CELL TRANSPORTpp. 103-106

Passive transport:•Movement across the cell membrane without energy

Diffusion: movement of molecules from area of high concentration

(CONC) to area of low concentration

• Molecules have kinetic energy• Concentration gradient: difference

between high and low concentration• Molecules move “down” gradient.• Molecules move until they reach

equilibrium (when all molecules are evenly spread out).

What characteristic does the cell membrane have?•Cell membrane is nonpolar and tightly packed•Small and nonpolar substances can easily pass through the cell membrane

Active Transport

• Requires energy• Molecules move from an area of

low concentration to an area of high concentration

• Move against the concentration gradient

Membrane pumps

• Carrier proteins that are active are called pumps.

• Protein binds to a specific molecule.• Protein transfers the molecule to the other

side.• Sodium-Potassium Pump: transports Na+

and K+ against (not down) gradient

Na+ out and K+ in

Endocytosis: ingest large molecules to move molecules into cell

• Membrane makes a pouch.• Pouch then pinches off and makes a vesicle.• Vesicle binds with lysosome to digest

substance.

Exocytosis: (the reverse of endocytosis) moving large particles

out of the cell