membranes 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.
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Section 3.5: Active Transport, Endocytosis, and Exocytosis
Key Concept: Cells use energy to transport materials that cannot diffuse
across the cell membrane on their own.
Methods of Transport Requiring Cell Energy:
1. Active Transport (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.
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